ELCO PT-Boat
by Glynn Guest

A fast electric stand-off scale model of the 80 Foot Elco PT Boat

BY GLYNN GUEST

This article first appeared in the November 1999 issue of Model Boats in conjunction with a free plan giveaway.It is reproduced here by kind permission of Model Boats.

Having an interest in all types of R/C model boats does keep me busy since there is always something new to try. This particular model proved very satisfying as it combined two favourite types, scale warships and fast electrics, into one model. To be honest a model based on the U.S. Navy's ELCO PT boats had been on my 'new projects' list for many years. I tend to collect information on a casual basis for these projects until something fires up my desire to start building. In this case the catalyst was the review of Kyosho's Streamliner kit, Model Boats January 1998. This model, based on an American luxury high speed open launch, showed me that such fast electric scale models were both practical and great fun to sail. After finishing off a couple of other modelling projects the ELCO PT file was opened and plans started.

The first ELCO boats were based on a British design by Hubert Scott-Paine, one example of which was bought and shipped to America in 1939. The success of this boat lead to the design and construction of the 70 foot ELCO PT boats. Al Ross described these boats along with an excellent scale drawing in the May 1998 issue of Model Boats (Vol. 48 No 569). These boats were followed by an enlarged design, an extra seven feet being needed to carry a total of four torpedoes. During early 1942 production standardised on a new 80 foot design which became the classic ELCO PT boat which most people are familiar with.

As originally designed the 80 foot PT boats were armed with four 21in torpedo tubes, two twin .50 machine guns and a single 20mm cannon on the stern. Torpedo tubes could be replaced with depth charges if the boat were to be used for anti-submarine duties. Quite a potent outfit on 38 tons. Three V-12 engines could produce speeds up to 40 knots in calm conditions. Later it was found that smaller and lighter aircraft torpedoes could be rolled overboard from simple racks, thus saving the weight and space taken up by torpedo tubes. This allowed extra weapons to be carried such a 40mm cannon on the stern, 37mm cannon in the bows and sixteen tubes for launching 5in rockets!

Details of the wartime activities of PT boats can be found in several books. My main reference was 'United States PT-BOATS of World War II' by Frank D. Johnson. It was published by Blandford Press in 1980. I found my copy in a discount book shop some years ago but your local lending library might be able to get a copy (ISBN 0 7137 1025 X). Barbarossa Books, who have advertised in Model Boats, list two titles which might be of interest, PT Boats in Action which is No. 4007 in the Warships in Action series and 'PT Boats at War, WWII to Vietnam'. There are also the excellent books on Allied Coastal Forces by Al Ross and John Lambert.

It took me a little while to decide which version of the ELCO vessels to build. The 70 and 77 footers were quite shapely, but the heavy armament of the late model 80 foot PT boats was too tempting. If you fancied something a little different then the contemporary 78 foot PT boat built by Higgins could be a viable alternative.

Model design

Having picked what to base the model on, the next task was to set the size, then design the structure. It seemed sensible to use the fast electric racing outfit I was experienced with, that is 540/stock motors with a six cell nicad packs. These racing models usually have a length of about 18-20 inches (50cm) and any attempt to reduce a PT boat hull down to this size (1 :48 scale) would result in a maximum beam of 5 inches (12.5cm). This could suit motors of less power but with my intended outfit, a grossly overpowered and unstable model was almost certain. After experimenting with other scales, 1:32 seemed to be just right. This gave a hull some 30 inches (76cm) long which was more than large enough for the motor, battery and R/C outfit.

Since realistic performance was desired, a target for the operating weight had to be set. With my fast electrics I usually aim for just over 2 pounds (1Kg) but this seemed to be unrealistically low for the PT boat's larger hull and scale details. After looking at several commercial vac-formed plastic fast electric kits, a target of 1.5Kg seemed reasonable. This was low enough for good performance without risking a flimsy model.

The next design problem was speed and power. I wanted the model to have the same full speed trim as the real PT boats. This has the bows lifted clear of the water but without the stern noticeably squatting. In the absence of any other ideas I used the method of obtaining dynamic similarity by multiplying the full size speed by the square root of the model's scale. Taking the full size PT boats to have a best possible speed of around 40 knots then this gave a model speed of just over 10ft/sec (3.2m/s) which looked like a reasonable figure. Now it was a case of playing with the data for different combinations of propellers and motors to find the most promising match for this speed.

Allowing for 20% 'slip', that is due to losses the propeller must turn more than model's speed might suggest, the RPM for a range of propellers was calculated. This quickly produced two options, either a small propeller and direct motor drive or a larger propeller with geared drive. With careful installation both methods can work well but I was drawn to the geared drive. Past experience has shown that geared drive can offer an excellent combination of speed and duration. Furthermore, the use of Graupner gear sets (Order No 1113 covers three ratios of 2:1/2.5:1/3:1) and a simple plywood motor mounting bulkhead makes it very easy to experiment with different motors, gears and propellers.

Estimating the power needed was a more dubious task. A fairly accurate figure for displacement models can usually be obtained but with a planing hull I was out of my depth. The best that could be done was to use fast electric racing experience and 'guess' that with a six cell nicad pack the current would be around 7-8 amps. With nicad packs made from 1.4 to 2.0 Ah capacity cells this would give full power duration of 10 to 17 minutes. Allowing for this being a scale model and so operating with a range of speeds it looked like sailing runs of 20 to 30 minutes would be achievable.

A lot of my calculations on size and performance were based on the combination of past experience and intuition. This is not always the most reliable way to do anything but nothing looked too optimistic. The next stage of structural design could start with some confidence.

After the model's size was established, the hull lines were drawn up. The most accurate lines I could find were in an old American model magazine. After a couple of hours work with pencil, paper, rule, calculator and (most importantly) an eraser, a reasonable hull shape was drawn out. Having decided to stick with my fast electric experience, a hull structure of 1/4 inch (6mm) balsa covered with 1/8 inch (3mm) balsa sheet was to be used. My racing models have proven that such hulls are easy and economical to build whilst still being tough enough to cope with the occasional sailing 'accident'.

After looking at the hull lines it was clear that the PT boat suited balsa sheet construction. In only three areas would the model have a none scale hull form. The full size vessels had a slight reverse sheer at the bows and deck camber. After looking carefully at photographs of actual PT boats I felt that a simple flat deck would not look too bad at this scale. The other deviation was with the concave section of the hull sides and bottom. Again I felt that simplifying the model with flat side and bottom panels would not be a serious crime. The aim was to produce a reliable and easy to build Stand Off Scale model and I defy anyone to spot these changes as the model flies past at full speed!

Material selection

Having commented that balsa hulls can be strong and tough, there are a couple of important points to make. Balsa can come in a wide range of densities and a little care is needed to select a suitable grade. It might be tempting to use very light sheets but such low density balsa can make the model weak and prone to local impact damage. The alternative of high density balsa would add unnecessary weight to the model and make cutting out the parts much harder work than it needs be. A medium grade of balsa is perfectly suitable for this model. I usually gauge the balsa sheets by their weight and resistance to being squeezed between thumb and forefinger. Good medium grades will 'give' a little when squeezed then recover with no visible indentation. I strongly suggest that you try this out on some scrap balsa at home rather than risk damaging a model shop's stock!

As for the adhesives, I know our aeromodelling cousins swear by Superglues but PVA woodworking adhesives takes some beating. Used correctly the bond is usually unbreakable, the wood failing first. It has a reasonable setting time which allows you to adjust joints without rushing. Some brands claim to set in 15-30 minutes but I tend to leave things alone for at least an hour. If the next stage of construction will stress the glued joints than I try to give them several hours rather than risk things coming apart.

If PVA adhesive has a drawback it might be that it is not waterproof. Occasional wetting does not seem to cause any serious problems provided the structure is allowed to dry out fully. As drying a model boat out after use ought to be standard practice anyway, I have never considered this to be a problem. Perhaps the biggest advantage for me is that PVA adhesives have hardly any smell and 'accidents' can be wiped up with a damp cloth. This enables me to get away with some discrete model building indoors!

Hull parts

This starts with the cutting out of the keel, deck, chine, transom, bulkheads 1 and 3 from 1/4 inch (6mm) balsa sheet. Two identical deck and chine pieces can be made by carefully cutting out the first one then using as a template for the second piece.

These items then need dry assembling together without glue to check their fit and accuracy. The best method is to work upside down with the deck on a smooth flat surface and pin the parts together. Any mismatch or minor errors can be easily corrected at this stage. The bulkhead slots may need slightly enlarging for a firm but not too tight fit. Small gaps could be filled with a sliver of wood when gluing the parts together. These parts ought to fit snugly together with no suggestion of distorting the hull structure. Anything which needs more than minor correction perhaps ought to be discarded and replaced. Do note that the ends of the keel and chine pieces are overlong and will need trimming back to lie flush with the transom when everything is glued together. This is deliberate and allows you a little more freedom for minor adjustments.

Drive line

I can strongly recommend the drive line shown on the plans. It was developed through several fast electric models and combines practicality with efficiency. If you intend to use a different drive line the do ensure good access and rigidity.

The second bulkhead, which forms the motor mount, is made from 1/8 inch (3mm) plywood. This should be placed into the hull structure then adjusted until it fits snugly at the right angle and position. It is a good idea to mark the position of all the bulkheads on the deck, chine and keel. This can make the final glued assembly less stressful. The hull structure can be dismantled for the next stage of construction.

The second bulkhead needs holes drilling for the propeller tube and motor. The position of the propeller tube can be found from the plans but the others depend on the type of motor and gears used. Most commercial shaft and tube assemblies only have a short threaded length of shaft protruding from each end. The Graupner gears sets I was going to use needed to fit on a plain length of shaft. The solution was to buy a slightly overlength shaft and tube, then cut the tube to the desired length. The bearing can usually be gently tapped free of the excess tube and reinserted into the shortened tube. When the shaft is fitted into the tube there should be a smooth length available for securing the gear wheel. The unwanted threaded part of the shaft could be cut off or left in place if it causes no problems, your choice.

The correct positioning of the motor mounting holes is vital if you want to get the gears properly aligned. My method is to fit the propeller tube and shaft into the bulkhead hole and then slip the gear wheel onto the shaft. This allows me to use the smaller motor gear to locate the position if the motor shaft. A good 'mesh' between these gear wheels can be made if a sliver of thin paper is placed between them. This ensures that the gear teeth make positive contact without the wheels pressing upon each other. Once the centre of the motor shaft is marked then the holes for the motor bearing and securing screws can be made.

If you do make a mess of these holes then it is worth scrapping this bulkhead and starting again. Only when totally satisfied with the fit of the motor, gears and propeller shaft can the next stage of gluing the tube to the bulkhead be carried out. To ensure alignment I secure the motor to the bulkhead then fit the tube and shaft along with the gears. A gap should appear between the tube and motor body and a piece of wood exactly this size is slipped into the gap. With a couple of elastic bands around the motor and propeller tube, the whole assembly ought to be firm. Provided the motor and propeller shafts are parallel and the gears mesh correctly then it should turn over smoothly with no suggestion of binding at any point.

Only when totally happy with alignment should the propeller tube be epoxied to the bulkhead. I suggest that you use a slow type of epoxy; it produces a stronger bond and avoids you having to rush things. Only a fillet of epoxy is needed either side of the bulkhead, excess amounts will not produce a stronger joint. It is assumed that you have ensured the tube surface is clean and grease free, I also like to lightly abrade the tube with a file to produce a better 'key' for the epoxy.

When the epoxy has fully hardened the motor, gears and propeller shaft can be removed before fitting into the keel. A slot for the tube needs cutting at the angle shown on the plans. The keel is reinforced at this position with 1/4 inch (6mm) thick balsa doublers between bulkheads 2 and 3. Likewise, a slot plus reinforcement is needed for the rudder tube. I used PVA for the wood/wood joints and epoxy for the wood-metal joints. It is vital to ensure that the keel remains straight and true whilst the adhesives harden.

When set the motor and gears can be refitted. You will probably find that the propeller shaft gear wheel fouls the keel and some balsa needs removing. Try to avoid any sharp corners when cutting into the keel as they could weaken it. Check that the motor and propeller shafts still turn smoothly. It is probably best to remove the motor, gears and propeller shaft before starting the next stage of construction.

Hull structure

Before starting to assemble the hull structure you need to make a decision about the deck access cut out. This could be made prior to gluing the parts together or afterwards. There are good arguments for doing it either way so I compromised by only cutting the transverse slots at either end of the cut-out. My reasoning was that leaving the cut-out in place would ensure that the hull structure was built correctly with no distortion. Making the more difficult transverse cuts, which run across the wood grain, beforehand, would only leave the easier longitudinal cuts to make on the completed structure. It seems to have worked for me but you can do it any way you like. Having previously checked the fit of these parts, this stage ought to be a simple assembly job. The first task is to glue the two deck pieces together. it is vital that they remain flat, and I used my desk top with a sheet of thin plastic to prevent me from sticking the balsa to the desk! A few weights and a couple of pins at each end held the two pieces securely.

You could leave the deck pieces to fully dry or, if working with care, start to add the rest of the hull structure. Bulkheads 1 and 3 plus the transom are stuck to the underside of the deck, but not the access cut out!, then the keel can be added. A cheek that all is square, but remembering the slope of the transom, and the two chine pieces can be fitted. A final check for squareness before pinning all the glued joints and the structure ought to be left for the adhesive to fully set.

It is a good idea to check the all the glued joints. Any gaps which have appeared as the adhesive sets ought to be filled. I will confess to running a small bead of glue along each joint then smoothing it into a fillet with my finger tip. This might well be 'overkill' but my models never suffer from disassembly through hard use or accidents.

The edges of the deck, chine and keel need sanding to form the correct angles for the side sheeting, see the cross-section on the plans. A sanding block which can bridge the space between the deck/chine and chine/keel spaces, is the only way to do this. You might find it is tricky to shape the keel around the propeller and rudder tubes. I sanded as close to the tubes as possible then finished off with a model knife. The excess keel and chine pieces were cut back to the transom and sanded smooth.

The rudder servo mount was built into the model before covering the hull sides and bottom. A good arrangement for access and linkage geometry is to place the servo over the keel just aft of the third bulkhead. The fore end of the servo was to be secured to a strip of balsa glued to the bulkhead, whilst the rear used a block of balsa glued to the keel. You may prefer an alternative, but however you install the servo it must be secure to prevent steering problems.

Sheeting the hull

The hull structure is covered with 1/8 inch (3mm) balsa sheet. The grain should run transversely, that is between deck, chine and keel. I found it convenient to use 3 inch (75mm) wide sheets for this task.

The hull sides were covered first starting from the transom and working forwards. Slightly oversize sheets were fixed between the deck and chine. The amount of glue used should be sufficient to produce a small bead when the sheet is secured to the hull. It is better to be a little generous with the glue as any excess can be removed easier than any missing glue applied later! It is a good idea to work on alternate sides of the hull as the job moves forwards. This minimises the risk of you inadvertently building a twist into the hull. Unless you are using very stiff balsa, pins ought to keep the balsa in place. It is vital that the butt joints between adjacent sheets are sound with no visible gaps. A slight 'step' between sheets ought to be no problem provided it can be sanded down later without weakening the sheeting.

It is vital that the glue has fully hardened before you attempt to remove the excess side sheeting. I prefer to use a sharp craft knife to trim off the bulk of the excess before sanding to make the sides match with the deck and hull bottom. Do not worry if the sheeting is less than perfect as a little filler can work wonders at a later stage.

Covering the hull bottom is much the same task as the sides. There is the extra work of making the sheets butt up against each other along the centre of the keel. You also have to fit the sheets around the rudder and propeller tubes. Again a neat job with sound glued joints is all that is required, as a little filler can eliminate any gaps. There is slightly more twist and curve in the bow sheeting so extra pins and perhaps elastic bands might be needed whilst the glue sets. After this the edges of the bottom sheets can be trimmed and sanded flush with the hull sides and transom.

Sand and fill

I will confess to being very happy with the hull at this point. The construction was simple yet the hull had a pleasing shape. After enjoying the fruits of my labours for a few seconds it was back to reality and the external surfaces were closely examined for any defects.

The joint along the keel was less than perfect and had to be filled. I used a tube of ready mixed domestic filler. Provided you give it enough time to fully harden it will bond well yet sands easily to blend in to the balsa sheeting. Some of the sheeting joints also displayed slight 'steps' which needed a combination of filler and sanding to eliminate.

The whole external surfaces were finished off with a fine grade of sandpaper. Do note that whilst sanding the hull you can radius the sheeting joint along the keel. All the other corners, that is deck edge, chine and transom, must be sharp. This is vital for both appearance and performance!

Surface sealing

The porous balsa surface now needed sealing and some more decisions were needed. Epoxy resins and fine glass cloth could be used to produce a very tough external surface. I did worry that the model's weight would rise by an excessive amount with this treatment and also questioned whether this level of strengthening was really called for. Once again I fell back on my fast electric model experience and opted for sealing the hull with cellulose dope and model aircraft tissue. This method adds very little weight and the tissue fibres have a significant strengthening effect. Tissue will not prevent impacts from causing surface damage but it does localise and minimise it. Unless you are seriously bad at sailing your models, a dope and tissue finish has a lot to recommend itself.

The hull was given two coats of thinned dope (50:50 mix) lightly rubbing down after each coat. These coats penetrate into the balsa to start the sealing and strengthening process. The hull shape lends itself to being covered with six panels of tissue, that is the deck, sides, bottoms and transom areas. I used yellow heavyweight tissue, a coloured tissue makes it easier to spot any folds or creases when sticking the tissue in place.

Slightly oversize tissue panels were cut to match each panel. If you have to use two pieces to cover a panel then start from the stern and work forwards. This will ensure that the overlap faces rearwards, making it impossible for the normal flow of water to peel it back. Thinking about it now it is probably impossible to peel back a well made tissue overlap, but this is a habit I have gotten into. If the tissue is creased then it could be 'ironed' flat. I never bother with this as a little care when laying the tissue will remove any creases.

With the panel laid over the hull, dope is brushed through the centre of the tissue. Using firm strokes the brush is worked outwards to the edges of the panel. Your free hand can apply a light tension to the edge of the tissue and help prevent creases. If any creases should form then the tissue must be quickly peeled back and re-laid.

The bulk of the hull surfaces are gentle curves, if not flat, but around the bows tighter compound curves occur. To avoid creasing the tissue, slits can be cut to accommodate these curves. It is also a good idea to wrap the tissue around the edges onto adjacent surfaces, e.g., the deck panel can overlap onto the sides and transom. Only something like a 1/4 inch (6mm) of tissue overlap is needed. This overlap prevents the tissue lifting and provides a little extra protection for the vulnerable edges of the hull.

When dry the hull surfaces must be checked for defects. Any tissue edges that have lifted can be brushed flat with dope. Creases can sometimes be carefully slit and re-laid again with the dope brush. If any bare patches appear then a piece of tissue could be doped over it, light sanding ought to allow it to blend into the surface.

A light overall sanding can be given to the hull before adding the spray strips to the bottom-side junction. My fast electric models have always used 3/16in (5mm) square hardwood for these strips but this size would have looked out of scale. A smaller strip 1/8 inch (3mm) square appeared to be a better size, a shade over scale but still big enough to work on a model.

Spray strips added after sealing hull
surfaces. Note elastic band used
to supplement pins when gluing in
bow section.

The spray strips follow the chine in more or less a straight line from the transom until they sweep upwards in the bow section. I had simplified the model's construction with straight chine pieces, knowing that the bottom and side sheeting process would produce this upwards sweep at the bows. Thus a straight spray strip laid along the chine edge working from the transom ought to naturally follow the desired path in the bows.

You might be tempted to stick the spray strip to the hull with epoxy and this is a perfectly good method. I opted to use balsa cement knowing that it would bond well to the doped hull surface. Either way you have got to drive lots of pins through the strip before fitting it to the hull, pushing pins into the strip whilst on the hull is just asking for an accident to happen. The strips ought to be overlong to aid fitting especially at the bows.

The strips can be glued and pinned in place starting from the transom and working forwards. I found it best to do this in two stages, stopping about three quarters the way along the hull, i.e., the easy part of the chine curve. Allowing the adhesive to set makes it much easier to attach the strips to the bow section. As stated earlier, the strips ought to naturally follow the desired upwards sweep. One strip is glued and pinned to the hull. I found it handy to slip an elastic band over the free end of the strip back to a pin in the other side of the hull. When set, the excess strip can be cut off and the second strip glued to the hull to meet the first strip at the bows.

The pins should only be removed when the adhesive is fully set. The excess strip can be trimmed from the strip after which I ran a fillet of glue along the top and bottom edges for a little extra strength. The pin holes will need filling before the whole hull is treated to a couple of further coats of thinned dope. Light sanding between each coat ought to result in a smooth surface suitable for painting.

Trial runs

I must confess to being impressed with those modellers who wait until a new scale model is totally completed before having the maiden voyage. If I were to attempt this then the model would undoubtedly reveal serious defects which could not be corrected without damaging all the detailed work. For this reason my scale models are usually given a trial run as soon as the hull is made watertight. So the bright yellow PT Boat hull was quickly outfitted as soon as the deck access hatch was cut free.

A rudder was needed and I opted for a generous blade area. It seemed best to start with perhaps too much rather than too little rudder area. My usual technique of epoxying a thin aluminium sheet blade around a steel shaft was used. Provided everything is clean and the bottom of the shaft is bent into a 'U' shape then this method will produce a slim streamlined but strong rudder.

Motor and gears installed to check alignment.

For the first runs a mild 540 motor was used along with a 3:1 gear ratio. The receiver and speed controller were fitted either side of the rudder servo in the rear hull compartment. A double-sided tiller arm was fitted so that a closed linkage could be made with two wires from the servo. It may take a little longer to set this system up but the extra security is well worth while. The nicad pack was made up in saddle fashion, that is two 3-cell blocks with a wire link between them. I was not sure about the balance point for this model so the battery pack was fitted into the first compartment between bulkheads 1 and 2. A vertical wire whip aerial was mounted through the deck just ahead of the transom.

Luckily the first chance to run the bare hull was on a bright calm day. Being cautious a P45 (low pitch 45mm diameter two-blade) propeller was used, previous calculations having shown that this combination could not achieve the sort of speed desired. My immediate reaction was a very safe model with good control both ahead and astern. Whilst not expecting high speeds the model ran with its bow rather low. This prompted me to move the battery pack backwards into the next compartment. The static trim looked better and full power now had the bows lifting into a more realistic attitude. The handling was still good and I had several minutes of fun trying to make do something naughty but it wouldn't.

The final test in this trial session was to try a larger propeller. Now I ought to explain that the water often used for quick test work is not the club's large and very safe lake, but a rather narrow stretch of water. So, as the model, with the larger propeller, shot across the water like the proverbial scalded cat I had very mixed feelings. These were delight as the model was still stable and safe, but combined with fear of doing something stupid. The model was promptly recovered before an accident occurred. At least I could now complete the model with the knowledge that it ought to sail safely.

Superstructure

After the elation of a successful trial run with the bare hull, reality hit hard. Completing the model was going to double the time and effort spent so far. This was largely due to the scale used as, whilst on my warships built to 1:144 scale I could get away with just suggesting the general shape of fittings, the PT Boat at 1:32 scale would need much more detail. Even so I had to draw the line somewhere and decided to limit details to those you might expect to see viewing the full size boats from something like 100 feet away. Thus I was able to use photographs taken of these boats from about this distance as my guide to detailing. If I could not see it on such a photo then it would not be essential for this model!

The actual superstructure of these boats was quite simple. From the bows rearwards is the chartroom, cockpit, dayroom and a raised hatch above the engine room. The model had been designed so that all these features could be built over the removable deck hatch. By extending beyond the edge of the deck hatch by about 1/8 inch (3mm) the superstructure would both hide the deck cut-out and produce a reasonable seal against any water thrown over the hull. Do make sure you clearly identify the front of the deck cut-out piece. Unless you have cut it out perfectly square, it will probably only fit into the hull one way!

Cockpit floor and engine room hatch added to removable deck section.

Dry assembly of superstructure parts on removable deck section.

Checking fit of superstructure on hull.

Hull and superstructure ready for painting.

The first things to make were the cockpit floor and engine room hatch from balsa sheet. Due to possible access problems later I sealed the surfaces of these two areas with dope and tissue. The chart and dayrooms were built up from 1/4 inch (6mm) balsa sheet to fit around the cockpit floor and hatch. There is a slight 'Vee' in the front of the chartroom which was too obvious to omit. Likewise a camber had to be sanded into the dayroom roof.

It is important that while building the superstructure that the deck cut-out is not allowed to bend in any way. This would affect the watertightness of the hull and might even fail to fit into the opening. I worked on a flat surface and weighted things down whilst the glue set.

A good finish on the superstructure was produced by covering it with thin card. The card was cut slightly oversize then stuck to the balsa with an Impact adhesive such as Evo-Stik. When secure the card could be trimmed to the final size. Slightly thicker card was used to make the shields around the cockpit area. A couple of coats of thinned dope and the card had a surface ready for paining.

The twin machine guns were fitted into two cylindrical gun tubs, one alongside the cockpit the other at the rear of the dayroom. I was very lucky and found a card tube of the correct diameter in my scrap box. Suitable tubes could be made by wrapping thin card around a former and gluing together. It should be noted that these gun tubs are raked forwards on the full size boats. This is an obvious feature that ought to be duplicated in a model. Now a confession! I took the easy way of adding the gun tubs to the superstructure rather than building them into it. This results in the non-scale feature of the superstructure appearing inside the tubs. I hoped that this would not be too obvious when the model was painted and fully detailed. After trimming and gluing in place, the tubs were also sealed with dope.

Thin card was also used for the deck areas around the gun mountings and the deck-superstructure hatches. The two tow rails in the bows were card strips stuck to the deck with balsa cement. The front of the chartroom had two wedge shapes which I assumed were some form of window or ventilator. They were too obvious to leave off so balsa wedges were cut and covered with thin card. Dope was again used to seal the card surfaces.

Numerous deadlights were cut through the full size PT Boats' decks. These were not always visible in photographs so I compromised by suggesting them with thin plastic card rectangles stuck to the deck. Windows in the sides of the chart and dayrooms were outlined with plastic strip.

A prominent feature of the ELCO boats was the six exhaust mufflers on the transom. At low speeds all the exhaust gases passed through them and exited underwater for near silent operation. When full power was needed the mufflers were bypassed by means of a valve arrangement at the top of each muffler. On the model the mufflers were simple wood shapes with the tubes being cut from aluminium tube. The valve linkages were made from brass wire. The final result was a reasonable representation of the full size exhaust system.

The final parts to add to the superstructure block were the engine room vent and the 40mm ready use ammunition stowage. Both were cut and shaped from light balsa block then covered in card. A couple of coats of dope and they could be stuck to the engine room hatch.

Wire work

Close up of cockpit area; note depression rails around forward gun tub.

Superstructure details prior to painting.

At this point the model had begun to take on the appearance of a 80 foot ELCO PT Boat and I was feeling happy. This is a dangerous situation since I really ought to remember that something always seems to go wrong now. In this case it was the depression railings around the machine gun tubs.

These rails were fitted to prevent over enthusiastic members of the crew from shooting pieces off their own vessel. The rear mounted 40mm gun had a relatively simple arch shaped rail but the machine gun tubs were something else. A circular ring was held above the top of the tub by three supports. The depression rails were fitted to the rings and these were the problem. Numerous variations in the rail shapes could be seen in the photographs of the full size boats. Such differences are not unexpected in a mass produced item where numerous parts would have been subcontracted out to many suppliers. There would also have been subsequent field modifications and repairs carried out to individual boats. I could not find one clear photo showing all the depression rails on a single boat and so had to make a reasonable amalgam from several sources.

In the interests of lightness I had hoped to make the depression rails from tubing but the curves involved defeated my limited skill. In the end copper wire, stripped from domestic electrical cable, was used. It would bend to shape easily and soldering gave an immediate strong joint. A spare piece of the card tube used for the gun tubs was used as a jig on which to build the ring, supports and depression rails. The supports were then secured to the tubs with epoxy.

The rear rail for the 40mm gun was formed off the model then epoxied into holes made through the removable hatch. When the epoxy had set the wire supports between the rail and the engine room vent were added; solder at the rail and epoxy into holes made in the vent. There were also two hand rails fitted either side of this depression rail.

The next pieces of wire work were two aerials. The aerial fitted to the corner of the chartroom roof carried a circular loop. The one fitted alongside the cockpit had a simple horizontal cruciform communication aerial. After struggling with the depression rails, these aerials were a straightforward task. I used a jig, from scrap balsa and pins, to keep the separate items in place whilst soldering.

Before retiring the soldering iron the deck cleats were made from bent copper and brass washers. This was a new technique for me and the end product looks reasonable. By the way, if you choose to solder these wire items then let me suggest the use of something like a 60 watt soldering iron. A smaller 25 watt iron can just about cope with the thick copper wire but it is so much quicker, easier and neater with the larger iron.

Gruelling guns

37mm cannon made from aluminium and plastic tubes plus sheet plastic.

40mm cannon - more complex than other guns but still made from aluminium and plastic with wire details.

Twin machine guns fitted into rear gun tub.

This stage was the low point of building my model. The guns were such a prominent feature of these boats and had to look right on the model. Perfection was not required but realism was a must. Now these guns were complex items to start with so when numerous variations were found in my photo references I knew it was going to be amalgam time again.

The 40mm cannon on the stern was a reasonably standard fitting but the two cannons forward could be mounted in many ways. Apparently the crews were given to modifying or adding anything which they felt could improve the effectiveness of their boats.

Eventually some reasonable looking sketch plans were drawn up for these guns and mountings. To keep weight down extensive use of plastic tube and sheet was planned. The gun barrels needed to be made from metal tubes for strength and stiffness. Aluminium tubing was the obvious choice and most model shops offer a suitable range of matching sizes. Another advantage of these materials is that they can be painted without the need for any of the surface sealing that wood demands.

The perfect opportunity to build the guns came when my wife and her friends went off on a day's shopping. Having the house to myself allowed me to concentrate on modelling, even the cat co-operated by staying in bed all day! The same technique was used on the three cannons. First the barrels were cut from aluminium tube and fitted into a body made from plastic tubing. The gun supports were made to match the body using plastic sheet. The two forward cannons were mounted on simple bases made from plastic tube with triangular stiffeners at the bottom. The rear 40mm cannon was more elaborate which means my interpretation contains some errors. After building it I found that two cylinders, containing the elevation counter-balance springs, ought to have been fitted below the gun body rather than the single one I used. The base of the 40mm mount appeared to be tapered but I used a plain cylinder. In fact a cork from a wine bottle was found to be about the right size and after a couple of coats of dope it was glued in place.

The twin machine guns were more of a problem as most photographs of them had many details obscured by the depression rails and crew members. The actual gun barrels were covered by perforated tubes. I did try to drill holes in some aluminium tube but made a complete mess of it and decided these perforations were not essential at this scale. Due to a lack of suitable aluminium tube I was forced to use brass in these machine guns. Again this fitted into a body made from square plastic tube. A few extra details were added from plastic card and strip before two guns were glued to a plastic mounting strip. I know this was inaccurate but without better information I decided to use the simplest way to install them into the gun tubs and hope that it would not be too obvious when sailing.

Torpedoes and rockets

Torpedo from balsa dowel with plastic sheet details.

Torpedo launching racks from plastic sheet.

5in rocket launcher from aluminium tube and plastic.

One appeal of these later model PT Boats is the visible torpedoes on the simple roll off racks rather than bland looking torpedo tubes of earlier vessels. After all these torpedoes were the original reason for building PT Boats.

Looking through the stock in a local model shop revealed some balsa dowel which was an almost perfect match for the torpedo diameter. In the interests of weight saving the lightest length of dowel was purchased. After cutting to the correct lengths the nose sections were radiused whilst the rear had a taper cut and sanded smooth. The important thing is to get all four torpedo bodies as identical as possible, any differences will strongly attract the eyes of everyone.

The torpedo bodies were sealed with several coats of dope, sanding between each to ensure a smooth base for painting. The rear fins were cut from plastic sheet and glued into slots cut into the body. At this scale the two sets of contra-rotating propeller blades really need including, I just used plastic strip for these blades. The final item was a small dome headed screw in the nose of each torpedo.

The torpedo launching racks were made up from plastic sheet. It was not easy to make out the construction of this item from photographs and, again, some variations were apparent. Rather than cut a circular notch in the racks to match the torpedo body I reversed things and cut slots in torpedoes to match the racks. This was much easier and neater with the bonus that whilst securely held to the racks, the torpedoes could be removed if required.

The final weapons to be made were the two rocket launchers. After the complex guns their simple structure was almost a pleasure to build. The rocket tubes were cut from aluminium tube then Superglued into blocks of four. These blocks were then stuck in pairs to plastic rod which was then fitted to a simple base from tube and plastic sheet. The tubes were normally carried inboard and only swung outboard when loaded. I thought it safer to sail with them inboard rather than knock them off the model on every docking!

Making a mast

Mast frame from plastic strip. Radar and radio aerials soldered up from brass wire.

Dinghy carved from balsa. Liferaft built up from plastic strip and sheet.

After all the problems with some details the PT Boat mast proved to be a relatively easy item to make. The full size mast was simple frame which was hinged to the dayroom roof allowing it to fold down onto an arched mast support. The mast was kept upright by means of an A-frame at the rear.

For speed the mast structure was made from plastic strip in a jig made from pins pushed into some scrap balsa. The top of the mast carried a radar unit. The aerial was soldered up from brass wire and the streamlined body it fitted onto was made from dowel. Another circular aerial had to be soldered together from brass wire and fitted to one of the mast uprights.

To ease transport and storage I opted to make the mast detachable. Lengths of wire were glued to the base of the mast and A-frame so that it could plug into holes in the dayroom roof. The mast hinges were suggested with some plastic strip. The mast support was also made from plastic sheet.

Boats

PT Boats usually carried a small liferaft on the chartroom roof just ahead of the cockpit. I found some half round plastic strip which had been an impulse purchase at a model show a few years ago. This was just the job for the edges of the raft and was stuck to a plastic sheet base. A few extra strips of plastic made the simple details of the raft.

A small dinghy was needed and it looked like the PT Boats were equipped with a simple plywood hard chine type. The easiest way to make it was to cut and sand it from soft balsa block. A few coats of dope, sanding between each coat, sealed the balsa ready for painting.

There were still a few details to make but I felt like now was a good time to start the painting process. Luckily I realised that the cockpit controls needed adding first. These were just a few items to suggest switches, dials and throttle levers mounted on a balsa/card panel. For the helm I took the soft option of using a ship's wheel from the scrap box.

Painting problems

Superstructure with details prior to painting.

Close up of cockpit area with controls and instruments suggested.

All details fitted for one last check before painting.

Close up of transom showing mufflers and exhaust details.

Anyone who attempts to paint a scale model will have encountered the 'shade' problem. This is where even though you know the colours used on the full-sized vessel, some discretion is needed to produce a realistic final effect on the model. The cause of this problem is that we view full size vessels at some distance and the intervening air tends to dull colours down. Over large distances and less favourable light conditions, most colours can become shades of grey. So, using exactly the same colour on a model but viewing it over much shorter distances can result in the model looking a little too bright for realism.

The PT Boat also gave me the problem of trying to figure out the exact colours used. There was a colour photograph of a PT Boat in one of my reference books but these cannot always be relied upon. Differences in light conditions as well as film processing can significantly change the apparent colour of vessels. After puzzling over the Humbrol colour charts I opted for a base colour of Matt Dark Green, paint No. 30. This would be applied to the whole model above the water line. The hull sides and superstructure would have a camouflage pattern of lighter matt green and black, the decks being left plain dark green. The hull below the water-line would be painted a dark gloss red. The use of a gloss paint in this area was for a little extra toughness.

As all the fittings required painting with matt dark green, spraying seemed the best way to go. Humbrol do offer this colour in 100 ml spray cans. I know the spraying cognoscente will decry crude aerosol spray cans but for the price of their compressors, airbrushes, etc., I can build a lot of models. Two cans were enough to cover the hull, superstructure and details.

The water-line was marked around the hull with a fine felt tipped pen and the underside painted with dark gloss red. I mixed Humbrol gloss red and black, No.'s 19 and 21, although their crimson, No. 20, might be a good alternative. The camouflage areas were lightly drawn in pencil then painted with Humbrol Marine green and matt black, No.'s 105 and 33. There is some scope for artistic licence as camouflage patterns were quite varied.

The torpedoes were another puzzle. Quite a few modellers have painted these items with metallic bodies and red warheads but this did not seem right for wartime conditions. In an American magazine I found a painting of a PT Boat which suggested that the torpedoes were left with a metallic finish. As all the black and white photographs seemed to show the warhead a different shade to the body I settled for using a 'gun-metal' paint on the body and 'steel' on the warhead. The torpedo propellers were painted with a copper colour. Details of the guns were also picked out with these metallic paints. The aim being to be subtle rather than glaringly obvious.

Final details and fittings

The last items to make were the ready use ammunition lockers fitted to the deck and two engine room vents. The lockers were just cut from some light balsa and covered in card before doping and painting.

The pins in the base of the mast pushed into the holes in the dayroom roof and needed no further securing. Likewise the slots in the torpedoes firmly gripped their launching racks. The other items needed glue to hold them onto the model. I opted to use Copydex, a latex based adhesive. It dries colourless to produce a very firm bond which is strong enough for the rigours of sailing but can be broken with a steady sustained peeling action. This is very handy if you ever need to remove items for repair or replacement.

The guns looked a little vulnerable, perhaps more to my hamfistedness rather than the stresses of sailing. I drilled a hole in the gun bases and glued a length of wire in place. The wire was then fitted into a hole through the deck sheet when the gun was glued to the deck. So far this has prevented me having to fish these items out of the lake!

Satin blues

The model looked smart but I was conscious of how delicate matt paints were to accidental damage. Even a gentle brush, such as might occur during a docking manoeuvre, could mark these surfaces. It seemed only prudent to spray the model with a clear satin spray. No problems were expected as I have used these satin sprays successfully before.

I waited for a dry and warm day before starting to spray in the garage. The first coat went on well enough and the model was put to one side with the intention of applying a second coat after the recommended one hour interval. I glanced at the model a few minutes later and was horrified to see that the matt paint had bubbled up in several places. The model looked terrible and I was convinced that nothing less than a complete repainting would have to be carried out. Still, there was nothing that could be done with the model still tacky so it was left for a couple of hours whilst I cursed my bad luck.

Returning to the model and I was amazed to find that all the bubbles had disappeared. If you looked very carefully slight surface crazing could just be seen but that was all. Having resigned myself to repainting the model I took the view that it was worth the risking a second coat of satin varnish. Again bubbling occurred but nothing like as bad as before and after a further hour these bubbles had disappeared.

At this stage I figured that my luck had been pushed about as far as it would safely go and applied no more satin spray. Luckily these two coats had produced the desired effect of toughening the model's surface. The colours had also darkened noticeably but this still seemed to give a realistic finish. I did learn one important lesson from this incident and that is in future always test paints and sprays on some scrap pieces not the latest model!

Bath trials

Rudder servo installation showing double linkage to tiller arm.

General motor installation. Note Nylon bolt bracket on bulkhead.

Hatch removed to show internal layout. Note the use of plastic foam to prevent anything from moving whilst sailing.

With the model completed some tests were needed to sort out the final details of the best motor-gears-propeller combination to use. For convenience these tests were carried out in the bath using an ammeter to measure the motor current. If you try this method then here's a couple of tips; first do not overfill the bath as a fast electric type of model will throw lots of water all over the place. Secondly, hold the model very firmly as the significant thrust created by these models could cause serious damage given half a chance!

The mild 540 motor used in the first trial runs part way through the model's construction was first installed to give me a 'yardstick' against which to measure other motors. From this it was clear that a current of several amps would be needed for realistic performance. Some 'stock' motors that I would normally use in racing models were tried but they drew very large currents unless small propellers were fitted. After numerous combinations had been tested, the best appeared to be a 545 using 2 1/2:1 gears and a 45mm propeller. A full speed duration of 10 to 15 minutes appeared possible and a healthy amount of water was churned around the bath. Incidentally the five pole '545' motor was one of the racing types, not the lower current versions which are suitable for more sedate scale models. It runs around 18,000 RPM no load on 7.2 volts and carries the identification 'YA 23 H5' on its body.

These bath tests did also show up another problem. The speed controller I intended to use was a very reliable one made by a well known R/C manufacturer. It has given me several years of flawless use in many different models but it did however show one problem in the PT Boat model. Being a very light and powerful model it needed fine motor control at low speed to ensure it could be sailed with precision. This controller was just too insensitive, even one 'click' on the transmitter trims could make the model jump from rest to a modest walking pace. I could see any attempts to use the model with this controller on a steering course to be very taxing indeed!

The answer lay within the pages of this magazine where I read about ASTEC HFR 15 electronic speed controller. A quick phone call to Allan Shillitto confirmed its suitability for the PT Boat and an order was placed. The unit arrived in a couple of days and was immediately installed into the model. What a difference! The motor could be made to turn over at a dead slow tickover speed which would be perfect for scale steering events. Equally impressive was the fact that it hardly warmed up when in use. To my simple engineer's mind this implies that the HFR 15 must be a very efficient unit. This left nothing else to do but charge the batteries and give the model a good work-out on the club's lake.

Sailing time

The first chance to sail the completed model was under less than ideal conditions with the wind making the lake very choppy. I was warned about the danger by one member who had nearly floundered with his normally safe pilot boat but returning home without sailing was unthinkable. The PT Boat had a very lively maiden voyage as it flew between wave crests. I might not have learnt much about its handling characteristics but at least it proved its stability.

The hull was surprisingly dry in these conditions with little water being thrown onto the deck. The simple 'plug in' deck access joint was effective in keeping the insides dry. I did later worry about the possibility of the superstructure becoming detached whilst sailing. A hidden latching mechanism ought to have been designed into the model but at this stage some improvisation would have to do. A model aircraft wing bolt seemed the easy solution with the threaded bracket fixed to the plywood motor mount, this allowed the bolt to fit through the cockpit hatch. By reducing the bolt length, just a few turns are needed to give effective but not too obvious security.

Later runs, under calmer conditions, showed that the model ran at the desired 10ft/sec (3.2m/s) with much the same trim as the full size PT boats. That is the bows clear of the water without the stern squatting. A straight course could be held by the model, any deviation by wind and/or waves being slight and easily corrected. A slight torque induced list was apparent at full speed but it is not worth the trouble to correct.

I had been warned that such a model would be difficult to steer at speed. Depending who you talked to the PT boat would either need the whole lake to turn in or the rudder would be so vicious the model would roll over! In fact the rudder control was excellent with the model immediately responding to the transmitter commands in a smooth and safe fashion. Full rudder movement, about 35-40 degrees either way, can heel the model over at full speed but without any danger. Such tight turns ought to be reserved for emergencies and high speed turns kept wide to maintain realism and speed.

Low speed handling was investigated next and this is where the ASTEC HR 15 speed controller really showed its value. The PT Boat could be made to creep along but still with full rudder control. Advancing the throttle stick would increase the model's speed by just the right amounts to give the perfect manoeuvrability needed for the typical obstacles in scale steering courses.

I had been warned not to expect any steering control when moving astern. In fact using the HFR 15 to avoid moving too fast and the model could be turned in either direction astern. Moving too fast astern makes the transom 'dig in' and can lose rudder control as well as swamping the model.

As for sailing duration my model uses six RC-2000 cells and I expect to get between 20-30 minutes sailing. This time does depend on the mix of high speed sprints and lower speed cruising. Such times seem reasonable as a couple of charged battery packs will give you up to an hour's enjoyment. If you use smaller capacity cells then the duration will be proportionally less, even so 1.2 Ah sub-C cells ought to comfortably give you 10-15 minute runs. I must comment that if you want to increase duration with this type model then the best method is probably to reduce the current drawn rather than adding mass with larger and/or more cells. It is easy to find yourself in a spiral of extra mass creates extra drag which requires extra power ........

One unexpected problem that did occur was an intermittent loss of control when sailing the model at distances over 100 feet (30m) away from the transmitter. As the R/C outfit being used in the PT Boat had worked perfectly in several more sedate scale models I was worried that my installation of the speed controller was faulty. Allan Shillitto was contacted and no obvious problems could be uncovered. It was then that Allan commented that some modern outfits can be short of range, something not spotted by the average boat modeller but becomes apparent with high speed models which must operate over greater distances. To test this I swapped the transmitter for an older one, about 20 years older!, and found that the model now behaved perfectly at ranges of 200 feet (60m) plus. It would be interesting to know if I was just unlucky or is this a more wide spread problem with basic two function R/C outfits?

Judgement time

It's fairly obvious that these plans would not be offered to the Editor if the model did not work. In fact to be totally honest, it succeeded better than I had any right to expect. Functional fast electric models can be a source of many problems usually centred on reliable performance and handling. To burden such a model with scale features and you could end up with something that looks attractive but is impossible to sail safely.

The 80 foot ELCO PT Boat model does not appear to have any vices. Even with my sometimes brutal handling it has so far not encountered any problems. That's not to say it's foolproof and successful construction demands competence in the basic modelling skills. Likewise, outfitting and operation of such a model will be fraught with problems if you do not bother to do it properly.

There is fair scope for trying different motors and 'tuning' the model to get the combination of speed and duration you desire. I have safely run the model a faster than the 'scale' 10ft/sec but it looks rather silly and significantly reduces the duration. It is your call but the PT Boat is not an 'out and out' racing model. Having said that it can beat a few kit based fast electric models!

Perhaps the most rewarding feature of this model is that it is great fun to sail. You can storm across the lake, carry out wide sweeping turns to return and finish with a slow and precise docking. Here is a scale model that looks like it is sailing with a purpose not aimlessly wandering across the water. My next project will be something different but I plan to return to high speed scale models before too long.