Building the GTM Snark 2 Unlimited Hydroplane

Building the GTM Snark 2 UL Hydro

The Snark2 is a semi scale unlimited hydro for 400 or 480 motors and 6 or 7 cells.

Start by trimming round the top and bottom halves of the hull. On the bottom so that there is an approximate 5mm lip all the way round the edge, and the top just inside the moulded in lip.

Identify the access hatch in the hull top and cut it out, this is best done by light scores with a knife. I extended the hatch area on mine to give greater access - don't go too far forward or the hull will be liable to twist.

Line the inside of the hull top round the access hatch with 5mm wide plastic strip to provide a lip for the hatch to seat on.

Decide where the turn fin will be located (inside, outside or rear of the right hand sponson (from the rear!!) Double the area with two layers of 2mm light-ply or similar on the inside of the sponson..

You can if you wish fill the sponsons with expanding foam - now is the time to do it BUT beware the extra weight!! Once it has fully expanded trim it around. Check it again before joining the hull.

Use light-ply or similar to double the transom. Place a piece of cardboard on the outside of the transom and draw round it. Cut it just inside the lines so that it fits inside the transom. Then use the template to cut round the light-ply. The light-ply should extend to just above the hull join so you must allow for this. Cut the light-ply - fit and glue it in place inside the transom.

Determine your layout by dry fitting the motor cells and radio gear etc. - Move it around until you get a good arrangement that puts the centre of gravity as close to the rear edge of the sponsons as possible and as central as possible. The tail of the propeller should ideally trail the transom by 1.5". This effectively sets the motor position!

With a flex shaft you have the opportunity to adjust the height of the prop. With a fixed shaft once it is in place it is difficult to adjust - the positioning exercise is therefore critical. A scale drawing can be a great help when trying to determine the position of the access holes - which will be in different places depending on your chosen solution. If you chose the Graupner drop in straight shaft set up the motor mount can be simply made, triangular in shape with a hole to fit over the nose of the coupling housing - leave 3-5 mm around the nose piece - .

Once you have decided on your layout the area which supports the motor and the shaft exit area should be lined with light-ply or thin (0.4mm) birch ply. This is essential in order to spread the motor loads which can cause the hull to split otherwise.

Dry fit all the hardware and the motor. When satisfied remove it all.

Glue the hull halves together (I use liquid Polystyrene cement). Finish the edges off all round. - Fill the hull with water and check for leaks. Fix them all now!!

Remove the protective covering from the moulding. If you are going to paint then carefully rub the whole surface down with wet or dry paper until you cannot see any shine at all. Wash with warm water and a drop of washing up liquid and pat dry. Apply the paint - make sure that tit is OK with plastic - you may need a barrier spray first, then primer then the finish. Don't go mad as paint is heavy… rub down between each light coat.

Re-install all the hardware. The turn fin needs to be small and angle slightly in towards the centre. Any twist in the fin or it's mounting will cause drag so care!

Install all the radio and repair to the lake for a test run.