Building an ECOfast electric race boat

Generic instructions for building an ECO boat

The critical dimensions for the hull set up are enclosed on a sheet supplied by the manufacturer. We recommend that you stick to them as close as possible - it took him a year to get the set up right. - That said you can move the motor mount rearwards slightly.

Drive Line

The stuffing tube etc is too long - shorten it as necessary. The red silicon tube is to keep things centralised during build - remove it for running - the boat runs on a single bearing at the exit point so line up is critical - we do this all the time so manufacturers instructions are not generally available. Donnie did an article on Rumrunner that may help. Here are some more pointers.

Install the stuffing tube motor and mount first - then you have a good working area.

It's a good idea to check where things will fit before starting - just tape stuff in place so that you can check C of G positions. With 6 cells they are generally in two threes - one close to the shaft and one spaced left (looking from the rear) - to counteract torque. With 7 cells then the 4 are placed on the left. This is not important at present. Just bear the final position in mind. Check that you can achieve a c of g from 25-40% from the rear by moving the cells, If it is too far forwards then you can move the motor position rear wards etc.

Cut the hole for the stuffing tube. Ideally the C of G will pass through the hole!!

Make a temporary mount for the motor - just oversize of the motor. This will be thrown away but bear in mind that the final mount will either need airflow holes in it or you will need to space the motor off the mount to give airflow. If you space the motor the mount must move rearwards by at least the spacer thickness. Tape a 1mm spacer on the outside of the hull where the measurement point is and mark the measurement point on it - remember this is the end of stuffing tube - not underneath the prop. The spacer will give you a small clearance for the prop.

Insert the tube complete with shaft and prop in the hole. Connect the motor - on it's mount and coupling and put the cooling coil (if you have one) on the motor.

Adjust the positions till you are satisfied that the manufacturers measurements can be achieved - and that there is sufficient room for the largest prop that you will use plus 1mm (so if you will use a 32 mm prop then stick that on the end of the prop shaft to do the line up). Make sure that the shaft is central to the hull and is straight along the centre line. Tack the shaft in place. Check again - and once more. This bit is critical and it is as well to get it right first time. Once satisfied epoxy it in place. It is best to line the motor and shaft up vertically to do this so that no pressure is applied to spacers etc.

Once it is all dry - use your dummy motor mount to make the real thing from 1.5mm to 2mm ply or 1 GRP sheet (old pc board) etc. The best motor mount I saw fitted the bottom of the hull and had two thin legs out to the topsides of the hull - Make sure you can get the motor out!! Slots for the motor mount may seem like a good idea but then you have to make sure the motor cannot move!!

Rudder

Once done move on to the rudder. The bottom is easy - the tube should sit flush with the outside of the hull. Make a mount for the top that braces the tube to the RHS and the transom. Best way is two pieces - The 'shelf' with a fair clearance for the shaft and then a tight fit for the shaft that you can glue to the 'shelf' when the set up is correct. The shelf can be cut to mount the servo and RX as well you will need a cut out for the servo. A standard servo and RX will fit but mini gear saves room and non moveable weight. Ideally the rudder shaft should be perpendicular to the water line when running.

The rudder supplied is a generic one… the size has been proven to work - start with that shape but….

The rudder should be sharpened at least on the front edge. Some racers prefer to sharpen the rear edge as well.

Better performance in turns may be achieved by trimming the bottom front of the rudder at 45 degrees for about 5mm and fairing this in to the rudder.

If the rear of the boat lifts out in the turns trim the top rear of the rudder at 45 degrees.

Water Cooling

A pickup for water cooling the motor can be made from a piece of Aluminium tube arranged so that the exit point from the hull is in a water pressure point from the prop. Generally slightly forward of the rudder post - and to one side and angled at about 35 degrees to the hull bottom. Make the hole and epoxy the tube in - fair it flat then file a lead in grove from the tube to about 10mm forward. The grove should be 1/16" deep at the rearward end. Connect up with silicon water tube. The exit should be forward in the hull and wher it will be visible so that you can check the water flow.

Finishing up.

RX and cells can be held in place with Velcro. The Velcro for the cells should be long enough to give cell hold for the worst case positions. The GRP will reject the velcro over time - so I superglue mine in. Cell position can be adjusted forward and rear and left to right to give the best run characteristics. It's a good idea to note down the best positions for specific conditions.

The bottom of the boat can be finished with a commercial car paint finishing abrasive - to give a real shine.

Have Fun Racing