Ok, some time ago (just over a year now) I decided that the whipper snipper in the shed with a broken flex shaft had more to accomplish in life other than the tasks of a mere garden tool. It was with this that i decided to build a boat!
It was a Ryobi 31cc trimmer. These seem to be common for use on 1/4 scale planes with a few mods so i thought it would be worth a shot. The engine was stripped from the trimmer and cleaned up. I then removed all the excess material from the plastic back plate, machined down the flywheel and it was mostly ready.
I then started browsing for a hull to plant this thing in. Cheap is usually my biggest objective so i ended up scoring some plans for a wooden hull from a man named Doug. He designed this hull himself and races with it so i figured it was a good start.
I built the base of the hull with the stringers and bulkheads but that was where it stayed up until about January of this year. I hadn’t even put the side boards on. Other things had me distraceted – Family, work, RC car, RC heli….
So, over the recent christmas holiday break i decided to get back into the boat. I stuck the sideboards on and started looking at it more seriously.
The engine is natively air cooled which i was thinking might be a problem (most RC boats have water cooling). So i shaved 3 sets of fins off the head in the lathe and proceeded to make a ‘cap’ for the head to run some water through as the boat ran. The hat was then bolted to the head using some gasket silicone to seal the water in.
I made up some engine mounts to secure the motor into the boat as well.
From here, i was a bit unsure of how to progress. I knew i needed a shaft from the motor down to the prop but there seems to be very little information on the net about just how this is accomplished. It was then that i met up with a man named Les. As it turns out, he has a big zenoah based boat and used to race boats regularly. Just what i needed – someones brain i could pick from.
I inspected Les’ boat, asked a heap of questions and i was on to the next stage.
I sourced some Teflon and brass tube for the flex shaft to travel through and also some other gear to make up a ’skeg’. I also bought a prop, drive dog and rudder off ebay. These you can’t really make….
The skeg was fabbed up using stainless and then secured to the boat using aluminium angle. I made up a brass ferrule to tie the flex shaft and straight 1/4″ shafts together. It was then all put together… I am using teflon in the skeg as bearings, we’ll see how well it holds up.
19/1/08 – I then spent about a day fabbing up a tuned pipe for the engine (with thanks to javapipe). It was very hard. I had to manually fold the cones into shape and then mig weld it all up. Very hard on just ~0.6mm stainless ( Some old heater flue i had ). It worked out ok tho, just not as pretty as i’d hoped…
Weekend 26-28 Jan 08 – The engine is now mounted, petrol tank and flex shaft in. I have also made room for the radio box and got that all sorted. I also finalised the manifold for the tuned pipe and I tried to start it for the first time in a year or so. Turns out that the carb was cactus now. Apparently the fuel pump diapragm goes hard and stops it form working. Not to worry, i ‘borrowed’ the carb from my current line trimmer and got it started (With the help of my mate Tim)
Stay tuned, hopefully it will hit the water this weekend!!