From time to time the WBA president receives a call from people wanting to sell or get rid of an old boat.

In my time as president this happened a few times and my Putt Putt Curlew is one such outcome.

About 12 months ago Chris Kelly received such a call from a fellow living at Somers, who wanted to get rid of two old boats, “free to a good home”. One was a mirror dinghy and the other described as a minihydro.

Given my interest in power boats, Chris thought I would like a new project. Not knowing what it was I asked for some pictures and David Gibson, who subsequently took on the mirror dinghy sent me a few pictures.

This did not really help my deliberations, as I thought what am I going to do with a single seat little 8 foot boat. After some deliberation, a message came through Chris from the seller that if no one took it he would sell the engine and burn the boat. I thought what have I got to lose, so went and picked it up.

The boat had been under a tarp and underneath David’s mirror, so had fared very well, better than the mirror apparently. The hull was in excellent condition and after a good wash I even contemplated not repainting, the finish was so good. However on closer examination there were some cracks in the paint so a repaint was done.

The little boat was originally powered by a Vtwin motor cycle engine but in the late 1960’s was changed to the current unusual engine.

The engine is a Sachs “Wankel” Rotary model KM48 engine of 8HP, made in Germany. These engines were used a lot in Snowmobiles in the US and also as stationary engines. I have also seen one on a German made “Hercules” motor bike.

Anyone familiar with the Mazda Rotary engines as used in the RX model cars will recognise the principle. It has a single rotor, with three chambers, therefore there is a firing pulse three times each revolution. With no reciprocating parts the engine spins freely up to around 6,000 revs per minute. It spins so freely there is a governor to prevent over revving.

Although technically a 4 stroke engine it has no sump so the workings are lubricated by a 50:1 fuel oil mix just like a 2 stroke engine.

When the boat was retired it had been running, and the owners’ grandchildren used to ride it and apparently it used to plane readily.

After repainting the hull in the original colour scheme, I cleaned up the engine and carburettor and did some research about how to set up the ignition timing. How do you find “top dead centre” on a rotary engine? Once we found a timing mark we were able to move forward. It needed a new ignition system, and my son Andrew recognised that the part was the same as in a Stihl chainsaw and was easily replaced via Ebay for $17 from China. Once that was replaced the engine started readily on the bench. There is a video of it running on the WBA forum.

The engine has since been installed in the boat and is ready to be tried on the water once we get some better weather, and I get it registered hopefully with its original number.

The propeller is very small, but the engine spins very quickly to 5,800 revs, but I suspect the propeller may be too small and I may end up with a lot of froth and bubbles, and not give enough thrust. The previous owner did say that the boat would plane with children in it but not with heavier adults. Sea trials will prove this. I have used tinnies with 8 hp engines and it easy to get them planning so this engine should be able to achieve the same thing.

There is no clutch or gearbox, so it will be interesting how I will manage to start the engine on board, as there will be instant propulsion. The idle speed is about 1,500 revs so it will be raring to go. (The old saying “one hand for me and one for the boat” I think)

I cannot find much information about the exact design of my boat, but overseas there is quite a following of what are known as mini hydromax. These are similar sized boats but powered by small outboard engines, and they get up and plane very quickly. If you have a look at this YouTube link -

, you will see these tiny boats putting on a very speedy show. The example shown has only a 4 hp engine.

Once I get the boat on the water I will follow up with a report about how it went.

David Stott.