Anyway, this reminded me of a skiff that my brother Keith had back in the '70's. There's an bit of a story to be told here, so I thought I'd do a new Topic on Surfacing Props and our experience with them. The skiff was originally powered by a Peugeot 403, 4 Amals and all, a popular choice in those days, but the time came for a new "modern" motor. We picked up a second hand Datsun 1600 SSS motor and set about freshening it up ready for action in the skiff.
At the first trial fitting, as we were lowering the engine into the boat, I asked Keith "are you going to cut a hole in the bottom of the boat for the oil pump?" Guess we'd overlooked the fact that the Datto engine had an external oil pump that protruded somewhat lower than the engine.
After scratching our heads for a while and lubricating the brain with a coldie or two, we decided to raise the back of the motor significantly to overcome the oil pump problem, thus reducing the shaft angle and creating a surface (or is it semi-surface?) prop skiff.
In our first effort, the prop was about 10 inches behing the transom. The problem was, the bloody thing wouldn't go. No matter what revs it was taken to, it just did about 10 or so MPH. We consulted an old family friend, Ernie Nunn (guess you've heard of him) who advised that the solution was very simple. As the boat started to move, it created a depression behind the transom, followed by a wave. With the prop only 10 inched out the back, it was in the area of depression and was spinning in air.
The next step was to lengthen the skeg and shaft so that the prop was about 24 inches behind the boat. This did the trick. It took a while to get the thing out of the water and onto the plane. but it went like buggery. Our guess is about 65 MPH. The speed was never measured, the old skiff fell apart before we could do any time trials in it.
So, that's our surface prop story. The principle works whan you get it right.
Below is a photo of the little skiff with rooster tail, quite an unusual sight.
And here is a link to a video showing how the Thai's use the surface prop principle, to it's extreme, in their long boat racing.
http://www.youtube.com/watch?v=mRvVOMPtwiI
