One of the most difficult design aspects to get right is an underwater exhaust. Powerboat builders and designers have been wrestling with these issues for years, and nobody–let us repeat that, nobody–has a pat answer. With conventional motor yachts, there is so much horsepower involved in propulsion that exhaust noise is a major issue. Add in engine rooms that are almost always near the center of the vessel, and the need for–and difficulty with–an underwater exhaust multiplies.
In our case the options are easier. We have very small power requirements, so noise and vibration are minimal. The engine room is all the way aft, so the noise is isolated from the living quarters. The aft location coupled with small engines and big rudders makes it possible to place an underwater exhaust, if indeed it is warranted, behind the prop(s) and rudder(s). This eliminates the inefficiencies that occur when you are injecting exhaust, and the related turbulence, ahead of the propulsion/steering foils.
In the case of the FPB 97, we have a scale model in Wind Horse with which to experiment, which is what we’ve been doing of late. We have set her up with extra payload, so that hull immersion forward and aft is closer to the FPB 97. In the case of the underwater exhausts, this affects the imersion of the exhausts, and how they sound during various sea states.
At the same time, this gives us data on the behavior of the canoe body in unusual (for Wind Horse) load conditions. There are some factors we’ve been studying that point us in a certain direction, and we are testing to see how these work.?Changing the trim, moving fuel/water forward or aft to immerse or raise the stern, allows us to get an idea of how the FPB 97 might react.
We are a ways from finalizing things…there are still some configurations to test, but we are zeroing in on a decision.
In the meantime, we’ve made a short video, taken going uphill against a 4-to-7 ft (1.2/2.1 m) sea.
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