I am applying about 110W in the video clip through a 1:2 gearbox at a cadence around 65 so prop is doing maybe 130rpm. The boat is doing between 5 and 6kts.
The prop blades are 40mm wide by 4mm thick aluminium flatbar filed into a NACA07510 section but mirror of the front edge on the trailing edge rather than a tapered trailing edge. As stated before the diameter is 540mm and pitch is 1300mm. The blades fold to enable coasting and shedding weed. It has very little slip because it is such a large swept area. The velocity ratio is only 1.015. You can see the blades flashing past in the video.
The mirrored section had no noticeable difference from the previous section that was standard NACA16410. The foil data shows that there would be some vortex shedding off the trailing edge but I am not going to notice that at the gentle speeds I am doing here.
There are pictures of the boat and another clip in rougher weather here:
Aim with this boat was to get the deck at the bow to carve through waves without diving. I am happy with the way it works. I would probably go for a bit more reserve buoyancy in the ends on a proa hull.
Yes - The rudders are what are referred to as dipping rudders - I have used these for a while now as the only drag is when I need to turn and they avoid collecting weed. The ones at present are taken from another boat. I am going to make simpler blades for this one as they work as deflectors rather than proper foils so the foil section is a waste and adds unnecessary drag.
Rick
On 29/08/2010, at 12:46 PM, jhargrovewright2@juno.com wrote:
Rick,
Very interesting.
Can you tell me more?
How are you powering the prop?
Are those rudders dipping type?
Any more information you can give?
Blade width, diameter, boat speed?
JIB
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