We hauled our boat out a couple of days ago to replace the zincs and clean the hull. We tried to measure the prop size. It looks like about 8.5 to 9 inches radius, so maybe a 17 or 18 inch prop? There is a bit more than 3 inches of clearance between the top and bottom.
We have a 3:1 reduction with a Thunderstruck 10kW drive. Our boat is a 1989 34 foot Pacific Seacraft sailboat with about a 14,000 pound displacement. Currently we are able to go about 3 knots with 1100 to 1400 watts and 4 knots with 2000 to 2300 watts. 5 knots requires a vibrating 4000 watts and we have never tried to go full bore 10,000 watts. I do not like the vibration and am still trying to figure it out. The prop shaft did not seem to have any side play so I am kind of ruling out the cutlass bearing. I think the problem is that the double sprocket chain coupler allows too much movement such that you are trying to handle 200 to 400 pounds of thrust through two flexible couplings (the cutlass bearing and this double sprocket). I really think that if we lock down the prop shaft with another thrust bearing in some sort of pillow block BEFORE the chain coupler that the vibration would go away. I haven't found that bearing and mount yet. The other idea is to abandon the Thunderstruck reduction and go with a 3:1 gear reduction that has a rigid coupling to the prop shaft. That would be harder/more expensive.
On the prop side of things, I am thinking we could upsize our prop maybe 2 inches? This would still give us 2 inches of clearance on the top and bottom. Perhaps going to 4 or 5 blades as well? This would mean we get more thrust for a lower speed (thus reducing vibration perhaps) AND we would get significantly more regen with the larger surface area. Sailing performance hit could be minimized by running the motor at a few amps to maintain max speed if we didn't want to regen. I don't really know where to start on the prop sizing thing though.
Posted by: lightdoesnotage@yahoo.com
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