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From what I've searched about ducted fans the slots are not beneficial at all and I'm not planning to include them on the duct I'm planning to mould for my boat.
Many thanks for your thoughts! It's just how I imagined it would be.
As far as I'm concearned your experience had very logic results when you talk about increase in thrust and slightly reduced top speed in your dinghy.
More thrust is obviously an advantage on an auxiliary outboard while a bit top end speed loss (which I suspect might have been caused by the extra drag) is something I'm willing to accept, although it may not even be noticeable on a boat travelling at 7,5 knots (Fulô's speed with its 5hp tohatsu at 3/4) because, as you surely know, the dinamic drag coefficient increases with speed and it is my conviction the the drag induced by the duct will only have sensible negative results at planning speeds...
Besides all this I also expect some reduction in the propeller aeration issues I experience very oftenly because of my offset engine setup being extra sensitive to boat heel (even on a trimaran)
Once again, many many thanks for sharing your precious experience!!
PS- I intend to build my duct out of wood/epoxy/fiberglass laminate to avoid bimetal electrolyses to arise from the assembly... Any alternatives?
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Last edited by pedcab; 10-26-2009 at 10:35 AM.