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Post by fiddyfish on Aug 25, 2018 6:24:27 GMT -6
Finally had some calm seas and was able to get out with my re-hubbed prop. No big difference in performance, maybe 2 mph improvement at WOT. Still only getting 23 mph. See attached for details. I'm definitely thinking that this prop has too much pitch, but will changing to a 15 inch pitch really give me another 10 mph?  |
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Post by gnrphil on Aug 25, 2018 7:17:38 GMT -6
First thing I'd do from here is raise your motor two holes, looks like it's at the second from the top. A 15 pitch prop will probably only give you another 400 rpm and if your motor is buried (which I suspect it is) that might just give you more slip and less speed. I could be totally wrong of course but those are my thought's at this time.
It's easier of course to try a prop and I'd interested to see the results.
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Post by freezerfiller on Aug 25, 2018 16:39:53 GMT -6
I don't think a 15 pitch will give you 1 mph. It will improve hole shot, but the only gain you will get is the equivalent of the Hp increase at a slightly higher rpm. I think you have something else going on. Are you running any trim tabs during these tests? I like Phil's suggestion about raising it, but I'd take a pic or vid of your cav plate while on plane before I did it.
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Post by fiddyfish on Sept 5, 2018 13:11:38 GMT -6
SUCCESS!!!! 35 MPH @5100rpm and still some throttle left. It turns out that my trim tabs were wired backwards, so bow down was actually bow up and they were down a lot. I had a friend run the boat while I watched in the stern and there was a huge wall of water on each side of the transom. Once I figured that out, I just retracted both of them . They are 9 x12 and so add a lot of drag when deployed. Then I started working with the motor trim. I keep it trimmed in until the boat climbs up on plane around 3700 rpm ( and is really working hard) and then start trimming out and the engine unloads a bit , the rpm increases, and the speed increases very rapidly. It ends up with almost all of the engine trim. I think part of the problem is still that my engine sits too deep, but that's something to correct in the off season.
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Post by gnrphil on Sept 5, 2018 13:56:35 GMT -6
Good news, yeah those tabs will slow you down. Raising the motor one hole will probably give you 2-300 rpm which will put you about where you need to be.
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Post by freezerfiller on Sept 5, 2018 15:39:32 GMT -6
Yep, trim tabs will do that. Glad you figured it out.
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