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Optimal prop for my Honda BF75

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WalleyeBrian

Member
Greetings, I’m wondering if I’d get better performance and ride quality if I change my prop on my Lund 18 Alaskan with a Honda 75HP tiller.

My current prop is a 13-1/4” x 15” Honda Turbo. At full throttle it pushes me along comfortably without almost any porpoising at 34.7 MPH at 5627 RPMs
If I trim it to absolute max speed but with massive porpoising, I get get to 35.9 MPH and 5784 RPMs.

I predict that even if I could obtain better performance changing the prop, it won’t make a big difference. But, it would be worth it to me if it makes even a small difference. My fishing buddy’s boat goes about 1.5 MPH faster than mine, and he beats me to spot-on-the-spot fishing locations (and likes to joke about his boat being faster). So, clearly the stakes are high ;-)

Greatly appreciate any advice!

Best regards
Brian
 
Well, I always say prop experiments are for folks who have plenty of money to throw away but can't get a lift to Las Vegas.

It sounds to me though that, if you're committed, you might gain a little something by taking out some "bite" (pitch).
The fact that it porpoises trimmed in all the way means it's pushing the bow down to the point that buoyancy (and speed) is pushing back. But have you tried moving some load around first? You might be a little nose heavy and shifting some weight is a lot cheaper sometimes than a new prop.

Don't get me wrong, I'm FAR from being an expert here but taking out a little pitch or decreasing the diameter can get you a fraction more speed but you may suffer on the hole shot end...especially if you carry additional loads occasionally.

JMO and should be taken with a healthy dose of salt...over the gunwale, not down the hatch.

Good luck.
 
I have a Honda 90 on a pontoon boat where I played with prop size. First prop was a 13p, and top rpm was just over 6k, with a speed of 24 mph. This thing would accelerate from a stop like gang busters, but the motor was sounding pretty busy at WOT. Second prop was a 15p, that top rpm was 5500, and not nearly as busy sounding. Surprisingly, top speed was up 2mph to 26mph at the lower rpm, but this prop didn't have the big kick on initial acceleration. Still has plenty for tubing though.

My point is, the 4 strokes don't always make their best speed at top rpm.....
 
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