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RoyBoy1256

Propeller size question-Mercruiser.

6 posts in this topic

I have a 1989 Lund Tyee (18.5 ft.) with a Mercruiser Alpa One. I currently am using a 14 1/2 diameter, 19 pitch 3 blade prop. I get out of the hole just fine but I can reach upwards of 5,800 rpm's and I don't want it that high (prefer to stay under 4,700). I use the hub assembly and my question is do I have to stay with that diameter and should I go to a 21 or a 23 pitch? I cannot find this info at Lund, and or, Mercury. I know I will be slower out of the hole, but my top end will be better. I run with some big boats and I'm always way behind and I don't want to buy both props if I don't need to. Would the 23 pitch be best??? Thx for any help.

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Yep... RoyBoy, this is the wrong forum unless you're running an 'iceboat'. You might want to contact Jay Soderbloom on the BWCA, Duluth forum. He can answer your question online or by phone. You've posted the info he needs, just the wrong forum. He's a GREAT guy to deal with and he knows his business!! Give him a shout. Phred52

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D'oh! thanks Jethro and more importantly Phred, I'll look Jay up! "This Father is Remorse..."

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Mistakes happen.

I would guess that you were so darn excited to hear some opinions and you overlooked it.

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Maybe its just me but inboards aren't intended to run/cruise WOT, at least not on larger boats. Having said that you could afford to drop some RPM's at WOT. Your boat isn't small but its not big either. For me its get it on plane fast then throttle back down to a good cruising RPM.

Your prop selection is going to depend a lot on the size water you use your boat, specifically the size waves and swells that water can put out. Why so? Well small water where your not going to throttling up and down to adjust to swells and waves is a pretty much get on plane and cruise. In those cases you have the trim to help get on plane as well. Larger water you will need to adjust to waves and swells constantly at times, so often that trimming in and out isn't going to happen fast enough nor is running swells and waves being trimmed in safe to do.

My use of inboards is on big water. There is nothing worse then being under propped when your ask your inboard for instant power while climbing swells. Then just as fast you throttle back when descending, then power again on the climb. As you can see trimming isn't an option and the prop will be doing all the work. For that reason I'd opt for the higher WOT but throttle down to a cruising speed of under 4000 RPMs. Personally I keep it at under 3500 RPMs. If I used the boat on smaller water I'd come up in pitch that hits close to max RPMs at WOT to increase my cruising speed and not worry about how well the boat climbs in big waves and swells.

Give Jay Soderbloom a call.

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