Prop size and pitch recommendations

[Lostsailor13]

I bought my rig overpropped,and have tried to find prop calculator to clear this up for me
The boat is 36ft,approximately 12 ton,has 140hp @ 2.57 and currently turns 26×21,and am curious about what size is recommended,how much am I overpropped,any input from the forum would be hugely appreciated and not wasted

 

[rslifkin]

To know how far off you are, what's rated rpm for your engines and what do you get at WOT now?

 

[rsn48]

Shhhh!! Been there, done that. There is prop software on the net that can help you out. Remember to not input your boats dry weight. No one wants to recommend a prop for you because they know all recommendations are estimates. I bought a Merc engine and leg and they didn't want to recommend a prop. But they do have prop software I used. I called prop shops in BC and Washington state and they would point in the right direction but not commit. Some shops will let you purchase and return as long as you are purchasing the next one from them. There probably will be a small percentage taken off on the returned product as they can only resell it as used.

 

[fgarriso]

https://vicprop.com/displacement_size_new.php

 

[Seevee]

I've had good luck with prop shop calculations. They should at least, get you in the ball park... close enough to make a minor pitch on the prop that will work. You might even be able to re pitch your current prop.

 

[sunchaser]

Weebles will know with a few more details.He has same vessel albeit with different engine and transmission.

 

[firehoser75]

I cannot speak to your specific circumstances, but I can relate my experiences.
When I purchased my boat, it was over propped. As used, with a clean bottom, the engine would not reach rated WOT, but at the (then) WOT, there was no visible black smoke, so we were not overloading the engine (much). Rated WOT is 2800 and we were getting about 2650-2700. I took the existing prop into the local prop shop and using specs from my boat and their software, they adjusted my prop (took 2 inches of pitch out) and now my engine will reach just over 2900 with a clean bottom.
The existing prop was original, and when tested after the boat build, the boat did reach more than rated WOT as tested. For that test, the boat had 3 people on board, with half fuel and half water and no "owner" loading. That is often the problem....... the way they are first tested (not real world), and how much "stuff" we, as owners add
My advice is to talk to the prop experts, that is what they do.

 

[Lostsailor13]

I spoke with Peter about this already his prop is 5 inches smaller with 85hp engine and a different ratio

 

[Lostsailor13]

The prop calculator link was 24x16 I'm turning 26×21 another factor I'd like to add in is trolling live bait,at tick over now the speed seems pretty good for mackerel,if anything maybe take off some pitch,I don't know,maybe just leave it

 

[Nomad Willy]

What’s your power rated rpm?
And what do you get at WOT?

Lets see what your rpm numbers are.
That must be a BW gear .. I’ve got the same ratio.
I’ve got and had an 18” dia. prop and a 13” pitch but you’ve got 3.5 times as much power.

All Willards were delivered over propped. Sad but it was fashionable in the day. My W30 has an 18” prop. It came from Willard w a 14” pitch and a WOT rpm of 2700. I had an inch of pitch removed (13”) and hit 3000rpm on the nose. Since then I’ve been favoring 100rpm over rated. And it needs to be said that the rated rpm is not a red line in any way.