Which Prop do I need?? Please help...

[mikem9992]

I've got an old, mid 70's 15' Tri-hull. The boat has got a volvo penta AQ120B motor with a 270 Aquamatic outdrive. I measured the prop that is on it now and it is a 15" three blade. The only markings that I can find on the prop whatsoever were on the back spindle portion and were 082011.

The prop on it now is aluminum and kind of beat up. We took the boat out last weekend and it seemed like it was pretty tough/took a long time to get up on plane, and then only ran about 25 mph top speed when it did. Any ideas what I need in a prop? Especially which pitch?
thanks

 

[steelespike]

Re: Which Prop do I need?? Please help...

I want to stress I'm no Volvo expert.I found on the net 082011 is a 15 X 17 LH rotation prop. I'm going to assume a AQ120B is 120 hp.
I my opinion on that little boat It should have excellent hole shot and around
40 mph.17" pitch would probably over rev.
From your description. I would check that the throttle is opening all the way,motor is in excellent tune and has good compression.Bottom is clean.
running on all cylinders.

 

[junior1113]

Re: Which Prop do I need?? Please help...

thinking a few factors are weighing in. what is wot rpm, how bad is prop, how bad is bottom of boat, how good of shape is the motor in, is there water in the beams? you should plane nicely with 17 p as long as wot rpm isnt to high

 

[mikem9992]

Re: Which Prop do I need?? Please help...

Fixed a couple of things now and it's running great. Still having prop problems though. Here's some more info. WOT should be about 4500 when planing, I get there and then need to back down to about half throttle to keep it in that range. It's really slow to plane, and tops out at about 25mph. I'd really like to get up to about 30-35. Any ideas what I should change?

 

[mikem9992]

Re: Which Prop do I need?? Please help...

Oh, forgot to mention, correct, it is a LH prop, 15". The boat also really wants to turn hard to the left, it's pretty irritating. Also, I've got a 15horse outboard on the back, left side, its not in the water when running. I've also got a 20 gal tank. Looks to me that the boat sits really low in the back, like it's not very balanced, but I can't think of any way to get weight to the front.

 

[hwsiii]

Re: Which Prop do I need?? Please help...

Mike, I need to know exactly what year, manufacturer and model of boat you are running. As well as verify the horsepower and gear ratio of the outdrive for me, then I can tell you what prop you need.

H

 

[steelespike]

Re: Which Prop do I need?? Please help...

Being really slow to plane and over reving don't go together.
I would expect that prop to over rev.But also get you on plane quickly.
A 20 gallon tank in the stern sure doesn't help.
There is a possibility the foam under the floor has absorbed water.
this could add 100s of pounds right at the stern where you don't need it.
carefully hole saw a shallow hole in the floor so you can inspect the foam.
If the floor seems the least bit soft suspect water intrusion.