PROP NEEDED

I have a 74 CC 20ft southwind but the motor was changed out and it is Left Hand
it has 13 x 13 LH ACME prop
I think the prop is a little to big first b/c it has pretty much NO clearance like not even a 1/8th inc
not sure if the spacing is closer b/c of the deep V all the way back or what?

SO... I think I need a 12 or 12.5 D with a 10-11.5 pitch?

Please of anyone has advice and etc please let me know also will sell this prop if anyone interested

Let me know if you want to sell the ACME.
I guess Ill have to shoot myself..... but I still want your prop!

Something isn't right, post a picture of the prop installed. A 13" acme should have at least 3/4" hull clearance even if its sucked all the way up to the strut.

If it is indeed a 13x13 Acme (431?) then yes that's way too much prop for a stock engine in that boat. Stock replacement size would be 13x12 Acme, and 13x11.5 is a popular replacement as well.

I have never heard of one of the larger v-hulls coming with a 12" prop from the factory. Our BFN did have pretty minimal clearance with the 13x15 it came with, though. So, if you wanted to use a conventional hand finished prop (Federal or OJ) then a 12" prop might be a consideration... though a larger, heavier boat like that would benefit from a prop with a larger diameter, in terms of performance.

Comparing prop diameter vs. hull clearance between different styles of prop (like the original Federal vs. a new Acme) can be tough though, as rake will have a significant effect. Most Acme models will increase hull clearance by ~1/2" as compared to the same diameter Federal, due to the extra aft blade rake that they have. Therefore, if youre saying that a 13" Acme has next to no hull clearance, then a Federal of the same size (which would have been the original prop) would not physically fit- which makes me question what the heck is going on with your set up.

Too much prop = a prop with more pitch than your engine is capable of turning efficiently. 30-40 extra hp from an engine the same size (cubic inches) as stock would not drive a prop size (pitch) change. The extra hp are going to be realized at a higher RPM, so you would run a stock sized prop but spin it a bit higher (say 4800 instead of 4400). A 13x13 Acme is too large of a prop for a 350 in a boat as large of yours. 13x12 would perform much better, and 13x11.5 probably even better than that.

We shortened the shaft on our BFN by 1.5" (from 41" to 39.5") and purposely minimized clearance between the prop and (new, 6A6) strut- ending up with 3/8". We still have about 3/4" clearance to the hull with a 13" Acme.

The only way the original poster could have ended up with less hull clearance than us with the same size Acme is if one of the following is true. I am operating under the assumption that the 79-80 BFN (pre- keel notch for the 14" prop) and 20' SW are pretty much the same boat from the waterline down- including powertrain/shaft/hull geometry.

1. Their shaft had been shortened further, which is possible with the original 6A strut. It could only be 1" shorter though, and even that might not be enough to leave <1/8" clearance between the prop and hull. Again, an original 13" Federal wouldnt come close to bolting up if this were the case.

2. The prop theyre basing their measurements on isnt really an Acme, or perhaps one of the few Acmes with less aft blade rake than is typical. (Im not aware of any 13x13 Acmes that fall into this category).

3. Something about their set up is really strange... combination of wrong strut (shallower angle?), wrong prop, etc.

ok I have looked at the prop again it is a 13 x 13 1" Super cup federal prop

I am was just explaining what I had to do get my I/O to get on plan and hold speeds with that much weight and I just need a prop to get on plan fast and hold speeds at low end for wakesurfing. I understand the rpm can run over and would need to watch it. as far as blades I have noticed that if you go down in pitch and add a blade per pitch it will help counteract the higher rpm b/c of extra weight and surface area.
When I get the boat out again I will see what the rpm set at WOT

I have a 12x12 lh that I bought turns out my boat was a lh its a nice one