SSM prop questions
 

Basically, boat sucks to plane off. 1990 38 Fountain, SSM IV drives, bullet is 1.5" below running surface. Transom is notched.

Last year, props turned in. Ran some 18x28 merc 3 blades. Boat was slow to plane, but they would hook up pretty decent. 78MPH at 5300.. Normal planing technique that seemed to work, was tabs down, drives down, bring RPM to 4000, and just wait till they grabbed. Then tried some 16.75 4 blade, round ear props I was told Bblades did. They have more of a rounded blade. These, seemed to plane the best, but still blew out alot. However, not my props. I spun these to 5000RPM, and 80MPH. This year I also have an extra 50-75HP per side, and engines need to be around 5300-5400 WOT.

This year, drives turning out. Got a pair of 17x29 Four blade mercs. Boat actually planed better/sooner with the old 3 blades. With these 17x29, its pretty much 4500RPM, and wait, a while. Havent got to do a WOT test yet, as I had a little motor issue.

I guess what I am asking is, is there anything that can be done to these 17x29 Merc cleavers, to aid in planing? I understand the pitch calculations, but talking about cupping, etc. A few people have recommended spacers for the drives, but I also dont want to hurt top end, as the slip numbers seem good with the Round ear 4 blades.

I think we may need to talk about this one on the phone.

You didn't mention the pitch of the round ears we made. These 17x29's you have now could be made into round ears too at the 16.25" diameter range.

Also, did yoiu change the retation from inward? Dropping the drives a touch may be a option but some WOT numbers will help to determine this.

Brett

Brett what do the round ears do for a speedmaster boat?

I have a 32 cat with a pair V's? just getting started prop testing with what we have local.

Induce stern leverage via positive trim capacity therefore creating bow lift.

Brett

cool thanks.

What horsepower do you have to run these props on our Fountain?

Hey Brett. Got to try a buddies 17x27 4 blade mercs today. Flat water, 97 degrees outside. 4700RPM and 69mph. Planed very well with these props. Props turning out right now. Boat seemed to run MUCH better with the props turning "IN" speed wise.. Propshafts are 1.5" below bottom, no boxes, notched transom.

As I said, last year, props turning "in" I turned the 16.75 Round eared 28p props to 5000, and was at like 79mph. It was a cool day. I installed a slightly larger supercharger, but right now I am still running 5psi of boost, which was the same as last year with the smaller superchargers, so power should be the same, or close.

I guess next step is to swap the drives back to turning "in" and do another test. Could the drives turning out cause a RPM loss as well as a mph loss?