I think I want a 4-Blade...Apollo?

[eja]

Hey guys (and gals),

I own an '89 Rinker 20'6 Open Bow witha Mercruiser 5.0/4-bbl (230hp) Alpha 1 setup. I am currently running a Michigan SS 20P prop, which seems perfect as far as WOT (51 mph GPS @ 4750) and fairly good hole-shot. BUT, the boat seems to want to porpoise at cruising speed, requiring me to trim way down to eliminate it. I will get it set back up and then it begins again (only minor waves). Well, my buddy read an article abut 4-blade props, and the increased bow lift, etc. His dad runs Outboards, and has a 23P SS 4-blade that we tried (just to see the difference) this past weekend. Obviously te 23P is too steep, but it seemed to have an positive impact on the porpoising that we all noticed.
I think I want to go with a 4-blade (with the correct pitch), but have a few of questions:
1. My SS 20P is kinda roughed at the leading edges. will this have an impact on the bow "lift"?
2. Can I have my SS 20p reworked to improve the bow lift?
3. Can I expect a 4-blade aluminum to have the positive impact I experienced with the 4-blade SS over my 3-blade SS?
4. Mercury Props Vensura vs. MichWheel Apollo vs ??
5. Stay with 20P?

Thanks!

 

[mole2]

Re: I think I want a 4-Blade...Apollo?

Do you have trim tabs? If not, that's what I'd be looking to add in your case rather than a new prop. It will help to keep the bow down and control the porpoising.

 

[Crownie2]

Re: I think I want a 4-Blade...Apollo?

There are Mercury dealers that load out props to try. See if you can find one and try some different ones.

Sounds like the 3 blade is almost perfect for you, though. I wouldn't go to a top speed reducing 4 blade unless absolutely necessary.

Yes, it is possible that your prop is in poor enough condition that it is not giving the bow lift you need and you have to trim up more as a result. Most boats I've run into will run pretty well at neutral trim for cruising and then add trim to go fast - unless there is a hull problem or weight distribution issue. Speaking of that, you may want to try moving weight to the bow, for example, to see if that helps.

A good accelerating and efficient prop like the Merc Enertia might be perfect!

Let us know how you make out.