What pitch prop should I upgrade to?

[bessary]

I have a 1991 Stingray 536 zpx, 17'-6" with a 175 HP 4.3 and Alpha 1 drive. I have an alum. 13-3/4" x 21 prop on it now. At about 4600 rpm's, which is just shy of the WOT of 4800, the boat registers by speedo, to be doing appx. 40 mph. The guy I bought it from said it'd do over 50. Ha!

I know I want to upgrade to a s/s prop, but I was also thinking of stepping up to a 23 pitch, keeping the same diameter.

Any suggestions? I want more top end.

 

[kenmyfam]

Re: What pitch prop should I upgrade to?

Do you know what the max RPM of the engine is ????

 

[Dhadley]

Re: What pitch prop should I upgrade to?

If you're at 4600 now, going to a 23 will pull the rpm's down even further. And going to a ss will probably add bite too pulling the r's down even more.

There are props made for I/O's. If I were doing it, I'd try a 14 1/4 x 21. Something like a Stiletto or the standard Turbo I or II. That should give you more lift which should reduce the drag (less wetted surface) and get you slightly more rpm and possibly more speed. But I wouldn't look for 10 mph.

The boat probably will do 50+. On the trailer behind a good truck..........

 

[Crownie2]

Re: What pitch prop should I upgrade to?

Stingray is one manufacturer that has a lot of information about past models on it's website.

For example, the standard propeller for a sea level 536 was a 13 1/2" x 23" aluminum with that engine. The optional prop was a 14 1/4" x 22" SS Turbo 1. The top speed (with Turbo) is listed as 51mph.

Therefore, I conclude that if you are operating at sea level, your boat has lost some of it's original performance over the years.

I agree that, depending on your gear ratio, a 20 - 21" SS bow lifting prop would probably be you best bet.

By the way, what is the gear ratio? is should be located on the port side of the drive.

IMO you should be getting about 45mph if the engine and hull are in good shape.

Bob

 

[redblur]

Re: What pitch prop should I upgrade to?

I just bought a 20" SS Apollo 4 blade from iboats for my 2001 Maxum 19' w/ 4.3. For $250 I thought it was a good deal.

I've only been out with it once for a real short time but it seems to be a perfect fit. I'd tried 23,21,19 and 17" three blade alum with similar resluts to yours. The 23, and 21 WOT RPMs were too low with no hole shot. The 19 and 17 WOT RPMs were too high but I had been using them because for skiing and tubing it worked the best, I just never ran it at WOT.

From my limited testing the 20" SS 4 blade has just about as good a hole shot as my 17" alum 3 blade and my WOT RPMs are right at 4800. Top speed measured by GPS is 47.3 MPH

http://www.iboats.com/mall/propfind...3342&cart_id=898742433&engine_id=448&pf_new=1