Prop Advice

S

sbbamafan

Member
Joined
Jul 28, 2001
RO Number
5516
Messages
54
I have a 99 Doral 270SC that I got in October so I have used it very much in the time I have had it. It has a 7.4L Mercruiser Bravo 3 and runs well. I tested a couple of others (same boat) and they ran bit better and faster but for other reasons relating to their condition, I purchased the one I have. It spins many more RPMs to get on plane (has no trouble getting there though) and by the time it does, there just isn't a whole lot more left between planing (3600RPM+) and top end. I has bothered me that I feel I have to run it faster/harder than I feel I should. I have just come to realize that my boat is propped differently. Mine is propped with 22 pitch and all the others I have see have 24. Should I assume I need 24 (maybe even 25)? The boat is 7100# dry, holds 100 gallons of fuel and I usually have 4 or 5 people on board. I boat on Lake Lanier in GA and the elevation (full) is 1071'. I purchased the boat from Lake Michigan where full pool was 577'. I have not verified but I am reasonably sure the ratio is 2:1.

I would really appreciate advice on this. Thanks in advance!
 
I would edit to say two things...I have NOT used it much and others did not run better - only faster.
 
What's the top end WOT specs for that engine, 4400-4800? Are you able to reach that or maybe exceed it? That's what's important, although don't cruise at that RPM. Even with a 1999, there is likely a limiter to prevent you from exceeding that safe max. You might try going to a 23 and confirm you can still reach that WOT. A good prop shop will help you fine tune your prop.
 
At wide open throttle your engine RPM should be at the maximum RPM which the engine is rated for. If it's not, make sure the hull is clean and look at changing the prop pitch. Merc does make a Bravo 3 XR prop which is a 4 bladed prop. It does make the boat plane faster.
 
Unlike the single props, the shops can’t really adjust the pitch much on the bravo 3’s, so you are stuck trying out different sets to find the right ones. Usually the manufacturer gets it right, so unless someone came along and messed with it, what’s on there should be correct. Does Doral still exist? If so, they should be able to tell you what belongs on your boat.

Did you try Mercruiser prop selector? Fwiw they call for a 22 pitch with a boat in your weight range. https://www.mercurymarine.com/en/us/propellers/selector/#!/step-one

I have 26’s on my bowrider, same motor, 7.4 mpi - but i only weigh 3,100 pounds. I have a spare set in my shed; can’t remember if they are 22’s, or 24’s. From 2006 until 2018 I had a small block in this boat, so needed the smaller props.

If they are 22’s they won’t do you any good, but if they are 24’s and you want to buy them, I’ll let you try them out, and if you don’t want to keep em, send them back and I’ll refund your money, your only cost will be shipping both ways. I think I had them tuned before the last season I ran them, so they should be in excellent shape. What do they go for on eBay, around $600 per pair?
 
I wouldn't start making prop changes until you can state what your WOT rpm is And it should be in the 4200 to 4600 range.
 
I am thinking I was able to pass 4600 which is the stated max for the engine.
 
Many newer engines have REV limiters so exceeding the upper limit is not possible even without a prop.

Prop shops will often lend a prop for a brief test.
 
quote:
Originally posted by Gregory S

I wouldn't start making prop changes until you can state what your WOT rpm is And it should be in the 4200 to 4600 range.

Click to expand...


If you go to a prop shop, first question, which engine? Second question, what is your WOT, RPM?
 
quote:
Originally posted by Stephen

What's the top end WOT specs for that engine, 4400-4800? Are you able to reach that or maybe exceed it? That's what's important, although don't cruise at that RPM. Even with a 1999, there is likely a limiter to prevent you from exceeding that safe max. You might try going to a 23 and confirm you can still reach that WOT. A good prop shop will help you fine tune your prop.

Click to expand...


Hmmm
 
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