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-   -   Prop selection (https://www.winnipesaukee.com/forums/showthread.php?t=24917)

LaFuga 08-23-2019 10:41 PM

Prop selection
 
Hi guys, I've got a 74 searay that's got a 2003 driveline in it. 305mpi mercruiser with a 19 pitch prop. I'd like to get a little more performance out of her seeing she weighs 4000 lbs. Not looking to swap motors or anything very expensive. She comes out of the hole pretty OK, and tops out at 40mph or so. What do you think I should do for a bit more performance? Change prop? Change air cleaner size? Any suggestions would be appreciated! Just want a little more out of her. There's about 370hrs FYI if it matters. Thanks!

8gv 08-23-2019 10:45 PM

By "performance" do you mean top speed or acceleration to planing speed?

TiltonBB 08-24-2019 06:43 AM

What RPM is your motor rated for at top end and what will it turn up now with your current prop?

MAXUM 08-24-2019 08:49 AM

This is in a 2003 drive train with 1.88 gear ratio in an Alpha I gen two stern drive.

I had a 19 pitch 3 blade was OK great hole shot, but ran about 25-28 MPH @3000 RPM. Top speed ~48 MPH @5500 RPM. Moved to a 21 pitch 3 blade, a bit of a dog out of the hole, 30-32 MPH @ 3000 RPM. Top speed 52 MPH @5500 RPM.

Moving to the 4 blade gave me the hole shot back I had with the 19 pitch... so quite pleased with the results. I should have added I have a 21 pitch 4 blade spitfire prop now. The thing that I was looking at mostly was that mid range MPH to RPM. I never run WOT but occasionally will if the lake is dead flat just because. Mileage on performance varies weight and hull geometry does play a part in how well any particular prop will perform.

Cal Coon 08-24-2019 09:12 AM

Quote:

Originally Posted by MAXUM (Post 318217)
This is in a 2003 drive train with 1.88 gear ratio in an Alpha I gen two stern drive.

I had a 19 pitch 3 blade was OK great hole shot, but ran about 25-28 MPH @3000 RPM. Top speed ~48 MPH @5500 RPM. Moved to a 21 pitch 3 blade, a bit of a dog out of the hole, 30-32 MPH @ 3000 RPM. Top speed 52 MPH @5500 RPM.

Moving to the 4 blade gave me the hole shot back I had with the 19 pitch... so quite pleased with the results.

I went from a 3 blade 21p ss prop to a 4 blade 19p aluminum prop, and it allows me to stay up on plane at lower rpm's/mph, better hole shot, and better fuel efficiency. I may have lost a little top speed, but I don't care about what the boat will do at wot, that's NOT where I run it 99% of the time. I have a 22' cuddy cabin with a 454/ Bravo 1 outdrive. Weighs around 3750 empty.

Dave R 08-25-2019 07:43 AM

With 4000 Lbs to push and a single prop drive, you should be focusing on reducing prop slip and getting the engine to rev to or beyond the recommended WOT RPM with a typical load. Thus, I would advise getting a 4 blade SS prop that lets the engine get to 5000 RPM at WOT, even if it's only rated for 4800 RPM or less. That 5 liter is a small block Chevy engine that will happily turn 5200 RPM without any issues. The 4 blade SS prop will provide excellent prop slip numbers and allow as much trim as the boat will take without blowing out.


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