Need a prop recommendation for 1991 Bayliner 2556 25ft Flybridge

[Timboat]

Hello all,

I have a 25ft 1991 Bayliner 2556 Ciera Flybrige with small block v8 Mercruiser 5.7L engine (with 1150 hours) and Alpha One Gen II outdrive. The boat is heavy ~6000lbs, plus 500-700lbs of fuel and usually between 6-10 passengers (girls).
The current prop is a 3 blade mercury aluminum 15.5diameter x 15pitch.

Over the past few seasons this formula has worked well for me. This year the performance is degraded.
For example, I used to hit WOT at 4400rpm at 28mph with 8 people onboard...This was great!
This year with 7 people onboard I can only get the boat to 3900mph at 23mph( it feels strained at that RPM too). And with 8 or more, no plaining at all...
Getting up on a plane even with JUST me onboard use to be to be faster last season. This season, much slower, like taking over 20 seconds and at lower top end MPH 28mph vs 30ph or so before.
So basically performance has got worse....
Why?

Concerns:
-Visually inspected prop. it looks smooth and clean, no dents. Do these aluminum props wear out, mine is old?
-I cleaned the hull. there wasn't much algae, just a tad (it's in a lake)
-Bottom painted the boat 3 seasons ago, some of the paint was flaking off, but most was in tact. Could this slow me down that much?
-Engine: changed the spark plugs, distributor, etc. The engine is running nice and smooth, sounds great, but it is 20 years old!
-Ethanol change in gas from last year...could this steal my performance.

I'd like to get the boat back to moving fast with lots of people on board.
Is there a prop that can get my heavy underpowered boat on a plane.
I would accept giving up on the higher speeds (>28mph) for a quicker planing experience at lets say (25pm) with 8 passengers on board.

My prop guy suggested a 16"x14 quicksilver aluminum 3 blade as the current 15.25" x 15 have might have too much pitch for me to plane with all this weight. But I am concerned about moving to larger 16" diameter.
I've also read that a 15.5" x 13 pitch has been used alot in my boat. But I am concened that 13 is not enough to keep my boat planing as it will fall of if I don't keep it about 22mph or so.

Suggestions?


Thanks again!

 

[jestor68]

Re: Need a prop recommendation for 1991 Bayliner 2556 25ft Flybridge

Sounds like a compression test is in order.

Of course, if the engine is losing power due to aging, your options are limited. You can drop pitch to get the rpm back where it used to be, or you can repower. There are products; like Restore, that you add to the engine oil that supposedly coats the cylinder walls and (as the name implies) helps to restore lost compression and power. It's a lot cheaper than the other alternatives.

A drop in pitch to a 15.5 X 13 will gain back the lost rpm as well as speed.

.

 

[Timboat]

Re: Need a prop recommendation for 1991 Bayliner 2556 25ft Flybridge

I went with a 16" x 14 prop and switched out the old prop (that had barnacles and flaky bubbly paint on it) and now the boat performs better. It gets on a plane faster for sure. More testing needed tho.
I'll also look into the compression test, but I did one last season and all 8 were within 10psi right around 160psi.

 

[Bondo]

Re: Need a prop recommendation for 1991 Bayliner 2556 25ft Flybridge

I went with a 16" x 14 prop and switched out the old prop (that had barnacles and flaky bubbly paint on it) and now the boat performs better. It gets on a plane faster for sure. More testing needed tho.
I'll also look into the compression test, but I did one last season and all 8 were within 10psi right around 160psi.

Ayuh,.... I didn't see fuel filters or a carb rebuild in yer done it list....

You should consider swappin' the gear ratio in yer drive,...

If it's the standard, V8, 1.50:1 ratio....
Ya could drop to a 1.65:1 ratio, to get into the more readily available range of prop pitches...

I see it often with the 305 motors in big ole heavy barges...

Btw,.... Ya say the ole prop was wearin' barnacles,... in a Lake,..??