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Prop Size? 27' Bayliner / 5.7L Alpha 1

J

jtoma878

Contributing Member
Time to replace prop. Lost one of my zincs and it chipped the prop.

Not exactly sure what size is on there now, IIRC it is a 15x21.

I know NOTHING about props. With a boat my size and the motor/drive I have, what do you guys suggest? Boat is used for cruising bay waters, maybe fishing a mile or 2 offshore in ocean.

All input appreciated
 
15x21 seems a bit big. I run a 14.25x21 not as big a boat, but similar engine and drive. What were you WOT RPMs?
Google search a prop repair shop in your area. It could probably be repaired for a whole lot less than a new prop.
 
I forgot to mention I'm looking for a little more top end... I'm running @ about 33 MPH max right now, I figure I'd be a few mph faster if my prop wasn't damaged.

I forget off the top of my head what RPMs that was at..
 
You need to be between 4200-4600 rpm at wot. Doesn't matter speed the all important number is rpm. You only need to be at wot for 3-4 minutes gps it and mark the rpm. Thats it.

So say your running a 21 pitch and your wot is 3800 you need to go down in pitch to a 17 pitch to get you around 4500 rpm if not your lugging the motor gonna kill it for sure.
 
Took her out yesterday... I am running 32mph @ 3400 rps @ WOT! I'm guessing this is due to wrong prop size or the fact that it is chipped/bent.

Suggestions on prop size??? I haven't taken current one off yet so I can't tell you what it is...
 
Listen most marinas will have props to try but i am sure if you start with a 17 see what rpm you are running wot. The marina wants to sell props tell them and they will work with you.

I wouldn't be surprised a 15 might even be the ticket. And get a spare.

Do yourself a favor do a compression test and post the result before you buy the prop no little chip is gonna effect performance that much. No if one blade was bent real bad then thats a different story.
 
I would suggest you first borow/beg/steal a shop tach (connected directly to engine) and make sure the boat tach is reading correctly. Also there is a switch on the back of the tach for 4,6,8, cylinders - see that it's in the correct position. 32mph at 3400 rpm in a 27 footer doesn't sound right.
If it is actually doing that you might try a 17 pitch - each 2" of reduced pitch should increase the wot by about 300 rpm (roughly). If you are actually turning only 3400 at wot, trimmed out, with normal load I'm surprised it even got on plane with a 21.
 
jtoma878 said:
Time to replace prop. Lost one of my zincs and it chipped the prop.

Not exactly sure what size is on there now, IIRC it is a 15x21.

I know NOTHING about props. With a boat my size and the motor/drive I have, what do you guys suggest? Boat is used for cruising bay waters, maybe fishing a mile or 2 offshore in ocean.

All input appreciated
Click to expand...


my prop chart shows the 5.7L with the 4000-6000lb 24-30ft boat will need a 14-1/2 X 15 or if on the higher wt side a 16X13 prop...
 
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