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I know nothing about props.... (alpha 1)

J

jtoma878

Contributing Member
Guys this is just something I have never been able to wrap my head around although I have tried to self-teach.

I have a 27' Bayliner with a single 5.7L merc aplha 1 outdrive. My alum prop is pretty dinged up and I'm planning on making the run from Miami to Islamorada in a few weeks, so I figure now is a good of time as any to replace it.

I'm looking for top end and efficiency. She gets up on plane pretty quick now, but I couldn't tell you what size/pitch I currently have on there. I'll be down this weekend and I am going to pull it off and see - but I thought I'd ask around here first for some options.

All feedback is appreciated. I'd like to be informed in addition to recommendations.

Thanks in advance!!

Joe T
 
I forgot to add, I am curious about a 4 blade prop if there are any advantages. Right now I have a 3 blade alum prop.

Also, is having mine repaired a good idea or just replace it?
 
There are diameter and pitch size numbers stamped on the prop. If it's a Merc. prop there will be a part number stamped on it. If it has been running good then replace it w/the same daimeter and pitch. Your engine should run 4800 RPM at WOT. If it doesn't run that RPM but lower then drop the pitch one number for every 200 RPM. For example: your engine maxes out at 4400 RPM and your prop has a 21 pitch...drop the pitch down to 19 to gain 400 RPM. Raise the pitch to drop the maximum WOT RPM.

If you want some more performance get a SS prop. The cost is 2.5 to 3.5 times aluminum. Shop around a bit and you can find them for under $300. Try Overtons.com. Do you carry a spare prop on board? Get the old aluminum propp refurbished and keep it for a spare. Someone will help if you post the prop numbers you find.
 
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Thanks for the quick reply. I have to be honest as of right now I'm getting 3300-3400 @ WOT. I am not sure if my tach is off (it might be) or if that's actual. I've been getting 28-31MPH top end (according to my Garmin - speedo on boat is toast).

Speed varies if I've had my diver come recently to clean the hull & outdrive. I know she's supposed to be getting higher RPM but I feel the drop is because the prop is bad and boat dirty. There's definitely some cavitation when getting on plane then it seems to go away.

This is why I'm asking about a size/pitch recommendation. It's been quite some time now with this prop so I don't even remember if the tach ever read 4k
 
Do you know the boat's weight fully loaded? I can sub your boat's data into a prop finder spreadsheet to get you in the ballpark.

A dirty hull and worn prop will cut down max RPM...not good on the engine. Repaired props generally loose their cup and should just be used as a spare.
 
Based upon your boat wt., engine and deep V bottom it calls for 13-14 pitch. A 4 blade will provide great hole shots but a little less performance at WOT.
 
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