Bigdamdork

What Size Prop?

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Hello everyone.  Quick question if you don't mind.  I have a 1985 Schock 35 and it's getting ready to go on the hard.  Currently it has a folding prop that is starting to show some signs of wear.  I'm pretty sure I want to replace it with a standard 3-blade stainless steel prop. I'm not seriously racing (just the sightseeing sailboat on his way back in from time to time) so I'm not especially concerned about the drag a fixed prop will give me.   Currently have a Yanmar 3GM30 @ 24hp on a 1 inch prop shaft.

In a perfect world I would like to get the prop before I pull the boat and put her on the hard in about a month.  Any suggestions on what size prop I should be looking for? 

Thanks for any help as always. This forum has been a real life saver for me as a new sailboat owner.  You are all very awesome for the help you supply.  

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About 16x10-11 Right Hand,  but that's a guess because we don't know the reduction ratio (2.42 or 2.62:1 from memory) of the gearbox. It will be stamped on the little plate on the back of the box. You'll need good eyes and a flashlight or just take a picture with your phone if  you can't get in easily. 3400 RPM redline for that model engine?

You'll not likely to find a stainless steel prop - most are bronze.

What is make of current prop, and what pitch? That would help too.

And it's criminal to slow that boat down with a 3 fixed blader. The 2 blade Flex O Fold do very nicely in powering tests, nearly outperforming fixed 3 blades.

You could also consider a fixed 2 blade prop too. That's a fairly easily driven hull form, and the lighter winds of Southern California means drag is important.

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What type of prop is on it now? If you are lucky it might be a maxprop, they can refurbish it and it will be indistinguishable from new. Other companies may have similar programs. Keep in mind folding or feathering props not only reduce drag sailing, but most offer much better performance in reverse. 

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C&C 35-3, 3GM30F @ 27hp. Max Prop set to 17X10. Captain Navy canvas, too much shit on board.

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Give a prop shop your top speed, rpm, reduction, HP, LWL, B, displacement  and your current prop size and they can tell you for whatever type of prop you want.  Folding geared props work really well in reverse, yet don’t give you that extra drag.  Expensive new, but worth it.  And you don’t have to worry about the prop freewheeling.  Regular folders aren’t nearly as good in reverse.  If you get one, like a Martec, then get one as close to square as possible for the best reversing.

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I have a folding Martec on a new to me boat, it will be leaving the boat shortly. In tight marina space there is almost no reverse power, it slows but thats about it and backing up is a big pull to port. 

I think prop choice needs to also consider where you need to go when not sailing, if its not a race program a really nice day get spoiled trying to manouver in a tight harbor. For me anyway

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4 hours ago, crankcall said:

I think prop choice needs to also consider where you need to go when not sailing, if its not a race program a really nice day get spoiled trying to manouver in a tight harbor. For me anyway

A feathering prop has much better reverse power than a fixed prop, and doesn't slow the boat down when racing.  It is an extravagance on a small (25-30') cruising boat, but fits the budget on a 35' racer/cruiser and should be a default option.

16x11 sounds right.  On my Express 37 with the same engine I have a 16" 2 blade Maxprop with the pitch set to 16 or 18 degrees.

If you do go with a fixed prop Campbell Sailor makes the nicest ones and they'll help you spec a prop for your boat.  Their pitch numbers end up a little different than other props due to the better foil shape of their prop and the smaller blade area.

 

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Again, thanks everyone for the advice.  Here is what is weird is a lot of the people I have spoken with say get away from the folding prop, but it sounds like it is a better option if I already have one.  I haven't spent a ton of time under the boat yet and I'm in line to get it hauled out and into the boatyard where I can do a better inspection of everything. I'm basing a lot of my "concern" on the amount of vibration I am getting when throttled up at about 60% of max (tachometer is broken...something that is getting fixed soon) and definitely when it's in reverse.  I might have a worn out cutlass bearing that is causing slop in the prop shaft.  


Either way I really appreciate the input that I should maybe consider keeping the folding prop.  I appreciate it. Thanks again. 

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Folding and feathering props are very different.

If you want a folding prop you should look for a geared one (Gori and Flex-o-Fold are two popular brands), they behave better especially under reverse.  The Martec props that I've seen aren't geared.

This article will help you understand the differences:

https://www.yachtingmonthly.com/gear/folding-and-feathering-propeller-test-29807

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39 minutes ago, Bigdamdork said:

Again, thanks everyone for the advice.  Here is what is weird is a lot of the people I have spoken with say get away from the folding prop, but it sounds like it is a better option if I already have one.  I haven't spent a ton of time under the boat yet and I'm in line to get it hauled out and into the boatyard where I can do a better inspection of everything. I'm basing a lot of my "concern" on the amount of vibration I am getting when throttled up at about 60% of max (tachometer is broken...something that is getting fixed soon) and definitely when it's in reverse.  I might have a worn out cutlass bearing that is causing slop in the prop shaft.  


Either way I really appreciate the input that I should maybe consider keeping the folding prop.  I appreciate it. Thanks again. 

If the vibration is your major symptom I'd be looking at your drivetrain for problems well before thinking the prop has "wear". As you say, cutlass bearing, poor alignment,.......

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