Sailing With A Fixed Prop

[GILow]

Originally Posted by GarthGregory

I have the same Janmar Diesel - this was supplied new with the Z F transmission . I have personally confirmed with the Technical Dpt at Z F Germany that the boat must be sailed with G/Box in neutral i.e. the prop free wheeling - the shaft must spinning at about 500 rpm while sailing at 6 knots - the estimate of a locked prop is a loss of about 1 x knot in boat speed .There is no apparent noise , but the seals / bearing must have a shortened life .You should check with your G/Box mnfr. Good luck

This is kinda misleading.

I think you mean to say the prop will free-wheel if not locked, so the gearbox should be in neutral UNLESS you have a means of locking it. Then it really does not matter, except that there is no harm in and plenty of logic to leaving it in neutral.

[Dockhead]

Originally Posted by Pete7

I would try rebuilding the Bruntons first before buying a new prop, likely only a bearing.

Pete

Of course I will. This is a something like 32" prop -- cost the larger part of ten boat bucks. I have just bought the £500 rebuild kit and will try to fix it while we're out of the water tomorrow morning. If I can't, then I'll fit the spare fixed prop and fix the Brunton at my leisure.


None of these other props are variable pitch, something I would not be eager to lose. This is a huge advantage of the Brunton.

[a64pilot]

Put some pre load on the blades, if only a tiny bit loose, the ball bearings will wear depressions in the race and lead to a sticking blade.
It may seem incorrect to tighten up something to ensure it will move freely later on, but you need to have no play.

The ball bearings are not designed to take a load, and if the roller bearing is even slightly loose they do, for the roller bearing to take all the load it has to have zero play.
I feel the only use for the ball bearings is to maintain a constant clearance for the seal.

I believe your failure was not brinelling, but false brinelling
https://en.m.wikipedia.org/wiki/False_brinelling

[Dockhead]

Originally Posted by a64pilot

Put some pre load on the blades, if only a tiny bit loose, the ball bearings will wear depressions in the race and lead to a sticking blade.
It may seem incorrect to tighten up something to ensure it will move freely later on, but you need to have no play.

The ball bearings are not designed to take a load, and if the roller bearing is even slightly loose they do, for the roller bearing to take all the load it has to have zero play.
I feel the only use for the ball bearings is to maintain a constant clearance for the seal.

I believe your failure was not brinelling, but false brinelling
https://en.m.wikipedia.org/wiki/False_brinelling

Thanks. That's interesting and something I didn't know and wouldn't have suspected



I noticed the stiff blade last time I lifted, last April. It didn't have the notchy feel from brinelling (or false brinelling). I know about that, because I've had that problem too


I'm not sure what the problem is; it could be a seal is out of position.

[a64pilot]

I don’t know, I’m surprised being “stiff” has an effect really.
I’ve been battling prop vibration since I got this boat, I’m convinced it’s from the difference in water flow from behind the deadwood to not, but anyway if I exceed 7 kts , vibration gets excessive, and while I’m sure it accelerates cutlass bearing wear, I wouldn’t think you would run a motor with the prop vibrating so bad that it causes any real damage.

Be interesting to see what you find on disassembly, and since your in Europe maybe give Brunton’s a call?

[Jim Cate]

Of course I will. This is a something like 32" prop

Really? A 32 inch prop on a ~100 hp engine? That seems kinda huge to me, unless you have a really big reduction gear.

And good luck with the bearing fix!

Jim

[GILow]

Originally Posted by Jim Cate

Really? A 32 inch prop on a ~100 hp engine? That seems kinda huge to me, unless you have a really big reduction gear.

Too right. My 96 HP only swings a 19”.

[SailRedemption]

Originally Posted by Jim Cate

Really? A 32 inch prop on a ~100 hp engine? That seems kinda huge to me, unless you have a really big reduction gear.

And good luck with the bearing fix!

Jim

Originally Posted by GILow

Too right. My 96 HP only swings a 19”.

We have a 24"x15" Variprop on our 56hp with 2.5:1. [emoji108]It's the tits for maneuvering.

[GILow]

Originally Posted by SailRedemption

We have a 24"x15" Variprop on our 56hp with 2.5:1. [emoji108]It's the tits for maneuvering.

That’s gotta be a two blade? Right?

[SailRedemption]

Originally Posted by GILow

That’s gotta be a two blade? Right?

Nope, three blade.

[GILow]

Fascinating. I don’t think I will ever even partly understand propellers.

[SailRedemption]

Originally Posted by GILow

Fascinating. I don’t think I will ever even partly understand propellers.

I know what you mean! But it was a huge improvement over the fixed three blade 17"x13" we had before with a 2:1..

[malbert73]

Yes the factor that is in play here is prop tip speed. So diameter is limited by clearance most often and also by tip speed. So with clearance and a deeper reduction gear you can translate pitch into diameter which is better for slow speed, non planing performance. Like a sailboat.

[Dockhead]

You guys won't believe what the problem was.

Loose shaft anode apparently caused enough vibration to destroy the cutless bearing.

There was still a bit of rubber left and the shaft was fine. Nothing wrong with the prop.

Motoring now smooth as butter.

Bank account lighter by nearly two euro boat bucks, but it could have been far worse.

Nice boatyard in Kalmar, by the way. Called Kalmar Marina, run by a guy named Jürgen. Very helpful pleasant and skillful people.

[JimsCAL]

Originally Posted by wingssail

We have used Martec folding propellors for 33 years (now on third one). They cost less than $1000 fob calif. and can be shipped fairly quickly.

They will free-wheel if the blades are open but shifting to reverse on our Yanmar 3JH with the cone clutch transmission has been no problem and stops the prop from spinning. We have 6500 hours on the eng/transmission. The blades fold and there is no torque on the shaft from the propeller trying to spin. It is also quiet, and definitely low drag. You could probably get a prop shipped to you by the time your other work is completed.

I also have used Martec props for many years. BUT they no longer sell new ones. Only refurb their old ones.