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Old 13-07-2013, 18:55   #1
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Stopping the Prop.

I want to find out how I can best stop my prop from rotating while I am sailing. I am not really interested in getting into a debate about the rotating or not rotating, as I just want it to stop turning to save on wear and I like it quite.
I have tried to leave it in gear and placed it into reverse, neither has worked.
I have a 50hp perkins with a 3 blade fixed prop.
Also, maybe someone could help with another prop question. My boat will do almost 7 knots at about 1500rpm but will not rev higher than this. In Nuetral she will rev A little over 2000rpm.
It seemes to me that I may have the wrong size prop as there is still a few rpm that I am missing out on when she is in gear. Or is this normal for an engine which is under load?

Regards Jeff
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Old 13-07-2013, 19:07   #2
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Re: Stopping the Prop.

if its in reverse and still rotating, something is broken. unless the engine is spinning backwards, and it will not be.

with a 50HP perk you will need to consult the manual for your model. it will have the prop size guide, and the RPM guide and limits. however it sounds very very low. a 50HP typically spins 3000RPM +/-600. do you see white smoke at full throttle? is the throttle cable adjusted correctly?

EDIT, or your tachometer is set wrong.
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Old 13-07-2013, 19:08   #3
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Re: Stopping the Prop.

Seems most folks are making brakes from golf cart parts or motorcycle bits.

I asked bulls prop shop in Beaufort nc about brakes last week... And there are not any commercial brakes he knows of.

Darrel at Sailcraft Services had the same answer...

I did get a suggestion I buy a very large pair of vice grips and use them to lock the shaft while making passages.
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Old 13-07-2013, 19:13   #4
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Re: Stopping the Prop.

I made a simple shaft break with inner tube rubber and a plumbers rounded vice grip using the rubber to protect the shaft engage the vice grip where rotation will lock it against hull. Don't give it enough room to swing far from lock position(you don't want it to slam into hull) helps to know which way shaft rotates.
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Old 13-07-2013, 19:16   #5
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Re: Stopping the Prop.

Don't waste time and money trying to reinvent the wheel. Simply put a pipe wrench on the shaft. Then tie a string around the key to remind you to remove it!!
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Old 13-07-2013, 19:40   #6
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Re: Stopping the Prop.

I found that useing the rotation to turn a alterntor, was a much better use of motion, so I made a setup just for this! The added power was great when we did it cus there just wasen't any fancy solar stuff around then! and this setup worked to keep my batterys charged for long periods of time! and not haveing to run the engine was sorta nice! Im sure that solar makes ya feel the same! power and no noise!! Any way a prop shaft turned alternator is free power after the up front cost of fabbing the set up ! Just a thought from a cheap cruiser
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Old 13-07-2013, 20:01   #7
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Re: Stopping the Prop.

Quote:
Originally Posted by scoobert View Post
if its in reverse and still rotating, something is broken. unless the engine is spinning backwards, and it will not be.

with a 50HP perk you will need to consult the manual for your model. it will have the prop size guide, and the RPM guide and limits. however it sounds very very low. a 50HP typically spins 3000RPM +/-600. do you see white smoke at full throttle? is the throttle cable adjusted correctly?

EDIT, or your tachometer is set wrong.
The engine model is a 104.22-100 series industrial model Perkins
Engine rating is DIN 6271: 47BHP/2800rpm
Engine Torque is 140NM/2000rpm
Gear Box is Borg Warner 72C Hydraulic.
The engine runs well with no real visablr smoke.
I am shore there is nothing broken and it did turn in reverse. But I did not leave it there for long.
How would I be able to check the Tacho?
Thanks.
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Old 13-07-2013, 20:05   #8
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Re: Stopping the Prop.

I have the same issue with the shaft spinning. There is actually the remnant of a disconnected shaft brake still mounted, but I am going to try the vice grips/innertube technique. Thank you for the suggestion. I love the power generating idea though.
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Old 13-07-2013, 20:07   #9
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Re: Stopping the Prop.

Does anyone have pics of a break system that works.
I read somewhere of a system that incorperated some form of twine that could break if the engine is started without first releasing it.
I am 100% posative that I will forget to release the shaft at some stage, so the pipe wrench or vise grip idea scares me.
I do not use a key to start the motor.
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Old 13-07-2013, 20:36   #10
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Re: Stopping the Prop.

Hoohaa what size is your prop? It does sound like you are 'over proped' if you can not reach max revs. From my research you should be able to reach 80% of max revs at the same time as you reach hull speed, in your case 2300rpm and you should still be able to go to 2800rpm (not much more increase in hull speed over 2300rpm). As it is a hydralic gearbox I am guessing the prop will still turn the gearbox? It did with mine and yes it was noisy I hated it, so switched to a Folding 3 blade prop.
As for a shaft break look at a simmilar concept to mountian bike push bike brakes to grip the shaft (rubber pads) linked to a leaver ?
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Old 13-07-2013, 20:38   #11
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Re: Stopping the Prop.

Shaft brake idea
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Old 13-07-2013, 20:45   #12
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Re: Stopping the Prop.

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Originally Posted by cal_d_44 View Post
Hoohaa what size is your prop? It does sound like you are 'over proped' if you can not reach max revs. From my research you should be able to reach 80% of max revs at the same time as you reach hull speed, in your case 2300rpm and you should still be able to go to 2800rpm (not much more increase in hull speed over 2300rpm). As it is a hydralic gearbox I am guessing the prop will still turn the gearbox? It did with mine and yes it was noisy I hated it, so switched to a Folding 3 blade prop.
As for a shaft break look at a simmilar concept to mountian bike push bike brakes to grip the shaft (rubber pads) linked to a leaver ?
Thanks Cal, I will have a good think about the break pad idea, would do the trick, just have to think of a nifty way to set it up.
Regarding the prop size. all I really know at this stage is that the diameter is 18 inches.
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Old 13-07-2013, 21:24   #13
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Re: Stopping the Prop.

Take a look at this link: SHAFT LOK INC.


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Old 13-07-2013, 23:14   #14
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Re: Stopping the Prop.

Quote:
Originally Posted by bobconnie View Post
I found that useing the rotation to turn a alterntor, was a much better use of motion, so I made a setup just for this! The added power was great when we did it cus there just wasen't any fancy solar stuff around then! and this setup worked to keep my batterys charged for long periods of time! and not haveing to run the engine was sorta nice! Im sure that solar makes ya feel the same! power and no noise!! Any way a prop shaft turned alternator is free power after the up front cost of fabbing the set up ! Just a thought from a cheap cruiser
Quite frankly I don't believe this works. You may be able to turn an alternator but not at the speed to generate any power. It would, after all your trouble, stop the prop from turning if you turned it on at max rpm. Perhaps if you could find a little tiny alternator generator you might get something for your trouble but it would cost more than that wiz bang thing shown in the other post. Maybe one of those things you used to see on old bikes that were the size of a large pill bottle that made perhaps a few watts at full speed.
On top of all that the drag from a turning propeller is worse than a stopped prop so you loose whatever you might gain from this lame generator idea.
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Old 14-07-2013, 00:01   #15
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Re: Stopping the Prop.

I have pondered on the prop brake problem and possible solutions a number of times over the years and found them all to much bother to implement. However once I went cruising and became a push bike user and began to take notice of push bike mechanics I noticed that many of them have disc brakes. It appears that a push bike disk brake could be quiet readily adapted for use as a prop brake.
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