Locked Prop vs. Freewheel vs. Boat Speed

Ross · Jan 8, 2009

I never concern my self very much with that. I am sure that free-wheeling drags a little more than locked but being three blades I can't hide it behind the keel anyway.

Don S/V ILLusion · Jan 8, 2009

If either was a good solution, they wouldn't be selling all those feathering/folding props.

Mike B · Jan 8, 2009

I always lock it, depending on the boat reverse is best. I had an Autoprop and the last boat and you needed to do it to ensure the blades feathered properly. Also had a case where I was running a boat with a mechanical fuel pump. Set sail, turned off the engine while in forward and it didn't want to shut down. Had to go to neutral, make sure it was shut down, then drop it into reverse. Must have been enough force on the prop to turn it over, much like hand cranking. Strange but true.
Mike

Cpt. Jon · Jan 8, 2009

I usually lock it by putting it the transmission in reverse. I don't concern myself with what position the prop is in and don't know if it makes me go slower or faster, I was told that it's better to do that when I bought the boat and have always done it. When at dock I usually do too, but that's mainly to reduce the amount of water coming in through the packing and thus running my bilge pump more often and using more battery power.

Ross · Jan 8, 2009

Don, They are selling bottled water! why not sell folding props.

Don S/V ILLusion · Jan 8, 2009

Ross said:
Don, They are selling bottled water! why not sell folding props.

That's it Ross - making fun of bottled water puts you on quadruple secret probation.
Props are unimportant compared with bottled water which is a crucial ingredient for my ice maker.

Don S/V ILLusion · Jan 8, 2009

Maine Sail said:
Really??

it's simple!

http://web.mit.edu/16.unified/www/SPRING/systems/Lab_Assignments/airpower.pdf

Lee Coller · Jan 8, 2009

I always freewheel. I used to occasionally lock the prop by putting the engine in reverse, it cost me about 1/2 knot when I did that and it was hard to get the engine out of reverse (the easiest way was to start it in reverse and put it in neutral). Last year at the Hunter Rendezvous (actually sailboat rendezvous as H&S decided to combine Jeanneau and Hunter) the Yanmar rep said Yanmar wants the engine left in neutral and that you could actually cause damage by locking the prop with the transmission.

Grizz · Jan 8, 2009

Does this count?

We're running a folding prop (2-blade, Martec) that spins in fresh, not bottled

, water and upon shut-down, the tranny is put into reverse. If we're in light air conditions, someone crawls into the aft 1/4-berth to set the marked prop/shaft so the blades are vertical. It allows us to think we're going a bit faster...

Mike B · Jan 8, 2009

Ross, I get the impression that you group feathering props in the same class as snake oil.
Mike

tsmwebb · Jan 8, 2009

Maine Sail said:
Do you lock or freewheel?

If you lock is it for better speed or for less wear on the drive train.

If you freewheel is it for speed?

You don't provide enough information to know if there is less drag locked or freewheeling. This can be calculated but why bother? If you have a decent knot meter you can sail with the prop spinning and then drop into reverse and see what happens... Obviously there is more wear on the tranny when freewheeling.

Most folders and feathering props need to be stopped to make sure that they fold or feather.

I've got geared folding props and I leave them in gear when I shut the engine down underway until they fold and then shift to neutral.

--Tom.

ITMaster · Jan 8, 2009

Freewheel for me Maine Sail

I had good discussions with the Yanmar Reps out of Largo Florida and Warren Pandy, Plant Manager of Catalina Yachts down there. They both say that it is their preferrence to let it turn and that it is better for the transmission and it offers less drag and resistance with that big old three blade than having it locked. So, I do that and I guess it is a topic that has as varied opinions as there are about anchors

This will get good I'm fairly sure. Ross, I'll have a bottle please

Capn Dave · Jan 8, 2009

Lett er spin

Just so happens in this months Boat US magazine, online version , There is less drag when the prop is free wheeling.

Fair Winds

Dave

RichH · Jan 8, 2009

Maine Sail said:
Not so simple those are air props not sailboat props.. Hydrodynamics and aerodynamics, while similar, are not one in the same..

huh? ..... at the subsonic speeds indeed they are VERY similar - identical in fact, the only difference is the density and viscosity of the fluid.

A spinning prop will transfer more energy to the 'vehicle' as more contact (viscous shear - skin-friction) with the fluid is realized with the net effect of more work being done in the transfer.
Even with a non-rotating three bladed prop at least part of one blade will reside in the wake of the 'deadwood'.

UD Navy tank tests have long ago answered this problem - a non-spinning prop consumes less energy.

tsmwebb · Jan 8, 2009

Capn Dave said:
Just so happens in this months Boat US magazine, online version , There is less drag when the prop is free wheeling.

Fair Winds

Dave

Do you mean: http://www.boatus.com/news/Tech_0109.pdf

If so, he is wrong. The answer is it depends on the prop and the speed involved. He's also incorrect about running twins on a single engine where the answer is also it depends... I've got a friend with a fuel flow meter on his voyaging twin and running both actually saves a tiny bit of fuel for him at slow cruising speed...

--Tom.

Roger Long · Jan 8, 2009

Don't freewheel it unless you have something in writing from your transmission manufacturer. Some don't circulate enough oil to the bearings unless the main gear is turning.

I saw some extensive research and calculations years ago. I remember that the conclusion was that there is a narrow speed range for any prop in which drag is slightly less when freewheeling but that drag is higher at other speeds.

It's pretty unlikely that your sailboat will be in the right speed range and you're adding a lot of wear to the stern bearing and transmission seals.