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avazquez · 10-07-2007, 05:33

Thanks a lot Gord...as I say, THIS SITE MAKES SAILBOAT OWNERSHIP SO MUCH SIMPLER....

rtbates · 10-07-2007, 07:15

Here's a very long winded and at times very funny thread on the 'lock' vs 'freewheel' debate from the Cape Dory forum.
Cape Dory Boats - View topic - Freewheeling propellers: the chopper theory

jean1146 · 10-07-2007, 07:32

I have a Mahe with 20hp Volvo.when sailing they recommend to leave the transmissions in neutral.

**GordMay** · 10-07-2007, 11:53

FREEWHEEL OR LOCKED PROP? ~ by Nigel Warren
As released by Cruising World Publications - October 1979
Body

"... The prop will create three times more drag when allowed to rotate than it will when locked ..."

Sonny · 10-07-2007, 13:24

I just checked the owners maual for the Perkins Sabre M65 and M85T.

It states " The propeller shaft of the NEWAGE PRM 260D and the ZF-HURTH HBW 250A REVERSE GEARBOXES CAN BE ALLOWED TO TURN CONTINUOUSLY WITH THE CONTROL LEVER IN THE
NEUTRAL POSITION.

44'cruisingcat · 10-07-2007, 17:30

I don't understand why so many manufacturers specify leaving the shift in reverse. As far as I can make out, the idea of leaving it in gear is so it wont spin, and if it doesn't spin, what difference does it make if it's in reverse or forward? Conversely if the shaft DOES turn, then if the gearbox is in reverse the engine will be turned over BACKWARDS - which could stuff your water pump">raw water pump at least.

BTW with a velvet-drive it makes no difference whether it's in forward neutral or reverse - the shafts still spins, and at the same speed too.

Tropic Cat · 10-07-2007, 17:51

Gord have you posted info on both sides of the controversy in this thread?

This thread comes up every now and then and it's the same recycled information each time. I had thought that this was settled a long time ago.

Here' the MIT paper on this subject. They plot 8 propellers locked and unlocked and compare them to folding and feathering props (which are much better).

http://www.merlinmortgage.biz/Storage/propeller.pdf

If your transmission allows it then freewheeling is more efficient and faster. As far as transmissions wearing out, that's up to the individual's boat.

Rick in Florida

**Alan Wheeler** · 11-07-2007, 01:25

Rick, I am interested in reading that info, but your link won't open for me. That maybe my computor with the problem, so can you Email it to me?

44'C... you ask a good question. The answer is not so straight forward however. So the first comment for anyone reading is to check the manual to see what is the recommended practice. The reason for a gear selection being recomended, is for oil distribution around the box. It simply ensures that the gears spin up oil over the gear sets to ensure the gears and the bearings are kept safe from wear. Some boxes this does not matter which gear is selected or even if it is neutral. Velvet drive being one as it is fully hydraulic. Where as "geared" boxes need to be locked or allowed to spin in the gear that is recomended.

**Ex-Calif** · 11-07-2007, 01:40

Rick - As I read their paper they did not test the propellers freewheeling, could not simulate the drag of the bearings and stuffing boxes and so their "conclusion" is a calculation that the drag is less on a rotating prop not a measurement.

Farmer's logic says fundamentally there is drag of the blades, you think it is reduced if the blades are allowed to freewheel. but you add to that the rotational friction of anything in the system. Rotational friction increases the faster you go as does hydrodynamic friction.

BTW - Our folding prop has not folded a couple of times as evidenced by the freewheeling noise. We pop the transmision in gear and the rotation stops immediately, then back to neutral.

The reverse vs. fwd gear position could be a result of different gear ratios in reverse with a lower gearing providing less liklihood of rotating the engine.

Tropic Cat · 11-07-2007, 04:33

Ex Cal, what use would the paper be in that case, and how could they state their concluions on the last page if that were the case? Please reread page one as it says how they tested.

Alan check your email

Rick in Florida

**Ex-Calif** · 11-07-2007, 05:00

Quote:

Originally Posted by rickm505

Ex Cal, what use would the paper be in that case, and how could they state their concluions on the last page if that were the case? Please reread page one as it says how they tested.

I am not quite sure what the purpose of the paper was except to perhaps get a Master's paper done. The experiment is flawed on many fronts. I have years of experience in test situations and their setup was limited and due to the constraints the results therefore must be limited. The most harmful and grievious error a scientist can make is to extrapolate results into the unknown due to the limitations of the test data.

I have posted the relevant paragraph from their paper. The statement is significant in the case of freewheeling vs. locking. I am not saying they are wrong but their data is not conclusive in this regard.

**GordMay** · 11-07-2007, 05:03

Quote:

Originally Posted by rickm505

Gord have you posted info on both sides of the controversy in this thread?
Rick in Florida

Perhaps.
I’m not responsible for the diversity of opinion extant throughout the world.

My posts often include links to Internet sites, content and services provided by third parties.
The views and opinions expressed on these linked pages are strictly those of the page author.
My linking to any third party sites does not imply an endorsement or sponsorship of such sites or the information, opinions, and/or recommendations offered on or through the sites, and use of or reliance on such advice, opinion, statement or other information is at your own risk.

Tropic Cat · 11-07-2007, 05:10

You know, I've read this paper many times and never caught that paragraph. Apparently they are using math to simulate free wheeling

I will say that this paper in undisputed in the industry and instantly used as a reference, just as I did.

Good catch

Rick in Florida

**GordMay** · 11-07-2007, 05:55

Quote:

Originally Posted by rickm505

... Apparently they are using math to simulate free wheeling ...
Rick in Florida

Which doesn’t presuppose any fault in their conclusions, unless their postulate is invalid and/or arithmetic is inaccurate.

Maddog · 11-07-2007, 08:35

Quote:

Originally Posted by GordMay

Perhaps.
I’m not responsible for the diversity of opinion extant throughout the world.

My posts often include links to Internet sites, content and services provided by third parties.
The views and opinions expressed on these linked pages are strictly those of the page author.
My linking to any third party sites does not imply an endorsement or sponsorship of such sites or the information, opinions, and/or recommendations offered on or through the sites, and use of or reliance on such advice, opinion, statement or other information is at your own risk.

Damn Gord! I bet our milage may vary too!

It's all good, keep doing what you do.