Reverse Gear while Sailing?

[Ex-Calif]

Originally Posted by a64pilot

Been doing a little pondering.
Maybe the difference is that aircraft props and helicopter blades are a very high aspect ratio airfoil, and boat props aren't, so it's an apples to oranges thing, maybe?

As an airplane guy I was a non-believer too. There are good studies and the debate rages...

I got a feathering prop so I wouldn't keep getting ice cream headaches over this - LOL...

@OP - My pat answer is do what the manufacturer says to do. I went to the end of the internet and back and could not find an online operators manual for this transmission. (Owners manuals for all kinds fo stuff are really hard to come by - wierd)

Anyhow - barring that I don't know how you harm a transmission if it isn't rotating so if it were mine I would stick it in reverse.

Internet opinions are worth the bandwidth they are carried on...

[crazyoldboatguy]

I can only state my claim based on experience. I have afixed 2 bladed prop on a full keel 28' Pearson Triton, which My family has owned for 50 years. If I allow the prop to free wheel, record the speed (GPS) and then put the transmission in gear I notice virtually no change in speed. If I locate the prop (marks on the prop shaft), I can get the blades behind the dead wood of the keel. No change in speed noted on my GPS. If the drag was as much as the entire hull, wouldn't I notice at least a little change in speed? 1/2 mph or something? Cruisers frequently use fixed blade props as the cost of folding props are very high. We're sailing - mostly not racing. Many on low budgets. All the math aside, in the real world, you just don't lose that much speed. Maybe my boat should take some upper level math courses 'cause she just ain't gettin' it.

[svlamorocha]

Originally Posted by a64pilot

A spinning prop should create more drag than a stopped one, this is very easy to demonstrate in an aircraft

You cannot extrapolate from aircraft to boats.

Aircraft fly in air and the "slippage" (boat word) of prop vs air plus the significant pitch angle helps the locked prop a lot. If I recall correctly from my school years someone worked out the theory that tells you the envelope of key ratios within which it pays to lock an airplane prop. Pitch angle is critical....the more pitch you have the more advantage to locking the prop..

I also recall having checked that if you apply that same theory to boats (with the correct parameters) you see that in water any reasonable combination of boat speed and propeller dimensions will favor unlocked prop. That has been verified in every test made on boats. We have discussed this and posted relevant data a while ago..

In fact you can do your own test using a boat. It is easy to find a 0.5kt difference between locked (more drag) and unlocked (less drag) prop when you have a prop that does not slip much, say a 3-blade prop that has a high "disk factor".

[weephee]

Thanks everyone for the replies. This morning, I contacted Marine Transmission Repair and Parts :: Kalamazoo Marine Gear.
These people specialize in marine transmissions and seem to know what they are talking about. The gentleman I talked to said you must keep the transmission in REVERSE when sailing. He said DO NOT LEAVE IT IN NEUTRAL OR FORWARD GEAR. He said this information is directly from the manufacturer. This is for the KBW10 transmission only. I didn't ask about other transmissions, so there you have it for what its worth. Thanks again.

[Maine Sail]

Originally Posted by weephee

Thanks everyone for the replies. This morning, I contacted Marine Transmission Repair and Parts :: Kalamazoo Marine Gear.
These people specialize in marine transmissions and seem to know what they are talking about. The gentleman I talked to said you must keep the transmission in REVERSE when sailing. He said DO NOT LEAVE IT IN NEUTRAL OR FORWARD GEAR. He said this information is directly from the manufacturer. This is for the KBW10 transmission only. I didn't ask about other transmissions, so there you have it for what its worth. Thanks again.

The KBW, if my memory serves me well, is actually a Hurth/ZF gear built for Yanmar. They just replace the "H" in HBW, as in Hurth, with a "K" as in Kanzaki and name it a KBW..

This is what Hurth has to say about their gears - Neutral or Reverse:



And then of course this is the Yanmar "official word":

PDF Version of Yanmar MSA

"Advisory Number: MSA08-003:

DATE February 8, 2008 Dealers and OEMs
TO: All Marine Distributors
SUBJECT: Gear in Neutral While Sailing All MODELS:

All Sailboat Engines

We continue to get questions regarding the correct gear position while sailing with the engine OFF. This advisory is issued as a reminder; Yanmar requires that if sailing with the engine OFF (not running) the transmission shifter must be in the neutral position or internal damage to the gear or sail-drive will result. This damage will not be covered by Yanmar’s Limited Warranty. Please instruct customers and dealers who deliver the sailboat to the customer, of the correct (Neutral) position for the marine gear while sailing.

If the customer desires that the propeller shaft not spin while sailing, either a folding propeller, shaft break, or other suitable device may be used. However, Yanmar accepts no responsibility for the selection, installation, or operation of such devices. Please also refer to Marine service advisory “MSA07-001_Yanmar Sail Drive Propeller Selection” for additional information.

If you have any questions regarding this advisory please contact a Customer Support representative."

[Tayana42]

Does this mean that with a MaxProp it is okay to leave it in forward? Or neutral?

[Suijin]

Originally Posted by Tayana42

Does this mean that with a MaxProp it is okay to leave it in forward? Or neutral?

For a MaxProp you want the transmission in reverse, as this allows the blades to feather properly. If you leave it in neutral it will spin and not feather, and if you leave it in forward it will spin the wrong way and lock in the "reverse" position, unfeathered.

[weephee]

Maine Sail, I just contacted Hurth Marine Transmissions: The Ins and Outs of Basic Service | Foley Engines and was told that the transmission may be left in neutral when sailing but output wear on bearings etc will occur and the fail safe position is reverse and never forward. I don't mean by any means to belabor this subject or argue with anyone but it is very important in my mind to get it right as I don't have the money to have transmissions rebuilt. Hope this helps someone somewhere with a kbw10 transmission

[atoll]

use a condom......reverse gear does not work whilst sailing......i have 2 children who can testify to this

[highseas]

If transmission is left unused for long periods,filling box with ATF is advisable also.The problem being bearings in upper part of box start to rust otherwise,as they are exposed to air.Of course you have to remember to drain to correct level before using.

[Stu Jackson]

This discussion reminds me of 1-2-B switches: four positions but only three posts.

Look, there are basically two kinds of transmissions on boats and three positions you can leave it in. Throw in the type of prop if you like.

Find out what transmission you have, and act accordingly.

Maine Sail has answered this question all over the internet.

The search term is "transmission position."

It's likely to come up again.

[barnakiel]

Originally Posted by crazyoldboatguy

I can only state my claim based on experience. I have afixed 2 bladed prop on a full keel 28' Pearson Triton, (...)

You sure reach the speeds when the prop starts turning?

We have a similar hull: full length keel; we have a 3 blade LARGE AREA prop. Ours will not start wheeling before say 3 knots. All other things equal, a 3-blader would start spinning before a 2-blader.

In the 3 to 4 knots bracket I find very little speed difference.

ALAS when our boat gets fully powered up and she is "flying" at 5 to 6 knots, every time I lock the prop, she slows down by up to 0.5 of a knot. Tested and verified with multiple GPS measurements.

So my guess is whatever YM and Segeln found, much as it may seem contrary to our guesses, is correct.

b.

[Pelagic]

Should we mention the use of Shaft Alternators"? )

[crazyoldboatguy]

Yeah, the prop spins, I can hear it. I don't doubt that the spinning/non-spinning prop adds drag. A simple understanding of physics demands it - and I am as simple as it comes regarding that. It's just that most folks don't worry too much about that as the loss of speed is not horrible - perhaps a little annoying. Unless racing, most sailors just aren't worried about 1/2 mpg loss - if they were that worried, they'd fly.

I am seriously looking at a prop shaft alternator. Lots of discussions here and elsewhere on that - almost as much fun as a stream on anchors or mono/multi hulls.

Some folks swear by those alternators - a matter of making sure your transmission will allow for free wheeling without damaging the output shaft bearing, getting the right set-up and not expecting to power the ac with it.

[gjordan]

I had a steel boat with a velvet drive transmission. The first passage (New England, Bermuda) almost drove me nuts with the howling of the prop. I didnt need a knot meter, I could tell by the howl. In Bermuda, I rigged a shaft break (a hook bolted to the coupling) that used a light line, so that it could break if I forgot to release it when putting the engine in gear. The speed didnt matter, compared to the noise. I had another larger boat, with a velvet drive, but the noise was only serious in the aft cabin, which I didnt use much at sea. My next boat will have a folder or featherer, for the silence and the slightly better speed on all points of sail. ____Just my opinion._____Grant.