Sailing with prop locked myth

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Tim R.

Tim R.

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May 27, 2004
3,626
Caliber 40 Long Range Cruiser Portland, Maine
I am currently corresponding with a sailor who has had his 2001 boat since new. It has 2600 hours on the Yanmar engine/Kanzaki transmission and the transmission has failed. I would consider this premature failure. For the last 12 years, this sailor has been sailing with his transmission in reverse because he read on the internet that it causes less drag than a spinning prop. As of 2008 a Yanmar service bulletin recommends sailing in neutral.

This idea drives me nuts. And you always read of people referring to the spinning helicopter rotors. That is not even a close comparison. A spinning helicopter rotor causes more drag than a locked rotor because it is spinning the opposite direction creating lift. Sort of like sailing with the engine running in reverse.

Forget about drag. Check your owners manual first. Then check with your engine/transmission manufacturer for any service bulletins. If you want to reduce drag, buy a folding or feathering prop(if compatible with your drive train)

Because of this sailors location, he may end up spending upwards of $5,000 to install a new Kanzaki transmission.

If you still disagree with me, buy a shaft brake. Do not depend on your transmission to lock the prop.
 
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capta

capta

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Jun 4, 2009
4,907
Pearson 530 Admiralty Bay, Bequia SVG
I'm really confused, Rich. Is this a hydraulic trans or gear?
Personally I can't stand hearing the shaft spin while we're sailing and the MaxProp has been great, but would putting a hydraulic trans in reverse (or forward) stop rotation? It never did on the Borg Warners. Putting a gear trans in either fwd or reverse should not allow the prop to spin, nor do damage to the gearbox, as far as I remember.
For eons, Borg Warner recommended that the prop not freewheel in gear or out, but I believe they have stopped that recommendation.
Just curious.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,701
Canadian Sailcraft 36T Casco Bay, ME
The Kanzaki gears use a cone clutch which is different from a clutch plate Hurth/ZF or hydraulic box. .

When locked in reverse the movement of the water over the locked/stalled prop can cause chatter and also cause the cones to "lock up". This can cause wear and premature damage to the Kanzaki more so then simply letting it freewheel.

In a "locked up" situation Yanmar used to recommend starting the motor in reverse then switching to neutral as a way to unlock it. Unfortunately many owners broke gear boxes trying to force them back into neutral and damaged the gear by locking the prop and the related "chatter" on the locked cones..

After lots of failures Yanmar finally published an MSA prohibiting the locking of their gear boxes in reverse if not using a "shaft brake"...

With a Hurth/ZF box you can choose either neutral or locked in reverse just never the same direction of travel, or forward, to lock it...
 
kloudie1

kloudie1

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Nov 6, 2006
10,052
Hunter 34 Mandeville Louisiana
Tim, any real info on what exact part first failed and the exact nature of the failure? I would love to have that transmission on my bench to do an autopsy on it.. I have dissected many a gearbox after failures to get at the root cause of the failures..
 
kenn

kenn

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Apr 18, 2009
1,271
CL Sandpiper 565 Toronto
[edit] OK explanations noted, thanks!

Also, why replacement, vs just repair/rebuild?
 
Tim R.

Tim R.

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May 27, 2004
3,626
Caliber 40 Long Range Cruiser Portland, Maine
kloudie1 said:
Tim, any real info on what exact part first failed and the exact nature of the failure? I would love to have that transmission on my bench to do an autopsy on it.. I have dissected many a gearbox after failures to get at the root cause of the failures..
Click to expand
The service tech stated their was wear on the cones.
 
Tim R.

Tim R.

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May 27, 2004
3,626
Caliber 40 Long Range Cruiser Portland, Maine
kenn said:
[edit] OK explanations noted, thanks!

Also, why replacement, vs just repair/rebuild?
Click to expand
They are still trying to determine which way to go but if it is close, the owner said he will pay the little bit extra for a new unit.
 
Chris Patterson

Chris Patterson

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Oct 17, 2011
2,809
Ericson 29 Southport..
Geez. My head is still swimming trying to figure out how anybody could think otherwise; concerning the drag test. Less drag with the shaft locked? Say whut???
 
TFrere

TFrere

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Oct 1, 2008
144
Morgan 382 Mandeville, LA
locked or not

I tested this theory one day. On a beam reach, I had a similar boat just off the aft port side and he was slowly catching me. I shifted into neutral to unlock the prop and I began to pull away. After a bit I shifted back to reverse and he was gaining on me again. I believe my boat is faster with my 3 blade prop freewheeling in neutral.
 
Tally Ho

Tally Ho

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Jan 7, 2011
5,463
Oday 322 East Chicago, IN
I have always sailed my Hunter 280 in neutral, once last summer i tried locking it in reverse to see what happened. At the end of the sail, I could not shift out of reverse. Ended up popping the cable out of the bracket when I tried to force the shift lever. Took a while to figure out thy I had not completely screwed up my transmission. From now on, always letting the prop free-wheel.

Greg
 
C

CarlN

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Jan 4, 2009
603
Ketch 55 Bristol, RI
I remember a test (but can't find it now) that showed a free wheeling prop had 50% of the drag of a locked prop.
 
centerline

centerline

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Mar 20, 2012
3,983
Cal 34-III, MacGregor 25 Salem, Oregon
Tim R. said:
This idea drives me nuts. And you always read of people referring to the spinning helicopter rotors. That is not even a close comparison. A spinning helicopter rotor causes more drag than a locked rotor because it is spinning the opposite direction creating lift. Sort of like sailing with the engine running in reverse.
Click to expand
yep, some people just dont know...
a spinning boat prop cannot be compared to a spinning helicoptor blade in any way possible other than it is spinning... the mechanical forces at work are completely different and anyone who has ever tried to make a comparison between the two has no concept of how helicoptors function, auto-rotatation or helicoptors in general....
or maybe its boats they dont know about:D
 
Chris Patterson

Chris Patterson

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Oct 17, 2011
2,809
Ericson 29 Southport..
-- the mechanical forces at work are completely different and anyone who has ever tried to make a comparison between the two has no concept of how helicoptors function, auto-rotatation or helicoptors in general....
or maybe its boats they dont know about--

Yeah, that was kind of my thought. Well, EXACTLY my thought when you get down to it. The correlation is ludicrous, and anybody that would argue differently has no clue of hydrodynamics.

The answer is as simple as sticking a paddle in the water flat, then rotate it 90 deg. To even have to test that concept is, well,.....
 
NotCook

NotCook

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Dec 29, 2008
806
Treworgy 65' LOA Custom Steel Pilothouse Staysail Ketch St. Croix, Virgin Islands
Our Borg Warner Velvet Drive manual says to let it free wheel. Besides, putting it in any gear has no effect unless the engine is running.

But, as others above have posted, it may vary by manufacturer - I'd go by what the manual says, unless that has been retracted by the manufacturer.
 
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Gunni

Gunni

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Mar 16, 2010
5,937
Beneteau 411 Oceanis Annapolis
kloudie1 said:
Tim, any real info on what exact part first failed and the exact nature of the failure? I would love to have that transmission on my bench to do an autopsy on it.. I have dissected many a gearbox after failures to get at the root cause of the failures..
Click to expand
There are at least two types of Kanzaki hydraulic transmissions, cone and plate. Both rely on a wetted friction surface to provide some element of drive slip. If the transmission is not being spun by the engine crankshaft, the cones (or plates) do not get their oil bath. No oil bath wetted friction surface engaged to a prop-spun shaft = damaged cones or plates, cooked transmission. Put the transmission in neutral and the cones or plates do not contact the drive shaft.

Mack Boring rebuilds the Kanzaki. It is a subsidiary of Yanmar. When they quoted mine, the rebuild was 1/2 of new. (problem turned out to be a jammed shift cable).
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,701
Canadian Sailcraft 36T Casco Bay, ME
Gunni said:
There are at least two types of Kanzaki hydraulic transmissions, cone and plate. Both rely on a wetted friction surface to provide some element of drive slip. If the transmission is not being spun by the engine crankshaft, the cones (or plates) do not get their oil bath. No oil bath wetted friction surface engaged to a prop-spun shaft = damaged cones or plates, cooked transmission. Put the transmission in neutral and the cones or plates do not contact the drive shaft.

Mack Boring rebuilds the Kanzaki. It is a subsidiary of Yanmar. When they quoted mine, the rebuild was 1/2 of new. (problem turned out to be a jammed shift cable).
Click to expand
Most of the clutch plate non-cone Kanzaki boxes are really Hurth/ZF gears with a "K" in front. A Hurth/ZF would be an HBW and a Kanzaki version would be a KBW...

The worst possible thing for a KBW gear is to leave it in forward when sailing and not change the fluid on a regular basis. These gears have a bronze thrust washer that erodes when metallic bits are shed into the fluid by leaving the gear in forward while sailing. Clutch plate gears should have the fluid changed at least annually....
 
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