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post #1 of 19 Old 11-10-2011 Thread Starter
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In gear or not ??

I have a Hurth/ZF gearbox and want to know should I select reverse when sailing ??
I had one on another boat I owned reconditioned a few years ago and the ZF agent who did the work told me it is essential to select reverse while sailing along so the gearbox is not being worn by the propshaft turning.
However my latest boat also has a Hurth/ZF box and despite giving detailed information on just about every other aspect of its usage/installation/maintenance NOWHERE in the user manual does it say to do this. So I'm left thinking if they make the thing they would be best placed to say what is essential or not and the agent is talking shite but........
If you ask around any marina you generally find views are divided 50/50 (like almost everything else sailing related). Does anyone have a difinitive answer AND the reasons ??
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post #2 of 19 Old 11-10-2011
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I put it into gear for 3 basic reasons.
1. I have a folding prop
2. Moving parts cause wear and tear.
3. It becomes quiet when the prop shaft is not moving.


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post #3 of 19 Old 11-10-2011
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Plenty of threads here and elsewhere on this subject.. Hurth's only admonition is not to let the gearbox rotate in fwd gear without the engine running.

We've always used reverse with a fixed prop, (mainly for noise/wear reasons) despite some strong evidence out there that a free wheeling prop is actually less drag. Now we have a feathering prop, but I still pop it into reverse to promote feathering.

Yanmar has specific warnings against locking in reverse for their Kanzaki gearboxes..

Here's more info:

http://www.sailnet.com/forums/diesel...e-sailing.html

Ron

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".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)

Last edited by Faster; 11-10-2011 at 08:48 AM.
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post #4 of 19 Old 11-10-2011
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I have a Hurth transmission and it goes into reverse under sail. I do this because of reasons 2 & 3 that St Anna mentioned above and I believe that a non rotating fixed blade prop creates less drag than a free wheeling prop. My reason is as follows.
Hypothetical situation:
2 helicopters suspended in air…rotors not spinning
All things even including the size and pitch of the rotor blades except…
Helo #1 the rotor is braked and will not spin
Helo #2 the rotor is allowed to freewheel

Helo # 1 will always hit the ground first
Drag will act on the entire plane of the spinning rotor as opposed to acting only on the blades of the non-spinning rotor. Ask any pilot that has done an auto-rotation maneuver….although that involves an increase in pitch right before impact…err…I mean landing.

That is my story and I am sticking to it.
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post #5 of 19 Old 11-10-2011
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Quote:
Originally Posted by Faster View Post

Yanmar has specific warnings against locking in reverse for their Kanzaki gearboxes..
Fast .... The Yanmar directive that MaineSail linked to in the other thread did not distinguish between gearboxes. What makes you say specifically Kanzaki ?

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YANMAR MARINE USA CORP.
101 INTERNATIONAL PARKWAY
ADAIRSVILLE, GA 30103
TELEPHONE
(770) 877-9894
FAX
770-877-7565
BSITE WWW.YANMARMARI
dvisory Number: MSA08-003
A
:
DATE February 8, 2008 rs and OEMs
TO: All Marine Distributors, Deale Sailing
SUBJECT: Gear in Neutral WhileODELS: All Sailboat Engines
M
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 ailing.
s
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 dditional information.
a
If you have any questions regarding this advisory please contact a Customer Support epresentative at (770) 877- 9894.
R
MSA08-003 Page 1 of 1 February 8, 2008

Andrew B

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post #6 of 19 Old 11-10-2011
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Quote:
Originally Posted by steveg353 View Post
I have a Hurth transmission and it goes into reverse under sail. I do this because of reasons 2 & 3 that St Anna mentioned above and I believe that a non rotating fixed blade prop creates less drag than a free wheeling prop. My reason is as follows.
Hypothetical situation:
2 helicopters suspended in air…rotors not spinning
All things even including the size and pitch of the rotor blades except…
Helo #1 the rotor is braked and will not spin
Helo #2 the rotor is allowed to freewheel

Helo # 1 will always hit the ground first
Drag will act on the entire plane of the spinning rotor as opposed to acting only on the blades of the non-spinning rotor. Ask any pilot that has done an auto-rotation maneuver….although that involves an increase in pitch right before impact…err…I mean landing.

That is my story and I am sticking to it.

Steve,

We're not talking helicopter blades. Fixed props can and do cause more drag when locked. This has been specifically tested now by MIT, The University of Strathclyde Ocean Engineering Department and Yachting Monthly magazine, all with sailboat props in water not helicopter blades in air ..

For those still in doubt, and stuck on old wives tales and helicopter analogies, I made a jig and towed it through the water and made a video of it.

I have also posed an open challenge for ANYONE to come to Maine and watch this demonstration for themselves. All you need to do is pay me for my time. The results are NOT EVEN CLOSE... Freewheeling is significantly less drag...

Prop Drag Test Movie - YouTube

The Hurth ZF can be left in neutral or reverse but never the same direction as travel..



And ZF's most recent statement on the subject which says the same thing:


Hurth/ZF Sailing Gear Position.pdf

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-Maine Sail / CS-36T


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Last edited by Maine Sail; 11-10-2011 at 06:14 PM.
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post #7 of 19 Old 11-10-2011
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Yanmar's letter sounds all messed up. They are lumping all drivetrains into one bucket, saildrives and propshafts with inboards as if they were all the same--which they aren't.

My understanding is that one of the key factors is how the transmission is lubricated, and whether it will properly be lubricated if the prop is being turned while the engine is not running. This same issue applies to cars with manual gearboxes that are being towed.

And that is going to depend on the details of how a particular transmission is made. I can't believe that every transmission Yanmar has ever used, from saildrives to conventional inboards, all follow the same rules. OK, I can believe it--but not without express confirmation from a native English speaker at Yanmar.

Too many corporate communications specialists have done too good a job convincing me that reading comprehension is a lost art, and most corporate communications simply do not respond on point, much less respond correctly or accurately the first time around.
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post #8 of 19 Old 11-10-2011
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Back in the day, most boats had a shaft brake to reduce noise and wear. And drag as everyone knew a locked prop was less drag.To be avoided unless you ran a generator off it. Now we are concerned about overheating the trans because the lube and cooling pumps aren't circulating If you have a hydraulic tranny,I don't see it matters what gear you leave it in,the tail stock is going to turn and the prop drag.If you use a feathering prop ie maxi you can put it in reverse before shut down and draw power off the shaft. Other wise neutral works for me.
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post #9 of 19 Old 11-10-2011
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Excellent utube test "Maine Sail".

An additional test without a prop would show the drag of the fixturing. This fixture drag subtracted from each test would give a more dramatic difference between fixed and rotating.

Regarding the helicopter. Two points:

First point: auto rotation in the helicopter only saves your life if the helicopter has forward motion allowing the helicopter to glide. Typically, this forward speed is 40 or 50 mph. Any helicopter dropped straight down blades spinning or otherwise will likely kill you.

Second point: What is the rational for the helicopter comparison? Is it to determine losses to determine which scenario has higher losses? If so, consider that when the helicopter blades are fixed, a huge torque is generated by the blades as the helicopter falls which cause the helicopter to rotate. This rotation of the helicopter causes drag losses as the huge mass of the helicopter is rotated through the air. Given that the potential energy of the helicopter is determined pretty much only by its height and mass, it is doubtfull the losses (work done) are any different whether the helicopter glides or drops.

On the other hand, a fixed or rotating prop has radically different losses determined undoubtably by the apparent direction of water flow across its surface. Much like a sail. Main Sail's video illustrates this quite dramatically. And the losses on a fixed prop are considerably higher. No doubt about it.

Bryce

Last edited by BryceGTX; 11-10-2011 at 11:45 PM.
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post #10 of 19 Old 11-11-2011
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Maine,

Do you have links to the reports you mentioned? I am very interested in them since I have experienced the opposite in fixed wing, single engine aircraft. I assumed it would be the same for a prop in water and am interested in why it isn't.
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