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-   -   In reverse while sailing? (http://www.sailnet.com/forums/diesel/95816-reverse-while-sailing.html)

flyingwelshman 01-17-2013 01:17 AM

In reverse while sailing?
 
This season was my first with a diesel (Yanmar 2GM20F). A few old salts at the marina suggested putting the engine in reverse while sailing (with the engine off of course). So I did this. It eliminated the sound of the prop spinning and, apparently, let me go a bit faster.

Then I read a notice from Yanmar saying that this wasn't a good practice and the engine should be set to neutral. So I did this and put up with the sound of the prop.

Last week I started a diesel engine maintenance course. Today the topic came up. An experienced sailor in the group insisted that the engine should be in reverse. One of the course instructors said that his mechanic insists that the engine should be in neutral. When the second instructor - a marine mechanic - came back in the room was asked the question, he insisted that the engine should be in reverse.

WTF?

Is there a definitive answer to this question? What is your rationale?

transmitterdan 01-17-2013 01:24 AM

Re: In reverse while sailing?
 
Your operator's manual for the gear box should give the correct answer. Some designs are ok to put in gear and some are not. There is no universal rule.

Dan

mdbee 01-17-2013 01:36 AM

Re: In reverse while sailing?
 
Do you think "old salts" know more than Yanmar? Also check with them to see if they have any updated info for your model.

Minnewaska 01-17-2013 06:34 AM

Re: In reverse while sailing?
 
Two issues. First and most important is what the manufacturer of your gear box says. That "old salt" probably didn't provide a written warranty with their advice. This topic has become an age old, wives tale, change in manufacturer recommendation, difference between models, conundrum.

Secondly, is which provides less drag. It's been shown that a spinning fixed prop creates less drag than one being held in place by a transmission in reverse. However, the spinning prop may make more noise.

Then add the boats with upgraded folding or feathering props. These are another story. Generally, you want a technique that puts them into fold or feather and then leave the transmission in neutral and it shouldn't spin anyway. For the feathering Max-Prop that we have, that requires putting the transmission in reverse, then back to neutral in a few seconds.

Maine Sail 01-17-2013 08:00 AM

Re: In reverse while sailing?
 
Quote:

Originally Posted by flyingwelshman (Post 976993)
This season was my first with a diesel (Yanmar 2GM20F). A few old salts at the marina suggested putting the engine in reverse while sailing (with the engine off of course). So I did this. It eliminated the sound of the prop spinning and, apparently, let me go a bit faster.

Then I read a notice from Yanmar saying that this wasn't a good practice and the engine should be set to neutral. So I did this and put up with the sound of the prop.

Last week I started a diesel engine maintenance course. Today the topic came up. An experienced sailor in the group insisted that the engine should be in reverse. One of the course instructors said that his mechanic insists that the engine should be in neutral. When the second instructor - a marine mechanic - came back in the room was asked the question, he insisted that the engine should be in reverse.

WTF?

Is there a definitive answer to this question? What is your rationale?


#1 The old salt is CLUELESS..

#2 The mechanic that had no clue or answer is not a mechanic I'd want to take a course from. Doh'.......


This issue is widely known in the Kanzaki cone clutch boxes. In 2008 Yanmar issued an MSA on this.

Your boat will NOT sail faster with a locked prop. MIT, the University of Strathclyde Ocean Engineering Department, Yachting Monthly, myself, and Dave Gerr the author of the Propeller Handbook all are in unanimous agreement that a locked fixed blade sailboat prop causes MORE drag not less. It has been tested multiple times with actual sailboat props at actual sailboat speeds in actual water... Old wives tales based on helicopter blade analogies die hard.


If your gear box is a Yanmar/Kanzaki NEUTRAL is the official Yanmar position when sailing. If you want to lock it you should use a shaft brake...


"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."


MSA .pdf Link

flyingwelshman 01-17-2013 09:01 AM

Re: In reverse while sailing?
 
Quote:

Originally Posted by Maine Sail (Post 977040)
Your boat will NOT sail faster with a locked prop. MIT, the University of Strathclyde Ocean Engineering Department, Yachting Monthly, myself, and Dave Gerr the author of the Propeller Handbook all are in unanimous agreement that a locked fixed blade sailboat prop causes MORE drag not less. It has been tested multiple times with actual sailboat props at actual sailboat speeds in actual water... Old wives tales based on helicopter blade analogies die hard.

Thanks for the comprehensive response.

That notice from Yanmar is the one I have seen.

I expected the RTFM responses, although they are not truely helpful. The anecdotal stuff and other citations - such as yours to the studies on prop spin - is great.

eherlihy 01-17-2013 09:29 AM

Re: In reverse while sailing?
 
To add for the benefit of others that will come across this thread;

The instructions that the transmission be left in Neutral while sailing are specific to Yanmar engines and transmissions.

Some other transmissions, including Hurth Borg-Warner, are OK with leaving in either Neutral (freewheeling) or Reverse (locked).

The image below is courtesy of Ron Hill and the C34 website
http://www.c34.org/faq-pages/images/Hurth-Xmission.jpg

seastory 01-18-2013 09:29 PM

Re: In reverse while sailing?
 
I used to follow the practice of shifting the transmission into reverse while sailing, but sometimes found it would get bound up in that position and it was very difficult to shift into nuetral in order to start up. Didn't seem healthy for the transmission, so I have been leaving it in nuetral ever since (about 6 years). A bit noisy, but no other problems in nuetral.

H and E 01-21-2013 07:37 AM

Re: In reverse while sailing?
 
My Hurth manual says you can sail in neutral. It does not say to leave in or out of any gear. What I found is that if I place it in reverse for a short time it will stay stopped from spinning for quite some time unless I get a boat speed above about 4.5 knots.

Rockter 01-23-2013 06:10 AM

Re: In reverse while sailing?
 
Well, Yanmar must have a rather strange set-up, but if they say that the gearbox must be left in neutral then indeed you must do so. I can't imagine why, but they know best.

BUT, the idea that a prop will be spinning everywhere I sail is simply silly. It will be noisy, it will wear the transmission, it will wear the stern bearing and will be very distracting.

Yanmar have just come off my future engines list. Good motors otherwise, but having to listen to a prop spinning, or having to fit a shaft brake as a matter of necessity??? Not for me.

On my old Volvo MD17C, I just put the gearbox astern and leave it there.


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