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Old 06-05-2006, 09:34   #31
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Lock it!

I agree with CSY and not only because the Hurth book says so. My Perkins mechanic ALSO says so and his explanation is that the bearings, seals and disks are all wearing as the prop shaft spins.

On the other hand I agree with Steve Kidson's observation about the difficulty of disengaging the gearbox after having locked it. This is because the gears are firmly engaged.

I also have some difficulty with my gearbox but it is not impossible to disengage. I don't like doing it because it puts extra strain on the control cable so I just slow down before I disengage.

This is what to do if it happens to you and you want to disengage. You can slow right down so as to take the load off first.

If it is more urgent than that you can bring the gear lever to minimum throttle and start the motor unless you have that clever little electrical interlock that will prevent your starting with the gears engaged. In this case there is nothing you can do. You must disengage first.

I have this switch on my new motor control mechanism but I have not wired it in.
It is supposed to be a safety device in case there are any lines in the water or someone in the sea when you start your motor but I think it is safer all round to be able to start your motor when you want to.

For possible lines near your prop and people swimming around you can use your eyes.

A possible alternative is to fit a manual switch somewhere convenient so you can override the interlock. Another switch
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Old 06-05-2006, 16:41   #32
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Sounds good Alan.
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Old 07-05-2006, 18:36   #33
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It's interesting to hear the different points of view, and heck, you all sound like you're right!!

I've been 'taught' that if the transmission has it's own lube resevoir, then sailing in neutral is the way to go. If engine lubed, lock it in reverse.

Rick in Florida
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Old 07-05-2006, 22:19   #34
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There are so many right answers, because there are so many box designs. All boxes can be split into two basic kinds and then the variances split out from there. Hydraulic and Gear. Under those two catergories, the designs are endless. As is the resoning for what is the best thing to do with the transmision when sailing.
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Old 08-05-2006, 04:09   #35
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You are very right Alan and in retrospect I realise I sounded too dogmatic in my posting. This is because I was focused on my set up which is a Hurth gearbox on my Perkins Prima.
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Old 26-07-2006, 14:32   #36
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Angry How to Strip Gears!

The manual for Technodrive makes it very clear that you should never engage gear when sailing without the engine - "when the boat is sailing (engine stopped) the gear lever must be in the neutral position".

I've just found out why the hard way, having taken the advice of a couple of club "experts" who assured me I would cause less wear and tear by putting the engine in gear to stop the prop shaft turning - I started doing that this season and guess what? yep, one knackered gearbox.

When I talked to the main dealer about it the first thing he asked was if I had been putting her in gear without the engine? Then he told me that was the biggest single reason for gears being worn or stripped and gave me a copy of the service manual with the quote highlighted!

So now I have to get the box out of the boat then strip it down and find out what needs replacing.

I hope this helps some of you guys to make up your mind - I just wish I had known this at the start of the season!
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Old 26-07-2006, 14:38   #37
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That sounds like a very good reason to avoid buying any boat equipped with a Technodrive transmission.

Jeff
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Old 27-07-2006, 16:57   #38
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An article in the most recent OCEAN NAVIGATOR magazine by Eric Forsyth, a man who has made multiple circumnavigations and sailed hundreds of thousands of miles has hooked his shaft to a generator and the freewheeling creates electricity. He notes that for his Westsail 42 if it slows the boat down it is not enough to notice and that in all the years he has been doing this it has NEVER adversely affected his transmission. According to the article he has been using this setup at least since 1991. That's a pretty good test.

Quote from Eric: "When I first installed a charging system 20 years and
200,000 nm ago, I was warned that allowing the shaft to rotate constantly could ruin the transmission. That has not happened; my Borg Warner is still performing perfectly without any maintenance in that period."

Like many things that create great controversey often times the real world application turns out to be very different than the armchair quarterbacking.

I highly recommend the article which outlines a creative way to generate electrical power passively with few parts and a simple setup.

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Old 27-07-2006, 22:46   #39
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If his Borg Warner is a "Velvet drive", then he will do no harm to it rotating in neutral. That is not the case with ALL tranys, only some.
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Old 07-01-2007, 16:26   #40
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Regarding what you said about Velvet Drives - I have been considering setting up a prop shaft generator on my Spencer 44 ketch but have been warned about the risks of excessive wear to my Velvet Drive hydraulic transmission. I thought about doing it anyway, skeptical of the real amount of wear in a slow turning, low load situation, where the gears are all fully bathed in the passive unpressurized fluid, at least every turn.
No one had a definitive answer for me, until I read what you said:

Quote: "A number of major gearbox manufacturers have dispelled an earlier unfounded fear of gearbox damage due to improper lubrication while freewheeling. However some gear box manufacturers do not advise leaving the prop to free wheel as this can cause mechanical problems within the box (overheating due to lack of lubrication).
Ie - From “Velvet-Drive”:
It has been determined by tests and practical experience that all Velvet Drive marine transmissions call be free-wheeled without risking damage in sailing or trolling applications. Caution should be taken to be sure that proper oil level is maintained prior to freewheeling as well as normal running. Freewheeling one propeller of a twin engine boat at trolling speeds will not cause damage to the transmission connected to the freewheeling propeller.
Extended periods of free-wheeling at high speeds may cause the transmission to overheat; therefore, it is recommended that transmission sump temperature be monitored and free-wheeling discontinued whenever 230 degrees F or 111 degrees C is reached.

All of this is good news to me and I am motivated to go ahead with the project while the boat is out of the water. Do you have any references to the studies, or elsewhere that I can confirm this opinion? What is your background? The shipwright I am working with will ask.

I would appreciate your thoughts also on weather I should go with a belt or gear or bicycle chain drive from the shaft to the alternator.

Thanks, Tim
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Old 07-01-2007, 17:12   #41
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As I type this I am waiting for a reply back about my ZF25 gearboxes that are attached to Cummins B3.3 rated at 65hp.

Our plan was while on passage to run one side for 3 hours and then the otherside for 3 hours in the belief that we would improve economy, yet still get around 8 to 10 knots of boat speed.

We wont have folding props and could well have 4 bladers similar to this.


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Old 07-01-2007, 17:40   #42
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I have a Twin Disc gearbox and the instruction manual stipulates that you must not put the box in gear to prevent the prop from spinning whilst sailing, otherwise damage will to the gearbox will result. They also advise that if the shaft is free-wheeling then the engine must be started and put in gear for a few minutes every four hours or so. They don't say why but I assume its to ensure that all parts of the gearbox get properly lubricated. Thats why I designed and fabricated a really nifty mechanical shaft lock.

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Old 07-01-2007, 18:08   #43
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That's right Chris. Some boxes are lubricated by a specific gear. When the box is being trailed, that particular gear does not get spun and so other gears and bearings will remain dry.
Originaly Velvet drives were recomended to be run every 8hrs, but Borg Warner have since changed their advice on this as seen above.
However, it is ONLY the Velvet drive that this can be done to unless the manufacturer has specified otherwise with their own box. So don't anyone assume it can be done with any box.
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Old 10-07-2007, 04:37   #44
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Quote:
Originally Posted by Pblais
For my Hurth transmission they are clear that it should be placed in in gear in reverse while under sail. Drag or no drag I don't need to be replacing transmissions. I have no clue if the three blade is Mickey up or Mickey down. Sometimes you do get lucky though.
Well, I also have a Hurth transmission with a Perkins 4108 and the manual clearly says letting the transmission spin in neutral will not damage it. I guess we have different models. Anyway I will double check and post again.
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Old 10-07-2007, 05:02   #45
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UNIVERSAL DIESEL WITH HURTH TRANSMISSION
Universal Diesel Engine Owners Manual - Sea Water Impeller Replacement - Marine Diesel Direct / Torresen Sailing Site

CAUTION
DO NOT LEAVE GEAR IN FORWARD WHEN SAILING. GEAR MUST BE IN NEUTRAL FOR FREE WHEELING OR SHIFTED INTO REVERSE TO LOCK PROPELLER WHILE SAILING.

AND/OR

ZF (Hurth) Owner’s Manual
http://www.capedory.org/manuals/Hurt...ion_Manual.pdf
Page 9
CAUTION.
Idling position of the propeller: gear shift lever must be in «O» position.
Use the shift position opposite to the direction of travel for locking the propeller shaft, otherwise the transmission will be damaged.
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