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Old 05-04-2007, 15:20   #1
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Prop Shaft Spinning when Sailing

I am currently cruising the Caribbean on my sailboat and am now in Bocas del Toro Panama. I have a question about my transmission that I was hoping somone might help me out with. While there is a Yanmar parts dealer here at very high prices, there are no mechanics or anyone here to provide assistance.

I have a Yanmar 3QM30F with a Kanzaki KH-18 transmission. After talking with other Hans Christian 33 owners it appears that the concensus is to put the gearbox in reverse when sailing to keep the prop shaft from spinning. For the past 1000 engine hours and 3000 miles while I've owned the boat I have occasionally tried to put the gear lever in reverse when sailing. With the engine off and the boat doing 5 knots under sail I put the gear lever in reverse, but the prop shaft continues to spin though a slight bit slower, slight sound of resistance. When I put the gear lever in forward the same thing. So I leave it in neutral to prevent any damage to the transmission.

When I asked on the Hans Christian message board someone indicated that my clutch plate is probably worn and could fail 'at any moment with out warning'.

As there are no places here to get the transmission rebuilt I am looking for a professional opinion before taking the transmission out of the boat and shipping back to the US for a rebuild.

Does anyone have any suggestions as to why my prop would continue to spin while in reverse? Is this truely an 'urgent' concern? If this is not normal what recommendations would you have? Is there anything else I should look at before considering sending the unit back to the US?



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Old 05-04-2007, 15:22   #2
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Forgot to mention. The transmission is internally lubricated, I believe it's call a bath type or something simular. It does not require the engine to be running for the transmission gears to be lubricated.

Damon
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Old 05-04-2007, 15:35   #3
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Put it in neutral

Yanmar advises to let the shaft spin in neutral. This transmission is designed with sailing in mind when using neutral. If you look at the mechanical drawings you can see that there is a mechanism designed to not allow the transmission to be "back driven" in reverse...it will free-wheel and wear that mechanism. There is probably nothing wrong with your transmission unless you let it run too long freewheeling in reverse or forward.

You might notice that at low speeds if you shift from neutral into forward or reverse that the shaft might stop but that is only until such force is generated to break the stiction of the free-wheel device.

Two nice things about your transmission: The lubrication does not require a heat exchanger cooled by seawater that might corrode through and ruin the transmission like some other makes; it is designed to accommodate a freewheeling prop in neutral, again, unlike some other brands.
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Old 05-04-2007, 16:58   #4
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Hi Rick,

Thanks for the encouraging words. In talking with another Hans Christian owner with the same engine/transmission he has told me that he sails with the gearbox in reverse, thus his propeller does not free spin. When I tested that on my boat my prop continued to free spin but I could also hear a bit of resistance (the tone changed some). We have let it free spin for some 1500 miles in the last couple years and really the only thing that bothers me is that I can hear it spinning.

I haven't looked at the shaft when the gear is engaged, will have to do that sometime and see if it does what you say. Something else I have notices is that if sitting perfectly still, say at anchor or in a slip, and the engine is running with the transmission in neutral, sometimes I notice that the shaft is very slowly spinning but a touch of my finger will stop it. Could this be from just normal engine vibration? Something else to ask is about the correct oil to use. The plate on the Kanzaki transmission states to use ATF but I have heard other owners say they switched to engine oil (same used in their engine) on the recommendation from Yanmar. I posted on a Yanmar web site and they did in fact say that engine oil would be better to us so we have switched to that. Any input on this?

Again, thanks for your assistance.

Damon
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Old 05-04-2007, 17:07   #5
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Damon and Dave, Hello from Chuck and Susan on Sea Trek. We are in Clear Lake. Sea Trek has a Yanmar 4JH3E with a different transmission than yours. But we have let the prop freewheel for several thousand miles and no issues at all. We too can here it but it lets us know what speed we are sailing by the sound it makes. Hope you guys are enjoying Panama.
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Old 05-04-2007, 17:15   #6
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Hi Chuck,

Clear Lake's a great place to be, we really enjoyed it there before taking off. Yeah, while sometimes it's a bit annoying to listen to the prop spinning when I'm off watch trying to catch some sleep, it does provide a good indication of speed when we're sailing. I've pretty much got the tone of the hum down so I know if I'm doing 3, 4 or 5 knots, speeding up or slowing down.

Just got to Panama a couple days ago, so far it's great. Rained the last two days so we haven't had a chance to see too much but we've got plenty of time to wait.


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Old 05-04-2007, 19:11   #7
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I can understand putting the motor in gear to stop the shaft from spinning, but why do people recommend reverse? Surely then if the prop did manage to actually turn, it would turn the motor backwards? Turning the motor backward, even just a little, could damage the rubber cooling pump impellors.

You could put a pulley on the shaft, and use it to spin a generator, then the noise of all those free amps being produced would be music to your ears.
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Old 05-04-2007, 19:16   #8
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That thought did cross my mind, adding a pully to the shaft and then to a generator, but I don't know if a bolt on system such as that exists or not. Would be interesting to find out though


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Old 19-09-2008, 12:52   #9
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In the Hurth transmission book it specifically says to only put in opposite gear of direction of travel,(this being reverse)It also states it wont damage trans. if left in neutral,I do wonder if putting in reverse when flying along at six knots is good for tranny though.
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Old 13-04-2009, 08:33   #10
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Propshaft Spinning when Sailing. A Question.

With a fixed blade propellor (2 or 3 blade) what give the most drag when under sail. (a) A rotating propellor, or (b) Locked propellor.

Would it no be better to have a fully feathering propellor with near zero drag.

Can you please advise.

Thanks, Peter.
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Old 13-04-2009, 10:31   #11
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Highseas, Bruadair, The Hurth HBW series(Now ZF-M series)is s dog style clutch that positively locks when engaged. Putting it in reverse (Not forward) will stop the prop. There is no chance of turning the engine over given the gear reduction and compression of the engine.

The Kanzaki is a cone style clutch and relies on the taper of the cones to engage the gears much like a Morse taper on a shaft. If the adjustment of the control leaver and related cables do not fully engauge the gear could slip. I would check to see that you are getting full movement on the trans leaver (At the trans) by disconecting the shift cable and shifting by hand to make sure you are getting full engagement.

I would follow Yanmars direction on neutral while sailing. especially if you hear noise.

Enjoy Panama
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Old 13-04-2009, 20:32   #12
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Quote:
Originally Posted by instinctyp View Post
Propshaft Spinning when Sailing. A Question.

With a fixed blade propellor (2 or 3 blade) what give the most drag when under sail. (a) A rotating propellor, or (b) Locked propellor.

Would it no be better to have a fully feathering propellor with near zero drag.

Can you please advise.

Thanks, Peter.
People have proven it both ways on paper. People on this forum have done the experiment and have discovered that it is different on different boats.

If you have a transmission that won't be destroyed by freewheeling, do the experiment yourself. Then you will have the correct answer for your boat.

Yes it is better to have a feathering prop for less drag. Some will say price and/or maintenance, or efficiency under power will make it not worthwhile.


John, love my Maxprop, glad it came with the boat and didn't have to make the decision whether I would spend the money for a feathering prop.
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Old 27-08-2009, 12:00   #13
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Just went through a fairly extensive search of the prior threads on this subject. The only on-the-water experimental results I could find reported here indicated that freewheeling was faster than locking. Didn't find anyone who reported faster locked based on actually checking both cases.
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Old 27-08-2009, 16:27   #14
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Positive - reach for Yachting Monthly issues from last year - more drag when locked.

However - how about a nice two-blade screw locked and hidden in the shade of the keel ??? If you let it freewheel it might actually give more drag!

Off course, a nice folding / feathering thing is the way to go on a sailing boat. Some designs auto-adjust the pitch when powering thus we can get optimum motor-sailing thrust with lower revs. Cream. But expensive too.

b.
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Old 27-08-2009, 17:51   #15
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As slow as my old boat is(named "Turtle" for a reason) I can't believe the few square inches of prop face is going to make much of a difference especially if it is free wheeling. .0003 of a knot isn't going to make or break my day. ...........m
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