Sailing with Shaft in Neutral

Brett · Post by **Brett** » Tue Apr 22, 2008 4:23 am

Hello,
I hope my newly acquired boat qualifies as a plastic classic. East Coast 31 built 1980 in Australia (probably not old enough)

To my question:-
This boat is fitted with a fixed three blade 16" prop and a shaft alternator which generates anything from 0 to 5 amps sailing.

Does the shaft freewheeling damage the gear box/engine??

The engine is a Bukh DV 20 with what I assume to be a standard Bukh gear box.

Any advice would be appreciated.

Post by **Tim** » Tue Apr 22, 2008 6:14 am

Many engine manufacturers specifically recommend that the engine be locked into gear (reverse) to avoid undue wear on the drivetrain. Yanmar, for example, recommends that the shaft not be left to freewheel. I always lock mine in reverse when sailing; I'd lock mine even if it wasn't specifically recommended by Yanmar simply because I can't stand the shaft and gear noise a freewheeling prop can make when sailing.

Beyond that, it's up to you. There have been some very spirited debates about this topic in other online venues over the years, but with little useful merit and few changed opinions at the end of the day.

bcooke · Post by **bcooke** » Tue Apr 22, 2008 7:21 am

Best source of info would be Bukh themselves.

The question is whether the bearings are getting lubricated and/or how long they can turn without lubrication.

http://www.bukh.co.uk/bukhhome.htm

-Britton

Brett · Post by **Brett** » Wed Apr 23, 2008 2:12 am

Thank you all.
I finally managed to get onto the local Bukh dealer here and the advice is that for their engines it does not matter in terms of wear on the gear box. They are splash lubricated so it's really only the additional wear on the stern gland and cutlass bearing.

I may sail around generating a few amps I think.

Without wanting to get into the additional drag of the spinning prop debate, (it looks like you need a be a rocket scientist for that one)
I have noticed that the rudder has a vibration in it when sailing over about 4knots which disappears as soon as you let the prop freewheel.

Having said that I suspect a fixed three blade prop is just a whole lot of drag period.

This is a great forum by the way.

bcooke · Post by **bcooke** » Wed Apr 23, 2008 6:53 am

I suspect a fixed three blade prop is just a whole lot of drag period.

Yep. The same stuff that makes it push so good when turning also makes it drag when stopped. Note: a turning prop creates a lot of drag too. And nothing is for free so those generating amps will load up the resistance even more. I am sure you know that though.

Brett · Post by **Brett** » Wed Apr 23, 2008 8:11 am

bcooke wrote:
I suspect a fixed three blade prop is just a whole lot of drag period.
Yep. The same stuff that makes it push so good when turning also makes it drag when stopped. Note: a turning prop creates a lot of drag too. And nothing is for free so those generating amps will load up the resistance even more. I am sure you know that though.

Quite right. There is a switch that disconnects the alternator and you can hear the shaft speed up as the load goes off it. So, no free lunch as the saying goes.
I'm kind of fond of the fixed prop though as this is a pretty heavy boat at 4300 kg and only 31 foot long, so under power the fixed prop certainly helps as opposed to a two blade folding type.

One day we'll get a feathering one.......