Odd noise

[Dougie the Mate]

When we were sailing across to Greenock yesterday I noticed a regular kind of a beating noise that I have never heard in the 9 years or so that we have had the boat. She was sailing nicely along but this was obvious even to Mrs Dougie. I eventually thought it was coming from below the stern. I opened the engine compartment and it seemed to be coming from the propellor. It occurred to me to put it into gear and the noise stopped. After a while I slipped her back into nuetral and can honestly say that we heard nothing after that. When it came time to run the engine she sounded fine.

Has anyone had a similar experience or does putting her into gear while she is sailing cause any harm?

Please advise.

[Nick]

.
All quite normal. The drag on the propellor can cause the shaft to turn if the engine is in neutral. With a fixed prop it is sometimes necessary to leave it in reverse gear, as when you put it back into neutral it will start turning again. With a folding prop, putting it in reverse folds the blades and you can then (usually) put it back in neutral and the shaft will not rotate because the prop remains folded.

Some people will tell you that with a fixed prop there is less drag if you allow it to rotate, while others will tell you this may cause wear on the shaft/gearbox/bearings. If I am sailing a boat with a fixed prop and it starts to rotate I usuallly put it in reverse and leave it there. On our own boat we have a folding prop, so I engage reverse momentarity then put it back in neutral.

[cpedw]

Our old Volvo 2003 gearbox doesn't like that at all. The prop is prone to revolve when sailing faster than 2-3 knots and it makes a quite annoying, though not loud, noise. Selecting forward gear doesn't stop it. Selecting reverse does stop the revolving, but it's then very difficult to restore neutral gear. It's so tough that it feels like you're doing no good to the gearbox.
I'd be interested if anyone can offer advice how to stop the revolving without compromising the gearbox.

Derek

[Aja]

I'd be interested if anyone can offer advice how to stop the revolving without compromising the gearbox.
Derek

Fit a shaft brake. Bit of a hassle - but saves wear and tear on the gearbox. Only other alternative is to fit a folding prop and follow Nick's advice of putting it in reverse and back to neutral.

Regards
Donald

[wully]

Our old Volvo 2003 gearbox doesn't like that at all. The prop is prone to revolve when sailing faster than 2-3 knots and it makes a quite annoying, though not loud, noise. Selecting forward gear doesn't stop it. Selecting reverse does stop the revolving, but it's then very difficult to restore neutral gear. It's so tough that it feels like you're doing no good to the gearbox.
I'd be interested if anyone can offer advice how to stop the revolving without compromising the gearbox.

Derek

Just start it in gear...on my morse controller I push in the warm up button, Give it some throttle, crank the engine then pull it into neutral once it's running.

[Booby Trapper]

Before I fitted my new shaft I used to get a bit of a beating noise at a certain speed if I was sailing with the engine in neutral. The spinning prop caused the engine used to oscillate quite a bit and this could be felt throughout the boat. Putting the gearbox into reverse stopped the prop spinning and stopped the oscillation. I reckon the shaft was slightly bent or out of alignment. After fitting the new shaft and aligning it properly it doesn't do it anymore. I still sail with the gearbox in reverse to stop wear on the gearbox,shaft seal and cutless bearing

[Clyde_Wanderer]

I also put the box (Hurth HB50) into reverse to stop the prop rotating and making a whirring noise.
This was a recomendation of Hurth.
The rotating is usually stronger and louder on a 3 bladed prop.
C_W

[sahona]

I can't stop our prop as the gearbox is hydraulic, but I find the noise assists in sail trim and efficiency as I can tune to the tune as it were. Very helpful as we don't feel the breeze in the wheelhouse, and I don't particularly like 'instrument sailing'.

[cpedw]

Just start it in gear...on my morse controller I push in the warm up button, Give it some throttle, crank the engine then pull it into neutral once it's running.

Isn't that naughty? It seems to go against my training and intuition. But compared to installing a shaft brake, it seems like a breeze. I will give it a try. Can you start the engine while still sailing vigorously?
On the question of a shaft brake, I've been aware of the idea for several years but have never found any reasonably priced devices. In fact I think I only ever found one for sale commercially. I've considered DIY but have been scared off when tackling the "what if we forget the brake and start the engine" question. Interlocks possibly, but how exactly?

Derek

[sahona]

Interlock shouldn't be a problem once the device is chosen and installed. There has to be a bit that moves enough to operate a microswitch. The wiring is simple - divert the wire from the ign switch to the start solenoid via the operating point (common) of the switch, the normally closed point then goes on to the solenoid and the normally open could go to a light or beeper to alert you if trying to start with the brake engaged. To be honest the brakes I've seen wouldn't self-destruct if the engine was started while engaged, as they consist of a disk on the shaft with a notch and detent. The resulting rattle would remind you to pull the lever pretty smartly!

[claymore]

Really surprised the BFG is keeping out of this, especially as he almost had to surrender his boat to us in Colonsay.....

[wully]

Just start it in gear...on my morse controller I push in the warm up button, Give it some throttle, crank the engine then pull it into neutral once it's running.

Isn't that naughty?

Dont think so... I hate the noise of the prop turning while sailing and snick it into reverse when we get the sails up. It sometimes comes out of gear easily, sometimes not. Starting in gear might take a few more amps but apart from that I can't see where the harm is.

[Pilgrim]

I see that Yachting Monthly are promising an article on "Lock your prop or let it spin? Definitive answer!" in next month's edition (available 31st May). Could be worth a read.

Best Wishes
Liz

[cpedw]

Really surprised the BFG is keeping out of this, especially as he almost had to surrender his boat to us in Colonsay.....

Dare I ask who or what is the BFG?

Derek

[Silkie]

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