Captain/Owner Sleeping at the Helm

[Jim Cate]

FWIW, when we stop motoring we simply put the transmission in reverse for a moment. There is a satisfying "clink" as the prop folds, and then we put the trans back in neutral.
The prop stays folded and the shaft does not rotate. If we do not go through this procedure the prop and shaft will continue to rotate if the boat speed is over ~ 2 kts.

Three blade Flex-O-Fold, Hurth mechanical transmission.

Jim

[gordonhinds]

Vibration can be from the prop turning often as it hasn’t closed properly. If you are worried about transmission damage you can start the motor, engage in reverse and stop the motor.

[StuM]

Originally Posted by waterman46

Perhaps someone could actually run a test. Only if you have a fixed prop, not folding or feathering. In calm conditions, flat water, get up to a set speed under power, stabilize speed (through water speed, not GPS) carefully, note the speed, then shut down the engine, leaving transmission in forward or reverse. Check prop not rotating. Note time it takes for boat speed to reduce to a fixed value, say 2 or 3 knots. Do the same but put transmission in neutral immediately after shutting down engine. Check for prop rotation. Compare time it takes for boat to reduce its speed to same slower value as in the first case. Any takers?

No need. Anyone who has raced a boat with a fixed prop has already tried engine in reverse versus neutral and noted the difference.

[JPA Cate]

As a matter of fact, one of the skippers on whose boat I used to race, had marked the prop shaft -- it had a 2 blade prop, and the idea was to vertically align it with the aft end of the keel -- so that we could all see the mark, when it was properly aligned. It was one of the newbie jobs for me, to check that.

This might have been 45 yrs ago or so.

Ann

[gordonhinds]

A prop that rotates freely with no engine engaged is slower than a fixed prop in most conditions. I think the issue is the vibration caused by the prop moving not the speed.

[Wotname]

Originally Posted by gordonhinds

A prop that rotates freely with no engine engaged is slower than a fixed prop in most conditions. .........

Interesting opinion but do you have physics knowledge to back up your opinion or any creditable source to support this opinion.

Perhaps a good starting place is to read this http://www.plaisance-pratique.com/IM..._sdarticle.pdf and see if your opinion changes.

Of course you are entitled to keep your original opinion but not entitled to present it as a fact.

[VChild]

My transmission is a new TwinDisc TMC 260 on a new Beta Marine (Kubota) engine. The owner’s manual for the transmission specifically states to sail with it in reverse gear if you desire not to have the shaft turn continuously. My prop is a 4 blade 24” diameter MaxProp folding prop. So, that is how I have always sailed until I had a serious unexpected surprise.
At about 3:00am, a couple hundred miles out of Pensacola in the Gulf of Mexico, on a passage to the Florida Keys, there was a decent breeze and we were making about 7 knots on a broad reach. I was on watch and my wife wasn’t feeling tired so she was standing in her favorite place, 2 steps into the companionway where she can still look out over the deck. She likes that spot because she can brace herself against either wall of the companionway when the unanticipated large wave hits in total darkness.
The background noise from wind and waves was significant. We were cruising along nicely when suddenly I felt a strong vibration and heard a loud high pitched whine coming from below. I raced down into the cabin to see where the sound was coming from. It was very loud and seemed to be emanating from the entire hull itself. I couldn’t locate the source. In what seemed like an eternity but was actually only about 10 seconds, I discovered that the engine was running. I quickly hit the kill button and all was smooth and quiet again.
Here’s what happened. When my new engine was installed, the new panel was placed where the old one was, on the starboard wall of the companionway. The old panel had an actual key switch to start the engine but the new one is just a push button. You can guess the rest. A large wave caused my wife’s behind to sway right onto the start button which started the engine.
Because we were sailing with the transmission in reverse, the engine started in reverse gear while traveling forward at 7 knots. Not good!
We were lucky though. The engine and motor mounts checked out fine, as did the transmission and shaft. However, we did slightly damage the new MaxProp. An internal shim washer got crunched. It continued to work but with a slight vibration. A few hundred dollars plus shipping and it was brought back to factory specs.
I now only sail with the transmission in neutral after getting the prop to fold. I am also going to install a small cover over the start button.

[Skipper John]

Originally Posted by Wotname

I believe it only applies to transmissions which are fitted with cone clutches (but I could be wrong).

AFAIK, unlike a plate (or disc) clutch a cone clutch requires a higher torque at the input end compared to the output engine to work properly. If the transmission is engaged whilst sailing and the engine is off, the torque provided by the prop (trying to rotate) is higher than the input end. Put another way, the cone clutch is now being driven by the wrong end and long term damage will occur.

But don't quote me, I may be off base!

I have had a re-think on the effect of sailing with a standard prop in reverse gear. It's the torque produced dragging the prop that can cause gear damage, not the thrust!
For example, my Yanmar 2GM20 takes roughly 2 engine hp to increase 1 kt from 5 to 6 kts or about 1.5 hp prop output. Assuming dragging a fixed prop slows the boat from 6 to 5 kts, it should take about the 1.5 hp. This equates to about 88 ft-lbs torque with my gearing. The small reverse gear pitch diameter likely sees a single tooth contact force up to 10 times that or about 900 lbs.

This is OK for a rotating gear but as a stationary gear tooth under vibrating load with poor lubrication it could damage the tooth surface.

Regarding the question of fixed or rotating prop when sailing I've had an epiphany. I always thought spinning caused more drag, however, an internet search for prop drag tests produced some pretty convincing proof that a fixed prop creates about twice the drag of a spinning prop.

Having said all this, l have a folding prop so none of this applies to my situation. The same goes for feathering props.

[Buzzman]

Originally Posted by LittleWing77

People who don't perceive they are doing anything wrong - to their mind - aren't doing anything wrong.

Know what I mean?
LittleWing77

Yep!! It's called 'Dunning-Kreuger Syndrome'....

[StuM]

Originally Posted by Buzzman

Yep!! It's called 'Dunning-Kreuger Syndrome'....

Not really, but I'll give you a pass because it's a similar Effect

[Gerrit Coetzee]

Originally Posted by SVHarmonie

If you are uncomfortable with the way the boat is being run, leave at the next port stop. If you are REALLY uncomfortable, ask to be left at the nearest port. If you are not that uncomfortable, then suck it up and put up with it. You are crew. You have very little say in the matter.

If you really want to try to change behavior, the best way in this case would be to show the owner how you use the timer on your cell phone to wake you every 10 minutes for a horizon scan. Even if you don't need to do this presenting it this way makes you less of an accusatory scold. It might work, it might not.

There is a reason many delivery captains charge extra if the owner is aboard for a passage.

There is but one captain. Nobody is perfect, lest anyone who think he is know it all.

[Gerrit Coetzee]

Originally Posted by Phisher

I recently crew....Whatever sleepy head were my thoughts. This man would not listen to me about several instances and situations. .....?

I gather you have some experience. That is good. Your OP's intention seems to vent air and seek justification.

But it all lacks evidently respect.

There can not be two captains on one ship, was my fathers advice.

Your approach and attitude is the stuff mutiny is made off.

Advice and keep your distance respectfully.

Crew can only via the 2ib override the captain in situations where he is clearly not of sound mind or taking decisions clearly risky. Any other conduct is breaking ranks.

You live and sail under the captain you choose.

Self-righteous and insubordinate crew can make a trip hell.

[Wotname]

Originally Posted by Skipper John

..........

Regarding the question of fixed or rotating prop when sailing I've had an epiphany. I always thought spinning caused more drag, however, an internet search for prop drag tests produced some pretty convincing proof that a fixed prop creates about twice the drag of a spinning prop.

..........

Congratulations and thank you for posting your epiphany!

[Wotname]

Originally Posted by waterman46

............
Perhaps someone could actually run a test. Only if you have a fixed prop, not folding or feathering. In calm conditions, flat water, get up to a set speed under power, stabilize speed (through water speed, not GPS) carefully, note the speed, then shut down the engine, leaving transmission in forward or reverse. Check prop not rotating. Note time it takes for boat speed to reduce to a fixed value, say 2 or 3 knots. Do the same but put transmission in neutral immediately after shutting down engine. Check for prop rotation. Compare time it takes for boat to reduce its speed to same slower value as in the first case. Any takers?

Plenty of people have already carried out real world testing. Some have already posted in this thread. I have personally done it on three different boats over the years.

Department of Mechanical Engineering, University of Strathclyde, Glasgow G1 1XJ, Scotland, UK have carried out similar tests. See http://www.plaisance-pratique.com/IM..._sdarticle.pdf

EVERY single one of them reports the same result. Not a single one has found that locked fixed pitch sail boat prop improves boat speed.

If that isn't proof enough, what more proof would you like or try it yourself.

[Wotname]

Originally Posted by waterman46

1) The point of autorotation was mentioned to show that really significant energy is stored in a prop dragged through the medium of air or water. Enough to nearly stop a descending helicopter with no engine. That energy continues to be constantly created, by dragging a rotating prop. That energy must be dissipated somehow. Not you, but some other posters seem to have missed this point. .............

Of course a free wheeling prop absorbs energy, no one seriously suggests otherwise. There are frictional (heat) losses, audio losses, stored energy losses, swirly water losses to name a few. Collectively this is the drag of the free wheeling prop.

A locked fixed pitch sail boat prop also has losses and thus drag.

The only question is which has the greater drag.

Empirical data consistently answers the question and the answer is (drum roll please), the locked fixed pitch sail boat prop has the greater drag.

This apparently upsets some pilots who seem to be offended by the notion and simply refuse to believe it.

As a ex-pilot myself, I can accept that what is best for flying is different to what is best for sailing.