Captain/Owner Sleeping at the Helm

[TabbyCat]

Originally Posted by OS2Dude

It surprises me that comments above act like being asleep while On Watch isn't a SAFETY concern. It is not a matter of 'His Boat, His Rules'. It is a COLREGS violation for there to be no one (awake) on watch, not to mention he put everyone's life in danger. There is more to being ON WATCH than keeping the boat on course. The auto-pilot can't make adjustments for unforeseen events or objects in the water.

And some of those other "objects" are other boats! Most folks follow the rhumbline between two ports. Twice on the way to and from NZ I've had close encounters with other boats and discovered that the crew onboard was asleep. (We hailed & hailed and finally a sleepy voice finally answered the VHF and admitted so). That is simply unacceptable. They have the right to put their own lives at risk, but not to endanger other boaters, with the idea that we will spot and avoid them!

[capn_billl]

Folding propellers do not auto rotate.

That reminds me, I need to shop for folding props.

[StuM]

Originally Posted by betwys1

So you think that locking a prop slows the boat?

In aircraft, It is well known that a stopped prop provides less drag than a wind-milling prop. I would be rather surprised if water-screws differed in that respect.
So what was that snip about know-it-all crew again?

Edited: I see you have subsequently researched the question and changed your opinion. Well done.

[StuM]

Originally Posted by BadDecisions

[emoji23] Also it is a mfg recommendation for"sail drives" did that cat have sail drives?

The OP said it was a 2016 Lagoon 45 charter boat. You won't find one of those other than with sail drive.

[StuM]

Originally Posted by PineyWoodsPete

The sailing equivalent is a free-wheeling prop with only shaft bearing and tranny gear drag, which is coupled to a high output generator - say 5kW, and this "work" will slow the prop rotation and have an adverse effect on boat speed just as a partially braked aircraft prop definitely will. With true free-wheeling, not nearly so much.

Good point. According to the "locked prop = less drag" theory, using regen would make your boat go faster than when freewheeling

[StuM]

Originally Posted by PineyWoodsPete

Uhhh, no such thing as a free-wheeling aircraft fixed-pitch prop I know of, unless you have devised a way to uncouple your Cub 4-banger from its prop.

If you read one of the earlier referenced technical papers, you will see what would likely happen if you had an aircraft with a freewheeling fixed-pitch prop in the event of engine failure. It ain't pretty!

[gah949]

If the catamaran has folding or feathering props and they are making a noise while you are sailing then it is OK to push the controls so they are in reverse momentarily to make the props fold or feather but immediately put levers back in neutral.
This will avoid the gearbox spinning and solve the noose problem.
Sailboats without folding props will have a shorter gearbox life and fixed props spinning constantly cause a huge drag and reduce the speed of the boat.
Any of the crew including the owner or skipper on watch is derelict in the well-being off all those on board in peril and the boat in danger of collision and sinking. It is your duty to make the skipper aware of anyone including the owner that the person on watch was sleeping.

[chriadel]

There is no way in hell I read this whole post. Scroll by, I know.Ya, ya, ya,....

[Skipper John]

I'm not sure what Yanmar's reasoning is for not having the gear in reverse when sailing. It may be possible they think it could cause "Brinelling" of the gear teeth due to loads imposed by the prop drag. However, if the prop drag is causing less than a knot of speed loss of speed it's hard to imagine that there is much force involved.

In my case I have a folding prop which does spin even when folded. So I have always had it in reverse when sailing. 25 years on my Yanmar and it works just fine.

I believe some types of transmissions have to be locked when sailing because the gears won't be lubricated unless the engine is running. I think Twin Disc units are like this. So check your manual!

[Uncle Bob]

Originally Posted by tootalltony

There are 2 schools of thought on this

Leave the engine in gear when off-------this will result in the shaft not turning and will save wear on the cutlass bearing and all the other bearings
on the drive shaft. This will mean no vibration and is the happiest position for the engine. The down side is that there will be some drag as the fixed props can't spin freely...........but this reduced speed is not even measurable

Captain Tony

This is not the result of those that have actually done the testing, documented it and recorded the tests and results.

Originally Posted by aeronautic1

“So you think it was a good idea to slow the boat and risked potential damage to the engines by locking the props contrary to the skippers wishes and the manufacturer's instructions? Now how do we deal with know it all crew?”

Treat them no different than know-it-all internet posters? It’s a known FACT that a free-wheeling spinning propeller creates more DRAG than a stationary propeller. Ask any pilot or flight instructor.

Thank you for your "compelling" factual note, I look forward to your recorded and documented dissertation refuting those that have shown the reverse is true. You do have a link or two to a reputable source that demonstrates your FACT, don't you?

[waterman46]

Originally Posted by NorthernMac

You sure about that?

Think about trying to compare the drag of a 10" diameter prop and a 10" diameter solid disk, the windmilling prop will have even more drag than the disk since it extracts energy from the entire area, compared to the disk where water will just move around it.

Yes! Thanks for this way of looking at the issue. And in terms of energy, a rotating prop is heating the transmission, which is a waste of energy. This increased drag is placed against the bearings, constantly rotating, so there is additional wear on the transmission. A non-rotating prop has zero rotational energy, so the drag of the blades against the relatively slowly moving water flow is the only energy loss, and there is no heating of the transmission.

If you don't believe a rotating prop can store energy, look up autorotation in helicopters. It is a way for a helicopter with a stalled engine to freewheel the rotor and descend, storing energy in the rotation of the blades, to allow it to brake it's fall when just above ground.

The helicopter uses the spinning rotor to store that energy. We want just the opposite, we want minimum drag, so we should lock our props when sailing.

An airplane wing has zero lift when it is stationary. Same wing has lift when moving forward above stall speed. Analagous to the motion of the sailboat prop in the water. When sailing we want the prop to have zero "lift" which would be drag in the case of the boat sailing. So we want the blades to be stalled.

Of course, you should follow the transmission manufacturer's recommendation and if they insist that the gear be put in neutral, then do it. But that won't result in minimum drag, even with a fixed pitch prop.

[waterman46]

Originally Posted by Wotname

If we argue the boat speed decreases when the prop is locked (as I firmly believe), then the energy that is being extracted from boat's momentum is equal to momentum of the swirly water behind the stalled prop plus the stored energy of the torque of the shaft lock.



....over

Not quite. A stationary object has zero dynamic energy. The prop could exert a huge torque, but if the shaft is locked, no energy is created or stored by that force. That torque can have zero retarding effect on the boat.



With a fixed shaft, the only energy loss is in the "swirly water" behind the prop.

[StuM]

Originally Posted by waterman46

Yes! Thanks for this way of looking at the issue. And in terms of energy, a rotating prop is heating the transmission, which is a waste of energy. This increased drag is placed against the bearings, constantly rotating, so there is additional wear on the transmission. A non-rotating prop has zero rotational energy, so the drag of the blades against the relatively slowly moving water flow is the only energy loss, and there is no heating of the transmission.

To prevent the prop from rotating requires a force. As we should all know, for a body in equilibrium every force requires an equal and opposite force. In this case, that equal and opposite force rotates the hull away from it's natural angle of inclination. The locked prop is in effect having to work against gravity.

If you don't believe a rotating prop can store energy, look up autorotation in helicopters. It is a way for a helicopter with a stalled engine to freewheel the rotor and descend, storing energy in the rotation of the blades, to allow it to brake it's fall when just above ground.

Of course a rotating prop stores energy. Every rotating object possesses kinetic energy. But that has absolutely nothng to do with comparative drag of a rotating object in a medium such as air or water.


The autorotation argument has been debunked multiple times. It's an entirely different issue which relies on changing the pitch of the blades to generate maximum allowable rotational speed from the movement of air upwards through the rotors when descending and then changing pitch when close to the ground to convert that speed to lift.

An airplane wing has zero lift when it is stationary. Same wing has lift when moving forward above stall speed. Analagous to the motion of the sailboat prop in the water. When sailing we want the prop to have zero "lift" which would be drag in the case of the boat sailing. So we want the blades to be stalled.

That's a total non sequitur. A stalled airplane wing has a tremendous amount of drag. If you'd ever stalled an aircraft you'd know that. (It's done all the time in initial flight training and in aerobatics)


You really should take the time to read some of the technical literature and empirical research findings previously quoted rather than relying on misapplication of half understood concepts which have led you to the wrong conclusion.

[StuM]

Originally Posted by waterman46

Not quite. A stationary object has zero dynamic energy.The prop could exert a huge torque, but if the shaft is locked, no energy is created or stored by that force. That torque can have zero retarding effect on the boat.

With a fixed shaft, the only energy loss is in the "swirly water" behind the prop.

Forget about the "swirly water" for a minute. (Whether a fixed prop or a free-wheeling prop causes more "swirly water"
is subject to debate. I haven't seen any conclusive research either way).


That torque has to be countered. If it weren't the whole boat would spin in the opposite direction. But that spin is countered in part by water resistance(drag) and by a small angular displacement of the hulls COG relative to the way it would float normally requiring a vertical force to oppose gravity. It's all energy consumed in the end. And the more energy that's consumed in various ways, the less there is to move the boat forward from the one motive force - the wind in the sails.
TANSTAAFL.

[fivecapes]

https://youtu.be/5i0WBv4ygNo?t=80

Free wheeling all the way down?