Stuffing box... Sailing.. prop left to spin

[a64pilot]

By torque sensing you mean for multi engine?
Only multi experience I have is helicopters and they are a little different.

Yes I was going to say all turbine engines and then remembered Garret’s they are different and much more difficult to set up with the Beta tube. My first flight with a Garrett was memorable.

[model 10]

Any TPE-331 will feather the the prop if the engine is not turning it. For an AG plane they have better responce?

[Wotname]

Originally Posted by a64pilot

Stopping or locking a prop, there is zero additional energy put into the system.

.......

Sort of but not quite, when one locks the prop (boat), energy is taken from of the thrust side and is added to the drag side of the system thus reducing the velocity of the boat. As a pilot, I know you are full bottle on vector analysis, at least as far as thrust, drag, lift and weight goes. Review my simple vector analysis (long post upthread) if this is not yet clear.

Regarding the conservation of energy. it is not all kinetic energy, there is some gravitational potential energy (GPE) as in the angle of heel to be considered as well.

Without invoking MIT entry requirements (), consider these aspects.

Slowing the prop down clearly require some energy to be expended and the more it is slowed, the more energy is required. Where does go? It is converted to heat (in the prop brake), angle of heel and turbulence (behind the prop). Also clearly, the most energy is expended once the prop is finally slowed from barely moving to locked (assuming all other aspects remain the same, namely thrust from the wind/sails etc). When locked, the energy is contained in the turbulence and angle of heel.

While it might seem that once the prop is locked, it is not "consuming" energy any more, it is in fact still converting energy from the thrust side to the drag side.

In my mind, the easiest way to show this is with (again) a vector analysis. If the prop is say turning clockwise when spinning, then to slow it, you need to apply a counterclockwise force to it. There are two vectors in play, a CW vector and CCW vector. In a steady state system, these vectors are in balance (just like the thrust and drag vectors are in balance when velocity is constant).

When the CCW force is increased enough to stop (lock) the prop, it reaches its maximum value and has to be maintained at the point (otherwise if it was reduced, the prop would spin again). Therefore the CCW vector has increased and the CW vector is reduced. This causes a change in the angle of heel of the boat.

Changing the angle of heel, changes the GPE of the system and in this instance, increases the GPE component.

So locking the prop changes the heel (by fractions of a degree) and increases the turbulence behind the prop (as it is stalled when locked).

The forces required to maintain the changes in the system (the angle of heel and the additional turbulence) reduces the force available to move the boat forward. Simply put, it slows down .

[Wotname]

Originally Posted by jmschmidt

As it's been said many times, a free spinning solid prop creates parasite drag equal to the surface area of a solid disk the diameter of the prop. A prop on a locked shaft creates parasite drag equal only to the combined surface area of the blades themselves. A two-blade prop, not much drag if the shaft is locked. A four or five blade prop with a locked shaft, a lot more drag but still not as much as if it were left free spinning. A lot of people don't believe that but it's true. Check with an engineer. A full feathering prop, doesn't matter because it shouldn't spin much, if at all, when feathered. If you transmission manufacture states not to lock the shaft by leaving it in gear when sailing, it's best to install a separate shaft lock and leave the transmission in neutral. Using your shaft to run an electric generator produces tons of drag. The faster you sail, the more electricity it produces same the greater the drag. Where do you think the electrical energy comes from? Same with a wind driven generator on a boat, sail or power, produces tons of drag too. When sailing it's best to lock the prop on a wind generator too. Unless you really need the electricity, run your wind generator when anchored. There is no free lunch in the world of physics.

I do agree with your last sentence

But...

Quick question - on a moving sailing boat (say 6 kts) with a simple fixed pitch three blade sailboat prop with the transmission in neutral (left to freewheel i.e. spinning), does it require any force (or energy) to stop the prop from spinning?

If YES (and remembering there is no free lunch), where does this energy come from and what it the result form the conversion of energy from one form to another?

If NO, then there is no need for any device to be installed to stop it

[Sardean]

Im going to tow my dinghy behind my yacht with it in neutral, then in gear and see if there is noticable difference. Maybe you pilots could tow your dinghy behind your plane's and get back to us lol

[davil]

Originally Posted by jhulmer

This is the response I got from Yanmar:

sorry cannot read the posting from Yanmar,could you either summarize or enlarge the size,when magnified on my screen just get too blurred.
thanks

[Wotname]

Originally Posted by davil

sorry cannot read the posting from Yanmar,could you either summarize or enlarge the size,when magnified on my screen just get too blurred.
thanks

Is this easier to read.
If not, essentially it says place transmission into neutral for all Yanmar transmissions when sailing with the engine turned off.

Not doing so may cause transmission damage and such damage is not covered by Yanmar warranty.

If you still wish to stop the prop from turning, fit a shaft brake, folding prop or similar.

It is dated Feb 8, 2008 and is issued by Yanamr USA. Its advisory number is MSA 08-003.

Finally it says to contact Customer Support for more detail on (770) 870-9894.

[peter57]

In the fluid air, a Gyrocopter' foil blade if not similar to a boats prop gives lift

While spinning the huge prop slows the decent.

If stopped it will near make free fall speed to the deck

[derfy]

Originally Posted by thedude0

Hi...maybe someone might know.. not sure with the older type of stuffing boxes... which also use a hose from the engine's cooling sytem to lubricate shaft...

if when the engine is not running and the shaft is left to spin whilst sailing ...does this cause any pressure on the shaft packing... since it is not getting the cooling from engine water system...?

I have been interested in this issue since acquiring my Morgan 44 last year. Had to swap out the Maxprop for servicing and cruised the boat using a backup 3 blade fixed prop for a few hundred miles. It is a Yanmar with direct drive transmission.

The first time I sailed the boat, I left the transmission in reverse, and discovered that it was impossible to manually return the shifter to neutral, so much torque had developed on the shaft that it jammed the gears. I had to hit the starter to break it free, so I could easily shift back into neutral.

I did not like all that torque on the shaft when left in reverse, and did not like burning up my starter to unjam the gearbox to get going again. It is clear the forces are huge when the fixed prop is dragging thru the water.

But I also am worried about wear and tear on the cutlass bearing, mainly. Not so much worry over the stuffing box ... it is dripping and keeping cool. Still, it is a wear point. I also worry about potential damage to the transmission with the shaft rotating free on the output side of the drive, with all the other internal gears not turning.

So I read all the threads here and on other forums, and found the reference Yanmar Server Notice already mentioned here. My Yanmar mechanic steadfastly promotes this policy.

Some threads have suggested that Yanmar did this specifically because they were getting complaints/warranty from the jammed-up reverse gear - people forcing the drive back to neutral and breaking stuff. It was claimed Yanmar had tried to get their dealers and service techs to train customers to give the drive a momentary click from the starter to unjam it, but were unable to get this practice successfully adopted broadly, and people were burning up starters. It is just another thing to remember when things are happening at the helm. So.. they just decided to tell people to let it turn. After all, the cutlass bearing is not their problem.

What I have done is (a) send off my Maxprop for an expensive rework ... this is the best solution for long haul sailing and should add 10-20% boat speed - especially in lighter air, and (b) I have started leaving the drive in neutral while I still use the fixed blade prop.

I am certain, BTW, that letting the shaft free-turn is not only significantly faster (I am an engineer and concur with the energy balance treatise presented here), but what really surprised me was the effect it had on the helm. I was not happy with my boat's helm ... it felt heavy, hard to turn, and non-seakindly (not easily balanced - klunky). Letting the prop free-rotate, interestingly enough, made the helm much much lighter to the touch. She feels like a sailboat now, instead of tugboat. I am sure the vortex created by dragging the fixed blades through the water was impacting the forces on my rudder (which is not too far from the prop).


So, now I have my Maxprop back from the shop and will soon remount it, making this whole issue go away. I am sure there will be new issues with the Maxprop ... another thread.

[joecat22]

Nice summary of the facts but we need to keep this a secret in case we get the chance to race against the airplane pilot sailors.

[Cheechako]

I've often wondered about the supposed "truism" that a stopped prop will drag less than a spinning one. It appears from this discussion/test results shown that a spinning prop drags less. My gut always said the spinning is relieving the pressure on the blade allowing it to "slip off". OTOH, the blades are in water and no matter how much they move or not move, they still have the same amount of surface area confronted with the water....? So how does spinning help?
So I still cant logic it out.
I can tell you this though. If you are casting a spinning type of lure fishing in water, you can tell if it's not spinning/tangled as it often feels like less drag retrieving it than when it's spinning.

[a64pilot]

Originally Posted by Ecos

Any TPE-331 will feather the the prop if the engine is not turning it. For an AG plane they have better responce?

Yes, and yes, the Garrett response is nearly instantaneous, however a good Ag pilot is not wearing out the throttle, they tend to manage energy very well, swapping altitude for airspeed. Ag pilots become very, very good at energy management or they don’t make it. I have never flown any aircraft that was as seriously underpowered as an average fully loaded Ag plane. Garrett’s are unpopular for several reasons, but one of the biggest is they don’t idle really and are noisy on the ground. Many Ag pilots only crank the engine once a day and an idling Garrett is obnoxious, and then if shut down, you have to manually rotate the prop of course to keep the shaft from warping and binding the turbine. However they are much less expensive.
A free turbine engine like a Pt6 it’s easy to leave the prop flat to see what the rate of descent is, and then feather to see how dramatic the difference is, of course you can’t feather a Garret and leave it running and most don’t like to shutdown an engine in flight, plus of course you can’t crank a Garrett when feathered, it takes the unfeathering pump to put the prop back on the start locks.
Garrett is a different animal, ours was set up to where starting was full manual with an enrichment switch, I used to say starting one was an Emergency procedure, particularly first starts.

[a64pilot]

I say there is no energy required in holding a prop stopped, cause there is no movement, therefore no work done.
Think of a parking brake on a car, it can hold one on a hill forever, no energy input required to keep it there. Stopped prop is the same as a parked car.
Takes energy to stop a car or prop, but not to hold one stopped.

[model 10]

[QUOTE=a64pilot, the Garrett response is nearly instantaneous,


In the mountians and small valleys, out west anyway, an AG Cat with a Garrett is the perfered machine.
I once flew a Flight Safety C-441 sim and put it in reverse at altitude and I remember sinking at 8,000' fpm.

[joecat22]

You are completely correct as long as the boat is not moving. You can lock down your prop all you want while on the hook and there will be absolutely no drag!