free spinning shaft makes whirring noise

[GILow]

Originally Posted by Jim Cate

So, Matt, how do you stop the shaft in the first place? If sailing fast when you shut down the engine, the torque developed by the fixed props we've had in the past was surprisingly large.

Jim

Yeah, you have to practically stop the boat. Any more than 3 knots and you haven’t got a hope of stopping the prop.

I just round up for a moment, duck below to fit the line, then get going again. Crude. But effective.

On the whole prop drag thing, I’m with the group that reckons a locked prop creates more drag than a freewheeling prop. I can feel it in my boat, that’s for sure.

But someone pointed out in a thread here a few years ago, when discussing the pros and cons of various feathering props and the like, that the drag is mostly a problem in light winds. By the time the boat is approaching hull speed in stronger winds the drag becomes relatively insignificant. They quoted some interesting numbers from handicap formulas that tended to support this view.

I would sure love a feathering prop, mainly to stop the racket from my noisey old transmission. That and the fact that I am dragging around a really big prop.

[Wotname]

Originally Posted by GILow

Yeah, you have to practically stop the boat. Any more than 3 knots and you haven’t got a hope of stopping the prop.

I just round up for a moment, duck below to fit the line, then get going again. Crude. But effective.

On the whole prop drag thing, I’m with the group that reckons a locked prop creates more drag than a freewheeling prop. I can feel it in my boat, that’s for sure........

.............

Do you feel the drag as a function of boat speed (decreased) or as a function of the angle of heel (increased) or both?

Hint - both occurs

[GILow]

Originally Posted by Wotname

Do you feel the drag as a function of boat speed (decreased) or as a function of the angle of heel (increased) or both?



Hint - both occurs

Ummmm....

I feel the added drag in light conditions. That’s when it is obvious. Funnily enough, it feels like I am dragging around a big bucket on a rope. By the time there is enough wind to drive the boat properly (>12 knots) I can’t feel the drag hit though I am sure it is there and measurable.

Can’t say I’ve noticed any effect on angle of heel, but with 10 tons of lead in the keel I wouldn’t notice an elephant sitting on the rail.

Curious to understand how it might effect angle of heel. Can you elaborate?

[transmitterdan]

The angle of heel necessarily increases with drag. It’s a direct consequence of the vector forces acting on the sails. If the drag increases so too must the lateral force on the sail to maintain a given speed. That extra lateral force is needed to produce a larger force vector forward to overcome the drag. This assumes sailing on a reach or upwind. Downwind the heel is probably not much affected.

Additionally, extra drag increases the stresses on various parts of the standing rigging for a given speed on all points of sail.

[Jim Cate]

If the drag increases so too must the lateral force on the sail to maintain a given speed.

But Dan, when the drag goes up and there is no increase in wind speed, you can't maintain a given speed... you slow down. There is a slight change in apparent wind speed and angle (AWS is reduced and AWA increased)... seems like those changes more or less should cancel each other out in terms of the heeling vector, and thus the heel angle shouldn't change all that much.

Or am I missing something here?

Jim

[GILow]

Originally Posted by transmitterdan

The angle of heel necessarily increases with drag. It’s a direct consequence of the vector forces acting on the sails. If the drag increases so too must the lateral force on the sail to maintain a given speed. That extra lateral force is needed to produce a larger force vector forward to overcome the drag. This assumes sailing on a reach or upwind. Downwind the heel is probably not much affected.

Additionally, extra drag increases the stresses on various parts of the standing rigging for a given speed on all points of sail.

Ummm. Yes. I know about how all the forces on a sail boat work.

But Wottie’s post seemed to imply locking the prop had an effect on the angle of heel.

THAT one had me confused.

[Wotname]

Originally Posted by GILow

Ummm. Yes. I know about how all the forces on a sail boat work.

But Wottie’s post seemed to imply locking the prop had an effect on the angle of heel.

THAT one had me confused.

Haven't got time right now for the long answer but here is the short answer.

As you understand all the forces on a sailing boat, consider the forces acting on that piece of string that you use to lock your prop. Now use the principles of conservation of energy and the balance of forces in a steady state model.

I reckon you will work it out but if you need more clarification, get back to me.

By the way, the change in the angle of heel will probably be in the order of a fraction of a degree (or less), but it will be there.

[Lepke]

I didn't read all the posts so hope I'm not repeating, but if you have access to the shafts, wrap several turns of line or flat strap around the shaft and tie to something solid.
If that's too much trouble, add shaft brakes.

[transmitterdan]

Originally Posted by Jim Cate

But Dan, when the drag goes up and there is no increase in wind speed, you can't maintain a given speed... you slow down. There is a slight change in apparent wind speed and angle (AWS is reduced and AWA increased)... seems like those changes more or less should cancel each other out in terms of the heeling vector, and thus the heel angle shouldn't change all that much.

Or am I missing something here?

Jim

Think about it this way. Assume so much drag that the boat is stopped with wind abeam. All the boat does is heel. Reduce drag and the boat begins to move forward. Apparent wind moves forward and heeling moment decreases as the boat gains speed. Less drag = more speed and less heel. Add drag and the reverse happens.

It’s possible to trim sails to reduce heel at the expense of speed.

Downwind is a different story.

But in all cases extra drag increases loads in the rig.

[Wotname]

Originally Posted by Jim Cate

But Dan, when the drag goes up and there is no increase in wind speed, you can't maintain a given speed... you slow down. There is a slight change in apparent wind speed and angle (AWS is reduced and AWA increased)... seems like those changes more or less should cancel each other out in terms of the heeling vector, and thus the heel angle shouldn't change all that much.

Or am I missing something here?

Jim

Jim, leaving aside TxDan's argument, I was being a bit naughty by introducing the heel angle concept. The truth of the matter is that the angle of heel change will only be very very small - my guess is a fraction of a degree.

But understanding why it is there is important IMO as it helps to understand all the forces involved when locking a fixed pitch prop. When the forces are understood, the result becomes clear.

Understanding brings clarity to the thinking mind - again IMO

[GILow]

Originally Posted by Wotname

Jim, leaving aside TxDan's argument, I was being a bit naughty by introducing the heel angle concept. The truth of the matter is that the angle of heel change will only be very very small - my guess is a fraction of a degree.



But understanding why it is there is important IMO as it helps to understand all the forces involved when locking a fixed pitch prop. When the forces are understood, the result becomes clear.



Understanding brings clarity to the thinking mind - again IMO

I am not going to stoop to acknowledging that the torque will change the angle of heel.

This is NOT a year 12 physics class.

[emoji846]

[GILow]

Originally Posted by Lepke

I didn't read all the posts so hope I'm not repeating, but if you have access to the shafts, wrap several turns of line or flat strap around the shaft and tie to something solid.
If that's too much trouble, add shaft brakes.

Yep, good system, similar to my approach.

However, I suspect the OP departed when a bunch of physics nerds hijacked the thread.

[GILow]

Originally Posted by GILow

I am not going to stoop to acknowledging that the torque will change the angle of heel.

This is NOT a year 12 physics class.

[emoji846]

Actually, taking the pure physics model even further, I can construct a force diagram that also changes the degree of weather helm by locking the prop.

Put THAT in your theoretical physics pipe and smoke it!

[Wotname]

Originally Posted by GILow

Actually, taking the pure physics model even further, I can construct a force diagram that also changes the degree of weather helm by locking the prop.

Put THAT in your theoretical physics pipe and smoke it!

Err... we covered that in year 11 (at the same time as we did LH & RH props) - try to keep up please...

[wingssail]

Originally Posted by FPNC

QUOTE=Capn Jimbo;2783781] Unfortunately like the BMW cyclist in Zen and the Art of Motorcycle maintenance, fixing a problem with an aluminum shim from a beer can just was simply untihinkable by a certain number of owners.


I own an old BMW motorcycle. Reason being... I can fix it with shims from a beer can.

The also make good burners for a burned out magma BBQ.