Comments Thread for Giu's Sailing Videos

[Rockter]

Saildog... that is a totally separate argument. Guil was arguing that the traveller ANGLE influences the heel, not the sail trim, per se. I have sailed a few years, and yes, the sail trim will, per se, change the heel angle.
The traveller angle will not, per se.

[Giulietta]

Originally Posted by Rockter

these are free body diagrams here. This is what I do for a living.

Rockter, so do I, but don't talk about it much...

speaking of simple body diagrams, maybe now you can see it. I couldn't make it any simpler. Mybe you are forgeting that the fulcrum is not the center of the boat, and instead is the center of bouyancy (I called it floatability before).



And in case you insist in the welded boom mast thing, I made a second diagram that includes the mast..



Off course the yeelow arrows are not at 90 degress as the oat is heeled by X and the forces applied are negative, not positive, as the force is pull not push.



Go on..try it..unless you don't agree with my models..

a) yellow arrows are constant forces, say 1.5 (any unit it doesn't matter) each to a total of 3

b) Total lenght of balance is 3 (again whatever you want to measure it with)

c) arm to the right is 1/3 of the arm to the left.

case 1 Traveler to the LEFT of the fulcrum

Traveler to the left F=W X moment arm

F = 3 x (1 + .5) = 9.6

(because the mast is to the left of fulcrum we have to add .5)



case 2 Traveler to the RIGHT of the fulcrum

Traveler to the left F=W X moment arm

F = 3 x (1.5 + .5) = 12

(because the mast is to the left of fulcrum we have to add .5

[Rockter]

Oh Guil.

I am not forgetting fulchrums.

The disturbing moment on the boat is the same for all your diagrams!!!

Show me why the disturbing moment changes. Show me why the restoring moment changes.

The yellow vectors have the same moment arm in all your diagrams. All of them.

How does the red chord alter any of the moments?

You don't draw the forces within the traveller chord. They are balanced within the structure, and don't change anything.

You are getting into the minutae of how the forces are distributed within the structure of the boat, and you are arguing that how you distribute them will right the boat. It does not matter how the forces are distributed from the boom and mast to the boat. The boat heels because of the EXTERNAL forces and associated disturbing moment, NOT HOW THE FORCES ARE DISTRUBUTED WITHIN THE BOAT.

The traveller chord angle will not change anything any more than the amount a car leans in a bend is dependent on your seat belt tension.

If you are right, every racing boat under the sun would have a horizontal traveller chord, anchored to the top of a post level with the boom. You must remember that the traveller chord is an action reaction pair, NO EXTERNAL FORCE ACTS ON THE CHORD, and its angle does not change the relationship between the boat and the wind (constant trim), does not change the centre of buoyancy (so does not change the restoring moment) and its tension does not heel the boat. It cannot, because the forces on it are balanced and there is no external force acting on it.

The wind heels the boat.... an external force with moment.... not the traveller chord.

When your boat is at equilibruim (heeled or vertical), you may say, as Newton does...

sigma{F} = 0 ...forces are balanced (or your boat will have a translational acceleration)

sigma{M} = 0 ...moments are balanced (or your boat will have a rotational acceleration)

Now, lock the boom, weld the boom, hold the boom yourself, however you fix the boom, you will not change those rules, and the traveller tension will not alter that obligation to meet those rules. You heel because of moments there Guil, not traveller angle. The traveller angle does not change the disturbing or the restoring moments.

I look forward to a racing boat design with horizontal traveller chord that helps right the boat. It won't happen.

I have always liked your videos there Guil, and I have watched them all. You have taught me a lot, but you are wrong on this point there Guil. The way that you fix the boom to the boat does not alter the heel angle of the boat.

Rockter.

[tomaz_423]

Rockter. I am with you in this discussion.
Alex, to me you are the main reason I keep reading sailnet and I respect you and your family, but in this case I think you are oversimplifying and ignoring other forces acting on the boat.

Let me ask you, Alex and Dog: If baron Munchhausen is pulling his hair really hard and the force of pull is going upwards - will he eventually pull himself out of the swamp?
No, because there other forces working in opposite direction and the whole action is cancelled out.

Same with the position of the traveller.
I agree 100% with Alex, that moving traveller to leeward side reduces the heel - but that is because doing so you changes a lot of other parameters - including sail trim, forces on the mast, forces on the wang, forces on the sheets, ....
So, for all practical aspects of sailing you are right.

The only problem is that if you want to keep the sail in exactly the same position and trim there are other controls which you have to change a lot - and even so it is not likely one would be able to trim the sail in the same shape. Because if you would - then you would not need the traveller in the first place.
If you take your picture in post 233:
To keep the sail on the lest boat to have the same twist and trim you would need a lot of wang tension. and the main sheet tension would be a lot less then in the right boat to keep the boom at the same angle...
And because the sail is not rigid - we most likely can not get the same shape.
We are arguing about details, but I think we all agree that reducing the wang to leeward reduces the heel. So, let us go sailing.

[camaraderie]

I am no sail trim expert and I don't think that anyone is arguing that moving the traveler won't change the heel.......but from Giu's diagrams I think Rock & Tomaz are correct about the forces. Maybe Jeff_H could weigh in here.

[SEMIJim]

Regardless of why lowering the mainsheet traveler gets a boat off her ear, it does. Or can, anyway.

Just w/in our last two sails I've finally managed to start integrating my book learning (which incl. what I've read here) with actually sailing our boat. (This mainly consisted of getting to the point I could relax, look at what boat and sails were doing, remembering what I'd read, and trying it .)

Last Sunday, heading back, close-hauled all the way in 15 kts with our 150 hoisted and a full main, she was on her ear until I eased the mainsheet traveler to leeward a bit. This accomplished two things, as I understand it: 1. As Giu notes, it somewhat changes where the lifting force of the mainsheet is exerted, bringing it to the low side (I guess this is the point in contention). 2. The main is slightly de-powered. (I suspect this had the greater effect.)

It worked for us. Easing the genoa slightly stood her up a bit more. We maintained the same course, got the rail out of the water, reduced the weather helm back to almost nothing--all the while maintaining, if not improving, speed.

Jim

[Rockter]

SEMjim...

You are right on your second point, as this changes the sail trim and the interaction with the wind, and hence changes the heeling moment.

You are wrong on your first point, as the mainsheet tension is an action:reaction pair within the structure of the boat, and PER SE, changes absolutely nothing but the mainsheet tension. It does not, DOES NOT, change the heel angle of the boat. As long as it does not change the sail trim, its angle is immaterial to boat heel.

The sail trim change that results from that tension, and/or tension angle change will heel the boat.... as every man and the ships' cats will know on this website.... but the angle of the traveller per se, nor its tension per se, do not heel the boat.

Even if you welded the boom to the mast at the goosneck to maintain sail trim (or locked the boom by any method, however absurd) and then took the traveller away, the heel angle will still not change.

The wind cares nothing about how the boom is fixed... as long as it IS fixed. The wind notices only sail geometry and those pretty curves, and from that, decides a heeling moment. The ship fights it with a reactive moment as the ship heels, and they compromise on a heeling angle that balances the two moments.

The traveller is helping to hold the structure together as this happens, but it does not have to be a traveller that does it. Anything that fixes the boom position will do.... well, at least until you want to change sail trim, then you are probably best with a traveller. A welded goosneck will be quite an inconvenience then. I smile.

Rockter.

[Giulietta]

Tomaz, that analogy to von Münchhausen, is pretty un-applicable..and to be honest, I don't even like the guy..

In your example, all forces are applied within the same body (man+horse), in what we are discussing there is an external force applying...wind...

also, remeber the boom wants to be pulled upwards, as the wind hitting the sail wants to lif it up, not sideways or down...

In an already heeled boat that affects the force..I am not saying it will right the boat or be a sloution for heel. I simply said it helps reduce heel...

A mast and boom attach to the boat on 2 locations, not just one. The mast in the center, transfering lateral loads onto the boat, the boom tail trying to lift up by action of the wind...(at least in Portugal our booms want to go up with the wind), and therfore pulling on the traveller...pulling. that is the issue..it pulls.

[Rockter]

Guil...

Your third paragraph?... are you back to the argument that traveller angle per se can change the heel?

The traveller tension is certainly helping pulling the boom down, but the other end of the traveller is pulling the deck up. Net effect on the boat is zero.

You can fix the boom any way you wish.... you will never change the heel of the boat with that traveller, at any angle, at any tension, unless you change the sail trim.

Never.

Isaac Newton governs that one, not Lewmar.

If your argument is extended, you will be able to jack the boat into the sky by tensioning the mainsail halyard. In reality, all you will do is compress the mast, as the mast gives the compressive reaction to your halyard tension action, both within the structure, and both changing nothing but internal stresses. The forces within the ship are still balanced, and gravity, and Archimedes, simply ignore your halyard tension, whatever it be.

[Giulietta]

Rock,

please....Look, I really really don't care, honestely...you win..take the cup home..really...