Jib question

The lift from the keel has to equilibrate the side force from the sails, so you have to ask yourself what happens to that force component too. See my post #25.

 

Yes. Maybe I expressed it badly (again). More speed makes the keel produce the same lift with less leeway.. doesn't change the outcome.

 

No offence, but I find this thread kind of depressing. To me it suggest that so many of all the amateur and semi-pro boat designers on the forum fail to understand how the sailboat really works. There is no magic in how the sailboat works, and there is no way violating the drag angle rule, sometimes called the sailboat equation: If you want to point higher, you push the tiller away from you, and either the water or the air drag angle has to diminish, to obey the rule. Probably the boat will go slower, which will decrease the under water drag, and possibly the air drag will be smaller, too, at a smaller wind angle. The end result is the boat will point higher. If you want to sail lower, you pull the tiller towards you (assuming you sit on the windward side ;-), and the boat will go faster which will increase its drag. The sum of the drag angles will be bigger, and the boat will sail lower. You think you are in control, but in reality you are always bound by the sailboat equation...

If so many of the "pros" don't know how the sailboat works, then probably at least 95% of the sailors have no clue... they just sail happily along without knowing or worrying about leeway, drag or pointing angles.

 

I think you need to add VMG to that synopsis as you can always point higher but usually slower than optimum
If your boat can generate apparent wind upwind like a multi/foiler/skiff etc then it also changes that

 

That phrase shoots on a bit too wide target, Mikko.

About your pic - it shows the basis of sailboat's operation, but lacks the fundamental indicator for the whole discussion here, the Vmg (as has been pointed out several times in my and other's posts). The whole point here is - will the Vmg remain the same, will it diminish or increase after the proposed jib trim?

Cheers

 

Funny, no response.. It's easy to pretend besserwisser and point possible flaws in others, but say no own opinion...

 

Okey let's then give something of my thoughts.. To think about what Eric suggested and why it might work..
Biplane has significant opening between the planes. Closer together disturbs the flow and reduces lift. If they were closer the angle of attack should be bigger to produce the same lifting force.
Same translated to sailboat: jib tack midship means narrower gap between the luffs and so for reduced lift. Jib tack moved to lee opens it and boat can point higher..
BR Teddy

 

except the angle of attach of the sail will change unless you drop the clew the same amount, then the airflow on the back of the main will change...
what does all that mean?

 

I was in this regard using the angle of attack as the angle of the combination of the sails, not as their individual sheeting angles thou with closer luffs the main prevents you to sheet jib as much as single sail would and therefore th main has greater angle of attack than it has in a cat rig. It's just that every sail more reduces the angle how high you can point.

 

Had to make a picture.. hope it helps.. (didn't understand myself what I wrote above )

 

I did not comment as I had no clue of the post, until now...

Makes sense to me...exactly the jib (lower) pic I plan to use on my outrigger, I ever get a main hull (vaka).

 

While considering the jib in isolation your sketch seems true, however in "post 50" I raised the question of the mainsail angle.
Your sketch shows the same sheeting angle for the main in both cases which would appear unlikely.
Surely the main will need sheeting in more with inevitable reduction in forward drive and speed, offsetting any benefit to vmg gained by pointing higher?

 

I think not. In normal sailing conditions jib luff midship the main is allready sheeted in (cannot sheat it more) and then jib accordingly so that it doesn't interfere with main. This means the jib rules the pointing angle and the main has greater angle of attack and therefore greater drag.
In the latter case jib can be sheeted closer to same parallel as the main and so the boat can point higher, the angle of attack of the main is reduced and so is the drag.

Better draft..

 

I like +1.

 

You guys keep talking about sheet angles and pointing angles. May I repeat once again that it is not the angle to wind which counts here, but the vmg? The pointing angle is just one factor influencing the vmg, the others being the sail drive force, the keel/hull lift and drag, the heel etc. Where are all these factors in your considerations?