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Old 04-09-2017, 18:05   #31
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Re: Replacing genoa with Code Zero

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Originally Posted by Dockhead View Post
This physics behind it are simple -- drag!

I've also experienced exactly the same thing.
Drag is a component, but it's not all of it. As when a boat is overpowered, & or, heeling excessively, her bow gets depressed. With a subsequent lifting of her hind quarters, including the rudder. And this often causes enough poor flow over, or ventillation of the rudder. Causing it to lose it's grip on the water, & poof, round up. Especially if waves are also pushing on the ass end of the boat during this time frame.

The shift in LCB, & CLR caused by too much jib also plays a role, but thinking hard enough to put that explanation into text right now would give me a headache. Not gonna' happen.
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Old 04-09-2017, 20:15   #32
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Re: Replacing genoa with Code Zero

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This is really interesting... I have heard of this but I can't think of a reason for it... perhaps someone better versed in the physics can help me understand it... What kind of boat was this?
It is, and dockhead maybe right, it may not be coe thing, and this maybe why I have trouble explaining why, BUT all I know is its real.
My last boat, a freedom had a large beautifully shaped main and a battened camberspar self tacking jib, never had this issue, both sails had a perfect shape, just didnt want to round up under any condition.
Now to be fair to the Genoa, I had 6 days of light NW winds, I was able to sail 5knots in approximately 7knots of true wind at 30° apparent, I couldn't do that on my last boat.
Always fors and againsts.
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Old 04-09-2017, 20:22   #33
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Re: Replacing genoa with Code Zero

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7,200 miles across the Indian Ocean(?) in a Catalina?

Gee, Dale, don't you know Catalinas are not blue water boats?
Apparently!! I've come across some boat snobbery already..lol. All I know is I sailed faster than most, had less problems than most and lived in more comfort than most.
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Old 04-09-2017, 20:25   #34
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Re: Replacing genoa with Code Zero

And flat water! Wave action played a big part in the rounding up.
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Old 04-09-2017, 20:29   #35
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Re: Replacing genoa with Code Zero

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Drag is a component, but it's not all of it. As when a boat is overpowered, & or, heeling excessively, her bow gets depressed. With a subsequent lifting of her hind quarters, including the rudder. And this often causes enough poor flow over, or ventillation of the rudder. Causing it to lose it's grip on the water, & poof, round up. Especially if waves are also pushing on the ass end of the boat during this time frame.

The shift in LCB, & CLR caused by too much jib also plays a role, but thinking hard enough to put that explanation into text right now would give me a headache. Not gonna' happen.
Ok, now we are getting somewhere, to me its more a hull thing, over powering the bow,bow getting depressed this is what I'm feeling, seeing but not explaining it well, the lifting of the hind quarters as you put it is also accentuated by the wave action as it passes under the boat.
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Old 05-09-2017, 01:37   #36
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Re: Replacing genoa with Code Zero

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Originally Posted by UNCIVILIZED View Post
Drag is a component, but it's not all of it. As when a boat is overpowered, & or, heeling excessively, her bow gets depressed. With a subsequent lifting of her hind quarters, including the rudder. And this often causes enough poor flow over, or ventillation of the rudder. Causing it to lose it's grip on the water, & poof, round up. Especially if waves are also pushing on the ass end of the boat during this time frame.

The shift in LCB, & CLR caused by too much jib also plays a role, but thinking hard enough to put that explanation into text right now would give me a headache. Not gonna' happen.
Yes, yes, of course, you are right, and this is a much more detailed explanation. I was grossly oversimplifying it. But it all starts with drag. Drag converts wind force to heeling, which causes weather helm hydrodynamically, and it slows you down, making the keel and rudder less powerful. If it goes so far as to ventilate the rudder as you describe, then you're really screwed. But drag is the enemy -- trim to reduce it as much as possible, even at the expense of power, when you start to get overpowered and when weather helm rears its ugly head. Feathering the main a bit helps enormously on a reach; and I will often take down the jib entirely (or the mainsail), rather than reefing a roller furling headsail. A reefed roller furling headsail, especially a big genoa, especially especially a big old baggy genoa, doesn't do anything useful once you have to reef it.





Wait a minute -- "hind quarters"? Are we talking about boats or horses? Never heard that term used in reference to a boat.
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Old 22-09-2017, 12:58   #37
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Re: Replacing genoa with Code Zero

My understanding of why a Genoa can cause a boat to try to turn to windward has to due to asymmetric water lines when heeled. This is obvious with a broad transom but can be an issue with other designs. In other words as the boat heels the profile it presents to the flow of water forces the bow to windward. And of course the rudder is less efficient which aggravates the issue. Boats with symmetric water lines are not as liable to show helm changes when heeled. The solution is to sail the boat flat by reefing the main which seems counterintuitive but in my experience can greatly help.

P. S. I am not an N. A. so you can have at me! :-)
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Old 23-09-2017, 03:35   #38
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Re: Replacing genoa with Code Zero

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Originally Posted by sailor_ed View Post
My understanding of why a Genoa can cause a boat to try to turn to windward has to due to asymmetric water lines when heeled. This is obvious with a broad transom but can be an issue with other designs. In other words as the boat heels the profile it presents to the flow of water forces the bow to windward. And of course the rudder is less efficient which aggravates the issue. Boats with symmetric water lines are not as liable to show helm changes when heeled. The solution is to sail the boat flat by reefing the main which seems counterintuitive but in my experience can greatly help.

P. S. I am not an N. A. so you can have at me! :-)
I'm also not an NA, but I believe what you wrote is exactly correct, and I think you explained it very well.

On my boat, weather helm is a practically linear function of heel angle. Reef any sail to reduce it. Even take away the headsail altogether. My boat sails fine on mainsail alone, although she doesn't point quite as high.
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Old 23-09-2017, 05:16   #39
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Re: Replacing genoa with Code Zero

It does not seem to be the waterline asymmetry so much as it is the SA center being outside of the footprint. The boat is being pivoted.

If you build an asymmetric hull model and sail it with genoa only it may actually get lee helm as long as it stays vertical.

The boat heels, the SA center moves outboard, the forces pivot the boat.

Look at windsurfers going very fast. You will see they are so very aft of their hull center, should get heaps of weather helm ... until you notice they are also so much hiked out towards the windward. The same rule, just an opposite case.

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Old 24-09-2017, 09:12   #40
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Re: Replacing genoa with Code Zero

Barnakiel: I will not argue your SA suggestion but how would you explain my observation that a boat with symmetric water lines is not so liable to change helm as it heels?
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Old 24-09-2017, 10:14   #41
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Re: Replacing genoa with Code Zero

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Originally Posted by sailor_ed View Post
My understanding of why a Genoa can cause a boat to try to turn to windward has to due to asymmetric water lines when heeled. This is obvious with a broad transom but can be an issue with other designs. In other words as the boat heels the profile it presents to the flow of water forces the bow to windward. And of course the rudder is less efficient which aggravates the issue. Boats with symmetric water lines are not as liable to show helm changes when heeled. The solution is to sail the boat flat by reefing the main which seems counterintuitive but in my experience can greatly help.

P. S. I am not an N. A. so you can have at me! :-)
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Old 24-09-2017, 11:07   #42
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Re: Replacing genoa with Code Zero

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Barnakiel: I will not argue your SA suggestion but how would you explain my observation that a boat with symmetric water lines is not so liable to change helm as it heels?
I think we are discussing the same thing only looking at different contributing factors. These factors may fight each other in some cases too (my guess).

My gut feeling is that these factors (asymmetry of heeled hull / relative movement of SAC / DC) may either work together or, possibly, with some hull styles/shapes work against each other.

In practical terms, it is easy to tell what the asymmetry of heeled hull does - build a model, heel it, make a pull test, observe how it turns.

One must also allow for the fact that many hull styles, as they heel (to the side) they will also tip (most of them, monohulls, forward), so the result of the asymmetry of the heeled hull is likely a complex (compound) thing too. One must observe that most monohulls in result of this forward tipping will have their keel foil working at an angle to the center line, thus aggravating the weather helm challenge.

To wrap it up, it is a complex (compound) thing and building a model was until recently the only way to find what a heeled hull will do. (See the Hiscocks' adventure building their hull in NZ).

I agree that very symmetric canoe body contributes to less helm as she heels. Our double ended hull shows nil excessive weather helm heeled (with sails trimmed) - my 100 pound partner has zero problem hand steering our boat for hours in any conditions (tiller steering). Well, done Mr. Norlin! Thanks!

The same lack of weather helm in symmetric canoe is clearly visible in e.g. yole ronde.

Cheers,
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Old 24-09-2017, 13:30   #43
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Re: Replacing genoa with Code Zero

"awful shape of a reefed roller furling "
Ergh. Whatever happened to the distinction between roller reefing, and roller furling?
Rigs designed for the former are adjusted in size. Rigs designed for the latter are simply rolled or unrolled to their full size, or full storage.
The sails are supposedly cut differently, and not at all the same.
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Old 24-09-2017, 13:45   #44
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Re: Replacing genoa with Code Zero

I guess it has much to do with the boat you sail and the places you sail. I have a 135% genoa and a 110% genoa. If I sail on places where 20K winds are the norm than I use the 110% if I sail on places where the wind is average 15K or less I sail with the big genoa.

Two sails permanently mounted on the boat diminish the sail performance, increase windage and diminish stability. With 3 is even worse. It is all a compromise. To you to chose the right one for your boat and the places (wind) where you will sail.

As my wife really hates strong winds I sailed this year with the 140% genoa. The 110% genoa is only better upwind with over 17k wind and much better over 20k and the sail to have with 30k or over.

With the big genoa I sail upwind faster than the wind till 5k of wind , wind speed with 6k and upwind is by far the most common sail position since with the boat making wind it will transforms a beam reach on upwind sailing.

I really don't have the need of a code 0 that I would have to take out probably with 9 or 10k of real wind. Only for racing, but that is on my boat. Each boat will be a different case.
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Old 24-09-2017, 13:55   #45
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Re: Replacing genoa with Code Zero

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Originally Posted by sailor_ed View Post
My understanding of why a Genoa can cause a boat to try to turn to windward has to due to asymmetric water lines when heeled. This is obvious with a broad transom but can be an issue with other designs. In other words as the boat heels the profile it presents to the flow of water forces the bow to windward. And of course the rudder is less efficient which aggravates the issue. Boats with symmetric water lines are not as liable to show helm changes when heeled. The solution is to sail the boat flat by reefing the main which seems counterintuitive but in my experience can greatly help.

P. S. I am not an N. A. so you can have at me! :-)
It depends on the boat. With winds over 15k and if I don't want to have a sportive and faster sail my boat can sail very well with only the genoa (135%), upwind or downwind.

I certainly prefer to have fun with more sail but sometimes my wife only let me go out (with strong winds) if I promise to use only the genoa so I have some comparative information that I have shared on my facebook page and my blog: with only the genoa my boat performance is about the same as a modern mass production cruiser of the same size (Jeanneau, Beneteau) with both sails and way better than the one of an older design with full sails.
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