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  #1  
Old 04-10-2010
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catamaran gust question

I was reading another thread on ASA certification, and it jogged a question I had that I still am not sure I understand. This cropped up in my own ASA marathon back in december in the BVI.

We were sailing a 42 ft. R&C catamaran in the Christmas Winds and decided to sail outside Jost van Dyke and to circumnavigate the island. I venture to say we were the only two student sailors out there that day, with sustained winds in the high 20's and gusts to over 32 a few times. We were sailing on the second reef, just us two noobies and our instructor ( we chartered the whole boat). I was at the helm, getting a real first hand feel for how a catamaran that size feels in solid 28 kts of wind and a following 8-10 ft. sea on the stbd. quarter. As we were heading out into it around the east end of Little JVD, my tendency was to head up into the gusts, as most of my sailing has been in monohulls in the past, and that's always what I did. Especially in my small 16 ft. AMF daysailor. BUT our ASA man told me that in a catamaran, you bear off in the gusts. As we came around headed more to the west and practiced white-knuckle jibes for the next few minutes...I meant to get a better explanation for why not head up into a gust on a multihull.....but my limited attention span was quickly overwhelmed and I forgot about it. And I just remembered, today, that I am not sure I understand this 100%. Since we are bound and determined to buy a catamaran of our own before the year is out, I thought I better ask.

Can someone explain why we steer downwind in a gust in a multihull, instead of heading up into the gust? I imagine it has something to do with the rigging, transferring load into hull speed instead of spilling it or heeling? I dunno. But I figure someone here will.
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Old 04-10-2010
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For two reasons you bear off in a multihull.

First any boat is typically longer than it is wider, so it is more difficult to sommersalt if forward stern-over-bow than to capsize it laterally.

Secondly when you bear off, you reduce the apparent wind, whereas when you head up, you increase the apparent wind

The same forces are true for a mono-hull, its just that there's little penalty for heading up and luffing, as the keel will resist the boat rolling over, whereas with a multihull, the price and can be extreme.
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Well, thanks, and that sounds a lot like the explanations I think I was getting, but I am still not 100% sure I understand it. Pointing any boat directly into the wind always seems to me like the best thing to do in a strong gust, whereas turning a cat more broadside to the gust seems counter intuitive...

(hey I had similar issues when I went from flying Cessnas to flying weight shift ultralights....that landing flare can be a booger when you forget to push the bar forward to flare instead of pulling the yoke back...as you are used to.)
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Old 04-10-2010
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Also, bearing off causes...

Quote:
Originally Posted by 2Gringos View Post
Well, thanks, and that sounds a lot like the explanations I think I was getting, but I am still not 100% sure I understand it. Pointing any boat directly into the wind always seems to me like the best thing to do in a strong gust, whereas turning a cat more broadside to the gust seems counter intuitive...

(hey I had similar issues when I went from flying Cessnas to flying weight shift ultralights....that landing flare can be a booger when you forget to push the bar forward to flare instead of pulling the yoke back...as you are used to.)
...

* the sails to stall, reducing drive
* the jib is blanketed by the main

However, in really strong gusts (micro-bursts) even on a large boat of any sort, that may not be enough. Then, the key is to get into the wind BEFORE the force becomes too great.

Your instructor was correct for the conditions. Thunderstorms are a different animal.

You can't really learn this on a large boat. Talk becomes theoretical. Go out on a Hobie cat in gusty weather - really, it is the only way to really understand when each method works.
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2Gringos—

The problem is that while pointing a boat directly into the wind sounds like a good idea... getting a boat to that point can be very dangerous on a multihull. Also, windage issues on a multihull, like high freeboard of the hulls, can make the boat not point into the wind well.

Also, in choppy conditions, many multihulls don't have the inertia or momentum to push through the chop and bearing off means they don't have to....
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well, dang. I can see I am going to have problems with this. Because until it makes sense to me, it won't make sense. And it doesn't yet.
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I know what the books say, but i've never pitchpoled by pointing up, and that is as violent as sailing gets. It seems to me when I am worrying about flipping over, the gusts are fairly unpredictable. Granted I'm a lake sailor, but the wind bombs can get pretty powerful. I never have to deal with ocean swells, but I'm with you gringo, I'm gonna keep pointing up.
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Yes, it is complicated.

Quote:
Originally Posted by sailingdog View Post
2Gringos—

The problem is that while pointing a boat directly into the wind sounds like a good idea... getting a boat to that point can be very dangerous on a multihull. Also, windage issues on a multihull, like high freeboard of the hulls, can make the boat not point into the wind well.

Also, in choppy conditions, many multihulls don't have the inertia or momentum to push through the chop and bearing off means they don't have to....

SD is right, of course, about getting straight into the wind or even pointing high. Some light cats - my Stiletto and any beach cat - can literally be blown over backwards by a strong blast, so you learn to fore reach with the traveler down during thunderstorm - actually, each take a different approach - so it is a matter of degree. Pointing high can even be unstable, as the boat tries to stop and fall back. Going into irons in rough weather is bad.

Which is why I suggest sailing a beach cat to learn. You will learn things in moderate and safe conditions that only effect larger cats in wild conditions. And it is a ton of fun. Either bum rides or get a used one and sell it after the summer.
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BTW, pointing up with the chute up is a disaster with any boat.

Quote:
Originally Posted by P8dawg View Post
I know what the books say, but i've never pitchpoled by pointing up, and that is as violent as sailing gets. It seems to me when I am worrying about flipping over, the gusts are fairly unpredictable. Granted I'm a lake sailor, but the wind bombs can get pretty powerful. I never have to deal with ocean swells, but I'm with you gringo, I'm gonna keep pointing up.
The boat powers up huge as you make the turn and you will be upside down. The same may go for big reachers. You may think you can come up and let them luff - it doesn't generally work out well - they may become so tangle in the rigging they won't come down.

If over powered seriously with a chute, bear off to dead down wind, get the chute down, and consider your need for further reductions.
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It may be that I seldom use anything but the Main and the jib. I know the boat powers up when you point, but it seems to me that it wants to jump right out from underneath me when I fall in a big gust. I feel much more in control of the situation pointing up and barely in control falling down. I have been in gusts that came in from the side and force you down. The impact on the bows is almost instantaneous. The next thing you know, there is an air bubble around your face because the trampoline is against your back, and you have already slammed face-first through a cartwheel.
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