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Old 28-10-2013, 13:53   #1
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Proper sail trim vs. points of sail for a cat?

The standard diagrams clearly don't apply quite as well to catamarans, points of sail, and main + jib angle. Specifically, cats cannot extend their booms out much more than 45 degrees (eg., beam reach).

So on a broad reach or run, we're stuck with that. We can't hang the main out 60, 90 degrees etc...

I've always just figured it out on my own but I see there really isn't much documentation about this subject (specifically for cats). The basic gist I've gathered is that you *can* let out your main and let the sail curl. The center of "the curl" will be a bit farther up the sail and it (the curl) will be closer to an angle exceeding 45 degrees.

But ... it would still be nice to see some diagrams made specially for catamarans, no?

I'm talking cruising cats here, 40+ and whatnot.
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Old 28-10-2013, 14:02   #2
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Re: Proper sail trim vs. points of sail for a cat?

Why can't the boom go further than 45 degrees?

Wouldn't you be better off putting the main away and using a spinnaker on a run, after all you don't need the faff around with a pole on a cat, or have I got that wrong?

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Old 28-10-2013, 14:04   #3
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Re: Proper sail trim vs. points of sail for a cat?

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Originally Posted by Pete7 View Post
Why can't the boom go further than 45 degrees?

Wouldn't you be better off putting the main away and using a spinnaker on a run, after all you don't need the faff around with a pole on a cat, or have I got that wrong?

Pete
Well, 45 may not be completely accurate. But at some point around there, your main sail battens hit the left or right rear mast stay.

Sure, sometimes you'll ditch the main and use a screecher or whatever. But I'm talking about those times when you don't want to ditch your main.
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Old 28-10-2013, 14:21   #4
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Re: Proper sail trim vs. points of sail for a cat?

Well, you ease your boom as far as you can. Not sure what you're looking for here.
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Old 28-10-2013, 14:28   #5
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Re: Proper sail trim vs. points of sail for a cat?

Back in the hey days of Hobie cats, we always used to tack downwind on reaches rather than run straight downwind because it was way faster. Not sure if this is at all relevant to a cruising cat as I have never sailed on one, so if I am displaying my ignorance here, just ignore me.

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Old 28-10-2013, 14:35   #6
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Re: Proper sail trim vs. points of sail for a cat?

Not many cruising cats benefit from tacking downwind. The extra speed usually won't make up for the extra distance. It can be far more enjoyable though.
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Old 28-10-2013, 14:37   #7
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Re: Proper sail trim vs. points of sail for a cat?

Plenty of monohulls have aft tending lowers that limit the boom going out a bit as well. In fact there really aren't that many boats that can wing a main out 90 degrees.
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Old 28-10-2013, 14:42   #8
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Re: Proper sail trim vs. points of sail for a cat?

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Plenty of monohulls have aft tending lowers that limit the boom going out a bit as well. In fact there really aren't that many boats that can wing a main out 90 degrees.
Cat rigged ones can.

Surprising this rig is so unpopular with people sailing the coconut milk run.

b.
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Old 28-10-2013, 14:57   #9
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Cat rigged ones can. Surprising this rig is so unpopular with people sailing the coconut milk run. b.
Exactly.
My cat rigged, biplane sails can be let out well beyond 90. Dead downwind, very little risk of accidental Gybe, huge view, VERY COMFORTABLE.
Fastest point of sail? Definitely not.
Coolest, easiest, best view point of sail? Abso-fricken-lutely!
Clearly not many boats are rigged like mine, but I sure as hell don't know why...?
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Old 28-10-2013, 15:02   #10
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Re: Proper sail trim vs. points of sail for a cat?

On the (racing) cat that I crewed on for a few races, the thing went so fast that the apparent breeze was pretty much never aft of the beam, so the mainsail never really needed to go more than 45 degrees off centre
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Old 28-10-2013, 15:16   #11
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Re: Proper sail trim vs. points of sail for a cat?

It is not so easy to answer a general question like this. As others have posted some boats, even monohulls, benefit from tacking/gybing downwind. It is also common for the apparent wind to move forward enough that you need to sheet in. I have a Seawind with a screecher and working jib and under some conditions go wing on wing. My experience has been this is more of an issue with light winds.

But I have also sailed with friends who have what I will call condomarans and in light winds they sometimes use the iron genoa going down wind.

Bottom line your question is too general for a general answer.
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Old 29-10-2013, 00:53   #12
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Re: Proper sail trim vs. points of sail for a cat?

General questions are hard to answer but generally speaking, with the right amount of sail area relative to displacement and wind speed/wave conditions you are going to be faster sailing off the wind than directly downwind, which is why it is usually preferable to use asymmetrical spinnakers rather than symmetrical spinnakers on a multihull assuming adequate sail area relative to displacement (likewise for a fast monohull). With that said, if speed is not the goal there is nothing wrong with a symmetrical spnnaker or having your main and jib out and sailing almost dead down wind (with preventer to avoid accidental gybe..)
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Old 29-10-2013, 01:15   #13
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Re: Proper sail trim vs. points of sail for a cat?

Sail trim no matter what the point of sail is to get the tell tales streaming -- if possible. So you reach a point where as you bear off far enough the sail stalls because you can't let it out anymore, and you've done as much as you can.

Of more interest would be finding or making a polar diagram for your boat for several different windspeeds.

In the link bring a horizontal line up tangent to the line on the diagram, and this shows you the best VMG for going downwind So for this boat in 20 (whatever windspeed units) of wind sailing at about 150 degrees is going to provide the shortest amount of time to your downwind destination.

http://www.caribbeanmultihulls.co.uk.../lrg/polar.jpg
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Old 29-10-2013, 05:56   #14
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Re: Proper sail trim vs. points of sail for a cat?

some good info here might answer your question
Twixter -* Sail Trim & Reefing
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Old 29-10-2013, 06:53   #15
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Re: Proper sail trim vs. points of sail for a cat?

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some good info here might answer your question
Twixter -* Sail Trim & Reefing

I wouldn't use that page. Main traveler 1/3 to weather for a beam reach is just one of several odd ideas about sail trim.
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