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Sail Trim Windward work

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leebitts
Navigator

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USA
122 Posts

Initially Posted - 07/29/2009 : 13:35:35

I had a frustrating race last night, did not seem to be able to get the boat to go to windward. Wind was 8 to 10 with gusts to 12 or so (estimated). Was using the 155, the car was on the inside track about the middle. Luffing was pretty good top to bottom in-line (using tell tales). We had the jib in pretty tight, a few inches off the spreader. The problem I think was that the main was getting backwinded ( it was luffing top to bottom in line though ). To correct, I brought the traveler more to windward. I remember that it was slightly to windward of the center which in that breeze did not seem right. In the gusts, I'd let the traveler out to keep the lee rail from going under. Any insight would be appreciated.

LeeBitts
1981 Capri 25 Hull # 142
Sailing in NH and Maine

Edited by - on

Steve Milby
Past Commodore

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USA
5909 Posts

Response Posted - 07/30/2009 : 15:11:14

Since nobody has responded yet, I'll start with a general comment.

Visualize the opening between the luff of the jib and the mast. As the boat moves forward, a large volume of air is moving through that big opening, and it is being funneled into the much narrower gap between the jib and the mainsail (called the "slot"). As the boat's speed increases, the volume of air that is moving through that slot also increases, and creates increased pressure. When the pressure on the backside of the mainsail is greater than the pressure on the windward side of the mainsail, the luff of the mainsail lifts. That's what's happening when a mainsail is being backwinded by a genoa.

The way to correct it is to increase the size of the slot between the mainsail and the leech of the genoa by easing the jibsheet, or to reduce the extent to which the jib overlaps the mainsail, or to flatten the mainsail. Any of those adjustments will improve the situation by reducing the amount of pressure that is backwinding the mainsail.

Edited by - on

joearcht
Navigator

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USA
243 Posts

Response Posted - 07/31/2009 : 05:35:02

Has anyone ever bought, seen or developed a polar diagram for the Capri? USSA sells them for $275.00. I'm not sure if they can do the Capri or if enough data is available for the boat to use a VPP, but I'm sure curious. The comments above make me wonder if this boat just needs to fall off a little during these wind conditions, a polar diagram should indicate this I think. Is anyone interested in pooling resources and pursueing development/purchase of a polar diagram for the Capri 25 class?

Edited by - on

HungryBear
Deckhand

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USA
3 Posts

Response Posted - 07/31/2009 : 09:13:40

When you say you had the sails "in pretty tight", so my first thought is that you had them flattened to the point that you lost power -- remember, they need to have some shape to work and trimming them flat is less power, not more. Also, you speak of working the traveler to keep the rail out of the water -- the Capri likes to be sailed flatter than that; while burying the rail is fun, it is not so much fast.

Too much heel, aside from being a slow way to move the boat through the water, is also as sign that the sails are over-trimmed and pushing you sideways more than pulling you forward -- also can be an indication that it's time for new sails. Older sails that have lost some of their shape will generate more heel and less forward drive than sails in good condition, with a stable draft locked in where it is supposed to be.

I would definitely try cracking off on the jib a touch though; letting the top twist open a touch to bleed of some of the pressure up high may also flatten the boat out a bit. Don't be afraid to rig down, either, especially working upwind. A properly trimmed smaller sail and flatter boat is usually faster upwind than an ill-trimmed larger sail on an over-heeled boat. Same thought holds for throwing a tuck in the main -- just remember that when you head down wind you're going to need to change up to more sail area.

Edited by - on

leebitts
Navigator

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USA
122 Posts

Response Posted - 08/02/2009 : 16:03:07

Thanks for the insight. The explanation of the slot was the most concise I've heard. I bought a few more books since this and did a little experimenting on Friday. I read somewhere that mast bend can flatten the main as it pulls the lower portion of the luff forward. The most efficient control that I found to get some bend was the vang. Being an old full keel cruiser that never had a vang before this boat, I thought they served the sole purpose of keeping the boom down when going downwind.

That being said, is it reasonable that I should have been headed off a bit more than I was? The rail was in the water once in a big gust, other than that reasonably flat (what ever that means).

Charlie

Edited by - on

Steve Milby
Past Commodore

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USA
5909 Posts

Response Posted - 08/03/2009 : 07:10:24

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by leebitts
 [I]s it reasonable that I should have been headed off a bit more than I was? The rail was in the water once in a big gust, other than that reasonably flat (what ever that means).

Charlie<hr height="1" noshade id="quote"></blockquote id="quote">
From your description, it sounds like you should have eased the jibsheet and steered off the wind 2-3 degrees. When racing, you should select and trim sails based on the ambient wind, and not based on the occasional short-lived puffs and lulls. In other words, select the sails that you're going to use and trim them so that the sails are driving with their maximum efficiency for the highest percentage of the time. During the short-lived puffs and lulls, you can make sail trim adjustments and adjustments to your course to reduce the bad effects of the boat being over or underpowered briefly. In between the puffs and lulls, you want the sails to be driving with all the power they can generate, and with the boat at it's optimum angle of heel.

It has been a long time since I sailed a Capri 25, but, as I recall, it likes it's 155 trimmed similarly to most masthead-rigged boats - about 6" from the spreader (give or take an inch either way, depending on the amount of chop and strength of the wind).

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 08/04/2009 : 13:08:28

Following on Steve's comments on trimming for the predominant wind, I find that I can react to puffs more quickly and effectively with the rudder than with sail trim.

On backwinding the main, when beating with that big genny and inboard sheeting, make sure your sheet cars are aft far enough that the sheet isn't pulling the leech inward, "cupping" the sail and obstructing the "slot". You want the air coming off the leech to be going virtually parallel to the aft half of the main.

Bending the mast, which flattens the midsection of the sail, is done by (1) having a properly tuned rig, and then (2) cranking down the backstay adjuster. When the backstay is eased, the forward lower shrouds should have a little more tension than the aft lowers. Tensioning the backstay pulls the top of the mast back while the forward lowers keep the midsection forward. The Capri sailors can describe the best tensions for initially tuning the rig.

Sailing too high while trimmed to tight can cost you in speed and cause leeway--your invisible enemy. Falling off a few degrees (as Steve suggested) and easing the sheets just a bit for optimal flow can substantially increase your speed, which in turn reduces leeway. Thus your "true course" might be the same as when you were pinching up, but you're going faster!

What compromise between course and speed is best to get to the mark fastest? Your GPS can help you learn that. First, it knows your true course (which isn't necessarily your compass heading), and second, it can tell you Velocity Made Good toward a waypoint--that is, how fast a straight line between you and the point is getting shorter as you sail on a given course. Sail too low and VMG drops. Sail too high and it might also drop. Maximize VMG and you you're making the best true progress toward the mark. The sweet spot is generally a little lower than the highest you can go--lower winds suggest a lower course, and higher winds let you sail higher.

Edited by - Dave Bristle on 08/04/2009 13:13:12

leebitts
Navigator

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USA
122 Posts

Response Posted - 08/17/2009 : 15:15:35

Thanks

I've been reading about putting the jib sheet more outbound. I guess on the capri 25 it would be on the rail on the toe rail. Anyone do that? I read it in a pretty generic sail trim book. I wonder if there is a way to use a tweaker to make that more easy to do?

Charlie

Edited by - on

abraxis
1st Mate

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USA
49 Posts

Response Posted - 08/19/2009 : 10:16:33

When running off the wind I keep a snatch block on the outboard tracks and "add" a lighter jib sheet thru it onto the jib clew for a better sail shape, while keeping primary sheets in place except for longer runs or in real light air. It's pretty easy to attach and remove lazy sheet with pressure off of it when working sheet is taut.

I'm in Maine for the warm seasons. in FLA for the winter where I sail my CAPRI 25 on Saratota Bay and The Gulf.

Edited by - on

leebitts
Navigator

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USA
122 Posts

Response Posted - 09/11/2009 : 04:09:04

I found a neat link with what looks to be pretty close to a polar diagram, here's the link
http://www.wyc.org/c25/SailingTips/TargetBoatSpeeds/tabid/510/Default.aspx

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