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Sail trim question

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dblitz
Navigator

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240 Posts

Initially Posted - 06/18/2006 : 10:13:54

Yesterday was the first opportunity we had to sail our "new" boat.
Everything went well during this first trial of the sails. One question that comes up, though, is that both leeches vibrate when the boat is close hauled, enough to be felt "through" the boat.
Tried adjusting genoa cars on jib with no success.
Only thing we didn't try was to change the tension on the split backstay.
Thanks for your ideas.

Daniel 86 "Solar Wind" #5339 C-25 FK/SR I/B Diesel

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/18/2006 : 10:32:22

You should have leech strings in both sails, I have not seen a sail sans one in a long time. Pull the string just until the flutter stops, no harder. Leeches that will not Harden with the leech string without creating a huge cupped effect are one of the tell tale signs of "new sail" time. It means your sail is really stretched out. This will seem a non-sequiter but it is not; I always harden and pinch in very high wind, most people sheet out and luff a little to depower in high wind. My sail does not flog, theirs do, flogging stretches and wears a sail more than anything because it causes the fabric to physically break down. If your leeches are that stretched out I would bet your luffs are as well. Stretched out sails cannot be controlled and depowered which makes them dangerous in high wind. I believe in the name of the safety of your family and the peace of mind of all those who love you you must order a new suit of sails. Enjoy!

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/18/2006 : 14:40:52

"Only thing we didn't try was to change the tension on the split backstay"

Won't do much for the leech flutter. Frank's advice is on the money.

Tightening the backstay puts an aftward bend in the mast and has two effects:

1)Tightens the forestay which depowers the jib a bit and also gives you better pointing ability.

2)De-powers the main.

Both the above help you in higher winds, especially when beating to windward. Light airs and downwind, you will often want to loosen the backstay to let the sails to generate more power.

To encourage the ability of the mast to bend a bit, your aft lowers should be setup a little looser than your forward lowers. (This lets the center section of the mast bow forward).

Have you 'tuned' your rig yet? Tuning = Adjusting for optimum performance under your prevailing conditions.

Edited by - on

Dave Bristle
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Djibouti
10005 Posts

Response Posted - 06/18/2006 : 16:34:11

These guys are good! Two silly questions: (1) Do you have your battens in the main? (2) When you tried adjusting your genoa cars, did you try moving them further forward, where they will tighten the leech and let the foot become fuller?

Sorry--I don't mean to demean your intelligence...

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/19/2006 : 22:30:15

We're on a lake that is almost always very windy. 15 Knots and better.
Should my mast be raked back? (and if so, would I use the aft lower shrouds)
A Beneteau 23.5 moored beside me has his raked back.

Edited by - stampeder on 06/19/2006 22:31:09

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/19/2006 : 23:25:06

who-boy,
Mast rake and pre-bend are two separate things. Rake will affect weather/lee helm. Pre-bend causes the sail to be raised with the pocket already pulled somewhat flat and therefore the mainsail depowered. Boats tend to have more weather helm in high wind and adding to that with aft rake would simply make the helm very heavy and the boat prone to rounding up. I sail in high wind a lot and my mast is actually raked forward to keep my helm more balanced. Masthead boats do not have a great deal of "bending" ability, no where near what a fractional rig can do. If I were tuning pre-bend into the mast then the lower shrouds would come into play. Harden the forwards to pull the midsection of the mast forward, after the prebend is there then tighten the aft lowers to your taste. If you have a split backstay then you will want the aft lowers a little loose so the backstay can bend the mast even more. If you have no split backstay then you might as well harden the aft lowers just until they start to mess with the prebend set by the forward lowers. You can also set the the prebend with the hardened fore and aft lowers on a boat with a split backstay and simply use the backstay to harden the forestay, seems like a loss of a tuning choice though.

Edited by - on

ClamBeach
Master Marine Consultant

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3072 Posts

Response Posted - 06/19/2006 : 23:35:43

Most C25's I've seen don't run a lot of rake aft... maybe an inch or two at the very most. Mine is set just aft of 'neutral'.

Other boat designs like lots of rake. The San Juan in the next slip likes a lot... my old Venture 23 liked a lot of rake too.

To rake (or un-rake) the mast, you must adjust all the shrouds... as you want everything to lean 'as one'. Simply cranking tension in the aft lowers may result in the dreaded 'inverted bend' (center of mast slightly bowed aft). [This is bad.]

While you are doing all this adjusting, it's important to periodically lay with your head at the foot of the mast and sight straight up the stick.

To start with everything should be nice and straight with the backstay untensioned.

Especially make sure there are no side-to-side curves or bends in the mast. If the mast is bent side to side... you've got tension out of balance in that plane and you must eliminate it by adjusting the stays.

Now loosen the aft lowers to let just a hint of forward bend appear in the mast with the backstay slack. (a wee bit here)

Now tighten the backstay all the way. The center section of the mast should now bow forward perceptibly... several inches at the very middle. (this is why the aft lowers are set up looser than the forwards).

Sheesh, time for bed. We should all get together and do a 'Wiki' on setting up a C25... post it in the tech section.

Edited by - ClamBeach on 06/19/2006 23:51:28

takokichi
Captain

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USA
321 Posts

Response Posted - 06/20/2006 : 06:48:49

I ran a lot of rake on tako kichi. As much as 5 inches at times. I found the boat to be very fast set up with significant rake and moderate pre-bend. It did have the effect of increased weatherhelm so I had to be quick on the mainsheet at times. But with the travler up and locked, vang on, and sheet constantly in play we went to weather like the engine was running. YMMV

Edited by - on

stampeder
Master Marine Consultant

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1608 Posts

Response Posted - 06/20/2006 : 12:29:59

I currently have the mast straight. I sight the mast and check the shrouds everytime I sail.
This lake is so windy that I'm usually sailing on the very edge of my sailing ability...so I want to make sure I'm optimizing my setup when I set out.
I have a split backstay, that gives me about 5 or 6" of rake when fully engaged (though I could probably tweak it to give me more)

Last Saturday we raced for the first time and the Admiral got comfortable with heeling - we had the rail in the water several times. We advanced along the learning curve significantly. Working jib was flat as a blade with cars moved aft, full main sail with traveler positioned to spill some air, outhaul,cunningham and boom vang working to flatten main. Because of the high winds most of the sailboats dropped their sails and quit. We hung in there with a Precision 23 and sailed at max hull speed. The Precision skipper is more skilled than I and he continually beat me maneuvering, but in the straighaways I could catch up and pass him.
So, if I understand correctly...I should leave the dock with the aft lowers slightly looser than forwards, and use the backstay to depower the jib and the main.
We race again tonight, and the wind is about 15 knots currently, I expect it will be windier on the lake.
Any advice is much appreciated.

Edited by - on

Frank Hopper
Past Commodore

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Pitcairn Island
6776 Posts

Response Posted - 06/20/2006 : 15:06:44

You have confused rake and mast bend. (In rake the entire mast leans back or forward.) When you pull on the backstay adjuster you are bending the mast, not raking it. Some of the mast goes forward, (the middle) and some comes back, (the top). That is the most powerful sail flattening device you have and it consequently hardens the forestay which reduces forestay sag which provides a straighter, flatter, cleaner entry into the wind for the headsail. You mentioned that the the traveler was positioned to spill some air; was it down or up? If you get your main seriously flat then down is great for a while, especially with a 110 which will not backwind the main much. If the wind is still too much and you are rounding up then soften the boomvang, let the boom rise a little, pull the traveller all the way to windward and the top of the sail will twist off and dump the air in the top of the sail; that will reduce heeling a lot. The amount that you soften the boom vang will control the amount of twist off at the top. You say you moved your cars back to flatten the sail, good; if you move them way back the foot will be tight and the top of the sail will twist off and dump heeling moment just like the main. I rarely do that, I usually have the cars where the headsail leach is not fluttering so the air is not disturbed when it reaches the main. Remember that forward speed is the best defense against broaching! It is better to be going fast a couple degrees off than be going slow but higher. The phrase is FASTER AND HIGHER, slower and higher in high wind is trouble.

Edited by - on

Lightnup
Master Marine Consultant

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USA
1016 Posts

Response Posted - 06/20/2006 : 17:59:23

Originally posted by fhopper@mac.com
A whole bunch of good sailing advice.

I rest my case.

Steve

Edited by - on

oldsalt
Admiral

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USA
578 Posts

Response Posted - 06/20/2006 : 18:39:51

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by takokichi
 I ran a lot of rake on tako kichi. As much as 5 inches at times. I found the boat to be very fast set up with significant rake and moderate pre-bend. It did have the effect of increased weatherhelm so I had to be quick on the mainsheet at times. But with the travler up and locked, vang on, and sheet constantly in play we went to weather like the engine was running. YMMV
<hr height="1" noshade id="quote"></blockquote id="quote">

Same here, and a new balanced rudder helped a lot.

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