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Go Back   SailNet Community > Skills and Seamanship > Learning to Sail
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  #21  
Old 10-12-2007
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Quote:
Originally Posted by Jeff_H View Post
Lastly, really disagree with the idea that "if your sails are basically trimmed correctly, and you are making the kind of fine adjustments that a skilled racer would use, those fine adjustments can't be measured by your knotmeter".
Provably false. I've seen it with my own eyes.

On our 1st race the half of the crew that knew something of racing and sail trim were unfamiliar with the boat and the sails, while in over-all decent condition, were blown. The other half of the crew (The Admiral and I) hadn't enough experience in sail trim/tuning to get the most out of her.

Here we are on the last leg of the course. A beat. I'm sitting on the windward side of the pushpit rail, looking at the sails and feeling the boat. All-of-a-sudden I just grab the end of the boom and pull it to windward a couple inches. Knotmeter almost immediately jumps by a half knot or so. (Note to self: Warn helmsman when you're going to do something like that, next time .) Then reminded myself the genoa, whose leech was flapping like mad, had a leech line. Went up and trimmed that. Added another one or two tenths of a knot. Then realized the mains outhaul was still fairly loose from a previous reach. Gave that a light tug. Added another tenth of a knot or two. All told: Those three tweaks added nearly 3/4 of a knot to our speed and allowed the helmsman to point her marginally higher.

(N.B.: If the sails weren't blown, depending on wind conditions, etc., different adjustments would've been appropriate. I was compensating for deficiencies in the sails.)

Jim
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  #22  
Old 10-12-2007
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Are you SURE that your sail is blown; or are you just having difficulty getting it sheeted down tight (not enough purchase) for close-hauled pointing? When you trim the main in it pulls both laterally and vertically. The vertical pull is what gets the sail flat but it takes a huge amount of force to crank it down. If you can't trim it in while going up wind you will need to luff the sails and then sheet it in or sheet it down tight while tacking. The boom should be parallel to the centerline of the boat if possible; of course the draft of the sail would be controlled by use of both the mainsheet and traveler.

If our main is not trimmed properly, there is too much lee helm and our pointing ability is bad (at windspeeds ~15kts and above). Once the main is properly trimmed we make hull speed with a much more balanced helm, but the boat will heel to about 25-30 deg. Sails are both relatively new.
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  #23  
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Quote:
Originally Posted by KeelHaulin View Post
Are you SURE that your sail is blown;
They're 31-year-old Dacron sails. Yeah, I'm pretty sure they're blown .

Quote:
Originally Posted by KeelHaulin View Post
or are you just having difficulty getting it sheeted down tight (not enough purchase) for close-hauled pointing?
In anything above about 12 kts or so that can be a problem on our boat. (This you know from the other thread, and will be solved with the new blocks.) But the wind wasn't all that strong that day. Maybe somewhere in the vicinity of 10 kts. Yes, the main wasn't sheeted-in hard enough, or the traveler not far enough to windward, for the tack. Thus the biggest difference made when I brought the boom over by hand. It actually ended-up just slightly higher than the centerline of the boat for best speed, btw. Then again: Our standing rigging was quite badly out-of-tune at the time, too. I'm sure that had something to do with it.

My point wasn't so much the boom angle change. That was a gross error. My point was more the two "little" changes I made (the leach of the genny and the mild tensioning of the mainsails foot) each resulting in a fairly significant change in boat speed--easily seen on the knotmeter.

If we weren't racing, I would've eased the genoa's leach and messed with its traveler and sheet to see if I couldn't duplicate the improvement there, instead. I suspect, however, that trimming that leach line probably resulted in closing the leach and powering the genny up a bit more efficiently than I could've achieved by other means.

Jim
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  #24  
Old 10-14-2007
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As has been mentioned it is important to know your boat, as every boat performs differently. My favorite activity is playing with crazy sail trim ideas and the knotmeter. That is how I found my boat likes the main with a bit of backwind above 10 knots. It freaks one of my friends out, who trims totally on sail shape. Despite having lost the bet before, he still insists it's trimmed wrong, and then loses the bet once again. lol. the backwind looks like someone is standing at the mast gently punching the luff. It drives him crazy, but after 10 knots it makes at least a .2 knot difference.

Know _your_ boat. Experiment every time you are out.

btw Jim, when I bought my boat the mast had a bend to port, that really screwed up the sailing characteristics. I had to replace the standing rigging right anyway so I didn't worry about rig tune then, but man oh man, the difference after the rigger got done with it. It was like a totally different boat, amazing what difference rig tune makes.

(rigger = Chris Tutmark, highly recommend him. He is well loved by the J24 racers here in Seattle, so he knows my size boat well)
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Last edited by tenuki; 10-14-2007 at 12:09 AM.
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  #25  
Old 10-16-2007
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Originally Posted by tenuki View Post
My favorite activity is playing with crazy sail trim ideas and the knotmeter. That is how I found my boat likes the main with a bit of backwind above 10 knots. It freaks one of my friends out, who trims totally on sail shape. Despite having lost the bet before, he still insists it's trimmed wrong, and then loses the bet once again. lol. the backwind looks like someone is standing at the mast gently punching the luff. It drives him crazy, but after 10 knots it makes at least a .2 knot difference.
It's possible that when the main stalls a bit due to pinching in the slot your weather helm reduces and the boat "finds" it's proper trim. It could be that your jib is sheeted too tight; or that your sailplan is unbalanced (too much power from the mainsail). Another consideration is that there may too much curvature in the main (either not enough halyard/outhaul or it's blown out). I think the issue is more of "sail balance" rather than whether there should be a reverse bubble at the luff. We've had that issue; now when we are properly sheeted the main is perfectly curved and the jib is sheeted in just enough to keep the slot from constricting. If the trim is correct the weather helm is minimal and the speed easily improves over 1kt. 0.2 knots is not enough to tell you if you are optimally trimmed; you should try getting the bubble out of the luff then try and trim the sails until there is minimal weather or lee helm.
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  #26  
Old 10-16-2007
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Originally Posted by KeelHaulin View Post
you should try getting the bubble out of the luff then try and trim the sails until there is minimal weather or lee helm.
Just not true, search the web and you will find plenty of _race_ tuning guilds that speak of getting a touch of backwind in the main. Here are a few. My point continues to be that every boat is different, and backwind isn't necessarily bad.


J29 class website trim tips.

Moore 24 class tuning guide
SF Sailing racing trim guide
North Sail's Main/Genoa interaction guide

If you still don't believe me (after all what the heck do J29, Moore 24, SF, and North Sails people know about sailing...) I invite you to come sailing with me. Bring your 20 bucks, you're gonna lose that bet.
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Last edited by tenuki; 10-16-2007 at 01:40 PM.
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  #27  
Old 10-16-2007
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This one, a North Sails - Sheilds class trim guide even has a picture of a backwinded main and states 'no bubble? more jib sheet!'.
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  #28  
Old 10-16-2007
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This got me to thinking why these 'wrong' things bother some people so much. Tell tales being trimmed deliberately to break half the time, deliberate backwinding, etc. I think they have this idea of a particular 'shape' being 'right' and aren't listening to the boat with their other senses and thinking about why. The 'visual/shape' school of sail trim is wrong in so many cases. Read through any of the North Sail's one design class trim hints and they are rife with 'strange' settings. Look at this one... North Sails J24 guide It has things like the following..

"so in light air we slide the draft back by sailing with 1/2-inch scallops between each luff hank. These wrinkles look pretty ugly, but they allow the draft to move aft to 44 percent, the proper position for light air. As the breeze builds, halyard tension should be slowly tightened until the wrinkles disappear in 12 knots true and up (usually when whitecaps just appear on the water). "

That would drive some people crazy, but it's faster...

or

"In up to 13 knots, the top batten points as much as seven degrees to windward of parallel with the boom, and the telltale on the top batten is stalled as much as 50 percent of the time- but the boat doesn't seem to slow down: it just points higher!"

again, some of the people I know would have apocalyptic fits.

I think this summarized it nicely.

"The Key to successful J/24 racing is not the memorization of this information, but the understanding of it. Why is mast rake so important? Why does a particular deck layout work, and will it work for your crew? Why do we sail with wrinkles in the luff of the Genoa in light air? You can only go so far by copying others without understanding why the technique is fast."

I'm as inexperienced and clueless as the next guy, but I can tell you this with assurance, the knotmeter is the final arbiter (+ pointing angle and the tiller). and only two things will get you fast, 1) trying to understanding why instead of following 'rules' or 'visual ideals', and 2) experimentation, sometimes crazy experimentation to find _your_ boat's particular sweet spots.

Sorry about the multiple posts, I just have this argument with a friend of mine all the time and I'm taking my frustration out on you guys. lol.
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Last edited by tenuki; 10-16-2007 at 03:52 PM.
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  #29  
Old 10-16-2007
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one last post on this topic. lol.

I was racing as railmeat with blt2ski last weekend in FWB and when we started beating on the last leg I couldn't believe how far he had the mainsheet traveler moved to windward in high winds. what?!?! was he crazy? But I didn't know his boat so I kept my mouth shut, but it bothered me. Until.... we gained all our way on the competition in that leg ( we had lost a fair bit on the first let, a downwind run struggling with an unfamiliar asym ) (came in fifth although I think we were close to last rounding the second mark). His boat loved it, he was outpointing everybody. If I had been trimming things we would have gone slower and pointed lower. His boat is totally different than mine and he knows his boat.

lesson learned.
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  #30  
Old 10-16-2007
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Yes; tenuki there are MANY ways to trim the boat in different wind conditions, and some boats may go faster or point higher with a bubble in the main. I am going to point something out on the SF Sailing.com trim guide:

Quote:
In heavy air over trimming the mainsheet will create excess weather helm. Some backwinding in the luff of the main is to be expected. Don't let a little backwinding trouble you - it is fast.
Please note the first three words were "In heavy air"; in SF Bay that usually means true winds over 25kts. By lowering the traveler and sheeting the main down hard you WILL get a bubble in the main because it is blocking the wind from the jib so much. It reduces heel, keeps the main flat AND creates the luff bubble that depowers the main enough so you don't have to reef and you can sail at maximum speed. I have suggested this before in other threads that discuss heavy air trim.

I did not read all of the links you posted; but the one on the Shields class boat also is showing some backwind of the main mostly so that the boat can point higher (pulling the jib in to where it is almost parallel with the main). I think what they are trying to show is that if you don't do this you won't point high enough. It looks like the main is huge for that boat and a bit of power loss due to backwinding is less critical than pointing.

A -slight- bubble or lightness at the luff is optimal in moderate winds. If it is more than 12" wide or so I think you are giving up some power. It's ALL about having a balanced helm; the rudder is a giant brake pedal if it is turned sideways to the water flow. I was just trying to point out that triming the sails to a correct shape is first and then adjusting things so the weather helm is minimized will give you the best overall performance.

Quote:
"so in light air we slide the draft back by sailing with 1/2-inch scallops between each luff hank. These wrinkles look pretty ugly, but they allow the draft to move aft to 44 percent, the proper position for light air. As the breeze builds, halyard tension should be slowly tightened until the wrinkles disappear in 12 knots true and up (usually when whitecaps just appear on the water). "
This is ABSOLUTELY correct! You increase the sail draft in light wind to get more lift. The way to know how light the halyard tension is is by seeing the pockets form at the luff! Yep; looks like poor seamanship; but it's not, and it's fast. We had our boat moving at 5 kts in 7 kts of apparent wind last weekend because of this and other trim settings!

YMMV...

Last edited by KeelHaulin; 10-16-2007 at 05:40 PM.
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