general confusion on leech tension

[Todd Smith]

This particular subject - twist or leech tension to depower - gets more confusing every time it comes up :bang:. There seems to be a different answer from everyone who posts and every source that I read .

Leech telltales flow: check. Sheet in till they curl, then out till they don't, OK. Make sure that they break together - again OK. Depowering? Everyone has a different answer :bang: . For my boat - it still seems that Rich's "blade out" "works for me" - but since my vang is not totally rigid - the boom does rise some when I sheet out.

What to do in a gust seems to be the SINGLE most confusing aspect of sail trim. :bang: .

OC

Oldcat,

I think the problem is that depowering is done in 2 time frames:

a) short term,
what to do when the gust hits,
this will be removed as soon as the gust is finished

b) long term,
what to do for a long time of strong or gusty winds
this will be kept until the winds calm some

For long term depowering, reducing draft is king ( ignoring reefing for the purpose of this discussion ) because a flatter sail creates less heeling force for the same amount for driving force.

For short term depowering, angle of attack is the only option, ease sheet or traveller. Twist is just the difference of angle of attack between the foot and head of the sail, so adding twist is just reducing the angle of attack in the upper sail.

I am going to have to try and observe the relation between leech tension/twist/draft depth some before I conclude anything. I can think of several factors that might effect this, such as mast flex.

Todd

 

[OldCat]

Todd,

To clarify, I am less concerned about long term depowering. I don't feel confused about this part of it. I adjust following trim guides for my specific boat (Catalina 22) and Don's stuff. Leech tension is whatever I get from adjusting to get the main sail leech telltales to break as evenly as I can. That seems to work...

Maybe I have not been clear, but it is the response to a gust that seems :bang: from the experts. What I do in a gust seems to work well for me - I follow the C22 trim guides with a tight vang = blade out per the second half of RichH's post as quoted by Scott. A note here is that I effectively don't have a traveller in a gust, it is too short and end boom. So, I am 'forced' to vang sheet. The vang is not made of "ultra-stiffium" so it allows some amount of boom rise when I sheet out - so good or bad - I get some added twist when I sheet out.

Here is a quote from a Catalina 22 tuning guide:
"Heavy Air (15+): Center the traveler and increase vang tension until the boom doesn’t raise when you let the main out in a puff (i.e. vang sheeting). Play the mainsheet in and out to control the heel of the boat. Don’t be afraid to completely luff the sail in the puffs. Don’t let the boat roll up as you will only go slide sideways. Adjust the cunningham to remove all wrinkles along the luff and pull the outhaul so that the shelf foot is folded tightly along the boom. Tensioning the backstay will open the leach and de-power the rig as well as giving additional headstay tension." (http://www.bartlettsails.com/html/One_Design/Catalina-22.html)

OC

 

[Don Guillette]

Old cat: In my opinion you are going about sail trim in the correct way - you are using what works for you on you're boat. Secondly, you're not guessing. You have a sail trim plan of attack.

On the Catalina 22 tuning guide: almost all of it is what we've all been saying in many different ways. There is one thing I'd like you to check out the next time you're out sailing. Crank on the backstay and obviously the forestay will tighten up - it should be pretty tight in the first place so you won't have too far to go. What I'd really like to know is when you crank on the backstay does the leech open up?

As an aside, when mates crank on the backstay they are focusing mainly on the mainsail. While they are admiring the mainsail they sometime forget what they have done to the jib, which on a masthead rig is the engine of the sailboat.

When I was researching for my book, I ran across an article about some aspect of sail trim written by someone in a sailing magazine but it didn't make sense to me but what did I know. A couple of days later I ran across an identical artlicle on the same subject in another sailing magazine written by Buddy Melges but this article was directly opposite of the first article. Everything in my book used the "old Cat method" - I checked out everything on my C25 and later my C30. If it worked, I incorporated it in the book. If it didn't, I junked it. I tried both techniques - Buddy was right and the other guy was wrong.

The bottom line is you have to check out everyting on YOUR BOAT and use what works for you. That is exactly the advise I always give on every aspect of sail trim I write about.

 

[OldCat]

Don,

Thanks. I don't care if I am right or wrong as long as I am learning - but confusion is not fun.

No wind last night so I 'messed about' rather than sail. I should be able to answer your questions this weekend.

OC

 

[Todd Smith]

Well, we had a great time sailing last night for the local beer can race. I saw 27 knots apparant upwind. For most of our sail we had a reefed main and a 100% jib. Lost of gusts where the traveller, then the main sheet were eased out.

Easing the mainsheet created a lot of twist, but the sail stayed flat.

 

[OldCat]

Well, we had a great time sailing last night for the local beer can race. I saw 27 knots apparant upwind. For most of our sail we had a reefed main and a 100% jib. Lost of gusts where the traveller, then the main sheet were eased out.

Easing the mainsheet created a lot of twist, but the sail stayed flat.

Over the last several years, I have been on both sides of this issue, no matter which side I take, there is disagreement out there about this issue. I can be wrong no matter whether I vote red or green on this one .

For my boat, blading out per the last half of RichH's post as quoted earlier in the thread seems to work well. I at least have the 'comfort' that what "works for me" is equivalent to the advise in the tuning guides for my specific boat.

Peace and Best o' Luck,
OC

 

[OldCat]

There is one thing I'd like you to check out the next time you're out sailing. Crank on the backstay and obviously the forestay will tighten up - it should be pretty tight in the first place so you won't have too far to go. What I'd really like to know is when you crank on the backstay does the leech open up?

As an aside, when mates crank on the backstay they are focusing mainly on the mainsail. While they are admiring the mainsail they sometime forget what they have done to the jib, which on a masthead rig is the engine of the sailboat.

Don,
I am getting used to two new items on my boat, the adjustable backstay and a new Geona. It turns out, both make a lot of difference. I can point higher and that is making a difference in what I need to do to get the main leech tales to fly, including sheet the main in more upwind.

On the backstay issue. C22 tuning guides specify 6" slack in the headstay, sometimes even more, in ZERO to 7 kts of wind. I have talked to a few other C22 folks on this - the general consensus is that the rig is set up with this slack. This is not typical for other boats, I know, but it seems to be C22 practice.

With a slack forestay, tightening up the backstay opens the upper leech of the main as it bends the mast and tightens the forestay. I seem to need a fairly high amount of backstay tension to open the leech in moderate winds, possibly to compensate for a 6 year old main sail being used with a brand new Genoa.

There are disagreements in some of the tuning guides, so it gets to be a complex topic. There are some mast rake and forestay questions for my specific model of C22 (the Sport model) that I need to play with. Everyone here has a different boat, so I need to filter advise through that as well.

Based on speed vs. other boats on the lake, we seem to be doing well. Now if the Admiral will let me buy a new main sail...

OC