DaySailer.org Forum

I've been having trouble trimming my main this summer. In (relatively) steady wind, if I get the leech tells streaming nicely then we start luffing. Not bad (flogging), but there is definitely some waving going on.

With apologies for leading the witnesses, could it be that the boom vang is too tight? The tells on the jib are streaming (outside) and fluttering (inside).

Yes, I should have experimented with it. But the question occurred to me now, when I'm not on my boat.

FTR, I have Intensity sails that are about a year old.

--john

Interim wrote:I've been having trouble trimming my main this summer. In (relatively) steady wind, if I get the leech tells streaming nicely then we start luffing. Not bad (flogging), but there is definitely some waving going on.

With apologies for leading the witnesses, could it be that the boom vang is too tight? The tells on the jib are streaming (outside) and fluttering (inside).

Yes, I should have experimented with it. But the question occurred to me now, when I'm not on my boat.

FTR, I have Intensity sails that are about a year old.

--john

John, I must say that the boom vang is the one sail control on the boat that perplexes me the most, so I feel your pain! I play with it and play with it, yet never seem to "get" what it's supposed to really accomplish. The best I can gather is "vang off when sheeted in/close hauled, vang on when boom is out to the side", in order to keep the boom from "skying". Either on or off, no in between, unless you are using the "vang sheeting" technique ...

Ask 10 different "experts" and you'll get 10 different replies ...

Missing is some indication of wind speed.

8-10mph winds.

Tim, you may have pointed out the problem. I set the vang before we leave the dock, and tend to leave it there unless the winds are strong and I want more twist. Maybe I want more twist and don't realize it

--john

When I was younger, I thought the vang was mostly for keeping the boom from lifting and I didn't give it much attention. It took a few years before I learned about its effects on sail shape. Now I understand that there are nuances to vang use that have significant effects on the speed, safety, and handling of the Day Sailer. But I think it's best for everyone if I leave the explanations to those who are far more knowledgeable.

I would recommend searching this forum for posts by Mike Gillum, who shares some of his typically helpful thoughts on this subject. Also, there are numerous articles to be found online, including these:

http://www.jet14.com/articles/schwenk_vang.htm

http://www.sailingbreezes.com/sailing_b ... ll0800.htm

Very good articles!

In the first one a very good point is made that I had forgotten (because I committed it to memory when I first installed the vang! ;-P ), and that is to NEVER tighten the vang with the main sheeted in hard! If you let the sheet out w/o easing the vang, gay-ron-teed something will break, either the vang attachment(s), or the boom itself if they are stronger. This rule of thumb applies to mid-boom sheeting - it may or may not apply to end-boom sheeting. Those more familiar with that setup might chime in ... ?

The vang's attachment does not give it the same mechanical advantage as the sheet (no matter the configuration). So, with the sheet, you can pull in tighter than you could with the vang. Your sequence of events will make the vant "responsible" for a load it could not achieve on its own. That's the translation of your scenario.

Exactly, and no matter how you word it, if you do it, something's probably gonna break! ;-P

I liked the articles too. I think I'll re-read them frequently to see if I can gain some understanding.

Given the discussion, it appears that I've been lucky to not break something.

--john

+1 for what willyhays said. Mike Gillum really helped me set up my boom vang so that it is enjoyable to use.

It does have different effects with different mast sections. My previous mast, that I broke, was much bendier than my present mast section and the vang worked somewhat differently. With a 20:1 set up and the angle of the vang shallower than 45° you get more "mast ram" effect, therefore controlling the mast bend as well as the leech of the sail. With my bendy mast if I pulled on full vang I would actually open the leech and flatten the sail by bending the mast. With less vang pulled on it would closed leech but flatten the sail. With minimal vang pulled on it controls the boom from rising but does not affect the sail depth much, though keeps it from twisting out as much. With no vang on, the boom is allowed to rise and the sail twists out and remain at full depth. With my stiffer mast it's hard to get it to open the leech by pulling on full vang, I probably need more rig tension for that.

When you use a powerful vang to control for boom height, and therefore the leech tension, your sheeting becomes more of a traveler, especially if you are using end boom sheeting with a high triangle bridle or a split tail sheet, as Mike uses. Also, you end up not having as much sheet load in hand because part of the load of pulling the boom down, actually a great deal of it, is done with the vang.

I don't know if it's luck but I have not broken anything yet and have had the set up for a number of years.

Some booms will have a hard time with mid-boom sheeting, and those I would suspect of having troubles with vangs used for vang sheeting. However, all the DS booms I've seen are on the beefier end. Also, those who like Mike or K.C. set up for van sheeting would expect the higher loads and would make sure that the vang fittings are up to the task and not underdimensioned...

As follow-up, I spent Friday on my local lake and played with the downhaul, outhaul, and vang. For the first time this season I felt like I got them all right.

When I docked (feeling very technical about my sailing), I was met with this from a powerboater:

"How does that *&%^$ think stay up?"

"Luck," I told him.

--jf

Touche'!

On my larger boat I have a back stay adjuster to bend the mast. I see more what the vang is used for on the DS now. Thanks.

Salty Dog wrote:On my larger boat I have a back stay adjuster to bend the mast. I see more what the vang is used for on the DS now. Thanks.

Can you elaborate? My understanding is that more rake creates more camber, and vang reduces twist. How do those interact? Are they two approaches that have the same impact?

(I bet not, but I don't understand).

--john