Demystifying the Mainsail

May 17, 2004
2,111
Other Catalina 30 Tucson, AZ
I spoke to a new Hunter owner yesterday and he told me “mainsail trim is mystifying to him!!”. I thought “no kidding, join the club!!”. On a fractional rig the mainsail is the most important source of upwind power.

The first thing a sailor has to understand is WHAT are ALL the sail trim controls for the mainsail (and jib) actually adjusting. Secondly, there is an “adjustment sequence” a mate has to follow so that the mainsail controls don’t work against each other. Obviously, you might think, the first adjustment is the halyard but the next time you’re out on the water check the boats you encounter and notice how many mainsail have a sag along the luff. These boats are “adjustment doomed” from the start as no matter what they do with the outhaul, traveler, mainsheet etc it’s going to be ineffective. The trimming tools such as the telltales and battens are not going to be giving incorrect adjustment input and the sailor will overtrim. It just get’s worse when he starts adjusting the jib and tries to mirror the poorly trimmed mainsail.

So what’s the answer? I think first it’s a matter of knowing what you’re looking at and what you’re looking for. Once you get to that point you have to figure out the correct setting for each sail trim control for each point of sail and wind condition. Once you get to that point your boat starts to liking you and performs at 100%.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
We teach new crew to break it into two parts:

Sail shape, and sail trim.

Sail shape is set according to apparent wind speed. On the main, it is backstay, outhaul halyard, and Cunningham. It gets dialed in according to point of sail, which always effects apparent wind speed. You set draft size and position with these. Fuller shape in a moderate breeze. In heavy or very light, flatten it out.

The big part is trim. For the mainsail, the biggest challenge most face is upwind trim in a moderate breeze. To do this, get the boat going upwind, then:

With the main sheet, Set the boom to be level with the waterline.

With the traveler, bring the main sheet to windward until the boom is on the centerline of the boat.

With the main sheet, adjust the twist of the main until the top batten is also parallel with the boom. When you do this, you will probably have to reset the traveler to keep the boom in place. The two controls work together.

Now play the traveler so the top tell-tell flickers; mostly flying but some times stalling. This is optimal upwind trim. In puffs ease the traveler. But bring it back up.

Vang should be off unless it is really breezy. Then set it to match your default boom position.

WATCH. Fast mainsail trimming is a FULL TIME JOB.


Off-wind is easier. Ease till they all fly. Then back just a touch. If they do not all fly, play with the vang or main sheet to adjust twist.
 

Sprega

.
Sep 12, 2012
115
O,day 27 Brownsville Marina
Main sail trim

Might I recommend the book Don Guillette's Sail Trim Chart.
 
Last edited:
Feb 25, 2014
95
Catalina 30 Grand Lake. Wyandotte, Ok.
I learned a long time ago about sail trim but feel I need to read up on all it again. While looking at a boat to purchase today the owner of 7 years did not even know what all the settings did and how they affect performance. He did not even know about the leach tensioner. and never messed with the boom vang. I gave him a quick lesson.
 

Joe

.
Jun 1, 2004
8,323
Catalina 27 Mission Bay, San Diego
May I suggest: "A Manual of Sail Trim" by Stuart H. Walker M.D.
Uh.... my friends... you're plugging your book on Don Guillette's sail trim forum. Don's contributions here are greatly appreciated and he sells his own book and trim guides through this site. I'm giving you this heads up because I can't imagine someone that knew this would plug a competing book on another author's thread.

Book recommendations are cool.... I just feel uneasy seeing them mentioned on this particular thread.
 

weinie

.
Sep 6, 2010
1,297
Jeanneau 349 port washington, ny
Uh.... my friends... you're plugging your book on Don Guillette's sail trim forum. Don's contributions here are greatly appreciated and he sells his own book and trim guides through this site. I'm giving you this heads up because I can't imagine someone that knew this would plug a competing book on another author's thread.

Book recommendations are cool.... I just feel uneasy seeing them mentioned on this particular thread.
yup... just re-read don's book yesterday to refresh my mind for the upcoming spring! Thanks again Don.
 
Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
Don's book is simply the BEST.

I don't care what links others post, but geez, why do that on this forum?

Foolish.

Don's guide is still the best.
 
Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
My apology. I'm fairly new here and didn't realize. Again I apologize.
OK, OK...

Don't get chased away. Sorry to be so harsh.

Just "territorial" perhaps.

Stu

PS Don's book is still better and clearer.
 

TLW

.
Jan 15, 2013
271
Oday 31 Whitehall, MI
My apologies, it's not "my" book, but obviously I wasn't thinking. Will try to pull it now.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Back to our regularly scheduled program, already in progress....

Main trim on fractional boat is a huge interest of mine. Without proper main trim the boat simply will not point. If your fract boat, in particular one that has a non-overlapping headsail (like Hunter B&R boats), does not have a traveler, you'll never get the windward performance your boat is capable of.

I wrote about this in more depth on a blog.

http://rarerarebird.blogspot.com/2014/01/the-importance-of-upwind-mainsail-trim.html
 
Last edited:
Apr 11, 2012
324
Cataina 400 MK II Santa Cruz
A different opinion: It's in no way disrespectful or inappropriate to offer up other resources on this thread. It's the internet, no one "owns" this or any other thread. All on-topic comments made with "good intentions" (you can figure that out) have a place. Don's efforts and contributions are very well appreciated here, and yes, his book and charts are a great resource for us to buy. That does not exclude that there are also other fine materials that we should be aware off. So, please suggest "Sail Trim", or any other material that you think we should look at. While these materials may be "competing" in the marketplace, they are all on the same team when looking at it from the perspective of a body of knowledge. There is a lot to learn about sail trim, thanks for all your help! Please keep those resources comming.
 
Nov 8, 2010
11,386
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
A different opinion: It's in no way disrespectful or inappropriate to offer up other resources on this thread. It's the internet, no one "owns" this or any other thread. All on-topic comments made with "good intentions" (you can figure that out) have a place. Don's efforts and contributions are very well appreciated here, and yes, his book and charts are a great resource for us to buy. That does not exclude that there are also other fine materials that we should be aware off. So, please suggest "Sail Trim", or any other material that you think we should look at. While these materials may be "competing" in the marketplace, they are all on the same team when looking at it from the perspective of a body of knowledge. There is a lot to learn about sail trim, thanks for all your help! Please keep those resources comming.
+1. Share everything. Share your fast.
 

TLW

.
Jan 15, 2013
271
Oday 31 Whitehall, MI
The book I suggested, and subsequently withdrew, is a very thorough work. It is not for someone who wants to "read" about sail trim, but someone who wants to "study" it. The brilliant author was head of a prestigious medical school, Olympic champion sailor, and America's Cup sail trimmer. This book and another he wrote on reading wind shift tendencies have become the definitive theses on their relative subject matter.

As a former educator, I know different people respond to, and absorb, information in different ways, and benefit from different sources. I know this book changed me from a boat owner to a 40+ race/regatta winner.

Just trying to be helpful.
 
Feb 26, 2004
23,353
Catalina 34 224 Maple Bay, BC, Canada
tlw, how about reposting it?

FWIW, I spent YEARS reading sail trim books, like those published by Sail magazine.

Until Don published his, it was still a mystery to me.

Don's is still the best for beginners to advanced old geezers like me, but, yes, there are others out there and Scott & Jack are right.
 

Sprega

.
Sep 12, 2012
115
O,day 27 Brownsville Marina
Mainsail trim

Having owned many boat over the years. I can say that my favorite boat to sail was a Maxi Fenix with a frac rig and a self tending non overlapping jib. Because of years of sailing and studying many resources on sail trim, I found the boat easy to trim and sail, always outsailing like sized mast head rigs and many larger boats as well. In an earlier post I mentioned the book that I learned the most from, it was some 25 to 30 years ago. I'm sure there is better stuff out there now days. By the way. I also had a overlapping genoa that saw very, very little use as the boat sailed so well in most wind conditions without it. Wish I still had that boat.
 
Jan 1, 2006
8,008
Slickcraft 26 Sailfish
Didn't Dr. Walker write a column for a racing oriented magazine? If I remember correctly his articles were brilliant in content but difficult to read. Or maybe I'm not smart enough. I think he knew more about wind than God. Anyway if I'm right about who he is, he was a elder in sailing when I was just learning. That would place his work in the "classic" category but hopefully not in the posthumous category.
We shouldn't intimidate posters from posting any source but particular not from this accomplished individual.
http://en.wikipedia.org/wiki/Stuart_H._Walker