Upwind Mainsail Trim: Shaping Your Mainsail, Part 3 - Draft Shape and Position

Welcome to our series on upwind mainsail trim. This video covers Draft Shape and Position, which is Part 3 of a four-part unit on shaping your sails.
TOPICS COVERED:
Sail Draft & Position
Terms
Benefits:
Improved Pointing
Overall Sail Performance
Wider "Groove" - better sail performance over larger range of angles of attack
Controlling Draft Position and Shape
Indications and Cues
Interactions and Challenges:
Sail design
Gust response
Effect of Older sails
In this series, we’re presenting a comprehensive review of basic and advanced mainsail trim concepts. We want the series to be useful and understandable for all levels of sailors.
Our strategy is to start with small bites and build them into a complete picture of sail trim. We’ll use a visual approach, and give you questions to think about during the presentations. We’ll stay practical, using theory only as needed.
Here the links to related content mentioned in the video
Velocity Made Good (VMG) sailzing.com/velocity-made-good-vmg/
Mainsail Telltales - A Better Approach sailzing.com/mainsail-telltales-a-better-approach/
Outline (text version of the content in this video) sailzing.com/shaping-your-mainsail,-part-3:-draft-shape-and-position/
Each topic will have a video and outline version.
Visit SAILZING.com for much more content to help you to sail faster and smarter.
Stimulating Learning for Sailors. SailZing.com
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[@Lozzie74]

Best explanation of sail shape I’ve ever seen!

[@SailZing]

Thanks! We appreciate that.

[@jamesa1116]

These videos are simply the most easily understood guide to sail shape and performance on the net. Start with the video (not part of the series) on Lift and Drag then follow these videos through from 1 to 4 then repeat as necessary. It will change your sailing from Monkey see, Monkey do, to that of a sailing Goddess or God - well, perhaps a few more sessions on the water, but with this knowledge, you will be a hell of a lot better. Thank you very much for such clear and helpful videos.

[@SailZing]

James, Thank you for the wonderful feedback. You describe exactly what we set out to do with Sailzing.com. We want to make learning advanced sailing concepts simpler and give sailors who want to sail faster and smarter one place to go for free learning. Thank you again! Please make sure to visit SailZing.com where most of the learning happens.

[@gromakovsky]

Thanks for the interesting videos on the sail trim. Looking forward to watch Part 4!

[@SailZing]

Thanks for the feedback!

[@Masus04]

Thank you for the detailed explanation. Can't wait for the parts on the foresail and reaching!

[@SailZing]

You are welcome!

[@bugstream]

Thankyou :) You've put this video together really well, very clearly explained.

[@grahampearce6462]

Excellent explanation, so understandable. Now my problem will be to remember it in the heat of the moment on the water

[@SailZing]

Thanks for the feedback. We feel your pain. 😉 We have companion articles on SailZing.com that usually document the top points from our videos. You can revisit those for quick glances to remind yourself.

[@martygingras8683]

Really, really good.

[@vidaplena6509]

Very good lessons

[@SailZing]

Thanks for watching

[@mikeayres345]

I need advice on the inevitable separation bubble just behind the mast, please explain.

[@larry9210]

I always wonder the percent increase in speed of an “OK” sail trim vs a very good sail trim. It would be great to see some videos on this.

[@SailZing]

We'll see what we can find.

[@joestevenson5568]

It will depend heavily on the hull. If you are already reaching the hull speed of a displacement boat with OK trim, then perfect trim will add nearly nothing.

[@BrotherCheng]

I'm confused about 11:30. Does tension on the leech help flatten it or hook it?

[@SailZing]

More tension hooks the leech.

[@MartijnDesijn]

if you mention: "the draft is 40% aft", at what height of the sail is this measured? boom level, half way, top batten?

[@SailZing]

The draft position is likely to be slightly different as you move vertically up the sail, so it's not one number.

[@MartijnDesijn]

@@SailZing thanks! Ok let me re-phrase my question: in many books like high performance sailing / illustrated sail tuning I read: draft position should normally be around 45-50%. And ideal camber/draft depth is 16% in medium conditions. Where should I measure this / look at the sail? Can i just do it at the easiest place, the boom with a tape measure? Or is it somewhere half-way up the sail, so you have an average?

[@SailZing]

@@MartijnDesijn It's best to measure at several places. The easiest way to measure is with software, such as SailPack Vision. This is a free download. Take a picture of your sail while sailing upwind, then upload the picture to the software. Draw draft stripes at various heights as instructed in the program. The software will give you the amount of camber as well as the max draft position at each stripe. Hope this helps.

[@wilfdarr]

3:29 "this drawing is exaggerated: with batons in the sail you probably couldn't achieve this shape". Wanna bet? Kirby 25, we were clawing behind an island, I was looking at exactly that shape! When I went to adjust the leach line skipper told me not to touch it, that it was perfectly set for when we come out into open air. I wanted to tell her that at the rate we were crawling along that may never happen. I closed my mouth 😁. It's a control: it's meant to be adjusted. My opinion of course.

Awesome! Keep it up! Would you like to be KZbin friends? :]