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Go Back   SailNet Community > Skills and Seamanship > Learning to Sail > Main Sail Shape
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Topic Review (Newest First)
10-30-2004 03:45 PM
Main Sail Shape

Ya know Dave, I think you just hit the nail on the head: if the wife is happy, you''re doing great! That''s probably the #1 thing to aim for--everything else is secondary. If she''s happy, then it''s likely that conditions are mellow, you''re not about to hit anything, you''re not yelling, and nothing expensive is happening. All good things. I think the wife might be the best instrument on board...


10-29-2004 09:42 AM
Main Sail Shape

Thanks Bob, it helps.

I have an outhaul and a cunningham, the outhaul appears to be as tight as it will get.
I do not have a vang or adjustable backstay.
I took a good look at the boat today (and other nearby ones), it appears that to add hardware that enables traveller adjustment will be easy. I can add a six to one block and tackle on each side. The boat already has extra line locks and a small winch that I don''t use.
I also noticed that I have the topping lift set too tight/short and can''t pull the boom down hard enough.

OK let''s see.
To increase sail power loosen the main sheet which will add twist. Moving the traveller to keep a good sail angle to the wind.
To lower sail power. Flatten the main, move the traveller off the wind, reef the sail.

I''ll probably continue to reef early, it''s easier inside the harbour or at my slip, and the most important thing is to keep my wife happy (she doesn''t like heeling over 10-12 degrees unless she''s driving).

Again, thanks
10-29-2004 07:45 AM
Main Sail Shape


The outhaul is a control line that pulls the clew (aft bottom corner) of the main backwards. Look at your boom and figure out what the clew is attached to. On some boats it''s attached to a piece of hardware that can be moved around at the dock but has no control line. If so, then you don''t have an outhaul.

If the outhaul is attached, then it''s led forward inside the boom and usually winds up with a jam cleat or similar securing device somewhere on the boom towards the mast. To adjust, you need to unload the sail and yank the outhaul hard. What you''re trying to do in a stiff breeze is pull all 3 corners of the main away from the center of the main, causing the main to flatten out.

There is sometimes a control line attached just above the tack (forward bottom corner) of the main, called a cunningham (sometimes called a downhaul), that lets you exert pull down on the tack as well. So your 3 tensioning controls are:
- Halyard (tensions head)
- Outhaul (tensions clew)
- Cunninngham (tensions tack)

Another main-flattening tool is an adjustable backstay. Look at your backstay to see if there is some mode of on-the-water adjustment. tightening the backstay will also help to flatten the sail, because it pulls the masthead backwards a bit, flexing the mast into a shallow curve, which matches the curve built into the main (the sides of the triangle of the main are not straight--they are usually curved outwards slightly for shape.)

If you have a light boom that can flex somewhat and an attached foot on your main, tightening the boom vang will also help flatten out by pulling the foot of the sail down.

All of the above might reduce weather helm by 10 degrees or so. You want some weather helm, right? Maybe 3-5 degrees. That gives you better lift from the rudder, reduces leeway and improves pointing. After that, the first steps are to flatten the main with the above controls (whichever you have).

Next, to further reduce weather helm, if you have a traveller that can be adjusted under load, ease it. It might be worth your while to upgrade your traveller with a better arrangement so you can ease it from the cockpit, and play it in gusts.

Reefing the main is the last stage of reducing weather helm. Sounds like you already do this. I think you''re ahead of the game already--most people don''t reef early enough. It''s amazing how much easier boats will sail and how much more fun you can have with a reefed main! Especially if you don''t wait to reef until it''s howling.

Hope above helps.

10-28-2004 02:55 PM
Main Sail Shape

Jeff, thank you for the reply.

The boat is an O''Day 302 and I have a 4 y.o. North Sail full batten main with a 140 genny head sail (also 4 y.o. North)
Part of the issue is I don''t have any way to move the traveller without going out on the cabin roof and physically moving it (no pulley set up). That would mean I''d have to furl the genny and turn into the wind. (another question, what is an outhaul?)

I did a search of this site and noticed quite a few posts on this subject. You''re rigth, I don''t have the proper or newer options on the boat. Oh well, part of the reason for buying this boat was to learn how to sail (maint., upgrades, sail, etc...) and one day live in the three 80"s (80 degree air/water with 80'' vis.
10-28-2004 01:37 PM
Main Sail Shape

To some extent it depends on the boat and the conditions of your sails but the most effective way to blade out (flatten) the mainsail you would tighten the main halyard, outhaul, and mainsheet and lower the traveller to leeward. Flattening the sail greatly extends the range of the sail before you need to reef. There are of course limits as to how much you can extend the range before reefing is necessary or simply more comfortable.

How effective flattening the sail turns out to be depends also how easy to use and conveniently located your hardware is, and the conditions of the sail. I don''t know if you are still sailing with the original sail that came with the boat but I would guess that you probably are. Over time sails stretch and sails get more stretchy. In a gust and older sail will increase in depth and automatically power up just when you would like them to flatten.

Easing the sheet can help keep a boat on its feet but initially easing the sheet powers up the sail and so increases heeling and weather helm. Easing the helm eventually does reduce weather helm but at the price of pointing ability and speed.

Also you really don''t have the some of the newer or higher performance options such as controling mast bend, which is probably the most effective way to quickly blade out a sail in a gust.


10-28-2004 10:01 AM
Main Sail Shape

I''m new to owning a sailboat so if I ask stupid questions, sorry.
I keep seeing people talking about weather helm and what to do about it.
I own an ''88 O''day and as far as I can tell the only way I have to control the main is with my "mid-boom" sheet and halyard.
How can I flatten sail, lower the traveller, control twist???
Right now to control weather helm I reef the main in sustained higher wind and/or let a foot or so out on the sheet.

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