Mainsail trimming

jimi

jimi

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I find this a bit of an arcane art, with my efforts being restricted to get the top tell tale fluttering 80%, just stop the luff breaking and attempting to keep the deepest part of draught roughly 30% ish back from luff. What other tips have you got?
 
I presume you have your genny set up already before tinkering with the main??
Even though I have a furling main I'm able to get most of the hundreds of tell tales flapping correctly.
Once set correctly it really makes adifference...
 
So, basically, I just keep the top batten parallel to the boom? Thats what I always did until some dinghy racing hotshot came on as crew and confused the hell out me.
 
Nope..... that depends entirely upon your sail cut......

The twist profile of the main has to match that of the genny for maximum effect..... too much and the genny will stall the main, too little, and you don't get maximum air flow/acceleration.....

Tune up twist with kicker and mainsheet/main traveller until the genny is just backing the main, and then bring in a fraction.....

also, important to note that the backing of the main can happen differently at different heights on the main, so experiment with twist, and depth to get the profile as close as you can to that of the genny along the whole length of the leech....
 
Jimi - hope I am not teaching my grandma to suck eggs but there is a simple device which may also help you on mainsail trim that can be made up at home from a transparent plastic sheet and permanent text markers.

Getting the chord depth - both amount and position fore and aft - just right on a mailsail (or indeed a headsail) is somewhat subjective if you rely only on your Mk 1 eyeballs with nothing more to guide you.

This simple device makes it all a lot easier and eventually you will find no need to refer to it, once you get more familar with your own sail settings.

The device is a strip of say 6 x 2 inches semi rigid transparent sheet, marked as a graph with 10 vertical lines equally spaced along it's length. Decide yourself what maximum chord depth you will ever want (suggest maybe 20%?) and draw in horizontal lines to the same scale. Maybe four lines - each 5% of the same scale - allows you to measure between 0 and 20% quite accurately.

On to this graph you can then use a differing coloured pen to draw in your ultimate chord profile. Maybe one with max chord of 20% but 30% forward for power and one with less chord maybe 10% but 50% aft for pointing. If you understand this explanation - each will look like and aircraft wing profile.

You use the device by physically getting below the mainsail and viewing through the plastic and aligning the sail luff and leach with the ends of the graph. Moving the plastic further from or closer to your Mk 1 eyeballs will allow you to use it at all points up the sail - not just along sail seams.

It is just as effective as those masthead cameras used upon early America's cup boats (remember the dark lines across the sail they once had which could show chord easier to the camera?) - but of course its is a lot cheaper to get and use.

And it works.

Good luck

JOHN
 
Yep thats about it,ignore dinghy sailors they talk a load of ****,I know I used to be one,and they have the irritating habit of bobbing up and down every time the boat takes on a bit of heel!The bit about getting the slot right is also important.
 
To really get it right you need slightlly different techniques for different wind angles, different wind strengths, different boats and different sails. Sadly the truth is there is no simple answer to this question. For starters it really is important to discuss it with your sailmaker. So often people have problems with their sails / sailshape that can easily be sorted out by a quick visit from the sailmaker.

The answer depends to some extent on the available controls. These will include all or some of sheet, traveller, bendy mast/ backstay, cunningham, outhaul, leech line and vang. You then need to consider depending on wind, sea etc what you want the sail to do ie. point, develop a lot of power, be stall resistant, have a high ratio of drive to lateral forces or whatever.

Finally you need to set the sail to achieve these objectives. Some rough guidlines are as follows. Light Air: Full sail with draft in the centre of sail. Then trim as NAS says. Medium Air: start to tighten cunninghham/main halyard to pull the draft forward. Also begin to flatten sail by bending the mast and tightening the outhaul. Heavy Air: The rule is get the draft well forward and flaten the sail ie. increase all of the adjustments made in medium airs. If the boat gets overpowered start by loosening the traveller.

Downwind in medium/heavy air power up the sail if desired by allowing more shape into the sail.

Finally it is great fun to get into the sweet spot - well well worth the effort!
 
And no one has mentioned the luff tension,downhaul,mainsheet traveller,outhaul adjuster,backstay tension adjuster,felt tip marker points for the 'just so' genny and jib sheet adjustments where they go through the block...
Got a good speedo device ? Go out and play with each and all ,even better go play fun racers against a sistership,you will be surprised...none of the above may seem particularly worthy of study or of import.. until a sister ship outpoints you !
 
[ QUOTE ]
So, basically, I just keep the top batten parallel to the boom? Thats what I always did until some dinghy racing hotshot came on as crew and confused the hell out me.

[/ QUOTE ]jDespite next reply, this is not quite right. You need to keep the top batten parallel to the sailing track. If you dont have the boom on the centre-line, this means it will be hooked in relation to the boom. I find that boom on the centre-line rarely happens, pointing that close in any waves is just not powerful enough. Another thing is that most of these posts relate to best trim when NOT overpowered, at which point reefing the main by backwinding is quite probable.

If you are going to start saily threads, Jimi, could you choose simpler ones !!! /forums/images/graemlins/cool.gif
 
Its a big subject that can be made easy. Get hold of a copy of "Sail and Rig Tuning" by a guy called Ivan Dedkam (I think thats the right spelling I've lent my copy to someone!). If you want to see what your settings are when you are sailing then jump onto the UK sails website for a useful programme called "Accu Measure" Its a programme that allows you to take a digital photo of the main/genny and then download it onto your computer. The programme will then give you all the details about what you had in the way of draft/depth/twist and more. Good for taking away the "seamans eye" if you want to be more accurate. The other good thing is that if you do it each year then you can see if your sails are becoming more baggy/losing their shape.

Fin
 
This is all a vast oversimplification. You have to play with your own rig, and work out what works best for you. Unlike dinghies, very few cruisers are "the same" as each other....
 
All right I'm confused. the translation from google is.....

"my small does shell, or my small shells? Is not this step?"

Shells!!!?????
 
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