How do you control (increase/decrease) mainsail twist ?

[Boo2]

Hi,

Q.a.t. : how do you control (increase/decrease) mainsail twist and how do you know when the twist is right for the conditions ?

Boat is a UFO 34 and controls available are a spring vang, cunningham, outhaul and flattener reef.

Thanks,

Boo2

 

[Strathglass]

Hi,

Q.a.t. : how do you control (increase/decrease) mainsail twist and how do you know when the twist is right for the conditions ?

Boat is a UFO 34 and controls available are a spring vang, cunningham, outhaul and flattener reef.

Thanks,

Boo2

Normally you would use the kicker (vang if you want to use an Americanism) but on my boat (Contention 33) I have a full width mainsail traveller and find moving it gives much more control.

I can pull the traveller well to windward when I want to introduce more twist. Thus I can have the boom well in and still have a good twist on the main.

The tell tails are a good indication if the twist is about correct.

Iain

 

[Stu Jackson]

Add the mainsheet and you've mentioned them all.

Others will add to the when. My simple one? When it stops backwinding and looks "right." Flat in light winds, fuller in medium, flat in strong, then reef.

The traveler only affects the angle of attack.

 

[William_H]

Mainsail twist

This is a function of the down ward tension on the boom and hence the leach of the sail. So you pull the boom down the leach becomes a straight line mast head to clew at the end of the boom.
If you raise the boom while holding it up to windward the leach is freed and so the top of the sail can fall away to leeward. Hence twist. Downward pull on the boom is achieved with boom vang or with the main sheet and wide traveller or combination of both.

However twist can be achieved on a fractional rig mainsail by cranking on the backstay. This tends to move the op of the mast aft so freeing the leach and top of the sail.
2 types of boats here built for match racing have the main sheet and the backstay tension control emerging from a pedestal in the middle of the cockpit. (Foundation 36 and Bakewell White 8) where the mainsheet hand controls both on a moment to moment basis. In a gust pull on backstay then ease mainsheet. In a lull ease backstay and crank on the mainsheet. All this while beating or reaching.

The outhaul and cunningham tend to relate more to overall shape of the mainsail. ie to enable it to be flattened (reduced camber) to enable you to more easily dump overall pressure when overpowered or reduce drag when beating. good luck olewill