How to 'properly' raise a Dacron Mainsail

[RichH]

This was originally posted on Don Guillettes "Sail Trim Forum" 2 years ago ...

It fully explains what to do via properly SHAPING a dacron mainsail so that your boat doesnt develop adverse 'weather helm' due to BAD mainsail shape .... all due to improperly RAISING it.
It also explains the most common 'developing shape changes' in a 'boltroped' dacron mainsail as it 'ages', and how to determine the 'developing bagginess' .... and what to do about it. Its all about correct mainsail HALYARD tension.

Properly raising a DACRON mainsail will result in less heeling, less sail 'baggyness', faster/safer boat, a boat that can now 'point' like a banshee ...... and of course, less 'weather helm'.

http://forums.sbo.sailboatowners.com/showthread.php?t=120970 see posting #1

 

[Bob J.]

Thanks for putting this up here Rich, I've tagged it for future reference.

 

[Witzend]

Rich, for a ferlowed mains that have tension always on, what is the expected effect on bolt rope shrinkage over time?
On a brand new sail how would you treat the sail when ferlowed, keeping in mind that changing the halyard tension may have negative effects on it ability to roll up properly?

 

[Jackdaw]

Rich thx for posting! I found this last night after a search query with your handle in it. The North main on my 260 might need 'the treatment'...

Funny about the message system here... if you inbox is empty, 50 messages in your send folder will prevent you from getting new messages. Note to self.

 

[RichH]

Roller Furling mainsails usually dont have 'boltropes' (a rather 'thick' rope inside a sleeve at the luff); but rather, have 'taped luffs' wherein the very small 'cord' (usually 2 cords sewn into the 'tape' - one that fits inside the foil groove and the other cord 'right behind' and outside of the foil groove) and is not usually stretched out ... and such a 'taped' sail shouldnt have its luff 'over-stretched' ---- the 'shape you bought is the shape you get'. Such 'taped' sails usually are designed for a very narrow windstrength range --- 12-15kts and they do over-stretch when beyond that range. You can 'adjust' the location of the point of maximum draft (fore/aft) by halyard tension ... but you must 'unload' the tape on the furler to do so, shape the sail by halyard tension .....and then must then unload that tension when you later furl/reef, etc. --- a big PITA that can easily jam a furler ..... or you can put undue strain on the furling system and can jam it or cause undue wear in the roller/ball bearings. One of the reasons that 'racers' dont use furlers.

The discussion that I posted is for mainsails that are attached to the mast by slugs/slides connecting to the boltrope (3 strand dacron rope inside the luff sleeve) or where the boltrope and its sleeve itself fits into the mast slot/groove. Boltroped mainsails are the 'most common' on cruising boats and this discussion doesnt apply to 'tape luff sails' or sails made from 'laminates'. For taped luff sails and laminate sails, the shape you bought is the shape you get and very little 'shape adjustability' is possible with halyard tension .... or you can 'bust' the sail or 'jam the furler'.

 

[Witzend]

Thanks Rich for clarifying.

 

[RichH]

Rich thx for posting! I found this last night after a search query with your handle in it. The North main on my 260 might need 'the treatment'...

Funny about the message system here... if you inbox is empty, 50 messages in your send folder will prevent you from getting new messages. Note to self.

If youre handy with waxed sail twine and needle palm ... you 'can' do this adjustment yourself --- just dont 'lose' the boltrope 'into' the sleeve or youll have to resew the sleeve by machine.

To make this 'boltrope' adjustment easier in the future, I recommend that any new sail be arranged with 'extra' boltrope length stored and attached to the headboard 'all ready to go'.
Then when you discover a shrunken bolt rope, cut the upper 'sail twine' binding, slip in more boltrope, and hand re-sew the boltrope to its sleeve with sail twine. Of course to do this you should have the 'actual'/recorded unloaded luff dimensions from when the sail was 'new' ... otherwise its hit or miss in the adjustment. A 20 minute job ... IF you saved/recorded those 'as new' dimensions.

;-)

 

[Don Crowther]

RichH
Excuse my ignorance but i'm having trouble wrapping my tried brain around this. Let me see if I've got this right. My "P" lenght is 41 feet so does that mean that after I have the mail halyard up that I should tighten it another 4 inches? This will give me better mainsail shape and reduce weatherhelm? Or should I tighten the main halyard to get the boom to 90 degrees?
thanks Don

 

[Charlie Jones s/v Tehani]

Interesting to me that no-one has even mentioned a down haul on the main. I haul the halyard to the peak, and set luff tension with the down haul using the sliding gooseneck. Does EVERYONE else have a fixed gooseneck??

 

[rardiH36]

Firstly, as a newbie sailor just a few years ago (still am but not quite so much), I soon observed that my two older mainsails wouldn't tension right no matter how much winch cranking I did on the halyard. Cutting the seizing between the bolt rope and the head or tack and milking the luff along the rope went a long way to better sail look and trim. Just as RichH describes!

But also, when raising my mainsails, I found it critical to first use the topping lift to raise the boom enough that after the mainsail halyard is tensioned, the boom will then drop down a few inches to the natural "hang level" of the mainsail when the topping lift is slackened. Naturally, also the mainsheet and boom vang must be slackened so topping lift can actually raise the boom. If the boom isn't raised first, now matter how hard I try, the luff will not fully tension all the way down to the tack. This is due to the off-angle pull of the halyard straight up against horizontal gravity pull of the boom, and also the sideways (aft direction) friction of the sail slugs in the track as the sail pulls backward/down from the boom weight. So when no weight from the boom -- no friction. (My mast track is in good condition and I use sailkote lubricant also).

When under full sail in moderate winds, and the scallops develop, then I can tension the lower luff with the cunningham.

 

[RichH]

RichH
Excuse my ignorance but i'm having trouble wrapping my tried brain around this. Let me see if I've got this right. My "P" lenght is 41 feet so does that mean that after I have the mail halyard up that I should tighten it another 4 inches? This will give me better mainsail shape and reduce weatherhelm? Or should I tighten the main halyard to get the boom to 90 degrees?
thanks Don

Yup. P=41ft. 41/10 = 4.1 = 4 inches ...... raise the sail 'just up' then add an additional ~4" of extra stretch by the halyard. Follow the directions in post #1 on setting correct halyard tension to achieve your best 'weather helm', you will get 'as designed' sail shape.

For your H34 when new, your dacron sail had it tack angle (angle between the top of the boom and the mast) at 88° .... use this for checking IF your boltrope has prematurely shrunk ... see post #1

;-)

 

[RichH]

Interesting to me that no-one has even mentioned a down haul on the main. I haul the halyard to the peak, and set luff tension with the down haul using the sliding gooseneck. Does EVERYONE else have a fixed gooseneck??

Downhauls went passe when cunninghams started to be applied. When racing you can easily stretch a sail past its 'black band' with a downhaul --- and get a DSQ.
My sportboat has a sliding gooseneck and downhaul but the downhaul also has pin stops to make it a fixed gooseneck. Yes downhauls are better .... but dont get caught with the tack below that 'black band' or your 'out' of the race.

 

[Charlie Jones s/v Tehani]

Yabut- I don't race, I cruise. Many miles last few years. I'll keep my downhaul

 

[Charles Erwin]

Rich -

This stuff is too interesting and your explanations are excellent because you tell us why things work rather than the more simplistic what one should do.

I am trying to understand sail shape - as distinguished from sail trim. I gather that sail design implies the sail is constructed in a manner that allows one to set the sail control tensions thus to achieve that designed shape. If one tensions the sail edges as the designer assumed -- things are good. But - this seems to be true only under the wind/sea conditions the designer assumed.

Accordingly luff tension is an important part of the process where the sailer tries to get the shape the designer intended.

Do you recommend setting the design luff tension (design tension = +1" for 10') in order to achieve design shape no matter wind strength?

If the wind is less than the assumed design value (assume 12 knts.) then applying design luff tension will move draft position forward to the 12 knt. position - perhaps too far forward - for wind under 12 knts. Would light wind conditions represent a case where we would not tension the luff as much as the 12 knt. design assumes?

Also - where wind is higher than the 12 knt. design assumption - do we want luff tension to be at the design tension and no more than that? Do we adjust luff tension at all in such conditions or do we leave it be at the 12 knt. design tension.

In summary - do we always raise the main to achieve design luff tension and leave it alone? Do we raise to design tension - then slack off thus to move the draft position aft - as appropriate - in winds from 1 to 12 knts? Do we we regard design tension as the upper limit - no matter that the wind many be greater than the 12 knts. assumed in the design?

Thanks for your views.

Chalres

 

[RichH]

Rich -

This stuff is too interesting and your explanations are excellent because you tell us why things work rather than the more simplistic what one should do.

I am trying to understand sail shape - as distinguished from sail trim. I gather that sail design implies the sail is constructed in a manner that allows one to set the sail control tensions thus to achieve that designed shape. If one tensions the sail edges as the designer assumed -- things are good. But - this seems to be true only under the wind/sea conditions the designer assumed.

Accordingly luff tension is an important part of the process where the sailer tries to get the shape the designer intended.

Do you recommend setting the design luff tension (design tension = +1" for 10') in order to achieve design shape no matter wind strength?

If the wind is less than the assumed design value (assume 12 knts.) then applying design luff tension will move draft position forward to the 12 knt. position - perhaps too far forward - for wind under 12 knts. Would light wind conditions represent a case where we would not tension the luff as much as the 12 knt. design assumes?

Also - where wind is higher than the 12 knt. design assumption - do we want luff tension to be at the design tension and no more than that? Do we adjust luff tension at all in such conditions or do we leave it be at the 12 knt. design tension.

In summary - do we always raise the main to achieve design luff tension and leave it alone? Do we raise to design tension - then slack off thus to move the draft position aft - as appropriate - in winds from 1 to 12 knts? Do we we regard design tension as the upper limit - no matter that the wind many be greater than the 12 knts. assumed in the design?

Thanks for your views.

Chalres

You pose very appropriate questions, especially pertinent for 'stretchy' dacron sails .... and it will take me a few 'weeks' to lay this down in simple terms and so that its understandable.
Until then take a piece of woven cloth with the fibers at parallel and at 90'° to an imaginary mast .... all shaping done, as you state, by 'tensioning an edge'. Simply watch carefully and observe how applying tension on ONE edge affects the shape of the flat piece of cloth ... if youre 'visual', I wont have to do all that write-up!

Until then here's some rules of thumb ....
• main halyard (boltrope not shrunken) ... put in sufficient main halyard tension so that you can come close to 'neutral' helm when on a beat - the different wind pressure on the sail will require different luff tension.

• "Start" with halyard tension that stretches out the boltrope for 15kts (addtl 1" for every 10-11 ft. of luff length) .... attain neutral helm, then slight release for 'slight weather helm'. .... then re-adjust the tension (up or down) of the other 2 edges (do trials and observe) - so that ALL telltales are flying perfect while you set the outhaul tension vs. MAX speed out of the boat ... of course youll have to tweak here and there to get all the tell tales flying.
Less halyard tension in lighter winds, more halyard tension in heavier winds .... the conundrum is in less than 5-7 knots - set up the shape like the boat is sailing in 18-20 knots (FLAT SAILS!) and simply follow the tell tales, especially looking to avoid 'separation stalls' on the leeward side.
*On my boats, the starting tension of 1"/10 ft. is when the applied tape stripe on the mast equals the tape on the halyard ... when these two marks line up Ive stretched out the boltrope preload; THEN after getting good 'weather helm', all my sail shape (edge) adjustments are soley to keep all the tell tales flying perfectly and with increase of boat speed .... AND the boat has VERY LITTLE weather helm (so Im not dragging the rudder at an angle).

• Referring back to that triangular piece of cloth .... in sail shaping there are ALWAYS 2 (or more) adjustments !!!! .... when you tension one edge the other 2 edges always loosen in reaction, and vice versa. Eg. Tightening the luff, takes the strain off along the leech or causes the leech to become 'flatter' or 'more open'... as the position of draft goes forward; Loosening the luff causes the leech to become 'tighter' and no longer as 'flat' but now beginning to curve-up toward the weather side as the position of max. draft does aft. Do a trial on that triangular piece of cloth and youll see exactly how this 'works'. --- Always TWO adjustments when sail shaping - 1 adjustment to get to the shape that you want to satisfy the tell tales; the SECOND (or more) corrects what happened to the 'other edges' in reaction to the first adjustment in the process. ALWAYS 2 adjustments when shaping a sail.

;-)