luff length and windward ability

[lilianroyle]

In an effort to better balance my gaff rigged smack, I was thinking of ordering a new staysail (the current one is a bit too small unless the main has a reef in). One option is to have a sail with a longer luff (about 15% longer) and I wondered whether this would have any discernable effect on the boats performance when going to wind. I've also got room on the mast for about another foot on the mainsail luff although I'm not planning to change the mainsail at present. Topsails improve windward ability as I understand it. Does anyone have any knowledge about how to maximise windward ability,and I'm not looking for a miracle, simply bearing this in mind while planning new purchases.
thanks

 

[oldfrank]

Regret that topsails are usually disastrous for windward ability - particularly if they aren't set properly - just like dragging along an airbrake. The additional sail area can however help downwind performance ... or inland, win a little more breeze over trees.

Improving windward performance really isn't as simple as ordering a new sail. You may find that you could improve it by simply narrowing your sheeting angle or ensuring your fairleads are in the right position. You should also consider what a larger foresail will do to the balance. My own boat gets lee helm if I leave the big jib up with a couple of slabs ... it's ... well different. My best advice is to go and talk to a professional. I might be inclined to deflect their over enthusiasm by telling them your budget early in the discussion.

 

[Woodlouse]

I'm going to say the opposite of Oldfrank here and state that Topsails are everything to gaffers when it comes to going upwind. Just make sure it's set up well. A good topsail should give you an extra knot of speed in every direction and might even give you an extra few degrees to windward.

You'll be wanting a staysail that uses as much of the stay as possible, if you need a reef in the main to balance the boat then you definitely need more sail in your foretriangle.

How are you set for jibs? (No pun intended.)

 

[dur]

Topsails upwind

When they're good, they're very very good,
And when they're bad, they're horrid.

 

[oldfrank]

Topsails up wind

Let's state a prejudice first. I regards topsails as an invention of the devil and the finest possible argument in favour of bermudan rig. That said, some of the new integral topsails seem to work very well indeed - in fact they're probably the only advance in gaff rigs in over a century.

The problem with topsails to windward can be explained simply. Most gaff rigs don't use a kicking strap (boom vang just in case there's an international reader). This permits an exaggerated amount of twist to the mainsail, which increases the higher up the rig (and further away from the mainsheet) you go. One result of this is nearly all of a topsail is almost never sheeted to an effective angle - just take a look next time your'e sailing to windward. If you're on the wind, most of the topsail isn't full and if it isn't full, it isn't generating any drive. Off wind it'll all pull and generate more speed. At least we agree about badly set topsails.

You miss my point about my old boat. I can't possibly take much more foresail - the boat has lee helm when the main is reefed - I don't have to put in a reef to balance the boat. I'm already somewhere near maximum.

 

[Woodlouse]

Let's state a prejudice first. I regards topsails as an invention of the devil and the finest possible argument in favour of bermudan rig. That said, some of the new integral topsails seem to work very well indeed - in fact they're probably the only advance in gaff rigs in over a century.

The problem with topsails to windward can be explained simply. Most gaff rigs don't use a kicking strap (boom vang just in case there's an international reader). This permits an exaggerated amount of twist to the mainsail, which increases the higher up the rig (and further away from the mainsheet) you go. One result of this is nearly all of a topsail is almost never sheeted to an effective angle - just take a look next time your'e sailing to windward. If you're on the wind, most of the topsail isn't full and if it isn't full, it isn't generating any drive. Off wind it'll all pull and generate more speed. At least we agree about badly set topsails.

You miss my point about my old boat. I can't possibly take much more foresail - the boat has lee helm when the main is reefed - I don't have to put in a reef to balance the boat. I'm already somewhere near maximum.

Crossed wires slightly. My second paragraph was aimed at the original post.

When sailing hard on the wind the mainsheet will be doing the job of a kicker. Gaffers don't tend to have them because they have heavy booms instead.

 

[dur]

... nearly all of a topsail is almost never sheeted to an effective angle - ....

Well it depends. With our modest topsail, in conditions appropriate for it, the boat usually stops sailing properly before any of the sails lift. The staysail backing the main is more likely to cause problems for us.

 

[cliffordpope]

Most gaff rigs don't use a kicking strap (boom vang just in case there's an international reader). This permits an exaggerated amount of twist to the mainsail, which increases the higher up the rig (and further away from the mainsheet) you go.

That's an argument for a true vang, to the gaff peak, I'd have thought, rather than the boom?

 

[oldfrank]

My apologies for any crossed wires.

I just don't believe that mainsheets and kicking straps do the same job when controlling amounts of twist in a mainsail. Many gaff rigs simply don't have sufficient room for a kicking strap between the boom and a cabin top ... but on the other hand I don't see many weighted booms to hold them down. Drive from any mainsail is partly original shape but particularly about getting the leech tension correct. Mainsheets are just not entirely effective in controlling leech tension. You ease the mainsheet to a puff; the leech tension radically reduces; your topsail backs ... and you're going slower.

Rather than some form of vang to the gaff - and the angle's pretty acute - an integral topsail with the gaff acting almost as a top batten provides far better control - particularly if a kicking strap can be included in the sytem. Really there is no difference between the theory of making gaff or bermudan rigs work more effectively.

 

[Woodlouse]

It depends on what wind angle you are on. With the main sheeted hard in, a kicking strap will go slack as the mainsheet will be pulling the boom down as well as inwards. On other wind angles, granted the mainsheet will not be acting as a kicker in any way, but most of the gaffers I've sailed on have solid booms that weigh considerably. The only ones I've sailed with hollow booms have been of such a size that the spar still weighs considerably more than a bermudan boom.

A well made topsail, that is set properly should not start lifting before the main does and the extra luff length is key to actually getting drive when going to windward. If the topsail starts luffing, then bear off a few degrees, and you'll go faster and get there quicker.

 

[oldfrank]

"With the main sheeted hard in, a kicking strap will go slack as the mainsheet will be pulling the boom down as well as inwards."

Mainsheets and kicking straps do different jobs. Boatspeed is considerably about leech tension on your mainsail. If you're effectively using the mainsheet as a kicking strap ("the kicking strap is loose") then by definition your mainsail will have a tight leech. Most boats only need a tight (closed) leech in middle wind strengths - in light and heavy weather most go faster with their leeches slightly open - usually by allowing some 'twist'. A 'hooked' leech (where the leech is so tight it curls up to windward) can be caused by too much sheet tension and really gives boat speed the kiss of death.

On a more advanced rig, this might be controlled by setting the kicking strap, loosening the mainsheet and hauling the mainsheet track well over to windward. The mainsheet adjustment ensures that the desired leech tension is preserved and the mainsheet cannot pull downwards and tighten the leech. This is largely what the stainless hoops were for in the middle of dinghies such as Merlins and 505s - the angle of the mainsheet to the top of the hoop is reduced to such an extent that the sail is only feathered when the sheet is adjusted and leech tension remains fairly constant.

I'm probably taking this discussion where it doesn't want to go ... but even gaffers go faster if they get their leech tension right!

 

[mikeinkwazi]

Falmouth

Regret that topsails are usually disastrous for windward ability - particularly if they aren't set properly - just like dragging along an airbrake. The additional sail area can however help downwind performance ... or inland, win a little more breeze over trees.

Improving windward performance really isn't as simple as ordering a new sail. You may find that you could improve it by simply narrowing your sheeting angle or ensuring your fairleads are in the right position. You should also consider what a larger foresail will do to the balance. My own boat gets lee helm if I leave the big jib up with a couple of slabs ... it's ... well different. My best advice is to go and talk to a professional. I might be inclined to deflect their over enthusiasm by telling them your budget early in the discussion.

Tell that to the guys that race Falmouth Working boats!

 

[oldfrank]

Any time they want to take an analytical approach to their rigs! OF

 

[dur]

On a more advanced rig, this might be controlled by setting the kicking strap, loosening the mainsheet and hauling the mainsheet track well over to windward. The mainsheet adjustment ensures that the desired leech tension is preserved and the mainsheet cannot pull downwards and tighten the leech.

Does this imply that the end of the boom is bending up and possibly downwind allowing the leech to open? I am not suggesting that is bad, just wondering what the mechanism is.

If you tightened the weather topping lift so it worked just against the final heaving in of the mainsheet, presumably you would open the leech slightly. I suspect then the leech would vibrate horribly. Does this mean that it is technically impossible to have a perfectly set gaff main (on the wind) in the absence of a kicker and battens?

 

[oldfrank]

Battens don't really come into the equation - they just increase the area of roach you can set. Topping lifts don't help much - a single topping lifts carves a crease across the mainsail, whilst a double would be incredibly difficult to use to set the leech.

Certainly a boom may bend downwards with a stern mainsheet - but the only real way to tell is by standing behind the sail (which may have to be on another boat) and looking at the leech from behind. Many people mark their mainsheet at the point the leech begins to close, to stop a mainsheet hand doing just that. Put simply, (and add some windage into the equation) this is why a gaff rig isn't as efficient as bermudan to windward. And before every gaff-rigged home for old gribble starts to shout at me - a gaff rig is more efficient off wind. It's just that the racing fraternity has largely forgotten about gaff rig.

 

[Rum_Pirate]

Do you have a flying jib?

 

[Woodlouse]

Certainly a boom may bend downwards with a stern mainsheet - but the only real way to tell is by standing behind the sail (which may have to be on another boat) and looking at the leech from behind. Many people mark their mainsheet at the point the leech begins to close, to stop a mainsheet hand doing just that. Put simply, (and add some windage into the equation) this is why a gaff rig isn't as efficient as bermudan to windward. And before every gaff-rigged home for old gribble starts to shout at me - a gaff rig is more efficient off wind. It's just that the racing fraternity has largely forgotten about gaff rig.

I don't agree this is through the lack of a kicker. More to do with the fact that the luff length of a gaff mainsail is half that of a bermudan boat with the same mast height, and when going to windward, it's luff length that counts. That is why a good topsail is invaluable when going upwind, because it can double your luff length, and while still not as efficient as a single sail, it's far better than nothing.

You say that the racing fraternity has forgotten gaff rig, and this is true. But I have to point out that those who do race gaffers still have not given up the topsail, even (dare I say especially) when going up wind, which rather disproves your original point about it being an airbrake.

As for improving gaff performance with a kicker, I can't comment. I've never seen it done, but I'm sure it's been tried. I just wonder whether any improvement wasn't really worth the hassle which is why the idea hasn't spread.

 

[Bajansailor]

I think that a yacht like Alice III, designed by Simon Rogers, is a good example of how effective a topsail can be - there is a nice photo of her on http://www.rogersyachtdesign.com/ but you have to go to 'Past projects', and then scroll down to Alice III.

OK, so she has a modern racing boat underwater hull form, but that high aspect combined gaff main and topsail is not really very far removed from those radical modern 'fat-head' mainsails (fully battened at the top) seen on all the big die hard racers these days.