Thread: Balanced Lug - percentage each side of mast

I have no big experience in balance lug sails... than they really better in gybe that unbalanced bermudian sails. My sails circa 10/90%, but differences and balance benefits are clear - BETH gybeing gently. I think - balance 30/70% can more improve it, that for example - sqare sails gybeing most gently.

Hi AJ,

The biggest limiting factor is the halyard system that I use. It is the nicest halyard system I have found for lug rigs, but you can't move the point where the halyard meets the yard back behind half way.

So if you want a tall peak it tends to reduce the amount of possible overlap in front of the mast.

Other halyard arrangements might be more tolerant and allow bigger amounts of sail area in front of the mast - but they do tend to be a lot more tricky compared to the simplicity of the one I use.

Putting the halyard back to far, or rather the PIVOT line back too far is that the sail might "sheet on" in a gust rather than want to ease off.

With balanced rudders you can get the same effect if the pivot is too far back - it is pretty exciting when it happens - the rudder tears itself out of your hand. The "rule of thumb" often quoted is a maximum "balance" in front of the rudder pivot point should be no more than 20 to 25%. The reason is that the force developed by the rudder (or sail) is not evenly distributed over the surface, but the front part of the sail or rudder makes the biggest contribution.

This is because that's where the wind or water direction is bent the most. And also explains why leading edge length is more important than area when flow around the foil is attached.

So as you approach the limit of where the pivot can be without anything nasty happening, sometimes a small change in conditions can be enough for the sail or the rudder to "flip over".

Of course square sails get around that by having "braces" to pull the luff back as well as "sheets" which pull the leach back.

MIK

Best wishes
Michael

Originally Posted by Boatmik

Hi AJ,

The biggest limiting factor is the halyard system that I use. It is the nicest halyard system I have found for lug rigs, but you can't move the point where the halyard meets the yard back behind half way.

So if you want a tall peak it tends to reduce the amount of possible overlap in front of the mast.

Other halyard arrangements might be more tolerant and allow bigger amounts of sail area in front of the mast - but they do tend to be a lot more tricky compared to the simplicity of the one I use.

Putting the halyard back to far, or rather the PIVOT line back too far is that the sail might "sheet on" in a gust rather than want to ease off.

With balanced rudders you can get the same effect if the pivot is too far back - it is pretty exciting when it happens - the rudder tears itself out of your hand. The "rule of thumb" often quoted is a maximum "balance" in front of the rudder pivot point should be no more than 20 to 25%. The reason is that the force developed by the rudder (or sail) is not evenly distributed over the surface, but the front part of the sail or rudder makes the biggest contribution.

This is because that's where the wind or water direction is bent the most. And also explains why leading edge length is more important than area when flow around the foil is attached.

So as you approach the limit of where the pivot can be without anything nasty happening, sometimes a small change in conditions can be enough for the sail or the rudder to "flip over".

Of course square sails get around that by having "braces" to pull the luff back as well as "sheets" which pull the leach back.

MIK

Best wishes
Michael

Don't mean to offend but,,,the way i look at it,,,a ballanced lug looks like a sloppy gaff rig.except the spars are not attatched to the mast..Can some one en lighten me?

Always thought the same in days of yore.
Took the TS to enlighten me. When running, that whole sail & long boom
moves the centre of effort waaaay outboard of the in-water centre of drag.
Turns into a Big Lever fighting the rudder.

Gaff does the same, plus needs additional strength in mast & halyards to
tension the sail. The halyard & topping lift have mechanical disadvantage on
the gaff with respect to its fulcrum against the mast. The only resistance to
sail twist is a vang plus weight of the boom.

Balanced lug keeps the centre of effort closer to the centre of the boat, and
the halyard/down-haul aren't fighting any mechanical disadvantage. The mast
doesn't have to fight a sideways pressure of the gaff or boom in fulcrum against it.
It's a low-stress rig, so can be made with lighter spars & cordage. Plus, as it
naturally resists sail twist anyway, a much lighter vang can be used.

It's not the perfect sail, but done the way MIK designs them, it sure is a
relatively low-stress way of powering a boat. In fact, now that I have acquired
a project TS16, I might talk to MIK about sail plan rather than winging it.
A cruising sail boat should be relaxing.
cheers
AJ

About all I could add to AJ's exposition is a little footnote from history.

Around the 1900s the balance lug was the premier small boat racing rig. The poor performing relative was the gaff.

The reason goes back to the most important single reason for performance improvement.

The control of sail twist.

The gaff doesn't and can't without adding vang or kicker. The balance lug has some naturally, not as good as having a vang.

The attached pic shows biting midge"s goat with its ten year old sail. Not much sign of inefficiency there!

Best wishes
MIK