Sail tuft position for Lug Sails

We provide leach ribbons on our standard sails. These are quite easy to use as in a previous article.

We don’t normally supply telltales in the body of the sail. There are some reasons and quite a bit of background around this decision.

sail testing Goat Island Skiff - reallysimplesails.com

Conventional sail body telltales should be at the maximum depth of the sail. That makes the windward telltale more accurate for judging the depth of the sail. If you can’t get the windward tuft so placed to fly then the sail is too full and the air is finding a short cut across the windward side leaving the windward tuft hanging or flipping around

Goat Island Skiff, Dorestad RAID, Netherlands - storerboatplans.com

The “problem” with lug sails is that you have a wake from the mast down one side of the sail. We know it has very little affect on the amount of actual power available, but it is going to mess up the telltales on that side.

I think that a telltale in the head of the sail near to or above the mast top will work.

And you might be able to get some others to work some of the time and make some decisions about settings on one tack knowing that they are more or less duplicated on the other, where the telltale might not be working so well

Leach Ribbon or tuft behaviour on lug and other sails - really simple sails

The way the leach ribbons work is that when a sail is oversheeted there is a wedge of separation that starts at the back of the sail. The wind can’t quite make it to the edge of sail without losing contact on the leeward side. Separation.

And the leach ribbons pick that up nicely.

Another function apart from sail setting is using the telltales/tufts for steering. To find the low acceleration part of the groove or the higher pointing. There is also a separation bubble at the luff – a regular tuft system won’t spot until the sail is actually stalled, but the Gentry tuft system will – link. That is why jib tufts are a bit more forward than on the main … in the hope that the separation can be spotted – because when it gets to the maximum sail depth then the flow on the lee side will separate completely, never make contact with the sail again.

Arvel Gentry - how sails really work

But EXPERIENTIALLY it is possible to sense all of this and you don’t have to have any tufts at all.

We know the feeling of power and speed drops when the boat starts luffing even a little. Drop down a little and the power available becomes exponentially larger through a very narrow angle. Drop away from the wind a bit more and it suddenly disappears.

That’s how we are teaching people on Lake Ta’al. To really note the feeling of being in the groove directly and to sense the radically different feeling of the boat. The power really comes on with a lug and it is clean and precise because of the unimpeded luff.

A few hours steering like this and sensing the power band is time well spent. Our students pick it up in an hour or so, any extra time is refinement.

I’ve realised in my own sailing the reason I don’t need to luff the sail to keep the right angle like a learner is because I feel the powerband directly. I think most people comfortable with steering do, but I’ve never really analysed it before.

The familiarity with the narrower power band means the steerer doesn’t need to do little trial luffs to find out where the wind is so often.

A mast or spar on the front of the sail will allow quite a range of angles of attack because it is rounded enough to help direct flow onto the sail without becoming detached so it is not as clear in this respect as a jib or lug luff.

Here is a link to the Arvel Gentry article. One of the great thinkers and explainers.

Arvel Gentry Tuft System

 


 

 

Leave a Reply

Your email address will not be published. Required fields are marked *