Monday, July 5, 2021

Fixing Mainsail Crease

Fixing our Mainsail Crease

You have to look carefully, but there is a diagonal Crease in our mainsail extending from just above the 2nd Reef Cringle down to the Clew of the mainsail.

This photo was taken as we crossed the start line of the Palm Beach Regatta Coastal Race in June 2021.
We're not racers! But a great opportunity to sail with a bunch of other boats is tough to turn down. We did well, beating our nearest competitor by 14 minutes over a 30 nm race. However, that crease really spoilt our sail shape. From all of the sail trim studies we have made over the past year (thanks Covid) we know that the sail should be smooth in order to allow laminar flow of the wind over both sides of the sail. The diagonal creases caused about a 2" ruffle in the surface of the sail.

I discussed the issue with a good friend with a lot of sailing experience. He suggested that I slack off every line on every sail trim system. That includes: Main Halyard, Lazy Jacks, Vang, Main Sheet, Reefing lines (4 lines - Reef #1 Downhaul & Outhaul, Reef #2 Downhaul and Outhaul) and the Clew Outhaul and finally the topping lift.

So that's what I did and the diagonal crease remained! I was getting worried that we had stretched the sail sometime over the past 5 years since they were new, that's a $3,000 error! Grrrr!

With everything slackened off, I shook the boom to see if there was anything still causing the creases.

Found it!!!

Our Mainsail was designed as a Loose Footed Main. The only point of restraint at the boom is at the Tack (front lower corner of the sail) and the Clew (aft lower corner of the sail). However, if the clew outhaul ever broke, the main would slap itself to death or at the least a very expensive repair. In order to protect the sail, the sailmaker installed a strap that went around the boom and through the outhaul (clew) cringle. The problem was that that strap was preventing the clew from moving when the outhaul was released !!! 

The strap is a piece of 1" webbing about 3' long with velcro sewn on both sides of the strap, so when it's wrapped around the boom, the velcro adheres the surfaces together. But the strap prevented the clew moving!

What's the purpose of moving the clew?

Good question.

The outhaul pulls the clew (aft lower corner of the sail) towards the end of the boom (the end furthest from the mast). As the clew is tensioned with the outhaul, the bottom of the sail is flattened. This reduces the depth of the sail and improves higher wind performance while reducing heeling. In light air, the outhaul is eased to increase the power in light winds or in choppy seas (that power is more consistent as the boat rises and falls and so helps push the boat through the waves.)

And, the whole reason for this. By allowing the clew to actually move for and aft, it eliminated the crease in the sail. This should result in smoother, laminar flow of the wind over the sail and that means better sailing! 

So, Thanks Ira! Your advice helped solve the problem.

See you out on the water.

Oh! what do I do about the safety strap? I'm making a new one that will have more slack and thus will allow the clew to move.

Old style 'spindle' sheaves
broken and worn.
And! While doing this I found the the Sheaves on each end of the boom that allow the outhaul to be trimmed or eased were failing. They were also simple spindle sheaves. I replaced them with Ball Bearing Sheaves. Now the outhaul is easy to adjust and the clew actually moves. Here's looking forward to seeing you on the water, and hopefully it will be as we head off towards the horizon.


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