the challenge…

 The diamond lug sail is a new type of sail. It is the result of 5 years of development.

Why a new type of sail?

The best single sail for high speed sailing is probably the windsurfing sail, however, windsurfing sails can not be reefed. Windsurfers just change the size of their rigs depending on the strength of the wind.

On a sailboat that is going on a journey, it is impractical to bring multiple sized rigs. Many small sailboats employ an unstayed roller reefable sail, however, these sails are hard to tension and they do well until the wind starts to blow over 20 knots.

Another option is the unstayed cat rig, which can be reefable, however, the cat rig usually has a tall mast. The mast must be lowered when passing under low bridges along coastal water ways.

The solution is a lug sail with a shorter mast. A typical balanced lug sail is excellent in most pointing directions and in most wind conditions, however, most lug sails are not designed to drive a boat more than 10 knots.

To drive a sailboat 10-20 knots, you need a stiffer sail.

The diamond lug solves this issue with 2 new features:

1) the upper spar is inside a luff pocket (similar to a windsurfing rig)

2) the top of the sail is square and is held in place with a peak batten

3) to make up for the increased sail area up top, the halyard connection point is moved upwards

4) just like other lug sails, the sail is easily reefable with 2 reef points

5) 2 half length battens can be used in the lower half of the sail but it is not yet clear if these are necessary

Scale model testing has been highly successful.

Plans for the diamond lug sail rig are included in the plans for the Wingmaran 15.

I may offer separate plans for the diamond lug sail once full scale testing is complete.