Sorry, It may be a Dumb One

[hriehl1]

I am trying to get my running rigging prepped for launch (this summer, come hell or high water).

My boom slides in the mast track. The gooseneck has an underside block for a downhaul-purchase using a line up from a low eyestrap on the mast, thru the gooseneck-block then back down to a cleat on the mast. This serves the same purpose as a cunningham on a fixed-boom rig... right... tighten or loosen the mainsail luff?

I told you it may be dumb.... Thanks... Hank

[okawbow]

That's right. You can adjust luff tension with the boom down haul. I usually loosen mine when I raise the mainsail. I haul the main up to the proper height, and then set the luff tension with the downhaul. I will sometimes loosen it on downwind runs or light air.

[CharlieJ]

exactly so

[Quetzalsailor]

I'been thinking about that comparison between pulling the gooseneck down and the function of a Cunningham since you first posted. I think that it's more complicated and is indeed different.

On our 1970 North East 38, the luff can be tensioned with the halliard winch and/or the two-part tackle pulling the gooseneck down. I'm quite sure that the winch has lots more mechanical advantage so I think that the tackle is better used to set the position of the gooseneck.

On a Finn, the halliard is latched at the masthead, thus setting the position of the head of the sail as well as reducing the mechanical dis-advantage of the combined tension in the luff adding to the tension of the halliard; a Finn's mast is remarkably thin and flexy. The Finn's boom is either fixed to the mast with very little vertical freedom and no horizontal freedom; the mast rotates. The Finn's sail shape is modified (flattened) by pulling the boom down with the vang and bending the mast. Additional flattening is done by pulling down on the Cunningham. There's enough advantage to pull a huge pucker into the sail along the boom while flattening the luff above.

On a Flying Dutchman, the halliard is tensioned by a multi-part tackle, the masthead maximum hoist is set by the rules. The gooseneck is set by the rules. The mast is not nearly so flexy as a Finn's but the bend is controlled somewhat more by adjustable lower shrouds. And both the vang and Cunningham have multi-part tackles.

[Hirilondë]

A cunningham is like a short cut. It is usually easier and faster to use than the down haul. It is easier to use when the sail if full and drawing but it does basically the same thing. Some boats have a flattening reef as well. It takes the shelf or serious belly out of the foot of the sail while having very little, almost nil sail area reduction. Used with the cunningham you get a really flat main.

[CharlieJ]

Originally, the Cunningham was designed as a rule beater. It allowed more tension on the luff, without extending the sail past the black band put on by the admeasurer. The down haul would pull the tack past that band, the Cunningham doesn't .

Invented by Briggs Cunningham in the 1950's

[earlylight]

Charlie has it exactly right. The sail can be built at maximum luff length with almost no luff tension and when the breeze picks up the luff can be tensioned using the cunningham without pulling the boom below the black band. This allows a maximum size luff on the mainsail under all conditions.