Due to a number of factors, the main one being that my mast is assembled without the requesite hardware but with a wiring chace down the middle ... I'm going to use boom jaws rather instead of a goosneck.
I'm presuming that for this, I'll need some sort of line to hold the jaws down as the sail is hoisted up. That "seems" easy enough, but my concern is that when the boom swings, the mast doesn't turn and won't the down-haul cause some problems? Also, should I attach the down-haul right in the end of the boom as close to the mast as possible, or should I try to have it as far away from the mast as possible. My thoughts with the second option is that might assist in holding the boom down when on a run.
AndrewB
Typically you'd have two lines holding the boom jaws. One is on the open side and is a loose loop of line attached at the ends of the jaw legs. This line is run over a hook or run through an eye. It prevents the jaw end of the boom from dropping to the deck as you lower the sail.
The other line is as you describe. It attaches directly below the tack and often is the same fastener doing the job. An eye bolt (serves the tack) with an eye nut on the under side which the down haul is attached. It doesn't need to be a tackle, just a line to a cleat further down the mast will do. If you do use tackle you can tighten the luff with it, as it will act much like a Cunningham on a Bermudian rig, which can be helpful in effecting sail camber in varying wind strengths.
To act as a vang, it would need considerably more "purchase". By this I mean the angle would have to be well out on the boom, which general is 1/5th to 1/4th the length of the boom, measured aft from the mast. This is usually done with a "boom bail" (half moon of metal attached to the boom) and at least a gun tackle (three part) to provide enough power to flatten the beast as the sail is freed up. A vang is a powerful sail shape tool and can really increase the effectiveness of the main, but not often seen on a non-racing gaffer.
The down haul, tack and throat tackle attachments should fall directly on a common line. In other words, if you stretched a string from the throat cringle, down the luff, past the tack to the down haul eye, it would hit all the centers of these attachments. If they don't then weird wrinkles, chafe and difficulty hoisting or dousing will result. This is why the throat halyard has to be spaced away from the mast a little. It aligns the throat tackle with the tack, so the hoist doesn't bind up against the mast or try to pull away from the mast during a hoist or douse.
If you can rig a separate vang, it's a powerful tool and well worth learning how to use it. Ditto a gaff vang which controls the amount of twist and gaff rise permitted for the conditions.
Thanks Paul.
Lets see if I understand what you are saying (I'm still on my first pot of tea)
I need one line that attaches to the open end of the jaws and is fastened to the forward part of the mast. This one keeps the boom up when the sail is lowered. This is a separate line from the one that spans the jaws (parrel?)
I need a second line to keep the boom down as the sail is hoisted. This one should be attached opposite the tack of the sail and attached lower down the mast.
If I wanted to improve sail shape I "could" rig a vang, but with the cabin in the way that's not practical.
I'll have to experiment to see how long these lines need to be in order to allow free movement of the boom - do you have any thoughts on that? I was figuring at least 8" or so.
To hold the boom up you can use stops, attached to the mast (one on each side) which will not permit the jaws to slide past them. The parrel will keep the boom in reasonable relationship with the mast and permit adjustment. The boom stops should be a little lower then where the boom normally lives when underway. This allows you to tension the luff with a down haul or Cunningham, without bottoming on the stops.
Or you could use the loop of line I mentioned in the previous post, which would be in addition to the parrel. The loop of line was used in admiral Nelson's navy with much success, but stops are a simpler solution, which don't stretch, break or wear out.
The down haul spaced 8" below the boom will permit enough movement, though rigging a tackle in that amount of space would be difficult. Most gaffers tension their luff with the throat halyard, so tackle on the down haul isn't necessary. A Cunningham is generally just a whip tackle.
A vang doesn't have to be permanently attached to the mast or boom. A common method on gaffers is to have the tackle clipped on the boom. When they free up the sheets, one end of the vang is un-clipped and attached (snap shackle) to a pad eye near or on the rail. As the boom rises, the vang is tensioned. Mounted this way, you'll relieve a lot of pressure on the main sheet too. In the event of a jibe, the snap shackle is released and attached on the other rail. This can be done during the jibe or after it's completed.
Just a line dangling from the boom can work as a vang, if run down to the rail and to a cleat or pin. You don't have the power of a tackle, but these sails aren't very big.
The idea is to pull the boom down so you can shape the sail, maybe getting rid of the annoying, speed robbing, diagonal wrinkle.
A gaff vang is usually double ended, so it falls on both sides of the sail, with only one side being tensioned at a time.