A gaff rig sail has two halyards. One is at the throat of the gaff, the part of the gaff that slides along the mast. The other is usually a multi-part rig that lifts the tip or peak of the gaff higher than the throat end. This multi-part tackle attaches in different ways on different boats to the gaff itself, but usually dead ends near the outer tip of the gaff, runs somewhere to the mast and then back to a block ( and possibly a bridle) somewhere near the mid-point of the gaff. From there back to the mast and down to the deck.
My guess is that your throat runs on that track on the mast and throat halyard is the one run througn the sheeve in the center. The other two are for the peak halyard. The reason ther are two is because one is part of the above mentioned peak halyard tackle, and the other turns the halyard to run down to the deck or base of the mast.
When the day comes to hoist your gaff sail you take both halyards in hand together and raise them together until the throat is at its highest point. Make the peak halyard temporarily fast and use both hands to get good tension on the throat halyard so you have a nice taught luff on the leading edge of the sail along the mast. Now make the throat haylard fast and return your attentions to the peak halyard. Haul up the peak halyard observing for wrinkles to run from the outer peak end of the sail diagonally toward the mast. This is the correct position to make the peak halyard fast and your sail will now set properly when it fills with wind.
When you get a little more advanced you can then play with the shape and depth of draft of the sail by adjusting the peak halyard tension slightly. A little lower flattens the sail, a little higher or tighter and the draft increases. This is why most gaffers have a multi-part tackle on the peak halyard for the gaff, so it can be adjusted while sailing if the conditions warrent.
I have never seen running back stays that had turning blocks on the mast. The tackle for running backs is always at the bottom end with a strong tang or the like on the mast.
Someone mentioned lazy jacks and I suppose that is another possible explanation for the extra blocks, but lazy jacks would not have to be run anywhere near to the mast head.
Peter
