Most Fireballs use continuous sheeting for their spinnakers, with a 'twinning system' to keep the crew from getting tangled up in the sheets. The sheets are usually tapered (ie, thin where they attach to the kite and thicker in the middle where the crew has to hold them). A benefit of going thinner at the ends is that in light airs there is less weight dragging the kite down, and the twinning system works better. Fireball chandlers can sell you tapered spinnaker sheets.

This shot shows the twinning system. The yellow rope with red and black flecks is the spinnaker sheet, which goes directly to the kite when it leaves the right hand side of the picture. The white rope with red and black flecks is the twinning line, which is tied to the metal ring. The spinnaker sheet goes through the ring, and has a bobble and a knot aft of the ring. The idea is that the knot hits the bobble, and the bobble hits the ring, enabling the spinnaker sheet to be controlled by the twinning line - see below.

You can see in this shot how the spinnaker sheet when under tension from the pole and kite runs until the knot and bobble hit the ring, at which point it can be cleated by the twinning system cleat as shown. The benefit of this is that the crew can now trapeze off this side of the boat, as there is no tension in the spinnaker sheet aft of the bobble. It is vital that the knot in the spinnaker sheet is put in the right place - the twinning system should engage to keep the pole from hitting the forestay. Note that the twinning system is only ever used on the windward side of the boat. You must uncleat the twinning line on the leeward side or suffer a nasty shaped kite.

When we get to the back of the boat (which has bizarrely changed to wood), you can see that the knot is capable of going through the pulley. The bobble isn't, but it will slide freely and won't hinder the sheet. This is the reason for using thin sheets and a bobble. You don't need to get the knot to come this far back when this is the windward side of the boat, but it is important that it will when this is the leeward side. Note also the way that the spinnaker sheet goes over and under the bridle, and see the footnote on this page for the no-knot alternative.

The same bit of boat as seen from the other side. The spinnaker sheet runs over the thru-deck pulley and is straightened out again by the side-tank mounted pulley. Then it heads for the thwart.

Where it goes through a free-mounted ratchet block and heads off towards the other side of the boat. The spinnaker sheet is 'continuous', and proceeds to got through the ratchet block on the opposite side, to the back of the boat and forward again to the kite via the twinning system on the other side. Basically, it's all symmetrical. Note the side mounted cleat, which can be used for stopping the slack in the sheet from pulling out of the boat and trailing in the water. Note also the protection on the thwart below the ratchet block (the ratchet block has a tendency to flap about and injure the varnish).

The twinning line is also continuous and symmetrical, and crosses the boat going above the jib sheets. When spinnakering, the windward side gets pulled in and cleated, the leeward side is uncleated so the slack is pulled through by the spinnaker sheet. There needs to be enough slack in the system that the leeward side twinner does not affect the leeward side spinnaker sheet. In effect, you want a twinning line which is about 4ft longer than the width of your boat.

Note that the knot in the spinnaker sheet is often dispensed with in favour of having the thick outer layer of the tapered rope come to the same point. Obviously this only works if the spinnaker sheet is made specifically with this in mind. In this case, the outer sheath has to be stitched very firmly to the inner at the point where the taper occurs, and it is this bit that hits the bobble. It's more elegant, but your sheet is a little heavier and it puts a lot more strain on the stitching for the taper.

For some more shots of the kite, and the info on the pole, click here.