The Mainsail
The name is a bit of a giveaway as to its importance and usually its size. Our main is a square topped sail some 74 sq metres or 796 sq feet in size, so it is powerful and is usually first raised and last lowered.
The sail is made of heavy duty dacron which is favoured by the cruising fraternity for its durability and resistance to UV destruction. The faster performance and racing cats opt for less durable but more crafted composite materials like mylar.
“The main” sail is immediately behind the mast running along the fore aft aluminium spar known as the boom and it is controlled on Cooinda by the mainsheet, topping lift and the traveller. Unlike monohulls (single hulls) most catamarans do not have a vang as an extra control of sail shape.
Ropes that directly control sails are mostly known as sheets, thus the mainsheet. The sail is raised out of its storage in a “lazy bag” which is attached to the boom, wrangled in place by lazy jacks which are light lines in place to guide the sail up or down. A rope made of dyneema,known as the main halyard (halyards are ropes that raise sails) is attached to the head of the sail and is dragged up the mast luff track up by pulling of the halyard which passes over a pulley at the top of the mast down and is fed back to the steering station or helm helped along by an electric winch there.
Once the main is up, the mainsheet is used to control the sail shape to efficiently maximise the lift created as air passes over the sail. Think of it as like a vertical wing as on an aircraft with the curvature creating the lift needed to drive the boat along. So depending on where the wind is coming from determines how much the main is let out or pulled in. Like all sailing boats a cat cannot sail directly into wind and cannot sail any closer than 30 degrees into the wind and in reality a cat is best sailed no closer than 40 degrees from the wind direction. The further off the nose the wind is until 180 degrees off, the more the mainsheet is let out to best maximise sail area and lift. To further enhance this efficiency and sail shape, the boom which is attached to the mainsheet, can be allowed to move further inboard or outboard using the traveller control which again are a couple of ropes fed to the helm station.
If the wind gets too strong, damage or failure can occur to the rig which comprises the spars (mast & boom) and thick stainless steel wires (cable like). So in these cases it is important to reduce sail area or “reef” the sails. For the main we can put in 3 different reefs, each substantially reducing the sail area more. So for each reef position we let the sail down then tighten it up in its new position. This can usually be accomplished by just one person from our helm station.
* Dyneema is a composite fibre with a strength 15 times that of similar weight steel and 40% stronger than kevlar.
