Lidgard Sails // News

28 March 2012

Mast Tuning Guide by Rod Davis

In general, the purpose of the mast is to support the sails and to aid their shape through controlled bend. To do this the mast has to have proper hardware with which to hoist the sails with minimum friction and to be able to change bend so that the crew can vary the mainsail depth for different wind conditions.

Masts, like any part of the boat, should have regular inspections. Every three months or so the whole mast section should be carefully checked for cracks. Often shroud attachments will get a lot of wear even to the point of tearing through the metal. Halyard sheaves should be free turning. Any excess weight should be taken out, like flag halyards, boom topping lift and unused halyards. Spreaders should be checked for sharp ends and chafe protection.

MAST TUNE

When your mainsail is designed at Halsey Lidgard Sailmakers care is taken to calculate the exact amounts of broad-seaming and luff curve so you can get a sail which sets properly and is easy to trim. The broad-seaming is applied to every seam and is matched and balanced by the luff curve in the front of the sail. All things being equal you should get a smooth, fast sail except when a sail is set on a mast that is improperly tuned. A mast out of tune can make your perfectly shaped mainsail look horrendous and detract from the boats performance. Before you make a call to the loft check your mast tune. The mast and the main must work together.

There are no mysteries to proper mast tune. Simply, the free-standing spar is supported by the shrouds and spreaders. They control the sideways or athwartships movement of the mast. Athwartships bend cannot be adjusted during racing so it is important that it is done the same for all sailing conditions. Fore and aft control and bend can be set up to change the mainsail shape for different conditions through use of adjustable backstays, mast partners and to a certain extend the boom vang. 

When tuning your mast you should first start with the headstay. The headstay controls the amount of rake or aft lean your mast has. This in turn effects the amount of weather helm you feel while sailing upwind. The longer the headstay the more rake and the more helm. On most boats we use two or three degrees of rake. Once you have decided on the forestay, pin it and forget it.

You need to get the mast lined up, athwartships along the centre-line of the boat and then adjust the rigging so that the entire mast stays in column when under load. To accomplish this, start at the bottom and begin by making sure your mast is centred in the boat. Measure the distance from the mast to the gunwale at the mast partners using a zero stretch tape measure. We've seen stock boats that do not have the deck partners in the middle. Once the mast is centred at the deck, wedge in some hard rubber chocks to keep it in place.

The next step is to get the jib hounds centred over the mast step and partners. With the rigging fairly loose, hoist the tape measure up a jib halyard (be sure to check if the halyard is on the centre-line of the mast) and measure from the jib hounds to the gunwale. Adjust and tighten the rigging so the distance on both sides is equal.

Now that the mast is straight in the boat, the upper shrouds should be tightened. A good rule of thumb is to tighten the shrouds enough so the leeward shrouds just become loose when the boat is heeled 20 degrees. Do this in a moderate breeze after you have done the dockside centring. Start off on the starboard tack and tighten the port shrouds on the leeward side. Make sure you count the number of turns you take up so you can duplicate the adjustment on the other side after you tack. You should end up with an equal number of increased turns on both sides so the mast remains in the centre.

The final step is to tighten the lower shrouds so the middle of the mast has the proper support and will not sag to leeward. Sight up the luff track to eyeball the mast to make sure it is as straight as possible. Normally the lower shrouds will be looser than the uppers.

Most smaller boats have rigs with single sweptback spreaders, one upper shroud and one set of lowers. Often experimenting with different shroud tensions and mast positions can have a large effect on the boat. Check with your local fleet champion to find out his latest mast-tuning techniques. A good tool to have on board is a shroud tension meter, which measures the actual load the shroud is under.

These devices are also handy if you trail your boat to different regattas. When you re-step your mast, you can use your tension meter to duplicate your previous tension settings. Failing this you should count the number of turns that you loosen on the shroud when you take the mast down so that when you put it back again you can tighten it by the same number of turns and end up with the same correctly tuned mast.