Rig Tension
How much tension should I put on the Rig?
By GSTDPeterO
Setting up your mast
Quotes from AOL Sailing Forum Leader, Bill Hamm, who recently suggested: "Unless you are racing, use care in over tensioning the rig. Unless you're looking for the last iota of speed, a somewhat loose rig is easier on the equipment. Just snug is usually just fine."
In the Sailing Forum we get many questions about keeping the shrouds tight enough to prevent the leeward shroud from going slack when on a tack. Not a good idea. Most boats today are plastic. Given enough shroud tension for long enough, you will find that eventually you will be able to slide into that narrow slip with ease. And if you pay for your dock by the foot, you may qualify for a lower fee if you habitually keep maximum tension on your backstay<g>. Not a good idea.
In last week's column I noted that Nigel Calder suggests 15% of breaking strength for upper shrouds, 20% for the backstay, and something less than 15% for the lower and intermediate shrouds, as these are shorter than the cap or upper shrouds. As you beat to weather your leeward shrouds will go slack. That's fine. Don't worry about it.
Before setting tensions, you need to position the masthead. I like to use a steel tape. Make sure the lower shrouds are slack. Shackle the tape end to the main halyard and run it to the masthead and cleat the halyard. Be careful not to jam the shackle into the masthead. Applying a comfortable tension, measure to one of the upper chainplates. Now go to the other side of the boat and see if, with the same tension applied, you get the same measurement to the top of the chainplate. If not, adjust your uppers accordingly, until you get fairly equal readings. Now measure to the backstay chainplate and record the result. This gives you a reference if you later want to correct a bad helm, or to simply duplicate this setting next season. If you don't have a better idea, I would start with about six inches of aft rake in the mast. Measure this at the mast step by hanging a wrench from the main halyard.
Now, using a Loos Gauge, adjust the uppers and then the backstay to Calder's suggested tensions. Measure to the shroud chainplates again. Did anything change? If so, re-center the masthead and adjust your tensions. Now tension the lowers. Then sight up the mast track, to see if the mast is straight. If not, adjust the lower and intermediate shrouds until the mast is straight.
You will want to check the mast while under sail to see if it is still straight. As the wind increases some forward bow in the middle of the mast is usually good, as it will help to flatten the main. If you are racing you will want to make adjustments based on the expected winds for each day.
Wait! We didn't check the forestay tension. Nope. Forestay tension is generally determined by the tension on the backstay. Many modern boats have some way to easily and quickly adjust the backstay, adding tension as the wind increases. Don't forget to ease that backstay on runs and once back at the dock.
For a simpler measure of rig tension, just walk around your club or marina and test the shroud tensions on other boats of similar size and style to yours. Be sure to check more than one. How do you know that the first boat you check is correct? Maybe he's the club champion. That might be a good place to start.
