Thursday, April 19

Basic Rig Tune

By Andrew Spaulding, Editor - Lakeside Story

Ahh, springtime in the boatyard – in the rush to get ready for launch date we often forget those promises we made to ourselves last fall. If it was in your thoughts to tune your rig and now you are thinking the better of it because you don’t have a ton of time to get the rest of your spring chores complete, read isn’t that tough to get your rig better than it was last season. I’m not saying that you’ll have it tuned perfect to the trained eye of the local sailmakers, but it will be better.

Step One: Make sure your rigging is ready to be tuned. Most rigs could use a good turnbuckle cleaning and re-lubricating. Clean the surface of all of your standing rigging. Dirt, old grease, and rust stains (we know stainless isn’t always stainless!) make it difficult for you to see cracks and other defects. This often is the longest part of the job since unscrewing the turnbuckles to clean the threads will take time. NOTE: If the mast is up during this process, loosen all the shrouds to hand tight and only disconnect one shroud at a time to disassemble and clean the turnbuckle. Lubricate the threads with a dry moly lube (molybdenum disulfide). Dry moly is made by multiple manufactures (CRC and Loctite being two) and is available at industrial suppliers such as Grainger, Fastenal or Dry moly is great for rigging because it resists galling and most solvents so it won’t come off easy. Also, its dry formula doesn’t attract dirt. Be sure to wipe off any excess dry moly as it is black and will stain your clothes and sails. Now you are ready to tune your rig. Start with all of the shrouds just less than hand tight. If you mast is deck stepped, be careful that your shrouds don’t get any looser than this during the whole rig tune operation.

Step Two: The forestay length will set your mast rake (distance fore and aft that the mast head is relative to the mast step with the mast straight). If the mast were to have zero rake the mast head would be directly over the mast step. Positive mast rake is when the mast head is aft of the mast step. More rake adds weather helm (tendency for the boat to round up to windward when the boat is close hauled). If you struggled with weather helm last season, shorten your headstay turnbuckle a couple of turns or vice versa. Most boats are designed to have some rake, so if you are looking for a starting point, I’d try a couple of degrees positive rake.

Step Three: Start at the top of the mast with all of the shrouds just less than hand tight. Since most mast steps are fixed athwartships, we must take it for granted that the mast step is in the center of the boat.  And since we aren’t getting involved in fiberglass work, we must take it for granted that the partner (hole where the mast comes through the cabintop) is centered between the chainplates. Believe me there are cases where these “givens” are not true! So, start the tune by getting the top of the mast centered between the chainplates. Pull a tape measure up the mast with your main halyard. Don’t pull too hard or let the tape run free because the main halyard shackle can jam in the sheave box at the top of the mast if it runs to fast. Measure from the top of the mast to the port and starboard chainplates. Loosen/tighten the cap shrouds as necessary until the measurements are equal. Likely this will take several tries. Tighten the cap shrouds evenly until the shrouds are taut. In most cases, this will be at least 5 whole turns past hand tight.

Step Four: Begin to tighten the rest of the shrouds working from top to bottom if your rig has intermediate shrouds. Once the shrouds are hand tight, tighten each side a couple of turns and then tighten the opposite side. As you cross the boat to tension the other side’s shrouds, sight up the mainsail track to see if the mast it straight (also referred to as being “in column”). Pic 1 shows a mast sight where the mast has a slight bend to port at the spreader. Assuming the top of the mast is centered; tightening the starboard lower shroud will fix this situation. You should see a bend in the mast if you’ve just tightened one side but haven’t done the other yet and when both are done to the same number of turns the mast should be straight. It is important to check each time for two reasons: when the shrouds are unevenly tensioned you will see bend in the mast and the amount you see will be an indication of how much each turn affects the bend. Secondly, if during even tensioning, you find mast bend you can adjust the number of turns to get it straight. While you are tensioning the rig make sure that you maintain some prebend. Prebend is the fore and aft bend of the mast. There should be a slight curve in the mast, so that the middle of the mast is forward. The amount of prebend that you should have depends on your rig and sail design. A small boat with a deck stepped rig should have about 1 inch of prebend. If the mast bends the other way (center of the mast aft of the top), we say that the mast is inverted…this is very bad in almost every case.

Step Five: Go Sailing. Check the straightness of the rig while sailing up wind. Adjust as necessary. It may take several tries to get the right combination of tensioning the different shrouds. If you have the feeling that perhaps you are tightening too much, remember that the rig is a system. Once the whole rig is tight, loosening the opposite side will often do the trick of making the mast look as if you tightened the offending shroud. Upwind if your leeward shrouds are slack they are too loose. The whole time check your mast column to maintain prebend. Take notes while sailing in different conditions so that you can fine tune your rig for next season.

As always, give us a call if you have any questions or send an email to

1 comment:

Bruce said...

Andrew, thank you for taking the time to write this very insightful piece on rig tuning.