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Project: Rig Tuning


This page contains Randy Hough's Marine Tuning Guide, reprinted with Randy's permission. Although originally developed for Catalina 27 owners, much of this material is relevant to C34 owners, as well. Randy cautions that this tuning guide should be used only for boats with riggin in good general condition; he doesn't trust any rig that's over 7 years old!


Basic Rig Tuning for Single Spreader Rigs (mast head / non-bendy spar)

You will require:

  • Wrenches to fit the turnbuckles
  • Lubricant for turnbuckle threads
  • Your boat in a slip
  • Flat calm (early morning)
  • Notebook
  • Beer


  • Your first mate or other crew (requires more beer)
  • A piece of piano wire at least two feet longer than the luff of your main
  • Loos (tm) tension guage

The Process:

  1. run around the boat and put a few drops of lube on the threads of each turnbuckle while you are making sure your wrenchs fit.
  2. loosen the shrouds to just short of floppy
  3. center the masthead athwartships, use the main halyard to measure to the cap shroud chain plates on either side of the boat. Adujust the caps until the measurement is equal P & S. Then tighten an equal number of turns until the caps are taught. (about hand tight on the turnbuckles)
  4. sight up the sail track on the aft side of the mast, it should be dead straight athwartships. Use the lower shrouds to bring the mast in column. Check for fore / aft bend. The mast should be straight, or have a very slight forward bow (masthead aft of spreaders). Tighten all lower shrouds an equal number of turns checking to make sure the mast is still straight, until single lowers are a little *tighter* than the caps, or double lowers are a little looser than the caps.
  5. have a beer, the mast is centered and straight!
  6. Use the spinnaker or jib halyard to heel the boat 20 degrees (listen for the china or television hitting the cabin sole) count the turns as you take the slack out of the "leeward" cap shroud. Note if the mast bows out of column athwartships, and which direction ("weather" or "leeward"). Measure and note the tension in the cap shroud while heeled with your guage if you have one. Check it against the rated breaking strength of the wire, it should be under 20% of breaking strength. If its greater than 20% STOP! the rig is not the correct size (unlikely on production boats), you haven't figured out how to read the guage correctly (likely, it takes some practice), or the boat is too tighly moored or aground. Ease the halyard.
  7. Clean up the broken china or TV. Tighten the other cap shroud the same number of turns that you took on the first cap. Use the main halyard to assure your self that the masthead is still centered
  8. If the mast bowed to "leeward" at the spreaders, tighten the lowers (about half the turns you took in the cap)
  9. Heel the boat the other way to 20 degrees (listen for Chapman's, Bowditch and your wine hitting the cabin sole) If you counted correctly the new "leeward" shroud should be just taught. The mast should be straight athwartships at the spreaders. Note any athwartships bend. Ease the halyard.
  10. Clean up the mess below (sheesh don't you *ever* learn?) If the mast was bowed to "leeward" at the spreaders tighten the lowers some more, the forward lower should be tighter than the aft lower. Sight up the mast to make sure it is still straight, use the forward lowers to straighten it as needed. In the unlikely case that the mast bowed to "weather" loosen all lowers an equal number of turns, keeping the forward lowers slightly tighter than the aft lowers.
  11. Secure below deck items (before you trash the sextant and binocs). Heel the boat to 20 degrees, make sure the mast is straight, and none of the "leeward" shrouds are loose, if they are, count turns until they are just taught. Heel the boat the other way, and take up the same number of turns on the other side.
  12. Have a beer, promise first mate to replace the china and TV, and pump wine out of bilge.
  13. Go sailing. check the mast for athwartships bow and use lowers to correct as needed (not likely). Tighten the backsaty adjuster, and sheet the main in hard, the mast should be dead straight fore and aft or have a slight (1") forward bow at the spreaders. The aft lowers should be looser than the forward lowers. Turn downwind. Ease the backstay and main. Take the spare jib halyard to the stem fitting and crank it tight. The aft lowers should be tight. There must be *NO* aft bow in the mast. If there is, ease the aft lowers equally, and take up the forward lowers the same mumber of turns.
  14. Have a beer, your rig is now tuned better than 90% of the rigs in your marina. Look at your notes, you should be able to create a tuning guide for your boat: Hand tight plus X turns for each shroud. If you have a tension guage take 3-4 readings on each shroud and note the most repetable one. (you didn't do all this work and not keep notes did you?)

Note: Your rig will must likely be tighter than most, and almost for sure tighter than the builders guide. Don't worry! Any well designed production boat that does not have a reputation for shedding masts, will sail all day heeled to 20 degrees. The tension in the loaded (weather) shrouds while sailing will be the same at 20 degrees of heel if the shrouds are loose or taught at rest, since the force to heel the boat remains constant (heeling force is transmitted to the hull by the rig). Sloppy rigs are slow and *increase* shock loads on the shroud system (the same twine that cuts your hand before breaking under a constant strain can be snapped with a quick jerk).

Advanced tuning


Take all the junk off the boat, fill the water and fuel tanks about halfway, pump out the holding tank. Look at the static hull trim. The boat should have no list (tilt) to port or starboard. See what you can move to correct the trim if needed. Fore / Aft trim is tougher, the boat should sit on her lines with normal crew in normal positions. Light boats where crew is a bigger percentage of total displacement will lie bow down (transom up) when unladen. You can go as far with this as you like: Lighter is better, move heavy items as close to the center of the boat as possible. If you need to correct trim, it is better to remove wieght from the heavy end /side than add wieght. Take everything you haven't *used* on the boat in a year off (save them for the next swap meet).

Light air adjustments

More bow down trim, crew below or just forward of mast, both anchors on the rollers (disguise yourself as a cruiser). Only enough water and fuel on board to get through the day. This trim decreases wetted surafce area on most hulls, reducing skin friction.

Mast Rake / Prebend

Tie that big rusty wrench that you never use to one end of your piano wire, hoist the other end to the masthead on the main halyard, to create a huge plumb bob. The wire should lie behind the mast, slap a piece of tape on the boom and mark where the wire crosses. This is your mast rake. Adjust mast rake using the *forestay*, longer to increase rake (wire further from mast) shorter to decrease rake (wire closer to mast)

Start with minimum rake. 0"-1" Your boat should have 2-5 degrees of weather rudder angle when sailing upwind. The higher the angle of heel, the more rudder angle is needed to balance the boat. More rake (masthead aft) creates more weather helm, less rake creates less or lee helm (leeward rudder angle *kills* upwind performace)

A good all around setting is 5 degrees of weather rudder at 15 degrees heel. Adjust rake (using the forestay) to get the balance right. Every time you change the rake, check the fore / aft bow (prebend) of the mast and adjust lower shrouds as needed to avoid inverting the mast (aft bow).

Light air adjustments

Increase rake to give more weather helm at low heel angles, the rudder must *never* have leeward angle when sailing to weather. Loosen the lower shrouds to allow the mast to sag to leeward at the spreaders to power up the main a bit.

Heavy air adjustments

Decrease rake to give no more than 7 degrees weather rudder just before you reef or shorten sail. (18-20 degrees heel max) Keep lowers tight so the mast is dead straight athwartships. More tension on forward lowers to prebend mast and flatten (de-power) the main.


Backstay tension controls jib / genoa luff sag and mast bend (depends on mast section) More sag = fuller sail (more draft, more power, points lower) Less sag = flatter sail (less draft, less power, points higher) Forestay length controls rake.

Ease the backstay, the forestay should almost flop. This is 0% backstay.

Tighten the backstay about halfway, measure the tension in the forestay and note it.

Add measured ammounts of backstay tension logging the forestay tension each time. Check mast bend also, if the mast bends more than 20 - 25% of the fore / aft demension od the section STOP. Tighten aft lowers to limit bend.

At some point you may notice that the forestay is not getting tighter when you add backstay, this is because the hull is bending . STOP , mark the backstay adjuster at this point (we call it banana trim... think about it...) this is 100% backstay. (if you have hydraulics, note the pressure) Don't worry if you run out of adjustment before the boat bananas, good stiff boats won't under normal loads, and most non-hydraulic adjuster systems don't have enough purchase to bend the boat

Mark the adjuster for 25, 50, and 75% backstay (or make a pressure chart)

Basic Adjustments:

Upwind: 25-100% backstay as needed to control luff sag / power to balance the boat.

Downwind: 25-0% backstay to let the rig move forward .


Keep a rig tuning log. Note changes and the boats performance. $40 buys a rig tension guage, these are great for returning to known settings and for catching problems early (after initial strech shrouds should maintain tension, if one is loose every time you check it, you *will* find something wrong with the rig).

Multiple spreader rigs are more complex to tune, but the order is the same. Center mast, cap shrouds first, then intermeiates and lowers.

Have fun!

Please send your comments and feedback to Randy Hough

Important: The opinions expressed here are those of the individual contributors to this page, and not those of the Catalina 34 National Association or Catalina Yachts, Inc. Additionally, this material has not been reviewed by Catalina Yachts, Inc. for technical accuracy. This page's maintainer cannot guarantee the accuracy of this information or the desirability of suggested modifications or upgrades. Please obtain assistance from a competent marine mechanic or boatyard prior to making any significant modifications to your vessel.  

Last modified by Phil Imhof, Wednesday, August 11, 2004 . Copyright 2001 by Catalina 34 International Association.  All rights reserved.