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post #1 of 122 Old 04-24-2008 Thread Starter
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Adjusting Your Rig, step by step.

Small introductory disclaimer (because you Americans love to sue people):

For the record it is my strong personal opinion and belief that any and all work performed in a boat’s rig should be performed and done by appropriate professionals, (that know what they are doing, because I have seen too many “rig professionals” that don’t have a clue of what they are doing), do it yourself only if you have at least 3 ounces of brain and if have been around boats long enough and know with a minimal amount what you are doing..If you don’t, PLEASE DON’T TOUCH IT, IT’s NOT FOR YOU.

If you damage your rigging, your boat and/or hurt yourself or others don’t come here blame me..get a life, I wrote this for intelligent people only.

This I write bellow is to help you get by should you not find a rigger near you. IT IS FOR INFORMATION ONLY.

Now the post:

A few months ago, one of our most dear friends here at Sailnet was stranded with a mast down problem, in a location where proper rigging professionals were scarce and the knowledge about rigging of the existing “rig professionals” was par to the local baker, veterinary and dentist…(I think he mentioned they were the same guy)…

So, and since he asked, I wrote him a small letter (sorry for the spelling mistakes and grammar), where I tried to explain to him how to set his rig in a way that would allow him to continue his journey and even get by in the future.

Please note this is my own experience, and other people may have better I say, I am not a professional, and do this based on my own experiences. So if you don’t like it, write you own and post here. It will only enrich the site. Please keep disagreements to PM level only, and I will discuss with you, should you not like or agree with me. Thank you.


First you need understand this:

We will do 3 basic adjustment types:

Lateral Adjustment
• Longitudinal Adjustment
• Sailing (done later) Adjustmet

1) Lateral Adjustment.

(NOTE: this has to be done in a day with no wind with the boat perfectly horizontal, shift weight if you have to, to balance the boat).

a) Install the mast, and make sure the intermediate and lower shrouds are lose, but attached.

b) Make sure the stays and back stays are attached but not over tightened. At this point you want the mast as vertical as possible.

c) Remove the boom, or lower it so its not pulling on the mast, we will need the topping lift.

d) If the mast is keel stepped, remove the centering thru deck bushings at this stage.

e) Once the mast is up and vertical by eye observation, take the topping lift or the main halyard and measure the distance from the top of the mast to the boat’s toe rail on port side. Repeat on starboard side, make sure the location of measure is symmetrical and at the same distance from the bow.
f) If the distances are not the same, tighten the side with the longest measurement.

g) Tighten the upper shrouds to a snug fit the same number of turns on each side, until the mast is perfectly centered.

2) Longitudinal Adjustment. (Rake)

(NOTE: this has to be done in a day with no wind with the boat perfectly horizontal, shift weight if you have to balance the boat).

Rake will help increase or decrease Weather helm. Aft Rake increases weather helm, improving pointing, forward rake does the opposite.

Normal rake is 1 to 2º degrees aft for cruiser boats and up to 4º deg aft for high performance racers.

a) Install a bucket with water under the boom by the mast.

b) Attach a heavy object to the main sail halyard and dip it the bucket but it should not touch the bottom of the bucket. (The bucket and water are used to dampen the swinging of the halyard.)

c) Measure P, which is the distance from the boom to the top of the mast.

d) Measure the distance from the halyard to the edge of the mast, at the gooseneck.

The distance should be as follows in the table:

Note, if you have a T shaped mast head, for halyard sheaves, add the distance of the T leg to mast to the above calculations.

Here is an example:

Our friend’s mast is 42 feet long, or 12,8 meters, therefore for:

0,5º Deg rake = 11,52 cm = 4,33 Inches
1º Deg rake = 22,4 cm = 8,66 Inches
2º Deg rake = 44,8 cm = 17,3 Inches
3º Deg rake = 67,2 cm = 26,3 Inches

He also had a mizzen mast, and in his case, the mizzen mast has 21 feet, or 6,4 meters, therefore, for:

0,5º Deg rake = 5,76 cm = 1,96 Inches
1º Deg rake = 11,2 cm = 4,33 Inches
2º Deg rake = 22,4 cm = 8,66 Inches
3º Deg rake = 33,6 cm = 12,99Inches

e) Measure the distance from the halyard to the edge of the mast, at the gooseneck.

f) Adjust the rake as needed, using the above table, using the stays and triatic also, (should you have a triatic), don’t forget that, ok?

g) Once all is where it should be, and the mast is where you want it, I would go with a rake of 1 º Deg for both masts for cruisers and 3% for racers.

h) Later on, once you sail, if you "feel" you need more rake use above numbers and adjust all again.

Note if you have a mizzen, for the triatic, you need a little help to get up there, but try to do it once with only one climb.

3)Dynamic Adjustment.

This will be obviously done later, if you feel you need more bend or better mast flexibility. See note further down, as at this stage we need to talk about tension in the rig.

The next step is therefore set the right shroud tension.


1) Shroud tension

We now need to tension the upper shrouds, so let’s tension them.
The values I calculated for our friend in the example are as follows:

a) All shrouds, including the upper, intermediate and lower are to be tensioned to 15% of the cable breaking load which in his case was:

3/16 cable the breaking load is 4850 lbs, so 15% of that is 727,5 Lbs

1/4 cable the breaking load is 7054 lbs, so 15% of that is 1058 Lbs

5/16 cable the breaking load is 12566 lbs, so 15% of that is 1885Lbs

b) The stays and triatic are to be set at 20 to 25% of the breaking load.

Use the same calculations above, to calculate the setting values, if you have a LOOS gauge, use it to set these tensions.

c) Now for the main shrouds, if you don’t have a Loos, or are just a cheap person, you can use a measuring tape. I did for many years.

You will need to attach a tape of at least 2 meters to the shroud, so that the zero or the beginning of the tape starts at the turnbuckle.

The rule is simple each 1mm of stretch means 5% of the breaking load, and that is valid for ANY CABLE IN A SHROUD, no matter what the diameter is!!!

So you want to have at least 3mm of "growing" or 0.11 inches stretch when you’re at the right tension, for 15% tension…cool huh??

Simple. Repeat the other side. Don’t do all 3 mm in one go. Do 1mm on each side and measure and adjust slowly so you don’t throw the mast off alignment.

Once the upper shrouds are tensioned, go to the next step.

2) Mast Pre bend

Once the masts are where you want them to be, and before we tension the shrouds, we need to set the masts curvature, or pre-bend.

For this attach the halyard that was in the bucket so it ends at the mast foot.

Now adjust the baby stay and or forestays so that the belly of the mast goes forward. Takes a few tries.
The max bend at rest should not exceed half of the mast diameter.

3) Max Mast bend (back stay and or triatic if you have one)

Tension the back stay on the mizzen first, (if you have one), so that the distance from the vertical halyard to the mast is half of the mast’s diameter (IMPORTANT - DO NOT EXCEED)

The mast bend when the back stay is pulled should never ever be more than 2% of the height of the mast from the top to the deck (not cabin). In our friends case with a 42 foot mast, at full back stay pull the mast top should not move back more than 10 inches. OK?

NOW IN THE WATER!! Dynamic Adjustment continuation of chapter 3 above.

OK so where are you going to set the intermediate and lower shrouds??


Easy. At dock, adjust the lowers so they are just tensile to the finger, use the Loos to set them equally port and starbord, they should be almost flexible at rest. Hard but not too much. These can only be adjusted once you sailed to measurel.


also at dock, Should have a flex of about ½ inch when at rest.

The lower shrouds adjustment

Now, when you go sailing, on the first tack, see if the mast is vertical and doesn’t bend sideways when you are on a tack.
Look from underneath and see if it’s straight.

If the mast bends to leeward, kind of like bellies to the low side, the lowers are too flexed.

Go to the lee side lower, and turn it a few turns, and note how many times you turned.

Then tack to the other side and see if its good. If its still bent, go on the lee side one and do the same number of turns plus a few more, repeat tacking and adjusting till all is good and straight.

The Intermediate shrouds adjustment

It’s the same as with the lowers, except now it’s the top part of the mast that "bends" to leeward if they are lose.

Those only adjust at the marina, ok??? You need to go up there.

So a recap:

1) Tighten by hand the upper shrouds till the mast is straight.
2) Adjust mast rake with stays and backstay/triatic.
3) Tension upper shrouds to 15% breaking load
4) Adjust mast pre-bend
5) Adjust back stay movement to not more than 2% mast lenght
6) Adjust lower shrouds while sailing
7) Adjust intermediates observing while sailing and adjusting at dock

Have fun.

Last edited by Giulietta; 04-24-2008 at 10:35 AM.
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post #2 of 122 Old 04-24-2008
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NICE post, very useful information!

I sail.
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post #3 of 122 Old 04-24-2008
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Giu, next time call me first about the disclaimer, we'll make the language stronger!!!
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post #4 of 122 Old 04-24-2008
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Thanks Giu

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post #5 of 122 Old 04-24-2008
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Wow, impressive post Giu. Thanks for that.
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post #6 of 122 Old 04-24-2008
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Alex, if I corrected the very few errors in this, it wouldn't sound like you anymore. Excellent advice, and it's good to know we tune essentially the same way, breaking it down into "at dock" and "underway" procedures.

I have 1/4" stays on the old, more race-oriented boat, and I swear since I learned about tuning I get a great deal more performance out of it, even though my back stay is fixed (no Navtec lever or wheel or ram).

A point here about tensioning: Don't bother trying to align your prop shaft and coupler until AFTER you have tuned the rig, at least at dock. I don't care for saildrives, but one advantage is that this problem of a tensioned rig "bending" the boat slightly is avoided. If you have the most common cutlass bearing and spade rudder set-up, align the coupler at launch just to motor to your dock and to the mast crane (if your mast is out). Tighten the stays just enough to keep the mast up, and then go back to the dock for a beer. If it's calm and you aren't drunk, follow Alex's fine instructions. Tune the rig at dock.

Leave the boat. Wait a couple of days. Come back and see if your prop shaft is still aligned. Maybe it isn't. Realign it now that the boat is bent according to the rig tension and not because it's been drooping off a cradle or jackstands all winter. You will probably find enough of a misalignment to make you glad you checked it out.
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post #7 of 122 Old 04-24-2008
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Thanks for an excellent set of instructions.

I have read through your post a couple of times already but I still need to reread it several times more to appreciate all its contents.

There are 2 comments I would like to make, always with due respect.

1. it would help to define the various types of stays on the mast for us non English readers.This to unsure that we correctly tighten the correct stay.

2. At one point you said you calculated the strength to be 15% of breaking strength. How do you arrive at this figure?

By the way you are spot on in your DISCLAIMER.

thanks again

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post #8 of 122 Old 04-24-2008
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Disclaimers don't mean squat anymore (who's smart enough to understand them?), you'll probably be in the middle of a class action suit soon from all the unemployed riggers that your information put out of business.

Thanks Alex, timely info., I should be stepping the mast within a month and I'll have this printed out and with me when I do.


SV Laurie Anne

1988 Brewer 40 Pilothouse

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post #9 of 122 Old 04-24-2008 Thread Starter
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Originally Posted by xuraax View Post

1. it would help to define the various types of stays on the mast for us non English readers.This to unsure that we correctly tighten the correct stay.

2. At one point you said you calculated the strength to be 15% of breaking strength. How do you arrive at this figure?

It's GIU !!!! Damn it!!!! (inside joke...don't worry)

Now, for your information, I have learnt the technical english they use in the United States, so that you know I use (with some difficulty) their terms.

Stays are all cables and/or lines that pull the mast in the longitudinal axis, forward or backwards, such as Fore stay, Stay, back stay, baby stay and Triatic (for mizzen masts).

Shrouds are the ones that are located on the sides, normally attached to chain plates, and pass thru the spreaders.

As far as the 15%, I said I had calculated it, but it was in response to a question my friend had asked. He sails a heavy cruiser in moderate to heavy winds, and 15% seemed like a good all around value for his case.

Shroud tension should vary between 10% and 20% of wire or cable breaking load. and stay between 15% and 30%.

Also the tension settings should vary with the prevailing wind strenghts the boat normally sails in. 10% shroud tension would be better as far as performance is concerned for a boat sailing in moderate winds, 20% should be better for racers and or for boats sailing in heavier winds, where less flexibility is desired.

In your case, and since I know Malta very well, and you want to race, 20% should be the right setting, and 25% for the stay.
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post #10 of 122 Old 04-24-2008
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Again; nice writup Giulietta. I was wondering about the difference between rake and pre-bend. When you measure pre-bend is that in addition to the rake? So first you measure the rake and then you put additional pre-bend on the mast?

I also have a question regarding the wedging at the cabin roof for a keel stepped mast. "Spartite" was installed at the partners so I can't remove and replace wedges. Can I add rake and bend with the Spartite in place or would trying to rake the mast at this point only result in bending? The mast already has a factory taper and pre-bend IIRC; it's a tall rig, the I is 52'. Visually I don't see much rake; but there is bend above the upper spreaders.
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