Cable/Fitting specs for 26S

[vizwhiz]

Wondering if anyone can point me to some specifications for the cables and fittings on the 26S...meaning...what diameter is the forestay/backstay/shroud supposed to be, what type of cable, what length from end-to-end, how much tension (in pounds)...etc. Starting to gather up the details...
Thanks!

[Sumner]

Wondering if anyone can point me to some specifications for the cables and fittings on the 26S...meaning...what diameter is the forestay/backstay/shroud supposed to be, what type of cable, what length from end-to-end, how much tension (in pounds)...etc. Starting to gather up the details...
Thanks!

As far as I know the forestay and back stay are 1/8 th inch and the shrouds are 5/32's. That was what was on ours from the previous owner. I made up new standing rigging last summer and put 5/32 on the shrouds and backstay. I had a new forestay made to work with the turnbuckle that has swaged on ends. Riggingonly.com made it up and I went from the 1/8th to 5/32 for the forestay. Since I'm using a longer Johnso lever I moved new hounds a ways up the mast for the new forestay and moved the top shrouds up to it also. I still have the lower original hounds on the mast and put a bracket on the double bow rollers so that I can still hook up the orginal forestay if needed as an inner forestay and can use the hankon sails we had before the furler.

The manual gives the stock lengths.....

http://macgregor.sailboatowners.com/ima ... f/1339.pdf

....good luck and get a loos gauge and use it. I'm much happier since I have and have the rigging much tighter than I thought it should be by guessing at it,

Sum

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[Catigale]

Viz - you dont really rig a boat to a given shroud tension, you rig to get a certain config of the mast in terms of rake and bend - this gives you the best sailshape.

The actual tension in the shrouds is a complicated function of all the other shroud tensions plus the weight/presence/absence of a furler/mainsail

Of course, it is important that all shrouds are tensioned to remove stretch (at least >10% of the breaking limit) and also tensioned under 20% breaking limit (5x safety margin).

[vizwhiz]

Thanks guys...I read through the manual and found the lengths as you noted, Sumner. Not sure what kind of gauge you are referring to...I suppose I'll have to look for that one.
And Cat, I appreciate the insight - I'll focus on mast shape. I'm guessing that means no need to make them tighter than it takes to get the right shape, correct?
Mast rake is supposed to be around 3-degrees from vertical...how do you figure that one? (I know how to do it mathematically, I'm talking about...on the boat!)
Thanks again!

[seahouse]

Hey Viz!

IIRC, use a plumbob from the top of the mast with the weight in a pail of water on the deck at the base of the mast (to damp the movement), then use your trigonometry, measuring out from the mast.

- B.

[hoaglandr]

I've wondered this too:

Mast rake is supposed to be around 3-degrees from vertical...how do you figure that one?

I get the plumb bob, but how do you determine if the boat itself is level? What surface would you suggest using to determine that?
I'm considering upgrading my shrouds as well after I complete all my other mods, but that won't be till spring at best.

Russell

[Divecoz]

I've wondered this too:

Mast rake is supposed to be around 3-degrees from vertical...how do you figure that one?

I get the plumb bob, but how do you determine if the boat itself is level? What surface would you suggest using to determine that?
I'm considering upgrading my shrouds as well after I complete all my other mods, but that won't be till spring at best.

Russell

http://sadoun.com/Sat/Products/Accessor ... ohnson.jpg

JOHNSON's are EVEN Made In America

[Catigale]

I'm guessing that means no need to make them tighter than it takes to get the right shape, correct?

It is important that they not be too loose...Latrec.

If you dont take the stretch out of the shroud, it fails under fatigue - much more dangerous than tension failure. Ill Venture (wrong forum?) to say that no Mac has had a shroud fail under tension that I can recall - the hull will fail first.

I think even when people have hit the mast on trees and/or ATONs (buoys) the mast has broken without shroud failure.

[Divecoz]

OK Cat and others..
What IS the desired degree or rake for the mast? Is the degree different for X v M?
On an X with the back stay, is it just an adjustment of the back stay to gain desired degree of rake and then the loos gauge to tension the shrouds?
On an M I will assume ....... its THEN much more involved due to the lack of a back stay and the rake being attained by adjustment of the furthest 2 , most aft shrouds??
Good Thread for the X .....http://macgregorsailors.com/forum/viewt ... +mast+rake

[Catigale]

Ill find the best rigging thread I can think of, but the backstay on the is NOT used to adjust rake..its basically there to have something to hold onto (except on Dead down wind)

[seahouse]

Yipes! Tuning fractional rigging (especially with aft-swept spreaders) is like finishing drywall! If you keep looking closely enough you’ll never be finished.

To get all the details I would suggest a good book on rig tuning, because, I, as others might be, am generalizing, and “he who generalizes, generally lies”. I’m describing an “M” because I have the photo from the brochure, which shows the rigging, in front of me. So your results may vary.

In an “M” the mast rake is set by the forestay length. You can use whatever datum is most suitable for leveling the boat, but I would expect that if you trim the boat so the factory location of the boot stripe is level with the water you’ll be pretty close.

Then adjust for the curvature of the earth, and the 500’ difference in sea level that occurs depending on where you are in the world. (Not).

Ballast in. Then use your plumbob (a string and weight) in a bucket of water and trigonometry, as I mentioned, to set your rake. More rake= more weather helm. I would think that 2% is good, 3% is lots.

Then adjust the top shrouds to remove the sag in, and set the tension of, the forestay. This will bend the mast forward in the middle, so you will want to then tension the lower shrouds to the amount of mast bend you choose. Of course, all this time keeping the mast vertical and straight as viewed from the stern. And maintaining the required slight “up from horizontal” attitude of the spreaders. Make changes with the same number of turns to the adjusters/turnbuckles on both sides to keep things in line bow-to-stern.

If you have a backstay, that is used to control the sag and tension in the forestay, instead of the top shrouds. Of course it will still have some effect on the mast rake.

The most accurate way to set the tension in a cable without using gauges is by measuring the elongation over a defined distance. The thickness of the cable then is not relevant, (1/8”, 5/32”) you just measure the amount of elastic elongation from the hand-tight condition.

For example, failure occurs at 1% elongation, meaning that a 2 meter long cable will fail when stretched 2cm, or 20 mm, when its ultimate tensile strength is reached.

Measure a practical length of the shroud, say, 2 meters, but the longer the better. With the shroud hand tight only, measure from the swaged ferrule to a point on the cable 2m up and tape that point exactly. Using Catigale’s 20% figure, which sounds about right for aft-swept spreaders, you would therefore tension the cable until the distance between the two points is 2m and 4mm. (That added 4mm is 20% of the 20mm ultimate strength).

Pre-tensioning the top shrouds is critical to reducing sideways movement of the mast. The distance the masthead moves laterally is reduced by half, over if there was undertensioning.

The primary risk of too little tension, in addition to the mast movement I mentioned, is shock loading. That will do the shroud, and associated mechanicals in long before fatigue does, I would expect.

Under moderate sailing conditions you should see no curve in the leeward shrouds.

Happy Holidays ! - Brian.

[vizwhiz]

Lots of great info...I feel like I'm in school, getting ready to take my practical exam...

Thanks everyone for the input. I'm trying to think of all of the "minor" stuff that could easily become major stuff and which would keep me from being able to get on the water quickly.

[hoaglandr]

Living in Florida should help....

Russell

[Catigale]

3 degree of mast rake.....

For an I calculate

Sin (3 degrees) = Offset of plumb bob from aft of mast / (Mast length)

and hence get that a plumb-bob hung from the top of the mast should touch the deck 1.36 feet from the aft part of the mast - that seems like a lot - Whats wrong??

[vizwhiz]

***EDIT: FIRST PARAGRAPH BELOW IS INCORRECT AND SHOULD BE IGNORED - HOWEVER I HAVE LEFT IT HERE FOR CONTINUITY OF FOLLOWING POSTS***
yours truly, vizwhiz

Cat,
To use the SIN, you would use the length of the plumb bob string (the hypotenuse)...to use the offset and the mast height, you would use TAN (opposite leg over adjacent leg) of 3-degrees... That way the plumb bob string length is meaningless - all you have to do is measure out from the bottom of the mast...although I would probably base this on the center of the mast (a few inches different)...and mark that point, then lean the mast until you get the plumb bob on that point.

BUT...HOWEVER...ALTHOUGH...if the mast "bends" due to the shrouds, then the whole rake angle measurement would be off...so how do you compensate for that? Or, do you set the mast rake with "loose" shrouds and then tighten the shrouds to get the little bend in the mast afterward?