friggin' with the riggin'

[comtech]

friggin\' with the riggin\'

i have just bought a new ( to me ) mast for my project sloop.
The dimensions match the yacht blueprints exactly,but the
standing rigging which is still attached to the mast appears too
short,the shrouds ending parallell to the mast step. As the mast will sit on a coachroof some 18 inches proud of the deck
this presents a problem ! but at least i can guestimate the neccesary increase in the length of the shrouds.
However i have no idea how to calculate the correct length of
fore and backstays,particularly as the mast was not specifically designed for the yacht and the yacht blueprints
give every possible statistic other than length of standing
rigging( presumably specified mast would have been supplied
with correct rigging).
would it be feasable to raise the mast by hand and simply
measure the shortfall. ( mast is 28 ft ,yacht is out of water
on trailer ,few good men available ! )
or should i just go for very long bottle screws !
any advice welcomed as craning in day is getting nearer.

 

[MoodySabre]

Re: friggin\' with the riggin\'

I'm sure Mr Pythagorus could help you.

Just draw a side view. You know the height of the mast and the distance at right angles from the bottom of the mast to the position of the back stay. So, assuming a vertical mast the length of the back stay will be the square root of the sum of the squares of the other two sides of the triangle PLUS the height of the mast base above the backstay fixing.

Ditto for the forestay.

Alternatively just draw a side plan to scale and measure the back stay and forestay.

Long time since I was at school but some things stick!

 

[nigelhudson]

Re: friggin\' with the riggin\'

[ QUOTE ]

would it be feasable to raise the mast by hand and simply
measure the shortfall.

[/ QUOTE ]

Why not attach warps to the end of the shrouds, forestay etc. Then raise the mast and tie off the warps to the chainplates. That way you can temporarily rig the mast, adjust as necessary and measure the exact extra lengths required.

 

[DaveS]

Re: friggin\' with the riggin\'

1. Forestay / Backstay
Presumably you have (or could measure) the vertical distance from mast top attachment point to deck stepping point, call it Y. You can also measure the straight line distance between the mast deck stepping point and forestay and backstay attachment points - call them Df and Db. The slightly trickier measurement is the height difference between the stay attachment points and the coachroof stepping point: this might require the construction of some kind of temporary height gauge - at its simplest a wooden batten with a spirit level to check its horizontal placed at each point and measure distance to ground (assuming flat or constant gradient and the boat is level on the trailer). From these measured distances you can obtain the additional heights (dYf and dYb) of the coachroof stepping point relative to forestay and backstay respectively.

To obtain the horizontal distances from the stay attachment point to the mast (Xf and Xb) you evaluate Xf = Df.cos(inv sin(dhf/Df))-Xfo and Xb = Db.cos(inv sin(dhb/Db))-Xbo where Xfo and Xbo are the horizontal offset from the mast centre to the forestay and backstay top attachment points respectively. The vertical distances are Yf = Y + dYf and Yb = Y + dYb. The stay lengths can then be evaluated Sf = sqrt(Xf^2 + Yf^2) and Sb = sqrt(Xb^2 + Yb^2).

This assumes no mast rake. If a mast rake is specified, of r degrees backwards, say, then increase Xbo and reduce Xfo by Y.sin(r) respectively; the latter may change sign but that's OK.

2. You could carry out similar calculations for the cap shrouds, but you might want to think laterally here. Starting from scratch gives you the opportunity to arrange your shroud attachments in line with the mast stepping point (assuming you have a tabarnacle) which will greatly simplify mast raising / lowering - even on the run if you use an A frame.

Of course you could just raise the mast and measure it all with string...

 

[machurley22]

Re: friggin\' with the riggin\'

Or if you don't fancy the maths how about a few short lengths of chain? As well as avoiding any brainache you would also be able to sail her like this while you experimented with rake etc.

No reason why you couldn't do a couple of seasons like this to get some value out of your second-hand rigging.

 

[comtech]

Re: friggin\' with the riggin\'

thanks for the advice
i did consider trigonometery, but the deck is quite sharply
raked with the forestay quite a bit higher than the backstay and with only rusty o' level maths considered this complication
might be the undoing of me ( and the mast ).
the scaled drawing seems less daunting as i was quite good at
T.D., but like your maths lessons , that was quite a while ago
thanks anyway !

 

[William_H]

Re: friggin\' with the riggin\'

Do you havee hinging base for the mast or pivotted mast step?
This is a worthwhile addition especially at this stage.
If it is a typical mast head rig with cap shroud chain plates abeam the mast base. What you do is fit a piece of stainless steel tube or long flat plate as an extension to the chain plate to a point level with the mast pivot. The shroud is fitted into the tube with clevis pin or similar so the shroud wire can pivot in the tube. The tube is stayed forward so it stays vertical when the mast is lowered. This arrangement keeps the side stays tight all the way down in the tilting back arc of lowering the mast.
This will almost certainly explain why the stay wire is short.

The intermediate stay wire usually goes to separate chain plate aft of abeam the mast so hopefully is long enough to reach the chain plates. Use shackles or a pair of SS plates to extend as necessary.

The easiest and most satidfying way is to erect the mast using halyards or warps to the mast top to hold it vertical while you sort out the stay wires lengths.
Start from a position of mast vertical for setting backstay and forestay. You can then add a little rake back if it seems a good idea after sailing it for a while.
I use an adjustable backstay and just fit or remove shackles or plates to adjust forestay length. Once the forestay is set it can stay that length.

If the backstay is short then a very elegant adjustment is to fit a pulley to the end of the wire and have a 7x19 flexible wire run from one side of the transom through the pulley to a 4X tackle to the other side of the transom.

Good luck I find it an exciting part of a project puting the mast up (presumably at home) olewill