Stay measurements

[seawolf]

In preperation of re-rigging my 1962 Columbia 29, I went up to the masthead with my tape and had a friend take measurements below. If I can trust his measurements to be accurate, this is what we came up with pin at masthead and spreader tangs to pin at chainplates.
Port upper: 34' 1 and 3/4"
Stbd uppper 34" 2 and 3/4"

Port Lower 18' 6 and 5/8"
Sbtd Lower 18' 7 and 7/8"

It seems to me if the port upper and the port lower are both approximately an inch shorter, ther would have to be a bit of an S shape in the top part of the mast if it were perfectly centered on the boat.
Should I worry about this, if the mast seems straight enough? Or get another pair of glasses.
Any ideas welcome.
Bob

[seawolf]

I forgot to mention, the rig seems to be in tune and visually the mast looks straight.
Bob

[Ian McColgin]

It would be interesting to have the straight line mast head to chainplate measurements to know if the truck is truely centered amidships. You can get this by bobbing a halyard assuming a calm day and assuming that your sensitivity to the pressure you put on the halyard is good or that you hang the lead from your lead line on the halyard end to give a consistent halyard stretch.

But a little asymetry in the boat's construction is also not impossible.

G'luck

Ian

[seawolf]

Can this be done with a halyard sheave that is off center to the masthead.
I have two masthead sheaves, and they are at each side of center.
Thanks

[Brian Duff]

its ok if the sheaves are off center a bit (such as double sheaves). To eliminate the possiblity of pulling the halyard harder on one side than the other, we tie the tail of the halyard to the shackle, and attach a steel measuring tape, then hoist to masthead and set up tight tight. The steel wont stretch, so your measures will be really accurate.

check that the mast step/ partners is centered between the rails of the boat, and that the chainplates are equdistant from the mast. if that is the case, split the difference of the measurements of the existing rigging port and starboard, then make the new rigging at the new numbers.

This is 'how its done'

[seawolf]

That sounds good. I will give it a try and see what I come up with.
Dividing the difference is good advise.
Just one more question regarding measurements.
Since I will be using the old wire as a template, can I omit any working elasticity value of the new wire and just make sure my new turnbuckles are at mid adjustment when making my final measurement against the old wire?
I believe any constructional stretch for the lengths mentioned above would not be a worry.
7/32" 1x19 SS longest length, backstay at 38' 1 3/4"
Thanks again to all for your kind advse.
Bob

[Brion Toss]

Hello,
Instead of measuring from the masthead, we simply make a pencil mark, as high as we can easily reach, on the front center of the mast. We measure down to the chainplates from there. Essentially we are measuring the hypoteneuse of a very short triangle, instead of a very tall one. At least as accurate. Several advantages: there is no worry about elasticity; we find out where the lower part of the mast is; and it's easier and faster by far.
Centering the bottom of the mast by measuring means we can sight our way up straight.
We also measure out horizontally to the upper shrouds. This will tell us if the mast is situated midway between the chainplates. If it isn't we can compensate accordingly when tuning.
As Ian pointed out, there might also be asymmetries in chainplate height. There are ways to check for this, even when in the water, but I've found that careful sighting from forward of the boat will usually reveal if the chainplates are significantly non-level. Sighting can also reveal if the whole mast is straight, but not coming out of the boat at right angles. I suspect that is what is happening on your boat
As for the measurements, if the tune is good you can indeed use the old wires as templates. The most constructional stretch you'll see is on the longest wires. In your case it will amount to less than an eighth of an inch.
Fair leads,
Brion Toss

[Brian Duff]

I am constantly reminded that this biz is all about the tricks

i never really think about chainplate height except by eye as I come and go, but I suppose it should be measured every time as well.

thanks again Brion, I like the idea of not having to spend time getting a tape aloft and then walking around the lowers and toppinglift with it...

[seawolf]

Thanks to all for the good advise once again.
Brion,
My lady Cheryl and I were in Port Townsend a couple of weekends ago on the 19th and 20th. We love your little town, and try to visit a few times a year.
We sure didn't expect snow in April, leaving the mid 80s temp of SoCal. Our boat is in Dana Point Harbor. Possibly the next time we are in Port Townsend, it will be during the work week and hopefully catch you in, to say hello. Thanks for allowing the layperson to join in and learn.
All the best.
Bob