Tuning Standing Rigging

smacdesign · **Posted:** 03 Aug 2016 12:56

Does there exist out there a mast tuning guide for the T37? When I was in cold storage the marina riggers tuned it after stepping. Now I`m outside with mast in and would like to know any guidelines for tuning uppers and lowers. While commissioning the first time under my watch, the PO was all feel and sight. Are their any specs to go by? I`m prepping for a Lake Michigan cross-lake race and would like to be well tuned. Thanks to anyone with some basic guide lines!

puffcard · **Posted:** 05 Aug 2016 19:57

I do mine very similar to this method.
https://theriggingco.com/2014/02/03/how ... boat-mast/

I do use my wire jib halyard to check side to side to center the mast, also looking at how the mast partners are fitting in. After getting the uppers set, I'll put a little pre-bend in the mast by carrying my forward lowers a lot tighter than the aft lowers. I do mostly by feel and have the rig set up pretty tight. When sailing upwind the leeward stays should not be flying around lose and the mast should have a slight bend aft (not to the side). When checking shrouds at dock, grab both sides at the same time, if you can. I also sight up the back of the mast up the main track. You'll start to get a feel for it. DON'T FORGET THE PINS...don't even motor to another slip without pinning. If things start looking like a tree branch, loosen back up and start over. Headstay and backstay, uppers, then forward lowers and lightly set the aft lowers. You can get a guessing start point by looking where the turnbuckles where set at before.

The Rake is very subjective on T37, most boats carry about 6=deg. I carry my mast almost vertical, only about 2=deg, seems very balance.

smacdesign · **Posted:** 07 Aug 2016 07:23

Thank you, Puffcard!

sailingsoulianis · **Posted:** 23 Jan 2018 22:51

I'm getting a lot of mast pumping at the dock. It never seems to happen while sailing, or at least I don't notice it. This was happening before unstepping, and after re-stepping it recently as well. However, lately it seems to be happening more often, maybe I'm just noticing it more.

I mentioned the pumping to the rigger who was helping re-step and his idea was to put a lot of tension into the forward lowers as puffcard mentioned.

I borrowed a Loos tensioning tool to look at everything after he was done, and the forward lowers were near 25% breaking strength which just seemed a bit high. But even with that much tension on them I still wasn't able to get any actual forward bend in the mast, it just felt like I was going to rip the chainplates out. This mast is STOUT.

This is where I left everything when I gave the loos back.

Port aft 9%
Port upper 18%
Port fore 15%

Forestay: NA
Backstay 24%

Star aft 8.5%
Star upper 19.5%
Star fore 14.5.%

But, I'm still getting a bunch of pumping and am at a loss for what to try next. Any thoughts?

puffcard · **Posted:** 26 Jan 2018 15:22

That pumping is a sign of harmonics in the mast, it actually is very annoying and can cause damage. The tension or really the compression, is the main component like a guitar string. Carbon fiber mast, tapered mast, multi spreaders rigs, all can do it. There is a lot of different things going on. I've seen people wrapping halyards around a carbon mast to stop it. But i think the best solution is to put more pre-bend in the mast. At less 3/4in for single spreaders and 1/2" for each double spreaders. Sails are designed for this bend. The straighter mast will go into harmonics faster than the bent one, good luck.

Also a question, are your mast partners installed and tight? This helps big time.

sailingsoulianis · **Posted:** 28 Jan 2018 23:30

We don't really have prebend and I know that is part of the problem, but I can't seem to get any in the mast no matter how much I crank down on the forward lowers.

Maybe I need to loosen the headstay a bit to bring the top of the mast aft a little bit more?

We have a very heavy rubber in the the partners. It was near impossible to get it in there (doesn't compress at all), but I suppose that could be contributing to it? What other materials have been used or are recommended.

Timshel · **Joined:** 29 Dec 2010 10:24 **Posts:** 193

Hi Kurt,here’s the factory owners instructions for the mast step.I tend to leave my rigging a little loose and pump up the backstay when I use the boat. Might meet you in the Bahamas in 12 months? Bruce.

sailingsoulianis · **Posted:** 02 Feb 2018 13:17

Thanks for sharing Timshel. I have the same original owners manual Smile

I followed those steps exactly after re-stepping.

Yesterday I started over completely goal of adding a little length to my forstay. With the way it was stepped I wasn't really able to get any aft bend in the mast at all. I slackened off everything and with no tension the mast was actually a little inverted (slight bend to the bow). So I'm not sure if something happened during shipping or what but that was interesting to see.

I took a few turns out of the headstay to lengthen it and then started tightening up on everything. I was able to get some aft bend in the mast without over-tightening the forward lowers which made me happy, but alas I'm still getting a lot of mast pumping here at the dock....

I left things a little looser this time. So I've got a little room to tighten up which I might try, but I'm starting to wonder if I might just be stuck with this one.

Seems like the battle isn't over yet.

Velera · **Joined:** 29 Dec 2006 09:38 **Posts:** 656

Seems like you are doing the right thing. You should be able to get 4” of aft at the top if you have everything set up right. I find that setting the all the stays and shrouds is best done first at the dock (getting tensions equal on the paired rigging as specified in the instructions) then going out and doing a final adjustment going to windward in about 12 knots of wind and making sure it looks right. This is a sewer pipe of a mast and the bend is not really all that critical. You want a bit of sag in the forestay (4”) when going to weather in a breeze and about 4” at the top of the mast for bend. Folks with hydraulic backstays can easily get into trouble here. I am not sure you can bend this boat, but you certainly could stress the fittings.
FWIW.
Ray Durkee
T37 #373

Tartan37.com

Tuning Standing Rigging

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