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Date Posted: - Tuesday - 07/21/09 - 4:03pm
Author: Doug Wilson
Subject: Rig tuning
In reply to: Lyle Harris 's message, "M31 tuning the rigging" on - Tuesday - 07/ 7/09 - 3:45pm

I'll be pulling both masts next month. The main has a bend aft, the rigger in La Paz said that was the design.
I wanted to pull both masts in May, due to woodpeckers in San Carlos, but the rigger there said that it would be better to leave them standing, rather than laid out horizontal for 4 months.
Funny how the folks who warned me of woodpeckers had aluminum spars, after talking with folks with wood spars said they had no problems over 10-11 years of storage there.
Will be interesting to see when I go back next month.

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Replies:

[> [> I have a theory about the mast bend -- Jared Kibele, - Thursday - 07/23/09 - 1:04pm

My main mast was very bowed when I got my boat (M31 #9 - I still need to submit info for the owner's page). I've been thinking about it a lot and trying to figure out if it's supposed to be that way for a long time. I decided it's not. I think it's supposed to be straight and raked aft by around 2 degrees like my mizzen is. I decided that based largely on this drawing: http://www.marineryachts.com/m31/sketch.JPG

On this drawing, the masts are completely straight and look like their raked back a couple of degrees. I also noticed that, in the drawing, the main shroud chain plates are in straight line with the spreader tangs and the masthead. In contrast to that, look at this photo of my masts: http://www.flickr.com/photos/kibele/2853986191/sizes/o/in/set-72157608843543865/ ...I've gotten the main a little straighter since then but it's still not perfect.

For a long time, I couldn't figure out how I could get the mast straight and I thought the problem was with the length of the fore and aft stays but now I think I've figured it out. I think the base of my main mast is the real problem. I think the base of my mast is vertical or possibly even raked forward a bit. If you look at the line drawing and imagine changing the angle of the base of the main mast while keeping the rest of the rigging as it is (so the masthead would still be in the same place), you can see that it would put the spreader tangs forward of where they are in the drawing and force the spreaders to angle back like they do on my boat.

So, to fix all this, I've got a plan. First, I'm reinforcing my saggy mast step (http://www.flickr.com/photos/kibele/sets/72157617972117480/) then I'm going to take down the main to replace my spreader tangs (there's a small crack in one). While the mast is down, I'm going to figure out some way to adjust the fore/aft angle of my mast step so that, rather than being vertical (or possible forward) as it is now, it will be angled back by about 2 degrees.

...and hopefully it'll all work out because it's a HUGE pain in the butt.

-Jared

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[> [> [> With you on that... -- Randall, Murre, M31, - Friday - 07/24/09 - 1:38am

Jared,

The situation of the main on Murre looks similar to yours, and though I've worked much of the "bend" out, the spreaders still have a significant aft sweep like those on your boat.

I too have decided that this is due to a small forward rake of the mast ***below*** the spreaders, but I'm less certain about the need to adjust the angle of the step. It is logical that the acquiescing of the coach roof could cause the mast to fall forward as the step droops, but that much? I measured the angle of rake in the drawing you reference and it's about 3 degrees. But that's a tiny adjustment at the step.

Just thinking out loud.

I've passively attempted to pull the middle and lower part of the mast aft by adjusting the lowers, but that didn't really work. I think to realign with a straight aft rake will require taking all stays loose and starting the tuning process from the beginning, which I have not yet done.

Good argument though. I think you�ve got the problem right.

RR

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[> [> [> [> I'm glad someone agrees -- Jared Kibele, - Friday - 07/24/09 - 1:30pm

I've talked to a number of people about this including a couple of boatwrights and riggers. Most of the time I've just gotten blank stares in response. ...I think this may be the first time I've been able to explain myself properly. Still, it's good to have someone who knows these boats so well agree with me.

I recently got a chance to see the inside of a slightly later Mariner 31 (hull #30-something just moved into my marina, John who's last name I can't remember - I have his card somewhere). I noticed that his mast step arch has two beams across where my boat (hull #9) only has one: (http://www.flickr.com/photos/kibele/3520930768/in/set-72157617972117480/). So I think my boat is particularly susceptible to having the roof cave in under the main mast and, with only one narrow beam, fore or aft tilting seems especially likely.

To complicate matters more, the whole deck and house including the coach roof were rebuilt by a previous owner so it's entirely possible that he angled the mast step incorrectly.

With my temporary compression post thingy, I've already raised the roof by about a half inch and I'm building steel braces for both sides of the mast support arch. I'm going to take the mast down soon and when I do, I think I'm going to brace the roof behind the mast support arch. Once that's done, I want get a bronze wedge made to put under the mast step to get the rake back into the bottom of the mast.

Should be a piece of cake, right?

-Jared

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