Mast Tang installation

[mariner2k]

Hi, I am re-rigging a 50 plus foot round, hollow Sitka spruce mast. I will need and attaching point for the lower fore and aft shrouds and well as the intermediates. I've gotten some info from the Riggers Apprentice book, but I still have a question or two.
First which is stronger, a soft eye and thumbs cleat or a bolted and screwed mast tang?
Second, in the more likely event I use tangs, the book suggest bolting through the mast. My question regarding that, does it weaken the mast to any significant degree and is there a rule of thumb on bolt size to mast diameter?
Thanks, Kevin

[benz]

My inclination is for a soft eye and thumb cleat, since that means the eye goes around the entire mast. The thumb cleat then is not being pulled outward, and the sheer force on it is minimal compared to the force on a bolted-on tang. My boat has this setup and it works flawlessly. Looks like you're in RI. Where at? we're probably neighbors.
Ben

[mariner2k]

Wickford shipyard. Good people, good yard. The mast I will be using was set up for thumb cleats in its' original usage. If I go that route I'm hoping the shrouds that were with that mast aren't too short. I really need to snow to go away before I can set it up on the lawn and take exact measurements.

[benz]

I live in Bristol, so pretty far off by RI standards--almost 45 minutes! Was the mast re-purposed at some point, that you fear the shrouds might be short? Are you adapting a mast to a different boat?

[mariner2k]

All of that. The original mast is in too poor condition to rebuild. When the boat was built in '88 a mainmast from another boat was used on this boat. I wish it were still good. It was at one time extreme overkill. But I have a good mast from my old boat which is, the right size but ultimately rigged differently. Going from single spreader to double. Returning to running backstays etc. About a foot wider at the plates also. But as I said, I'll need to set up the old mast in the yard and see what is what with the shroud lengths. Once the snow disappears, of which I'm sure you're aware. The tangs are a consideration at this point, but not if it compromises integrity. The old mast is set up with thumb cleats and the shrouds are in excellent condition, and quite oversized. I've also considered moving the thumbs down if possible.

[Brion Toss]

Hello,
From this perspective, it seems that the important matter is not soft eyes vs. tangs, but whether or not the basic design and dimensions make any sense at all. You mention one mast that was extreme overkill, and another mast from yet another boat (always a red flag). I urge you to take a breath and look at what the boat needs here. Calculate, then fabricate.
Fair leads,
Brion Toss

[mariner2k]

Hi Brian, thanks for replying. I had to chuckle. This has been in the planning stages for about three years or more. I haven't been really rushing this at all. The newer mast is also more than adequate. I had a local shipbuilder do the math for me. The general consensus is that the old mast was to big and heavy for the boat. There is a story as to why it was used for the boat,,,basically, because it was available.
The new mast however, needs to be rigged a bit differently, so I can't just use all parts from mast "a" on the newer mast "b". The newer mast actually has heavier rigging. It would be a waste not to be able to use them. They will be very close. I would prefer to use the thumb cleats, but if I cannot, I wanted to know if adding tangs would weaken the mast. The project got shelved a little because of our harsh winter. I will check locally but I like to run things by here also.

[Brion Toss]

Hi again,
Oh, good, that is good to hear. Getting back to your original question, then, properly-made tangs will not weaken the mast, and are less likely to cause decay and tuning issues. So, much as I like soft eyes, there's nothing wrong with moving to tangs. The big thing is to provide adequate distribution of load, with things like "finger" extensions, and bushings around the throughbolts. Let me know if I can be of help with the details.
Fair leads,
Brion Toss

[mariner2k]

My biggest concern was the through bolts. Are there any examples of tang styles online that you know of? If I do use them I envision long finger extensions, meeting at a plate where the bolt is placed (through a sleeve), then extending to the double clevis hole.
I don't know if that paints the picture but is it what I have seen on some other masts.
On a 7" diameter mast, what should be the maximum or necessary bolt diameter?
Thanks

[Brion Toss]

Hi again,
Bolt diameter is relative to shroud load, not mast size. Same bolt size as clevis pin is a rule of thumb, unless there are two shrouds on one tang (like lowers). What do you mean by "double clevis hole"?
As for images, look through the ones here:
http://www.sailspar.co.uk/yacht-prod...ittings/tangs/.
Note that the tangs are independent of the backing.
Fair leads,
Brion Toss