Do you want to be informed on new Posts on this Thread? (members only)

Sail & Rigging - Mast Compression Tubes-Professor?
06 November 2013 - 02:56
Join Date: 20 March 2011
Posts: 88

Mast Compression Tubes-Professor?

Did Nautor not use a compression tube at the tangs for the lower shrouds?

In re-assembling Hatha's mast (44-004), I see that the holes where the bolt goes through the tangs for the lower shrouds are just large enough for the 35mm bolt to pass through, and the same size as the holes in the tangs.

I have the old bolt which shows wear from the wire halyards so there must not have been a compression tube, and I don't see how it could have fit inside the mast if there had been one. I can't remember there being one when I disassembled the mast.

Am I correct in assuming that the location of the tangs, near the joint where the 2 mast sections are sleeved, along with the extra surface area provided by those works of art that are the tangs, made a compression tube unnecessary? What about up top at the shrouds? There I have a larger hole (22mm) in the mast walls where I will need to fit a tube, but I suspect that may have been drilled out in error by the people that did the re-furb work.

As always many thanks for input

Tonyh 44-004 Hatha

06 November 2013 - 10:44
Join Date: 02 January 2008
Posts: 1547

Dear Tonyh
Compression tubes were not used here, as the loads are mainly along the mast. When you put in the tang bolts do not tension the nuts hard, this brings no advantage. There are holes for split pins in the bolt and the nuts, and this determines how far the nuts should go on.
If you have wire halyards it would be advisable to lead them aft of the lower shroud tang bolt, as the mast head tends to bend aft. For the top shroud tang it needs to be checked where the halyards come down from the sheaves.
Also with rope halyards this reduces chafe.
Kind regards

06 November 2013 - 16:32
Join Date: 20 March 2011
Posts: 88

Dear Professor

Thank you for your help, no more wire halyards

I am having a new 35 mm bolt made, the stainless nuts on the original aluminum bolt did not come apart well after 40 years. Now I see that we can copy the old setup exactly, and pre-drill the split pin holes.

I have not forgotten that you had asked for our pre-tensioning info and will get that to you when we finally get to sail. We still have a ways to go though before that happens.

Best regards


06 November 2013 - 18:58
Join Date: 02 January 2008
Posts: 1547

Dear Tony
Thank you for the information.
Take care that there are no threads on the tang bolt where it bears on the mast wall, or against the tangs.
Is the new bolt aluminum? If not you may consider making it hollow, i.e. using a tube. Then an internal thread and a bolt could be used each end, provided a safe locking system can be devised.
Kind regards

07 November 2013 - 02:12
Join Date: 20 March 2011
Posts: 88

Dear Professor

Thank you for the heads up about the threads, that is one of those things that can be missed in the communication with the fabricator.

We are using 316 stainless tube, plugging the ends, threading and putting the nuts on just as original. The fabricator will pre drill for the pins so I'm not doing it at the yard with a cordless!

Thank you again for your advice


  • Threads : 1701
  • Posts : 10215
  • Members: 820
  • Online Members: 0