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Centaur Mast compression loads and lower chainplates

Posted: Fri Jun 22, 2018 8:42 am
by CentaurTilly
I have two problems with my 1974 Centaur, which I would be most grateful for help and guidance with.

1. My cabin deck head has dipped about 12 mm immediately under the mast foot, and the compression post has deformed the GRP seating unit on which it is mounted by about 5 mm. It has been like that for at least the 3 years we4 have owned her. Bizarrely, there seems to be no obvious deformation of the upper deck where the mast shoe is fitted. Do I need to do anything, and if so what?

2. My port side for'd cabin window has been leaking. The Lower shroud plate, which, bizarrely, is mounted on the narrow strip of GRP above the window, has lifted and twisted the GRP, causing a crack some 60 mm long to develop from the for'd upper corner window fixing. I suspect this may have been caused by a collision, causing a sudden large shock loading to the port side shrouds, as there is some evidence of damage repair to the hull in that area.

I have repaired the crack, and re-sealed the window, but am now minded to make new and longer chain plates for the lower shrouds, and relocate them to the beefier bit of GRP between the windows. I note that most Centaurs have relocated the lower shroud chain plates not aft, but to for'd of the windows. However, I am concerned that in that case, only the mast foot and the back stay are left to resist the for'd loading imposed by the rig. I realise that moving the chainplates aft will reduce the angle to which the boom can swing out, but would be happy to accept that limitation.

Any advice would be most welcome!

Yours aye,

Re: Centaur Mast compression loads and lower chainplates

Posted: Fri Jun 22, 2018 9:52 pm
by TyroSailor
The location of that chainplate above the window was a rare design fault, corrected soon after your boat was built by putting the shroud plate forward of the window. Mine was built the following year and has this. I've seen some Centaurs with a metal (presumably stainless steel) strap vertically down from the shroud plate, obscuring a little of the (more than adequate) window. It's not a very elegant solution but I'd be doubtful about making any other mdification to the rig without expert advice.

All four of my windows leak.

Re: Centaur Mast compression loads and lower chainplates

Posted: Sat Jun 23, 2018 8:19 am
by CentaurTilly
Dear Steve,

Many thanks - most helpful. On reflection some of the for'd force from the rig is taken by the sheets.

I did consider a vertical strap across the window, but the laminate under the window is only about 70 mm deep, so not easy to achieve a decent anchorage of the lower end of the strap.

I quite like the large cabin windows, but they are unusually large compared with other makes.

I thought the mod of moving the chainplates for'd had been done by the owners, rather than by Westerly, so if Westerly subsequently moved the chain plates to for'd of the cabin windows, I will do the same. Not as straightforward, because there is a step in the cabin wall, but I'm sure it can be done.

Thanks again.
Yours aye,
Charles (Tilly).

Re: Centaur Mast compression loads and lower chainplates

Posted: Sat Jun 23, 2018 11:14 am
by Jolly Roger

The most likely reason for the dip in the deck head under the mast is rot. There should be a plywood pad under the mast to stiffen the deck and spread the load of the mast over a larger area. This probably has some cables drilled through it, but not properly sealed against water (or the sealant has dried out). There is no simple solution, but yes you should check it out. The mast compression post could also have some rot or shrinkage. The solution will require the mast to be removed to take the weight off the deck. Until the exact cause is known, a repair cannot be proposed. You really should get a surveyor or boat builder to have a look.