View Full Version : spreader attachment on a round wooden mast
11-13-2005, 10:46 AM
I'm rigging a 50' birdsmouth sitka bermuda mast and need some opinions on the best way to attach the spreaders. The rigging plan calls for two SS bars screwed to the fore and aft edges of the spreaders, from one side, across the mast to the other. The bars are screwed to the mast where they cross. This makes everything a solid, ridged unit, quick and easy to do, but it seems to me that any slight misalignment or movement of the mast could cause a twisting force on those fasteners that could crack the mast. Another method I've seen is a pair of L shaped brackets for each spreader. The brackets are screwed to the mast and a thru bolt attaches the spreader. Because the mast is round, these would be a lot more trouble to make but it could allow a small amount of fore and aft movement so the spreaders could self align without torquing the mast. Opinions appreaciated.
[ 11-13-2005, 10:47 AM: Message edited by: kc8pql ]
11-13-2005, 12:24 PM
You need flexability of spreaders if they are high, near the upper stay terminus, as in a schooner's foremast. But a single spreader rig in that size on a mainmast or sloop should have ridgidly fixed spreaders as planned.
Either lay it out on ground - my favored way - or draw and loft up with care but it's not so hard to get the correct spreader up-cock to bisect the angle the stay is put through there. If you're fearful, make the up-cock a trifle less than called for and have small stays angle down at 45 degrees from the mast to the spreader tip both to anchor the spreaders and provide support for when you go aloft to stand on the spreader prior to a show-off dive or cannon ball.
Spreaders each made of two longer pieces of wood and suitable spacer blocks here and there should at the mast end be wide enough, counting spacer, to really embrace the mast and the fore and aft metal straps that join them should only have a bit of plain bow, no compound double S's.
With this rig, you'll just need one screw through the forward plate into the mast and one through the sailtrack and spacer and aft plate into the mast. It's only a bit of shere strain and I'd not bother through bolting that, especially as you'll have some other strapping and possible a lateral through bolt just below the spreaders for the lowers' tangs.
Varnish the undersides and paint the tops white.
11-13-2005, 02:56 PM
I don't quite get what you're describing but just a point.....any through bolts you use should have compression tubes to stop the fitting crushing the timber. It's worth doing a good job on these and its not hard. For example, I detected some movement in a fitting one year and it had oviously stressed the compression tube and pulled it enough to enlongate the through hole very slightly. I engraved some discs( washers if you like)of a harder wood in with a router and epoxy ,and that and a rebedding of the fittings plus some extra fastenings cured the issue.
11-14-2005, 06:53 PM
Thanks Ian. What you describe matches my rigging plan. Your how to helps.
Michael s/v Sannyasin
11-15-2005, 05:54 PM
I've never yet gotten a look at the top side of my spreaders, but from below, you can see that the spreader is built to wrap around the mast and sit on cheek blocks. I believe that there is a hole in the spreader on each side that the cheek block acutually slides up into which locks the spreader in place. The only bolting would be cheekblocks to the mast, and I'm going to guess that they'er through-bolted to each other.
Please ignore the sorry state of the finish on the mast!
11-15-2005, 08:10 PM
Originally posted by Michael s/v Sannyasin:
Please ignore the sorry state of the finish on the mast!Maybe it's time to see the tops of those spreaders
Thanks for the pic. Another method to think about.
John R - Kitenui
11-16-2005, 03:09 AM
These photos show another method using overlapping castings
which are through bolted using compression tubes as per John B s earlier post in this thread.
unfortunately this shot is taken from above but the spreader is bolted to a shouldered platform which is an integral part of the casting and determines the sweep (fore and aft) and the dihedral (angle above horizontal)
This is a shot of the forard of the lower fittings on the bench during initial cleanup and polishing. This shot shows the shouldered platform a little more clearly
and finally a shot of the crane
11-16-2005, 03:52 AM
pretty sexy fittangs there John. ;)
Being somewhat short of the half mil that was spent on that boat, I adapted the existing stainless bands/ tangs I already had when we switched from bermudan to gaff. Not so pretty but strong ,and they haven't moved at all.
[ 11-16-2005, 04:06 AM: Message edited by: John B ]
John R - Kitenui
11-16-2005, 04:18 AM
A hell of a lot lighter than all that yellow stuff too :D I am going to have to put some cheek blocks under Kitenuis lowers too next time I pull the stick. She has a hefty bronze one on the upper castings but the lowers are gradually working their way towards the deck; about a couple of mm a year. I personally dont like the idea of through bolts but that's just me.
11-16-2005, 08:15 AM
Here's a pic of a fabed attachment from Bob Steward's book designed by Philip Rhodes.
No welding involved, but I could see the close bends for the spreader heel tangs being tough to do.
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