View Full Version : Extending Mast
07-29-2000, 05:03 PM
I'll try again, seems like I was going to get no response from the alloy mast concept. Has any extended an existing box section mast or have any ideas how you would ??
07-29-2000, 07:20 PM
The actual approach to extending I'd use is the same as I've actually used for repairs - scarff in new stuff.
The problem is: How big an extension? Loads from sailarea increase exponentially, so you'll need a correct rigging and structure design first. Then, if the existing mast sections meet that, you could extend.
Locating the extension could be fun. Again, I'd start with a correct design of a finished built-from-new mast. Given normal tapers, you could probably find a place to cut somewhere in the lower half, maybe a third of the way up.
Putting it together for a box section has lots of options. The one I used in a repair about 25 years ago was to cut each plank of the box at a different place and to cut along existing glue lines so that no scarff of any of the four parts was within 3' of any other. The wood lost to the kerf didn't matter since the new wood could be shaped to fit it. Each part had a 12:1 bevel. All the elements of the scarf took up almost 15' in the end, including some new wood to restore the mast to its original height after removing the damaged part. So it was an extension of what had been left.
I've used a cloths pin scarf in solid sticks but wasn't convinced it would work for this application, as it was a very bendy rig.
03-23-2002, 12:14 PM
As it happens the 56' Sitka box-beam stick on my 1939 41' Casey Cutter, "Woodwind", is sitting in my back yard as of this posting.
Had only been owning and restoring her for the past year when I noticed the base darkening beneath the varnish at the keel step. Pulled it recently for a thorough examination.
Discovered the previous owner didn't mention he botched up an earlier split at the base with a questionable scarf and short plug. No limbering for drainage, and sealed with epoxy all around the OUTSIDE base where she steps on the keel.
Now rotted to the point where a foot or two are beyond salvage.
So here's the plan. Will cut it square and plug it with a solid treated post cut at a sharp angle topmost. Liberally epoxy, (after CPES of course), that topmost area to create an inpenetrable basin for condensate and leakage. Then limber at the lowest point of the angle for drainage. Finally will piece in more spruce with staggered butt joints at a slight bevel to increase the epoxied mating surface but nothing like a real scarf.
Here is the theory. Base of mast on a keel step does not undergo any real flex. Straight compression load only. Scarfing around the solid plug under compression should be completely unecessary since you really just want a sturdy pedestal below the partners.
Why do otherwise with a short extension at the base?
OK so let me have it. No need to be gentle now.
03-23-2002, 01:13 PM
I'm interested in why your lenthening the mast. Is it an H-28.If so what are the dimetions now? hows it handle? wieght of boat?and why the for the extra hiegth.I'm aboat to build a new mast myself for my H-28 and was going to add a few feet.
03-23-2002, 04:44 PM
By any chance is she iron fastened?
03-23-2002, 11:30 PM
Vince, what are the chances of cutting that plug at an angle in both directions and limbering at the corner?
03-25-2002, 09:55 AM
Vince I think the idea that the base of the mast will only be subject to pure compression loads is true only in theory on your old boat . If the mast is wedged tight at the deck and there's any stretch in the old rig ( you probably hesitate to set it up bar taunt ),there'll be some lateral load on the mast foot . If a major piece of rigging parts the strength of the connection at the step may determine if the mast stands or falls . If it breaks loose down in the bilge there could be catastrophic damage .
I would look carefully at the size , shape , and fastening schedule of your mast step to get an idea of how much lateral force the designer and builder thought prudent to anticipate .Your mast repair should be strong enough to break the mast step out if it was used as a lever ( or some other part of the mast should carry away first ). To that end it seems like the plug should slide inside at least a distance equal to 12 times the thickness of the wall material . Sort of a structural lap joint as opposed to a structural scarf . I'd slide the plug in as far as possible . The question , I think , is does the plug alone have enough meat to match the strength designed into the mast step when the step is loaded laterally ?
[ 03-25-2002, 02:43 PM: Message edited by: Bill Perkins ]
03-25-2002, 11:18 PM
Try forgetting the old silver coin under the heel when you step it... use a tab of Viagra instead!
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