I posted this a few weeks ago and still haven't decided on the the best course of action. Would love more input, maybe this forum might attract some of the more technical guys.
OK, she's broken again. Always seems to happen when
funmeter is pegged. 20 kt gusts on flat water, hull flying with a crew of 3. Gave it up and the rig gently floated down, no real collateral damage. Biggest disappointment was that we had to give up on such great conditions! Looking for advice on a permanent repair.
The wingmast is a Graham design, built with Gougeon Bros techniques(epoxy/ply with a light S glass sheath, and now some additional carbon uni), meticulously constructed, but apparently not completely up to the sailing I put to it. The tang has an S glass core, anchored deep inside the mast, with a carbon sheath supposedly distributing the load to the outer surface of the mast. All that remains looks fine, with the exception of the bow shackle (1/4
pin in a 1/2
outside dia ss ferrule) that simply tore its way thru the composite.
Here are some ideas posed so far. 1) Sandwich the remaining tang with a couple of ss cheek plates. Thru bolt and epoxy to tang. Fill void betwen plates w epoxy and hi desity filler. Wrap w/ additional carbon. Use larger dia ferrule to distribute the load.
2) Cut out damaged area. Replace missing area with carbon plate (prepreg, autoclaved material), 1/2" thick, wrap w/ addtional carbon. Use larger dia ferrule or Spectra loop to attach to shrouds.
I have some doubts about the ability to bond the ss plates to the remaining tang, and any thru bolts or pins would probably exert the same kind of point loading that blew it out in the first place. The manufactured carbon plate should have much greater tear resistance than the orginal layup, but getting it securely bonded to the rmaining tang could be tricky. And is it ENOUGH stronger. This is a 36' mast, 11' boom with a big squaretop main, and it seems to generate huge forces (I have issues with the boom too!). Any more brilliant ideas out there? I'm counting on you guys!
Dave 509 276 6355
Edited by davefarmer (07/13/07 06:14 PM)
a pic of the remaining tang
the piece torn out
hi dave, i think this can be resolved, contact usa151@aol.com so i can send you pictures ...
hans
With Hans' invaluable assistance I've decided to have a substantial ss tang fabricated that wraps (with 2 legs per side) all the way back to the aluminum mainsail track (screwed to track), possibly with 2 or 3 studs from the leading edge directly to the track. Anyone know where I can find 12" ss threaded rod (8-32, 10-24, 12-20)?
Dave
call or webvisit to Small Parts Co., Miami= $ but in the mail fast, and they will tell you what the material actually is.
Did the shackle saw thru the carbon? SS tube section insert? Kevlar wrap?
I don't think it sawed thru, although it's possible.
Sorta looks like it blew out in one last gasp. It did have a ss ferrule set into the tang. A reasonable amount of carbon was wrapped over the tang, no kevlar.
My current intent is to have a custom ss tang fabricated that wraps all the way back to the aluminum mast track on the aft edge of the mast, and screw to it (as well as epoxy).
Dave
Did the repair this weekend, went well. Had the ss tang fabricated here in Spokane, and within 3 hrs of arriving in Rollins had it epoxied and bolted into place. Post cured it overnight, had the stick pointing skyward by 2pm. Took a nap, was awakened by wind at 6 PM, and was flying a hull til dark. Success! Thanks Hans!
Dave
how about a pic of the repair?
eric e
How about a pic of the boat sailing after the repair?