[Public-List] mast beam repair

Thu Jan 7 06:21:45 PST 2010

Even Epoxy glue joints fail for things like tabbing and gluing things in sheer.  For tab joints, the recommended solution is to use slots cut through the material, and strips of fibreglass.  Don Casey's book This Old Boat (2cd version) has a picture in it of how to do this.  I would guess that just wrapping the entire beam in 3 places with 3" fibreglass would work well.  If you go to an art store and buy some acetate, then you can glue all the layers up at once and get a glass-smooth result.  The procedure is:

Base layer - smooth plywood or the like
1-2 layers of felt (to distribut the pressure
acetate
epoxy (apply to all of acetate, fibreglass and wood)
fibreglass strips 1/4, 1/2, 3/4 positions, wrap all the way around the beam, meeting at the TOP - you want to be able to tension these to make sharp corners
Wood layers - with epoxy applied - consider thickening with wood flour unless your layers are perfectly smooth
fibreglass strips,
acetate
1-2 layers of felt
waterbag from pool store (or sand if you are outside) - use warm water as this will help the epoxy set and penetrate nicely.  Waterbags do not stick to epoxy and in and of themselves make a fairly smooth surface, so for small areas, you can just use it directly.

Use duct tape on the "side" of the laminations (this is what the bottom will be when it is in place) - duct tape does not stick to epoxy on either side unless you get the epoxy around the edge of the duct tape - you and also use a piece of acetate here, but it will not result in as smooth an appearance as there isn't any way to get the weave fully filled without a bit of pressure and being flat.  You could try not epoxying the sides so that you can epoxy them later under pressure.

The ideal way to apply pressure is actually with a vacuum bag, and that also produces glass like surfaces.  

If you just wrap something without the pressure/acetate, it is very hard to get clean edges as the glass tape has a seam that tends to pull up and make a hard ridge.  I've done both for building my Spindrift 10N dinghy, and this method works quite well, although not as well as vacuum bagging.

Bill.

----- Original Message ----
From: "crufone at comcast.net" <crufone at comcast.net>
To: bikecharles <bikecharles at earthlink.net>; Alberg 30 Public List -- open to all <public-list at lists.alberg30.org>
Sent: Wed, January 6, 2010 10:14:37 PM
Subject: Re: [Public-List] mast beam repair

Hi Charles, 

When I get to this repair on my boat #133 I plan to jack the beam up to it's proper/original position determined by how the doors fit the casing trim into the v berth.  This part has been done over the past year after the mast was removed . 

 A template will be made of the lower curved surface of the beam so I know what the shape of the inside curve is. The beam will then be removed from the boat and the laminates taken apart. After the laminates have been  cleaned up and sanded they will be relaminated using an Epoxy a dhesive. A form will be made from the template and the laminates laid and secured to it with pins and wedges. 

After the whole mess is cured it will be cleaned up and reinstalled back into the boat as it was originally. 
The original adhesive functioned well for about 43 years. T he laminates have not broken but the adhesive has given way allowing the laminates to slip against each other.  I like the look of the wooden beam and wish to retain that appearance. I expect the Epoxy repair to last beyond the rest of my life time. That works for me. 

Another advantage of removing the beam is that I will be able to inspect the upper surface of the beam for any deterioration from possible water intrusion. I should also be able to better seal the passages for the wiring which passes through the coach roof adjacent to the mast step plate from the underside of the coach roof. 

Michael #133----- Original Message ----- 
From: "bikecharles" <bikecharles at earthlink.net> 
To: public-list at lists.alberg30.org 
Sent: Tuesday, January 5, 2010 9:08:39 PM GMT -05:00 US/Canada Eastern 
Subject: [Public-List] mast beam repair 

Thanks to all who provided input on my last inquiry about the mast beam.  I'm still pondering the best approach to repair the mast beam on Sea Hawk #221.  I've contacted the outfit mentioned on the A30 website about the Aluminum Sister Plates for the mast beam.  They've become a bit pricey these days...$420.00 before shipping.  Considering the simplicity of the repair and the relatively low cost of the raw materials, (about $145.00 for for the Aluminum),it would make sense to fabricate them myself.  Does anybody know of an existing pattern or schematic for the plates.  Additionally, I was curious if those that have done this repair removed, repaired or did anything to the old tabbing on the beam or is it just left and covered?   
Thanks again 
Charles 
Sea Hawk #221 
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