> My wooden boom split in the middle near the end where the clew is attached
> to a cleat mounted on the boom. The split is about 8-10" long. Any
> suggestions on repairing it? I am wondering if I can epoxy it together,
fill
> the screw holes, and reposition the cleat.
HI Ed,
I have never repaired a wooden boom, but I have seen and done repairs that
lasted for years on wooden rudders on racing dinghies. There are usually two
pins that go thru the rudders near the top for attaching to the rudder head
castings on racing dinghies. The split always goes from the pins up to the
top of the rudder blade, running with the grain of the mahogany. They split
due to water absorption (read: deteriorated varnish) or too much weather helm
all the time or a combination of both factors.
Here's the "shippy" <grin> way to do the repair for a rudder, with suggestions
for your boom. Before anybody protests that I'm making too big a deal out it,
let me just say "different strokes for different folks <bigger grin>.
Get some hardwood (if possible, use the same kind of wood) dowels of
appropriate diameter. For the rudders ( 0.75 inches thick), the dowels used
are less than 1/4 inch diameter, or a 1/3 to a /14 of the thickness of the
rudder. On the rudders, the split is usally about 3-4 inches long and three
holes (sometimes two) are drilled.
First, Wash with soapy water, then wipe with acetone. if there are any dark
stains on the wood, bleach them out with oxalic acid. Sand off any lifted
wood grain on the surface of the wood. Prepare the crack in the wood by
removing any splinters and make sure you can clamp it so the crack closes
perfectly. Then, using marine grade epoxy or polyesters resin, thickened with
an adhesive epoxy resin filler (so that any gaps will be filled), coat as much
of the surface of the crack as you can. Clamp the crack, squeezing out the
excess resin, wiping of excess. Cure for 48 hours at 50F or warmer. Remove
clamps. Sand off any epoxy drips.
Drill holes the same size as the dowels or maybe a 32nd larger perpendicular
to the split in the wood, parallel to each other. Test with a spare piece of
dowel to be sure that you can force the dowel thru the holes snugly but
without using so much force that you split the dowels with your rubber hammer.
Cut dowels a little longer (1"?) than needed to go thru the holes. Coat the
holes and the dowels with unthickened resin. Drive the dowels into the holes
with the rubber hammer or wooden block so that there's excess on both sides
sticking through the wood. Wipe off excess with acetone. Cure until the
epoxy has passed its "like hard rubber stage", probably 6-10 hours, depending
on the resin used.
Sand the excess dowels ends flush. At this point, if it were my rudder or
boom, I would wrap the split section with a light-weigth layer of E-glass
extending several inches past the split, so that it was stronger than the
original.
This next step is really optional, depending on how compulsive you are. If it
were my rudder (boom), I'd probably wrap the whole length in E- glass. For a
boom, "surfboard glass" would work well; it's really thin and becomes totally
transparent when wetted out with resin. I'd probably use "surfboard" resin,
it has the best UV resistance, but if I already owned the other epoxy I might
not spend the extra $14 at Tap for a quart of specialty resin and hardener.
The first coat, I'd use "tacky" resin or additive (available at Tap Plastic),
to get the glass to adhere without air pockets to the curved surface of the
boom (that's probably the trickiest part of this whole job, but at least you
don't have to deal with square corners. Corners are tricky when you're laying
glass.)
Finish up with three to six thin coats of resin over the area to make a
moisture barrier. Sand the area first with 120 to provide a good surface for
the resin to mechanically "key" into. Use a roller to get thin coats, not a
brush. Apply each succeeding coat while the resin is in its "hard rubber"
consistency; if you let it get past the stage where you can dent it with a
finger nail, you'll have to sand it before applying the next coat.
The last step is a applying a good UV barrier. Most, if not all, resins are
inferior to marine grade varnish in UV resistance, but much more scratch and
chip resistant. Wash the area with water to remove the amine blush left by
the resin before applying varnish or else the varnish won't cure. (Also, wash
off the amine blush with water (not mineral spirits, etc) if you let the resin
fully cure between coats. Failure to do so makes a sticky gooey mess!)
Here's a list of the materials I'd use with guesstimates of cost based on my
recent experience:
West System Repair Kits: Little foil packs of West Epoxy resin and hardener,
pre-measured. about 2-3 each, or $10 for five. I keep several on the boat
for emergencies. I highly reccomend using the West System; I haven't had a
bad batch of resin since I switched to it. Also read their free booklets
available where ever the West System is sold.
Adhesive Filler - West #403 or 406; 403 is especially good for gluing wood,
406 is the most versatile with very good bonding, fairing. and sanding
properties. Both cure to an off white color. Both are adequate to get the
job done well. About $8 a container that will last for many projects.
Surfboard resin - available from Tap plastic. $10-11/quart. Hardener is $1.00
per tiny bottle. West has a similar UV resistant epoxy resin for wood
coating, I haven't heard much about it though.
Varnish: I'd finsih any resin with and easily maintained coating like Armada
or spar varnish. don't skimp of\n the varnish -- make sure you're getting
marine grade UV resistant vanish. I don't trust the varnishes at the hardware
store. <your opinion may differ> Recommended thickniess for durability is 20
mil. that's 6 or 8 coats. Should be able to maintain that with one or two
coats of touch up a year. I hate varnishing! <grin> Wood is pretty, but
stainless steel or aluminun or plastic is more time sailing, less time
varnishing. Even paint is more UV stable and harder.
Surfboard glass - available from Tap plastic. $5/ per yard. One yard should
do it?
Tacky resin - Available from Tap plastic. Never used it. Wish I had on my
last project with a curved surface. My more experienced friends told me to
not be so penny-wise and pound foolish next time.
Dowels - whereever you can find them. Check with a woodworkers specialty
store.
Gloves - West Marine, Tap plastic. Get the green ones, latex gloves dissolve
with resin. $1/ pair.
Plastic Mixing pots - West marine or Tap plastic. Worth the $0.85. After the
resin hardens (48 hours), you can pop it out and resuse the pot. rotate thru
4 or 5 of them and keep reusing them.
Sand paper - The red stuff works best and is available at marine stores and
professional automotive supply stores. The light green stuff made by Norton
company is almost as good and available at most hardware stores. The light
brown stuff won't last 2 minutes before clogging.
Oxalic acid - available at any hardware store. a few bucks. one bottle of
crystals lasts years.
General tips: always wash with water (for amine blush) or acetone/spirits
(for grease and wax) before you sand, to avoid sanding the contaminant into
the wood grain. Also, washing before sanding reduces clogging on the
sandpaper.
Last word of caution -- moisture and UV will eat your boat over 5-20 years.
The epoxy will protect it from moisture forever as long as you keep varnish
over it. I haven't yet found a varnish that lasts forever, but right now I'm
using Armada (similar to Cetol but I like the color better) because it's
easier to apply and get a decent finish than traditional varnish. I'm not
that good at varnishing... can't keep the dog hair out of the final coat
<grin>
Good luck , Ed. With a repair like this, you shouldn't have to worry about it
ever splitting agina, unless you drill too many holes in the boom or let it
get moisture inside. Install your fasteners so they compress the wood rather
than split it. It will be stronger than new and have a gorgoeous, durable
wood grain finish.
If you have any questions, email me. I'll try to answer them, and if I don't
know the answer, I know folks who do.
Judy B.
Judith Blumhorst, DC
HMS18/P19 Fleet Captain, Potter's Yachters
WWP-19 #266 "Red Wing"
SF Bay, CA