Repairing Coamings

[C-195]

Last month took the coamings off my Commander since one is split about half-way the length of the board.  Last owner sunk a big lag bolt through the end into the deck but even that gave way over time.  

Since the coaming is weight bearing for the winches I want to repair it correctly.  Advise is welcome.  Think my options are as follows;

1. sink wood biscuits on either side of the split.  Then hold the split open as far as I dare and slather wood glue into the split and also glue the biscuits into their slots and clamp shut until dry.
2. finish ripping the coaming so I have 2 pieces and repeat as above.  

Pictures are here.  Thanks in advance.

[bill@ariel231]

You are on the right track thinking biscuits and epoxy. I had a similar issue to fix on A-231. some details are on posts 41 and 42. although i used beech biscuits with no issue, you might also want to look into making teak or fiberglass biscuits as suggested by Ebb.

http://www.pearsonariel.org/discussion/showthread.php?1230-A-231-Periwinkle/

good luck, it is a fun project.
bill

[Ariel 109]

I wouldn't split the board in two, nor use biscuits.  Epoxy and proper clamping should be all that is required.  Good luck with your new boat!

[ebb]

Nearly everybody's coamings have split because they are attacht to the sidedeck with a hard
right angle cutout at the end of the cockpit that is designed to split by  pushing  and pulling
on the unsupported part of the plank.   It's a 'natural'.  Shows coamings are made with real wood!
Don't know what or why I said 'fiberglass or teak biscuits', if I did, have to amend it.

Will go with Ben and Bill and glue the split together.... FIRST.  The split FITS together and the
irregularities will Probably make a good bond.  There are some problems, especially if the coamings
at one time were varnished with the crack open and splinters, or any other crud is in there.

Carefull cleaning  by hand is called for.  Dental picks are good. Try not to gouge the face.  Do some
 careful dry runs clamping together to see if it wants to close up OK. Choice of glue is worthy of
 discussion.   I'd use epoxy - because it's clear,  easy to use. Thickens with cabosil.   Mix up a
loose gel  so that it doesn't run out the crack while gluing - stays in there  while cranking on the
clamps at the same time.  You want squeeze-out.  Old surfaces aren't great for gluing...
Want to prime inside the crack surface wilh liquid first.  Let it run out. Dry wipe it off the TAPE(~~)
Do the priming just before you do the thickened epoxy. I like to dab with a two-inch bristle brush.


But imco, it's really important to add some kind of reinforcement where the crack is, because
the same random forces will crack it open in the same place...... again.

[As for fiberglass dowel inserts: There are  nice precise dowel-rods available in small diameters
 like 1/4"  & 3/8"  You want to improvise a jig* so that you can drill 1/4" (my choice) holes up
into the plank from the bottom.  Maybe 3 or 4 inches deep,  crossing the split.  A jig is needed
 to make sure  deep holes do not wander.  Holes are straight, and must stay centered all the way.
These solid white fiberglass rods (Tap Plastic) are made with oriented strands of glass.  They will
work well, but I think better dowels are made with  mahogany wood - which has definite grain.
Precise  (1/4" diameter is exactly 1/4")  HONDURAS MAHOGANY DOWELS are available from
Constatines. Wouldn't do larger  than 1/4" dowel in 3/4" coaming. 3/8" OK in thicker coamings.]

After you have the crack closing good in trial clampings,  then wedge it open  just a little more
at the end where the crack begins.  A little helps a lot.  Might clamp the coaming
at midway where it isn't separated yet so you don't split it any more.  Then....mask the split...
 
~~TAPE the crack  on both sides , on both faces, with wide blue (3M 60 day painter's) tape.
Just the empty crack shows.  Try to use single long strips that you trim with an Xacto knife to fit.
This allows  slathering room for lightly gelled epoxy applied with  two inch bristle and acid brushes,
flexible puttyknife or plastic spatula. Remove wedge. Carefully draw split closed. with bar clamps.    
Lift off squeeze-out from tape with puttyknife, wipe with dry folded dry paper towels.  Remove final
squeeze-out  after final check to see that coaming has not cupped during clamping.   Clamp  firmly
- but not too tight.  (If needed, improvise CROSS PLANK CLEATS and spring clamps to keep plank
flat while curing.) After partial set, ie  no longer wet-sticky, but gummy,  slice off the  remaining  
ridges of squeeze-out with  a sharp flat chisel.   Pull the tape before epoxy sets - so it doesn't bond.
Cured epoxy is harder than wood coaming - make sure there is no pronounced ridge - which can
cause uneven sanding on the old surface.


DOWELS.  Set up a movable JIG* for  deep HOLE DRILLING.  Space them where ever wanted.  
Think you need  no more then one every ten inches along the bottom - could have more
- with maybe a couple dowels three or four inches apart at the beginning of the crack.
Textbook is to shallow GROOVE THE SIDES (2, 3) of the dowels with a western hand saw  
(makes a wider  channel than a pull saw).  This will allow dowels when coated with  epoxy
 to be tapped home by letting captured air in the hole to escape. Chamfering the  tips helps, too.

Your coamings look quite weathered.  Imco, the two-stage gluing & doweling should be
compleated before any sanding prep.  Would NOT run the boards through a planer or  drum
sander.  The sander would be the better choice, but once the sanding progresses the temptation
for a perfect surface will probably end with coamings  too thin to be usable.

Glue the coaming together first.  Then do the doweling, separately.  Mahogany dowels at least
 an inch deep beyond the crack - into good old healthy wood - drilled thru the bottom edge
 - is the best way to go.   Imco same wood cross grain dowelling makes a closer bond than
glass or threaded metal.  Sand, leaving the coaming blocks attacht,  if in good condition.  
Would pre-dowel new coamings same way, anticipating  they will want to split otherwise.
Just long winded opinion.  Just ideas.  Ebb's really not a frikkin know-it-all.
.........................................................................................................................................
*JIG:  Drill a 90degree  dowel- sized hole thru a square piece of 1 1/2"-2" wide hardwood stock
that matches the width  of the  coaming.   Glue or screw  two extension legs to the sides of the jig,
making a 'U'  to clamp  onto the edge of the plank.  Drill a test piece in scrap before drilling
 a coaming.   And tap in a long dowel to check if it's actually parallel  with the sides.
Drilling deep  holes with the coaming flat, will make it easier to clear the holes while drilling.
Need to acquire an 'extended reach'  drill bit (8" - McMasterCarr). Not a short-flute 'aircraft' bit..
.........................................................................................................................................
After sanding, seal with two coats slightly thinned epoxy.  All over.  Add 10 coats good UV varnish.
If you have converted to LeTonkinois,  coat the bare wood and mount the coamings between
coats.  Imco, warm butyl tape or Dolfinite are better bedding compounds than tube rubber.

[SkipperJer]

I had almost exactly the same crack in my starboard coaming. If I clamped it together the board would not lay flat. Enough wood had been worn or rotted out of the gap that it was distorted if pulled together.  I put the coaming flat on waxed paper, filled the crack with epoxy that had sanding dust from the coaming mixed in with it, and let it set.  When finished it showed up as a dark-ish line that got wider by the aft end of the board.  It's been holding up just fine for three years.  The strength is in the epoxy. Don't split it. Just glue it up and sail