Originally Posted by BigSmile
1)The beam that forms part of the stern boomkin has a deep crack, that extends from the end to a mounting location for a stern railing pad.
I would love to get some advice on the repair and/or fill. The wood is bone dry now. I'm thinking it is best to do repairs
and fills before oiling.
2)Also, some smaller gaps between the lattice. Originally had epoxy, but with expansion and contraction, that didn't hold.
Appreciate any guidance. Thank you.
Bit of uh --controversy-- here, so, just for grins, let's examine BigSmile's inquiry in a little more depth
. I've got a couple of hours to burn...
First some context.
The square patch looks suspiciously like a stanchion base. If that is true, then the next question is 'are there lifelines
or railing at the top of the stanchion'?
, the cause is pretty clear, too much outboard
pressure was put on the lifeline and/or stanchion, and that pressure found a weakness, probably induced by the termination of the tenon and the thinness of the mortise. A closer look at the picture might serve to illustrate this hypotheses.
If the stanchion is topped by a rail, then the question becomes, Is it welded on or held by setscrews? A welded rail is much more rigid and unlikely to give; those held together by setscrews are notoriously unrigid and susceptible to deformation. Rigidity to a setscrew fastened rail can be added by either drilling and through-bolting (I use 316 10-24 pan head
machine screws and nylocs), or drilling a 3/16" hole through the rail fitting and stanchion and tapping for a 316 1/4-28 x 1/2" pan head
Once we've got the rail sufficiently rigid to spread the stresses out over all four mounting points, we can address the dastardly split plank. Short of replacing it entirely, some sort of 'repair' is necessary.
To begin with, probably the best initial thing to do would be to drill out the retaining dowels and remove the plank entirely. Then the actual situation
could be assessed and the proper fix could be determined. All the joints could also be properly cleaned and prepared for regluing, and the cracks could also be properly cleaned, glued and clamped before the structure is reassembled.
For the 'edge screw it for added strength' camp, the potential for added strength is directly proportional to the amount you can tighten the screws.
To get any significant added strength, the technique used here is very important, primarily because of the grain orientation but also because of the joint construction itself.
In outline, the split plank should be through drilled all the way to the tenoned cross-member, where the hole transitions to a pilot diameter for the tensioning screw.
In detail, for any significant added strength and to minimize (not eliminate) the very real danger
of splitting, here's a plan of action.
First a material and tool list. We'll assume the split plank is 3" wide and 3/4" thick. So you'll need: 2 ea. 3 3/4" #12 316 pan head sheet metal screws (silicon bronze would be better but good luck finding them) a 7/16 Forstner bit (to drill a flat bottomed hole), a 7/32" drill bit for drilling a through hole in the split plank to allow clamping to the crossmember, and a long 5/32" bit for drilling a pilot hole in the crossmember.
To start, drill a half inch deep hole with the forstner bit into the edge of the split plank. Then take the 7/32" bit and drill through the split plank (if you haven't disassembled the structure, take care not to drill into the crossmember!) If you have taken the structure apart, a drill press helps to keep the through hole centered. Finally, use the 5/32" bit to drill the pilot hole for the screw, drilling about 1/8" or so deeper than the length of the screw. (better to be too deep than too shallow) If you've take the structure apart, dry fit and clamp the structure back together so you can use the through hole in the split plank as a jig to properly place and align the pilot hole in the crossmember.
After all the drilling is done, do a final clean up and dry fit, if the wood is oily, clean with with MEK as per Minaret above if you're using epoxy (or any other glue really, as far as I know the oil will inhibit bonding with all glues). Finally liberally apply your chosen glue to both surfaces, clamp and then screw.
After a day or so remove the clamps, re-drill the dowel holes (to the next oversize if necessary) and glue in new dowels. Wait another day, sand and finish or not as desired...
A picture describing the 'theory' behind this method. hope it illustrates the advantage of using pan head versus counter sunk heads in this application.
A word about 'crack prevention'. While teak is strong and dense, it is a far cry from crystalline. In fact a better description would be laminate. For this reason, drilling more holes will make further splits more likely, because more area is left unattached to adjoining areas. The principle is much the same as grinding too much sound material from around a small crack in a fiberglass
repair; as more longitudinal fibers from the original structure are severed, the weaker the original structure becomes. (this of course doesn't hold for chop strand construction)
And finally, Minaret's suggestion of a plate screwed and glued to the underside, though maybe somewhat tongue in cheek, has merit. Or maybe four appropriately sized L-shaped plates as backing for the stanchion pads and screwed (or even through bolted) to the crossmembers...