I just picked up my new/used 2001 Merlin II. Yippee!.. and spent until 2am milling longer drops for the seat. The seat drops now use 6" SS screws.
I notice that the heads of the screws are counter-sunk into the wood gunwales. I’ve always seen and used washers under the seat and thwart screws. What are the pros and cons of one method vs. the other.
Thanks.
PS I’m off for my first paddle in the Merlin II. Yippee again!
I prefer not to countersink. Interrupts
more wood and leaves more end grain open to moisture. However, in some cases it might save skinned knuckles.
You might consider bracing your seat hangers against the hull with little slabs of minicell. Will firm things up a bit.
One big con for me is thumb bashing
on the washered screws as they are above the plane of the gunwale.
I have always preferred counter sunk or flush screws. You might think that they would sink further with the pressure pulling the seat down but so far that does not seem a big deal.
My Wildfire has countersunk screw
heads in cherry and even though I’m about 250 they haven’t been a problem. Admitedly I kneel 95% of the time, but do sit occasionally, and even when kneeling a lot of weight is on the seat.
Prefer it to the washers as per Kim’s observation.
I recomend a washer …
– Last Updated: Oct-24-11 10:35 PM EST –
...... there are options to choose from .
For basic flat head fastners (typically called countersunk type) , there are 3 types of trim washers available .
If not sure what these are just google them , they will be self explanatory once seen .
1.,... plain trim washer
2.,... flanged trim washer
3.,... flush trim washer
All can be had in in various non-corrosive metals such as stainless , brass , bronze , etc. ... most can be plated with a non-corrosive plating as well such as chrome , zinc , nickle , ect. .
If you want the fastner head to be flush or slightly below surface level use a flush washer .
Both flanged and plain trim washer set on the surface and are raised up . The flange type add more support strength than a plain (non-flanged) due to the flange .
Another worthwhile trick to consider if you are going to use a raised type trim washer ... is to just begin (not complete) a countersink bore in the wood to a dia. a tad over the fastners thread width . This allows the trim washer's interior to mushroom just ever so slightly down into the wood upon torquing (as opposed to crushing the wood) .
My 2006 Magic
came from the factory with what I consider overly-countersinked hanger screw holes. Easily over 1/2 the depth of the inwale. After a week’s trip to the BWCA I discovered a horizontal split that required repair.
What I ended up doing was installing brass threaded inserts and using a small countersink to champher them to support the screw head shoulders. No additional problems.
I plan on re-railing the hull sometime next year, and am torn between shallor countersinking and usig trim washers. I just do not like the idea of skinning my knuckles.
Jim
threaded brass insert …
… if it’s what I’m thinking of jsaults , that was a really good (and imaginative) idea you came up with … pretty neat .
Was it the type that use a flat screw driver to install ??
Hate raised screwheads
Screwheads screw up everything. Your rack, your friends boat that you rescued over-gunwale, and your hand. I’m not a fan.
McCrae wrote about overdrilling, filling the hole with epoxy, and after the epoxy cured, drilling right-sized through the epoxy. So you have an epoxy lined hole, and you know how McCrae deplored half solutions. He’d have to overdrill, epoxy, and re-countersink the depressions for the heads, too. He wouldn’t be able to stop himself (I miss poking fun at him).
An overdrill-epoxy-redrill procedure would not only leave a strong gunwale, it would disperse the load of the screw through the whole gunwale, resist splitting, and permanently seal the wood grain inside the hole against moisture. Will brass inserts do that? I don’t know about brass inserts, btw, anybody got links?
Anybody remember McCrae writing about doing that? Seems like it might be in the archives.
~~Chip
different wood
I have found cherry to be the least prone to the screws sinking in,ash nexr,and spruce a problem even with washers. I too would like a strong solution to flush gunnel screws-maybe a large headed stainless,non countersunk screw recessed slightly with a fostner bit-if they make such a screw?
Turtle
Truss heads.
– Last Updated: Oct-26-11 8:08 AM EST –
Good luck finding them long enough without going up to 1/4 X 24, though.
http://www.jamestowndistributors.com/userportal/show_product.do?pid=1130&familyName=%2310-24+S%2FS+Machine+Screws+Truss+Phillips
Tried-and-true carriage bolts are an alternative. I've found that most of the injury caused by exposed heads is due to deformed driver slots with sharp, ragged burrs. Carriage bolts were invented to eliminate the issue altogether.
http://www.wooden-canoes.com/material.htm#hardware
Yep. Plain old brass 1/4-20 insert.
It is large enough for the 10-24 hanger bolts to slide through. I did fabricate a “driver” out of a bolt and a couple of jammed nuts as I wanted the insert to set true - only one chance for success in this situation. The counter-sunk hole that Bell drilled in the inwale was 3/8, the same size as the insert needed for it’s pilot hole. And I lubed everything with Watco before installation. I was really worried about splitting the inwale, but it went in just fine.
Jim
Yeah, truss heads would be nice.
The basic design of the flathead, or oval head bolts creates a wedging action. Those of us who are heavier obviously split wood more efficiently.
Chip. I like the idea of the epoxy fill. But when I was doing these repairs I had not yet started to play with it. BTW, I lubed the inserts with Warco (liberally) as an aid to installation and to seal the grain.
Jim
We’re dealing with relatively
small dimensions in the section of an inwale here. I’d want to avoid severing as many fibers as possible by limiting the diameter of the through-holes to the necessary minimum. Oversizing and filling with thickened epoxy is ill-advised, IMO, as is countersinking. If you look at the tensile strengths of these long, narrow machine screws and bolts, you’ll find they are more than adequate. If anything, it’s the structural integrity of the rail and the fatigue caused by lateral forces on the fasteners that present risk of failure.
As you know, Jim, a good idea for heavier paddlers is to beef up the thickness of the inwale by sistering a batten to its underside.
Dad gum! Is that what I done?
“sistering a batten”…Thanks! Al least now I know the technical term for my woodhacking, err, woodworking.
Jim 
I made that up.
Sounds good, though, eh? ;^)