When installing new thwarts, with attachment underneath the inwales, should the thwarts fit tight against the skin of he canoe or should there be some amount of space?
I usually…
fit them leaving about an 1/8" from the hull. I also soften the corners and edges with a sanding block.
I do too.
I leave a small gap. On Royalex boats the material will deform somewhat and bulge outward if there is continuous pressure from a thwart.
I have not had a composite boat crack from a thwart pressing against the hull, but have heard about it happening.
I would leave a gap, but then fill it
with some dense foam such as minicell. Hull integrity will benefit somewhat from the bracing effect of the seats, but the foam will prevent local damage if something levers the seat crossbars hard against the hull.
Trick is to leave a gap
… and still have enough wood so that the hole isn’t so close to the end of the thwart that it will just tear out if things get sub-optimal out there.
I Leave a Gap
of about an 1/8". Seems that almost every thwart I’ve replaced has been rotten at the ends so now I cover each end with a layer of resin. Don’t know if that is good or bad but so far it seems to be on the good side!
A New Respect
It gives you a new respect for canoes when you see the additive effects of deck plates, a seat , and two thwarts on a flimsy envelope of fiberglassed cloth.
Someone gave me a canoe that had been upside down, covered with a tarp, on a picnic table for close to a decade. The gunwales showed only a vestige of their wooden origins, but bizarrely, the deck plates, the woven seat, and the thwarts - protected by the hull - were remarkably intact… Carrying it without the gunwales was like carrying a large dead fish.
I replaced the gunwales and was facinated at how nicely the boat stiffened with the addition of each cross member. Basically, five peicces of wood converted it from a squishy, formless envelope into a very serviceable watercraft.
Thanks for your advice. I fully applied it!
Sweet
It’s always good to salvage a canoe. I found a Mohawk 12’ pond hopper in the trash years ago. Cleaned it up and loaned it to a friend – who used it in a fishing tournament to win a kayak. Years later I loaned it out again to another friend. Finally gave it to a neighbor for his son.
History
– Last Updated: Oct-18-13 6:56 PM EST –
A Curtis, Bell and Placid, the protocol was to champher all sharp edges on a stationary belt sander and use a matchbookto space the thwart/grip ends from the laminate before boring the thwart's screw hole. Don't know about others.
The physics behind this is simple. Rails want to straighten, thwarts are inserted to make them bow and will install with zero clearance if allowed. the matchbook guaranteed some space.
Recent anti smoking campaigns have rendered the paper matchbook scarce. Wish I'd put a caliper on one before I gave up cigars. Now, they may go away completely. Some enterprising individual can make millions selling replacement plastic tabs to boat builders.?
SUB OPTIMAL! Love it.
Thwart placement
Personal preference. Newer factory boats seem to leave a space. I salvaged an old Sawyer Cruiser once. It was probably wrapped at one time. After persuading the aluminum gunwales to return somewhere near their original contours, it was very helpful to add 2 new thwarts fore and aft up against the aluminum to help the boat hold its shape. It firmed up the hull a lot. White ash shaped with a spoke shave and sanded. The thwarts and new cloth and epoxy saved a boat that was headed for a landfill. I paddled it for more than 10 years and sold it for $400.
As I recall
from my mis-spent youth a match book cover is about .015". I believe this is so because when we were without the proper tools (usually), we would set the ignition points (spec’d at around .015") on our old Ford jalopies using a match book cover. They were never in short supply as we all smoked like fiends. It is a wonder we survived any of that.
Peter