Shop vac with crevice tool. Sponges and the ilk do nothing to get the stuff in the cracks and joints. I use a shop vac then Q tips. Wood ribbed canoes are a beast to clean of sand and you really have to if you have a dacron boat cause the sand will work its way between the dacron ( or canvas) and the wood planking.
WIth a wood canvas canoe blasting it with water from the inside guarantees you will force the sand in harder and have a potential future problem.
You are right. Once home I do dry-scrub loose and shop vac off the accessible bilge debris before hosing the canoe down, so that gunk doesn’t end up washed into the gunwales or thwart ends. Sadly I don’t have a long enough extension cord to reach most of the places I trip, so I do use a sponge in while in the canoe to remove the boot or barefoot crud I have tracked in before it creeps into bad places.
I have seen older composite boats with wear areas right at the heel foot brace or pedal area, sea kayaks especially, perhaps from grinding sand against the hull for years. I don’t own any Dacron or wood ribbed canoes. Or any wood & canvas, so thankfully I’ve never had to go full Q tip and tweezers..
But on plastic/composite canoes with vinyl or aluminum gunwales the amount of debris that loosens from between the gunwales and thwarts with the canoe set upright can be impressive, especially if you haven’t blasted that area for a while (or ever). Gunk dribbles down the outside and collects in the bilge in startling amounts.
The underside of deck plates too. Or maybe especially. I have large drain holes or scuppers in all of the deck plates, even a ½ inch drain hole can become occluded with hosed out debris. That is where the hosed crud collects, and it doesn’t help that the covered deck plate area of the canoes I store outside are incredibly attractive to wrens. They can build new twiggy nests in the deck plate recess as fast as I can remove them.
BTW, the cheapest outside storage bird occlusion I have found is stuffing a small, partially deflated Dollar Store beach ball in the stems. It’s worth a couple of bucks not to see eggs splatter on the windshield at the start of a trip. How’s your washer fluid?
I am not a gram weenie, but I have blasted out enough sand, dirt and even small pebbles to account for at least a few ounces, and it sure doesn’t hurt the butt end longevity of thwarts and yokes to rid that debris.
Integral carbon gunwales and thwarts have value there beyond just weight savings. Dammit, I really can’t afford a modern boat.