Canoe seat strength

[cs]

Meant to take photos last nigth, but didn't get a chance, so I will have to explain without photos.

As some of you know I've finished my canoe (ain't got it in the water yet). I made the seats frames out of white oak. The frames are approxmitly 3/4" thk. x 2-1/2" wide. I have sit in these seats and they seem to do fine for me and others have sit in them. When someone over 160 lbs they seem to have a lot of flex in them.

Is this accetable or maybe I should add a stiffiner at the bottom of the frame?

Chad

[MJC]

What are the dimensions of the opening?

How wide are the frames?

How did you "cover" the opening?

[cs]

The opening is about 12" by 18" and the seat is laced with 2" wide nylon webbing.

Chad

[Iceboy]

Chad, the new cane seats in my f#$%glass Old Town Stillwater flex about 3/4 of an inch with a heavier person on them. I don't think a little flex will hurt unless you hear a sickening crack.

[Ian McColgin]

The webbing may concentrate the strain towards the center of the seat braces. Just make a parallelagram of force based on how much you depress the strapping and you'll see.

Woven cane is better at spreading the load which is why caned chairs and canoe seats can be made in such delicate shapes.

Some very interesting furniture has been made by ripping long curvey slots in plywood whereby the saw's kerf leaves the effect of a free-form slat construction. I'd think that 1/4" plywood with the outside grain running fore and aft and a series of parallel cuts that stay an inch and a half away from the front or back edges might make a nice flexable seat that conforms comfortably.

Or you could, as my old canoe instructor with the marvelous name of Rocky Brooks used to say, insist that the seats are not NOT! for sitting on but just for leaning against in a relaxed kneal. Only 'sports' sit on the seat.

[Bob Perkins]

Chad,

When I was at WoodenBoat School last year - We had *almost* the same exact question for Greg Rossel.

We were building seats out of 1/2" Cedar for a small boat. When we attached them, they seemed to have a lot of flex and we were concerned.

The answer was very simple - when the boat is in the water, the boat will move instead of the seat..

I *think* this applies - the canoe will move to counter the seat, so don't expect as much flex as a seat attached to a fixed surface.

Take Care,
Bob

[Dan Lindberg]

Chad,

It's OK for the seat frame to flex, I fact, you probably don't want to make it so big that the deflection is minimized, as the seat will be VERY heavy. The only concern I would have is that you used good clear, straight grained material for the frame.

I make my frames out of 7/8 WO but I'm a big guy, about 320, for little guys under 200, 3/4 should be fine. smile.gif

As for the kneeling, that's that eastern thing, here in the midwest we know seats are for sitting on. It's hard enough to hold and watch the rod and depth finder and dig out bait (leeches) while stting much less while kneeling. smile.gif

smile.gif ) good one

"The answer was very simple - when the boat is in the water, the boat will move instead of the seat.."

Dan

[Keith Wilson]

Sorry guys, the wood of the seat doesn't know or care whether the canoe's in the water or on land. The stresses in the seat frame, and the deflection relative to the supports, will be exactly the same in either case (ignoring hull shape distortion, and dynamic effects from waves). Trust me on this; it’s my business.

I added stiffeners to the rear seat of the canoe I built, about 3/4 x 1-1/2 with the long axis vertical, glued and screwed to the seat frame. You can cut them to a pleasing shape if you like, and the weight's not much. The frame was mahogany, which isn't as strong as the more normal ash or oak. I don't think the frame would have really broken, but the sag was unnerving.

And seats are definitely for sitting on. My knees get stiff enough after a couple of hours in a boat as it is.

[ 08-26-2004, 11:49 AM: Message edited by: Keith Wilson ]

[Popeye]

.. well not exactly identical loading, there will be a smoother dynamic load on the seat, since the hull displaces water.

howabout a stancion?

[cs]

Popeye I thought about that, but I would like to keep the area underneath the seat clear.

I think that the seat flex is more un-nerving than anything. I will try to get a chance tonight to look at adding a stiffner. I have extra oak to do this with.

Chad

[Dan Lindberg]

Chad,

A bit more info for you on seat frame.

The following are some frame cross sections and materials. The 1st dimension is the cross piece, the 2ed the stretcher, the 3rd the thickness.

1 5/8 - 1 3/8 x 13/16 Cherry This is Old Town sizes. OT usually uses Ash. A light seat.

1 3/4 - 1 1/2 x 15/16 White Oak My dimensions, holds my 320 lbs just fine. smile.gif A heavy seat.

2 - 1 3/4 x 7/8 Phil Mah My dimensions, also holds my 320 lbs just fine. A heavy seat.

1 5/8 - 1 5/8 x 7/8 Ash Dimensions of a long time W/C builder. A light seat.

Any of these cross section/material combinations would work fine for you.

Dan

[Popeye]

http://www.coldcreekcanoe.com/belted.jpg