I picked up a Bell Wildfire in the Kevlar Deluxe layup a while back. From what I can gather the Kevlar Deluxe was made before the white gold but is similar. The seat was mounted at the gunwale for kneeling and so I lowered it by a few inches since I am a sitter.
One thing I noticed was that the gunwales flex a bit when I sit in the canoe. I am only 5’10" 150lbs so I was a bit suprised that it flexed like that. I have read a post on here where somebody had similar issues with the white gold layup. Here is a link.
So the options as I see them are:
- Add a carbon belly band to where the seat is to add stiffness/support.
- Add something under the seat to brace it against the bottom where there is more support.
- Do nothing and just paddle it or trade/sell it for something else so I don’t ruin a really nice canoe.
- Add a bottom mounted seat.
- Other options?
What would you do?
I had a White Gold Flashfire
I raised the seat of that boat to paddle it kneeling but I did paddle it sitting a few times and didn’t notice any distressing amount of flex, and I weigh considerably more than you do.
I had the gunwales off of that boat, as well as a Black Gold Bell Wildfire. The bare Flashfire hull was very noticeably floppier than the larger BG Wildfire hull, as would be expected.
I would consider trying an additional thwart mounted just behind the seat.
You couuld support it from below
– Last Updated: Aug-12-15 4:04 PM EST –
The shape of the hull within the zone of tumblehome on Bell canoes is naturally very poor at resisting the downward stress applied by a hung seat. I'm not saying it's a bad boat, but I saw the gunwales and hull of a much sturdier hull of similar design (on a different high-quality brand) fail completely due to the seat load of a stocky friend of mine, so I'm not surprised a lighter person would at least see some flex. How much does it flex? Maybe it's not enough to worry about.
If you want to have stiffer seat support, and since the boat already has an inefficient arrangement of the hull for resisting that load, reinforcing the hull itself seems like a not-so-efficient way to go. Placing a post beneath the seat, with the bottom of the post resting on an elongated "foot" along the keel line would provide the best result from the least material. You could also construct such a support out of minicell foam. If you were a kneeler, this would be a bad idea, but for sitting, it would be fine.
Oh, I like Pete's idea above, too. Though less efficient in terms of "engineering", it would help a lot, since the gunwales must flex in, in order to flex down, and you'll be stopping that inward bending action at the location of the thwart.
– Last Updated: Aug-12-15 4:18 PM EST –
Thanks for the suggestions.
It is hard to quantify how much it flexes but it is enough that it is noticeable and you can feel it move a bit when paddling hard. Also, it does flex down and in so the thwart idea may be good to try.
I can test with a piece of 1x2. Cut it down to size and put it that location to see if it stops the flexing or at least helps. If it does I can mount a proper thwart
I had thought about the minicell foam. I was going to buy some bulk foam and fit it so it was thicker than I needed so when it gave a little under my weight it would still offer some support. I am not sure how long that would hold up as eventually it would get give more and offer less support.
Quick and Easy: Wooden Post
– Last Updated: Aug-12-15 5:06 PM EST –
I have no familiarity with minicell foam, and don't know if it would compress a little over time.
I replaced a combination thwart/seat back in my smallest rowboat on account of the fact that I'm tall and needed more legroom. I replaced it with a thwart which has about one foot of rearward curvature, so it still "thwarts" at the same location while mostly occupying different space than before. Long story short, I was worried about someone sitting on the thing, or me accidentally falling on it, because with all that curvature, such an event would put enormous stress on the gunwale attachment points. I put a wooden post under the peak of the curve, and it works great. If I wanted to, I could literally stand on what otherwise would have been a very damage-prone structure.
I have used thwart to hull foam
pedestals on a half dozen canoes and have never noticed minicell losing its support over time. Ethafoam may, because the bubbles tend to erode, but minicell holds up.
the seat mounted on the rails acted as
a thwart making the rails much stiffer . doubling the span of a beam makes it many times more flexible and so does reducing the number of points of support… if the flexing is horizontal in nature, add a thwart or two.
If the flex is up and down stiffening the sidewalls should help . if the boat has shouldered tumblehome I would look there first. if you put your hand on the side of the canoe and bounce on the seat you may be able to feel where it flexes.
As already noted, …
– Last Updated: Aug-12-15 8:05 PM EST –
... the tumblehome shape leads to a weaker orientation of the hull, in regard to the direction of flexing that is at the root of this problem. Also, as noted, adding layers to the hull will be the least efficient method for stiffening that over-stressed zone (my friend's experience with the failure of a much more robust hull from this same kind of stress suggests that an efficient method is the safer bet). Also as noted above, the downward flex that is occurring must be associated with inward flexing too, so it's not either/or.
I don't know what you mean by "doubling the length of a beam". I see no analogy of that kind. However, the seat on hangers now has flexible connections to the gunwales, and those connections will do almost nothing to resist the movement of the gunwales in an inward direction (a necessary part of the downward flexing, as dictated by the hull shape in that zone).
Think of it this way. If you have a piece of cardboard that is too flexible for a given purpose, which modification will be more effective at making it a whole lot stiffer - adding another layer or two to the sheet of cardboard, or adding material in a way that changes the overall shape from that of a sheet to a much larger, three-dimensional structure? The two ideas suggested above represent the second method.
So my game plan will be
Add a temporary thwart without drilling and see if that helps.
I am also going to shape a municell foam pedestal and see how that works as well.
I will use whichever works best or a combination of both.
Thanks again for all the suggestions.
About that beam anology. I should have laid some groundwork. When the gunnel is subjected to lateral forces, it reacts in much the same way a structural beam reacts to vertical forces. With no midpoint restraint (the high mounted seat or a thwart) it is a single span. Say 16 feet. One thwart, two spans @ 8’. Two thwarts, three spans. etc. Shortening the span yields disproportionate reduction in deflection. And the same goes for beams continuous over two or three spans. So that center thwart has a dramatic effect on flexing rails by cutting the lateral span in half compounded by the fact that it is continuous past the end of the thwart.
This is oversimplified in that the thwart is only backed up by an equally floppy rail on the other side
but they work together to yield more stiffness than the sum of their parts.
I couldn’t tell what you were getting at the first time, but now it’s clear.