Laminated Wood Seat frame failure postmortem and re-engineering

[sailsman63]

The center seat looks like the mount is cantilevered about six inched inside the hull. If the seat to mount joint flexes at all then the torsion has to absorbed by the hull.

Well, the seat to mount joints were not intended to flex at all, though I do take your point. The cantilever is closer to 4" but still....

@Jim Dodd: I agree that the brackets are not so great looking. (Hey, they were a prototype! Even if I stuck to the concept, They are scheduled for a replacement) In practice, seats mounted on the top surface have turned out to be too high when all the weight in the canoe is humans. The original swing rig would have had the seats about 3" lower but I had spacing issues, and could not mount them in all locations.

I have found that the brackets take a lot of space. I intended to remove any that I was not using for a particular trip to save room.

Hull mount blocks are starting to look more attractive, but I'm still concerned about flexibility of arrangements. For reference: In the last week and a half, I've paddled in the following load configurations:

- Solo flatwater+ breeze, 140# paddler, both unloaded and a 50# test load.
- Tandem, 2x 140#, light day gear. Local river/creek with moderate current and occasional riffles. Lots of snags.
- Triple flatwater. 140#, 170#, 180#, no gear. This one was a heavy (over)load, but worked out surprisingly well on sheltered water.

This variety of uses is typical for me (Except the big triple, but that may repeat occasionally)

For those who use their tandem in multiple ways: How do you manage to reconfigure for trimming a load? In all these cases, if I'd had seats locked in a single location, I'm not sure how well things would go.

I'm actually using throwable PFD cushions as temporary seating except for one of the ends, as the lower center of gravity is desirable.

Any thoughts on ideal/close to ideal positioning, or adjustable seating with a hull mount?

 

[Jim Dodd]

I've always hung my seats from the gunnels.
So my theory is to hang them low. I can always raise them easier than lowering them. Add more cushion, or shorten expensive stainless bolts, and hanger brackets.

I guess attaching blocks to the hull, I'd tend to do the same, easier to add, than subtract.

Jim

 

[Alan Gage]

I big dry bag partially full of water is a nice way to adjust trim.

Alan

 

[sailsman63]

Alan Gage how big a bag are you using for this purpose? I'd think you would need at least 5 gallons for this technique to make a difference.

For this to be viable, though, is have to settle on fixed fore/aft locations for the seats. Any guidelines? I found that having a front seat with the front edge 65" from the stem is too far back... the bow paddler can't get any turning leverage. Other things to keep in mind?

 

[Alan Gage]

how big a bag are you using for this purpose? I'd think you would need at least 5 gallons for this technique to make a difference.

I don't know. It would probably hold 3 gallons if completely filled. Since I'm always solo and only need to offset the weight of a 30 pound dog it's great plenty. I don't know how much you'd need for your tandem; it would depend on your weight and seat placement. One thing that helps you get by with less weight than you think you'd need is that you can place it way into the stem. You can always use a couple bags if you need more weight.

I can't help much with tandem seat placement. Today I need to figure out placement for seats in the tandem I'm building as well as if I want sliders or not. I'll measure the seat placement in my dad's old Penobscot 16 (mine is 16.5') and probably just go with that. I don't get too worked up about tandem seat placement since I never know what the bow and stern paddler weights will be or extra loads (dog, cooler, camping gear) will be coming along. That should get it close and I can use the front slider (if I go that route) to adjust trim on the water or else just use that dry bag partially filled with water.

Alan

 

[sailsman63]

Gonna have to do some thinking on that. I'm expecting unpredictable loads, which is why I went with three sliders in the first place. What type of slide rig are you considering? Everything I saw had issues, which is why I had the canteliver things in the first place.

How narrow are you willing to go for seat width? 18" sort of forces me closer to the middle of the canoe, especially if I drop them deeper.

 

[sailsman63]

Well, I got a chance to run a bit of an experiment with weight, solo. 50# sandbag, as far up as I could get it. The float bulkhead makes that about 24" back from stem. This was just barely enough for an acceptable day-paddle trim, if I sit front seat reversed style.... Not nearly flat enough to solo trip, though.

 

[Muskrat]

If it were me I would go with a non-adjustable center seat that is easily removable, mounted to the hull on blocks with spring clevis pins. Stern seat I would also mount fixed, but probably not removable. The only one you should really need to slide is the bow to adjust trim of a variety of passengers.

Solo empty sit in the center. Like Alan, I like a dry bag or cooler to slide around for trim adjustments.

Solo with a tripping load I sit in the back with all gear up front, but with a center seat you could split the gear front and back.

Also, your bow and stern sliders seem too close to the middle of the boat to me. I weigh about the same as you and I like my stern seat mounted as far back as possible so I don't have to reach out over the gunwales. It also helps since as light weight guys we usually have heavier people up front, so my weight all the way back has more leverage.

One other note. I notice you don't have any thwarts. Why not?

 

[Muskrat]

For perspective, I measured my stern seat in my Mattawa (15'8"). The front of it sits 40" from the stern. It's about 24" wide inside the gunwales there. I'm 5'7" 135. The seat is on 4" hangers. I started out with the rear seat farther forward, would have made life much easier had I mounted it farther aft to begin with.

 

[Cruiser]

Although I am new to this forum, I thought I might as well offer my $.02

As pointed out maple is very hard and the epoxy doesn't readily penetrate as it does on most wood, that makes the initial application of unthickened epoxy pretty essential, light clamping is also a good idea to keep the actual bond thickness to a minimum. For the tighter grain wood (maple, walnut) I like to use 5-10 of that 30 or so minutes of work time, to just let the thin epoxy soak in well.

I started out with sliding seats and ended replacing them with fixed versions, I found the sliders a bit of a pain and load shifting seemed to be an effective balance control measure. I use a seat design similar to what you built :



that joint is 2 dowels and epoxy using cherry ( I also thicken with cherry wood flour, I like the joints to pop a bit). The frame is 5 plys of 1/4" x 1" cherry, steam bent to shape and then epoxied together. I have 3 installed and they have taken up to 350 pounds, no failures yet. Not sure if using a cedar core is really a good idea for a seat and webbing anchor, maybe straight hardwood and smaller dimensions would perform better. If you were after the wood contrast, cherry can offer the same contrast.

I am with Jim, the rail supports look very cool, but I worry about the forces being applied to the hull. The idea of fixing the seats and adding a removable centre seat seems like the optimum idea. I suspect this option will give you the highest flexibility and will probably save weight as well.


Brian

 

[Alan Gage]

Although I am new to this forum, I thought I might as well offer my $.02

I started out with sliding seats and ended replacing them with fixed versions, I found the sliders a bit of a pain and load shifting seemed to be an effective balance control measure. I use a seat design similar to what you built :




Brian

Nice seat and an even better looking boat in the background. Welcome aboard and don't be a stranger!

Alan

 

[Jim Dodd]

Yes, I'll echo Alan's Welcome, Cruiser !

I'm thinking we have pleasantly crossed paths over at BMB ! I also recognized your nice storage rack on the wall.

Again Welcome !

Jim

 

[Cruiser]

Thank you for the welcome, I was looking around a bit for a site that covered camping more, this one seems to have a it .... what could be better than wilderness camping in a craft you built ... I know it works for me.

 

[sailsman63]

Thanks for all the thoughts.... still "Reviewing... the Situation.... I think I better think it out again!" (Fagin, as portrayed in the musical 'Oliver!')

Cruiser Very pretty boat, there! Thanks for sharing your experience with sliding seat arrangements. I'm starting to come 'round to a similar veiwpoint. I went with a cedar core partly for a lighter frame (Which worked out well in some respects) and partly for the pleasure of trying to figure out the engineering on such a structure. I'll compensate a little better for some of it's weaknesses in the next incarnation.

The slide structures turned out to be a bit of overreach, though I still think that the concept has a certain elegance, if executed properly.

Muskrat Several good points and questions in there. In order:

- Clip out Center with sliding bow: I'm still not entirely sold on hull block mounts in the center. The hull is at it's widest about 5" below the gunwale, due to how the knuckle turned out, and is still fairly wide at the height I'd want the seat. Also, if I pull the center seat for tripping, that leaves the blocks poking into the hull center. (Has anyone managed to catch gear on this sort of thing?) If, on the other hand, I stay with the gunwale hangers, I get to take all the mounting hardware off if I remove the seat.

You're the second to recommend a sliding bow seat. Outside of my custom rigs, which need to be re-thought, what sort of sliding arrangement would you recommend? I'm not too proud to borrow from anything that I think makes sense....

- Solo empty in center: So far, I've had issues with this location. It may simply be a lack of technique, but I have trouble with directional control from this location. Even heeled over (Learning a bit from watching guys do 'Canadian Style') I have to put a lot of force into the correctional 'Hook' at the end of my stroke, and still end up under-correcting. That may be something to discuss in a different thread, though.

- Solo load rear seat with gear up front: probably the way I would go so far, but I need a lot more than 50# of gear to trim correctly!

- End seats too far in: Definitely with you there. One of the things that's going to change. Reaching over the gunwale is less of an issue than it would seem, that part of the knuckled design is performing as intended, but you do have a point about turning leverage.

- Lack of Thwarts: the full up slide rigs were supposed to take on that job. I did add hard points for a carry yoke, but was in too much of a hurry to build it. That's on the agenda to be added, and a couple of the original slide attachment points will be perfect for 1/3 length thwart placements if I need to remove the carry thwart to seat a center passenger.

- Dimensions: 40" stem to front of seat sounds about right. I'm looking at 42," But I apparently have a finer entry on the hull. At that point, I have barely 19" width at the gunwale, and that's on the flared portion of the hull. By the time that I drop the seat 7"-8," which is what I'll probably go with, I'll have a hard time fitting 18" down there.

 

[Cruiser]

When I first decided I was going to build my own canoe(s) I had to think about the build issues and what type of boat to pick that would do all the things I wanted. After much thought and frustration, I came to the conclusion that I could build a really good solo or a really good tandem ..... I couldn't see how to build a really good solo/tandem.

My final solution was to build a solo first (primary mission) and then a tandem .... short story, have you considered a second build?

A lot of advantages to having a dedicated solo boat and none of the compromises you are currently trying to work out, plus the right solo will make you look forward to getting out in it. I love my first tandem and I am hoping my current tandem project is even better, but my solo is just a different beast ... sorta like driving the family minivan all week then getting into a sports car for the weekend ..... it carries my gear, is fast, stable, maneuverable and is lighter at the portages.

After building a canoe there is also the itch to build another to consider, maybe you just need a good scratch.

Brian

 

[Muskrat]

Cruiser has the right idea. Build another boat, a dedicated solo. You did such a great job on this one, I'm sure everyone here would love if you did another build.

You don't want to hear my thoughts on a sliding seat. I would copy a commercial slider like in a wenonah with (blasphemy ahead) aluminum tubing. Your boat is way too pretty for that. Maybe a slider is too complicated, often a simpler solution is the most elegant. Instead of a slider maybe just make a rig that has several notches for like three different seat positions. One for your lady up front, and a couple others for your bigger paddling buddies.

For the center seat, if you prefer hangers go for it. I personally like them better than blocks too, but making a hung system that is quickly removable is more difficult. I wouldn't worry about blocks impeding gear storage, in fact they could give you something to tie gear off to.

My canoe is short and wide so it spreads out pretty quickly. Just mount the seat as far back as you can comfortably fit it. Wing it back there and then adjust the bow seat accordingly. After some more time in the boat you may find yourself raising the seat. I like my stern seat high with the bow seat lower so I have more balance control than the bow paddler.

There is an article at paddling light for calculating seat positions with a little algebra.

http://www.paddlinglight.com/articles/how-to-calculate-canoe-seat-position/

I've probably given you more questions than answers. Maybe the natives had it right with ultimate adjustability. No seats.

 

[sailsman63]

Hmmm... I'm not going to completely reject the idea of another build. After all, I wouldn't mind going semi-pro someday, and the current boat was my third....

At the moment, though, I don't think I can currently justify the storage space a second boat would take up, and I may also have to consider finding a different shop space. (Reasons that have no place here.) I've not really considered a dedicated solo, that would make me re-think everything I think I know about how a canoe is supposed to handle.

One advantage to being the lighter guy is that I don't really need a wide seat, so I can fit further back in the stern with no trouble, even with a fine entry. I also may end up with a higher stern seat, especially if I can keep any load fairly low. In my last build, I would often end up on the stern deck, but that was because I had a heavier, non-canoeist in the (fixed and lowered) bow seat. (This was on occasions where I could persuade my Dad to try to fish out of a canoe. He prefers his high bow casting platform for hunting Northern Pike.)

One thing that may mitigate a higher seat is my hull form. The cross-section is rounder than some. I won't call it unstable, since I have managed to stand in the unloaded hull. However, it does not develop much hydrostatic righting moment when rolled, and does not require much weight shift to roll in the first place.

Seat hangers are something that I would re-configure only when necessary, and the way I have things set up, require less than five minutes with a wrench to remove.

I don't really consider aluminum as a blasphemy, just not what I would use in this case. I'm less concerned about the details of the slide itself, as i know I can build some strong, light beams, but I keep bumping into things on the idea of how they are suspended. I originally built the twisted lamination the way I did specifically to avoid a full-width spreader at the wide end of the slider setup. I'm starting to think that would only matter if I intend to run in the bow-reversed configuration solo.

Sort of weird thought: absent of mathematically determining trim moments, how do you estimate trim when floating, that is, how do you tell that your bow is high, etc?

 

[stripperguy]

Sort of weird thought: absent of mathematically determining trim moments, how do you estimate trim when floating, that is, how do you tell that your bow is high, etc?

Once you're familiar enough with the handling characteristics of your hull, you'll know instantly of you're stern heavy or not.
Until then, a pair of eyes from a short distance should be able to judge your fore-aft trim.
Some of my racing buddies would use electrical tape at the bow and stern to help gauge the trim. Then again, their hulls were translucent, and they could see the black tape through the hull. I suppose your wood strips are not thin enough to see through.
Most of my hulls have strips that I intentionally make parallel to the waterline, partly to help determine trim.

 

[Muskrat]

Bubble level

 

[latremorej]

No Title

I found this image on Google a while back while contemplating sliding seats. I saved it but cannot remember the who or when.