I am planning to install tie down points with 1Ē webbing, gflex and fiberglass, on a Wenonah ultralight canoe. These points will tie down packs, camping gear and air bags. My question is whether, for strength, to install these on areas where there is a foam core underneath, on areas where there is not foam core underneath, or does it matter? Also, is the center area of the hull better/stronger than the chines area or the tumblehome area? Are the rib areas a good place for them? Would the areas with foam underneath have chance of delaminating under stress?
This summer, I plan some extensive practice time overturning the canoe and reentry, etc. I like tying in gear and would prefer not to debate that. These tie down points will see some significant stress keeping heavy packs in place, etc., and so I want to locate them in the strongest areas possible. Your collective thoughts would be much appreciated. Thanks.
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It may not matter, but if you want to ..|
Posted by: guideboatguy on Mar-19-13 3:38 PM (EST)
I would avoid placing tie points over |
Posted by: ezwater on Mar-19-13 5:23 PM (EST)
the foam core or its margins. An exception might be made if a tie point is only going to serve light duty.
Why not the margins?|
Posted by: guideboatguy on Mar-19-13 5:41 PM (EST)
The margins are a weakness zone, not |
Posted by: ezwater on Mar-20-13 12:31 AM (EST)
a strength. The chines are also a problem area. I'm assuming his tie points are going to do something significant. Now, if they're only going to snub down his laundry basket, then he can put them anywhere.
Okay, but how are ultra-lights used?|
Posted by: guideboatguy on Mar-20-13 8:03 AM (EST)
I'm curious why the chines would be weak|
Posted by: clarion on Mar-20-13 8:23 AM (EST)
To my thinking the chines - being an arch - would be the strongest place for attachment. What am I missing?
I agree with you|
Posted by: guideboatguy on Mar-20-13 8:53 AM (EST)
Along the same lines as a stiffening member, the curved chine will be effective at transferring a point load forward and backward some distance away from the point where the force is actually applied, effectively spreading the load over a much larger area, and thereby reducing stress per unit of area.
You're looking for a stiff attachment |
Posted by: ezwater on Mar-21-13 1:38 AM (EST)
point, but stiffness doesn't matter as much as choosing a place where the tie won't get in synergy with other stresses to cause damage.
I was thinking about that last night...|
Posted by: guideboatguy on Mar-21-13 8:54 AM (EST)
... and I could envision situations were anchoring inside the chines might not be best, as it would create a zone of compression rather than tension and the hull might be less resistant to crumpling than stretching. Also, it might tend to not involve the full contact area of the anchor pad. For this particular boat though with its ultra-light hull, I think we may now be in agreement that the parts of the hull which are not stiffened (as well as the part over the top of the foam core, even though overall that's a stiff location) are likely to be quite "floppy" when pulled on by tie-downs.
I assumed an ultra-light to be paddled|
Posted by: clarion on Mar-21-13 9:04 AM (EST)
... and treated like an ultra-light. I would agree that on a WW boat that could be expected to take some chine hits I would not want to add those stresses.
Posted by: LeeG on Mar-20-13 9:07 AM (EST)
The sloped transition from the tapered core floor and between the ribs has a doubled layer of cloth that is quite rigid.
Confirms my hunch to avoid the foam|
Posted by: DaveO1 on Mar-19-13 8:05 PM (EST)
Both you guys post great information, and I appreciate your answering my specific questions. You are confirming my hunch to avoid the foam.
Super high quality scissors can make |
Posted by: ezwater on Mar-20-13 1:46 AM (EST)
cutting Kevlar easy, but I cut Kevlar with cheap office supply scissors.
Is Kevlar really necessary?|
Posted by: LeeG on Mar-20-13 9:12 AM (EST)
A couple of follow up questions|
Posted by: DaveO1 on Mar-20-13 10:09 AM (EST)
If I am reading you correctly, you are suggesting that the Kevlar patch should go under the strap tie-down. My simplistic thought was to put the Kevlar over the strap ends. I assume putting the Kevlar under is to reinforce the hull there, yes? Putting the Kevlar over the strap ends is overkill for holding them in place and just the epoxy is plenty sufficient, yes?
Posted by: guideboatguy on Mar-20-13 2:00 PM (EST)
Dave, Kevlar is often a better "inside" |
Posted by: ezwater on Mar-21-13 2:38 AM (EST)
cloth because of its strength in tension. Another benefit is that while glass may yield tiny shards, Kevlar will not. But glass cloth can be used for inside tie points. I've used it for thigh straps in decked c-1s and have not gotten itchy knees.
well, whatever you do -|
Posted by: Mattt on Mar-20-13 8:45 AM (EST)
don't ask Wenonah for thier opinion.
Unnecessary and rude|
Posted by: DaveO1 on Mar-20-13 10:52 AM (EST)
Mattt, if youíve read even a few posts by g2d and guideboatguy, you would know that they know as much as anyone about this stuff. I highly value their opinions. Moreover, they are generous enough to take the time to answer questions in writing, with considered, follow up dialogue.
Posted by: mrmannerz on Mar-21-13 9:35 PM (EST)
I'm not mad, but I have a question|
Posted by: guideboatguy on Mar-21-13 11:22 PM (EST)
What calculations are you referring to? Based on the assumption that you want the anchors to be on a stiff part of the hull rather the floppy parts which will flex severely in response to very small amounts of force, what was incorrect? I'm open to the possibility that unexpected forms of failure might be possible when subjecting the stiff, more-curved parts of the structure to extreme force, but even g2d seems to acknowledge that this isn't a situation where such forces will be a concern, and interfering with the repair of collision damage wouldn't seem to be an issue in this case either. If you think, or even if Wenonah thinks, that anchoring to the floppy locations on the hull must surely be better, I'd love to see how that would turn out. I've seen a couple of lightweight canoes with such accessories installed, but at the time I didn't have a reason to remember where the tie-downs were placed, and no reason to ask the owner how happy he was with the job either.
its a general comment|
Posted by: mrmannerz on Mar-22-13 9:08 AM (EST)
about your engineering logic having seen many of your posts. You need to be careful, because you do talk a good enough game that some people might believe you as gospel and do some damage....watch out for unintended consequences. For instance, in this case you viewed the area where the two skins converging over the edge of the foam to be something like "half of an I-beam". A few problems there. I-beams aren't designed to be loaded in tension on the flanges...the flanges are there to stabilize the web (half I-beams are shitty things to mess with anyway, but that's a different matter). More importantly, it's structurally NOT half an I-beam, but, in 2-D a wishbone with the anticipated load pulling the two legs of the wishbone apart. That's not good, because there is a stress multiplier where the two skins (legs of the wishbone) meet. Assuming the foam to be of minimal strength in tension, the load goes to the skins (leg of wishbone), the stress seen at the crotch of the wishbone is 2,3,4 or more times what simple calculations would show, and voile, you pull the skin laminations apart...oops. As an engineer, my first move would be to call Wenonah and make an inquiry as to where to put the attachments...because, I don't know for sure where the best place to put the attachments is, but they most likely do. There's at least an hour into this whole forum line, some of it is okay and some of it is wrong. Wenonah might actually have a 1 minute answer to the question. In engineering, you don't engineer what you don't need to engineer. "I don't know" is a really good phrase for any engineering student to learn and use...keeps people from getting hurt.
Let's try it a little simpler|
Posted by: clarion on Mar-22-13 9:17 AM (EST)
Forget the pack. Certainly having anchors for air bags would be worth doing.
Posted by: mrmannerz on Mar-23-13 12:53 PM (EST)
for airbags, it just won't matter much. Design-wise, put them somewhere off of the ribs...just so they are more out of the way when the bag is not in use. Position them where they hold the airbag securely. Structurally, the boat is good for sliding over a beaver dam, a round submerged rock, log, etc. Without wasting time doing any math, the load from the airbag attachment will be less than those normal mishaps. My previous comments were more about misleading "engineering" knowledge, so to speak.
But a 45 pound pack tied in at a couple |
Posted by: clarion on Mar-23-13 2:52 PM (EST)
.... points is in a much different category altogether?
I don't buy it either|
Posted by: guideboatguy on Mar-23-13 4:35 PM (EST)
Like I said|
Posted by: mrmannerz on Mar-23-13 4:52 PM (EST)
My original points in this discussion were about bad engineering being tossed around. The pack, the airbags...they're both insignificant. Glue the tie downs where ever you want.
That's all good|
Posted by: guideboatguy on Mar-22-13 9:34 PM (EST)
Posted by: guideboatguy on Mar-20-13 1:27 PM (EST)
it's a lot of weight...y/n? even for a |
Posted by: bigspencer on Mar-24-13 11:49 AM (EST)
hull that might, at first, seem to be easily rollable....maybe not, just my $.01. I usually do the old tether routine. Making it easier to roll/recover...then you can reel in the pack(s). If not for rolling, but portaging I've found that having a bizarrely(sp?) scuppered area in the gunwales for tying in..effectively hanging stuff I can't carry. Granted it takes time for preventative gunwale upkeep, but makes portaging easy.
Apology to guideboatguy|
Posted by: mrmannerz on Mar-24-13 12:19 PM (EST)
My sincere apology to guideboatguy. Earlier in this long series of posts I read him the riot act on "bad engineering". It occurred to me today that I had him confused with another frequent poster.
Hey, no problem, but thank you.|
Posted by: guideboatguy on Mar-25-13 12:55 AM (EST)
Thanks. Also, I'll admit I'm a bit less confused now. I tried to remember the incident you mentioned at the start, and I just couldn't remember ever responding to you in anger before, so naturally I thought MY brain must be shrinking. Actually, I'm pretty sure it is, but perhaps what I believed must have been a forgotten argument never even happened, which is a nice thought.
Summary of my learning from this thread|
Posted by: DaveO1 on Mar-25-13 4:43 PM (EST)
I called Wenonah customer service. The fellow I spoke with was very personable and knowledgeable. The discussion naturally zigged and zagged a bit. At first, he said to avoid the foam if you can. Then, he pointed out that the footbraces are on the foam. We talked about how the seats are attached to the foam core hull, and how much force that exerts. By the end of our chat, he seemed to suggest that the placement probably would not matter.
Posted by: LeeG on Mar-25-13 9:56 PM (EST)
2) Kevlar is better than fiberglass for this application;