Woodstrip VS. Canonball

[Alan Gage]

Northwest canoe has their web cam running today and did some drop tests on cedar panels with a canon ball. All laminations were 1/4" strips with 6 oz glass on each side. The difference was wetting out the glass on dry wood, wetting out the glass on wood that already had epoxy applied, and wetting out glass on wood with penetrating epoxy thinned a couple different ways. Interesting results.

I don't know how long the video will be up in this form. The fun starts about 10 minutes into it. Hopefully they'll put together all the rest of the footage they took and release a real video of the test.

https://www.youtube.com/embed/6p8RDXt1dew

Alan

 

[memaquay]

Alan, I would be very interested in seeing these results, but my interweb hamster only grinds out video at about a minute an hour. Any summaries?

 

[Alan Gage]

I thought of you when I was watching it knowing the types of waters you normally ply with your strippers.

The basic setup was a roughly 7' tall PVC tube down which they were dropping a 9 pound canon ball onto flat pieces, which I'm guessing were 18" square, of laminated 1/4" strips with 6oz glass on each side. The pieces were supported on what looked to be a pair of 2x4's on edge. They were clamped to one of the 2x4's.

The first three test drops were all pretty similar. One piece was laminated on dry wood and on the other two the wood was first sized by giving it a coat of epoxy before glassing. It was still green when the glass was applied. The difference between the two that were sized was that one was done with standard epoxy (they were using MAS) and the other was done with MAS penetrating epoxy for the sizing coat and standard epoxy for the actual lamination. None of these three pieces fared very well, pretty much complete breaks. Not real pretty.

Improvement started to show on the 4th test. Again, it was sized with the penetrating epoxy, but this time it was thinned 50/50 before application. Laminating the glass was done with standard epoxy. The panel certainly took damage from the canon ball drop but it wasn't much more than a stress crease as opposed to a break.

The final panel was very impressive. Same as the 4th panel but this time the sizing coat was thinned even farther (60/40) and they used a little pointy sheep's foot roller during lamination to help with penetration into the wood. On this drop the panel deflected and bounced the canon ball about 4 times, the first one where it didn't just land with a thud (or snap). You could see a small stress crease on the inside and outside at the point of impact but not much damage at all.

There was a weight penalty to go along with it, they'd kept track of the panel weight. They had a 52 pound tandem finished in the shop that was done with the standard sizing and they figured the toughest layup would add about 10 pounds to that boat.

One thing I would have liked to seen was regular epoxy thinned for the sizing coat instead of penetrating epoxy.

Alan

 

[Alan Gage]

Watched a bit more of it tonight. After the standard panel tests they start breaking out beefier panels that they use on their 24' North canoes. One with 8oz. glass outside and kevlar inside and one panel with layers of fiberglass, carbon, kevlar and foam. Those were very tough and even after repeated drops showed very little damage, and what damage there was wasn't going to end your trip.

In my earlier post I'd said they used the little roller, they call it a pin roller, during lamination but upon watching it again they don't make it clear if it was done during lamination or before the sizing coat to add some pin holes for better penetration. I'd guess the dry hull was rolled before the sizing coat.

Alan

 

[Alan Gage]

Pin roller:

http://www.aircraft-spruce.com/catalog/cmpages/vb9060porcupineroller.php

Alan

 

[Mihun09]

I won't have time until the weekend to watch more but the first test was a good laugh. Heck, all you guys with thinner strips and 4oz or less glass best stay away from rocks.

 

[Alan Gage]

I won't have time until the weekend to watch more but the first test was a good laugh. Heck, all you guys with thinner strips and 4oz or less glass best stay away from rocks.

Either that or stay away from civil war reenactments using live ammo.

Despite the test results I still rely heavily on empirical evidence. Mainly that I've yet to do more than scratch any of my lightweight hulls despite hitting my fair share of rocks. One of those being in an 18.5' sub-30 pound wood strip tandem at 6mph when we had a direct hit on a rock just below the surface that the bow paddler didn't see. I was amazed we stayed upright in the racing hull and just as amazed when I didn't see water pouring in through a giant hole. Flipped it over when we got to the take out to find the sharp stemless bow slightly flattened at the impact and nothing more than a scratch partially down the side where we skidded over the rock.

What I'm really for is purpose built boats. If I paddled the same lakes and rivers Memaquay does with the same frequency I'd build heavy boats too. But I don't so my boats are built to suit the conditions they'll see. Some are built heavier than others depending on where and how I'll use them. No sense bringing a CJ Jeep to a drag race or a Corvette to a rock crawl.

Rock strike:

_MG_6494 copy_web by Alan Gage, on Flickr

Alan

 

[memaquay]

I'm going to try to find time to let this load tomorrow. I haven't had too many problems since I started double layering the bottom. However, I have worn out a few hulls with only one layer of six ounce on the inside and out. I was going ot go for weight savings with my new build, but I think I will use multiple layers again.

 

[Holmes375]

While interesting I'm not sure how much these kinds of tests equate to use in the real world. I'm not an engineer but I believe a curvature, even slight, increases the strength of a given area. Additionally, when a boat strikes a rock the boat is not immobile even under pressure from moving waters.

I build primarily with 1/4 inch strips as I like the additional meat for fairing and I use commercial B&C stock where that thickness is much more readily available.

The hardest hit I've ever taken in a cedar strip was in my first kayak - a low deck Guillemot Night Heron. The aforementioned size strips with 6 oz cloth in and out on the hull, an extra layer on the football.

I was coming down the Lewis river channel in Yellowstone, an area featuring volcanic rock and lots of it. I was taking pictures as I came down the channel traveling about 4 mph. Dodging surface rocks and working a DSLR was probably not one of my better decisions and it wasn't long until I struck a rock hard while looking through the camera. The impact felt like a minor car crash with the kayak stopped dead to rights in a diagonal broach. The camera went airborne and I was almost completely ejected from the cockpit even though wearing a full neo skirt.

The boat wasn't holed as expected but had a nasty glass bruise and light dent. No water ingress and I repaired the boat easily upon my return home.

Two years later and in the same boat, I took another hard mix up on Yellowstone lake as I was coming around the aptly named Breeze Point into West Thumb. A storm was brewing and they're to be taken seriously on that lake. I was 5 miles away from my take out and thought I could push on through the wind but coming around the point I smacked right into the brunt of it. Got rolled a couple o' times and then washed into some large protruding rock formations hard enough that I ended up with a few broken toes before it was over. The storm turned into one of the biggies with 50-60 mph winds causing me to spend a few hours holed up as it raged. The boat was sound and I paddled it back that evening on an eerily calm lake after the storm. Again the boat was repaired easily at home cutting out 6 or 7 impact bruises and glassing in some patches. No wood replacement was necessary either time.

I don't have any experience with the lightweight builds like Alan or Stripperguy but I'd like to do one someday. I was one of those who always thought strippers were more furniture than trippers but I've certainly changed my mind over the last decade. I don't beat my boats purposely but I don't treat them like a fragile weenie either. Well, my BlackLite Northstar Magic gets the kids glove treatment but that's because I'll never again convince myself to drop that kind of coin on a canoe

 

[stripperguy]

Layer and a half below the water, extra layers at the stems, preferably with dynel or nylon, and 3/16 or thinner strips have yet to fail in some very harsh use.
I don't baby my boats, they're built to be used. Rocks hits, beachings, beaver drags are every day occurrences, no big deal. Wear through at the stems is generally the worst that happens.
I have had a puncture, entirely my fault, when dropping a hull on a spruce stump. Stump pierced clean through the hull, fortunately above the waterline.
Pinning a stripper though, will not end well, and I have the picture frame remnants to prove that.

Even my lightest builds will support me (welterweight limit) unsupported for more than half the length of the hull.
Those videos and test results that Alan linked above don't really equate to real world loads, but do give a great indication of how tough a stripper can be!!

 

[memaquay]

The canoes we build are always carrying a heavy load, and they are not babied. I found out about ten years ago that a single layer of six ounce on the inside and out was not sufficient. I can qualify that by saying that it would definately get you through a trip, but for long term viability, we're talking over 3000 tripping kilometers per canoe, over several years, a double layer was needed on the bottom. All my trippers that I built single layer and let the club use have now been retired and are used for spare parts. Likewise for trim. I keep the gunwales beefy. We have pinned a couple of our canoes and escaped with a few deep scratches on the exterior hull.

Here are a few shots of canoes in use. I don't have any of the dragging and beaver dam lifts we often do.

 

[wysedav]

Stripperguy, I hope you're right...that's pretty much how I'm building my boat. The test seems a little extreme, at 22km/hr (~14mph) the 9lb ball is hitting with about 15x the energy as if it was hitting at 3.5mph which is a more normal speed. It was pretty interesting though, I never would have guessed using the pin roller with penetratin epoxy would help that much.

 

[memaquay]

For general information, I have clocked my canoe on the GPS going over 10 mph through strong rapids, and that is usually when contact occurs.

 

[Holmes375]

For general information, I have clocked my canoe on the GPS going over 10 mph through strong rapids, and that is usually when contact occurs.

Ya, rapids can be surprising in the speed they'll shoot a boat. Even on my local river, the North Platte, the spring runoff rapids will often send me along at bursts of 8-10 mph. And this is a river with a 3-4 mph current.

I think a double layer is key to durability in a normal to hard use boat. I apply the second layer on the bias and I do pre-coat my builds before the cloth is applied. I may try that pin roller on my next build - interesting that it made such a noticeable improvement.

In my reality impact damage is not my primary concern although it must be considered. My later builds were all done more towards resisting abrasion. Using different materials and varying weight materials in specific areas have helped achieve this goal. And doing so has created an incredible inventory of varied remnants for other projects

 

[Mihun09]

I suppose it depends on "how" you hit the hidden rock. Going less than one mile an hour, Christine had the bow go over a submerged rock which got under her at the stern, the cracking sound was loud enough for me to hear a hundred feet away. It broke a couple of strips (1/4") and split the glass (6oz). It did not penetrate the interior but there is water damage to the wood and it will require a significant fix. When I do that in the Spring I will also add a football of 6oz for additional protection.

 

[Holmes375]

Yup, too many variables for generalizations. Overall though I do think well built strippers are much stronger than many realise.

 

[Alan Gage]

They released an edited video, which makes it easier to watch:

https://www.youtube.com/watch?v=-jKtyL59qeI

They left out one test, which was the penetrating epoxy not diluted with xylene. If I remember correctly, on the original video, it looked to have the same failure as the original dry panel. But perhaps the autopsy showed differently.

Alan

 

[Jim Dodd]

Thanks Alan !

Interesting test that Dennis set up !

I wonder if you could add xylene to the RAKA using their 350 hardener? Guess I'll have to try it.

I'd also like to see the same test with an extra layer of S-glass on the outside, and regular laminating resin.

I've always applied a seal coat, but always let it dry just past the sticky stage, to allow easier handling of the cloth.

An extra layer on the inside might be prudent !


Jim

 

[Alan Gage]

Thanks Alan !

I wonder if you could add xylene to the RAKA using their 350 hardener?

Jim

I played with this a little on my last build as I wanted to coat all the wood trim with epoxy to really seal it up and wanted it to soak in as much as possible, which meant I wanted it really thin. It seemed to work but I have no way of testing the final hardness other than it didn't seem softer. Setup time was much longer. The stuff left in the cups would have a stiff jello like consistency for a couple days or more but what as brushed on the wood seemed to set up hard. When I mixed it something like 60/40 (xlyene to mixed epoxy) that seemed to be too much and even after a couple days the thwarts were a tad sticky, which I finally wiped off with xylene. Something like 10-15% seemed to give me a nice thin mix that setup fairly normally.

Alan

 

[memaquay]

I have had two failures, both caused by sharp impact with a lot of weight overtop. In both cases, the exterior glass held, the interior glass split. It would seem to be that a sensible builder looking for enhanced strength would double layer the interior. However, I can't bring myself to do this, and still double layer the exterior.