Replacing Floatation in a FG canoe

[Chip]

The Mayfly was made in Austin, Texas around 1975. It is an 18.5 foot, fiberglass canoe with unique "shedding" decks.



A foam “bun” had fallen out from beneath the upswept deck. This was likely placed in the canoe as floatation. Fiberglass is heavier than water, so I assume the foam was intended to provide enough floatation to keep the canoe from going to the bottom if it was swamped.

Here's a photo of the "bun"

​

Inspection under both decks revealed a “footprints” where the foam had been installed. I matched the bun I had to the footprints and determined the one I had went in the bow, and there was not but a footprint in the stern. I think the stern floatation was missing when I got the boat.

Footprint of the bun under the bow deck:


I cleaned up the bun and the underside of the bow deck. I ran beads of FlexGlue on the bun, stuck it back in the bow, and weighted it with a couple bricks.



I had to prop up the stern a bit to get the (upside-down) top of the deck approximately level, I poured two-part urethane foam into the stern deck. It’s exciting to work with urethane foam. You have 45 seconds to get the two parts mixed and poured. I started out by measuring urethane part A and B into two separate cups. At the canoe, I emptied the two cups into a third cup. The urethane liquid parts are thick and pour slowly, so it took ten seconds just to get the two liquids into a mixing cup. Then I stirred the mix with a home-made stirring paddle in an electric drill. It looked well mixed after 20-25 seconds. I was well past the 40 second mark before I began pouring the mixture into the stern.

Propping up the stern to make it level:




Measure twice, mix once, and make it quick!



Thank you, Mike McCrea, for coaching me to make a mixing paddle for the drill. This made it easy to quickly and thoroughly mix the urethane.



Sorry, no time for photos of mixing and pouring. Below photo shows the pour about 1 minute after I poured the mix into the stern.



Here's my home-baked "bun," fully expanded. I'll take a drill and add channels to make sure water can pass on either side of the bun when the boat is racked for draining.



I’m pleased with the results. After a day, the bun in the bow is firmly attached under the deck, and the foam in the stern covered the old bun’s footprint, plus some, is well adhered, and completely cured stiff. With floatation in place, I am now comfortable letting the Brownline go to it’s new home on Rockhold Creek.

 

[Glenn MacGrady]

Nice job and documentation, and it's good you're satisfied with it.

I'd have been tempted to stand the canoe up vertically and pour or spray some sort of appropriate foam fully into the ends. As I understand it, the buns are attached underneath the deck and don't reach the hull bottom. That means they won't provide any floatation for that heavy hull until the water level in the canoe reaches up to the buns. If that's just a few inches, it probably doesn't matter.

Meanwhile, to be safe, how about actually testing the floatability by sinking the canoe in a lake or pool, preferably with two adults sitting in it. If it doesn't really float sufficiently, it may still need to be bagged as well as bunned.

 

[Mason]

I'd have been tempted to stand the canoe up vertically and pour or spray some sort of appropriate foam fully into the ends. As I understand it, the buns are attached underneath the deck and don't reach the hull bottom.

We used to do that for Old Town Royalex canoes for river travel. Lean the canoe on end against the shop, tape up the insides, and pour it in. Works well.

 

[Guest]

It’s exciting to work with urethane foam. You have 45 seconds to get the two parts mixed and poured. I started out by measuring urethane part A and B into two separate cups. At the canoe, I emptied the two cups into a third cup. The urethane liquid parts are thick and pour slowly, so it took ten seconds just to get the two liquids into a mixing cup.

If there is a next time use a flexible spatula to help hurry the viscous contents out of the two cups more rapidly. “No honey, I haven’t seen your spatula. Not lately anyway”.

I replaced that kitchen one with a better quality silicone spatula; still have the old one in the shop and still use it occasionally. Couple bucks at the grocery store, it might be time to get me a new one.

Then I stirred the mix with a home-made stirring paddle in an electric drill. It looked well mixed after 20-25 seconds. I was well past the 40 second mark before I began pouring the mixture into the stern.

This made it easy to quickly and thoroughly mix the urethane.

Chip, happy that DIY paddle stirrer worked for the urethane foam. It sounds like stirring by hand would have been racing the clock even more. With 2-part foam floatation a very thorough mix may be critical.

That DIY zip-tie stirrer is a relatively new trick for me, learned when mixing silicone caulk and mineral spirits to make DIY silicone seam seal; thoroughly stirring that stuff by hand was enough of a PITA, and it has a much longer working time.

Of course I only learned that trick after hand mixing several batches. The paddle stirrer was not only much faster, it made a far more thorough mix, dang near frothy if stirred too fast.

https://www.canoetripping.net/forums...as-seam-sealer

(BTW, that seam sealing marathon was 2 years ago. All of the tents, flies and tarps sealed with that DIY mix, some once seam weepy/drippy, are still going leakproof strong. I’ll never buy Sil-net again)

I have since used that DIY zip-tie stirrer trick for all sorts of things, especially down at the bottoms of old paints and sealants. Most helpfully on the remains of a 5-gallon can of old deck sealant/stain.

That can that had only the little 2” wide screw off cap for stirring access. The remains of that sealant stain had separated, and the bottom stain layer was near putty like; trying to wigglewaggle a long stir stick through that wee lid hole got me nowhere.

A few futile minutes of stick stirring was soon followed by a couple minutes spent making a long zip tie stirring paddle, and that crap was MIXED. Effortlessly mixed.

Uh, Chip, one paddle stirrer hint I guess I maybe neglected to mention; on an open-top container of anything, especially less viscous stuff or mixes (think, oh, maybe mineral spirits floating on a layer of silicone caulk), it pays to stretch a rag or paper towel across the opening before you turn on the drill to prevent flying spatter.

Hope you didn’t end up with urethane floatation forearms. Look, Chip has custom swimmies.

 

[Chip]

Glen and Mason,

I like the idea of standing the boat on end and pouring more foam into the stems. But, I'm not sure what would be gained. I think with the floatation I added, the floatation now approximates what was in the boat when it was new. It certainly isn't much floatation, and I think is merely intended to keep the boat off the bottom. Filled with water, it would be wallowing gunwale deep, and to improve on that would require a lot more floatation.

A not-so-swell aspect of the Mayfly's decks and gunwales is that it is nearly impossible to drain water out of the boat. The gunwales are U-shaped, catch the water, and encourage the water to flow into the cavities beneath the upswept decks. I just enlarged the drain holes at the tip of the decks to 3/8" (9mm). Still, it always seems like vegetative detritis that is mixed with the bilge water clogs up the holes, and it is tough to get that out of the pointy ends of the boat. So, drainage would need to be accommodated if the ends were filled with foam, or anything else.

I once had a decked boat branded Kanoe Latvija. It wind cocked terribly. I had a rudder added. They stood the boat on end and poured in resin to solidify the stern before drilling it to add the rudder hardware. So, I guess I was aware of the technique, but never thought of it in this instance. Rather than rethink the problem, I just tried to replicate what the maker had done.

Mike,

I tried out the zip-tie stirrer mixing a can of water sealer, which is low-viscosity stuff. The benefits of a variable-speed drill quickly became apparent. At full speed, surf was up! The urethane was thicker, I was gentle on the trigger, and was able to keep the urethane in the mixing cup. The instructions from US Composites explicitly state thorough mixing is essential. Two days later I was scrapping hardened foam off the stirrer. The stirrer shaft was an old tent pole, with a hollow (female) coupling at the end. The urethane parts that got inside the coupling escaped thorough mixing and were still all gooey. So, I believe them, thorough mixing is important, and with the time constraints, the paddle stirrer was essential.

Thanks for the spatula hint.

 

[ppine]

In a boat that long, you could also fill two chambers fore and aft like modern boats. It would be a nice safety update.

 

[Odyssey]

That was some good handiwork to keep that boat afloat. With some tender loving care the Mayfly may well last forever.