Can Grumman 17' aluminum canoe sink when tipped over?

I read that Grumman aluminum canoes have flotation tanks built in and won’t sink by itself (assuming no additional attached weight when tipped over)? I would like to hear comments from those who have tried to sink an aluminum canoe, or at least those who have good knowledge about aluminum canoes.

Please do not assume aluminum canoes are heavy and will sink by themselves, as many plastic canoes are much heavier for the same size.

My (used) 17’ standard version (at around 75 lbs) does seem to have intact flotation tanks at both ends, though I have not opened them to check (if previous owners removed flotation). Should I open them to check though? Is Grumman’s flotation provided by foam or air? I do see some microscopic holes around the tanks, but nothing obvious.

I read from the following thread that if flotation tank is filled only with air and tank has a major hole, then the canoe (not sure if that canoe was a Grumman though) can be sunk:
http://bwca.com/index.cfm?fuseaction=forum.thread&threadId=286166&forumID=12&confID=1

I can easily DIY additional flotation with sealed gallon-sized water bottles. 8 bottles can easily fit in the 17’, with each one providing 8.35 lbs of flotation (8 bottles would provide 67 lbs of flotation, if I calculated it correctly). Those bottles can be noisy though and take up space. So I prefer not to add them, unless necessary. How many should I add, if I should add any?

Thank you.

PS:
Our Grumman won’t have any additional weight attached, when it is tipped over (all weight on it will fall into water). We do not paddle in heavy rains. Total additional weight (people + gears + food/water) should be always under 450 lbs.

it may be styrofoam… Over the years it degrades and you can lose it. Our old fleet from the '70s required additional flotation which was glued to the sides because the tanks flotation had lost its integrity… Little chunks of styrofoam will escape over time.

Its instructive to take it to a beach and then capsize in shallow water… The canoe should not disappear and should stay with gunwales above the water. If not it needs additional flotation secured in… You want to minimize the weight and volume of water in the canoe when capsized and just attaching water bottles only acts as buoys to mark your sunk canoe… It won’t help you get the canoe out of the water.

the weight of a full 17 foot canoe full of water exceeds a ton.

There are formulas for you if you want! http://newboatbuilders.com/Flotation_Course/Lesson_06_other.pdf

far easier just to sink the boat and have help…

Got my answer quickly from Marathon Boat Group, by calling them directly. They said if those flotation tanks have foam blocks in them, if owners have not removed them. With foam blocks there, the canoe would NOT sink by itself. But without foam, it could. And opening up flotation tanks will not damage anything.

I found a serial number on side of my Grumman and it ends with 81L-7A. So they said it sounds like a 1981 standard 17’ model. Its length and weight (75 lbs) does match up perfectly with Grumman’s brochure.

The answer is it shouldn’t, but it might. Solid polyethylene, aluminum and composite canoes have no inherent buoyancy. Resin and fiberglass (or other structural fabrics), solid PE, and aluminum have a specific gravity greater than 1.0, unlike Royalex and three-layer roto-molded polyethylene which have foam cores. The foam core allows the material to displace enough water without adding too much weight and that makes the overall specific gravity less than 1.0.

There are some composite canoes that do not have flotation tanks. Some of these have enough buoyancy as a result of foam bottom cores and side ribs, balsa wood cores, or pieces of exposed foam attached to the hull or the seats to keep them afloat. There are also some composite canoes without tanks, usually ones designed for whitewater use, that are intended to have supplemental flotation attached, usually air bags, that will otherwise sink.

In those canoes that do have flotation tanks, the tanks may be sealed or open. Non-sealed tanks need to be filled with some type of material less dense than water, otherwise they will eventually fill up and provide no flotation. Sealed tanks contain only air and can sometimes develop leaks that allow water to enter. This would be unlikely to result in the canoe sinking quickly out of sight, but if the boat remained swamped for any length of time, enough air might be displaced by water to allow the boat to sink.

The non-sealed tanks in aluminum canoes have some type of foam installed and depend on enough material displacing enough water to provide some degree of positive buoyancy. But as Kim said, foams can degrade over time. Styrofoam is notorious for “pilling” and losing small pieces over time. Other foams can shrink significantly over time including some that are used in PFDs. Also, foams with an open texture like open cell foams and styrofoam can absorb a significant weight in water. So if your boat is old and you can’t examine the foam, you can’t be absolutely certain that it is not a “sinker”.

Also, most manufacturers do not provide enough flotation to do much more than keep the boat from sinking. When fully soused the boat may be very low in the water with just a little bit of the stems sticking out above the surface, if the boat remains upright. And if you have enough heavier than water gear attached to the hull, you might possibly overwhelm the buoyancy provided by your flotation tanks.

.

Judging from 30-40 year old Boy Scout Grumman canoes I have seen and rescue trained with, there should be no reason to suspect they will not float, unless someone has tampered with the flotation chambers, that are filled with foam, I believe. At various BSA camps I have been at, I have never seen one sink below gunwale level at the water surface , even ones that have substantial dents or damage on the end.

Never say never
You know the adage about assuming
We had some out of 17 Grumman boats at camp that were 30 plus years and at that point needed supplemental flotation
Others didn’t

“My (used) 17’ standard version (at around 75 lbs) does seem to have intact flotation tanks at both ends…”

Since you have a boat. The question shouldn’t be about ALL Grumans, just yours. Go out and capsize it. If you’re worried about it sinking put a tether to it and do it near shore.

Thank you, gents.

Will capsize it, when I get to a clean beach.

I managed to partially open up one tank. Foam inside feels very solid and intact. Many screws have rust and are difficult to impossible unscrew, so I could not take out the entire foam to examine (therefore could only feel it with my hand squeezed inside). My drill broken down, which did not help. Will have to buy a high power drill later and some replacement screws later.

I sprayed pressurized water into flotation tanks and did not see foam piece come out.

I will also strap some sealed water bottles under canoe seats. That should display some more water. Not bad for a 1981 canoe.

I am guessing the Grumman will right itself, if capsized. Its two flotation tanks are at the two very ends, which also curve up and inward. That probably would help righting it too.

Again, as I said before, anything that I will attach to the canoe will either fall out in capsize or be much lighter than water.

One often overlooked cause of Styrofoam degradation has to do with how the boat is stored, and that being, whether it is easily accessible to carpenter ants. I have seen the flotation in a few boats end up riddled with void spaces due to the nest-building activity of carpenter ants. Carpenter ants are supposed to “only” build their nests in very rotten wood. The thing is, Styrofoam has a degree of hardness and consistency that is similar to rotten wood, and if the ants find it, they may well decide to call it home. Naturally the flotation of a boat that spends years sitting on the ground in or adjacent to a wooded area is more prone to being adopted as a burrowing site than one stored indoors.

If the foam looks intact and fills most of the tank you are probably OK. If the foam does not fill the tank, get some closed cell foam and cut some pieces to “top off” the tank.

@zzffnn said:
Thank you, gents.

…………… Will have to buy a high power drill later and some replacement screws later.………………….

New bits are often more important than “high power” drill.

BTW Foam does not make the canoe self righting… You will find that once swamped its easy for it to roll upside down… It will tend to float that way… If you get it sunny side up swim into it and find how unsteady it is despite being on the surface. Kids absolutely love to do this.