Sponsons below the waterline

[dhdallas]

I have a square stern 11' 2-person fiberglass canoe with a weight capacity of 350 lbs. I need to increase that to 450 lbs. If I buy the foam sponsons made for a Sportsal/Radisson canoe and mount them just BELOW the waterline, that should make a noticeable difference, wouldn't it? Yes, I know it will add drag but I am using a motor so that is not an issue

 

[Chip]

Let me be Chief Brody to your Quint. "You're gonna need a bigger boat."

I don't mean need--I'm sure you can make it work with the boat you have. My question is why mess with it? Just get a more right-size boat.

My $0.02, and over-priced at that.

 

[Jim Dodd]

I'm not an engineer ! I believe, Sportspal/Radisson meant for those Sponsons, to add flotation, to an aluminum hull, in the case of a capsize, not to add capacity.

They may have also wanted more stability, by widening their hull.

An aluminum hull. without flotation, would sink.

As Chip suggests, I'd get a bigger boat to fill the bill.

 

[Gamma1214]

@dhdallas, welcome to the forum.

I'm certainly not an engineer but, yes, I would think that the addition of sponsons below the waterline would increase your ability to load (or overload) your boat. That said, I'm not sure how you could properly estimate the amount of floatation gained.

Given the current displacement of your hull, I doubt that the addition will result in an almost 30% increase in capacity.

Unfortunately, I suspect that Chip & Jim are correct: you'll probably need bigger sponsons or a larger boat in order to displace that additional 100# of water.