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Old 05-21-2020, 01:57 AM
Mesquite-oh is offline
Join Date: Sep 1999
Location: La Frontera, US of A
Posts: 919

Would water trapped in between layers of my kayak underwater be negatively or neutrally buoyant?

Would water trapped in between layers of my kayak, under the waterline, affect my kayak's weight and buoyancy?

Here is the real world situation: I have a two layer inflatable kayak which has a vinyl bladder interior wrapped by a flexible tarp and nylon exterior. I got a half inch tear in the exterior tarp bottom. I am guessing that water is going to get past the exterior layer and get trapped (or flow in and out) between the tarp bottom and the inner bladder. Just wondering if my kayak would be harder to paddle or the same. I am guessing harder to paddle but I can't wrap my head around it.
Old 05-21-2020, 02:50 AM
kaylasdad99 is offline
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Join Date: Sep 1999
Location: Anaheim, CA
Posts: 33,264
Was the buoyancy of your kayak ever assessed BEFORE the water was introduced?
Old 05-21-2020, 03:26 AM
GMANCANADA is offline
Join Date: Mar 2003
Location: Toronto
Posts: 590
We have a hard shell Bic sit on top kayak that developed a leak below the water line, so a similar situation.

Over time, the leak affected the buoyancy since it was added weight. It was somewhat harder to paddle in a straight line, since you're paddling extra weight, but where we really noticed it was the handling. As you manoeuvred, the water's weight would slosh around and throw off your balance.

Yours may not be so bad, since it's not a big cavity, but I think you'll notice it.
Old 05-21-2020, 08:00 AM
brossa is offline
Join Date: Feb 2005
Posts: 1,226
The water 'in the bilge' will be neutrally buoyant, but before it got in there that space was occupied by air, which is positively buoyant. So the net effect is less buoyancy overall. By how much depends on how much water is getting in. You've reduced the effective hull volume from whatever the shape of the kayak used to be to just the volume of the bladder. In some inflatable craft that I've seen, that would be a big difference, but it would depend on the geometry of your kayak.

Handling will also be affected, because now you're adding the mass of the bilge water to the kayak, since you're bringing it with you instead of moving past it. If there are, say, 10 liters of water now trapped in the kayak, that's significant added mass. Consider how the kayak would handle with 10kg of loose ball bearings in the bilge.
Old 05-21-2020, 08:41 AM
Stana Claus is offline
Join Date: May 2002
Location: Way South of the N Pole
Posts: 422
In your particular case, unless the gap between the outer covering and the inner bladder is significant, I don't think the difference will be terribly great. From what you describe, the inflatable bladder is what's providing the displacement. The outer shell is there to protect the bladder from punctures and abrasions. So unless the outer shell stretches and separates from the bladder, there shouldn't be a significant amount of water between the layers. I would probably try to patch the tear in some manner, not so much to prevent leakage, but to keep the tear from lengthening.
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