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Old 05-31-2020, 03:46 PM
 
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Putting balloons full of helium in would HELP. The question is how much. Take a beachball, fill it with helium and see how much weight it will lift. Roughly from some quick googling a 12" diameter balloon will lift .03 pounds.


The reason they put foam in boats, canoes, and kayaks is so that when water gets inside the hull it can't fill it up. All these hulls are 'displacement' hulls meaning they displace an equal amount of water. So the only way to hold a larger load (a 200 lb person instead of a 150 lb person) is to make the amount of water it displaces larger. That means a larger hull. putting more 'stuff' inside the hull won't help unless it is lighter than the air it is replacing.
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Old 05-31-2020, 04:03 PM
 
Location: Loudon, TN
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Quote:
Originally Posted by otterhere View Post
So adding pool noodles, say, along the length of the floor of the kayak (inside), wouldn't buoy it up in the water?
No it would simply make it more difficult to paddle and steer. The shape of the hull and keel are instrumental in allowing you to move smoothly through the water and to have a boat that tracks in a straight line. As others have said ... GET A BIGGER KAYAK.
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Old 05-31-2020, 04:12 PM
 
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Quote:
Originally Posted by TheShadow View Post
No it would simply make it more difficult to paddle and steer. The shape of the hull and keel are instrumental in allowing you to move smoothly through the water and to have a boat that tracks in a straight line. As others have said ... GET A BIGGER KAYAK.
I said inside; not outside (the hull).

About the inflated beach balls fore and aft, they WOULD fill the empty spaces that water would otherwise occupy in the event that waves washed over the rim and help keep it from sinking; right?
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Old 06-01-2020, 07:09 AM
 
Location: Wooster, Ohio
1,331 posts, read 955,421 times
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Quote:
Originally Posted by otterhere View Post
I said inside; not outside (the hull).

About the inflated beach balls fore and aft, they WOULD fill the empty spaces that water would otherwise occupy in the event that waves washed over the rim and help keep it from sinking; right?
If:
They remain in place
They remain inflated
They don't get punctured when you need them to keep your kayak afloat.

If it were my kayak, I would take it to a recycling facility (looks like they only pay $0.18 a pound here for aluminum), and buy a larger kayak with built-in flotation. Boat flotation requirement were established in 1977; it's long since time to retire any boat that does not meet these standards.
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Old 06-01-2020, 07:28 AM
 
Location: Wooster, Ohio
1,331 posts, read 955,421 times
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Originally Posted by KemBro71 View Post
Thanks for this!

I wonder how large the balloon(s) would have to be for a kayak + heavy person. I'm thinking at least 300#.
Because volume varies as the cube of the radius, 300 lbs would require a 22.35 foot balloon, while 50 lbs would require a 12.3 foot balloon.
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Old 06-01-2020, 12:03 PM
 
Location: on the wind
10,658 posts, read 4,839,826 times
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Quote:
Originally Posted by mshultz View Post
If:
They remain in place
They remain inflated
They don't get punctured when you need them to keep your kayak afloat.

If it were my kayak, I would take it to a recycling facility (looks like they only pay $0.18 a pound here for aluminum), and buy a larger kayak with built-in flotation. Boat flotation requirement were established in 1977; it's long since time to retire any boat that does not meet these standards.
Kayaks were intended to store the paddler's gear inside the hull. Either gear or air. Kind of ironic to not understand why you can't add buoyancy to a kayak. Think about buoyancy the way the inventors of kayaks did. They hunted and killed seals/whales much too large to cram into their boats. When they killed something, they attached inflated skin bags to it and towed it. The inflated bags add buoyancy, they don't make the dead seal lighter. Maneuverability in those boats was critical...swamping or disabling the kayak meant death. The bags didn't encumber the kayak and they could cut the seal loose in an emergency.

As for requiring flotation, consider that most if not all states require boat operators of vessels under a specific length to have PFDs (ideally wearing them but at minimum possessing them on board). Instead of requiring the boat to have flotation, makes more sense that the passenger should. They end up having that flotation regardless if the boat swamps, sinks, or they end up in the water next to it.

Many kayak models already have internal bulkheads that create flotation in bow or stern. Cheapo "toy" models don't tend to. You access the bulkhead areas through hatches on the top of the hull. Of course if the hatch gaskets leak or you don't tighten them down correctly, they won't provide flotation. For a boat that doesn't have functional bulkheads, closed drybags behave like flotation...that is, they don't permit water to replace what's packed inside them which probably weighs less than the same volume of water.

Some kayak manufacturers make inflatable "float bags" to fit their hulls, but you can buy generally shaped bags from paddling suppliers. If you plan to be out on the water and won't have a lot of gear with you, you blow up the bag and stuff it into the ends of the hull whether bulkheaded or not. You can also buy bulk closed cell foam blocks, trim them to fit your hull and use them when you don't have enough gear to fill the space. Some people use inflatable exercise balls.

As they say, "whatever floats your boat." Just remember that all these ideas simply keep the boat from sinking if it swamps, but they won't make the boat sit any higher in the water.

An interesting article on flotation by the very well-respected kayak builder who built mine:

Flotation

If anyone wants to read kayaking accounts guaranteed to keep you up nights, try this:

https://www.goodreads.com/book/show/...s_Deep_Trouble

You'll never look at that afternoon paddling trip the same way again.

Last edited by Parnassia; 06-01-2020 at 12:45 PM..
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Old 06-01-2020, 04:14 PM
 
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I've held off chiming in seriously, because I simply have not been able to believe that basic physics could be so poorly taught these days that the underlying principles are not obvious. Regrettably, I appear to have been wrong.

I'll keep it simple:

A cubic foot (a cube 1' x 1' x 1' in dimensions) of fresh water weighs roughly 62.4 pounds.
When a cubic foot of surface water is displaced (moved aside by an object that is ALSO a cubic foot in size) that object will:
Float if it weighs 62.3 lbs, but ONLY .1 lbs worth of the cube will be above the surface of the water.
Sink if it weighs 62.5 lbs or more.
Float exactly 1/2 submerged and 1/2 above the surface of the water if the object is still one cubic foot, but only weighs 31.2 pounds.

Any boat or ship displaces water. Boats with an overall load of more than 62.4 pounds per cubic foot of displacement sink in fresh water. Boats with less than 62.4 pounds per cubic foot float in fresh water.

The key to flotation is NOT what is in the object being floated. The key is the density of the water itself, which is being displaced. Because of the greater density of salt, the extremely salty water in the Dead Sea has a density of more than 75 pounds per cubic foot. That means an object that is a cubic foot in dimension and weighing the same as a cubic foot of fresh water will float in that sea. Since whipped cream is not dense at all, no average boat could ever float in a vat of it. A vat of molten iron would float rocks - which is indeed one of the ways iron is purified. The melted rocks and debris at the top is called slag, and skimmed off like cream off the top of a bottle of non-homogenized milk.

It makes no difference what is contained within the hull of a boat. What matters is the total displacement ability in relationship to the weight of what is being floated.

When the idea of helium or hydrogen is used as a help for buoyancy, similar equations apply to gasses or liquids. Helium and hydrogen balloons are less dense than the air, and will rise in the atmosphere to a point where the density of the air is low enough to balance that of the helium plus the skin holding it in. When helium is compressed into a small party tank, its density increases, meaning that the cubic foot of compressed helium weighs a number of times MORE than a cubic foot of uncompressed helium. A boat with large balloons attached could float higher in the water. In some cases where a wreck is retrieved from the sea bottom, balloons are attached to the wreck to make the whole attached mass of wreck and balloons and ropes less dense than the water.

As the famous line in "Jaws" stated, to fix your problem, "we're going to need a bigger boat."
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Old 06-01-2020, 04:56 PM
 
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So what is the purpose of float bags?

(I didn't take physics.)

Thanks for the goodreads recommendation!

I love disasters as long as they're not happening to me.
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Old 06-01-2020, 05:18 PM
 
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https://www.google.com/amp/s/www.wik...oyancy%3famp=1

Float bags are meant to prevent your kayak from swamping. Mostly it’s used in open waters.
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Old 06-01-2020, 05:24 PM
 
7,949 posts, read 4,468,698 times
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Quote:
Originally Posted by otterhere View Post
So what is the purpose of float bags?

(I didn't take physics.)

Thanks for the goodreads recommendation!

I love disasters as long as they're not happening to me.
Quote:
Originally Posted by Parnassia View Post
...
Some kayak manufacturers make inflatable "float bags" to fit their hulls, but you can buy generally shaped bags from paddling suppliers. If you plan to be out on the water and won't have a lot of gear with you, you blow up the bag and stuff it into the ends of the hull whether bulkheaded or not. You can also buy bulk closed cell foam blocks, trim them to fit your hull and use them when you don't have enough gear to fill the space. Some people use inflatable exercise balls.

As they say, "whatever floats your boat." Just remember that all these ideas simply keep the boat from sinking if it swamps, but they won't make the boat sit any higher in the water.
....
It displaces empty space inside the kayak so it doesn't fill up with water when you get swamped. Mine came with closed cell foam already in place. Doesn't take much since a kayak is fairly light by itself. Keep in mind, they DON'T
a. keep you from getting swamped
b. increase the load capacity of a specific boat

Like has been said, you're going to need a bigger kayak to carry more weight. If there's one near where you live, I'd suggest either taking a kayak trip with a good outfitter or visiting a good outdoor store with someone who knows kayaks. They'll be able to give you a good demonstration of all these questions and since you'll be able to see and touch the equipment or better yet, get wet, it will make so much more sense than reading on line.
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