---

Here is the topic.

If you have two Kayaks that are the same lenght and have the same beam and you fill the void or space between the inner and out shell of one kayak with foam. And you leave the other with nothing but sealed in with air. Which one would be able to carry a heavy load. I said the one with the foam core. They guy at work says the boat with just air between the shells. He says the reason is because the foam has weight to it and cant hold as much as the one with just air.

So what say every one on here which kayak would be able to hold more cargo?

Thanks
Jay

---

The foam would add weight to one boat. The volume would be the same between both boats. The boat with more weight (foam) will displace more and sit lower in the water. It would take less added weight to swamp the foam-filled boat than the air-filled boat.

So the foam filled boat could carry less weight. But in reality, the difference would only be a few pounds.

That is assuming the two boats are exactly the same otherwise.

---

If all you are talking about is weight and displacement, the foam boat, being heavier, would carry less weight. In the real world, the boat with the foam core would be much stiffer, because of the shell / foam / shell lamination, and therefore the shells could be made thinner and lighter while retaining the same stiffness. The boat could be made lighter than the one without foam, and it would then carry more weight.

---

I would have to agree that just putting foam in does not equal more buoyancy. I guess I would be stating the oblivious to say if the foam were on the outside of the hull it would displace volume and float higher with more weight.

---

As a Naval Architect I feel somewhat qualified with my answer. The amount of weight that a boat can carry is equal to the mass of the water that it displaces when empty. Adding the foam effectively amounts to cargo and will take away from the total. So the boat filled with air will carry more weight on deck by the weight of the foam added to the hull of the kayak. In the end you could argue that it is just how you loaded the weight.

---

I am not a Naval Architect, but I did take Physics as a Junior in High school. That makes me equally well qualified to answer this question and I concur with the obvious answers above.

The answer is so obvious I kept waiting for the punch-line; I assumed it was a trick question.

---

How about this for a punchline:

There is no replacement for displacement?

---

Hey! That's pretty good.

---

No there is no punch line. After I mde the thread I should have deleted right away. Because after typing out my first response and then rereading it. I said to myself "self that just doesn't make any sense. Air weighs next to nothing compared to what foam weighs. Of course the boat with air is going to carry more". Then I went back and replayed the conversation my Co-worker and I had. And that is when I found out where we both went off course and how this thread came about. He and I were talking about 2 differnt things. I was talking about a boat that was filled with a closed cell foam could still carry a load even if the hull had a hole in it. While the other air filled boat would then sink do to water now filling the once Air filled boat. And he was talking about a swamped boat and somthing else as well. Once I brought this up to him we both agreed that we had once again started talking about something and then both of us end up talking about something else completely different.

Any way thanks for the replys to this thread.

Jay

---

As obvious as it may seem to some, it isn't to everyone. I remember a conversation with a college a while back about him wanting his small aluminum jon boat to float a bit higher in the water. He passed an idea by me of adding pourable foam into two large storage spaces under each of the seats.

I think some folks just associate foam with flotation and don't put much thought into it beyond that. The fact the foam itself adds mass just seems to escape consideration sometimes.

---

I said the one with the foam core. They guy at work says the boat with just air between the shells. He says the reason is because the foam has weight to it and cant hold as much as the one with just air.

If the guy at work is not your boss today, he will be by next Monday.

---

Hmm. Start out talking about the same thing and end up with completely different subjects. Sounds a little like being married!

---

Depends on the kayak, ocean kayak- yes, non-ocean kayak completely different story. Picture a non-ocean kayak that can take on water if your not wearing the stupid skirt for it. Fill that with foam. Boat A filled with foam, which is simply glorified air that can not be overtaken when the boat is taking on water. Boat B filled with air, begins taking on water. Put a giant weight on both boats. Boat A floats, boat B sinks.

---

I am not a Naval Architect either, however I am a retired US Navy Sailor who's spent many years on board huge metal floating cities which makes me equally well qualified to answer this question and I too agree with the statements above.

With that said, I'd rather be out at sea in a boat that has holes in it that's filled with foam than be out at sea in a boat with holes in it that's not filled foam....

Just sayin'.....lol.

---

I think I know a boat built just like that... lol

---

Yep, we're seeing eye to eye here. Lol.

---

Try the other way around... But thanks for playing just the same....

---

Frankly, you guys make my head hurt. Think i'll stick to fixing helicopters..........

Duf

---

Lol, a device that's not supposed to fly but does.

---

The initial thread sead nothing about holes in the Kayaks but I will agree that no foam will cary more weight.

---

but if the air hull fills with water it will sink...
the foam hull won't...
that's not the question though is it... : )

what if you cut it in half ?

---

Just for one more twist and to see this through
Well here's the theory..
We have two identical hulls hermetically sealed.
One with our world famous foam the other with compressed air.
The compressed air one will be pressurized until the weight of both hulls are exactly equal.
http://docs.engineeringtoolbox.com/do..._chart.pdf
Which hull would take on more weight before being swamped???

---

The foam filled one, no doubt.
Consider this: Pounds Per Square Inch - the air hull would have to be considerably thicker to withstand the PSI in air needed to equal the weight of the foam.

10 PSI applied to a 10 square inch area can lift 100 pounds.

Just a thought

---

Just to state the obvious, adding foam would mean more weight and thus displace more water. But that would not translate to having the ability to carry less as that would prove to be on the advantage as compared to the boat with just an empty shell. It would carry more but the one with foam, in my opinion and experience with boats, would be much stable across the water, in normal real world conditions. But when put on a controlled environment, I would think only a few measures would determine the capacity.