I'm replacing the wood seats and transom in the new yacht. Is this Styrofoam under the seats really functional?

Only if you want the boat to float.

1 minute ago, Jig Man said:

Only if you want the boat to float.

Details...

 

 

In all seriousness, paddle craft that are not made out of buoyant material such as ABS have some kind of flotation mechanism.  Some build an air tank into the structure or many use styrofoam.  Otherwise that polyethylene kayak fills with water and goes straight to the bottom.  Might be worth putting back or even replacing 

I think it's a coastguard requirement water craft have enough flotation foam in then to keep them from sinking.  If not, it's still a pretty good idea to have it. They can be standing on end, but they have to float.  That's so if it does capsize or something, the occupant will still have something that floats they can hang onto.

If that piece will fit the new seat, I would just glue it back in.  Closed cell flotation foam is kind of expensive and a bit tricky to work with.  You only have a few seconds from the time you mix it until it starts expanding at almost a 10:1 ratio if it's warm.  If you put more than the space will hold, it makes the space bigger.

I’ve got a boat very similar, all 3 benches are foam underneath. Why take floatation out???

18 minutes ago, TnRiver46 said:

I’ve got a boat very similar, all 3 benches are foam underneath. Why take floatation out???

I suppose if the 3 pieces of Styrofoam will keep it from sinking to the bottom then great. I find it hard to believe that the 3 pieces will keep the boat buoyant. 

 

I'll put them back when I reassemble the seats. 

8 minutes ago, slonezp said:

I suppose if the 3 pieces of Styrofoam will keep it from sinking to the bottom then great. I find it hard to believe that the 3 pieces will keep the boat buoyant. 

Only 1 way to find out, swamp it in a shallow pond. ?

10 minutes ago, slonezp said:

I suppose if the 3 pieces of Styrofoam will keep it from sinking to the bottom then great. I find it hard to believe that the 3 pieces will keep the boat buoyant. 

 

I'll put them back when I reassemble the seats. 

It’s better than no foam is my policy 

Well, without it you have an aluminum anchor.  I had the same in my Gregor and I too wondered if it would float the boat in a capsize situation.

If you know the weight of the boat with the foam and the dimensions of the foam then with a little math it could be determined if the foam is big enough to keep the boat from sinking without doing an actual test.

29 minutes ago, Tennessee Boy said:

If you know the weight of the boat with the foam and the dimensions of the foam then with a little math it could be determined if the foam is big enough to keep the boat from sinking without doing an actual test.

Too much work involved. 

Be surprised.  Figure an average of 60lbs per square foot of foam, that one piece looks like it has several square feet in it.

25 minutes ago, Way2slow said:

Be surprised.  Figure an average of 60lbs per square foot of foam, that one piece looks like it has several square feet in it.

And my 14 foot v hull with 3 bench seats doesn’t weigh much over 300 lbs I would imagine. I’ve picked it up with the assistance of one other person a few times 

I meant, one cubic foot has a flotation value of 60 pounds (it will keep 60 pounds afloat), not one qubic foot weighs 60 pounds

 

Depending on the density rating, 2 pounds, 4 pounds, etc, is how much it weighs per cubic foot (I think it's based on per qubic foot)

 

Also based on the density rating is how much it will float per cubic foot.

1 hour ago, Way2slow said:

Be surprised.  Figure an average of 60lbs per square foot of foam, that one piece looks like it has several square feet in it.

Cubic foot? A square foot isn't much. 

Yes, it's cubic feet, I didn't even notice I had been typing Square feet.  Kinda hard to get any meaning in volume out of a square foot.

When guys start adding front decks and sealed compartments to boats like this, I always wonder if it will sink like a rock if swamped. 

9 minutes ago, E-rude dude said:

When guys start adding front decks and sealed compartments to boats like this, I always wonder if it will sink like a rock if swamped. 

They'll pack spray or mix-liquid foam into certain areas. Like around the rod-tubes in the rod-compartment. A little here and a little there adds up fairly quickly.