Addition of expandable foam for added buoyancy in sandwich construction

Hey Guys,

A good day to you all, so i just wanted to know if it is necessary to fill vacant spaces with expandable foam for positive buoyancy with sandwich construction or will the foam core used for construction be sufficient enough to provide the same.

Thank you,

 

That can be a complex calculation, what kind of boat ?

 

40 ft catamaran

 

A problem that needs a proper study, with all the data at hand. It is unlikely that a sandwich hull would have buoyancy to keep a 40' boat afloat, and particularly afloat upright and level.

 

First question is how thick is the foam in the sandwich?

 

A tiny boat can easily be made to be positively buoyant with a foam core, as size increases, less so, as core volume doesn't increase in as the cube of the length, but displaced volumes do, if scaled up proportionally.

 

20 mm for the running surfaces and 15 mm for the sides

 

So by calculating the void spaces which can be filled up with expandable foam, I.e volume and since we know the mass of the object we can arrive to a density and if lesser than the density of water it floats? Theoretically , am I right?

 

Depends what you already have in those spaces, or wanted to use them for, but it could be a diminution of utility of the boat. Is this a power cat, with what power/ drive line ?

 

Generally speaking, buoyancy foam is restricted to smaller craft, by the time a boat is large enough to accommodate self-inflating life rafts, that is the preferred option. Of course that isn't a means of keeping the boat salvageable, but passenger safety is paramount. You would basically lose the greater part of the sub-floor space to foam, expensive, and with the complication of the possibility of water intrusion into the foam, over time.

 

After the necessary storage holds are sorted out the rest of the vacant spaces? And we are looking at quad outboards with around 1500-2000 hp

 

I think you'd be better off with block polystyrene than pouring foam, but maybe more difficult to install, and to fill the area. It is probably more feasible with outboards than inboards, especially shaft drive, to be installing such buoyancy material. But you have to have enough to be sure the cockpit does not go under water, allowing free water to enter the drains, wash around your feet, and collect one side of the boat, especially the side that has let the water in. If you wet deck and cockpit sole is close to the waterline at rest, this could be a potential problem.