Originally Posted by breakfluid
there is a bung in the floor of the forward hull, inside the boat.. its for a chamber thats shaped like an arrow... I tried pumping air in but it just comes straight out again so is it for ballast?
to form a kind of hull shape?
You are right, yes, it is to form a nice little bump in the underside of the floor. It's called the keel tube. It gets pumped up to around 240 millibar / 3.4 psi same as the rest of the tubes.
On my boat, the valves have a little green knob down in the center (see picture):
they can be pushed in and turned to "inflate", where it holds the air when you stop pumping, or "deflate" where it lets the air right out. Perhaps the valve for this has something similar?