The ones that put out a mist of water, like a spray and wipe bottle. Fill it with a soapy water mix and spray all deck area. Stuff a air line up the bung hole and pressure up a little.

Look for the bubbles.

Do the same on the hull arround all the welds, seams and chines.

Could also just be the bung leaking. remove and reseal it

Fill her up on the trailer, use dye if you have to.

how would you fit a bilge pump to a sealed hull as well it is fiberglass do you cut a hole then put a s/s plate over it ?

Get some  condey's crystals from the chemist, mixed in water they turn it a reddish colour that is non staining if you're going to usr dye.

On my boat the leaks wasn't the bung but the whole piece that holds the bung. Took it off, cleaned all the surfaces and whacked a heap of Sifaflex on it and screwed the bit back in and cleaned the residue off after it was set.

Putting even 2-4 psi inside a structure not designed to take pressure, which has large surface areas can do enormass damage, so your deck area in square inches multiplied by the presure i.e x4 equals bang!

Just saying be careful.

Thats true, don't want it dropping through the trailer!

  Water  will do dont fill it right up as iana said to much preassure will delaminate the floor from the stringers and possibily the chines.

I have a slightly more scientific method of finding leaks in vessels that is 100% accurate, with no pressure. You need friends in the refridgeration trade and a mate who is a chemist. If all else fails PM me and I will help.

I had the same prolem with my swiftcraft and all it was , was the bungs. Replace the whole bung including bung housing and that will more than likely fix your problem. Seal the bung housing with marine sika.

thanks heaps to all of you response was great nice to see people ready to help others I will try replacing the whole bung plug assembly(there are 4 of them) first what silicone do i use please

Sika flex marine ( 921 ) i think silicon , try keeping it off your hands is a good tip

thanks again got the sika and will try it but what about putting a bilge pump in ?

Put a bilge pump in for sure but make certain that you have stopped the leak. Relying on the bilge pump to control the water isn't the right way to go, it should only be there in the case of an emergency.

To find out if it's the fitting thats leaking, take the bung out, wrap some insulation tape round your garden hose so its going to be a reasonably firm fit in the bung hole. Jam the hose in to the hole and turn the tap on, give it a couple of minutes them remove the hose and quickly replace the bung keeping as much of the water still in side the hull. Use a dry rag to dry the area round the fitting off and look for leaks.

If you install a bilge pump in the sealed hull, you will need to also install a breather line to allow the pressure to equalize, otherwise it wont pump.

 ITS FIXED!!!!the guy I brought it off thought he was doing me a favour and put all new bung plugs in it and got the ones with the wrong thread so they never tightened up on the washers hence the leaking, luckily he had left the old ones so took the washers of the new ones and put on the old ones, hose in the hole and bung plugs in no leaking yee ha thank you every one that commented think we could solve all the worlds problems if they just left it to fisherman one last question should I still put in a bilge pump considering I would have to cut into the floor to install

Most time you will never need it but if it was me I would fit one jusy for peace of mind knowing its there.

 I will thanks again guys.

Thanks for letting us know the outcome of your problem. I wish more users would do the same.

Re the bilge pump, can you supply more info. For instance is your hull divided into water tight compartments, Are the water tight compartments still water tight? no screw holes etc. Is there an open area for bilge water, i,e a sump.

It is the sump where the bilge pump should be fitted, to pump out water should a wave come over the side, or you have just washed down the deck.

I don't think putting a bilge pump in the sealed section of hull is a good idea.

put the boat in on sunday and lovely and dry when it came out great the hull has a sealed floor the area underneath has two bung plugs on the transom and that is it no other way in as far as I can see so although the floor is sealed the area itself is not because of the plugs does that make any sense