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Leak Testing

Few things are more frustrating than bringing your boat in at the end of the day and finding out you have been carrying an extra 40 or 50 pounds of water inside your hull. Worse yet, you have no idea where it is coming from. Even a small leak can let a lot of water in. A 1/4" hole can sink a 30 foot boat over night. There are a couple of relatively simple tricks that can allow you to find out in a hurry. I have explained them below. None of them require a bunch of skill or that you be the consummate do it yourselfer. Even if you can't repair the leak yourself it still helps to know exactly where the water is coming from.


A shop vac or leaf blower, duct tape, paint brush, a bucket of water, car wash soap or the like, food colouring. saw horses,a set of extra hands and the beverage of your choice. (I personally use Samuel Adams) If you don't already have an inspection port in your boat this is a good time to put one in. It only takes about 20 minutes to do, and it will save you a load of aggravation.


I am assuming that your boat already has an inspection port 2 is even better and 3 is over kill. Unscrew the ports and place the vacuum cleaner hose through it. If you have at least 2 ports you can go ahead and tape the vacuum cleaner hose in place.(See Fig. 1) Open any other ports, plugs etc. With the vacuum cleaner on blow, turn it on and see what happens. Our goal is to pump air into the hull and create back pressure that will force the air out through the leaks. IF THE HULL BEGINS TO EXPAND TURN THE VACUUM OFF IMMEDIATELY!!! If you have only one port you may have to put duct tape over part of the hose to block air flow. If you have more than one port you will have to create back pressure by putting duct tape over the second port. Do it one piece at a time until you can feel some pressure build inside the hull.(See Fig. 2) You may at this stage want to close any drain plugs so you can test them for leaks. When you are ready your boat will look something like Fig. 3.

FIG. 1 Vacuum Cleaner End Sealed To Port w/Duct Tape

FIG. 2 Second port partially taped to provide back pressure.

FIG. 3 Vanguard 15 Hull Ready To Test (1 port closed, 1 port w/vacuum, 1 port partially taped)


Mix up your soap solution. I like car wash soap which seems to bubble well. You can use any soap that will bubble easily i.e. dish washing soap, but don't try liquid hand soap it won't bubble well enough. Do not make the solution foamy. That will only make it hard to tell where the bubbles are coming from. (Do not put the dye in yet)

Turn on your vacuum and begin to work your way around the hull. Be methodical so you don't miss anything. You want to test around any fitting, hardware, crack, joint etc. where water can pass through into the hull. SEE MY LIST BELOW!!! Use the paint brush to flow the soap solution on. (See Fig. 4) You need a nice puddle to allow the bubbles to form. It may take 10 or 15 seconds for the bubbles to appear. Work a small area at a time and watch. The bubbles may be hard to see. When you are done with the topsides flip the boat over and do the bottom. (Let gravity be your friend.)

FIG. 4 & 5 Flow the soap solution on and watch for bubbles to form.

Dan's Favorite Leak Spots:

Hull / Deck Joints or Rails, Through Hull Bailers and Scuppers, Drain Plugs, Inspection Ports, Loose Hardware, Dagger or Center Board Trunks where they join the deck or hull, Mast Step (Especially on Sunfish or Laser), Coaming on Sunfish, Bailer Hoses on Vanguard 15s, Cracks on the hull or cockpit that look to minor to be all the way through.

Step 3:

Spots you can't reach, ie. Sunfish Mast Steps, can be dye tested. Put some food colouring in water and pour the water into the mast step. Let it sit for a while and then look inside the hull. If you see the dye in the boat, then you know the step is leaking. Through hull bailers like the Vanguard 15s can also be tested this way.

If you still can't find the leak, KEEP LOOKING. DO NOT I repeat DO NOT ever try to find a leak by filling the hull of your boat with water unless you want to wreck it. Boats were not designed for the enormous stress of sitting on land with several thousand pounds of water in them.

DAN I STILL NEED HELP!!! then please feel free to contact me, I'm more than happy to help. Follow this LINK.