How Do I Find A Mystery Leak?

andyatos

Active Member
Thread starter #1
After using the usual water with dish soap while pressurizing the hull to find the major leaks when I first got the Sunfish, I thought I had the hull completely sealed. But I've got a minor leak that I can't find. After several hours of sailing I'll end up with about 3/4 of a large boat sponge (8" by 4" by 2") worth of water inside the hull.

The thing is, I've done two painstaking water with dish soap investigations of the entire hull surface trying to find this mystery leak with no luck. No bubbles, no subtle hissing. So, how do I find this thing? Fill the hull part way with water while on the trailer and look for water dripping on to the garage floor?

It appears I still have the same amount of water in the hull when it's windy and there's a lot of water splashing on the deck and I'm heeling and dipping the gunnels as I do when the wind is light and only the hull is in the water. To narrow the search area I thought about taking just the hull, launching it, tying it up or anchoring it, waiting a couple hours then pulling the boat. At least that way I'd know the leak had to be coming only from where the hull was displacing the water it was sitting in.

Any ideas? I really would like to use the inside of the hull for gear storage because my wife and I are using it for day long exploring, beach and picnic outings. I can't do this if I've got some water inside the hull.

Thanks,

- Andy
 

L&VW

Well-Known Member
#2
After using the usual water with dish soap while pressurizing the hull to find the major leaks when I first got the Sunfish, I thought I had the hull completely sealed. But I've got a minor leak that I can't find. After several hours of sailing I'll end up with about 3/4 of a large boat sponge (8" by 4" by 2") worth of water inside the hull.

The thing is, I've done two painstaking water with dish soap investigations of the entire hull surface trying to find this mystery leak with no luck. No bubbles, no subtle hissing. So, how do I find this thing? Fill the hull part way with water while on the trailer and look for water dripping on to the garage floor?

It appears I still have the same amount of water in the hull when it's windy and there's a lot of water splashing on the deck and I'm heeling and dipping the gunnels as I do when the wind is light and only the hull is in the water. To narrow the search area I thought about taking just the hull, launching it, tying it up or anchoring it, waiting a couple hours then pulling the boat. At least that way I'd know the leak had to be coming only from where the hull was displacing the water it was sitting in.

Any ideas? I really would like to use the inside of the hull for gear storage because my wife and I are using it for day long exploring, beach and picnic outings. I can't do this if I've got some water inside the hull.

Thanks,

- Andy
You need more sponges! ;)

I suspect most of the water that seeps into my Sunfish(es) enters through the daggerboard trunk. If I were so inclined, I might sprinkle talcum powder around areas of suspicion.

You could use the trailer and fill the hull with two inches of water—as you suggest. Leveling the trailer might be necessary to keep the water from soaking into the Styrofoam's expanding foam (again). :confused: Or, you could just have lunch while anchored, peering into the hull periodically.

Inverting the boat in the lake, then applying soapsuds to the inside of the daggerboard trunk might disclose the problem. You'd have immersed all of the seam between hull and deck—eliminating all the deck's possible leaks—plus you'd have the gentle air pressure required for the test.

.
 

Wavedancer

Upside down?
Staff member
#3
After using the usual water with dish soap while pressurizing the hull to find the major leaks when I first got the Sunfish, I thought I had the hull completely sealed. But I've got a minor leak that I can't find. After several hours of sailing I'll end up with about 3/4 of a large boat sponge (8" by 4" by 2") worth of water inside the hull.

The thing is, I've done two painstaking water with dish soap investigations of the entire hull surface trying to find this mystery leak with no luck. No bubbles, no subtle hissing. So, how do I find this thing? Fill the hull part way with water while on the trailer and look for water dripping on to the garage floor?

Thanks,

- Andy
Please DON'T do that!
Rather re-investigate suspicious areas:
Trunk (see L&VW post)
Splashboard
Bailer area
Mast tube
Area/gasket around the porthole

PS: You did seal the breathing hole for the soap bubble test?
 

Webfoot1

Active Member
#4
The hull seam often splits around the splash guard area due to flexing. It also may split
in other places. It's really easy to remove and reinstall the rail so I'd spend a couple hours
with the drill and pop-rivet gun just to check it off the list of problems. Then all you
have left is the dagger board when right side up. Provided you don't have an old style
rudder mount. Have you resealed the bailer? Easy to do with 3m 5200 as the bailer
sits above the hull with a small gap. Check the joint between tub and deck, It likes to
pull away also.
 

andyatos

Active Member
Thread starter #6
The hull seam often splits around the splash guard area due to flexing. It's really easy to remove and reinstall the rail so I'd spend a couple hours with the drill and pop-rivet gun just to check it off the list of problems.
Yup, did that when I split the hull to repair the bow. Sealed up all the rivet holes then 5200-ed a white rub rail to replace the trashed aluminum one.
Have you resealed the bailer?
Glassed it completely over from the cockpit to the hull. Hate the bailers on the Sunfish. They always seem to get caught on stuff, tweaked, cracked and leak... when others use your boat that is. :cool:
Check the joint between tub and deck, It likes topull away also.
Now that sounds interesting. Can you be more specific? How would that allow water to get into the hull when the wind is light and the deck is always dry?

Like I said, it's a stubborn mystery leak that doesn't seem to want to reveal itself.

Thanks!

- Andy
 

andyatos

Active Member
Thread starter #7
Or, you could just have lunch while anchored, peering into the hull periodically.
I like that idea. Especially with the talcum powder. Completely dry out the inside of the hull, launch the boat only, spread some talcum powder immediately then check through the forward wall of the cockpit inspection port for signs of the leak.

Inverting the boat in the lake, then applying soapsuds to the inside of the daggerboard trunk might disclose the problem. You'd have immersed all of the seam between hull and deck—eliminating all the deck's possible leaks—plus you'd have the gentle air pressure required for the test.
Another interesting approach. Thanks.

- Andy
 

Webfoot1

Active Member
#9
Now that sounds interesting. Can you be more specific? How would that allow water to get into the hull when the wind is light and the deck is always dry?

Like I said, it's a stubborn mystery leak that doesn't seem to want to reveal itself.

Thanks!

- Andy
Because if you have a big leak you can't pressurize the hull to find the smaller leak.
There is a small vent hole in the front to the cockpit wall, tape that over. The way we
test aircraft fuel tanks is to pressurize to 2.5 psi. and see if it holds for 24 hours. You
can do the same by installing a air fitting and pressure gauge on a inspection port cover.
If you can't hold any pressure at all you should be able to turn up the pressure till you
hear a hissing sound. As for how much pressure a Sunfish hull can hold before it pops
a seam I don't know. I'd think 1 psi. would be pretty safe but that's a guess on my part.
I always get a little water in the hull of my Sunfish but for what I do I don't worry about
it. I just suck it out with large syringe and call it a day.
 

andyatos

Active Member
Thread starter #10
Because if you have a big leak you can't pressurize the hull to find the smaller leak. There is a small vent hole in the front to the cockpit wall, tape that over.
Yes... the vent hole I covered with duck tape during all 3 of my hull pressurizing/dish soap leak tests. ;)

I did Leak Test #1 after my first sail upon taking possession of the boat. A sail that filled the boat with about 5 gallons of water. Test #1 immediately revealed 2 leaks (short cracks) where the daggerboard case meets the hull. Repaired that area, split the deck at the bow, rebuilt the bow, repaired and re-mounted the splash guard, re-sealed the gudgeon and stern drain plug, removed the cracked and broken auto bailer and glassed that hole closed at the cockpit and the hull.

Did Leak Test #2 and couldn't find any leaks. Continued to sail yet would still find 3/4 or so of a large sponge's worth of water in the hull after sailing. So, I did Leak Test #3... very carefully. Still couldn't find any bubbles or hissing. As I said, the mystery leak that doesn't want to reveal itself.
You can do the same by installing a air fitting and pressure gauge on a inspection port cover. If you can't hold any pressure at all you should be able to turn up the pressure till you hear a hissing sound.
One would think that this approach would eventually uncover my mystery leak... as I have thought about doing a leak test with more internal pressure.
As for how much pressure a Sunfish hull can hold before it pops a seam I don't know.
And that, sir, is the $64 question.

Cheers,

- Andy
 

beldar boathead

Well-Known Member
#11
'Yup, did that when I split the hull to repair the bow. Sealed up all the rivet holes then 5200-ed a white rub rail to replace the trashed aluminum one."

I assume that when you put the deck and hull back together that you glued it with something pretty good, like epoxy?
 

andyatos

Active Member
Thread starter #15
Drop a "Revenge Rodent Smoke Bomb" in the hull, put the port cover
back on and pressurize? One attempt would only cost $5.67 before tax.
Want to hear something funny, Webfoot? After I responded to your last post I thought about posting again with the following joke.

"Hey... maybe I should just make a camp fire inside the boat, seal it up and see what happens. Or... maybe not."

A smoke bomb. Excellent idea.

- Andy
 

L&VW

Well-Known Member
#17
Did Leak Test #2 and couldn't find any leaks. Continued to sail yet would still find ¾ or so of a large sponge's worth of water in the hull after sailing. So, I did Leak Test #3... very carefully. Still couldn't find any bubbles or hissing. As I said, the mystery leak that doesn't want to reveal itself.
While sailing, the daggerboard trunk is being stressed—and water is surging upwards inside the daggerboard trunk.

That's where I would look next.

Or, toss one of these little $19 lightweight "transfer" pumps into your inspection port—takes 2 AA batteries—and which seems to drain collected water down to almost nothing:

 
#18
Mast hole or dagger board slot are the two parts of a fish that get alot of stress when sailing. I just repared a leak in the mast port that I could not see. Take a strong flashlite and shine it into the hole. Pay close attention and look for any imperfections. . Now fill the hole with water and see if it ends up in the hull. If it does that is where your leak is . now empty the water out of the hole and sponge it out of the deck. Cable tie a piece of sponge to a dowling to get the last bit out. Do the same with a rag to dry the sides of the hole. Now tape a small paint brush to a stick or narrow board and coat the inside of the hole with fiberglass resign. Let it dry for at least 8 hours and repeat. Once that is dry refill the hole and see if you still get water in the hull. If you do then you may have to cut a hatch near the tube and fix it from the outside. When applying resin make sure it does not pool up at the bottom of the hole. . If its an old fish the mast may be a bit wobbly when rigged. Take underwater tape and make one wrap on the mast just below where it meets the deck. The tape is probably 2 or 3 inches wide. Double check your measurements...Th e tape ,once applied is hard to get off and you will need a half a bottle of Goo Gone to get the adhesive off the mast. .Caution: although it is underwater tape make sure what you apply it to is clean and dry. Hope this helps.
 
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