Question about leak test

davavd

OldNSlow
I've done 2 now. I read the instructions, here and on Yahoo (more carefully the 2nd time :eek:). The 1st time, I used a small electric leaf blower :eek: and got bubbles at the bailer and around the top of the daggerboard trunk. I realize my method may have caused one or both of these leaks. I have fixed both leaks. On my 2nd test, i used a bicycle pump with a needle, stuck through duct tape over the vent hole. I got no bubbles anywhere, but I don't think I ever had much pressure in the hull, because there was not a good seal at all around the needle where it went through the tape. :confused: I also have an air compressor available.

How do YOU do your leak tests?
 
I use a bicycle pump, even if the connection is leaking you will still see the leaks when you pump it. I only pump a few times as I don't want to make more leaks.

-Erik
 
I don't think I ever had much pressure in the hull, because there was not a good seal at all around the needle where it went through the tape. How do YOU do your leak tests?
Sometimes I find the duct tape I use splits so I add a piece of plastic electrical tape to get a better seal.

If your inflator "needle" rips too large a hole, try poking a hole using a pin then insert the inflator.

If you are using the deck drain plug opening, are you taping the vent hole closed during the test?

If you are using the deck drain plug opening and the inflator is wobbling and enlarging the tape hole, close up the deck drain and switch to using the vent hole?

Using the vent hole, you could forego tape and bed the inflator in plumber's putty... or silly putty... something like that.

While pumping air into the hull, crack open the deck drain plug and soap it. When it begins to bubble you know you have built up pressure.
 
I have used a hand pump that came with an air mattress.

Did you seal the top of the mast step? Unless you want to test it as well (a good idea, BTW).
 
Did you seal the top of the mast step? Unless you want to test it as well (a good idea, BTW).
Oooo..., thanks for reminding me... In my preliminary testing, I tape off both the mast tube and daggerboard slot. After going over all the small stuff I poke a pin hole, first in the tape over the mast tube opening then in the tape over the daggerboard slot. If either of the pin holes show bubbles I investigate further.
 
Sometimes I find the duct tape I use splits so I add a piece of plastic electrical tape to get a better seal.

If your inflator "needle" rips too large a hole, try poking a hole using a pin then insert the inflator.

If you are using the deck drain plug opening, are you taping the vent hole closed during the test?

If you are using the deck drain plug opening and the inflator is wobbling and enlarging the tape hole, close up the deck drain and switch to using the vent hole?

Using the vent hole, you could forego tape and bed the inflator in plumber's putty... or silly putty... something like that.

While pumping air into the hull, crack open the deck drain plug and soap it. When it begins to bubble you know you have built up pressure.

All excellent suggestions, thanks!
 
I am about to perform this test myself.. does the shop vac taped into the inspection port method create too much pressure inside the hull?
 
I'd be careful about overpressurizing the hull when you perform a leak test. With all that surface area, even a fraction of 1 psi of internal pressure translates into hundreds (or even thousands) of pounds of load spread over the entire hull/deck.

When I did a pressure test, I simply bought a small rubber plug (from hardware store) that could be quickly fitted into the side drain hole (with normal plug removed), and taped off the small pressure equalization hole in the front wall of the cockpit. Then I inflated the hull by blowing it up by mouth at the drain hole and inserting the rubber plug. And even with just a couple dozen breaths to inflate the hull, I could hear the hull move, and a couple tiny snapping/strain noises signalled it was time to let some air out... -- !!

So I'd be a little leery of using a shop vac or other uncontrolled source of air pressure to inflate the hull. You could easily split / separate the top half from the bottom, or cause other internal damage if enough pressure was quickly applied inside the hull.
 
I'd be careful about overpressurizing the hull when you perform a leak test. With all that surface area, even a fraction of 1 psi of internal pressure translates into hundreds (or even thousands) of pounds of load spread over the entire hull/deck.
Lets see..., the max recommended pressure stated in the factory guide is 3 ounces per square inch.

3 oz = 3/16 lb or 0.1875 psi

1 sq ft = 144 sq in ... so we get 27 lb per each square foot of boat surface area, Maximum.

... taking some artist's license, let's square off the hull profile and say it makes a 14' x 3' rectangle ... or 42 sq ft.

42 x 27 = 1134 ... so the total force on one face of the hull would be equivalent to putting a 27 lb sand bag on each square foot of its surface (on the inside), achieving a gross weight of 1134 lbs. (pressing outward)

Every additional 1 psi increases the outward force against one surface of the hull by 144 lb per sq ft or a total of 6048 lbs.
:eek:
...now where'd I park my Hummer

You can make a visual pressure indicator from a short piece of plastic tube and a latex glove.

  • Tape one end of the tube into the glove
  • Tape the other end of the tube into the deck drain opening
  • Pump in air through the vent hole
  • When the glove inflates and does the Queen's wave you are at max.
  • If the glove begins to look like a cow in need of milking or a balloon with spiked hair your over doing it.
So I'd be a little leery of using a shop vac or other uncontrolled source of air pressure to inflate the hull. You could easily split / separate the top half from the bottom, or cause other internal damage if enough pressure was quickly applied inside the hull.
;) absolutely​
 
Sounds like a nice safety margin. If we assume that the lowest seam on the boat (hull daggerboard bottom seam) goes one foot underwater and water pressure increases 0.445 psi per foot of depth then the max pressure a seam has to withstand is 64.08 pounds per square foot.

Hum, I wonder what the pressure is for two kids jumping up and down in the tub. Sure causes my head to exceed max pressure.:D
 
Hum, I wonder what the pressure is for two kids jumping up and down in the tub.
I don't have that exact formula at the moment, but it's nearly proportional to the pressure rapidly and repeatedly applied to their backside a short time later. ;)
 

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