What is an "air test"?

Steve Kaplan

New Member
I bought a 40 year old sunfish last summer. It has sat for a year. Somehow it got gallons of water in the hull even though it hasn't been sailed since I bought it. I noticed a new small plastic drain on the deck next to the metal drainplug. I drained the majority of the water out of hull in April. Went to try to sail it today for the first time. It has a fair amount of water back in the hull. How could gallons of water be getting inside the hull when it is not being sailed? And what exactly is an "air test" and should I do one, and if so, how is it done? Thank you very much! Steve
 
Water has a sneaky way of entering the Sunfish hull. When not being used, overnight condensation can enter the hull and collect. It is recommended that the hull be stored on edge--with the upper-deck's drain down and open.

Water-weight can be absorbed most readily within the yellow foam "glue" that holds the white Styrofoam blocks in place. Those big Styrofoam blocks keep the deck from bending under foot or knee. It's a slow process to cause the foam to lose its water "load".

The fastest way to evaporate collected water is to install two inspection ports and direct a fan to run day and night for weeks. Results start right away and taper off. A Sunfish weighing 128 pounds is a very dry Sunfish! ;) (Weigh on-edge using a bathroom scale; peer over the deck). Help is recommended, but not necessary.

Water can enter while sailing or while being moored (through the floor's [broken] bond that holds the bailer). Suspect areas include hardware, a fractured hidden edge bond under the aluminum trim, bailer, the mast step, and daggerboard trunk.

Use a (very) low pressure air source to pressurize the hull, but first tape-up the tiny vent hole hidden behind the "hook" (or serial number plate), apply a rich soapy-water mix with a brush . Apply to every possible point of entry and look for bubbles. Those bubbles indicate a leak of water in the opposite direction.

To test the daggerboard trunk, tape up the opposite opening of the trunk.

Sealing the leaks permanently be done in a variety of ways: Look using this forum's "search" feature.

:)'
 
I just read a post from an aircraft guy (here) that suggested a very low pressure - AFTER I already used 5 lbs. He suggested 1 PSI. I think it could take a little more than that. There are some good videos on youtube of soap spraying.

We can breathe up to about 14 PSI.....so my take is that 4-5 PSI should be fine. In fact, I used my mouth (over the small hole) to pressurized my MF the first couple times. At about 6PSI the hull started to make a few noises so definitely don't use very high pressure (I have seen people at the Club seemingly not paying attention to excess pressure put into Sunfish - but those were very leaky ones, so it probably didn't matter).
 
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1 PSI is more than enough! Let's put it all into perspective....
If the boat were submerged to a depth of 2.31 feet, the pressure on the hull would be 1PSI. Your boat will never be submerged to 2.31 feet (or never was designed to be) so water coming in is well under 1 PSI.
Let's say the deck area on a Sunfish was approximately 15 sqft. You are welcome to do the math but this is a consultative number. 15 sqft is equal to 2160 sqin. At 1 PSI internal pressure x 2160 sqin = 2160 pounds of pressure trying to rip the deck off. It doesn't matter how much the boat leaks, if the gauge on the internal air pressure reads 1 PSI, the destructive pressure is still the same if it didn't leak at all. At 6 PSI I am surprised the boat stayed together. Safety is no accident people.
Dale
 
Luckily I had no tight seal where the air pumped in - so although the pump was set at 6, it was relying on me holding it into the hole which it didn't fight tightly into......
In any case, I probably put 2 PSI solid into it - I'll keep it to <1 in the future.
I don't think it would have "blown" as I let up as soon as I heard even a slight "creak" and with no fittings holding the air in there it acted as it's own safety.

Lots of Folks seem to use shop-vacs which produce quite a bit more than 1 PSI. Then again, many folks may ruin their boats!
One dude used a leaf blower! I think I had the right idea the first way - using my breath, which did fill it up (probably to <1 PSI).

One result says Team Vanguard was at less than 1/2 a PSI. I wonder, tho, given the boat moving through the water and the waves/wind/etc. against it, if that's enough. That spec would be close to only 1 foot of depth, which the boat could get in real world use.

It's amazing water gets in there because there is nothing visible larger than a pinhead on the rolled seam (which are now sealed with 4200).
I'm going to monitor it and since I never keep the boat in the water...if I have to bail out 1/2 a cup after a two hour sail, I'll just live with it.
Given the 6" inspection port it's easy to dry.
 
Static water is one thing, moving water another. When we did river rescues we were told moving water, at surprisingly slow speeds, can exert 6 psi on a flat plate surface. That is why you're not going to wade across a stream chest deep, in moving water, to rescue someone. And that is how cars get washed off of roads. And why they called us for Helicopter Search and Rescue.

That said, the hull is designed to keep water out, but not so much to keep shape when pressure is gong the other way, so the deck can bulge and internal blocks can tear loose from the adhesive foam. Pressure is one thing, volume another. We try to use low pressure, low volume air. We don't put a tight seal on any port that we are blowing air into, there is about as much air coming out as there is going in. Small cordless shop vac has been our favorite air source recently.


These cordless vacs are very handy for cleanup, sucking out a bilge, and no threat of electrocution in the boat yard.
 
To my knowledge there is only pressure - when dealing with air. Volume is only the size of the item being tested in this case.
I'd stuck on my breath for now since I am sure it is at least 1PSI.

Important note would be how bad the hull in question might be. Since mines holds pressure (from breath) for at least 1/2 hour, I blow it up and put the screw cap back in- this allows the soap to be sprayed for a while in silence and without holding anything against the hull.

If the hull leaks like a sieve you'd prob want constant air pressure (hook up some string and tape to get some low pressure blowing in) while you find the big leaks. Once you get the leaks down to only smaller ones, then the vessel should hold pressure.

Speaking of pressure holding- has anyone determined about how long a "good" hull would hold that 1 PSI or so of pressure to be considered fairly water-tight? 1/2 hour? 1 hour?

I suspect a lot of hulls end up holding pressure on dry land but when flexing in use might open up some hairlines.
In my case I think (hope) the large Chine repair I am now finishing will do the job for my purposes....just to set a goal, I'd go for 4-6 oz of water in the hulll (I have access port to easily remove) in two houses of sailing.
 
There are 30+ designed holes in a Sunfish, plus 30+ feet of seam and seams around trunk, mast step, bailer hole and cockpit tub seam. If you have a 40 year old boat that is holding air pressure for more than 5 minutes please send a photo! And then go to see why the vent hole is plugged up. Sunfish hulls should stay at ambient air pressure unless someone has purposely taped over or plugged the vent hole, it is part of the design to keep hulls from popping seams or detaching blocks. Alcort saw fit to put drain plugs in all of their boats for a reason.

The areas to focus on are the areas below the waterline. There inevitable small leaks around any of the plethora of fastener holes on the deck. Plus if someone added one or two or three deck plates, there's a really big hole plus 6 more smaller holes.

As for volume and pressure, I'm referring to the apparatus being used to pump air into the hull, it can be rated per the volume of air delivered at different psi.
 
Ah, a challenge! I know it holds for more than 5 minutes.
But you are right - being super-sealed doesn't mean much if one good crack expands with weight and load and is under the waterline. Still, I'm taking it as somewhat of a challenge to get it as dry as possible.

Do a lot of MF and Sunfish sailers put rear (transom bottom) drains in? My Rocket has one. In one sense they are a PITA but if a boat is extra wet it could be handy for draining.
 
Here is a Video of the hull holding air for 11 minutes.
I know I've had it hold at least 1/2 hour - so I guess I am doing well in that regard...

I put the deck plate in - and sealed it property. No leaks there.
One of the leaks (but prob not relevant to water) was a screw hole in that brass hook thing at the front of the interior well- 3 screws, but 1 of them had no backing (no wood inside) and it leaked a lot- it was the first leak I detected as it immediately made noise when I blew into the drain.

 
That's right, A minifish. Fewer holes to mess with.

We are dead set against adding holes behind the waterline. Bits of foam and other innard things can clog a stern drain. And they are notorious leakers. One other issue is lifting the stern to drain water can end up damaging the gudgeon if one is not paying attention. Since you are on the right track of fixing leaks I wouldn't drill that hole.

 

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