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| How much internal pressure can a glass hull take? http://www.hobie.com/au/en/forums/viewtopic.php?f=9&t=35501 |
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| Author: | zupe [ Wed May 11, 2011 11:43 am ] |
| Post subject: | How much internal pressure can a glass hull take? |
Can I put 1 psi or 2 psi in an H17 hull? Anyone have experience with gauges and filling a hull with 1-2 psi of air? Maybe Matt can say something here. Thanks, Dave |
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| Author: | MBounds [ Wed May 11, 2011 11:53 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
Don't do it. The consequences of misjudgment can be severe. If you're leak testing, a shop vac turned on "blow" and held about an inch from the drain plug opening works just fine. With the boat on the trailer, rudders up, you can tape the hose to hang below the rudder, blowing in the right spot. Helps if you're working alone. |
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| Author: | zupe [ Wed May 11, 2011 8:27 pm ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
thanks MrBounds, I have the hulls in my house upside down on the floor and it's hard to soap test them. My curiosity is mounting on just how good the hulls are. I made up a nice shrader valve, dial gauge, and drain plug assembly....... :/ You say consequences of misjudgment, are you talking more than 2 psi? I have nice low pressure gauges, 0-5 psi oil filled. I figure the hull volume is so great compared to my 5 gal air tank it would be hard to go past 1 or two psi. But I do want to be careful. Once in a while I hear air exhausting from a removed drain plug on the beach. I'm amazed by the small woosh of air that comes out. And I think to myself, nice hulls. Thanks, Dave |
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| Author: | Yellowboat [ Wed May 11, 2011 11:11 pm ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
you would be amazed at how much volume of air is in that 5 gallon tank. boyles law applys if there is no temp change( there would be, lets assume not to keep this example easy) boyles law p1*v1=p2*v2 if you have 90 psi in a 5 gallon tank, there is ~ 231 cubic inchs per gallon. so the eq would look like this: 90 psi * 1155 cubic inchs= 2psi*v2 so v2= 51975 cubic inchs or ~ 30 cubic feet of air. I don't know what the volume of H17 hull is, but I'd guess that 30 cubic feet is enough to fill the hull up atleast twice. |
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| Author: | MBounds [ Thu May 12, 2011 5:03 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
zupe wrote: My curiosity is mounting on just how good the hulls are. I made up a nice shrader valve, dial gauge, and drain plug assembly....... :/ So . . . you're going to do some destructive testing to find out?I know someone who exploded a 16 doing what you are contemplating. There's a lot of energy in compressed air, and it gets expended all at once. I want to hear the story you're going to tell your insurance company when you make that claim. I don't know what pressure the hulls can withstand and I really don't need to know. I know how to check for leaks with a vacuum cleaner - which actually works better if the boat's upside down. There's no other reason to pressurize a hull. |
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| Author: | hrtsailor [ Thu May 12, 2011 5:41 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
Do the math. Assume a 16' long hull averages 1' in height (that's being conservative) which means 16 sq. ft.. At 1 psi or 144 pounds per sq. ft. the total pressure trying to force the hulls apart would be over 2300 lbs.. More than a ton. If a vacuum cleaner used as a blower could develop 12" of water gauge pressure, that is close to 1/2 psi or about 1100 lbs of force on the hull. |
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| Author: | MBounds [ Thu May 12, 2011 5:59 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
BTW, if you do this, we need pictures. You could do it MythBusters style - stand behind a Lexan screen while the pressure goes up. Don't forget the high-speed cameras to capture the BOOM for slo-mo replay! And closeups of the destroyed hull-deck seam (because that's where it will blow). |
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| Author: | gary eudy [ Thu May 12, 2011 7:26 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
why be stupid? a large leak is easy to find a small leak is no concern |
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| Author: | buxton [ Mon May 16, 2011 4:55 pm ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
I've done it. Had a second regulator at the end on my compressor hose set at 1psi and my blow gun on the end of the regulator, I then put the tip of the blow gun against the drain hole. I was able to find 2 small leaks with no problem. Maybe not recommended but doable. If I find the time in the next couple of weeks, I'll do it to a spare hull with corroded pylons and video it. Buxton |
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| Author: | buxton [ Fri Jun 17, 2011 4:12 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
This week I took an old drain plug, drilled it out and tapped it with an air tool coupler so I could connect the hose right to it, I then drilled a hole in the side of the hull about mid ship so I could install a pressure gauge in there. I had 7psi coming out of my compressor and the hull went to 3psi before the bottom blew out. I did find 3 leaks I had to repair to get the hull to blow. There was a lot of hull expansion before it let go so I wouldn't try it on a hull you want to keep. I'll try to get the video on youtube this weekend. |
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| Author: | SNovak [ Fri Jun 17, 2011 7:14 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
Actually, this isn't quite right. In order to use Boyle's law, the pressures have to be absolute. both the 90 psi and the 2 psi are relative to the atmospheric pressure (gage pressure, psig). the absolute pressures will be 90+15=105 and 2+15=17 psi (psia), respectively. this works out to about 4.2 cubic feet of air- probably no where near enough to blow your hulls apart. Having said that, I still wouldn't try this on a hull I ever wanted to use again... Yellowboat wrote: you would be amazed at how much volume of air is in that 5 gallon tank.
boyles law applys if there is no temp change( there would be, lets assume not to keep this example easy) boyles law p1*v1=p2*v2 if you have 90 psi in a 5 gallon tank, there is ~ 231 cubic inchs per gallon. so the eq would look like this: 90 psi * 1155 cubic inchs= 2psi*v2 so v2= 51975 cubic inchs or ~ 30 cubic feet of air. I don't know what the volume of H17 hull is, but I'd guess that 30 cubic feet is enough to fill the hull up atleast twice. |
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| Author: | gary eudy [ Fri Jun 17, 2011 7:36 am ] |
| Post subject: | Re: How much internal pressure can a glass hull take? |
Have you ever seen a safety video of a truck tire blow up? this issue keeps coming up for some reason. |
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