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| Hull is air tight... add vent hole? http://www.hobie.com/au/en/forums/viewtopic.php?f=13&t=36161 |
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| Author: | Daredevil [ Mon Jun 13, 2011 4:43 am ] |
| Post subject: | Hull is air tight... add vent hole? |
I remember reading somewhere in the forum that you do not want your hulls airtight... The other day as I unscrewed one of my ports I noticed a "whoosh" sound from pressure in the hull. Should I drill I pilot hole somewhere for a vent? Is there a stock vent location that is clogged? |
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| Author: | Chet3 [ Mon Jun 13, 2011 5:56 am ] |
| Post subject: | Re: Hull is air tight... add vent hole? |
I read the same thing on the forum and had one airtight hull. I followed their recommendation and drilled a very small hole (1/16") in each of the port covers. I have only used the boat one time since and it did not seem to trap air or get any water thru the hole (it was not a rough day though). |
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| Author: | matt922 [ Mon Jun 13, 2011 7:14 am ] |
| Post subject: | Re: Hull is air tight... add vent hole? |
just take a hull port cover off before taking the plugs out |
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| Author: | MBounds [ Mon Jun 13, 2011 7:57 am ] |
| Post subject: | Re: Hull is air tight... add vent hole? |
matt922 wrote: just take a hull port cover off before taking the plugs out Either one will release any pressure inside the hull. The order you do it in will make no difference.The factory vent hole on the 18 is in the forward crossbar saddle. A small hole in the port cover will serve the same purpose if the factory one is plugged, but is not as protected from water intrusion. Not a problem unless you plan on spending a lot of time upside down in the water. I'm just religious about the drain plugs. They're screwed in right before the boat gets in the water and taken out as soon as the boat's out of the water for the day. They're not in long enough to develop any serious pressure difference in the hull. |
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| Author: | Chet3 [ Mon Jun 13, 2011 8:05 am ] |
| Post subject: | Re: Hull is air tight... add vent hole? |
I drilled the holes in the port covers because I was concerned about overpressurizing or vacuum in the hulls due to temperature changes. A hot hull in the sun goes into cold water and the air in the hull contracts causing a vacuum. The opposite is when the boat comes out of the water and hulls heat up and are pressurized. I have seen first hand what that vacuum can do to a wood kayak I built (now has weep holes in the bulkheads). Either way I drilled the holes in the port covers and now I should not have an issue and I doubt much water could get thru the 1/16" hole even if it were completely submerged for an extended time. |
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| Author: | mmiller [ Mon Jun 13, 2011 3:30 pm ] |
| Post subject: | Re: Hull is air tight... add vent hole? |
Quote: They're not in long enough to develop any serious pressure difference in the hull. Hot day / cold water. Nearly instant pressure change once the boat hits the cold water. Reverse is cold water sailing and then leaving on the hot beach. |
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| Author: | MBounds [ Mon Jun 13, 2011 6:19 pm ] |
| Post subject: | Re: Hull is air tight... add vent hole? |
mmiller wrote: Quote: They're not in long enough to develop any serious pressure difference in the hull. Hot day / cold water. Nearly instant pressure change once the boat hits the cold water. Reverse is cold water sailing and then leaving on the hot beach. Mmmm, not quite, since the air in the hull needs time to cool - and it's in an insulated container (foam core). Air itself (especially 100% humid air) is a pretty good temperature moderator, since the water phase change soaks up/bleeds off a lot of energy. I've never seen a vacuum drawn on the hull, when I pull the plug - only overpressure. But Matt's right - extreme temperature changes (say 40+ degrees F) will create a significant pressure differential. Lemme dig out my old thermodynamics book and I'll figure out exactly how much. [edit]I even remembered the Ideal Gas Law (PV=nRT) before I got to the thermo books. Since V, n and R are constant, P2=P1(T2/T1). Extreme case - going from 50°F (283.25 Kelvin) to 120°F (322.04 K). Assume P1 = atmospheric pressure = 98 KPa P2 = 98 KPa(322.04K/283.25K) = 111.46 KPa ΔP = P2-P1 = 13.46 KPa = 1.95 psi 2 psi is borderline blowing the boat apart. |
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