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Old 23 March 2020, 05:39   #1
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Intentional under inflation

I have a 3.6m 4 chamber aluminium floored SIB. The manufacturer recommends that all four chambers are inflated to 3.43psi. Having experienced a split seam on a previous craft due to sun heating pressurisation I am uncomfortable at the recommended pressures. I always deflate a little when the SIB is parked up out of the water to avoid sun baking issues. The tubes feel adequately rigid at 2.5psi and so that is the pressure I have been using for the past couple of years. I wanted to know whether you knowledgeable folk think I'm being daft and that I should fully inflate or is it okay to run slightly under pressured
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Old 23 March 2020, 06:05   #2
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Running under inflated can give poorer performance and allow movement between tubes and floor leading to chafing damage.

It can be a bit of a pain but I deflate/re-inflate as needed during beach stops etc.
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Old 23 March 2020, 11:31   #3
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With the Sib floating, 2.5 PSI inflation is hard enough to achieve a nice water performance, no need to pump it up to their max recommended working pressure unless max loaded.

When beaching always maintain the Sib floating near the shore to avoid over inflation specially during hot sunny summer days if plan taking the Sib out of water.

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Old 23 March 2020, 14:54   #4
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Lots of boats run at 3 psi that would give you enough room for expansion from 20 degrees C up to 30 degrees C of course test pressure is slightly more that the 3.43 psi for your boat. I run all my boats at the recommended pressure when it gets hot I just blip the valves to let a bit out.
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Old 24 March 2020, 11:02   #5
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I think I run my boat in the hottest location. I have 40 deg change from morning to 2 pm, the hottest time. I start at 3.5 psi and as the boat gets noticeably hard I burp it. If I’m out all day the boat feels soft when heading back at 6pm so I top off. My zodiac dealer said it can go to 5 psi before they are in danger. PVC welds are stronger than old glue seems so factor that in.
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Old 24 March 2020, 11:36   #6
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New tubes after being glued at the factory are tested to 5 PSI for a day or 2 to check if loosing pressure. There's no water performance difference inflating tubes to 3.0 or 3.5 PSI.

It's normal to achieve a huge pressure loss during afternoons or nights. That's why must carry a foot or hand pump to pump up the tubes to your preffered PSI inflation numbers. Be aware that darker fabrics colors such as black, dark grey reatains more heat and consequently bumps more PSI up than white, light gray ones when exposed to sun.

Overinflation will blow up any seem, the glue it was assembled with gets old and looses its bonding properties over time, all inflatables will experience this the sooner or later depending on brand and the glue quality employed.

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Old 24 March 2020, 13:44   #7
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I'd inflate them to the recommended pressure or very close. If worried, it is a fairly simple job to fit pressure relief valves. Most commercial spec. inflatables have them as standard.
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Old 24 March 2020, 15:13   #8
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I'd inflate them to the recommended pressure or very close. If worried, it is a fairly simple job to fit pressure relief valves. Most commercial spec. inflatables have them as standard.
I'd love to fit relief valves but each chamber only has one entry that is used for inflation. How do you fit additional valves? Is there a combined inflate & relief valve available?
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Old 24 March 2020, 16:12   #9
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I tried to do retrofit relief/fill valves but could not find ones for my setup and max pressure. Adding them to tubes is doable. And if you use the same “”fill “ pattern I suspect you can put one on every other chamber.
Just make sure which way the baffling is bulging.
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Old 25 March 2020, 04:33   #10
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my new excel has one relief valve in the bow so thats filled first then the others go soft when it lets pressure out
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Old 25 March 2020, 04:52   #11
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my new excel has one relief valve in the bow so thats filled first then the others go soft when it lets pressure out
That's interesting, I assume by inflating the bow first, the inter-chamber seals will bulge into the side chambers and so those bulges offer relief to the sides in the event of the bow pressure relieving itself. Sounds interesting. I'd have to cut a new hole and re-enforce it after I insert the inner seal ring. I'd rather just do that once so this solution sounds good
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Old 25 March 2020, 05:13   #12
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That's interesting, I assume by inflating the bow first, the inter-chamber seals will bulge into the side chambers and so those bulges offer relief to the sides in the event of the bow pressure relieving itself. Sounds interesting. I'd have to cut a new hole and re-enforce it after I insert the inner seal ring. I'd rather just do that once so this solution sounds good
yep if you go on to the polymarine site they show how to fit and supply all you need. when i picked the boat up they pumped it up for me first going round to fill all compartments so the tubes were full that takes stress off the baffles then they topped the bow up to working pressure moving to the stern doing each side equal as you say when the valve blows off the next compartment has room to move so you get volume & pressure loss into the bow compartment if that makes sense
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Old 25 March 2020, 06:04   #13
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Quote:
Originally Posted by jeffstevens763@g View Post
my new excel has one relief valve in the bow so thats filled first then the others go soft when it lets pressure out
Quote:
Originally Posted by bobfather View Post
That's interesting, I assume by inflating the bow first, the inter-chamber seals will bulge into the side chambers and so those bulges offer relief to the sides in the event of the bow pressure relieving itself. Sounds interesting. I'd have to cut a new hole and re-enforce it after I insert the inner seal ring. I'd rather just do that once so this solution sounds good
Think that's how most tubes are designed to be inflated, bow to stern, the internal baffles 'cup' towards the stern so fill the chambers front to back with the baffles shaped towards the stern
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Old 25 March 2020, 15:10   #14
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Baffle positions on my boat for info

https://www.excel-inflatables.co.uk/...D%20XHD435.pdf
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