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Old 19 May 2015, 11:02   #1
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Inflation Questions

A few questions for the more experienced SIB'ers out there... Having trouble planing, and just want to rule out the apparent #1 cause of SIBs not planing (underinflation).

1. Is it safe to inflate Zodiac tubes 0.5psi higher than the stated 3.5psi inflation pressure? Would doing so offer any extra ridgidity?

2. I inflate my buoyancy tubes with the valves in the closed position, since they are one-way and will let air in when closed. I find that with the cross bars still in the adapters, the valves will stay open more often than not, letting the air out. I removed those bars at the recommendation of my dealer. Is inflating like this going to make my Bravo BTP12 Manometer electric inflator read a higher pressure than what's actually in the tube?

3. Can one tell if their tubes are underinflated or overinflated by the "feel" of the tubes?
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Old 19 May 2015, 11:13   #2
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Originally Posted by kestrel452 View Post
3. Can one tell if their tubes are underinflated or overinflated by the "feel" of the tubes?
Hi..I have a Quicksilver 4.3m inflatable SIB..and have never put a pressure gauge near it.

I just top it up with the hand pump..until it passes the "thump test" In other words..I give it a thump with clenched fist..and it bounces off when righ pressure is achieved. Nothing so scientific as PSI or millibars. Its 10 years old now and the previos owner just did a thump test on it...so no harm has ever resulted in it.

It is a wooden floor though..not a new fangled air floor that needs pressure tested.

It planes no problem at all. It has an inflatable keel under the wooden floor..which I deflate if Im hauling up a shore for a while. If I forget to inflate it again..it still planes easy..but causes a bit of a bow wave.

Perhaps that answers some of your question.. unless its an air floor SIB.. IMO..its not critical

Engine is 25HP for this SIB
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Old 19 May 2015, 11:16   #3
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1) I wouldn't. And no, probably not. Underinflated show up with the boat sort of arching in the middle as you try to climb out of the hole; or flexing as you hop over swell and chop. Put as much weight as you can forward, whack the throttle open, and see if you climb out.

2) No idea. My Bravo 12 (the box-like grey job with the adjustable shutoff - don't remember the model) specifically says valves should be open to inflate (though I suspect that's to allow the squirrel cage high volume stage to run.) Can you open the valve and allow the pump to inflate it and feel how taut the material is?

3) Experience helps, but you need to get a feel for what "correct" feels like. Which means you have to be pretty sure of the pressure.

jky
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Old 19 May 2015, 14:05   #4
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Inflation Questions

Theoretically shouldn't do any harm to inflate to 4psi, but also wouldn't offer any performance benefit. Zodiac recommend .24 bar (3.5 psi), but also give a range between .22 and .27 bar (3.2 to 3.9 psi) as an operating range. Just be careful of any pressure increase caused by temperature rise/hot sun if running at 4psi.

I also inflate with the one way valves in closed position with both Bravo and Genovo battery pumps and no cross bars in the adapters.

Properly inflated tubes feel rock hard and offer a nice ping when flicked. In my experience people who don't use a gauge (at least initially) are amazed how hard a correctly inflated tube feels. I also contribute to the theory that 90% of a sibs performance comes with the last 10% of pressure.👍
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Old 20 May 2015, 15:15   #5
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Properly inflated tubes feel rock hard and offer a nice ping when flicked. In my experience people who don't use a gauge (at least initially) are amazed how hard a correctly inflated tube feels. I also contribute to the theory that 90% of a sibs performance comes with the last 10% of pressure.👍
Amen to that.

My FC470 RU performs like a wet noodle once the pressure is below 2.8 psi.
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Old 20 May 2015, 21:48   #6
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Being new to ribs and having tubes black at the front and grey at the back temp makes a huge difference to my tubes.

Its now winter so my Zodiac sits in my garage cooling down to 0-10c, when the sun comes up it quickly rises to 22-24c and the black tubes obviously warming well above that.

Question is should I be constantly checking throughout the day and what harm can come from driving home on dark or during cold cloudy days when the tubes become a little soft?

Even summer with temps in the high 30's we can get a sudden hale storm dropping temps dramatically.

Cheers Jon

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Old 21 May 2015, 06:49   #7
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as gurnard says pump up solid job done trouble with psi is pump up on trailer put in the ogin psi changes pump up on dull day sun comes out pressure changes. i have pressure relief valves on mine pump to recommended pressure and leave they stay good all year might have to top up when its a really cold day
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Old 21 May 2015, 07:01   #8
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A mate has I think a humber? Yellow and black tubes and she blew a seam on one of the really hot summer days last year, its an old rib and I guess the extra pressure found a weak spot
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Old 21 May 2015, 11:55   #9
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A mate has I think a humber? Yellow and black tubes and she blew a seam on one of the really hot summer days last year, its an old rib and I guess the extra pressure found a weak spot
you can not beat the pressure relief valves lee well worth the money but in the old days we use to undo the dust cap which is the last seal for the air and if they looked a bit hard we just touched the valve to let a bit out.
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Old 21 May 2015, 21:57   #10
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Does anyone know if these are relief valves? (doesn't say in the book)

If the rib is up on the plane how can slightly soft tubes effect performance, surely the tubes are skimming above or only slightly touching the surface?

Sorry for my ignorance Im new to owning a rib and also living in an area they are not popular due to the harsh conditions. This site also states to search for an answer rather than starting a new thread on something already covered.

Jon

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