Tubes pressures

Roy Smith · 22 November 2005, 17:56

Ok I know i should know better.
But how do i know when i have the right pressure in the tubes. Is there a pressure gauge you can buy.It seams that i eaither put to much in or not enough, some say 2.5 lbs others 3.5.
Any help ?

codprawn · 22 November 2005, 18:00

Glad you brought this up cos i was wondering as well.

I think going by what feels right is a very good way. On my SIB it makes a hell of a difference - the harder the tubes the faster and more rigid the boat is but the ride is worse.

On a RIB as there is a hull to keep it all rigid some people say the tubes should be slightly softer as they will absorb knocks and wave motion better. Also I suppose there is less chance of them bursting - maybe that Goldfish RIB on TopGear would have been ok with a bit less air in the tubes???

Alex Brown · 22 November 2005, 18:14

You can buy pressure guages that you pop into the air-in one way valve in the tubes (whatever they're called). I bought one directly from Humber when I got the boat and always check the pressures when pumping up the tubes.
There should be indication somewhere on the boat as to how much pressure the tubes will take - mine is on the yellow spec sticker that Humber attach to the console.

Humber insisted that I have pressure release valves when I purchased cos the tubes are a darkish colour, so in theory I shouldn't be able to over pressurise the tubes.

I'd be more concerned about the tubes being lower in pressure than running at their spec'd pressure cos they move around a lot more with less pressure which for sure will end up damaging something, or unsticking something somewhere. I may be completely wrong here, but surely when they're pumped up properly, the strain on the tubes is spread over a larger area - if they're not so pressurised that strain could end up all in one location?

In my case, the boat handles and feels a lot better with the tubes at full working pressure than not. The tubes also spend a lot of their time in the water, even when the boat is moving unlike a lot of ribs.

-Alex

Roy Smith · 22 November 2005, 18:17

On our last Rib a 7.5 Cobra if we pumped it up to what every body said was the right preasure the tubes used to bit into the rear end if to soft the we used to get a funny noise because the tubes used to vibrate in the water

gingercoastie · 22 November 2005, 18:18

I got a pressure guage with the boat, plus instructions to keep the tubes at 2psi.

Roy Smith · 22 November 2005, 18:27

Where can i purchase the said gauge as i cant find one in the chandlers, and they look at me in a funny way when i tell them what i want it for, is this normal for a 46 year old male or am i to becoming possesed by my RIB

Alex Brown · 22 November 2005, 18:31

I'd bet that if you can't get one in a local chandlery you could buy one from Scorpion or Humber directly?

-Alex

codprawn · 22 November 2005, 18:48

http://www.inflatable-boat-supplies.co.uk/

LOADS of good stuff here!!!

Pete7 · 22 November 2005, 19:45

Roy, there are differing thoughts on tube pressures, some like them hard, me I prefer them to deform slightly with an open palm. Remember that changes in air temperature will have a dramatic effect on the pressure in the tube. So don't blow them up hard early morning or in the evening during the summer or you risk damaging them during the heat of the day. Equally they will go soggy during the winter if they haven't been pumped up since the summer. What the temperature under a cover too, dark coloured covers really heat up the boat inside.

You won't go far wrong if you can deform the tubes slightly by hand.

Pete

Tim M · 22 November 2005, 20:32

My local chandlery has them for about ten quid. You shouldn't have much trouble finding one.

paul tilley · 22 November 2005, 21:05

try polymarine for a pressure gauge . the mod use 1.5psi as a working pressure and 2psi as max pressure

jwalker · 22 November 2005, 22:22

Anyone know what pressure blow-off valves blow off at?

roycruse · 22 November 2005, 22:31

Quote:

Originally Posted by jwalker

Anyone know what pressure blow-off valves blow off at?

depends on the valve - they come set at various different pressures

Rogue Wave · 22 November 2005, 23:01

Quote:

Originally Posted by jwalker

Anyone know what pressure blow-off valves blow off at?

David Mannings are triggered after about 2 snakebites

Hugh Jardon · 22 November 2005, 23:05

Quote:

Originally Posted by jwalker

Anyone know what pressure blow-off valves blow off at?

typically 3.7 or 3.8 psi is what i have been told by three different tube manufacturers

Jackwabbit · 23 November 2005, 06:12

Our club also has an Avon CCRC520, (for those that don’t know this SIB has a flexible floor so it can be rolled up without taking the floor out) with a few divers onboard it would wallow all over the place

& take for ever to get anywhere. Then the subject of pressure cropped up, so I phoned Avon & asked the magic question & was told it should be run at 2.5psi. After a rummage through the back of the boat shed we found the Avon pressure gage, & next time out we pumped it up to said pressure.
Yes the boat went a lot better but it was a harder ride for the people onboard, the biggest problem was when we just touched a breakwater with the port rear tube.
There was a resounding BANG

followed by that sinking feeling,

3 out of the 5 tube chambers were completely deflated.
On close inspection after getting it out of the water showed there was a 3foot split in the back tube, & the next 2 chambers had blown the ends out of the baffles.
On having it repaired it would appear this is common when they are inflated hard (it’s a bit like sticking a pin in a hard balloon as apposed to a soft one) the sudden loss of pressure in one chamber caused the baffle to go in the next one & so on.
So be aware if your rib is hard (oh err misses)

& you bump into anything be prepared for a bang rather than a hiss.

jellis · 23 November 2005, 08:56

Quote:

Originally Posted by jwalker

Anyone know what pressure blow-off valves blow off at?

I don't know if it's any help but I have a two step valve in each chamber, first blows at 3.5 psi and deals with normal over inflation and temp changes etc. and the other which is MUCH bigger blows at 7 psi, designed to let go if you impact something hard

atb

Jon

Simon Hawkins · 23 November 2005, 09:08

The tubes should be inflated to a pressure where you can push them in a little. If a tube is blow up so it has no flex then this will be reflected in the boats sea handling characteristics. Think of a tube like a shock absorber, the harder it is the less pressure it will take out of an awkward landing. Having said this you do not want them so soft as to affect the stability of the boat, as after all this is all the tubes do.

Simon

Scary Des · 23 November 2005, 09:15

Some interesting stuff here and here

Des

roycruse · 23 November 2005, 09:27

Quote:

Originally Posted by Jackwabbit

Then the subject of pressure cropped up, so I phoned Avon & asked the magic question & was told it should be run at 2.5psi.

Are you sure it wasnt just the floor that was supposed to be at 2.5 PSI and not all the tubes.

I used to have a Metzeler SIB that had a honey comb deck and it had to be at a much higher pressure than the tubes.