Tube Question

[timw]

As a relatively new owner of a Rib (4 months), I would like to know how often it is reasonably expected to top up the air in the tubes.

They've never gone flat, but I've noticed them a liitle squidgy a couple of times over the time I've had the boat,(on cooler days), and I've topped them up with air a couple of times.

Is this normal and to be expected?

Thanks for any advice

[gingercoastie]

The same has happened to my tubes, but I have put it down to the reduction in air temperature.

[Keith Hart]

The 'hardness' of the tubes will vary quite a lot with the air temperature. First thing in the morning they may be a bit soft but by the middle of a sunny day they will be quite hard.

I think all tubes will loose a little pressure over time but ther RIB guys should tell you how often to expect to top them up.

Keith (all inflatable) Hart

[Richard B]

Tim,
At this time of year we're putting air in every weekend as it gets colder. Remember to release some pressure next year as the air will expand again as it gets hotter.
Have you sorted out your throttle cable?

[timw]

RichardB thanks,

I 've asked them to sort the throttle cable when the engine is serviced and winterised this week.

Hope to be able to meet up on the Solent in the spring.

[Christopher]

The majority of RIB owners probably run their tubes at around 1.75 to 2psi. For every degree centigrade in temperature change, you must allow for a pressure drop(or increase) of 0.058psi.

So if there is say a drop of 5 degrees in the temperature from when the tubes were inflated, the natural pressure drop in the tubes will be 0.29psi. This would be a reduction of 17% at 1.75psi

[Cookee]

Christopher - Is that all hyperthitical, or have you got a pressure guage that reads from 0 to 2 psi with an accuracy of 0.001 psi?

[MeMe]

Tim forget all this p.s.i lark (no offence anyone). I've experimented with pressure guages, electric pumps with psi metres etc. In truth it's as simple as this, "just top em up as and when required". Some like 'em softish and don't pay too much attention to the pressure and some like 'em rock hard.
I pump them until the pump gives good resistance (foot pump) or I can depress the tube with my thumb about half a centimetre.
My Zodiac needs air about every other weekend. My pals Caribe needs it every other day whilst his Yam 380s never needs any.
If you have a leak you'll know about it as the tubes won't just go soft they will go down.

Ask 10 ribsters and get 10 different answers.

[timw]

Thanks,

I really wanted to see if I had a leak, and as they are not going flat, I haven't.

I don't mind topping them up as long as that's normal which it seems it is.

Many thanks

[Arek Pawelek]

If You want to know if there is a leak, check if all tubes are softening at the same rate. If all chambers are loosing air in exactly the same rate, there is not a problem. If just one or two - then you have to get a glue before going to sea!

[Christopher]

Originally posted by Cookee
Christopher - Is that all hyperthitical, or have you got a pressure guage that reads from 0 to 2 psi with an accuracy of 0.001 psi?

0.058psi for each degree of temp change is the formula which has to be applied to any tests carried out to check whether a tube is holding air.

To be technical for a moment, all tubes have to meet an ISO standard which is number 6185-3. This standard calls for the tube to be inflated to the approved working pressure, and then put through a 24 hour inflation test. The starting and closing temperatures have to be recorded and for each degree of change, the formula of 0.058psi is applied. The test also requires there to be no more than a 1 % change in the barometric pressure over the 24 hour test period.

All very booring stuff but a requirement under the RCD directive for EC marking.