Self Inflating Tubes???

[bigdav]

Hello there.

Im a newbie to this forum and to boating, so please forgive my stupidity.

On Tuesday I discovered that the tube on my rib seem to have been deflated by about 50% of the air inside. The tubes stayed deflated for 2 days as I didnt have time to pump it up on Tuesday. Today, when I arrived home (its a much warner day today) the tube seems to be almost fully inflated again!!!

Is this normal for atmospheric pressures to affect the tubes in the rib to this extent. (I was convinced I had a puncture! Or am I just going mad?)

Any advise would be greatly appreciated.

Thanks
Davin

[JSP]

Never had them change by about 50% but they can go very soft when the temp drops and can go very hard when it gets warmer. With this nice weather we're having this week I'd keep your tubes a little deflated

[captnjack]

pressure is highly correlated to temperature (linear).

If they are plump in the water you can split a seam on the trailer. You should adjust the pressure based on the temp.

[Polwart]

Originally Posted by captnjack

pressure is highly correlated to temperature (linear).

If they are plump in the water you can split a seam on the trailer. You should adjust the pressure based on the temp.

Yes but that is actually a correlation to temperature on an absolute scale (ie. Kelvin). A temperature rise of even 30 deg C (a very extreme swing for the UK) is actually only going to cause about a 10% rise in pressure. Even if a black tube went from 0 deg C to say 60 deg C (which would be too hot to touch) then the pressure would only increase by 20%.

If there is actually a pressure change it may be more likely down to moisture content - but my suspicion is that tubes which "fail" in hot weather - do so because the glue softens not because the pressure increased. Afterall how do you soften glue to do repairs? gently use a heatgun.

[chewy]

The tubes on my SR4 are grey and in the sun or in a little heat will go nice and hard/operating temperature on the night they will be really soft again.
The above is when the boat is left on the trailer.

[entropy]

Here is an example of the effect of temperature on tube pressure. These are photos of one of my old Avon Redshanks (not a RIB I know, but it's still a fun boat, great for taking on a camping trip). The first photo is after the boat had been inflated in the afternoon. The second photo is the next morning, when it was about 30F cooler. This was in Maine USA, during the fall, when the temperature can swing quite a bit from night to day.

As the day warmed up the boat regained pressure without me adding any air. I always knew inflatables were sensitive to temperature, but I was quite surprised by how great the effect can be until I saw this. At least in this case the effect was to "deflate" the boat, so no worries about damage. You can imagine the potential pressure increase if the boat had been inflated on a cool evening and then the sun got to it the next day. I was always careful about not leaving an inflatable out of the water in the sun without deflating it a bit first. This made me even more cautious.

[Channel Ribs]

Originally Posted by bigdav

Is this normal for atmospheric pressures to affect the tubes in the rib to this extent. (I was convinced I had a puncture! Or am I just going mad?)

It is fairly normal. The front of our boat shed goes from full shade to full sun so over the course of a day RIBs parked there can go from unusably floppy to rock hard. The ideal (with tubes that do not leak) is to have a happy medium where the tubes are good both when sold and when hot.

[bigdav]

Originally Posted by Polwart

If there is actually a pressure change it may be more likely down to moisture content

This kind of makes sense to me as yesterday morning there was a very heavy dew on the grass and it was later that day I discovered the tubes almost back to normal pressure.

The boat does not sit in direct sunlight and is parked on its trailer under my car port, therefore the temperature difference could not have been that much.

[purdster]

keep mine in my car port as well and its exactly the same as yours - best not to leave it with too much air in

I normally deflate the tubes slightly when at home and pump it up before going out on the water

[9D280]

I also keep mine slightly deflated when on the trailer - I've seen the bow go rigid as I tow to the water with an early morning departure as the sun got higher - even seen it go floppy again as the sun went behind a cloud.

It's surprising how little radiation it takes to heat toobs.