Durability of a 20 years avon of a carefully folded hypalon kept dry and aboard

[dancrane]

(Quote on the same subject, dated December 2014)... The pressure in the tubes is only 3 PSI so it does not stress the material very much
My Redcrest is coming up to her 46th year & this has never been a problem

Thanks...I have clearly misunderstood pressure in inflatables versus atmospheric pressure.

If 3 PSI has worked for you for...55 years, I'm content it will be safe in my boat too!

 

[johnalison]

Not sure what you mean there. Mine are wood one piece oars & are just the right length. Have later ones been supplied differently?

That problem with the bracket normally happens if the bottom 2 legs of the bracket have not been engaged in to the bottom 2 sockets on tha dinghy. Without all 4 being engaged & without the aft tube being fully inflated to its max 3 PSI it will always sag.
Have yo checked that it is in properly. It can be difficult to fit. I use some fairy liquid to help it slide in. However, the bracket tends to erode & the plastic covering disappears & it will not go in without a struggle.

My 2000 Redstart has a plastic bracket which is much easier to use and without corrosion problems. I have not had a problem with the outboard sinking down as in the photo. I have the impression that that dinghy was not fully pumped up and there appears to be a crease in one tube. I was told by the Avon man that I couldn't over-pump the dinghy with the foot pump, but later pumps came with a release valve.

 

[dancrane]

I could easily move the pin to change the angle of the outboard leg so that if the boat wants to bend as seen in my picture, the angle of thrust will still be close to horizontal.

My priority is whatever is best for the boat - either pumping it up hard as if it were half a century newer, or angling the engine to nurse her under lighter pressure.

Although I suppose nothing would be more sensitive to an ancient inflatable's declining toughness, than rowing, and leaving the o/b ashore or on the yacht.

 

[Refueler]

My 2000 Redstart has a plastic bracket which is much easier to use and without corrosion problems. I have not had a problem with the outboard sinking down as in the photo. I have the impression that that dinghy was not fully pumped up and there appears to be a crease in one tube. I was told by the Avon man that I couldn't over-pump the dinghy with the foot pump, but later pumps came with a release valve.

Early O/Bd brackets were steel with plastic coating. But in latter years - they produced a Glassfibre version that of course would not corrode and lighter.

I wanted a GF one when the 2nd one gave out ... but the price was WOW !! Are you kidding !! So I found a 2nd hand steel one on the Barge at Bursledon .. That was over 20yrs ago ... I cleaned up the metal and Hammerite'd it ... still today its in good nick ..

 

[Bodach na mara]

Thanks...I have clearly misunderstood pressure in inflatables versus atmospheric pressure.

If 3 PSI has worked for you for...55 years, I'm content it will be safe in my boat too!

The 15 psi of the atmosphere is Absolute pressure. The 3 psi in the tubes is Gauge pressure. That is the pressure inside the tubes is 3 psi above atmospheric and is actually 18 psi Absolute.

 

[dancrane]

Thanks for that.
I knew I was wrong, just not sure how.

Does anybody know how much a sunny day affects Avon pressures if one has filled to 3PSI during shade?

Does one leave it to luck, or are the valves designed to let off pressure if too much is within?

It sounds clever, at least for the era when my examples were manufactured. Perhaps something made this century could be added in place of the valve covers, to ensure no more pressure than is acceptable, is held?

 

[Daydream believer]

If it is hot I let the pressure off a bit as a matter of course. The same with our safety boat RIBS, those inflatable sections are rarely as hard as my Avon & we always deflate them a bit in hot weather.

 

[Bodach na mara]

Thanks for that.
I knew I was wrong, just not sure how.

Does anybody know how much a sunny day affects Avon pressures if one has filled to 3PSI during shade.

This problem has often puzzled me. It is a pity that nobody has devised a pressure release valve but I suppose that there would be a danger of the boat deflating while in use. Being a physics graduate, I don't know why I have not (until now) calculated the change in pressure but here goes.

Firstly, some assumptions. Because we have to work in Kelvin temperatures I assume a cool temperature of 7 degrees Celsius (280 K) when the dinghy is inflated to 3 psi on the gauge which is 18 psi absolute. Not that I have a gauge of course. When the dinghy gets warm in the sun the temperature of the fabric is almost too hot to touch and I have assumed that the air inside reaches 57 degrees Celsius, or 330 K. The pressure increases in proportion to the Kelvin temperature so it reaches
18 X 330/280 which is 21.2 psi, or 6.2 psi above atmospheric pressure.

Not having a gauge that works for an Avon, or any other, dinghy i have no idea whether I am inflating the dinghy enough to start with but I can say that none of mine have exploded*. Of course when the dinghy is in the water the temperature of the air inside will not reach 57 C and possibly that is a bit high anyway. Also I doubt that the temperature when I inflate it is ever as low as 7 C. So the result I have calculated is a worst case scenario. More realistic would be 17 C to 47 C (the lighting brains of forum readers will have realised that the numbers are chosen for easy arithmetic) and a final pressure of 18 X 320/290 = 20 psig which is a mere 5 psi above atmospheric.

* None of mine have but my wife reminds me that one of our friends was ashore on Staffa and came back from the cave to find a pile of hypalon where he had left his dinghy.

 

[Daydream believer]

* None of mine have but my wife reminds me that one of our friends was ashore on Staffa and came back from the cave to find a pile of hypalon where he had left his dinghy.

Goats?

 

[dancrane]

Excellent calculations that even I could follow, many thanks.

 

[Refueler]

My Narwhal let go when pumped up and left on the lawn one summer many years ago. It was pumped up in the morning - by mid afternoon it had 'blown' ...

I took it to a Service Centre (Ron Hales) who immediately condemned it for two reasons :

1. That the seams were blown for long sections
2. That inflatable repair liquid had been used previously.

The two factors together prevented any chance of successful repair.

Whether the hot summer alone was the cause ? I tend to think that a combo of heat / pressure and the ageing seams combined led to its failure.

 

[doug748]

Back in the day there were a number of complaints about problems with small Narwhal dinghies. I once saw one in a Salcombe workshop that was largely a pile of loose panels.

 

[Bodach na mara]

Goats?

I never thought of that but the owner said that it had split. He was annoyed because earlier in the year he had sold me his boat, as he had bought another. During that negotiations he threw in his black Avon Redcrest as he had bought a shiny new grey one to go with his new boat. It was the shiny new one that burst, leaving him to cadge a lift out to his boat for himself and family and head to Oban to get to a chandlery to buy a new dinghy.

I should add that this was many years ago before there were any pontoon berths in the Western isles for cruising boats other than in the few marinas that were then open.

 

[Refueler]

I have a 'chinese' copy of an inflatable ... double inflatable floor - wood transom ... split dual chambers .... seats etc.

It really looks nice - rides well on water ... up to 6HP even though its a 2.5m .... BUT - it has a leak !

My previous gardener had it for fishing on the river ... he tried fixing the leak but gave up ... left it here.

Its a fwd seam that has a tiny leak ... it deflates in about an hour ...

I removed his patch and now need to find a way to remove the horrible gungy mess he used to try fix it ... I might try the 'Goo Gone' I bought for my sail ... but I have an idea it won't work ... then its what to do ??

 

[dancrane]

One really must ensure one's gardener has a boat of sufficient quality for his leisure hours.