Dinghy Pressure due to temp?

[C420sailor]

You get your pressure set perfectly. Then drop the dink in cold water.

Shrinkage is real.

[StuM]

Originally Posted by C420sailor

You get your pressure set perfectly. Then drop the dink in cold water.

Shrinkage is real.

Not a major problem when the water termperature is around 28°C

[Wotname]

Originally Posted by sanibel sailor

conversely, 2.5 psi at 60, 1.5 at 50 and essentially completely deflated at 35. And that's not true.


For this rule of thumb, from the wiki article...
Hence, for a tire filled to 32 psi, the approximation usually made

if you look at the article's table, the increase decreases as initial pressure decreases.
I would extrapolate an inflatable goes up 0.1 psi for 10F.
I am too lazy to calculate using Kelvin and Boyle's Law.

Opps... Wottie is wrong - again! But I disagree about when the temps are around 35F, it was 30F here this morning and I along with most others things were severely deflated - although the dinghy wasn't - but soft nevertheless.

Originally Posted by AndyEss

👍🏼

Heck, if you filled it with helium, you would be a very small way into being a dirigible, and not just a mere dinghy

Yeah but not for long! Helium would pass through the tubes like water through a dirty mossie net.

[AKA-None]

It doesn’t matter what the atmospheric pressure is as an inflatable expands due to the pressure differential. As you raise the temperature with a confined gas the pressure goes up unless the container can expand to equalize its volume and retain the same pressure differential.
Since a rib is designed to not do this, essentially constrained then the pressure will rise. How much it would raise has a relation to how much the rib can expand.
Boyles law if I recall correctly

[AndyEss]

Originally Posted by Wotname

Opps... Wottie is wrong - again! But I disagree about when the temps are around 35F, it was 30F here this morning and I along with most others things were severely deflated - although the dinghy wasn't - but soft nevertheless.


Yeah but not for long! Helium would pass through the tubes like water through a dirty mossie net.

I dunno, maybe as long as several million parsecs, or so.
I keep getting a disproportionate feed of helium related topics on quora, so I tried to sneek it in here

[chrisr]

seeing as how we are talking about temperature, this seems like an opportune time to mention that degrees kelvin is named in honour of lord kelvin...who happens to be a distant relation of mine

you've no idea how long i've been waiting to drop that into conversation...


meanwhile, as regards dinghy pressure : please correct me if i'm wrong but don't the valves on a RIB bleed off pressure if it get's too high ??

cheers,

[AndyEss]

Originally Posted by chrisr

seeing as how we are talking about temperature, this seems like an opportune time to mention that degrees kelvin is named in honour of lord kelvin...who happens to be a distant relation of mine

you've no idea how long i've been waiting to drop that into conversation...


meanwhile, as regards dinghy pressure : please correct me if i'm wrong but don't the valves on a RIB bleed off pressure if it get's too high ??

cheers,

I love it. I have always believed that the modified Shraeder valves on deflatable dinghies were pressure relieving.
On a hot, summer, Mexican afternoon, while dozing off into your siesta, nobody wants to pop outside and relieve his dinghy’s pressure

[DockDoc]

https://www.calculatorsoup.com/calcu...al-gas-law.php

The relationship that is most important is Temp and Pressure because your volume will not increase (that much) until something blows, and your moles and gas are not likely to change unless your sail extraplanetary.

The higher the temp, the higher the pressure. I deflate my dinghy until I can indent it easily with my knuckles. If it creases when we sit in it on the water I pump it up.

One thing most forget is that the dinghy chambers have baffles, so if you lose one chamber the remainder will stay afloat and inflated. Having nearly equal pressures in the chambers is very important so you don't blow an internal baffle between to unequally inflated chamber it there is an increase in pressure from temperature change.

I was a white water rafting guide for ten years, cant even begin to count the number of rafts that went BOOM in the California sun. Keep the pressure down!

[stinkpots]

Originally Posted by CAELESTIS

Ok, engineers, if I have a 10 RIB inflated to 3.5psi at 70*F, what is the psi at 90*? What about 115*F?

Thanks!

I think you are going about this backwards.
I am the captain of a large RIB rescue vessel and we have very clear manufacturer instructions as follows.
Pump up the tubes to the manufacturers recommended psi AT THE HOTTEST PART OF THE DAY. Never pump up at the coolest time of day. When it cools down the tubes will be softer but leave them soft so that they do not overinflate when it gets warmer.

[jlcarreiro]

Does the water temp factor in?

[wsmurdoch]

Our air floor gray Achilles was happy for days and days in the Bahama sun; tight in the heat of the day and a little squishy at night. We brought it aboard and stored it upside down on the foredeck for the sail to the next island. During the day, out of the water, in the sun, with its black bottom facing the sky --- bang and whoosh. The air floor blew out the seam around the hole in the floor that gives access to the valve on the inflatable keel. It was a serious bit of work with more failures along the way to repair the damage.

I wish there was a relief valve incorporated in the inflation valves.

[stinkpots]

Originally Posted by jlcarreiro

Does the water temp factor in?

Water temp does not fluctuate much day to day whereas air temp and direct sunshine is the main issue.

[Clivevon]

Originally Posted by AndyEss

Try avoiding dark colored inflatable dinghies - or dark dinghy chaps. Right now my nearly 5 y o inexpensive PVC West Marine dinghy has a coat of blindingly white, rubberized roof paint. It makes a world of difference in how hot my dinghy gets in the strong Mexican sun.

How is that working in terms of protecting against UV damage? Is the paint flaking off? What kind of paint did you use exactly?

[waterman46]

Originally Posted by stinkpots

I think you are going about this backwards.
I am the captain of a large RIB rescue vessel and we have very clear manufacturer instructions as follows.
Pump up the tubes to the manufacturers recommended psi AT THE HOTTEST PART OF THE DAY. Never pump up at the coolest time of day. When it cools down the tubes will be softer but leave them soft so that they do not overinflate when it gets warmer.

Good practice. But most of us need to inflate our dinghies on deck before we go ashore in them. The beach is probably the hottest place you could imagine so better to let some air out after you get there.

Originally Posted by zemurray

Inflate it with nitrogen. problem solved. ��

Why? Air is basically nitrogen with O2 and CO2 thrown in for good measure (and life).

[donradcliffe]

Just remember that the temperature of the air in the dinghy on a sunny day is NOT the outside air temperature, and you will be fine. If the dinghy is on the beach or on the deck, it will be a lot hotter, if it is in the water it will be cooler.