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Discussion Starter #1
So... being from Colorado its a necessary evil to drive up and down in elevation when going on trips. I've been trying to figure out the perfect pressure to keep it at when setting off from home so that I can get over the mountain passes but not have a floppy boat and loose straps once you come down.

Has anyone actually measured pressure changes as they go up and down in elevation? Just curious what the actual PSI difference is between a pass like Eisenhower or Monarch pass and Denver and Western Slope.

I don't have a pressure gauge so but was hoping one of you all did and did some data recording. Kinda tempted to get one of those new fangled valve caps with the pressure reader in it and setup a gopro on my next trip over the mountains.
 

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Cool idea, but temperature changes though the day may have just as big of an effect on the size of your raft and the looseness of your straps. As you know we get 40 degree temperature swings routinely in CO. I've got a pressure gauge, but it's easier for me to just check/loosen/tighten the straps. PV=nRT!
 

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Pressure

I live in Summit County at about 10,000'. We have place in Salida and I often bring the raft back and fourth, or to other places like Moab. I must go over a pass no matter what direction I go from here. Air temp and moisture like rain or sleet make a big difference. I don't think it can be an exact science and it is different every time. You just have to get a feeling for it. I actually go by the sound and feel of letting air out of the vales to make my choice. I find that to be more accurate than pushing on the tube of the raft or squeezing it. The valve air pressure coming out is better for me to identify what I need to do.
 

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Never measured pressure in town and at the top of the pass. Inflate just firm enough that it isn't floppy in Denver, in the morning. Drive to the river. Top off. Launch.

How do you gauge that you ask? Leaning on it with your palm/fist should yield you a good 3 inches of give but will spring you back (If you do it limp wristed it can tweak your wrist and give you an excuse why you can't keep up in the flats.) That is enough to keep it from bouncing around much on the trailer in town. Strap it down FRAME to trailer just firm but not full pull.

If you did have a gauge, the .8-1psi range in denver is about right. That takes about 20-30 strokes per chamber to top off depending on your destination elevation and temp. If its high altitude and warm where you launch you may not top off at all. Ive gone from Denver and launched at pump plenty of times and never put in a stroke.

I know, you're thinking 1 psi seems low. Once you actually build pressure at all in the boat it climbs quick. For reference, sitting at home, a 12' NRS goes from 1 psi to 2.5 (which is about what I run; palm test yields about an inch of give) with 20 pumps per chamber.

1 psi is where I can walk on the boat and feel sorta stable. .5 feels a little squishy to walk on but the boat is definitely to shape .


All this depends on your comfort level. Some people, I'll leave out names, are very concerned and will always make 3 stops minimum to check air and strap pressure, which is fine. The main thing is don't leave denver or the takeout with the boat topped off. If your boat is old, it is super hot out, etc. error on the side of softer than hard. Common sense goes a long way.
 

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I started rafting in Alaska without a trailer and this was never a concern. Moved to the Front Range and was paranoid as hell after buying a trailer and reading several other threads on here about pulling rafts over mountain passes. After years of trailering my raft all over the state, I would totally agree with zbaird's experience and advice. I have a gauge from my early paranoid days but rarely ever pull it out of my captain's bag.
 

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Discussion Starter #6
Hmmm... thanks for the input everyone but I was sort of hoping for something more scientific. I'm sure someone smarter then me could do an actual calculation with algorithms and such. I did try looking that up, but all the ones I saw were pretty in depth and beyond my math ability.

I'm sure temperature does come into play, but since all of my rafts are white in color its not nearly as big a factor as it would be for someone with grey or blue or any number of darker colors. All around I think its not as big a deal as elavations changes... I've never left a floppy boat out in the sun and come back to it fully inflated like happens going over a mountain pass.

I've come to the same basic conclusion as you all have after trailering rafts over passes the last 4 or 5 years. I worry less about it these days and just take it to semi soft at home and the take out (I've been doing Westwater a bunch lately).

I might have to get a gauge and do the data collection myself.
 

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My name's Andy and I'm the guy ZB's talking about. Zach still likes to give me shit 15 years after I got my trailer and was just getting the hang of trailering from Denver to the Desert.

Zach's spot on in his post above. If you've just barely enough pressure so the boat's not too squishy you can go up to the tunnel without popping it - though it'll be tight enough to "ping" the boat up at the tunnel.

My routine these days is to leave Denver with just enough pressure so the boat's not too sloppy on the trailer, then stop at somewhere around Grizzley Creek and top it off really well before continuing on to lower elevation.

I did some research once on the pressure change with altitude and, IIRC, 5000 feet of vertical change results in about a 2.5 psi increase. So whatever your boat is in Denver, add ~2.5 psi for the pressure at the tunnel. That said, you'll probably be about about 15 - 20 degrees cooler on the air temp going over the pass which helps temper the pressure difference due to altitude change.

Part of the reason I like having a fairly firm boat while driving, and top it off when it gets squishy, is to keep a steady tension of the straps. As opposed to having the frame, and all that gear lashed to it, bouncing down and then back up, with momentum, against the straps.

As for heat, I just can't imagine it's good for a boat to put that much stress on the seams and get the glue hot under those conditions, especially with the kind of heat a dark boat can generate in the desert sun. I saw a post on the GCPBA list once about a beached boat popping when left in the sun during a hike. When I got my first raft, the outfitter who sold it adamantly warned about airing it up in the cool of the morning and then driving out into the scorching desert heat . I think he'd learned that lesson the hard way... (hence my paranoia when I started trailering)

YMMV,

-AH
 

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Tube Pressure

I have a gauge. It was created by the creator of the K-Pump. (Gauges) He says most tubes should be 5 psi. However when working in the grand I keep my tubes around 7-10 PSI.
Granted we run really stiff boats in the Grand.

Kokopelli Packrafts introduced a solar powered valve cover that is a pressure gauge at the Paddlesports Tradeshow last week. https://kokopellipackraft.com/product/trib-aircap/


In 30+ years of working with a raft guide I've never seen a boat explode from over pressure, but I suspect it can be done. That includes 100+ degree days in the Grand when we pumped boats in the morning in the 60's and left them in the sun (floating on 40 degree water) for hours. The tubes had to be cooled down before customers or guides could get on the boats, but no blow tubes.

I do think it is interesting that what the manufacturer says the pressure should be what most guides pump their boats too is very different.
 

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Discussion Starter #9
I too have never seen one get anywhere close to blowing but I've heard anecdotal stories of it happening both on on a hot day in the sun and going over passes due to elevation change.

Rather then it being a real issue of actually blowing the seams...I think its just gonna lessen the life of the boat. Like someone on here said...especially when you add heat to the mix it will just put stress on the seams. I think the I-beams in the floor are particularly prone to separating which is one of the reason floors have Pressure Relief Valves.

I've borrowed one similar to the K-pump one when a friend had it. I don't think Kokopelli actually created that valve cap one...they just sell it. Aire, NRS, Cascade, Downriver and others all sell it as well.

Here is the website... https://www.triboutdoor.com/aircap

I like a nice stiff boat and tend to inflate pretty hard too...maybe not up to the 7-10psi level but definitely more then 2.5psi (except the floor). I just checked the Hyside manual and they said tubes at 3psi... so even 5psi sounds excessive.

As to Andy's comments....I'm actually surprised the pressure difference was that much but I guess it makes sense. If we combine Rec Law's and your comments....seems like you could get away with inflating to 1psi at home (in Denver or Grand Junction for instance) and still be safe. 1 psi sounds kinda floppy still but maybe not so bad its moving around all over the place.

I did just edit this because of looking at the Hyside manual. Probably different for each Raft manufacturer though.
 

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Brandon at Hyside recommended 3 pounds for cat tubes and 2 for round boats. They are not going to blow if you go over that a little bit. I was going south from Delta and checked my pressure going up Dallas and Lizard Head and found the sun shining on the east tube made more of a change than elevation. I don't think there is a hard and fast rule that will work. I am with Andy and stop and check until you're sure. I would hate to miss a trip because of a blown tube.
 

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Andy, You are one of the names I left out but not the only one.

Rec law, If its true, those are crazy pressures, especially on big 18' tubes. 4 psi is super hard and more than enough. I am not even sure most raft pumps will allow you get to 10psi. 5 is rock hard. 6 has almost no give. I don't know of any raft manufactures that recommend 5psi. I think Maravia says 2.5 max running pressure and SOTAR says 3-3.5.



I run most everything in the 2.5-3 range. I use the palm test and if leaning on the boat with my palm flexes it about an inch, I'm in the 2.5 range. Now I see why people are showing up at the shop with 4, 5,6 foot tears. 5-10 psi is nuts.

Even though it could yield endless work for me, I highly advise against running boats above about 3-3.5. If you run in the 4-10 range, make note of my number below. TIA
 

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I regularly boat the Lochsa and drive over Lost Trail pass (7,000' ASL). Down at Lowell, it's only 1,500' ASL.

I used to stop and check partway up, but I've found that dumping the excess pressure when I load the boat results in hitting the top of the pass and it's less firm than it is when I'm pumped up to rafting pressure. I don't have a gauge, but based on Zach's description, I probably run at ~2.5psi. I'm sure that cooler air temps on top also help (as I'm usually on the river in the heat of the day and headed there Fri evening and home Sunday evening). I don't check anymore.
 

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Air pressure changes with altitude. I lived in Oregon and when driving from low altitude 1k feet on the Rouge over to Klamath Falls (5k pass elevation) there were big differences as I either ascended or descended. I usually made two stops each way to dump or pump and readjust straps.



Moved back to CO decided to look into see if it was different here. I remembered from college that air pressure changes in a non linear fashion, however I found that the curve is still pretty steep at normal (sub 20k) elevations. So I found a table of pressure at altitude and the pressure difference from 1 to 5k feet is a full 2 PSI and 5k to 10k (Denver to Tunnel) is also 2 psi. For me going from 8k to 10k is less than 1 psi. I dont claim to be a physicist but you can think of it as a force balance. So if you think of a raft inflated to 2 psi and take it from Denver to 10k (ignore temperature changes), the atmospheric pressure is reduced by 2 psi which if you balance across your tube the interior pressure could be 4 psi. However if you think of your raft now being exposed to double the recommended pressure it does make it a litte nerve wracking. Conversely if you have your raft at 2 psi at 10k it could conceivably be close to flat by the time your reach denver (which has happened on my trips over the cascades.










However as many have pointed out temperature is important, perhaps more important. So I looked into this and found a few things from the internets. The plot below shows that an inflated football will experience about a 2 psi increase from freezing to 70 degrees. Going back to the example from before if you fill up in denver at 2 psi and drive to the tunnel you should expect pressure to increase by 2 psi but if the temp drops from 70 to 30 you would expect a drop of 2 psi. I think that your average raft tube exposed to sun can get much hotter than ambient air temp so temp is probably the bigger driver most of the time.










So to be on the safe side do what everyone else has said inflate to not squishy and keep an eye on them. :)
 

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So with my old cat tubes, I went by the zbaird method of trailering up and down the mtns. I have a newer and larger set of tubes (29" in diameter), and I'm finding in 2 seasons of the drive west and back that they fluctuate alot more. I recall reading Andy's past post about stopping to let out air, and the thinking he's nuts. With these fat dudes, I feel like the volume is a factor I'd never considered when buying them. Enough so that I've stopped several times to let out air or tighten very loose straps.

Maybe I'm the one who's nuts, but going from 25" to 29" seems like PSI fluctuates more.
Maybe material plays into as much as temp does?
Maybe I should get a gauge and try to determine if there's a sweet spot of PSI.
Or maybe, I'll just eyeball it and give zbaird some future business!
 

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The bigger the tubes the less pressure they need to be hard. It is not the volume of air but the diameter of the tube (maybe someone has a chart for this). With tubes that big, 2.5psi is going to feel pretty hard. So a 2 pound gain from denver to vail pass is significant. I'd shoot for a couple more inches of give (.8ish) and call it good. I did mention that if your tubes are old etc use a little extra caution.
 

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Andy's findings above are in line with what I've found. Live in Boulder (~5400') and regularly take the raft to Avon and stay around 9,000'. Without touching it and without any dramatic weather-related changes, I find that I've typically lost about 2 PSI from Avon to Boulder. I don't deflate for the tunnel or Vail Pass (but do occasionally get anxious if we find ourselves sitting in traffic...).
 

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Next time just stop at the top of the pass and measure the pressure on a normal weather day and then stop and measure at the bottom.
 

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I don't have a pressure gauge so but was hoping one of you all did and did some data recording. Kinda tempted to get one of those new fangled valve caps with the pressure reader in it and setup a gopro on my next trip over the mountains.
This sounds like an interesting experiment and could be a pretty cool time lapse video. We'd be happy to donate a gauge to the cause if you're still interested in doing this. We've done a bit of testing on the Whitebird grade down to the Salmon river, seeing about a 1 psi drop in a Hypalon raft inflated to 2 psi.
 

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Discussion Starter #20
This sounds like an interesting experiment and could be a pretty cool time lapse video. We'd be happy to donate a gauge to the cause if you're still interested in doing this. We've done a bit of testing on the Whitebird grade down to the Salmon river, seeing about a 1 psi drop in a Hypalon raft inflated to 2 psi.
Cool...that sounds great to me. I can't promise that I'll be able to do it until early next year since its the off season...but I'll definitely be getting out in February or March.

I'll shoot you a pm and we can figure it out.
 
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