semi-rigid plastic sheeting

[AllDownhillFromHere]

Hello all, I have a GoLite Pinnacle. It has a 1/4" foam pad in the back I suppose to give support, but it does nothing, the pack 'sags' with anything over about 20lbs in it. I've replaced it with a piece of 1/8" craft birch plywood, and it really wakes the pack up, I can go to almost 40lbs now. I'm still tweaking the shape for optimal stiffness vs. weight, but I worry that ultimately the plywood will get wet and fail. Does anyone have a good source for an ~ 1/8" plastic material that's as flexible and rigid as plywood, but also won't be brittle and/or crack under repeated flex?

[Cheyou]

Why bother ? It's a frameless pack use it like it was made for less then 20 lbs.

Thom

[zelph]

Spray the board with clear polyurethane, 2 coats ;-)

[zelph]

Big box stores sell poly-carbonate sheet for storm door window replacement.

[Dogwood]

As far as I understood the GL Gust was replaced by the Pinnacle. Later the Jam and even later Jam 2 entered GL's pack line up. All were meant to have virtual frame sheets and carry light to UL wt loads. I think the 60L Pinnacle was offered for those with UL but bulky kits. The idea was that a CCF or inflatable pad(partially inflated) was used as a frame sheet not a piece of birch 1/8" plywood or rigid plastic sheet.

At the Pinnacles pack wt combined with single use? plastic sheathing or 1/8 birch panel it puts the wt up higher than packs currently available near or in the Pinnacles pack volume WITH INCLUDED SUSPENSIONS...such as the ULA OHM. The OHM can handle 35 lbs at 63 L volume!

[Puddlefish]

Maybe look at plastic cutting boards. I have a few that are just over 1/16th of an inch. Might find something that serves.

[AllDownhillFromHere]

Good suggestions guys, thanks. I thought about urethane, I might end up doing that. And making a spare or two to be at the ready for emergency maildropping. The poly window sheeting just feels brittle, I've had it crack under flex before (in other applications). I think that "cutting board" material is the way to go, if I can find an approx 8" x 24" sheet of it.

[Puddlefish]

I went and measured, my largest are only 20 inches.

[TTT]

If it extends beyond its design and carrying capacity you might find straps tearing and coming apart.

[Dogwood]

Big box stores sell poly-carbonate sheet for storm door window replacement.

Thin 1/8" thick polycarbonate used for signage oriented vertically should work. It has some flex and is stronger used in this fashion. If you can make a 1/16" flexible cutting board work great but I'm going to say it's going to be too flexible for 35lb loads in the Pinnacle which is easy to do with it being a 60L pack.

[AllDownhillFromHere]

If it extends beyond its design and carrying capacity you might find straps tearing and coming apart.

I thought about that, it's not so much past the design, I think it was something like 35lbs. It's just that it completely sags out well before that. It might have been a packaging issue, when the pack arrived it was folded flat, leaving a horizontal 'crease' in the foam pad, but even without that, the foam pad really has no rigidity. The most I see putting in it is 45lbs, possibly a touch more with full water containers, but that would only be a day or two.

[Maui Rhino]

US Plastics sells HDPE in 2'x4' sheets. You can cut down some of the .060" thick sheet to make a nice frame sheet. Another good solution is to make a frame sheet out of the corrogated​ plastic used in signs. It's likes plasticised cardboard. I made one with two layers, cut so that the ribs e on opposite diagonals to give it rigidity. The sign kit I bought came with a wire frame to stand it up. I cut the wire into an H-shape, then curved it to match my back, and taped it between the two layers of corrugated plastic. Worked great.

[Malto]

I thought about that, it's not so much past the design, I think it was something like 35lbs. It's just that it completely sags out well before that. It might have been a packaging issue, when the pack arrived it was folded flat, leaving a horizontal 'crease' in the foam pad, but even without that, the foam pad really has no rigidity. The most I see putting in it is 45lbs, possibly a touch more with full water containers, but that would only be a day or two.

How about an option for free. There are three possible reasons that you would need to beef up a pinnacle.
1) you are overloading it which I don't think is the case, assuming you are still doing the PCT.
2) your gear is low volume and doesn't fill the pack.
3) you aren't packing a frameless pack correctly.

I am guessing it is the third. Dogwood started down this path, let me go a bit further. You very likely have the materials at hand to provide plenty of frame support for weights up to 35 lbs. using a folded air mat is the easiest way of providing structure. Tent pools and other items also will help. BUt the biggest thing I found was to avoid creating hinge points in the pack and getting the volume of your pack as tight as possible.

I found the easiest way to avoid hinge points was to pack alternating layers of hard then soft. For a thru type of hike it would be 2nd food bag, then quilt and bivy, then first food bag with my small cook set, tarp and clothing bag on top. My pack is much smaller than yours but I push the layers together as tight as possible. This gets the pack into a single rigid structure with no frame. Toward the end of a food leg my gear is too small to get tight so I often, as Dogwood has suggested, leave some air in the mat to take up volume. This is also the time that my pack weight is the lowest.

I would play around with your packing, it is free and gimmickless. If you mucosa try a frame consider plastic corregate like this

https://www.sigmasignsupply.com/coro...JqAaAmmo8P8HAQ

[TTT]

You can get cheap Corex board which is corrugated, waterproof and light

[orthofingers]

Will 1/8" craft birch plywood delaminate if it gets wet. If you have a scrap, I'd throw it in a bucket of water for a few days and see what happens.

Our local lumberyard carries sheets of 1/4" luan plywood (which is actually thinner than 1/4") and it is pretty light but fairly stiff.

I believe you can also get it in what's called 3/32" thickness but again, is thinner than that.

The luan has a waterproof adhesive holding the plies together. I've left pieces outside for three or four years before they start to fall apart provided they weren't in ground contact. I think one piece would easily last for a season or two and you'd only need a piece maybe 14"x 22"

[zelph]

political yard signs are made of corrugated plastic. Ask a politician for a donation :-)

[Dogwood]

I thought about that, it's not so much past the design, I think it was something like 35lbs. It's just that it completely sags out well before that. It might have been a packaging issue, when the pack arrived it was folded flat, leaving a horizontal 'crease' in the foam pad, but even without that, the foam pad really has no rigidity. The most I see putting in it is 45lbs, possibly a touch more with full water containers, but that would only be a day or two.

The crease had very little or nothing to do with the pack collapsing. The foam sheet is not for creating a full frame sheet suspension that transfers a 30+ lb load to the hips. The foam sheets the Gust, Pinnacle, Jam, Jam 2, ULA CDT, etc etc etc are not meant for full suspension support in 15lb + loads. It's there mostly for comfort against your back so stuff recklessly jammed into these frame less packs don't poke through into your back and with very light 15 lb or less loads, hence GL's Compactor system(pack volume reduction system).

It sounds like you're trying to make the Pinnacle work for you. Review some old Pinnacle user comments on how they did that. This is what I've dealt with as a GL Gust, GL Jam 2, ULA CDT, and MLD Burn pack user...all frame less packs. Recognize how the GL Pinnacle or any of these frame less packs were designed to function by the user adding rigidity of a virtual suspension.

These packs are not designed with the expressed UL intention to add 1/8" plywood, plastic sheets, Corex, polycarbonate, political plastic signs, etc. to create an added wt frame sheet IMO! They were designed as frame less ULTRALIGHT/LIGHT WT packs that the user was expected to understand how to transfer wt by packing appropriately, using ALREADY AVAILABLE BACKPACKING GEAR to make a frame, LIKE A SLEEPING PAD, knowing how and when to cinch down changing load volumes, etc.

REGARDLESS, even with an adequate virtual frame/suspension, NONE of these packs were designed to comfortably and routinely carry 45 lb loads. If you expect a comfortable carry with your kit and pack durability in a 45 lb full volume load you may have the wrong pack or paired kit.

Again, there are FRAMED packs available in the GL Pinnacle volume category that are in the same pack wt class.

[atraildreamer]

political yard signs are made of corrugated plastic. Ask a politician for a donation :-)

...or, ask a Hillary supporter where they tossed Donald's signs?

...or, ask a Donald supporter where they tossed Hillary's signs?

[Venchka]

2 part epoxy resin designed for marine plywood will encapsulate the plywood and it will never fail. West Marine sells it. You won't need much. 2-3 coats should be plenty. Be sure to coat the open edges.
Wayne


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[Venchka]

Testing plywood for Water durability:
Place in your dishwasher. Come back in a month. Real Marine Plywood passes this test. If it's still made.
Wayne


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