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Weight loss

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Weight loss

Postby balzaccom » Tue Apr 17, 2012 9:30 am

Boy--I really need to get out more!
Had some fun with this yesterday: it's from our blog on backpackthesierra.com

Is there a mathematical solution to the challenge of ultralight backpacking? It seems that an engineer would be able to develop an equation that could be used to fine tune our equipment. It would have to address a number of variables. I am not an engineer, nor do I play one on TV, but I did have some fun working through this problem:

W = the weight of your pack when you leave the trailhead. The goal is to manipulate the other variables to achieve a very low value for W. Lighter is better

P = the price you have to pay for your equipment, in dollars. Please convert from Euros, Rubles, etc. if required.

And somehow our equation needs to reflect that as W is reduced, P usually increases.

In fact, as W approaches zero, P probably arrives close to infinity—or at least beyond the reach of normal people. In other words: Priceless. Ouch.

Instead, let’s set up the equation to reward people who do this lightly and CHEAP.

So with all that in mind:

LET

W = Weight in number of pounds you carry. Note that this will NOT be what you WANT to carry which will always be N-1 (where N = # ounces you are carrying).

C = $800—the rough price we paid for our backpacking outfit. You will have to use your own numbers here to see how you compare.

P = the Price you must pay for the gear (in dollars, pesos, rubles, etc.) per pound

So the final equation reads like this:

P = C/W

Do you want to buy a new tent? What if the new tent weights three pounds?

P= 800/3 = $266.67.

Is that a good deal? Let’s compare that to staying with your old, four pound tent:

P= 800/4 = $200.00

Is paying $66.67 worth it? Maybe. Most of us would agree that paying $20 would be worth it, if we could save a pound on our pack weight. Many of us would pay a lot more for that!

What about a new 1.5 pound tent?

P= 800/1.5 = $533.33

That makes some lightweight gear seem like a screaming deal!

Now let’s look at my own list, bearing in mind that we are NOT ultralighters, and that my wife and I certainly believe in some creature comforts. So we carry about fourteen pounds each, not including water and food.

P = 775/14 = $57.26 cost per item per pound.

So I am presenting that as the BTS (Backpack the Sierra) constant. Let’s round it off to a nice round $60 per pound.

So how does your pack stack up? The real goal here isn’t to get the pack weight to zero—it’s to see how cost effective your kit is. Do you get by with lower cost equipment, but stuff that might weigh a little more? Or do you go for the ultimate lightweight gear, even if it costs you more?

And how do those answers fit into the equation? I would assume that other regions, which require more or less equipment, have somewhat different answers. Our own answers for winter camping would be like this:

P = 1000/18 = 55.55. That’s pretty dang close to the BTS constant!
Balzaccom

check out our website: http://www.backpackthesierra.com/



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Re: Weight loss

Postby markskor » Tue Apr 17, 2012 10:38 am

Obviously you have way too much time on your hands –
Let’s play along anyway –
(Weights rounded to .25 lbs)
If all prices retail? (and rounded to $25)

My summer rig - carried:
Sleeping bag - $450 2.5 lbs WM Badger
Pack - $300 4 Gregory
Can - $250 2 Bearikade
Tent - $250 2 TT Rainbow
Stove - $100 1 MSR
Pad -$100 1 Prolite+
Fishing -$400 2.5 Heinz 57
Vest -$150 .5 WM Flite
Rain shell -$200 .75 TNF
Fleece -$75 .75 TNF
__________________________________________
$2275 17 lbs

If assuming retail - C/W ... 2275/17 = 134 = P...whatever...
However, these were not the actual prices paid. True price skews the C but not the W. Hence using real prices paid will bring my true resultant P down to ~81.
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Re: Weight loss

Postby Hobbes » Tue Apr 17, 2012 5:48 pm

balzaccom wrote:Is there a mathematical solution to the challenge of ultralight backpacking?


Yes, it's called MYOG. Of course, if you factor in personal time spent on research, design & finally production, the cost can go exponential! LOL. Seriously though, if the time spent on MYOG is otherwise non-billable (non-productive), as in, you're watching TV, etc rather than working, then the gear cost is simply the cost of the materials. Unless you're using super expensive cuben, first quality fabrics like M50, silnylon, etc can be quite reasonable @ around $10-15/yard.

I just finished building a nice M50 quilt filled with 12oz of 900FP down - good enough for 10,800 cubic inches. This equates to around 2.7" of loft (10,800/(80"x50")), or over 5.4" if measured as a bag (top/bottom), which puts it in the 25-30 degree range. It cost $170 and weighs 17oz.

I also built another, slightly oversized tarp that measures 8.5'x7.5'x5', along with a 1' rain peak, with 6 yards of 1.3 silnylon. Material costs were around $70 - it weighs 14oz complete with guys & stakes.

Last, but not least, I built yet another pack, this time out of 1.3 silnylon (1.1 rip+coating) rather than 1.9 ripstop. 1.3 sil has a very high tear strength, and since my fully loaded 3 night/4 day pack comes in @ around 13lbs, it is well under tolerance. Packs really don't use much material - just a yard, so material cost is under $15. In fact, I use 1/4" neoprene for both the shoulder and hip pads, and it cost over $10 alone.

The nice thing about building a pack is you can really dial in a custom fitting - both to your own body and the gear you plan on using. The one I just finished was expressly designed to snugly fit my pad (cut down Ridgerest) - tarp/quilt on the bottom and BV450 in the middle (rain gear & clothes go on top). In fact, I measured the tolerances so tight, I really don't need a compression strap. Everything sits in there snug as a bug (without stressing the seams), which with the hip belt, creates a very nice stable pack. Oh, it weighs 7oz.

I've been moving towards a SUL target for a few years now. Every winter I have a chance to think about what worked, what didn't work, what I really want/need, etc and figure out ways to achieve those goals. No one is getting any younger - I figure if I want to still go to the places I want to go with minimum fatigue and maximum freedom/comfort, then I might as well take advantage of available technology by developing some core skills (ie sewing) in which to "do my thing".

As I mentioned above, my 3 night/4 day pack weighs 13lbs going in and 8.5lbs coming out. Another key component is figuring out how to get food calories above 170 calories/ounce. 4.5lbs of food @ 170 calories/oz = 12,240 calories, or over 3k calories per day. With that much energy & a light pack, a fellow can motor quite fast along a trail, or even make pretty good time XC.

There are way too many good lakes to hunt for GT, and it makes no sense (at least to me) to voluntarily handicap oneself in that endeavor.
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Re: Weight loss

Postby Wandering Daisy » Tue Apr 17, 2012 8:22 pm

No cheating! You have to also count those pricy little items- camera, GPS, Ipod, sunglasses. What about shoes, socks? Trekking poles?

my camera = $400 ; 8 oz. $800 per pound! ouch!!
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Re: Weight loss

Postby balzaccom » Tue Apr 17, 2012 8:38 pm

Yes--well I made our tent, so you are right: that kept our costs low

And of course Daisy is correct, too. Although our camera only cost about $225, the price per ounce is breathtaking!
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Re: Weight loss

Postby Jimr » Wed Apr 18, 2012 10:34 am

Considering the exercise is an attempt to answer the question of bang for your buck to lighten your load, I think variable cost and weight would be a more practical consideration. In other words, if you would not replace your camera, GPS, fishing gear, trekking pole, etc. to lighten your load, then don't consider them in your calculations. Keep it to only those items C & W that would be considerable in UL decision making. If you wouldn't consider it as a possible replacement to lighten your load, then consider it overhead and remove it as a constant. The pertinent items are the variable costs.

Also, to be meaningful, costs would have to be future valued to compare with today's dollar. Most of my gear was purchase with 1985 dollars. That means I would have to multiply all of my 1985 costs by 113 % to get comparable numbers for evaluating a purchase today.

I played with this on a spreadsheet using only variable costs & weights (made up, of course):
Original P
New P
New P as a percentage of Original P
Delta P as a C & W
Delta P as a percentage of Original P

Delta P and DP as a percentage of OP are probably the best use for making cost/benefit decisions.

When Delta P is negative and close to or equal Original P, then you've managed to shave off weight consistent with the price originally paid. So, the increased cost of replacement for the variable item was offset by it's value in weight reduction. Higher negative numbers represent less value.

Delta P as a percentage of OP is targeted around -1, which would represent that your decision shedded weight at a cost that was equal to its original P

If either of these numbers are positive, then you added weight rather than reduced.

EDIT: (or paid a lower price than the original item for lighter gear. This would make Delta C and Delta W both negative with a resulting positive ratio the assumption is higher C for lower W)

EDIT 2: I guess I have too much time on my hands as well. Bringing it down to a single item analysis boils down to this. (C2/C1)-1/(W2/W1)-1. -1 means you paid an equal price per pound to shed the weight as you did to purchase the weight in the first place. Moving right into higher negative values means you paid -x.xx times more to shed the weight than you did to purchase the weight. Less than -1 approaching zero means you paid less per pound to shed than the original purchase and a positive number means you either paid less overall for the new gear for lower weight or you paid more and added weight.


Personally, although it's a fun number game, it would not be meaningful to me when considering new gear with the aim of reducing pack weight and cost.

EDIT 3: Perhaps it would be meaningful to me if I had several combinations to consider. If I wanted to know what combination gave me the best bang for the buck and I wanted to replace my tent, sleeping bag and maybe pack and was considering several combinations, say between 2 tents, 3 bags and do I really need a new pack. I could plug in each combination to see what happens.
Last edited by Jimr on Fri Apr 20, 2012 11:12 am, edited 1 time in total.
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Re: Weight loss

Postby Wandering Daisy » Thu Apr 19, 2012 8:53 pm

Good analysis Jimr. However, when I consider reducing weight for backpacking, EVERYTHING gets put on the table, including my camera. Nothing is "overhead". I just replaced my old camera with a new one, that cost twice as much. At least it weighs the same. The easiest way to reduce weight with no cost is to simply not take something. Every trip I agonize over taking Crocs. I really do not need them for camp shoes, but if I have to wade, they are worth the weight. The other big decision is tent vs bivy. I have done about half and half. My rule of thumb for fishing gear is that I have to throw out the same weight of food as the weight of fishing gear, so the pack weight is the same. If I cannot catch fish, I am one starving sad sack!

Lately my analysis has been more of an optomization. Minimize pack weight; subject to having adequate gear to assure a low probability of starving, hypothermia and misery; a moderate porobability of ordinary discomfort in camp; and limited to an upper annual $ limit of new purchases.
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Re: Weight loss

Postby Jimr » Fri Apr 20, 2012 9:47 am

When using Delta ratios it doesn't matter if you put everything in because if it is not in consideration, then Delta C & Delta W are zero. When I played with this, I merely added the constants that were not of issue in the decision as "Other" so total pack weight comparisons could be measured. When focusing on the subject matter only, the constants may be eliminated, but for overall weight optimization, all things are considered, especially if you are targeting a certain weight threshold. Even though weight is considered with a new camera purchase, I'm fairly certain weight was not the motive to purchase such a high ticket item.

At the end of the day, I seriously doubt this type of analysis is any more than mental gymnastics for those of us with too much time on our hands. Very important in business, but moot with respect to our pleasure. A SWAG is probably just as good of an approach.

Personally, I'd like to shed some of my 1985 gear to reduce my carry weight. I currently carry a full pack (7 days) with one full bear can at about 58lbs (heavy). The old Qualofil bag is heavy and the tent is 3 man. I could buy a new bag and a smaller 2 man tent and reduce several pounds from my back. I like a little extra room in my tent, so I always opt for a size one person larger than the occupants, so a 2 man is what I'm willing to go down to for solo trips. Comfort vs. weight consideration. The portion of my disposable income allotted for new gear is limited and I want some of that to go toward resurrecting the fly tying hobby of my youth because my son wants me to teach him to fly fish and tie flies. Available funds vs. priorities consideration. I've decided I can shell out to replace one item. My tent is in great condition and I rarely go solo. I normally go with my one backpacking buddy. I think I'll replace my bag. Comfort vs. finances vs. priorities vs. normal situation. At this point it is a shopping comparison trip to get a flavor of how much bang I can get for the bucks I can spend, then find the balance between weight, efficiency rating and price. Not once will I consider the cost/benefit ratio of my decision. Sounds like we run the same types of decision trees. I'd bet most of us do.

If I could replace pack, tent and bag, there would be a myriad of choices to consider. With this scenario, a cost/benefit analysis to find the best combination when all other variables are fairly equal would be an interesting exercise, give or take a quart.
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Re: Weight loss

Postby oldranger » Fri Apr 20, 2012 4:28 pm

The cost of backpacking equipment is low if you compare it with other ways of spending money outdoors--motorhomes, pickup camper rigs, horses, boats, alpine skiing etc. I told my wife that if my coronary artery issue stopped me from backpacking I would buy a boat. She encouraged me to keep on backpacking but maybe she just wants to get rid of me and pick up a new model!

The point is that at my point in life if it is lighter and I think equally useable I can buy it. That has not always been the case, though.

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Re: Weight loss

Postby Jimr » Fri Apr 20, 2012 4:36 pm

My wife wanted to trade me in for a newer model, but I gave her a cost/benefit analysis of her choices and she decided it was cheaper to keep me.
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