P.S. this post has nothing to do with Arduino, Open Source Hardware, Open Source Economics, or anything like that. I was just going through my old pictures and found this, so I thought I'd share!
This story is a little old now, but a few summers ago Chris and I decided we didn't have enough danger in our lives, so we were going to build a sail boat to learn the principles of sailing. We didn't have enough money to justify buying a used boat, or even renting one, so we built a bottle raft and then later stuck a sail into the middle of it. Unfortunately, I don't have any pictures of the raft when it had it's blue tarp sail, but I'll say this much: it didn't work. We had to paddle pretty hard to keep it going, and it definitely did *not* tack against the wind.
So without further ado, here is my personal guide to building a bottle raft -the getting in trouble part comes at the end of the post:
Step 1: Find bottles
Find lots and lots of bottles. This was really hard for Chris and me until we discovered something... Thursday night was recycle night a few towns over. So we popped along in a little nearly broken down Subaru, and went from house to house picking out all of their nice bottles. We had the pick of the litter too, so we chose hardy, durable bottles.
You might think that 2-litre soda bottles are nice, but they're not. The problem is that they're too narrow, and they'll slip and pop out from under the boat if you're not careful in later steps. Also, I've seen a lot of tutorials recommend using 1 gallon Poland Spring water bottles - which are equally terribly, because the tops just pop off when you submerge the bottle. A good rule of thumb is: if you can take the cap off the bottle in a popping motion with your thumb, the bottle will leak, let in water, and you'll sink. On the other hand, using bottles with screw caps is ideal because they're thicker.
The perfect bottles are detergent and bottled water ones:
No, I'm not sponsored by Tide. In fact, I hate the way it makes clothes smell, but they make great raft bottles. Chris and I did calculate that it was almost worth just buying detergent just for the bottles, since we'd just dump out the detergent and save time scouring the neighborhood for the good bottles. If you value your time, then yes, it's worth just buying detergent and dumping it out. But if you don't, and you have good music to listen to, and a good story to tell neighbors when they see you taking their bottles, it'll probably just take a few hours. Another rule of thumb:
- An average family household does laundry once a week, and runs 2-4 loads of laundry
- The average bottle of detergent is good for 20-30 loads of laundry
- On average, a household is buying a new bottle of detergent once every 8 weeks, or every 2 months
- That means a household throws out a detergent bottle once every 2 months, or ~60 days - this is about right from my experiences growing up having to do laundry, so this checks out
- That means that you'd need to visit 60 households before finding 1 detergent bottle
- Not all households put their bottles in a recycling bin (let's say optimistically 80% do), so now you have to go to 75 households
- This seems bad, but there's a catch - recycling only happens 1 day a week, so everybody batches their bottles together at once, and so you actually get to reduce the time step earlier by 7, since you're synchronizing when you're checking everyone's detergent-throwing-out-status, so now you have a good chance of finding a bottle with every 10-11 houses you check
- The final step is a good and bad thing: some people seem to employ a multi-phase, or "stage-gated" recycling process (if you will), by which they keep a recycle bin in the garage, that they fill up first, and only when it's full will they put it out for collection. This is bad because this means there are some houses just sitting there - in front of your eyes, and you KNOW they MUST have a detergent bottle waiting to recycle, but you just can't GET IT! On the flip side, however, you know that when they finally do put their bins out, there's a pretty good chance (about 50%) that it will have a detergent bottle if they took 1 month to fill up the bin. On the other hand, there's a 25% chance the bin will have a detergent bottle in it if they let the bin sit for 2 weeks
- The nice thing is that you can easily tell if someone has put a recycle bin in front of their houses, so the transaction costs of checking are very low - just drive by the house, and if there's a recycle bin in front of the house, then check it for bottles. If not, don't check for bottles.
- Last tip: there's about a 1 in 50 chance there's a detergent bottle in the trash bin, hidden from plain site, but luckily most people put detergent bins on top of the trash, so there's a fairly good chance that if they didn't recycle it, it's the huge thing preventing the trash lid from fitting on snuggly, and you can see it. Again, visual inspection reduces time taken.
I can't help it - here's the Laundry-Dumpster-Diving-Time-Tradeoff-Equivalence equation:
W - loads of laundry / week (typical: 2-4)
L - loads of laundry / bottle (typical: 20-30)
New bottle bought = bottle thrown out
New bottle bought = L / W (range: 5-15 weeks)
New bottle bought (days) = L / W * 7 (range: 35-105 days, or ~1-3 months)
Pr - probability that house throws out detergent bin in recycling (assume: 80%)
Divide by 7 for single day-synchronization:
L / W * 7 / Pr / 7
Pt - probability that house throws out detergent bin in trash vs. bin disappears as kid's school project (assume 90%, round lower for technically-inclined neighborhood, or around the date of science fairs)
((1/Pr)(L / W * 7 / 7) + (1/(1-Pr))(Pt)(L / W * 7 / 7))
Tr - Time required to visually inspect recycle-bin (~5 seconds)
Tt - Time required to rifle through trash bin deposited detergent bin (~30 seconds)
((1/Pr)(L / W) + (1/(1-Pr))(Pt)(L / W))
So clearly, for the return, it's not worth spending the ratio of time on checking garbage, since you'd expend a *lot* (~20x) more labor for a garbage-bin collected detergent bin than a recycle bin collected one. Plus they're really messy.
Number of houses to check: (1/Pr)(L / W)
Time spent checking: (1/Pr)(Tr)(L / W)
Time spent fetching: Tf (assume: ~10 seconds)
Time driving from one house (with recycle bin) to another: Th (assume ~60 seconds)
Total bottles needed: B
You have to drive and check every house: (1/Pr)(L / W)(Th + Tr)
You only have to fetch when you find: Tf * B
Total time needed: B* ((1/Pr)(L / W)(Th + Tr) + Tf)
Search: ~700 seconds / detergent bottle
Fetch: ~10 seconds / detergent bottle
B (from next section): ~35 bottles
Total time required: ~7 hours of driving around looking for bottles
How does this funny math validate empirically? From experience, about 1 in 8 houses has a detergent bottle, you're willing to do it for about 3 hours before you get sick of the smell and want to shower, so you spread it across two nights, and two weeks...
Which is just what Chris and I did :)
Step 2: Calculate how many bottles you'll need
You would have thought this step would come first, but here experience has taught me otherwise. Start by finding out how difficult it is to acquire good, solid, quality bottles, and then work backwards. This will tell you what kind of design to go with. For instance, I've noticed that the Northeast seems to be a fiend for large detergent bottles, while the Midwest prefers the smaller types. The South seems to not use detergent, so you don't find too many in their trash (oh, and I don't think all Southern states have recycle night trash collection either, which makes finding bottles even harder).
- Each gallon of displaced water is about 8 pounds (about)
- 2 grown guys plus non-floating part of the boat is about 400 pounds (adjust accordingly)
- 400 lbs / 8 lbs = 50 gallon bottles
1 detergent bottle is between 1.5 and 2 gallons, so you'd need about: 25-33 bottles
Here's the part that trips up mathematicians. Notice that this is only for break-even. If you meet break-even, as Chris and I discovered, you get a boat that usually is partially submerged on one side, or just sort of hovers there in the water, bobbing in and out.
Add another 10-20% bottle buoyancy, however, and you're actually capable of floating above the water most of the time.
The truth is, you never really know, so Chris and I grabbed tons of extras, and we chose the number based on how many we thought we'd need, and then brought extras just in case.
Step 3: Design ideal boat
For Chris and me, it was something like this:
Notice the punt-style main mast sail (forget how we thought it was going to attached to the base), the triangle shape out in front (forget that it would just steer sideways and not help thrust at all), and the outboard motor (for when we got tired of rowing).
Step 4: Reality sets in
A trip to Home Depot indicated a few problems with the plan: how to attach the mast to the platform?
Nevermind the outboard motor, since Chris actually had one lying around. We did notice, however, that it would require it's own ~25 bottles to float, not to mention the undercurrent would probably rip the bottles off the base, so we scrapped that idea. But only after debating about it furiously.
So instead, we got a few wood planks and 2x4's, and built a solid reinforced base (that's Chris with the drill):
Construction fencing makes a great way to secure the bottles to the underside:
You'll actually notice that there were some 1 gallon jugs in there... that's how we discovered that they're horrible sources of "robust buoyancy."
It was quite simple, actually - we used a staple gun to attach the orange fencing to the board, and that was pretty much it.
Step 5: Put "boat" in water
And, if religious, this would be the appropriate time to pray to an appropriate deity... actually, we also started to draw a crowd, since it was a weekend, and this was the New Haven shoreline. I'm pretty certain the New Haven shore crowd doesn't usually get a chance to see this type of work (stupidity?) in action...
That smug grim on my face is because someone just yelled out, "you're going to sink" and I'm thinking, "you're not on a homemade bottle raft, and I am, mwhahahahaha." Chris and I took turns on the "manual outboard engine location". We built a separate platform for the outboard engine, thinking at worst if it tore up the bottles underneath it, we'd still have the other section to be safe on. Seemed to make sense at the time.
Step 6: Get in trouble
We stayed on the raft for about 5? hours, and had no problems. In fact, these pictures were taken at night time, for proof - this is us looking back at the New Haven coast.
The one problem we had, was we made a serious tactical error. We brought a Weber grill on the boat too, thinking, sure, at some point we were going to get hungry and why not cook out on the boat?
Both Chris and I failed to anticipate what the view from land would look like with a fully lit Weber grill and charcoals starting light up. Apparently, someone called the police, thinking we were in danger and on fire and maybe trying to commit suicide in a blaze, when really we weren't, we were just hungry. The police drove up on that ramp in the second picture above, turned his siren on, fired a flare into the air, and called the mini-coast guard (do they exist?).
Anyway, we threw the Weber grill into the water to douse the fire, and rowed back into shore. The policeman said we were perhaps the dumbest guys he'd ever seen, but said it looked fun, and next time we should either not try the cook-out part, or maybe pre-cook everything and bring it out in a cooler.