Project rRaft - Building a Raft out of Water Bottles

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Picture of Project rRaft - Building a Raft out of Water Bottles
rRaft is short for recycled raft. Inspired by Reishee Sowa, who lives on a water bottle island in mexico, this is my attempt at a similar feat. While many people have duct taped a couple hundred bottles together in the past and called it a raft, mine is sturdier, has a real deck, and is indefinitely reusable.

The entire process of developing Project rRaft was documented at

WARNING: General safety rules, as well as some state laws, dictate that you should have at least one PFD for each passenger of a boat. In the pictures, we are not wearing any, but also realize we did not row very far off shore. Go boating at your own risk. Also, be careful with any tools and such that you use.
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Step 1: How Many Bottles?

Picture of How Many Bottles?
For ease, I will split this step in to two sections. The first will explain the math/science that went into picking a bottle goal, and the second will quickly tell you how to figure out how many bottles to collect.

Section 1

I wanted my raft to support myself, and a friend if the opportunity arises. I weight 170 lbs, and i'm factoring for a friend who weighs the same. That's 340 pounds. Add in the weight of the boat plus extra buoyancy to keep us above water, and we're at 400-500 pounds of needed buoyancy.

  • The average water bottle contains .5 Liters of water.

Archimedes' principle, or the law of upthrust says:

"A body immersed in a fluid is buoyed up by a force equal to the weight of the displaced fluid."

Thanks to scientific measurements, one liter of water supports one kilogram of weight.

If each water bottles supports half a kilogram, which is about one pound, than you need just as many bottles as pounds you wish to support. I used exactly 450 bottles in my raft.

Section 2

First, decide how many pounds of cargo your raft should support, that number is roughly how many .5 L bottles you will need.

Easy as that!
hey say me and my friend way 190 pounds together, but we want to use 2L bottles instead .5l .How many 2L bottles would we need to hold are weight and are bout will be around 20-100 pounds?
2L bottles will support about 4lbs each. You want to go over as much as possible so you actually float, instead of simply not sinking.
what are other alternative for material? we are going to use it for our investigatory project.:)
and also can we use it in flash floods??thanks!:))
using it in flash floods actually sounds like a goog idea
I am currently making a raft based (mostly) on your design with my two kids and we are having a blast with it! Great instructable and great idea!! We are using empty gallon milk jugs because that is what we have in abundance!! lol ... We are finishing up the fourth pontoon now and will probably do sea-trials this week! I'll post again when we see how she fares! THANKS! for a great instructable posting!
temp5 years ago
Exactly how cold was it. Cause it looks like there are many green trees, your pool is still open, and there is no ice / snow. Therefore it is not fall winter or very early spring. In late spring and summer the water is never cold!
Weissensteinburg (author)  temp5 years ago
It's Florida...the leaves don't fall and the water doesn't freeze. That doesn't mean anything less than a polar bear could bare that water.

(get it, bear-bare? hehe)
hey i liv in florida too! how old r u?
LOL!!! look at my pic click it you cant see it well !
Haha. I will admit, that made me laugh.
if leaves are still on the trees the water's warm enough to go swimming. And if you're in florida you shouldn't even complain about cold water. I was swimming in te ocean today. I live just north of boston. That was cold.
enemigo3 years ago
when you´re counting bottles don´t forget to take into account the weight of the deck material.
stronglad3 years ago
Can I do this with Arizona tea jugs?
Weissensteinburg (author)  stronglad3 years ago
Sure, you'll just have to do the buoyancy conversions yourself.
madara0093 years ago
do you know how much weight a 2 liter soda bottle would hold up? i want to make somthing like this and it might be faster to get soda bottles instead of water.
RHkramer is correct, by the math stated. 1 kilo weighs nearly 2 pounds. Therefore, if you weighed 100 pounds, you would need 50 bottles.
You'll need more than that. There's the weight of the bottles themselves and the raft. In addition, that figure will only neutralize your weight -- You would be weightless in th water, but far from securely above water. You need extra bottles to actually feel like you're on a raft. Also, a two liter bottle will support two kilos, so 100 pounds would be 25 bottles for a neutral weight.
My guesstimate, without doing any real calculations, is about 4 lbs. per bottle. An empty bottle will hold up about the same weight as the weight of the amount of water it will hold, plus or minus a little bit, depending on how heavy the material of the bottle is (minus for materials heavier than water, like glass, plus for materials lighter than water--I'm guessing a lot of plastics are lighter than water, but I don't know for sure (fill a bottle, leave the lid off, and submerge it, see if it floats or sinks).

Also, if the bottle collapses slightly in water due to the weight of the water pressing against the outside, there will be a little less volume and thus it will support a little less weight.

A liter is a little bigger than a quart, a gallon of water weighs about 8 lbs, so a quart weighs about 2 lbs, so guesstimating that 2 liters will support about 4 lbs won't be too far off.

You could also simply fill the 2 liter container with water and weigh it--like I said, it will support about the weight of water it contains. (If you want to be precise, you could subtract the weight of the air the bottle will hold when we call it empty, but that is negligible. You will have to account for the slight collapse of the bottle underwater (as mentioned above), so if you weigh the bottle full, figure it will support a little less than what you weigh.

Of course, you'd want to figure on using more bottles than this caculation indicates, to account for all kinds of things, including the potential of bottles springing leaks due to collisions, abrasion, or whatever.

Hope this helps!
WOW! Thank you! this is really helpful! i think ill start building one next week lol
You're welcome!
The Landon4 years ago

You can get a lot of bottles at small businesses that you´re familiar with, like restaurants. Once I went to a small casino to get bottles (not familiar with) and got like four BIG and FULL black bags of 2l bottles.

dzent14 years ago
Dang, that looks fun! And you're right, the CEO at Home Depot is a genuine a-hole and it just kind of trickles down from there. I quit them a few years ago and won't EVER be back because they're run so poorly. Loews all the way, or the local hardware store where the old guys know everything there is to know about everything!
How many bottles would you guess be needed to support around 120lbs.?
 121, plus the weight of the raft. But thats to be neutral, you need extra buoyancy.
Cool. Thanks.
Hey Weissensteinburg, thanks for replying to several of my comments from a while ago. Because of that, I started to collect some water bottles, now I think I have enough to hold me above the water. I'm gonna be building a kayak for this one race that is going to be held this Sunday. Hope I can build it before Saturday and test it before the race. Thanks for all help from before.
So, if I wanted to build a raft to support (for example) thirty pounds, I'd need at least 30 5 Litter water bottles?
Weissensteinburg (author)  Rock Soldier4 years ago
No way! You'd need about thirty .5 liter bottles. The average plastic water bottle is .5 liters. If you want the exact amount, it's easier to work in kilograms. One liter of air will support one kilogram of weight in water.

30 lbs = 13.6 Kg

So to support 13.6 Kg, you'd need 13.6 Liters of air. That's 27.2 average water bottles. Remember you also have to account for the weight of the plastic and that the 27.2 number is only to equalize the weight. You'll want to use extra if you really want it to act like a boat.
Sorry, I meant .5L. Now, I have a question. How many Kilograms equals a pound?
Weissensteinburg (author)  Rock Soldier4 years ago
About 2.2 lbs equal one kilo
the picture blocks the third step D:
whenever it does that just refresh the page
Weissensteinburg (author)  koolmuffin134 years ago
What do you mean?
Derin4 years ago
You also need one of these if you need a PFD :)
ednolan4 years ago
I made one over the course of a few weeks. It works fine, and I didn't have to use the pipe frame or even paint the raft. I was able to get the bottles a lot faster by picking them out of the school's bottle recycling bins, which are usually full. Great idea!
Weissensteinburg (author)  ednolan4 years ago
That's great. I used the recycling bins at my school, until they got rid of them. Could you post a picture of yours?
Keep in mind that that photo is of the first test. I think I will eventually paint it, and I didn't really have an oar, so I was using a piece of driftwood and I had someone on shore with a rope to pull me in. (you can also see the picture at
Weissensteinburg (author)  ednolan4 years ago
Looks like yours turned out really well. It's great to know someone was actually able to use this.
smessud4 years ago
Just to add more data on buoyancy .. 1 litre of pure water weighs 1 kilo but 1 litre of salt water weighs more. Your 2-liter bottle would float 2 kilos in a river, but it will float slightly more in the sea.
ReCreate5 years ago
Could i use those 5 Gallon Bottles that are used for water Like the ones in the Picture,I ended up with about 20 of them.

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