Can I use plastic bottles/jugs as flotation?

Hello all,

I have a 14' Semi v with 3 bench seats and a casting deck, while doing some renovation I realized the previous owner removed all the foam. As the username implies I really don't want to drop a couple hundred bucks on foam. (although if I have to it's not a bad investment)

But I was wondering if I saved 2 liter soda bottles, antifreeze, oil jugs etc, if it would stop my boat from sinking should I become swamped. with the casting deck I have I would say almost double the space the boat originally had for foam so even if they arent as efficent per cubic foot I think I could pull off flotation potentially unlevel though.

Not sure about the bottles, could be ok. As to the user name, better to be el_cheapo than El Chapo. :mrgreen:

There is a guy that works at my local tire shop that saves
all the quart plastic oil bottles for his boat flotation.
that seems to be the better choice as the HDPE will last
forever out of UV exposure and is more durable than the soda/water bottles.
check with your local quick oil change stores and see if you can score their plastic bottles.

Pool noodles probably a better choice.

They would work - plenty of boats have sealed air cavities as their emergency flotation. I would make sure you caulk the lids on with a $1 tube of silicone caulk from Walmart, they only work because they're water tight, since you're not spending anything on them in the first place a trifle spent on insurance wouldn't be bad.

Just need to make sure they're secured to the hull - IE make sure they're in a compartment they can't pop out of and that the decking above them confining them in is attached to the hull.

Nothing says you can't be thrifty while being cautious!

Don't expect them to save your outboard @ the back of the boat though if you have them piled up under the front deck.

RiverBottomOutdoors said:

Pool noodles probably a better choice.

Click to expand...

I think pool noodles would be more expensive than free bottles, also don't know how well they would do if some gas got on them, and I believe they can eventually water log partially.

onthewater102 said:

They would work - plenty of boats have sealed air cavities as their emergency flotation. I would make sure you caulk the lids on with a $1 tube of silicone caulk from Walmart, they only work because they're water tight, since you're not spending anything on them in the first place a trifle spent on insurance wouldn't be bad.

Just need to make sure they're secured to the hull - IE make sure they're in a compartment they can't pop out of and that the decking above them confining them in is attached to the hull.

Nothing says you can't be thrifty while being cautious!

Don't expect them to save your outboard @ the back of the boat though if you have them piled up under the front deck.

Click to expand...

It's just a 75 mercury 9.8, so not a huge loss if so. But can't a small 2 stroke survive being submerged in fresh water? (assuming I don't have it running and intake water)

I think at this point, it's a math problem. a 2 liter bottle should hold 4.4lbs of weight right when it's completely submerged. I weighed my boat, (while on the trailer) with all my gear in it and it came in at 960 pounds. Not really sure what a little trailer with 8 inch tires weighs. May just have to put my boat in the water then drive to a scale and weight the trailer so I can subtract that. Right now lets assume 150 pounds.

960-150 for trailer + 600 for 3 guys (mostly just do 2 guys but worst case) =1410/4.4=320.4 so maybe 330 to have some extra safety factor.

So I think the real question is can I fit 330 2 liter bottles in my boat? I don't know that I can I'll just have to experiment.

el_cheapo said:

... can't a small 2 stroke survive being submerged in fresh water?

Click to expand...

Sure! We've even salvaged those dropped into saltwater, running or not ... there just more work and more likely to have an electrical component die a premature death.

The rule is, especially with saltwater immersion, LEAVE it in the water until you can absolutely take it out, go through it completely and immediately and get it started! We used to call it 'pickling' the motor.

el_cheapo said:

...960-150 for trailer + 600 for 3 guys (mostly just do 2 guys but worst case) =1410/4.4=320.4 so maybe 330 to have some extra safety factor.
So I think the real question is can I fit 330 2 liter bottles in my boat? I don't know that I can I'll just have to experiment.

Click to expand...

You don't need to account for the people's weight pound for pound for the purposes of your planning - you're not looking to satisfy some logic you can defend in court as is probably the case with any commercial boat builder - people float in water, the fatter they are the better they float, so only work with the dead weight of gear, batteries, etc. when planning what you need and if there's still room, great. If you're getting really nerdy wood is also close to neutrally buoyant - so while your decking is adding a lot of weight in the event of submersion it will not require much flotation to support it.

The issue you're going to run into is the irregular shape of the bottles, you're not going to be able to make efficient use of the space under the deck, which is where Johnny's suggestion about the oil cans makes a lot of sense. Not because of the HDPE plastic, but because they are smaller and easier to nest together. Beyond your front casting deck you can still nest them fairly regularly in the cavities between the ribs along the main deck of the boat and add them in areas you can't reasonably fit a 2 liter soda bottle.

As a side note, there's a guy in Mexico that built an island out of old plastic bottles and fishing net. He lives on the island, it's so buoyant he covered it with sand and he rents out space to eco tourists.


https://www.bbc.com/news/av/world-latin-america-35948481/the-island-built-on-recycled-plastic-bottles

onthewater102 said:

el_cheapo said:

...960-150 for trailer + 600 for 3 guys (mostly just do 2 guys but worst case) =1410/4.4=320.4 so maybe 330 to have some extra safety factor.
So I think the real question is can I fit 330 2 liter bottles in my boat? I don't know that I can I'll just have to experiment.

Click to expand...

You don't need to account for the people's weight pound for pound for the purposes of your planning - you're not looking to satisfy some logic you can defend in court as is probably the case with any commercial boat builder - people float in water, the fatter they are the better they float, so only work with the dead weight of gear, batteries, etc. when planning what you need and if there's still room, great. If you're getting really nerdy wood is also close to neutrally buoyant - so while your decking is adding a lot of weight in the event of submersion it will not require much flotation to support it.

The issue you're going to run into is the irregular shape of the bottles, you're not going to be able to make efficient use of the space under the deck, which is where Johnny's suggestion about the oil cans makes a lot of sense. Not because of the HDPE plastic, but because they are smaller and easier to nest together. Beyond your front casting deck you can still nest them fairly regularly in the cavities between the ribs along the main deck of the boat and add them in areas you can't reasonably fit a 2 liter soda bottle.

Click to expand...

Boom and there you have it


Very nice :clap:

Pool noodles are cheap and are a proven solution. Search the forum for more info.

onthewater102 said:

el_cheapo said:

...960-150 for trailer + 600 for 3 guys (mostly just do 2 guys but worst case) =1410/4.4=320.4 so maybe 330 to have some extra safety factor.
So I think the real question is can I fit 330 2 liter bottles in my boat? I don't know that I can I'll just have to experiment.

Click to expand...

You don't need to account for the people's weight pound for pound for the purposes of your planning - you're not looking to satisfy some logic you can defend in court as is probably the case with any commercial boat builder - people float in water, the fatter they are the better they float, so only work with the dead weight of gear, batteries, etc. when planning what you need and if there's still room, great. If you're getting really nerdy wood is also close to neutrally buoyant - so while your decking is adding a lot of weight in the event of submersion it will not require much flotation to support it.

The issue you're going to run into is the irregular shape of the bottles, you're not going to be able to make efficient use of the space under the deck, which is where Johnny's suggestion about the oil cans makes a lot of sense. Not because of the HDPE plastic, but because they are smaller and easier to nest together. Beyond your front casting deck you can still nest them fairly regularly in the cavities between the ribs along the main deck of the boat and add them in areas you can't reasonably fit a 2 liter soda bottle.

Click to expand...

I found the boatbuilders handbook that includes flotation requirements for them. Starting with page 25 here
https://uscgboating.org/regulations/assets/builders-handbook/FLOTATION.pdf

If I'm understanding right it basically shows that your right you really don't need to count pound per pound not even with things like the aluminum hull. which sounds weird to me, I can understand things like wood, people, and coolers floating but metal?

But here's a little math incase anyone wants to check me, and incase anyone wants to reference this in their future builds.

Hull 205 pounds x .63 would make 130
People 600 pounds x .25 = 150
Motor 65 pounds x .75 = 49
Gas can actually counts as flotation but it's not secured down so I'm just not counting it one way or the other
wood 10 pounds x -.56 = -5.6
Battery 60 pounds x .75 = 45
Misc boat junk 75 pounds I'll count at full value just incase

This would lead me to believe I need 443 pounds of flotation to be neutrally buoyant, that would be 100 2 liter bottles or about 200 quart oil jugs.

Likely what I'll do is just stuff as many as I can in but make sure it's at least that number for this to be viable. The jugs themselves will weigh something as well.

Make sure you're calculating the atmospheric pressure inside the bottles. Fill your bottles with hot air and then when it turns cold they won't be as buoyant. Good luck checking the air pressure in 100 bottles, I struggle to do this with just two tires on my boat trailer.

You do realize by the time you're done gathering all this material, figuring everything out & securing it you could have worked half that time flipping burgers, quit after one shift basically and bought all the foam you would have needed?

Granted, you would lose bragging rights to having employed the absolute cheapest flotation option out there, but you would have more time to spend on your boat.

RiverBottomOutdoors said:

Make sure you're calculating the atmospheric pressure inside the bottles. Fill your bottles with hot air and then when it turns cold they won't be as buoyant. Good luck checking the air pressure in 100 bottles, I struggle to do this with just two tires on my boat trailer.

Click to expand...

Sounds like a winter time project.

onthewater102 said:

You do realize by the time you're done gathering all this material, figuring everything out & securing it you could have worked half that time flipping burgers, quit after one shift basically and bought all the foam you would have needed?

Granted, you would lose bragging rights to having employed the absolute cheapest flotation option out there, but you would have more time to spend on your boat.

Click to expand...

I work a desk job, I've been at work every time I've posted here or thought on this. I'll just tell my friends to save their bottles for me, then it's 4 bolts to pull each bench open throw them all in as tight as possible and put the bolts back on.

I've got to live up to my name.

I can't remember where, but somewhere I saw where a guy put the bottles in the compartment then poured expanding foam around them. Objective was to save on the amount of foam needed.

Now that is a smart idea! Doubly good seeing as sealed bottles can't get water logged over time.