PET Bottle Floatation

My guess is Australian Capital Territory.

 

There are quite a few things to consider with buoyancy materials, type, amount, and how it is distributed. And in a boat with a self-draining cockpit, considerations of being able to restrain entry of water when/if the floor level goes lower than sea level. Neglect that and you could have a lot of free water sloshing around that can easily upturn it. Concentrating buoyancy along the centreline will exacerbate that.

 

I was looking at regular 2 liter plastic bottles (from name brand soft drinks) as flotation a while back.

Their ruggedness and abrasion resistance had impressed me during a a previous "fun" use when my boys were pre-teens. First I pressure tested some up to around 200 psig without failure. Then I made "compressed air over water rockets". I found that even after repeated impacts on pavement from 100 ft, they retained 100 psig pressure without failure.

They are petroleum product tolerant. I used a 16 oz version for storage of gasoline + two cycle oil mix for multiple years. I have also examined bottles subjected to multiple years of UV exposure (sunlight) with no detectable loss of mechanical properties.

Pressurization is not essential for surface level flotation, but adds assurance that loss of flotation will not occur with submergence. It also assures that if a bottle is submerged for an extended duration it will not leak water in with temperature changes.

I came up with a way to pressurize them to around 5 - 10 psig. It involved a pressure feed "hood" over a loose cap to allow pressure in and then the cap could be tightened. A bottle with a hose attached was used to "calibrate" judging pressure by feel. Getting a really good seal on the cap was verifying by no loss of pressure over multiple days. The pressure check (i.e. "quality assurance" verification) for a test run on a bunch worked pretty good.

 

Rick Tyler
They look really interesting, I will look into those further.

Submarine Tom
Mr Efficiency hit the nail on the head! Australian Capital Territory.
and to all the fellow Aus. out there I'm not in Politics nor am I a public servant, or have ever being one.

Village_Idiot
I think the amount of time spent coating balls in resin, or turning balsa ones, even the thought of making Aluminium balls would drive you mad. It would be a tedious horrible job, even on CNC machinery. Not to mention all the lost hours of work. I would shudder to think of just producing 100 of these let a lone a thousand.

Now that is something I never even thought about on this journey, for some reason I always envisioned that water would be leaking in through the hull at some point and I would be taking on water from the underside. I think this is due to 7 corrosion holes in the hull My mind tends to think it will be a hull breach that sinks us not a green one over the top.
Well that puts a new spin on things, so is it now, what is the lesser of two evils or which one is the more likely to happen?
Cheers

Katoh

 

What is the set-up with the scuppers for the self-draining floor ? I think a non-return flap or similar arrangement you can lock shut if the holed boat settles with the floor level below water level, is a sound idea, though if the hull is completely foam-packed, would be unnecessary. But filling it completely with buoyancy material seems impractical from your description. And then any openings into the underfloor area to run cables etc. that might provide a point of entry for water to spill onto the cockpit floor have to be considered.

 

This is an interesting subject. I am thinking before you even start looking at filling your hull with anything, you look at the feasability of whatever you use keeping it afloat.

The sealed unit in the hull is only to keep the boat afloat if it gets flipped and from photos I have seen there is not much of the hull above the water when it is upside down.

This could mean you need virtually 100% filling of the hull space to remain buoyant.

So, what you need to know is the weight of the boat. Then, work out what volume is required to keep it afloat to enable you to work out the number of bottles to use.

I am feeling that the bottles would have too much void between them to enable anough floatation.

The smaller the type of flotation used means less void between units, however small means of flotation ie ping pong balls (Mythbusters are entertainment and not to be taken seriously) have the undesirable result of escaping from the hole thus made from a collision.

In my opinion, do the maths first, and don't run into things that might put a hole in your boat.

 

Katoh, this link may help: http://www.sealifedesigns.com/sealifeshop.html
They're Naval Architects and that foam Microlene is a flexible polyethylene which seems to be in use in plate alloy boats, I'm sure they'll be able to advise on suitability of it. Not to be confused with Polyurethane, which does seem to create corrosion in alloy.

 

Gentlemen
I think its about time to post a few photos with some explanations, this will help matters no doubt.
Photo 1 shows the front half of the motor well and the fuel well, the fully welded floor around. the 3 holes you see in the motor well were created by me to locate a corrosion spot and inspect hull integrity. Two of these holes will be be welded shut prior to filling the hull with whatever is finaly decided? At this stage I plan to keep the most forward hole as it is directly over the keel line and gives me access to both sides.
Photo 2 shows from the motor well looking forward and quite a good indicator why some of the ideas brought forward were not possible, good ideas thou.
Photo 3 and 4 show the drain pipes for the self bailing floor, notice there are no scuppers installed, this will end up being a different thread, possibly will be ball and socket type scuppers.
I hope this helps, the more I study the hull the less I am convinced it does not hold any type of floatation at all. The cavity between the motor and fuel does have foam but very little and I believe that to be more for insulating around fuel lines.

Cheers
Katoh

 

Hmmm, I hadn't considered manufacturing them - that would be maddening! I was thinking more of a spray-on resin coating tennis balls...

From the looks of your boat, I'd think a good welder/metalworker can open the deck up for you (to fill with blue/pink foam board from the hardware store), then patch things up to original condition. You should be able to find a good metalworker at decent rates if you shop around.

 

Village_Idiot
Funny thing is I'm doing all the metal and welding work myself, and really dont want to go pulling that deck up. Before every man and his dog jumps down my throat, I do realise that would be the ultimate rebuild and in many circumstances the right thing to do.
But really when you look at it there is no point in doing that. I am also toying with the thought to leave the darn thing the way it is, its survived till now and with 7 holes in the hull and a bilge pump not working , how I dont know, but I didn't rescue it from the bottom of the Pacific, It came on a trailer. I think this whole thing is just peace of mind knowing that something is there to keep you afloat, a slow leek, and a fried pump, well it might be enough to get you home.
At present I am still leaning towards the 50mm polyethylene balls, pump them in, push them around, I'm sure you could get at least 1.5m3 of balls in there.
Cheers

Katoh

 

The thing is, you don't know what is needed to keep it afloat. Sounds like all you're doing is slowing the sinking process.

Perhaps your money would be better invested in good survival gear and insurance.

-Tom

 

Tom
Safety gear and insurance, dont even come into this equation, as one is required by law and the other is just stupid if you dont have it. I dont know if you would call it slowing of the sink, I suppose its one one way of putting it. I was on a boat once were some poor plumbing started letting in water in to the hull, the pumps never switched on and there was no way to tell that there was a problem till the sponsons were full, thank goodness that had floatation or it would have been a long cold swim back.
I do realise the correct thing is to remove the floor and place in block foam slabs, the one thing I dont understand is how the boat ever got passed/registered without it, unless it has sealed compartments that I dont know off, but pulling the floor up is a place I dont want to go to.
I still am really interested in these 50mm polyethylene balls, they can be pump through that one hole all around the hull. The only thing I quirey is will they build up a static charge?
Cheers

Katoh

 

It takes a good fright for a lot of people to realise the necessity of buoyancy materials in a boat. Every vessel needs it, failing that a self-inflating life raft which is not practicable in small boats.

 

There are a lot of commercial boats out there with little to no floatation. I would recommend plenty of safety gear at a minimum. If you are going offshore - think there are some smaller lifeboats for boats of your size, for around several thousand dollars. Search Amazon for lifeboats for a start.

If you can make several hatches completely waterproof, that would be similar to having built-in floatation chambers. At a minimum, you may want to foam the empty chambers (using closed-cell spray-in foam) for extra insurance. It is also not unreasonable to weld floatation pods onto the transom, about an inch above the bottom of the hull (many have done it) - that would provide several hundred pounds of extra floatation, also.

 

I could not have written that better myself, Well Done!
If anything if you can slow the process,its better than nothing at all. I have to disagree with the life-raft's, there are some mighty fine little rafts available in the 2k mark which are suitcase(small) / Briefcase size that will handle 6 people, would be an excellent investment for a smaller boat.
The price for 50mm balls from china was a little more than expected, time to look in to those bird-balls.
Village_Idiot
You must be a mind reader as I was just about to post this, as your post came through, How true is what you say! Look at it this way, if I really got that paranoid I will fill he cuddy cabin up with pool noodles , got to be at least 4m3 of space in there maybe double if not more, now do the maths on that, its overkill with a passion. I just think we have to be sensible about the hole thing, safety first yes, saving the hull well? maybe not.
Great advice from all, and very much appreciated!
Cheers

Katoh