Wild thought PVC pipe flotation scheme

[sdowney717]

I was reading of someone using PVC pipe for a vacuum chamber and thought why not use endcapped thinwalled PVC pipe for flotation. Place it between the floors in a wooden boat. Get the thin schedule 20 pipe and glue ends on it. I dont know how much positive buyouncy would be required to keep the thing afloat in case of a hull failure. At least the weight of all the running gear plus some percentage factor. I have lots of available empty space between floors. Any thoughts on how impracticle or practicle this might be? Has anyone ever come up with positive buoyancy scheme for large boats?

[John Blazy]

Hey if it works - go for it. I've often considered PVC for pontoons on some weird small craft I'm doing, and I know it will seal well.

The only drawback I could possibly see is the time and cost vs 2part foam. Personally, I would cut up 2" blue styrofoam insulation and put it in - just a bit cheaper.

PVC will crack when it flexes after its real old, but if buried away from sunlight, it'll last.

Put in the PVC and secure it in place with urethane foam-in-a-can.

[TimothyB]

Aside from UV problems, PVC is pretty much a generational lived material. That is to say, it lasts a loooong time. ;)

You'd want to use larger diameters of pipe since that would give more flotation given the same volume. Tie them down with strapping which is attached to the keel(son) and/or the frames/floors.

You just need to figure out the weight of water you are displacing and compare it with your displacement to know if you have positive flotation.

Lets say you use 6"x24" pipe. That has a volume of .78 cubic feet, which means it displaces 48.68 pounds of water. So its just arithemetic, really. If you have a 30,000 lb boat you would need 616 of these pipes to equal the displacement. Given that it is probably something like a 35-45 foot boat at that weight, you could probably manage it. You'd need 30 of the pipes per station (about) given 20 stations to do it.. which is probably doable. You'd have to hide em in the space between the planks and ceilings as well as the bilge, but you could do it. Make sure you take into account the weight of the pipes themselves, so you'll probably have to add some for that.

That being said, it would probably cost something like $1000 - $1200, if you bought all of it at once from a wholesaler. Retail I just found Sch 40 6" PVC drain pipe for $1.92/ft. Not a bad price. Plus the strapping and fasteners. Still, not bad for positive flotation. It is definitely more expensive than blocks of foam, but I think it is more bulletproof.

You could go cheaper by getting Sch 10 PVC pipe. It is 1/2 the weight and thickness of Sch 40. It has thinner walls, but hey, thats not really a concern here since it won't be subject to wear. And if you ever get punctured and a few of the pipes get torn, no big deal.. you'll have the other 610 to keep you out of big blue.

Personally, I'd leave some margin for error and make sure I weighed the boat all fueled up and in cruising trim, after she has been in the water for a month or so before I finished setting flotation. Take advantage of the fact that this method is so portable and configurable! And I'd make sure I talked to a Naval Architect, or The Designer if possible, to give me peace of mind about the method.

[paul oman]

look at plans for a pvc pontoon boat once that included floation calculations. Very disapointing - a lot less floatation is a 6 inch dia cylinder vs a 6 inch dia square box - you would be surprised how much 'non pvc' space remained under your deck.

For a little daysailer I owned I stuffed those swimming noodles into the vold spaces.

regards

paul oman
progressive epoxy polymers

[JimConlin]

For ballasted boats, the analyses i've seen conclude that the necessary volume of buoyancy would take more of the interior than you'd want to sacrifice. For smaller ballasted boats, giving up the ends of the boat to tanks seems to work. H-12's are an example of this. For larger ballasted boats, large inflatable bags would work, as would work, as would using an extremely thick foam core in hull construction.
For lighter boats, there are several other options that appeal to me. Multihulls lend themselves to multiple watertight bulkheads. Inflated buoyancy bags for kayaks and dinghies are inexpensive, light and work well. Two-liter beverage bottles are inexpensive, light, tough, long-lived, removeable and adaptable to odd shapes.

[TimothyB]

Well, I agree that boxes have more volume than cylinders. smile.gif

I think the poster was trying to ask, though, how feasible IS PVC pipe as a flotation mechanism, and I thought it was feasible from many angles. Ideal? No. The cheapest? No. Best flotation for volume? No. But strapping down PVC is incredibly easy, the PVC wont soak up moisture or degrade, and although they would take up alot of space, you could definitely hide them behind the ceilings and in the bilge.

If I wanted to do permanent flotation, and build it into the boat's structure, of course I would do enclosed box shaped voids shaped to the hull, filled with a light closed cell foam. Or I would build the foam right into the boat's hull, if I was doing glued epoxy construction.

For a planked hull though, you can't really beat closed cell foam, blown or panels.

[Ron Williamson]

Instead going to all that trouble,you could use 2 litre pop bottles for way less money.
R

[Dan McCosh]

How about used wine bags? Seriously, I would think that if floation was supposed to take over after something put a hole in the hull, you might want something for flotation that you couldn't put a hole in.

[TimothyB]

2 liter pop bottles degrade pretty darn quickly and become brittle and crack when temperature cycles.

..and as I mentioned, I dont think a few of these tubes popping would endanger the boat if it filled with water. As I mentioned previously, PVC certainly is not the ideal material for this, but it is simple and quick to put together, and easy to install, and can be removed, and can easily be repaired or replaced.

If he wanted a perfect solution he wouldn't have asked about PVC flotation :) This is in the same realm as roofing tar as seam compound. It works but it's rough and crude.

That being said, if I wanted a simple flotation system, I wouldn't use PVC. I would make airtight boxes, with multiple air tight compartments (for redundancy and structural support) in them, out of plywood and scrap plastic tooled to fit into the crannies and nooks, cover them with epoxy and be done with it.

[John Blazy]

My mom (of course) is bugging me to put flotation into my boat this winter, and have been putting a lot of thought into it. Easy to just go with blue Dow styrofoam, cut into the underside of the decks, but then I've been thinking more of the airtight compartment idea.

I put in all kinds of effort to epoxy this boat and make it redundantly air tight, so why not close in two or more sides between the transom and aft bulkhead or in the bow and have an air tight compartment?

Then I thought of access ports to store stuff inside these spaces and thought of snatching some of my wifes tupperware bowls, cutting the bottom out of the bowls, screwing / sealing them around an appropriate sized opening, and then popping the lid on when done.
Bummer part is that she'd inevitably see the tupperware :rolleyes:

[Paulyboy]

I remember reading about someone once making a Gilligan style raft out of 4" pvc pipes.
The water line was level with the top of the raft.

[sdowney717]

I once put soda pop bottles in the bilge of an older fiberglass runabout. They were ok but after 3 years of temperature cycles they had lost a lot of volume. What did hold up were those 1 qt rectangular soft polyethylene plastic motor oil bottles. They had not degraded at all.
You would need so many of them and that would be hard to gather up.
I did not know schedule 10 was around. I would definitely go with the lightest stuff. UV is not a concern as it would be in the bilge. Inflatable is nice but what happens if it fails to inflate? A passive system of flotation seems best to me. Instead of larger pipes, I was thinking of smaller diameter pipes packed into various places.
On the blue foam, that wont absorb any water?

[Venchka]

Inflatable flotation bags are always inflated, or at least when the boat is in use. Inflated with hot air from the Skipper.

Beware of putting all the flotation in the bilge. You need flotation "up high in the ends" as has been stated by folks who know. So, if you put the flotation up high in the ends and some more in the bilge, the boat ought to be ok.

Wayne
In the Swamp. :D

[Bob Cleek]

There's no better flotation device than a terrified man with a bucket! LOL I guess you guys are talking here about sailing dinghys that are expected to be dumped with a fair degree of regularity. If that's so, there's nothing better than a couple of innertubes, one in the bow and one under the stern seat, inflated to fit. The rest of this stuff is really out there, guys! Then again, if you are THAT worried about your boat sinking, maybe sailing isn't your game. The possibility, however remote, that your keel may fall off and your hull split in two is what makes sailing exciting. Just remember the first rule of fun... if it's safe, it can't be fun. Dangerous is fun.

Now, if you want to talk about PVC pipe, it seems like it's time for another potato cannon thread! (Ah, for the good old days...)