Extra buoyance

Hi PAR, I could not resist to take a peep in how far the water has penetrated the 2 liter bottle. I had a big surprise. The empty bottle weighs 49 gram and the filled bottle 149 gram. I made a few cuts in the bottle and now after 2 weeks the weight is 3 gram more. This is because I could dry the outside of the bottle, but due to Capillary Viscosity‎, the water sticks in the crack. I am not too sure that with only a 2 liter bottle one can proof that the absorption is less than 1 %. But I am not unhappy with the result. Still 2 weeks to go. Have put it back into the water again and now it should stay at 152 gram. Bert

 

It was not disappointing, but what the sales person said, was sales talk, to state less than 1 % moisture absorption. From the photo you can see that it was kept for more than a month in dirty water with a heavy piece of metal keeping it, below the surface. The next photo shows after 6 weeks, the bottle had picked up some growth. I dried the bottle, cleaned it out and forgive me, also bashed it a few times hard on the wall to get the water out from within the gap created by the knife. Although, I am not too sure whether it was a very scientific exercise, but weighing after cleaning and drying, it as increased from 149/153 to 168 gram. When I placed my cheek on the gap and the peeled of piece of plastic, I could feel the moisture. Yes, I will definitely use it, as it will no doubt be beneficiary. I will however place a sensor in the compartment, to be filled with this stuff. I will then be able to detect whether I have a leak or not. Bert

 

I believe your math is way/weigh off. You shouldn't count the weight of the bottle, you are testing the foam.

You started with 100 grams of foam in a 49 gram bottle. The bottle still weighs 49 grams. The 100 grams of foam has absorbed 19 grams of water, which sounds to me like a 19% absorption rate.

Somewhere in this thread you said it would take $300 or £300 to fill the tanks with foam. If you get water in them, you have to dig it out and throw it away. That's 300 moneys in the trashcan. It is also not very easy to dig foam out of sealed containers. You'll probably have to cut some huge holes in the containers to do it.

Put a $10 6" round hatch in them and be done with it. It's the only simple way to tell if there's a leak.

 

Life is never that simple. The 100 gram of foam represent more than 2 kg/liter in seawater. Thus having absorb 19 gram of water somewhere between the cracks, means less than 1%. My wife always says, "I can prove anything with statistics, it depends what you want to hear". The salesrep is right, it is less than 1%, others will say no 19%. Yes I have round hatches in the extension, but need the guaranteed buoyance. Bert

 

I'm thinking your math is way off also. A cubic foot of air will displace about 60 lbs of water. If the foam noodles were 1 foot square by 5 feet long, they would displace roughly 300 pounds of water.

The area of a 4" circle is only 12.56 square inches, a 12" square is 144 square inches. The smaller area divides into the larger area 11.46 times, so if 300 is divided by 11.46, it comes out to 25.95 pounds of displacement for each noodle.

A 4" noodle may support a large person in the water, but that is because we are 60% water, which weight becomes neutral when we are in the water. Fat is also less dense than bones and such, so that helps a human's buoyancy. This is what I could find about that...

I don't know where that guy got his figures from, but if they are true, one of those pool noodles could float a lean guy that weighed about 370 lbs, but maybe 30 or 35 lbs of lead would sink it.

 

Oh, sure that's right. I was comparing to the weight of the foam, this is comparing to the weight of the water displaced.

Still, I wouldn't bother with foam. Will your boat sink IF water gets in the extensions? Does it stay in the water all the time? Are you way off shore where it's life threatening? Is your boat not constructed reasonably well?

IF I was to put foam in them, I would use chunks of expanded polystyrene or more likely 2 liter plastic bottles that can be easily taken out of the hatches. Then you can easily check for leaks. IF you do get a leak I assume you'll fix it right away and even if you can't completely fill the extensions full, there would be enough flotation to keep catastrophe away.

How big is this boat ? What is it constructed of?

 

I just found this thread and it very interesting, but I have to disagree with this statement.
I have an old German wine glass that is marked .25L. I drink one glass a night with dinner. Therefor to collect 36 bags of my favorite box wine requires less then two years! So Mr BertKu you must be a teetotaler to believe I'm a lush!
Cheers
Oh and please pardon if someone has already pointed this out, I'm not through with the thread.

 

I agree with you. in a 5 liter bag you can have 20 glasses of 0.25cl 36 bags x 20 = 720 days. I definitely think a sailor is going to wait that long. Or not? Bert

 

Well if I'm in a hurry it seems it would be pretty easy to knock that down to just 6 months. I mean two glasses a night, one with dinner and one watching the kabuki theater that passes for evening news then twist my wife's arm to share that drinking exercise and we're good to go!

 

In general, there is no sailor who is going to wait for 6 months.

SAM-SAM. I made a decision. I will be filling 2 liter coke bottles with foam, but cut the top with the screw top off and paint this area with waterproof sealing paint. In that way, it fills the area better with foam protected by plastic and further sealed by the waterproof sealing paint. I notice that a parallel test of foam directly submerged for the same time under water, absorbed 20 times more water over the same period. (PAR please note, you have been right) With the method as explained above, I hope to limit the absorption effect. It means that my extensions will have together with the boat closer to 100% buoyance. Good enough to discover at one stage of another whether I have picked up a leak, before the boat takes too much water on.

Calculation: original certified buoyance 75.8% (Maximum weight 580 Kg and buoyance volume of 440 Kg)
Old: light weight 220Kg (hull)
New dead weight. engine 40 Kg, solar panels 39 Kg, Metal brackets 22 Kg, weight extension 40 Kg, weight batteries 102 Kg, weight cabling 12 Kg, weight crew 3 x 75 kg = 225 kg, Misc. 20 Kg
Old volume of buoyance + new buoyance extension = 440 + 180 = 620 Kg.

Total dead weight 720 kg 86,1 %
I am much happier with 86%, than with 75%.

Bert

 

Interesting how people approach some things. Not being critical.

I figure if the flotation works for day or so, should be fine.

Noodles are easy, easily replaced, soft and quiet and low cost etc., match my sailing habits on smaller lakes and even crossing Lake Mich etc, which is the point, the sailing part, seems to me.

 

I made a mistake here. EPS, expanded polystyrene, or white beadboard, takes small balls of polystyrene, heats them up and sticks them together. That leaves spaces for water absorption.

XPS, extruded polystyrene, the blue or pink foam, confines the foam as it expands so the spheres are mashed together, leaving "no" spaces for water absorption. This is the foam I meant.

http://www2.owenscorning.com/literature/pdfs/10018681.pdf

But I think the pool noodles, made from polyethylene foam, are even better.

 

Every country has their own rules to go onto the sea. We have some stringent rules to avoid that other people risking their life's for silly errors, like low buoyance. Unfortunately I need the highest possible percentage for the re-certification of the boat. It is fine for local waters or rivers, nobody worries too much. Does that explain why I approach it differently? If I had listen to the sales representative, with his story of less than 1% water absorption, I would have had a problem one of the other time. Bert

 

Thanks for the pdf file, very interesting. I certainly will look at pool noodles and see what they cost and whether they really does not absorb water. If no water absorption, I may swing towards pool noodles. If some water absorption, I will go for my solution which should be good enough. Bert

 

Bert, Makes perfect sense to me.

Heck, I have no clue what states here require. I figure if Minnesota doesn't care, I don't care, long as they keep boat up until help comes...if it ever came to that.