Buoyancy questions [Archive] - The WoodenBoat Forum

Wayne Jeffers

10-02-2002, 09:55 PM

Salt water weighs 64 lbs./cu. ft. Fresh water weighs 62.5.

Figure the volume you'll be displacing with your flotation, and subtract the weight of whatever fills your flotation volume. Foam is maybe 4 or 5 lbs./cu. ft. Air is negligible weight.

For example: One cu. ft. of foam in sea water will give you about 64 lbs. minus about 4 lbs., or about 60 lbs. of buoyancy.

If you're going to use foam, make double sure it won't break lose when you need it most. I prefer to have it fully enclosed or supported in some other way, not just stuck to the bottom of the thwarts with Liquid Nails.

My own preference is for air tanks, because I don't trust foam not to soak up water eventually, but foam can work, too.

Wayne

Joe ( Cold Spring on Hudson )

10-02-2002, 10:35 PM

Here is the floatation I created for Annette after I capsized her and found out how well the floatation in the transom seat worked and how NOT having floatation in the bow causes the boat to capsize perfectly vertical, with no possibly way of righting the boat. I built 2 wooden boxes out of Oakum marine plywood. Screwed and epoxied with dense foam filled inside. I think it looks nicer than most flotation boxes under thwarts.
http://groups.msn.com/_Secure/0OAAAAGIUc0LmlFDKtqC!!5EH4wjDJZL85JBqwRFW3H0PvWvG0 bu!lGUP!ItRHdEIDKUOdQLDOjLjfssPOtCysi8AbABvAGcA/Flotation

[ 10-02-2002, 11:36 PM: Message edited by: Joe ( Cold Spring on Hudson ) ]

mmd

10-02-2002, 10:58 PM

The problem with air is that it is so easily displaced by water - in other words, you find out that your air floatation container leaks, usually when you are wishing that it didn't. Closed-cell foam is the norm. Pundits say the the maximum volume of air for the minimum volume of material to contain it is to fill the floatation compartment with ping-pong balls. :rolleyes:

My boatbuilder buddy Whammy has the local sailmaker whip up fitted white dacron covers for his "Bluboard" foam block floatation in his Herreshoff prams. They are zippered so the foam can be taken out to be dried and de-mildewed, and are firmly fastened to the underside of the thwarts with stainless dome snaps so's they can be removed easily. :cool:

Meerkat

10-02-2002, 11:15 PM

Some information on styrofoam at http://www.aeromfg.com.au/styrofoam.html especially about gluing.

http://www.hendersonmarine.com/Catalog/01-04%20Styrofoam%20Buoyancy%20Billets.pdf has some information on calculating floatation requirements for floating docks using styrofoam brand billets (blocks). 11.11 cu. ft. of foam will support 290#

EdenRose

10-02-2002, 11:34 PM

MMD,
As a matter of fact I have a Herreshoff pram and
I am trying to figure out how to add floatation to it too. Gardener says put it under the thwarts. It sounds like the way you suggest is
a good way to finish it off. How sturdy are these snaps?
I saw a similar pram to mine at the Port Townsend
boatbuilding school that simply lashed the fenders
under the thwarts when out rowing.

How do you determine how much positive floatation you need, assuming there is no designer to tell you?

David Tabor (sailordave)

10-02-2002, 11:35 PM

IIRC.... USCG regs state that if you are using air tanks for flotation they cannot be formed from some part of the hull (or words to that effect) IE if you're holed you don't want the air tank to leak! If you use air tanks they are "supposed" to be separate from the hull, IE double walled...or air bags. Check out this link; you can read the entire document on line and download

http://www.uscg.mil/d17/download.htm

EdenRose

10-02-2002, 11:41 PM

Meerkat,

Thanks for the foam links. Sounds like epoxy works good. I might use that under decks.
Making fabric bags for use under thwarts seems best for the foam that will be in the open.

Of course ping pong balls would be fun, but I want to hear water on wood not the rattle of
plastic balls.

mmd

10-03-2002, 12:35 AM

EdenRose, the placement of the foam under the thwarts will cause the boat to float upright, but almost awash. the snaps merely hold the foam in place, the floatation force is borne by the thwart. Each snap has a holding power of about 5 pounds, and a snap every 4 inches equals about 100 lbs holding force x three thwarts = about 300 lbs. That is more that enough to float the boat without popping the snaps.

The response from Wayne Jeffers is correct about calculating approximate "floating power" of foam. If your boat is wood, it has inherant floatation, too. Figure that your wood boat submerged weighs about 60% of it's weight on land. You want to add about 120% of this weight in floatation so the boat will float a bit higher than awash so you can bail. Say your boat weighs 200 lbs: 200 x 60% = 120 Lbs. 120 lbs x 120% = 144 lbs. Wayne tells us that foam provides 60 lbs floatation per cubic foot, so 144 lbs divided by 60 lbs/cu.ft. = 2.4 cu. ft. of foam should do the trick. Given the shape of the boat, say 40% of the foam under each of the aft and midships thwarts, and 20% in the bow works out to one cubic foot of foam at the stern and middle, and half-a-cubic-foot in the bow.

Now the disclaimer: I am "shooting from the lip" in the above example. The actual numbers (floatation per cu. ft. of foam, the percentage of floatation of the hull & foam, etc.) may be quite different than stated. Also, there are guidelines for such stuff available from ABYC, USCG, and here in Canada, from DoT Marine Safety Division. Seek and ye shall find. Please don't place faith in the ramblings of a sleepy naval architect who didn't check his regs because it is 2:30 am and he started work at 8:00 am yesterday and is going to do it all over again in a mere five or six hours.

Good night, all.

EdenRose

10-03-2002, 09:29 AM

MMD, Joe, Wayne et al,
I have posted several questions on this forum
while building this boat and I have to say
this is the quickest and most useful set of
answers (without a lot of digressions) I have received.
(Great looking photo Joe. I like the bronze knees
on the thwarts).
Thanks

Tonyr

10-03-2002, 04:05 PM

I have styrofoam under the thwarts (stern sheets, and two forward of that), which are formed like open bottomed boxes, so that water can drain freely, and the foam can dry. Did a test capsize this summer, and floated a bit bow down, but otherwise satisfactorily (i.e. could just bail fast enough to keep ahead of the flood from the daggerboard casing). We have since added a five gallon water container (empty!) under the half deck forward to give lift there.

The standard we used was to require that we could control and row the boat ashore when full of water, even if slowly.

The box/thwarts are glued to the hull and have contributed considerably to its stiffness. They do take up room, but look better than any other way of holding styrofoam than I know.

Regards, Tony.

Joe ( Cold Spring on Hudson )

10-03-2002, 08:09 PM

EdenRose Thanks for the compliment. I have to say it feels good to step outside the Misc. Thread and feel useful without any hassle.

Steve Lansdowne

10-03-2002, 08:09 PM

I know my solution may not look great, but I put "funnoodles" under my Whisp seats after cutting them to length. They are inexpensive, in the right color (I choose bright orange for safety), and can be tied on via ropes through the center hole. I put three side by side and then two side by side in the spaces above the three, and then tied them all together using a trapezoidal piece of clear plastic at each end through which I drilled holes for the rope. I then inverted these and tied them to the undersides of the seats, thus they are easily removed. Here's a photo.

http://www.imagestation.com/picture/sraid34/p7cc2bb2c90a68584410e30e9f6f860e5/fd381b69.jpg

[ 10-09-2002, 07:57 PM: Message edited by: Steve Lansdowne ]

Meerkat

10-04-2002, 02:20 AM

EdenRose;

That reference that Dave Taylor posted pointing at the Coast Guard requirements tells it all. I learned a few things from it, even though I had glanced at it before.

* Polyurethane is better then styrofoam generally.

* Sailboats are exempt (but it's a good idea to do it anyway)

* _All_ boats have to have a Hull ID (HIN).

This last one is the one that sort of surprises me!

I like the idea that you can mix up the 2-part polyurethane, pour it into your cavity (no cracks! ;) ), slice/level off the top, seal it with a plywood cover and fillet and tape it for eternity. I think I would seal the cavity with epoxy or some such first - and maybe consider using one of the truely waterproof epoxies rather than the everyday stuff.

(Excuse me while I think out loud and hope to get some responses...)
Now, if I could just figure out how to calculate the volume of a triangular space, I could hopefully put in that floatation in the bottom part of the Whilly Boat's bow and stern compartments and still have room for dry/sealed stowage. On the other hand, do I want to have access to those areas in the event of damage? What about a double wall at the outside edges (very light weight - doorskins?) and bottom filled with foam leaving the bow and stern stems (double-ender) accessable), leaving a space around the centerline accessable from a watertight deck hatch. That way, the spaces left would not use part of the boat's hull for the water-tight space and could thus pass the CG's requirement for a bouancy compartment (sort of a belt and suspenders idea). Same idea with foam cubes instead of expanded in place foam? Would that imply that I would have to have easy access to those compartments?

[ 10-04-2002, 03:21 AM: Message edited by: Meerkat ]

stan v

10-04-2002, 06:27 AM

Meerkat, here's what I did. I'm still in the process of rebuilding my 24' offshore fisherman, fiberglass or course. But the stringers, deck (sole) and hardtop are all wood, with epoxy. After fishing this boat for 7 years, I realized how little the storage was used, except for stuff that was seldom used. So I started filling up the rebuilt storage areas with foam. Lots of foam. What I have left is storage areas that hold rope, chain, fishing rods, and tackle (under my new rebuilt seats), and battery compartments. Everything else has been foamed. What's the worst case senario? If I hit a log while running offshore at 30 mph, I break the glass, but the foam in the compartment keeps the water out of the boat. Leaves me with drying out some foam, and repairing some glass. No big deal, and I don't have to worry about going down. Storage space, unless it's for safety stuff, is a waste. I keep an ice chest for fish, since we keep only what I want to clean and eat, and release most of what we catch anyway. Good conservative. :D

Wayne Jeffers

10-04-2002, 08:59 AM

meerkat,

I used the pour-in-place foam when I built my first boat. In the years since, I've come to believe this was probably not the best choice, although after 10 years I see no obvious problems.

Epoxy is resistant to water penetration; it is not waterproof. Even assuming the foam has zero water permeability, there is a likelihood of water collecting between the wood and the foam where it will keep the wood damp. Evidence suggests that even closed-cell foam can become waterlogged over time.

I've come to believe there is no adequate substitute for ventilation. Flotation can consist of air chambers, air bags, or foam, but I think it is wise to provide for ventilation and for possible replacement of air bags or foam. Pour-in-place foam does not allow for ventilation or periodic replacement, if necessary.

In the boat I'm just now finishing, I chose air chambers fore and aft with kayak-style hatches for ventilation. This may not be appropriate for all circumstances, but I will be sailing on inland lakes where there are invariably other boats nearby and that are small enough that we could swim to shore if necessary. The air chambers were mainly to ensure that the boat should be easily self-rescuing.

If I were sailing along the seacoast or on the Great Lakes, where I might have to depend upon the upturned hull to provide a place to climb out of cold water for an extended period, I would have chosen foam blocks of some sort.

As to the HIN issue, this is not something the CG is aggressively enforcing on homebuilt boats. ;)

Wayne

Matt Middleton

10-04-2002, 09:50 AM

Meerkat- here's a link where you can find the formula for the volume of a pyramid: Math for Morons Like Us (http://www.thinkquest.org/library/lib/site_sum_outside.html?tname=20991&url=20991/geo/solids.html)

Go down to the volume of a pyramid- that would at least approximate your bow and stern shapes, if I'm thinking correctly. You might would be better to use the area of a trapezoid for your "B" in their equation, since it better approximates your hull section. (Imagine the pyramid with a frame as a base, and the height being the distance from the frame to the inner stem.)

Here's my suggestion, for what it's worth:
Use your two part foam, but line the compartment first with plastic (big garbage bag or similar) so that the foam doesn't stick to the boat. Now you have a removable block of foam that occupies the most possible volume.

Now for the method of holding it in the boat:
Fasten cleats to the underside of the deck forward and seat aft, as well as the hull underneath. Attach the foam to a piece of ply, which is cut to fill the space between seat/hull and deck/hull. This can be screwed to the cleats with maybe only 4 or 6 screws, because the foam will mostly be held in place by the bouyancy forces when swamped, capsized or upright.

You would, of course, have to leave an area of the foam volume cut out so that it could slide past the cleats, mast, and anything else lurking under the deck and seat. The ply panel could be recessed, so you still have toe room and a bit more storage/floor space.

Does any of that make any sense?

Advantages would be:
No need for watertightness (which practically doesn't exist)
Foam can drain, or be removed to dry or replace if necessary
No white plastic watertight inspection hatches on your pretty wood boat
Also leaves boat reconfigurable, should you so choose, with minimal effort.

Disadvantages would be:
Careful forethought required when "casting" foam so that it remains removable in the desired direction- may have to insert temporary mold pieces to accomplish this.

Anyways, just a thought I had when I read your post. Good luck!

EdenRose

10-05-2002, 01:34 AM

I want storage and buoyancy, so rather than fill up both front and aft sections with foam,I am going to distribute it under three thwarts and
forward deck. My boat design asks for 240 lbs
of buoyancy and I think I can get that easily enough. I also intend to lash two large dock fenders inside the boat.

Todd Bradshaw

10-05-2002, 02:39 AM

Fun facts about pour-in foam:

First, when it goes off it gets REALLY hot. Trying to contain it inside a plastic bag probably won't work since the bag is liable to melt. On a boat with 1/4" planking, if you pour a block in the end of the hull, you probably won't be able to touch the outside of the hull until it cools down.

Second, the stuff can exert a whole lot of pressure on the hull as it expands. I've heard some really nasty creaking and cracking noises when pouring end tanks in strippers - the kind of noises where you don't know what it's doing to the boat but you just try to put it out of your mind because at that point it's too late to do anything about it. I've also seen it come shooting out of a small access/pouring hole and fly about five feet due to miscalculating the amount needed for the chamber. We always called it "Blow Foam" after watching it shoot all over the room.

Third, it's not very dimensionally stable. It quite often shrinks with age and it sticks well enough to the hull that it will take it with it, distorting the end of the boat. In the fiberglass canoe industry, this is quite common. The fiberglass bulkhead stays put and the hull sides forming the walls of the end tank behind it get pulled in. They're called "suck lines" and they don't go away. If you look at enough glass canoes, you'll see what I mean. Wooden boats are usually stiff enough to resist, but it could happen on occasion.

Fourth, the stuff will soak up plenty of water if given the opportunity. I had one fiberglass sailboat that I rebuilt where somebody had cut a hole in a flotation chamber and then let the boat sit with water in it. It took me two years to get it ventillated enough to dry the foam out enough that it didn't feel soggy - and it probably still wasn't dry on the inside.

Fifth, the fumes are really poisonous when the stuff kicks. Don't think for a second that you're going to stand around tooling it as it expands. You pour it, leave the area and come back later to see what happened. It's not like the stuff in the spray can that you get at Home Depot, this stuff is "Industrial Strength".

Am I saying that it's a bad product or that nobody should use it? No, it can be quite handy and safe to use in kind of a toxic, stinky fashion, but before using it, you need to know what you're in for. If I had just completed a fairly lightly constructed boat, like a glued lapstrake, I'm not sure I'd reach for the big can of blow foam.

ion barnes

10-06-2002, 06:23 PM

Just about every kind of foam is hydroscopic or they will absorb water. Also they are easily damaged by UV and just being banged about. I was told by the guys from Glacier Bay refrigeration that blue SM styrofoam will not absorb moistue. I have a piece that I glued together as a test with epoxy and doorskin ply and left to set with a bend of several inches . When cured for a couple of days, I could stand in the middle of the arch and it only deflected an inch! The arch is about 28" long and 4" wide. Says something for the shear strength of the foam and poor quality ply. anything else?

Matt Middleton

10-06-2002, 09:57 PM

Todd- I guess that two-part stuff does get pretty hot. I had remembered my college's SAE Formula team creating molds for seats by filling a garbage bag with foam, and sitting in it for a while until it started to set. Maybe they were using the foam-in-a-can from HD- Great Stuff is a brand name I may or may not be remembering correctly.

Does that stuff continue to expand after it sets? I was thinking you could pour it (or whatever foam you'd use) in to the boat before the decks were on, so it could expand upward. You'd then trim off the excess.

It's definitely messy stuff, though, but I think the end result would be worth the hassle of using it.

Ionbarnes- what is blue SM styrofoam? What's it used for?

Matt Middleton

Todd Bradshaw

10-06-2002, 11:08 PM

Matt,
If you sit on a garbage can full of the stuff sold for boat flotation, you'll have some very interesting explaining to do when you get to the burn unit. They must have used the spray can type for making seats, which is much more docile as it goes off.

We were usually pouring foam into a mostly sealed chamber and through a fairly small access hole. If you have a big open-topped area to fill, most of the excess might just go up, where it could be trimmed off later but I'm not sure it all would. It always seemed like it exerted a lot of outward pressure and the reaction is extremely fast (hold the mixing can a few seconds too many and you have a serious problem). It's almost like the top of the blob skins-over and limits upward movement before the stuff inside has completely finished expanding. I don't know the exact mechanics of the reaction, but that's the impression I always got. I did see a plastic duckboat yesterday where they had just stood the boat on end, poured the foam into the end, let it expand into a blob with a domed top and painted it to match the inside of the boat. Not the most classy approach, but at least it didn't blow out the hull/deck seam, so perhaps it works OK if you have a big enough open top on the compartment.

The other option would be to do several smaller pours to eventually fill the area. It might be a bit more controlled. The expansion is over in a few minutes and that's as big as it will get. Shrinkage over time may begin immediately and continue slowly for two or three years.

Joe ( Cold Spring on Hudson )

10-07-2002, 06:39 AM

WOW Talk about thinking the same kinda thing at the same time. This weekend wile roaming around Home Depot I saw a can of that Foam in a Can "Great Stuff " and was wondering about its buoyancy properties. I'm rebuilding a Plywood Weekender Sailboat and there is no floatation that I can find. So I'm thinking of drilling some holes in the coaming ledge and the seats and spraying that foam in there just to have some bouncy. What do ya all think? Remember this isn't a big buck Mahogany on frame sloop its a 20 year old plywood sail boat with a lot of damage.

Wayne Jeffers

10-07-2002, 08:12 AM

Joe,

I think you'll find the foam-in-a-can is tremendously expensive for flotation. Read the label of the can and you will note that it expands only to two or three times it's original volume. Since the can is only about half full (the rest being gas for pressurizing), for three or four bucks (or whatever a can costs these days) you get a hunk of foam that's not much bigger than the total size of the can.

I came to realize this a few years back when I thought I would improve an Igloo ice chest where the lid was hollow molded plastic, without insulation. I drilled several holes around the edge and shot in several cans of foam. I never did get the lid filled and realized I was wasting my money.

You should be able to find sheet styrofoam insulation. It's a lot cheaper, if there's a way to open up things enough to get it inside. The two-part pour-in foam would be a lot cheaper than the foam-in-a-can.

Wayne

ion barnes

10-08-2002, 01:44 PM

Blue SM stryfoam is used in house construction. Nothing is ever cheap! Its all relative to each other. Spray-in-a-can is expensive for large areas, two-part foams are marginally cheaper I think, and yes they do create heat when expanding so add in small quantities , do not try to contain the excess it will not increase the floatation capability. the physical dimensions of the compartment is what you have to work wimth and thats it. As I said before everything else is hydroscopic, so for a real uptown piece of work, blue foam is the way to go. Cheaper you say? OK when you go to Home Depot , look at the other foam boards that are available. PS If your structure is ( ie. seatbox) is lightly constructed to contain the expanding foam , Trying to contain it will break the box, or deform it

EdenRose

10-08-2002, 09:56 PM

Is Blue SM styrofoam the best product to use?
How do you compare buoyancy between products.
Is it the difference between the weight of
the product you use to displace water and the water itself? I guess styrofoam would be
close to the weight of air.

mmd

10-09-2002, 12:17 AM

The critical part about foams is their resistance to absorbing water. Waterproof foams are referred to as "closed-cell" foams. The blue construction foam referred to above is used to insulate concrete building foundations below ground, and is one of the better foams for floatation due to it's high impermeability. There are less dense foams available, but most absorb water too readily or are too expensive. The blue construction foam is readily available in pretty large thicknesses, is relatively inexpensive, and does the job.

EdenRose

10-09-2002, 11:50 PM

Good, I will grab blue foam from Home Depot.
Thanks for all the valuable help.

ion barnes

10-10-2002, 01:52 AM

Eden Rose, The thing to keep in mind is, KEEP THE AIR CHAMBER FULL OF AIR. The purpose of the foam is to contain air. Its like having a box full of ping pong balls but on a minature scale. The volume of the box dictates the amount of weight it will float minus the weight of the foam or whatever you choose to use. You may find reference to some foams as 2lb or 6lb foam and this refers to the weight of one cubic foot of foam. What you need to be aware of is they will all support the equivilant of one cubic foot of water, minus the weight of the foam which is minor. As a real cheap alternative and I mean THIS IDEA IS REAL CHEAP!! Take a garbage bag and fill it with styrofoam peanuts and tie off the end and stuff it into the seat cavity. BE WARNED OF IMITATION PEANUTS. IMITATION PEANUTS are made of potatoe paste and melt when they get wet! They resemble cheese twists without the veg dye or flavouring. They also dont squeek like the stryo ones. In doubt, put a couple under the tap briefly and watch! Packing peanuts can be found anywhere someone is shipping or receiving. Many places are looking for a place to unload them and your thwart box is a more useful place than the landfill. Right?

mmd

10-10-2002, 09:12 AM

ionbarnes, my concerns with packing the floatation compartment with styrofoam peanuts are as follows:

1.) You usually have no way of knowing whether the styrofoam is closed-cell foam or not, therefore you do not know if the peanut will eventually absorb water itself.

2.) The peanuts do not pack together tightly, leaving airspace between them. This is called permeability, and when the boat is submerged these air pockets will fill with water.

If the styrofoam peanuts when packed have a permeability of 15%, and the styrofoam has a density of 2 lb/cu.ft., then the best you can expect of its floatation ability is:
64.0 lbs (weight of salt water per cu. ft.)
- 2.0 lbs (weight of styrofoam)
- 9.6 lbs (loss due to permeability)

equals 52.4 lbs floatation per cu. ft if the foam is closed cell type.

This is the equivalent of foam floatation of a density of 11.6 lbs/cu.ft., which is rather heavy. If the styrofoam is not closed-cell type, it is reasonable to assume that it will eventually absorb up to 20% of its volume in water, reducing buoyancy by a further 10.9 lbs/cu.ft., giving it an effective density of a whopping 22.5 lbs/cu. ft. which puts it on par with a block of white pine as a floatation material.

Sorry to rain on your parade, but the ambition of floatation materials - and regulatory bodies' rules - is to predict with confidence that the floatation volume will exclude all of the water all of the time.

EdenRose

10-10-2002, 09:44 AM

MMD,
Darn, I was hoping to get rid of the thousands
of packing peanuts Harbor Freight sends me
every time I get an order of C-clamps. They somehow always get out to the box and fly all over the yard.

mmd

10-10-2002, 09:54 AM

They make great beanbag chairs. A local kennel uses them for mattresses in their doghouses. Blow 'em into the spaces between the beams in your shop ceiling as insulation. Our local solid waste handling facility recycles them.

Ian McColgin

10-10-2002, 10:32 AM

I'm a big fan of pour in place foaming. Filling the space with junk, whether peanuts or resealed soda bottles, is not an efficient use of the space as there's unlikly to be more that 50% of the space really devoted to bouyance. You can easily use up 3 cubic feet of boat interior to get barely 100# floatation.

The stuff is nasty if it soaks up afterwards. yopu'll know if you keep thinking that a male cat sprayed your boat.

Full pours are tricky as it gets so hot and expands so fast. Even with releaving holes, the first pour I did lifted the deck off with me standing on it, and that was just the bow of a little dory. And it was so hot I feared fire.

I keep nice little jars - just about 4 oz each - one for each part. Fill each jar. Pour into a paper bucket. Stir with paint stirrer on electric drill for maybe 15 seconds max, and pour. Repeated little pours can be made to blend nicely with each other if you make each new one into a valley left by old ones.

Even when all the foam appears to be out, there's some left. If you stack the used paper buckets on their sides, you'll get some entertaining tounges hanging down. Use them to decorate the jack-o-lantern.

G'luck

Tom Lathrop

12-10-2004, 06:46 PM

Before using foam in boat, I tested the blue styrofoam that everyone's talking about for water absorption. I cut pieces as large as could be sunk in a 6 gallon mud bucket, laid some lead on top and filled with water. Of course, I weighed the foam on a digital scale first. After several months I remembered it and after drying off, weighed it again on the same scale. There was no difference to the nearest tenth of an ouce.

This says to me that the closed cell blue styrofoam is a good material for floatation. From other experience, I know that the white foam used in portable coolers, packing material, etc. is definitely prone to water absorption. Peanuts fits that category also and much of this stuff is biodegradable these days.

I also epoxy coat the bluefoam just in case something like gasoline comes in contact with it.

11-03-2005, 07:33 PM

we used to tip wooden rowboats all the time when I was growing up. They never sank and,further, we learned how to get all the water out in a reasonable time. And! no flotation in them!qm

ssor

11-03-2005, 08:45 PM

Great stuff canned foam is a fine adhesive for blue extruded styrofoam. just cut the sheets to fit and squirt the canned foam in around it. use a little 3M spray adhesive to attach polyester cloth to the foam and paint the works with acrylic paint.

Alixander Beck

06-17-2006, 11:32 AM

I have heard of using 2 litre bottles as bouyancy. I am researching this application for an Enterprise Dinghy that I have. The idea is to fill the for and aft bulkheads with many of these 2 litre bottles.

the percieved advantage is that the bulkheads will be able to remain breathable and the bouyancy will not deteriorate.

I imagine it is much like the ping-pong ball principle and in fact I may use those to fill up the spaces around the bottles.

JimConlin

06-17-2006, 02:45 PM

The last time I felt (USCG regs) the need to put buoyancy in a dinghy, i got real simple and cut ply panels to fit under all thwarts, bonded a 2" slab of blue (or was it pink?) styrofoam to 'em and bonded a strip of appearance-grade ply to the visible faces of the foam. These assemblies were screwed up into the thwarts. Cheap, effective, and very quick to do.

The current project is a lightly built trimaran and if it's holed the forward sections of the floats are by far the most likely place. I'm thinking i'll stuff those sections with 2 liter beverage bottles..