Tuesday, November 24, 2015

To Foam or Not to Foam

So you are building a boat and wondering whether to put foam in the flotation chambers. I'll share my thoughts. But in the end, you have to decide.


Are you required to have flotation?

First, let's ask, "Am I required to have flotation?"

Do your own lawyering - review the applicable regulations and decide for yourself.

Me? I don't mass-produce boats for sale and I don't care what the regulations say.

Should you have flotation?

Whether required or not, should you have flotation?

Remember that you boat's hull is it's flotation. The hull is the primary flotation. Hopefully you have built a hull that floats.

If for some unexpected reason, your hull suddenly stops floating, it would be nice to have other flotation, such as secondary flotation.






The remainder of this post will use the term "flotation" to mean "secondary flotation."

I am not concerned with my hull suddenly not floating. I count on workmanship and seamanship to ensure that it floats. I have many boats without flotation and I am quite comfortable motoring, rowing or paddling without flotation. However, if during construction of your boat you encounter a convenient means to provide flotation, why not include flotation?

If you install lockers for storage, think about installing the locker access on the top and everything beneath being water-tight. That way, the only way water can get into the locker is through the top. If you have water that deep in your boat, you have bigger problems than the locker flotation..

Storing fishing gear and ropes in the locker reduces it's buoyancy but it still has some trapped airspace that has flotation.

You can't fill the locker completely with foam, otherwise it cannot be used for storage. Maybe you can fill it partially with foam.

A common flotation space is between the deck and the hull bottom.

I decided to use the space between my deck and my hull as secondary flotation. There are twelve separate bulkheaded chambers below my deck. I did not install any foam.



I also install a forward locker with a lid that will provide some secondary flotation.






To Foam or Not to Foam

Foam or airspace? 

Airspace or plastic soda bottles? 

Plastic soda bottles or ping-pong balls?

First, let's talk about the advantages and disadvantages of foam and airspace...

If you have a hull breach below waterline, it would be nice to have foam to minimize water intrusion. Of course foam would be nicer than air, obviously foam is the way to go!

But wait...what if you do not know about the leak? It's a pin hole and is slowly saturating your foam. It has been there for years. Then, one day, you think, "Gee it sure was hard pulling the boat onto the trailer. The boat seems heavier than normal." 

So you launch the boat and notice that the starboard stern seems to be lower in the water than the rest of the boat. This leak and saturated foam is not that bad since, well, you have been motoring around with it for a while and never noticed it until today. And even today was a good day of boating and you did not notice the list until pulling the boat out and re-launching. 

If a tree falls in the woods and nobody hears it, does it make a sound?

If a boat's hull leaks and it doesn't affect the boat, does the leak matter?

...not until the foam starts to rot. 

Now you discover that the entire flotation chamber is saturated with water and the foam is doing nothing more than keeping the water in. 

So you drill a hole to drain the chamber and three years later the water has still not completely drained from the foam and the foam is moldy and starting to rot your wooden boat hull.

As you embark on severely intrusive surgery to remove the foam (in medical terms, a foamectomy) you cuss the foam and wish you would have never installed it. You really wish your flotation chamber was just a sealed airspace.

Now let's flip the scenario... 

You are planing along at 25 knots when you hit a submerged steel shipping container. It blasts a hole 6-inches in diameter in your hull. After picking your teeth out of the steering wheel, you think, "Boy, I sure am glad that I have foam." So, in this case, foam was the right choice, unless...

You are planing along at 25 knots when you hit a submerged steel shipping container. It blasts a hole 6-inches in diameter in your hull. After picking your teeth out of the steering wheel, you think, "Boy, I sure am glad that I have bulkheaded airspace chambers."

In this scenario, foam is a good idea if you have no bulkheads. But if you have bulkheaded airspace chambers, is foam a good idea? Yes, until you develop a pinhole leak that you do not know about.

There is no clear-cut answer to the "To foam or not to foam" question.



What is foam?

The word "wax" represents many things. The moon has a "waxing" phase. You can "wax" philosophically. There is floor wax and candle wax. Ocassionally one mobster "whacks" another. 

Like the word "wax", "foam" is a generic term for many things. 










If you are wearing shoes, there is probably foam in the sole. If you are sitting, there is probably foam in your chair or sofa. 

Foam is a lattice with air space. Like a house of cards but the cards are glued together for strength.



The world's neatest foam is Aerogel. Google it or read about it in "Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World" by Mark Miodownik.

In "closed-cell" foams, each chamber is surrounded by six cards and there is no way out. Theoretically, water cannot move through closed-cell foams. In reality, regardless of what the foam salesman says, no foam is 100% closed cell.

In "open cell" foams, each chamber has an opening to other chambers and water can flow through. Although, due to the tiny size of the chambers and the surface tension of water, the water does not move easily through.






The most common types of foam used for flotation are rigid and flexible foams. Here is a description of the four common boat flotation foams.

There is lots of technical information on these foams but be leery of the manufacturer's information. They have a way of twisting the facts to enhance sales.

Urethane

Often called "urethane," polyurethane rigid insulation is commonly used for boat flotation foam. It is the coolest of all foams because it comes as a liquid aerosol in a can or a two-part liquid mix. You can spray the liquid into odd-shaped spaces and watch it expand. Or, you can mix parts A and B and poor the mix into odd-shaped spaces and watch it expand and fill the space.





If you mix A & B, move fast, it starts to expand and cure soon after mixing. And, don't mix and pour big batches. Use several small batches to avoid the expansion exploding your flotation chamber. 

It cures solid in minutes.



But, the liquid form is nasty dangerous toxic. Consult the MSDS and use PPE!!

Urethane foam has excellent resistance to liquid hydrocarbons (oil, gasoline, diesel, etc.)

Other than the toxicity of the liquid form, the down side of urethane is that it is open-cell and, over time, it absorbs water. If submerged, it will saturate in a matter of months. Once saturated, it will take months or years to dry out. 

I once took a saturated brick of urethane and dried it in a soil-drying oven. It took six months in the oven to completely dry out. When saturated, the water weighed ten-times the weight of the dry foam.

Urethane foam is usually white or orange in color. Its dry density is typically two or four pounds per cubic foot and its compressive strength is 15 to 25 pounds per square inch.


Styrofoam - Expanded Polystyrene

Like "wax" and "foam," "styrofoam" can mean a variety of things. With respect to boat flotation, the two common styrofoams are expanded polystyrene and extruded polystyrene. They are quite different.

Expanded polystyrene is the most common type of styrofoam. It is what foam coffee cups and styrofoam coolers are made from. It is tiny white foam beads stuck together. The beads are small but you can see the beads. If you crush it, it becomes are pile of white beads. It is often called "bead board"




Similar to urethane, it is made by mixing chemicals together and allowing the mix to expand and cure. The mixing and curing are done at the factory. The resulting blob is cut with hot wires into rigid boards. The boards are usually 2 or 4-feet by 8-feet and 2 to 4-inches thick.

Although not as permeable to water as urethane, expanded polystyrene absorbs water. It is kinda open-cell. The voids between the beads are connected for free flow of water. Although no foam is completely water resistant, the beads themselves are fairly water resistant.

The challenge with rigid board insulations is fitting them into odd-shaped spaces.

Styrofoam - Extruded Polystyrene


Extruded polystyrene is a type of styrofoam used commonly in wet environments. Although not completely water resistant, it is considered to be "closed-cell" and it is fairly water resistant. It takes years, maybe decades, of submersion to saturate it. It saturates faster under a thermal and vapor-barrier gradient. Once saturated, it practically never dries out.

Unlike the beads in expanded polystyrene styrofoam, extruded polystyrene is not granular. You cannot see individual grains.

It is commonly available in rigid boards that are usually 2 or 4-feet by 8-feet and 2 to 4-inches thick.

The Owens-Corning brand is pink.


The Dow brand is blue.


It is available in compressive strengths ranging from 20 to 150 pounds per square inch.

The challenge with rigid board insulations is fitting them into odd-shaped spaces.

Both expanded and extruded polystyrene foam have very poor resistance to liquid hydrocarbons (oil, gasoline, diesel, etc.). They melt into goo when exposed to gasoline.

Polyethylene

Polyethylene is a soft foam insulation. It is considered to be "closed cell" and performs well in wet environments. It is kinda hydrophobic - water don't like it and it don't like water.

Its most common use is tubes for pipe insulation but it is also available in sheets. For a research project I was provided chips of polyethylene that were made by chipping sheets. I don't know if the chips are available commercially.





Of the four insulations described, polyethylene is the best in wet environments. It is soft with no structural strength and very low density.

Polyethylene foam has good resistance to liquid hydrocarbons (oil, gasoline, diesel, etc.)

It can be expensive.

Alternatives to Foam

There are many alternatives to foam for flotation. Two that interest me are plastic soda bottles and ping-pong balls.

Plastic soda bottles are polyethylene plastic and they last forever. They are filling up our landfills and not degrading. They are available in sizes ranging from 4-ounce bottles to 2-liter bottles. You could use a variety of sizes to fit your flotation chamber. The upsides are they will probably last forever and they cost nothing. The downsides are they don't fit snuggly together and removal, if needed, would require intrusive surgery.




I don't know much about ping-pong balls but I am intrigued. They are plastic but I don't know about their longevity. They won't fit snuggly together but removal, if needed, would require only a small hole and a vacuum hose.






To foam or not to foam?

If you decide to foam, at least now you have some ideas about what foam to use.


Monday, July 20, 2015

Hully Cow!

Stitching is an awesome time in S&G boat building since your 2D planar pieces rapidly become a 3D boat. At one moment all you have are several flat panels. A few hours later you have a boat.

I usually call this moment "Stitch Day". However, working alone with panels that are 3 feet x 24 feet, this stitch job will take more than a day. Maybe I'll call this "Stitch Week"

Lowering side panels from ceiling where they
have been stored for a while



Lowering...




Separating and placing the side panels on the continuous deck



Getting close...





Really close...




Installing spreaders...





Got a few stitches in to stitch the side panels to the deck...

Working alone, I am having a bear of a time getting the panels lined up and held in-place then letting go to install a few stitches. 

One stitch at a time...


The top of the 9mm side panels is flimsy so I installed some temporary stiffeners. The future backer, knees and shear deck will provide permanent stiffening. I installed the temporary spreaders then used a level and plumb bob to get the panels and deck symmetrical. The temporary knee braces will hold it that way until gluing is done.

Temprorary stiffeners, spreaders and knee braces
Back to stitching. All stitches are coated with paste wax before installing. Epoxy doesn't stick to wax so the stitches are easily pulled after the epoxy cures.

Stitching the stem




Once the stitching is done, the gluing part of "stitch and glue" can begin. Gluing is applying fillets made of thickened epoxy then overlaying the fillets with fiberglass tape set in epoxy. 

There was a time when I would try to lay a perfect fillet, let it cure, sand it perfect then lay the fiberglass tape on top of the sanded fillet. Never again...

I prefer to install the tape before the fillet cures. This provides a primary bond between the fillet and the tape. But, more importantly, it means I do not have to shape my fillet perfectly. I can be lazy when shaping the fillet. I apply the epoxy-saturated tape while the fillet is still soft. I use my fingers (wearing latex gloves, of course) to shape the fillet after the glass tape is laid on top of the fillet. I work all of the air bubbles out of the tape at the same time.










Once the fillet and tape cure, the stitches are pulled.


Wubwails

I decided to install three rubrails on each side panel. The rubrails will serve to stiffen the 9mm panels and add some pretty trim. Two rub rails will be 11 and 21 inches down from the shear line. The last rub rail will be at the shear line. The rub rails will be installed using temporary clamping screws, installed from the inside of the side panel, so no screw holes show in the final rub rail.

Dry fit of lower rubrail. Masking prevents the oozed-out
epoxy from contacting the side panel.


I cut saw kerfs in the rubrails in the area where the rails must curve with the side panel. This makes bending the rails easier, prevents straightening of the side panel and reduces residual bending stresses in the completed rubrails. The kerfs are filled with thickened epoxy after the rail is installed.

Saw kerfs in lower rub rail. There is a mirror image of the
rub rail in the shiny side panel.




Saw kerfs in lower rub rail




Completed installation of starboard lower rub rail. Yikes that
side panel is dusty. Good thing I vacuumed the gluing area before
installing the rubrail.



Completed lower and mid port rubrails

With the lower and mid rubrails installed, the 9mm side panels are not so flimsy and I can remove the temporary top stiffener. This allows access to the top of the side panels and the knees and shear deck can be installed. I put in some temporary spreaders midway between the lower and mid rubrails.

New temporary spreaders. Screw holes thru side
panels are at the rubrails so no holes are
visible on the outside.


After spending 2 weeks getting the sheer deck installed, the side panels are now stiff enough that temporary spreaders are not necessary. I sure got tired of stepping over those things. 









It is time for another flip. First, mount some temporary supports and wheels.







Flip her.



Viola! That was too easy. 



A fly in the ointment! In my UV the Captain blog I concluded that I will omit UV protection from the BW. However, I have been approach by a friend who is very interested in buying the completed BW. I am willing to omit UV protection from my own boat but I am not willing to omit UV protection from somebody else's boat. So, with the possibility that the boat will be sold upon completion I have changed my mind and will apply UV protection.


After completing the boat bottom, the sides were lightly sanded to remove the sheen and provide a profile for the varnish to adhere to.

Sides lightly sanded

Two coats of Pettit Flagship varnish were applied tot he sides.




Completed bottom and sides





Completed bottom and sides


And don't forget the sculpture!




THE FINAL FLIP !!!

Wheel carriage in place







Tires in place




Up...





...and over





Time to plane and sand the tops of the inwhales and rubrails flush with the sheer deck then class the edge of the inwhales and rubrails.

Planing the top of the rails



Rails sanded flush with the sheer deck



Glassing the edges of the rails




The dross will be sanded
away later.



Dross removed from the sheer deck, weave filled, ready for varnish