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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction
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  #1  
Old 06-28-2010
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Small boat floatation?

Hi,

We have owned a Marshall Sandpiper for 30 years. We love this huge little catboat. It has been sailed in the Gulf of Mexico and the Bay of Fundy and for the past 15 years has enjoyed the waters off Mt. Desert Island, Maine. Fun, safe, easy, spacious, attractive,... We enjoy it very much. BUT!

A crack appeared in the stbd seat where my butt resides when motoring. We have a small obm on a bracket mounted on the transom. Perhaps 30 years of supporting an ever increasing load finally resulted in a minor failure of the fg surface? Last July I taped over it to exclude rain and after last season I explored this fissure. I found a layer of saturated 1/2" balsa under the seat surface. Further investigation revealed that the space under the balsa sandwich contained planks of bead board that were so wet they dripped water when I was removing them (after considerable demolition of the seat). The bead board was so wet and heavy that it would break into short sections as I lifted it out of the boat. 4 large trash bags filled with very wet bead board were ultimately recovered. I am not a small person but I could only carry one of these loaded bags at a time they were so heavy with water. I intended to weigh them but alas...

I have since poured marine foam into the spaces under both seats. I have the replacement balsa ready to install and am hoping for an early July launch. I will share some pictures later.

What concerns me is how little flotation this would have offered if we had needed it to keep the hull afloat!! How did it get so wet? It was useless!

The construction of this fine little boat involved glassing a liner into the finished hull. The liner is the cb trunk and the seats with a contiguous floor between them. Before the liner was installed it was fitted with 2" x 6" bead board planks running the length of the seats roughly "filling " the space under the seats. This floor established the roof of the bilge space. This connection of the space under the seats with the bilge provided a chamber with 100% humidity and ultimately wrecked both the bead board's buoyancy and the balsa's integrity. Both seats were in the same condition.

When I began pouring foam into the space that defined the seats it would flow beyond what I thought were the seat spaces into this space under the floor. Because the foam is so reactive its flow was limited but I am sure it sealed this gap. It certainly threw off my calculations for determining foam volume for just the seats.

We now have a Sandpiper with seats full of closed cell marine foam (2 lb. / cu.ft.). We also have a little boat with a foam sandwich construction that will be lighter and I am guessing a little stiffer. It will now deliver some buoyancy if it is ever needed. The bilge volume will have been reduce a little aft of the cb trunk. No foam is visible in the bilge where the lead sits. If the hull is ever holed under the seats it will not be catastrophic since the space is full of foam and no path remains to the bilge.

How many small boats are out there with useless flotation? A very large number I am guessing.

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Old 06-28-2010
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There are probably a very large number of boats with bad floatation chambers, whether they're filled with water-logged foam or wood or just leak. This happens on Boston Whalers all the time, and they're advertised as unsinkable.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
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—Cpt. Mal Reynolds, Serenity (edited)

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Old 06-29-2010
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pleas post photos, this is usefull modification tips.

I know thers a few places in my boat id like to spray foam into.
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Old 06-30-2010
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I will post photos as soon as I am done. It was an interesting problem and if seeing it will help somebody else correct a potential life endangering problem like this I will be most happy. What I hoped I would do by adding this post was alert folks who assume their little boat has flotation, that it may not! One of the very attractive things about a catboat is its safety. With a barn door rudder that doesn't extend below the skeg and its beam to length ratio, the boat will usually round up before it capsizes. This is an important feature in these cool waters off the coast of Maine. To discover that my boat would have probably gone to the bottom if it had capsized was disturbing. I was expecting that part of the design and construction was sound since there was no way of inspecting it without considerable demolition.

I poured this foam. That process has pitfalls and I will be glad to discuss what I learned if someone wants to send me a message.

I have also sprayed foam. For the catboat application, I was just filling the spaces that are the seats, a pour was adequate and much less expensive than a spray kit. A quality spray kit will allow you to fill almost any void completely and quickly with minimal mess. I filled the space under the cockpit floor in a Rhodes 22 with a spray kit. All that required were two, 2" holes. With the rest of that kit I filled the voids between the deck and the liner and it resulted in a very positive flotation calculation for that boat.

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Last edited by downeast450; 06-30-2010 at 05:24 AM. Reason: correction
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Old 06-30-2010
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Be aware, that unless the poured foam is encapsulated in fiberglass, it will eventually either breakdown or absorb water... That is just a fact of the type of material it is.
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 06-30-2010
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Yes, anyone who plans to use foam on a boat for flotation needs to understand that it requires protection from water, perhaps air (Ozone) and UV. It would be acceptable to foam an icebox to improve its insulating capabilities without worrying about encapsulating the added foam. I plan to pour some foam around one of ours. I will build some baffles to constrain where it goes but encapsulating it is not a concern in that application.

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Last edited by downeast450; 06-30-2010 at 06:51 AM. Reason: content
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Old 09-17-2010
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Quote:
Originally Posted by sailingdog View Post
Be aware, that unless the poured foam is encapsulated in fiberglass, it will eventually either breakdown or absorb water... That is just a fact of the type of material it is.
I am not sure this is fact. My Etap 26 has a foam cored rudder. There was a large piece missing from the trailing edge of the rudder just below the water line. It was caused by ice floes during the 25 years the boat remained on a mooring, with one week out of the water every two or three years. I took the rudder apart, and found water in some voids not actually foam filled. I chopped out all the foam, and ALL of it was DRY! None of it was waterlogged.

My entire boat is foam cored. I have drilled holes check for water. I have found water in voids under the foam many places. Digging out some foam though it is always completely dry. Putting what I dig out in bucket under water, and it doesn't seem to absorb any.

Gary H. Lucas
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Old 09-19-2010
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If you need NONSTRUCTURAL foam for flotation, one alternative are the spray cans from the hardware store for filling cracks around windows and doors in a house. For big areas, styrofoam billets from the lumber yard can fill most of a space and the spray foam will fill what's left and hold everything in place. You can get expanding foam or non-expanding foam. It's cheap, quick and easy
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Old 09-22-2010
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Gary—

ETAP themselves say that the foam they use will absorb water gradually, up to 5% by weight. Their foam, being structural, is probably heavier and more resistant to water absorption than the foams used in other boats. AFAIK, the denser the foam, the more resistant it is to water absorption, since it has less air filled spaces in it.

From an article on an Etap:

Quote:
It should be noted that even closed-cell foam tends to absorb moisture over time, which will add weight to the hull and decrease the flotation qualities of the foam. According to Etap, long- term tests have shown that the foam the company now uses will absorb a maximum of 5 percent of its volume. In the 38i, this represents about four gallons or 32 pounds of water.
I doubt you'd notice if the foam had absorbed even the full 5% that ETAP says is possible.



Quote:
Originally Posted by GaryHLucas View Post
I am not sure this is fact. My Etap 26 has a foam cored rudder. There was a large piece missing from the trailing edge of the rudder just below the water line. It was caused by ice floes during the 25 years the boat remained on a mooring, with one week out of the water every two or three years. I took the rudder apart, and found water in some voids not actually foam filled. I chopped out all the foam, and ALL of it was DRY! None of it was waterlogged.

My entire boat is foam cored. I have drilled holes check for water. I have found water in voids under the foam many places. Digging out some foam though it is always completely dry. Putting what I dig out in bucket under water, and it doesn't seem to absorb any.

Gary H. Lucas
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 09-27-2010
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I ended up ripping out cockpit sole of my father's center-console OB in order to remove the saturated poured foam. I dug it out with a turning spade, about 20 pounds per shovelfull. I've replaced it with blue styrofoam billets, cut to fit in the spaces, and have rebuilt the deck. It's now about 1200 pounds lighter. My daughter's looking to go waterskiiing with the 55hp motor instead of trolling.
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