The foamed dinghy argument...

I found this interesting and thought it was a good idea. Apparently the people in the comments are quite offended.

What say you?

He wrecked the boat in my opinion.

The foam only adds weight, not bouyancy, making the boat even more overweight.

The foam is not waterproof as far as I know and the can foam I experimented with actually acted like a sponge if water made it past the harder outer coating.

The push in plastic caps are probabky not watertight so water will probably get to the foam.

If you are going to do it, use pour in foam made for flotation.....but remember it will not increase basic bouyancy, just increases rigidity and unsinkability.

How can foam reduce buoyancy when it’s used in large blocks for floating piers? All those are, are big blocks of foam encased in plastic.

Read what bouyancy really is.

Its about the volume of water displaced. Don't change the volume, add weight and the boat sinks deeper. They would have had to spray the foam on the outside of the hull to increase the volume with a lighter than water material to increase bouyancy.

The foam under the dock theory is probably what the two wannabe naval architects in the video thought too.

Probably.

I really don’t care one way or the other. I just posted it for discussions sake.

Plenty of boats use foam for positive flotation, however I don't think that increases load. It only prevents it from sinking when swamped. What they've done is possible reinventing what Boston Whaler did decades ago, but not actually solve their problem at hand.

Adding positive floatation will not increase freeboard, allow the vessel to plane easier or increase capacity or load.

When I’m thinking about flotation i use 60 pounds of floatation per cubic foot of trapped air. I think it’s actually a little more. If the space is filled with foam, you have to reduce the bouancy by the weight of the foam. Flotation foam seems to run between 2 and 4 pounds per cubic foot.

You must use closed cell foam or it will absorb water and become useless. I think all spray can foams are open cell foam. If anybody knows of a closed cell spray can foam, please let me know.

Well, I just learned something new.

That's another way to ruin a boat!

The scary part is the two wannabes actually sound like they know what they are talking about.

Enough that others would folllow their very flawed reasoning and procedures.

psneeld said:

Read what bouyancy really is.

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Here:

Stability of Boats and Ships


(It's imaginary)

I've been using closed cell expanding foam in voids for 40+ years. Available as a spray or mix and pour. It doesn't absorb water, bonds itself to materials it's in contact with, can be easily shaped and comes in different weights per cubic foot. I most commonly used it in spaces under floors in fiberglass I/O drive boats. I normally us 2lb/cu.ft mix. It quiets the boat, stiffens the floor and provides a space that can't be flooded. Hull full of water still floats. When a bottom is damaged, any water is stopped within inches of any opening. It also makes repairs easier.
I carry a 16' Bayliner I/O, open bow with a foamed in bilge. I don't think the foam added 50 pounds. The boat is quieter, especially in pounding waves, the hull stiffer, and the new floor is supported.
I also used it in new steel commercial boat construction for insulating and sound deadening. A foot thick or more around fish holds and 4"-6" thick around crew areas. In a completed hull, in the galley (over the engineroom), with several diesels running, no engine noise except the outside dry exhaust. Easy to maintain crew area comfort levels and -20°F in the holds.

Fresh water weighs 63 pounds per cubic foot.
Salt water weighs 64 pounds per cubic foot.
Air has the buoyancy of the water it displaces minus .08 pounds per cubic foot (weight of air).
Basically there are 2 types of foam, open cell and closed cell. Open cell absorbs water; closed cell doesn't. Open cell foamed boats will continue to increase in weight over their life as they absorb moisture from the air. Moisture will find it's way past the plugs.

Ted

Somehow those guys remind me of the old Sven and Ole jokes. This one comes to mind:

Ole and Sven went fishing one day in a rented boat and were catching fish like crazy. Ole said, "We better mark dis spot so
ve can come back tomorrow and catch more fish."
Sven then proceeded to mark the bottom of the boat with a large 'X'. Ole asked him what he was doing, and Sven told him
he was marking the spot so they could come back to catch more fish.
Ole said, " Ya big dummy, how do ya know ve are going ta get da same boat tomorrow?"

Foam filled boats? What about Boston Whalers? They seem to make it work to the point where they're "The Unsinkable Legend".

Foam is often a good thing, but filling a hull with it doesn't increase bouyancy until you go from normal conditions to some level of flooding.

BWs included.....

I didn't notice them saying anything about making the boat more buoyant. The goal is just to make it more rigid, which they seem to have accomplished. The long term question will be whether the spray foam pulverizes from use and the boat reverts to its original flexing.

They're fishing in the rain with silicone seals on holes to open cell foam. The water will enter and be retained by the foam and the boat will become heavier and heavier.

It's not a matter of IF it will happen. It's more of an issue of WHEN.

Double skin plastic/poly dinghies are popular here as tenders for hire/charter boats. I used to use the marinas spare ones occasionally,though no idea if they were foam filled. But many definitely held water between the skins, to a greater or lesser degree,and they rowed like it, directionally unstable. Often felt way heavier than a 10ft dinghy.

ssobol said:

I didn't notice them saying anything about making the boat more buoyant. The goal is just to make it more rigid, which they seem to have accomplished. The long term question will be whether the spray foam pulverizes from use and the boat reverts to its original flexing.

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At the very beggining, he discusses too much weight to carry and it being a problem. He says he is looking for a little more bouyancy......then at minute 9:14 I am pretty sure the second guy says the bouyancy is better than before after specifically being asked hows the bouyancy.

While it may not have been the only objective, both guys lack the badic understanding of it and are going out on a limb modifying boats without it...or even the most basic concept of the right materials for the job.

psneeld said:

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While it may not have been the only objective, both guys lack the badic understanding of it and are going out on a limb modifying boats without it...or even the most basic concept of the right materials for the job.

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I find it interesting that you have attacked THEM more than the idea.

That’s because while the idea is incorrect, those guys are idiots. And of the worst kind too: totally unaware and certain they aren’t.

psneeld said:

At the very beggining, he discusses too much weight to carry and it being a problem. He says he is looking for a little more bouyancy......then at minute 9:14 I am pretty sure the second guy says the bouyancy is better than before after specifically being asked hows the bouyancy.

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That was the thing that struck me. It is obvious, at least to any TF members, that simply adding foam to a (formerly) sealed airspace will not increase buoyancy.

toocoys said:

I find it interesting that you have attacked THEM more than the idea.

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Well, maybe because they are the ones that are promoting such a stupid idea? It isn’t their fault they are ignorant I suppose.

toocoys said:

I find it interesting that you have attacked THEM more than the idea.

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That doesn't strike me as an attack on them as much as it is a critical analysis of the modificationss they made to the boat which will not accomplish their objective of greater buoyancy, increases weight, provides a media to absorb and retain moisture thereby increasing weight more in the future and will ultimately devalue the boat.

When I rebuild my dinghy, I staffed with foam from old/use life jackets. It cost me $1 a piece. Why use expensive junk that soak the water?

These guys were mostly interested in stiffening up the dish-panning deck, even though they misused the term of buoyancy. I was very amused at the end when the guy wiggled back and forth with the boat in the water saying how much better the boat felt because until the open cell foam absorbs a lot of water, the boat only weighs as much more than it originally did by the net weight of the 12 cans of foam they put in it. They clearly misunderstood the concept of buoyancy.

Boston Whaler developed their legend while designing into their radically new cathedral hull boats the added weight of the closed cell foam. They are indeed heavy boats for their size. They did not add "buoyancy." They simply eliminated the empty places previously filled with air where water could fill the space with buoyant foam.

I am an old Navy trained salvage officer, and I know from buoyancy. I am most amused with this one. Glad somebody posted it.

toocoys said:

I find it interesting that you have attacked THEM more than the idea.

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The job didnt do itself. They did the job which is based on a false premise. Liability will be with them, not the job.

toocoys said:

I find it interesting that you have attacked THEM more than the idea.

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no point is attacking the idea, it sunk before the launch.