Foam Floatation

[Freedom77]

I just read the article about the V-23 that sank on the lake. Sounds like there wasn't enough foam floatation aboard. Manufacturers put the floatation in to keep boats from sinking all the way. MacGregor claims their boats are unsinkable. So was the Titanic. When I Got my V-25 the bow was packed with large blocks of foam. I cut them into smaller pieces and added more foam under the V-berth. I also packed foam blocks in areas which were not good for anything else, i.e. under the cockpit sole and under the stern quarterbirths. Every time I get a piece of electronic equipment I try to find a place to put more foam. Better safe than sorry. Fair winds...

 

[shine]

Thats a good idea. I think I will do the same thing with my mac 21.

 

[Timo42]

:dance:Something we can agree on.

One suggestion would be to wrap the big foam blocks in heavy plastic sheet and duct tape, keeps the mess down and the boat cleaner.

 

[Freedom77]

Hey Timo42, great idea!!

 

[timebandit]

Mine were smelly and dirty so I washed them in a little bit of dish soap and bleach and when dry painted them with latex house paint, white.

Something to remember-------

If water does not come in the boat will not sink so in bad conditions, keep all the hatches and the pop top locked down and you will be just fine.:dance:

Think of it like a "BLEACH BOTTLE" with the cap on after all that is what the REAL sailboat owners call us.

 

[Freedom77]

Good advise. You can fill the cockpit of a Mac to the top with water and it will drain in a matter of minutes. I did it once in my driveway just to test it. It's also a good idea when you put the poptop down to burp the corner to get the air out and seal the lid. Fair Winds...

 

[rgranger]

Hey all

I restored a V222 this spring. Rats had made a home in the foam and it was full of fecal mater and urine.

So.... not worth keeping the old foam.

I went to Home Depot and got some of the 4' x 8' x 3" pink foam boards (foundation insulation). That stuff is nice. It is one solid piece of extruded styrofoam so no little balls of foam coming lose and getting all over the cabin. And it is pre-scored so it breaks nicely into 2' wide strips. Cutting it with an exacto knife is a piece of cake. I attached a ratchet tie-down strap to the stringers under the cockpit sole and filled it in with these pink boards. Then tied it all in place with the ratchet strap. That way it won't come lose and float about if I ever do fill her with water.

I also once read a post where a guy used the expanding foam and put it into 30 gal garbage bags, placed the bags where he wanted it and it expanded to fit. The garbage bags were so it would not stick to the hull wall in the event he ever wanted to get it back out again. Seemed like a nice trick ... maybe one I'll try someday.

 

[r.oril]

All this talk about foam made me look at my 26D. I found some under the forward berth and some in the radio compartment. Don't think this enough? I like the foam in a bag idea from Timo.

 

[Doug J]

Should be more in the cockpit coamings, and under the cockpit seats.
Any styrofoam I remove, I replace with closed cell foam.

 

[Fred]

I figure that a 4'x8'x3'' foam sheet displaces 8 cubic feet of water @ 62 lbs/cubic-foot would give you ~500 lbs of buoyancy. For a V25 you would need about 2500 lbs of buoyancy thus you would have to install 5 such foam sheets. Does that make sense?

 

[Sumner]

I figure that a 4'x8'x3'' foam sheet displaces 8 cubic feet of water @ 62 lbs/cubic-foot would give you ~500 lbs of buoyancy. For a V25 you would need about 2500 lbs of buoyancy thus you would have to install 5 such foam sheets. Does that make sense?

I've wondered about that, but I think that it has to do with things don't weigh as much in the water since they displace water and aren't as heavy as the water they displace, so they just need a little help to stay above the water. Kind of like what a person weighs vs. how much a life jacket displaces, yet it holds them above the water. Well it holds their head above the water. I think if you wanted to hold the whole boat entirely above the water then you would need a lot of foam, but in the Mac videos only a little bit of the boat is above the water.

I'm thinking about adding more foam, since I've removed a little, not much. We carry a lot of water containers on the boat (up to 30 gallons) and I'm increasing that to over 40 and most of the time a number of those are empty, yet are closed. I would think that they would help,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac-Venture Links

 

[nemosuit]

I figure that a 4'x8'x3'' foam sheet displaces 8 cubic feet of water @ 62 lbs/cubic-foot would give you ~500 lbs of buoyancy. For a V25 you would need about 2500 lbs of buoyancy thus you would have to install 5 such foam sheets. Does that make sense?

Ahhh.. at last! Something I know a little bit about! :dance:

The pink insulation is not styrofoam: it is extruded polyethelene foam.

Some differences include (as you already mentoned) the pink stuff isn't a mass of little compressed granules: it's an extruded foam sheet. That makes it less messy to work with.

Also, the pink stuff can be fiberglassed, but styrofoam will just melt under polyesther resins. But you don't really need to fiberglass the pink stuff, since it doesn't absorb water. For floatation purposes, it's good as is.

However, the pink stuff will disolve in gasoline, so beware there.

About your buyoancy calculations: essentially correct. Each sheet is 8 cubic feet: figured at 62.4 pounds per cubic foot of fresh water; or 64 pounds per cubic foot sea water; each sheet has a potential displacement buoyancy of 499.2 or 512 pounds, respectively.

(Minus the weight of the foam, which I'm deliberately overlooking since it's only a few pounds, and we're dealing with simplified estimates here.)

For the purposes of illustration, let's go with your number: 500 lbs positive buoyancy per sheet of foam.

Let's say your Mac 25 hull weighs 2500 lbs dry: If it were completely flooded with water; and you had five of these sheets installed within the hull, so that they were submerged along with the boat; the boat would be floating with the top of the cabin right at the surface.

(Actually, the boat would be riding higher than that, because the materials it's made of has at least some additional displacement buoyancy that we're deliberately not crediting here, so as to keep the illustration simple.)

If we add the weight of the mast, boom, sails, and rigging: that will push the hull further down into the water. But remember, we've got some buoyancy from the hull material itself we haven't accounted for yet. (I'd need the thickness and square inches of all the material used in the hull to calculate that, and I'm not going to do it before going to bed tonight! )

But for the sake of KISS, let's say the weight of the rigging is offset by the buoyancy of the hull material. Again, the boat is floating with the cabin roof at the surface, and the sails up in the air.

Actually, without doing the math, I'd think the displacement buoyancy potential of the hull material could be considerably greater than the weight of the mast, sails, and rigging. So again, with five of those pink foam sheets situated down low in the hull, we've got the boat floating: maybe with as much as the cabin roof, foredeck, and the cockpit gunwales above the surface waterline. (That's just a guesstimation, but I don't think it would be too far off.)

Bottom line: yeah, she'll float. Want additional freeboard when flooded? Toss in a couple extra sheets, but remember: keep it all down below what you expect the flooded waterline will be. Floatation that's stationed above the waterline adds to weight, not buoyancy.

Hope this helps.

VBR,

Pat

 

[Scott B]

Ahhh.. at last! Something I know a little bit about! :dance:

The pink insulation is not styrofoam: it is extruded polyethelene foam.

Pat

Close, but not quite. The pink insulaton is closer to "Styrofoam" than the white coffee cup / cooler type foam.

Styrofoam is a trade mark of Dow which manufacture Dow Styrofoam SM, and like the pink insulation is an extruded polystyrene. The white coffee cup foam is expanded polystyrene.

Styrofoam became a genric term in NA for the white foam insulation.

 

[rgranger]

Well it looks good in my boat and I can whole heatedly recommend it.



Rob

 

[r.oril]

Got it
" So again, with five of those pink foam sheets situated down low in the hull, we've got the boat floating".
Thanks for the info!

 

[timebandit]

Foam, Foam my butt!

The only reason I keep the foam in is so that I won't stuff the boat with a lot of crap.:naughty:

The thing that will keep my boat from sinking in calm water is me!

First the bilge pump--- 10 seconds.

Second thing is to find the leak.

Third is to plug the leak or at least slow the water to a dribble so the pump can handle it.

Since our boats have liners it may be hard to reach that big gash opened up by that coral head so it will have to be stopped from the outside.

How?

Stuff it with anything from a sock for small holes to towels, sail bag, life jackets, whatever.

If you can't stuff it, cover it with that square cushion that floats that you use for a back rest or that 8 X 1 1/2 foot cockpit cushion. You might even take that blue tarp and tie it off and walk it down the boat and let the pressure of the water hold it aginst the hull and not have to get wet at all.

Oh my, what to secure the patch with? How about that 300 feet of main anchor line or the 200 feet of line on your lunch hook or maybe some of the old halyards and sheets your kept aboard for spares.

Cat's and tri's turttle but mono hulls with their ballast locked just roll back up.

 

[Sumner]

Got it
" So again, with five of those pink foam sheets situated down low in the hull, we've got the boat floating".
Thanks for the info!

I don't think so....

...........Let's say your Mac 25 hull weighs 2500 lbs dry: If it were completely flooded with water; and you had five of these sheets installed within the hull, so that they were submerged along with the boat; the boat would be floating with the top of the cabin right at the surface.

(Actually, the boat would be riding higher than that, because the materials it's made of has at least some additional displacement buoyancy that we're deliberately not crediting here, so as to keep the illustration simple.)..........VBR, Pat

your Mac from the factory had way less foam in it than that and it floats. Remember we just don't want if going to the bottom. If the boat is on its side or whatever and part of it is above the water it is not going to the bottom.

If you put something in the water that is one cubic foot and it weighs the same as the water it displaces it isn't going to float or sink. If that cubic foot of material weigh less than the cubic foot of water it displaces it will float either at the surface or some point above it depending on how much less it weighs than the water it displaces.

If that cubic foot weighs 10 lbs. more than the water it displaces then we only need 10 lbs of buoyancy to get it to the surface, not the total weight of the item.

Therefore you don't need 2500 lb. of additional buoyancy to get a 2500 lb. boat to the surface, just the difference in weight of what the boat weighs vs the weight of the water it is displacing.

Listen to TB and his suggestions. Since I've been reading this stuff the only Mac that I've read about that has gone down was the one mentioned above.

c ya,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac-Venture Links

 

[nemosuit]

Close, but not quite. The pink insulaton is closer to "Styrofoam" than the white coffee cup / cooler type foam.

Styrofoam is a trade mark of Dow which manufacture Dow Styrofoam SM, and like the pink insulation is an extruded polystyrene. The white coffee cup foam is expanded polystyrene.

Styrofoam became a genric term in NA for the white foam insulation.

Okay, I think I see what you're saying. And yes, I've seen the extruded Styrofoam boards you speak of: they are indeed comprised of foam, not granules. (I mentioned granules because many are familiar with styrofoam cups, coolers, etc.) So the difference there is in the terms "extruded" versus "expanded".

And you're right: the pink foam I'm describing is closer in appearance to the polystyrene (Styrofoam) board in that they are both extruded.

And actually, there are Styrofoam insulation boards availabe in pink, blue, gray, and white.

But while both extruded foam boards might have similar appearances at first glance, the pink foam board I'm talking about has a different chemical makeup and different mechanical properties. And that's important to anyone thinking of using it for additional buoyancy nowadays.

It's extruded polyethelene foam board insulation. Also made by Dow, the trade name is Ethafoam, and it comes in pink 4' X 8' sheets. I just bought a quantity of it at Lowes last month. A 2" sheet was about $20. When I went to the store and asked for pink foam insulation board, they steered me to racks of Ethafoam. Didn't see any pink Styrofoam; only white.

Here's a link about polyethylene foam:

http://www.wisegeek.com/what-is-polyethylene-foam.htm

Comparing the differences: extruded Styrofoam is more brittle, less flexible, and more prone to breaking up into small pieces when bent or tooled. If you squeeze a piece of it in your hand, it will crumble. It also disolves in fiberglass resin.

In contrast, extruded Ethafoam is more spongey and resiliant. Squeeze a piece of it in your hand, and it will spring back to shape again and again. Ethafoam is also impervious to fiberglass resin.

We've probably all seen Styrofoam and Ethafoam used in protective packaging for, say, electronic components. Ethafoam is coming into more frequent use these days. A comparison of the two types will show them to be very different in physical properties. (Try the squeeze test I mentioned above.)

Both Styrofoam and Ethafoam are used for boat floatation; but Ethafoam is more durable in the long run. That's why I recommend extruded polyethylene foam over expanded, extruded, or compressed-granule Styrofoam.

Hope this helps.

VBR,

Pat

 

[nemosuit]

Foam, Foam my butt!

The only reason I keep the foam in is so that I won't stuff the boat with a lot of crap.:naughty:

The thing that will keep my boat from sinking in calm water is me!

First the bilge pump--- 10 seconds.

Second thing is to find the leak.

Third is to plug the leak or at least slow the water to a dribble so the pump can handle it.

Since our boats have liners it may be hard to reach that big gash opened up by that coral head so it will have to be stopped from the outside.

How?

Stuff it with anything from a sock for small holes to towels, sail bag, life jackets, whatever.

If you can't stuff it, cover it with that square cushion that floats that you use for a back rest or that 8 X 1 1/2 foot cockpit cushion. You might even take that blue tarp and tie it off and walk it down the boat and let the pressure of the water hold it aginst the hull and not have to get wet at all.

Oh my, what to secure the patch with? How about that 300 feet of main anchor line or the 200 feet of line on your lunch hook or maybe some of the old halyards and sheets your kept aboard for spares.

Cat's and tri's turttle but mono hulls with their ballast locked just roll back up.

 

[nemosuit]

I don't think so....

your Mac from the factory had way less foam in it than that and it floats. Remember we just don't want if going to the bottom. If the boat is on its side or whatever and part of it is above the water it is not going to the bottom.


If that cubic foot weighs 10 lbs. more than the water it displaces then we only need 10 lbs of buoyancy to get it to the surface, not the total weight of the item.

Therefore you don't need 2500 lb. of additional buoyancy to get a 2500 lb. boat to the surface, just the difference in weight of what the boat weighs vs the weight of the water it is displacing.

Listen to TB and his suggestions. Since I've been reading this stuff the only Mac that I've read about that has gone down was the one mentioned above.

c ya,

Sum

Our Trips to Lake Powell, UT - Kootenay Lake, Canada - Priest Lake, ID

Our Mac Pages

Mac-Venture Links

Hi Sum!

"your Mac from the factory had way less foam in it than that and it floats. Remember we just don't want if going to the bottom. If the boat is on its side or whatever and part of it is above the water it is not going to the bottom.

Correct, but in the analogy I gave, I was trying to describe a 2500 pound hull with no additional floatation (except that which we added) and no consideration for the buoyancy of the hull material (we figured that in later by guesstimation.) In that scenario, a boat hull that is 2500 pounds negatively buoyant, filled with 2500 pounds of positively buoyant foam, will float with the top of the structure just at the surface of the water, and most of the boat submerged.

"If you put something in the water that is one cubic foot and it weighs the same as the water it displaces it isn't going to float or sink."

It will rest, barely submerged at the surface, in a state of neutral buoyancy.


"If that cubic foot of material weigh less than the cubic foot of water it displaces it will float either at the surface or some point above it depending on how much less it weighs than the water it displaces."

Actually, it will definitely float with a portion of it structure above the surface. And as you say, that portion is determined by the difference in displacement buoyancy and weight.

"If that cubic foot weighs 10 lbs. more than the water it displaces then we only need 10 lbs of buoyancy to get it to the surface, not the total weight of the item.

Therefore you don't need 2500 lb. of additional buoyancy to get a 2500 lb. boat to the surface, just the difference in weight of what the boat weighs vs the weight of the water it is displacing."

Correct. But to illustrate the principles, I was describing a theoretical boat that was 2500 pounds negatively buoyant, with no consideration for factory-installed foam (other than we supplied with the foam boards) or for the potential buoyancy of the hull material itself. We added 2500 pounds of foam, and that brings us to neutral buoyancy. Later on, when I mentioned the weight of the rigging versus the potential buoyancy of the hull materials themselves, I stated that the boat would probably ride higher than that with that much foam board added. And that would also equate into the fact that you could at least keep her from sinking with less additional foam. Actually, we're saying the same thing here.

"Listen to TB and his suggestions. Since I've been reading this stuff the only Mac that I've read about that has gone down was the one mentioned above."

Sum, I think you know I value and respect the info shared by all you guys in this group. I have no fear of my Mac, or any Mac that has foam insulation installed, sinking.

I wasn't speaking of a 2500# Mac with factory foam installed, or taking into consideration the potential buoyancy of the hull material itself, because I don't have the specs on that.

And you're right, if we add those factors into the mix, we don't need 2500# of additional foam to keep her afloat.

I was trying to illustrate the principles of buoyancy using a theoretical boat that was 2500 # negatively buoyant, with an additional 2500# of foam floatation, would achieve neutral buoyancy.

I added that, in reality, such a boat would also be affected by the weight of additional rigging, versus the displacement buoyancy of the structural material itself; and that in all probabiity, those factors would result in additional positive buoyancy.

I supposed I could have worded it better when I said "your Mac", but it was late, I was going to bed, and the written word is so finite and easily misrepresented. I did my best to explain the principles involved. If I expressed them in a way that conveyed something other than what I was trying to explain, I apologize. I'm only human.

Still, if the reader will look at my post as trying to explain the general principles of displacement and buoyancy, odds are that knowledge will enable him to adapt the math to any specific vessel he has in mind.

That's all I was trying to do.

VBR,

Pat