Flotation Foam Mac 25

[JeffT]

Does anyone know how much flotation foam should a Mac 25 1980 have in it?
The P. O. removed all of the foam. I would like to replace it before the next season.
I just don't know how much to install.
Please comment.
Thank you,
Jeff T.

[Bob McLellan]

I have a 1976 Venture 25, essentially the same boat you have. First - all the area under the V berth is filled with chunks (broken pieces). If I were to redo that area, I would use solid small blocks that would fit together closely. The airspaces between the chunks would only fill with water if the boat were "holed". Next, in the laz, under the cockpit, there is a battery and four pieces of solid foam 1x1x4-ft each. When I say solid foam, know that I mean closed cell foam like a white foam coffee cup. You can buy closed cell foam in sheets 2-inches thick at Lowes or Home Depot. Use TiteBond glue to glue the pieces together since is waterproof (but not for prolonged under water use). It will not "eat" the foam. but will hold it together. I would stick foam in every crevice I did not need for storage also.

[Paulieb]

I agree - as much as you can fit. Just make sure it's evenly distributed throughout the boat, you don't want float lop-sided.

Paulieb

[JoeVacs]

One cubic foot of styrofaom ( 12inchx12inchx12inch ) will float aprox 200 lbs. There are variances in density, but if you base it on that, and put at least one third more than the total weight of the boat, it's contents, and the weight of occupants, you should be fine.

[waternwaves]

the above number should be corrected. seawater is 64.1 lbs per cubic foot.... and a 200 lb weight will sink a 2lb block...the foams have various weights from about 2 to 9 lbs.

[JoeVacs]

Well, I will admit that my results were less than scientific. I took the floatation blocks out of my boat when I rebuilt it. When putting them back in, I wanted to know if I needed extra blocks. I took a block with me into my swimming pool and cut it down until it just barely held me at the top of the water. OK, my body has some bouance of it's own, sure. And the density of the foam will vary. But in my unscientific study, a one foot cube floated me. If I had been in salt water it would have floated me a little higher though, not less, because salt water has more bouancy.
So, if I had hung a 200lb weight onto the block it may have sunk, this is true. Without further data available (which now that I'm curious, I will retest in the spring ), I would venture to guess that a safe assumption would be that a 12inch cube would float at least 100lbs. Would you agree with that ?

[Hamin' X]

It depends on the foam used. When helping a friend design a floating dock, we used the figures supplied by DOW, the manufacturer of the Styrofoam that we were going to use. They used 55Lbs/ft3.

~Rich

[waternwaves]

sorry,

I gave you a trick answer for a trick question.

since your body is mostly water, 16-20 lbs of flotation is enough to keep your head out of the water.

but to keep your body out of the water, you need to displace an amount of seawater equal to your weight. in this case.......lets say my weight is 250, I would be looking at a little over 4 cf of foam to keep me just out of the water........ the water line on this precarious perch would be fully submerged on the blocks and I would still get wet.

I am going to be sloppy here and try to simplify without going into the mass/weight/density.

the foam in the boat is to support the fiberglass and motor, and on an x boat........that means I need a considerable amount of foam..... the boat is filled to obtain that flotation. for example the density of the combined Epoxy/fiberglass.
for this case we'll use for a 50/50 combination by volume, the density of the composite would be 1.85 g/cc or a little over 1.7 times that of seawater. Since we want to keep the boat at the surface, not necessarily supporting a lot of weight.......we then need .7 times the weight of all the fiberglass and goodies that sink inand on the boat for a target number for flotation. The empty X boat without any flotation needs about about 1000 lbs of floatation. on the X, balsa wood is used in the deck structure, so this provides a couple of hundred lbs of floatation, the interior liner traps some air if the stern is low........ and voila.......you can make a cute picture like macgreger with people standing on a submerged boat. Assuming 800 lbs of floation is needed.....that is about 14 cf.

however we have motors and batteries on them.

Engines density is a bit more dicey. they are dense metal... mostly aluminim (2.7 x sea water)/some steel. (8 x seawater)......probable safe to use a density of 5 to 1 over seawater since we only have pistons, gears, shafts, fasteners and piston liners made of steel. so basicly we can consider the engine to be almost dead weight......and the displacement bouyancy for our purposes is less than 1/5 of 340 lbs outboard.....so we will need almost 5cf of foam just ot support that and 1 battery. now water tanks, waste tanks, fuel tanks that are partially empty, a foam filled mast, all help keep the boat on the surface.

these are the two major things that require most of the bouyancy on the boat.

between them almost 20 cf of foam/balsa and empty tanks will keep a macX from sinking.

just as a check......the sealed empty ballast tank provides over 1200 lbs of floatation. hence the pics in other threads of how high the mac was sitting in the water.
so if the proverbial 12" sq foam block weighs about 4 lbs. it will support about 60 lbs. in salt water

[THE CUSCUS]

Why all this talk of sinking your boats? How many Mac owners have actually been so unfortunate to fill their boat with water? What about all the other makes that don't have all the foam blocks in them? I don't see a rash of news stories about sailboat sinkings. With the proper and safe sailing techniques, and proper respect for the weather/wind one shouldn't need to have all extra space below filled with foam blocks. One shouldn't be lured into a false sense of security, just because there is enough foam in your boat. It was a great marketing scheme that Macgregor came up with! Take out the foam, sail safe and enjoy all the extra storage space you have.

[JoeVacs]

Why all this talk of sinking your boats? How many Mac owners have actually been so unfortunate to fill their boat with water? What about all the other makes that don't have all the foam blocks in them? I don't see a rash of news stories about sailboat sinkings. With the proper and safe sailing techniques, and proper respect for the weather/wind one shouldn't need to have all extra space below filled with foam blocks. One shouldn't be lured into a false sense of security, just because there is enough foam in your boat. It was a great marketing scheme that Macgregor came up with! Take out the foam, sail safe and enjoy all the extra storage space you have.

If you were driving out into the middle of the Sahara desert would you take a spare tire ? I would. Do you have a fire extinguisher in your boat and in your home, I do. I hope to never need it, but I sure hope it's there if I do. Stuff happens. Unforseen things. Better safe than sorry. Foam blocks are cheap insurance. Cheaper than paying to have your boat resumed from the bottom.

[snotnosetommy]

Gotta agree with JoeVacs. While I don't wanna rely on foam to replace good seamanship, I do often have "innocent" passengers aboard, and if I screw up or hit something I want every advantage I can get, especially at night or cold weather. Life jackets just keep you afloat long enough to die from hypothermia. My Mac 25 came with v-berth and entire under-cockpit area full of foam. I made my mods and stuck it all back in.

[JeffT]

Thank you to everyone who responded to my question.
I have found a surplus of large format "pool noodles" that I purchased for a little over a dollar a piece.
I plan to fit these flotation noodles into every available crevice, just to be sure.

[Snyds]

ANybody use "great stuff" spray foam insulation stuff?

[rgranger]

ANybody use "great stuff" spray foam insulation stuff?

I have... A few years ago I restored a Coronado 23'. And I filled some of the spaces between the hull and the liner with expanding spray foam (great stuff). It is okay and does a good job but there are some things to consider.

1) It sticks to everything and can (does) make a tremendous mess.
2) You can buy two part mixes that will give you the volume you need. Most chandlers carry it... Great stuff would be too expensive to fill a V-birth.
3) Unless you expand the foam into a plastic bag or use visqueen between the foam and the hull, you will have a huge job if you ever need to do fiberglass work on the hull because you will need to chisel out the foam, then sand off the residual foam before you could work on the hull.

I don't remember where I read this... I once saw a post where a guy took some heavy duty garbage bags and filled them with packing peanuts. Then stuffed those into his V-birth. Seems like a good idea. He claimed it worked well but I doubt he actually flooded his boat to prove it..

I just pulled all of the foam out of a V222 that I recently purchased. A family of mice had made a home in the boat. The foam was filthy, full of mouse droppings and other nasty stuff, chewed up and basically not reusable. I'm looking at the pink foam board that Dow makes. ... and I might go with the peanut idea for the v-birth area as a replacement.

I'll let you know how it works... but I won't be flooding my boat to prove it.....

[noahvale]

I was talking to my Mom and Dad about sailboats. Their first sailboat was a Venture 22 which had the distinction of being the slowest boat in their yacht club. Once they had a wave come over the side of the boat which pretty much filled up the cockpit and cabin. The gas can floated, tipped over, and the cap came off. The gas started dissolving the styrofoam blocks! They made it back in and had a big mess to clean up, and another good story to tell at the yacht club.