To Foam or Not To Foam

[Seadog]

To continue a discussion from another thread.  I'm a novice at the fiberglass boat rebuild game.  Figureing this stuff out as I go along. Wanted to see if anyone has some insight into adding foam back into those water logged foam filled stringers that seem to be so prominant.  

The current consensis is that the foam adds buoyancy, reduces hull noise and vibration, adds some structural rigidity and makes for a better ride.

But it also will absorb water from the inevitable water intrusion that will happen over time and that once it gets wet, it's almost impossible to get it dry again.

Anybody able to enlighten us?

[steved]

I am really out of my element technically here, but let me offer a reflection anyway. It seems pretty clear that the foam provides a number of not insignificant benefits. Let me suggest that there is at least one more important benefit of the foam that has not been mentioned so far. As it gradually gets wet, the foam helps the boat remain stable by capturing and reducing the mobility of the water. The water is going to be there anyway, right? How much water do you think was in the 30 garbage bags of foam that came out of the stringers? Think about that much water sloshing around in your boat and the impact it would have on speed, stability and safety. But if the water is absorbed by the foam, due to principles of physics governing capillary action, it will distribute itself evenly. And the foam will prevent it from sloshing around. Of course, it would be better if the water wasn't there at all, but water in foam sounds better to me than water alone. And if the old girl makes it another twenty years before you have to open her up again, that sounds pretty good to me.

[JimCt]

What about the foam they use for dock floats?  Don't know about your area, but foam's been used reliably for floats here for years.  In fact, bet you a beer there's a foam float in your toilet tank; ever see one of those sink?  How about foam mooring floats?  Heck, even a foam cup will float forever.  As I said in the other thread, I can't believe there isn't a foam that will stay dry in a stringer.

Steved's got a good point about dampening the water movement once they're soaked but I can't believe this is what the designer had in mind when he specified foam filled stringers.  

Clearly, we need a Foam Expert to weigh in to settle this for once and for all.

My $.02.

[Radioshop]

I'm toying with the notion of coating any foam I reinstall in some sort of waterproof coating.  Epoxy maybe?

[Seadog]

That's a good idea Radioshop but how can that be done? If you pour in the 2 part foam into access holes in the tops of the stringers how ya gonna coat it once it expands?

I guess it would be possible to form the foam first, into the shape desired, lay the preformed stuff in the hull, coat it with epoxy then glass it in.  Just never heard of it done that way. I'm a novice at this game, maybe that technique is used all the time.

[JimCt]

What is AS using now in the stringers?  Maybe they've corrected the problem in the newer boats.

[Radioshop]

Option 2 Seadog.  I don't think it's usually done that way.  There may be a good reason for that too.  I'm still doing homework.

[Jerry-rigged]

The current consensis is that the foam adds buoyancy, reduces hull noise and vibration, adds some structural rigidity and makes for a better ride.

The foam will only add Buoyancy if the hull is full of water - it will help the hull not sink if you hole the hull, but adding foam will not decrease the draft.  Under normal operation, the Foam actually takes away from the total reserve buoyancy of the hull (adds weight), but not much.

I'm toying with the notion of coating any foam I reinstall in some sort of waterproof coating. Epoxy maybe?

Before you re-build the stringers, Epoxy coat the inside of the hull (or even add a layer of 12oz bi-ax, with exoxy insted of polyester), then build your hollow stringers with epoxy resin instead of the *-ester resin.  No more worrys about water in the foam, until you drill a hole....

Jerry

 
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[Radioshop]

Before you re-build the stringers, Epoxy coat the inside of the hull (or even add a layer of 12oz bi-ax, with exoxy insted of polyester), then build your hollow stringers with epoxy resin instead of the *-ester resin. No more worrys about water in the foam, until you drill a hole....

Duh? Why didn't I think of that?  Intelux has this epoxy bottom paint that might do that job well.

[Seadog]

Maybe I'm confused about foam.
Let's try this example:

Lets say we have two 1970 Aquasport 222's. These two boats are identical in every way and have the EXACT same weight.  the only diference is one boat has foam filled stringers, the other boat has no foam at all.

If we put both boats in a saltwater swimming pool side by side, I agree that the draft on both boats will be about the same.  

Now lets add a load of say 750 pounds in the same place on each boat, say just behind the console.

Won't the boat with the foam be sitting higher in the water. Won't the boat without the foam have a deeper draft?

I thought the foam had a bouyant effect of lift. I could be wrong.

Radioshop - I'm not convinced that fiberglass laminates layed with epoxy are 100% waterproof. Are you?

[Jerry-rigged]

Maybe I'm confused about foam.
Let's try this example:

Lets say we have two 1970 Aquasport 222's. These two boats are identical in every way and have the EXACT same weight.  the only diference is one boat has foam filled stringers, the other boat has no foam at all.

If we put both boats in a saltwater swimming pool side by side, I agree that the draft on both boats will be about the same.  

Now lets add a load of say 750 pounds in the same place on each boat, say just behind the console.

Won't the boat with the foam be sitting higher in the water. Won't the boat without the foam have a deeper draft?

I thought the foam had a bouyant effect of lift. I could be wrong.

Radioshop - I'm not convinced that fiberglass laminates layed with epoxy are 100% waterproof. Are you?

The foam only adds buoyancy if the hull if full of water.  Think about it.  To add buoyancy, you must displace water  The only time that the foam will displace water is if the hull is full of water - I.E. you swamp the boat.  The foam will displace water inside the hull and (hopefully)prevent the hull from going to the bottom.  This is how Boston Waler is UNSINKABLE.  Every available free space is foamed in, so even if you have water in the boat up to the top of the gunnels, the boat will still float.

Under normal operating conditions, the foam only adds weight - but not much.

To use your example:

Lets say we have two 1970 Aquasport 222's. These two boats are identical in every way and have the EXACT same weight.  the only difference is one boat has foam filled stringers, the other boat has no foam at all.

I don't think the foam in the stringers is enough to keep it from going to the bottom, so lets say that the 222 w/ foam has about 32 cubic feet of foam (enough to provide 2000lbs of flotation), which would weigh about 50lb (or so)  I am guessing that the 222 has a PPID of about 550

(PPID=Pounds Per Inch of Displacement - that is add 550 lbs, evenly distributed, and add 1" of draft to the hull)

The 222 with the foam will draft about .25" more than the un-foamed boat, until we swamp them.  Then the unfoamed boat goes to the bottom, but the foamed one still floats.

Hope this helps.

Jerry

[Seadog]

Hey thanks Jerry!

Now that makes since - the foam has to touch the water, to displace it, to have bouyancy.

Hope you don't mind me asking but do you work in  the Marine Industry?

[Jerry-rigged]

Hey thanks Jerry!

Now that makes since - the foam has to touch the water, to displace it, to have bouyancy.

Hope you don't mind me asking but do you work in  the Marine Industry?

LOL - Nope, but sometimes I wish I did.

My wife is in school right now, out in about a year.  For the last few years I have been wanting to build/rebuild a boat, but don't plan on starting until my wife gets out of school. In the mean-time, I have been reading everything I can find on boat building, boat repairing, boat design, materials, construction, etc.  

Because of my lack of hands-on experence, I usally try to not post much on these boat restore websites (except to ask questions), but in this case, I felt I knew the anwser.

BTW, I was basing my example on this boat: http://www.boatplans-online.com/proddetail.php?prod=C21 I am guessing that the 222 would have similer numbers, but be a bit heaver.

Jerry

[Seadog]

(PPID=Pounds Per Inch of Displacement - that is add 550 lbs, evenly distributed, and add 1" of draft to the hull)

DAMN! So your just a regular guy who likes the boat game like the rest of us! LOL!

I was hopin you were a Naval Architect or at least a Marine Engineer.

[JimCt]

Spoke with AS this A.M. and asked about the foam material they are currently using.  Basically, the rep said the foam used now is probably better at resisting water absorption but feels that all foams will take up water over time.  In short, things haven't changed much.

  The suggestion of using epoxy to line the stringer boxes makes sense to me.  West System epoxy comes to mind since it's formulated for marine use.

  The rep also said that the main reason they and other builders use foam is to deaden the high frequency transmission of the hull.  A wood hull is quiet because the structure, made out of hundreds of seperate pieces, is a poor resonator.  A glass hull is only one or two pieces.  Apply a high frequency source to it (outboard) and it'll transmit the hf energy throughout pretty efficiently.  At certain frequencies the hull may even amplify.  Foam in a hull will absorb hf.  More foam = quieter boat.  

  Maybe were stuck with it?