Pour foam versus Polystyrene Blocks

Designs for inboard or outboard power

Moderator: BruceDow

tclark
Posts: 17
Joined: Tue Jan 11, 2011 10:43 am

Pour foam versus Polystyrene Blocks

Postby tclark » Fri Mar 09, 2018 2:13 pm

I am trying to determine what foam to use in my Scooter boat.

I am a bit leary about using the pour foam, it seems messy and can be strong when expanding.

I can purchase blocks cut to specific sizes of expanded polystyrene foam. The salesman says it is a closed cell foam, tighter and more water resistant than Polyurethane. They use it in docks and say it is like the foam material in an ice chest. It can't be glued down with Epoxy as it will melt it.

Are there any recommendations from you all regarding flotation foam?

User avatar
hoodman
Posts: 1580
Joined: Thu Nov 10, 2011 8:48 am
Location: Lafayette, IN

Re: Pour foam versus Polystyrene Blocks

Postby hoodman » Fri Mar 09, 2018 2:44 pm

If epoxy will melt it, I would be concerned that it might not resist gasoline or oil. That could cause problems. One thing you can do with pourable foam is to pour it into plastic tubs and make your own blocks.

User avatar
Bill Edmundson
Posts: 10881
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Pour foam versus Polystyrene Blocks

Postby Bill Edmundson » Fri Mar 09, 2018 3:25 pm

Polystyrene + gasoline = napalmed.

I like closed cell polyethylene. I buy the sheets and cut it up. Then I glue it in.

Correction: I like the polyurethane foam. thanks Pete.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

PeterG
Posts: 485
Joined: Mon Dec 03, 2007 7:08 am
Location: Connecticut

Re: Pour foam versus Polystyrene Blocks

Postby PeterG » Fri Mar 09, 2018 3:45 pm

Polyurethane or polyethylene closed cell foams are preferred, either pourable or in blocks. You want closed-cell so it won't absorb water. Blocks can be made from sheets or from pours you do yourself like Matt says. Here is a Glen-L newsletter article that has great info for you:

https://www.glen-l.com/weblettr/weblett ... ation.html
Murphy's Law: Anything that can go wrong, will go wrong.
Griffin's Law: Murphy was an optimist.

User avatar
kens
Posts: 4522
Joined: Wed Nov 12, 2003 5:25 pm
Location: Coastal Georgia

Re: Pour foam versus Polystyrene Blocks

Postby kens » Fri Mar 09, 2018 5:17 pm

Why foam?
All foam absorbs either water or oils, or gasoline over time, and it has weight.

If you have to build a mold, to pour foam, to fit your hull, then why not just build a empty box full of air?
Secure it under the floor and you're done.
Air is lighter than foam, and air doesnt absorb water nor gasoline.
Oak is over rated, everything about it takes extra time; then it warps, splits or checks !!! :roll:

bobinpowayca
Posts: 400
Joined: Thu Jun 16, 2011 1:40 pm
Location: Poway, CA

Re: Pour foam versus Polystyrene Blocks

Postby bobinpowayca » Fri Mar 09, 2018 9:29 pm

Well, here's my 2 cents on why I went with pour-in-place foam. By the way, I'm not too worried about long-term absorption of fuel and water because in all the cavities where I used it the floor above it is sealed, i.e. when I built the floor I finished it as closely as I could to the hull sides, and then filletted all the joints with quick-faire, then 2 coats of primer and 3 coats of bilgekote on the floor. I also primed and painted the inside of the hull and frames the same way, so the foam is encased is primed and painted chambers. And at my age I'm not worried about the foam degrading. :D
One reason is flotation - the foam is 2 lbs/cuft. Water is about 62 lbs/cuft.; I figure I've got over 12 cuft of foam so that's 720 lbs of positive flotation, over twice the weight of my outboard motor plus the batteries...
Another reason is it firms up the floor - where I've foamed under the deck it's solid, there's not much flexing at all. I weigh 215.
And an important thing to me is that if I hit a rock or something under the water - say something that might punch a hole maybe the size of a saucer in my hull (remember, we're talking 3/8 plywood here), I don't have to worry about the water rushing in - I will just have a big divit to fix later, like a ding in a surfboard on a much bigger scale. I know you can call vessel assist or the coast guard but I'm scared to death of sharks and wouldn't feel comfortable waiting for them in a swamped boat.
Also I don't have all the voids in the bilges that you can't get to so can't keep clean and can harbor trash, bilge rats, fish bait etc.
But pouring it can be really messy and it reacts almost immediately (20 sec?) so you have to get a technique down and just do as much as you can control so it doesn't get out of hand; I was doing one section and I poured too much too fast and it busted the deck up off of the frame and hull side it was glued and screwed to - lucky I didn't crack the hull. So I had to cut that whole area out and re-do it.
I guess the foam's worth is in what the boat is going to be used for. Bob
Attachments
IMG_1212.JPG
accessible bilge only area under floor not foamed
IMG_1159.JPG
in one hole and out the other, start at deep end
Bob
_______________
Built the Glen-L 17 (1988), Geronimo (2018)
PBR support (1968)

User avatar
Bill Edmundson
Posts: 10881
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Pour foam versus Polystyrene Blocks

Postby Bill Edmundson » Sat Mar 10, 2018 8:08 am

As Bob said, be careful foaming a closed area. If the foam develops 1 psi, that is 144 pounds per square foot trying to pry your boat apart. I just had my driveway leveled. They pumped closed cell polyethylene under the low areas. The foam lifted the concrete.

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
Roberta
Posts: 6064
Joined: Tue Jul 31, 2007 5:23 pm
Location: East Troy, Wisconsin

Re: Pour foam versus Polystyrene Blocks

Postby Roberta » Sat Mar 10, 2018 8:38 am

Paul "Mr. Hotrod" cast his in place leaving the decking off. Once the foam cured, excess was trimmed and the decking applied over it, He was careful to fully epoxy encapsulate all the wood surfaces before casting the foam and applying the decking. The foam Glen L sells is easy to work with and expands at a slow rate, so it can be controlled and maneuvered into place. Doing it like Paul did does take pre-planning and some extra construction.

I used Glen L's foam and cast blocks of foam, The blocks were shaped to fit, when necessary, and placed in HD plastic zip-lock bags and secure by straps or light plywood braces between structures. I can remove mine, if necessary, to inspect and repair, if ever needed.

I believe coast guard rules require outboard powered boats need to have floatation such that the boat will float level, if swamped, while inboard boats need only have sufficient floatation to prevent sinking.

Roberta
Roberta "Queen of the Boat Builders"
Built Zip "Oliver IV", Super Spartan "Jimmy 70", and Torpedo "The Glen L".

User avatar
Bill Edmundson
Posts: 10881
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Pour foam versus Polystyrene Blocks

Postby Bill Edmundson » Sat Mar 10, 2018 8:52 am

The USCG Regs. are not real clear for us. After you dig in I think it's OK for home builders to die.

But, here they are: http://www.uscgboating.org/regulations/ ... TATION.pdf

Bill
Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

User avatar
Bill Edmundson
Posts: 10881
Joined: Wed Nov 23, 2005 6:45 am
Location: Birmingham, AL, USA
Contact:

Re: Pour foam versus Polystyrene Blocks

Postby Bill Edmundson » Sat Mar 10, 2018 9:19 am

Mini -Tug, KH Tahoe 19 & Bartender 24 - There can be no miracle recoveries without first screwing up.
Tahoe 19 Build

bobinpowayca
Posts: 400
Joined: Thu Jun 16, 2011 1:40 pm
Location: Poway, CA

Re: Pour foam versus Polystyrene Blocks

Postby bobinpowayca » Sat Mar 10, 2018 10:46 am

Thanks for the links. Actually I have no idea which way my boat will float if it gets swamped. Doesn't surprise me though that the coast guard has several pages of regulations and calculations on how to determine if my 16 ft boat will float level if swamped. They are a regulatory agency after all. Bob (too late now)
Bob
_______________
Built the Glen-L 17 (1988), Geronimo (2018)
PBR support (1968)

User avatar
gap998
Posts: 378
Joined: Wed May 20, 2015 5:40 pm
Location: Wales, UK

Re: Pour foam versus Polystyrene Blocks

Postby gap998 » Tue Mar 20, 2018 12:50 pm

Bill Edmundson wrote:The USCG Regs. are not real clear for us. After you dig in I think it's OK for home builders to die.


Literally had me laughing out loud! :lol:
Gary

Planning a whole fleet, but starting with a Zip...I think.

"Just when you think you've made something idiot-proof, someone builds a better idiot!"


Return to “Power Boats”

Who is online

Users browsing this forum: No registered users and 16 guests