Flotation - Combining Foam and Bouncy Balls

[Jim Hawkins]

The boat is a Nautico catamaran and the deck is spongy and needing replacement. BUT the main reason I want to redo flotation is that this boat sits in the canal and every time we get a heavy rain I worry about the bilges and whether the boat will be floating when I get back to it.

The twin hulls are not completely filled with foam and as is common with some old cats they fill with water. Down inside each hull is a bilge pump and a third one on top of the deck. I want to redo the deck to eliminate the plywood, fill the hulls with high density foam, use one topside bilge and glass directly on top of the foam. I glassed on top of foam on another boat 10+ years ago and it's holding up great.

My plan is to cut down on the amount of foam I will need by filling each cavity with those nearly indestructible bounce house balls and then let the foam fill the voids around them.

The boats in the following pics are not mine but stuff I pulled off the net, perhaps even from someone in this forum.

The boat with the empty hull is identical to my cat. So, anybody done anything like this?

 

[kcassells]

To begin I'm not sure how you would calculate the flotation value of the balls, volume, longevity, weight.
I doubt your balls will maintain air/buoyancy for 3+ years. JMHO Good luck.

 

[Jim Hawkins]

Figuring the volume of foam needed is just a couple simple geometry equations. Count the number of balls in a void and then figure their volume and subtract from the volume of the cavity. The balls are very strong that's the point of using them instead of empty water bottles or other things people sometimes use.

 

[kcassells]

Volume is a simple recipe to calc. Any how this same question comes up every year or so. Try searching thru archives on the search engine Iboats has.

 

[Jim Hawkins]

I did try searching, I found people using odd things for flotation and people using foam but not together.
The balls are considered "crush proof" and the ones I've seen are very tough. Why do you think they won't hold up?

 

[jbcurt00]

Comes down to math:

W 3in balls, you'd 'need' 64 to 'fill' a cubic foot

Does a cubic foot of balls offer more then 60lbs of flotation or wiegh less then 2lbs, and cost less then 1cubic foot of flotation foam?

In a cavity well filled w roind balls, will flotation foam even flow well into a labyrinth of voids to adequately then fill the cavity?

In a sealed compartment, will balls expand and contract w bot/cold cycles? Expand and contract enough to be a problem?

Since they are intended to be used in a dry environment, are they actually sealed balls? Seems I've held some that had a hole in them just smaller then 1/8in. I know I've held some that had a weld seam all the way around them, so they'd been made in 2halfs and seamed together. Hit/cold cycle split them?

How do you plan to ensure both:

Balls are well encased and cavities well filled w foam
Keep balls from moving while you are foam an area

Seems an attempt to reinvent the wheel, in a Rube Goldberg-esq kind a way....

Plastic bottles and pool noodles arent a good flotation plan either.

 

[Jim Hawkins]

You guys make good points. Re-doing the math I would not be saving money unless I can find something durable at little or no cost as the foam works out to about the same as the balls. Still, I'm not giving up. This project is for January and that's why I'm researching now. Also, I'm in the Florida Keys so expansion and contraction will be less of an issue than in the great white North. Back to the search engine...

 

[chevymaher]

LOL why does everybody hate the foam. It is greatt and easy to use.

 

[Jim Hawkins]

I LOVE the foam. I hate that for 4# foam I will need about $1,000 worth to fill my hulls.

64 cubic feet or 3 - 20 cubic ft kits at $264 per kit plus tax and shipping...

Am I going to find a way to stretch it ? Youbetcha.

 

[jbcurt00]

Why 4lb, typical is 2lb?

 

[Jim Hawkins]

Why 4lb, typical is 2lb?

Because 4 lb is for structural use. I will be glassing directly on top of the foam.

 

[tpenfield]

Use the bouncy balls for their intended purpose and likewise for the flotation foam.

 

[Mad Props]

Are you doing the calculations to figure out how much buoyancy you need, or are you just assuming you need to entirely fill your hull? you may not actually need $1000 worth of foam.

 

[emoney]

And from where are you planning to purchase the foam? That can be a huge factor in cost. You can save probably 1/2 by going direct to a manufacturer, as opposed to a Marine Supply Store. Glad you've chose against the balls to add fill. As I've got a bounce house for my grandkids and I can tell you, those balls do deflate, some worse than others and they're expensive, imho. I could only imagine what kind of "rattle" could occur if the foam filled around fully expanded balls, and then they deflated 3 months later, lol.

 

[Scott Danforth]

use the 2# foam to fill 90% of your hulls, then use 8% foam to top it off.

 

[sphelps]

if you plan on using poly resin don't forget it will melt your foam ...

 

[Jim Hawkins]

if you plan on using poly resin don't forget it will melt your foam ...

Last time I did it 10+ years ago using poly resin I didn't have a problem. That boat deck is still solid today.

"use the 2# foam to fill 90% of your hulls, then use 8% foam to top it off."

That's along the lines of what I'm thinking.

Also, as far as the question about filling the hull vs just enough for flotation I want to fill the hull to minimize any room for water to collect below decks. I know in a perfect world water wont ever get in there but...

 

[Redtruck12]

I thought poly was okay with foam?

 

[sphelps]

I know it will melt the blue closed cell ridged foam . I thought it did with the 2 part expandable .. I guess I was mistaken ..

 

[chevymaher]

No 2 part expandable wont melt. I was glassing right on it all over.