Expanding foam. Good idea or not?

[windward]

Hi guys, I need your help. I am building a Dumas Creole Queen (thread on Scale Boats) I have made the hull and now need to attach the decks but before I do I would like your thoughts on filling the vacant chambers with expanding foam. As you can see from the pic the hull has 2 channels down the length each side and the front from the bow to frame7 is also covered. The model sits very low in the water and on one other thread they put a sheet of foam on the outside of the hull to increase buoyancy. I would like to add smoke and lights etc which I know will only add more weight. The 2 channels down each side seems like a good idea to increase buoyancy and maybe more make it more stable? The other consideration is does this stuff expand and contract once set? Will I have trouble blowing the hull apart in extreme hot weather. I am a bit nervous about modifying the buoyancy and finishing up with a disaster!! Your thoughts and experiences would be great as I need to decide what to do so I can get the decks down. cheers Ray

[woodybob]

Do not use the foam from your local hardware store. Only use A/B foam from your LHS. It cures within 30 minutes, without any further expansion.

NHP expanding foam. http://www.flashglue.com/HTML/NHP_frameset.html (http://www.flashglue.com/HTML/NHP_frameset.html)

"Forms rigid polyurethane foam up to 25 times its liquid volume. Ideal for model boat floatation, model railroad scenery, potting artificial floral arrangements and arts and craft."

http://www.rcgroups.com/forums/showpost.php?p=10070172&postcount=4236
http://www.rcgroups.com/forums/showpost.php?p=10146075&postcount=4362

[tigerbay]

Do not use the foam from your local hardware store. Only use A/B foam from your LHS. It cures within 30 minutes, without any further expansion.

I have no knowledge of the specific foam cited in the above post.

But the expanding foam I am familiar with will expand a bit more than you want. This has caused hulls to distort or even to burst.

[LtDoc]

Ray,
If the idea is to make the hull more buoyant to carry more 'cargo', I'm afraid adding foam to the inside of the hull just won't do it. Making the hull larger, adding the foam to the outside of the hull, thereby increasing the amount of water the hull would displace, would make it more buoyant, it would handle a heavier 'cargo'.
But, if the idea is to keep the thing from going to the bottom of the pond/lake/river when it sinks, then adding foam inside the hull would take the place of air which could/would leak out. It would probably keep the "bottoms up!" boat on the surface.
Rats! Back to the drawing board...
- 'Doc

(Sort of 'off-topic', but still something to remember, is that a spray-in type expanding foam will require air to do that expanding and then curing. You'd also be very happy if you can guess the amount of 'goop' to spray into the enclosed space! Unhappy if you guess wrong and bulge that space past it's stretching point (a lot like my 'beer-gut'?). Been there, done that... yeah, yeah, with both of them. Both sprung a leak.)

[patmat2350]

Can't say that it won't burst a fragile hull, but there is hardware store foam which is intended for use around windows... lower expansion to avoid distorting the window frame.

If you use solid foam carved to shape... make sure it's not "open cell" (like green florist's foam), as that will soak up water like a sponge!

[Aerominded]

Do not use the foam from your local hardware store. Only use A/B foam from your LHS. It cures within 30 minutes, without any further expansion.

TOO true!!! :eek: do not use hardware store foam... what a nightmare... been there, done that... the HW stuff is very agressive in its expanding and takes a very long time to stop... Don't go there!!! :eek:

[John Pilot]

Hardware store stuff will work in a pinch, but I don't like it. Make sure you have plenty of expansion room (at least one side of the area you spray it in should be open) and when they say "expands to 10 times its original volume", they're not kidding! :eek: Expect lots of cutting and a long cure time for the inner part of the foam. In other words: avoid it if you can! :p

[windward]

Thanks guys for your advice. The overwhelming response is to leave the stuff alone. I will try to save weight where I can and hope it's floating above the low line of the deck when finished. The real Creole queen sits very low in the water :D cheers Ray

[keith S]

Only use the 2 part foams that expand. The stuff in the rattle can is useless for floatation purposes. Be ware that if you use a 2 part foam that it is a chemical reaction and does create heat. This stuff also expands vertically so side preasure is not too great. But if it leaks through a bulkhead to an area that is covered the risk is warping and blowing off the deck/sides.
I have used the 2 part stuff from the hardware store when building plugs before. Stuff is tough, but easy to shape once hardened. Then it was able to be glassed with polyester resign as is.

[Olscuzbut]

Just as a matter of interest, I used expanding foam to fill the space created under a stone bathtub after leveling it. Next day I found that the whole tub had lifted 1/2 inch more than I wanted. Had to do some fancy tile work to make it all fit again.

[woodybob]

The most important thing about using any expanding foam is not putting it into closed areas. Using it at this point http://static.rcgroups.com/forums/attachments/1/7/6/2/5/4/t2061796-41-thumb-creole.jpg (http://www.rcgroups.com/forums/attachment.php?attachmentid=2061796) of your hull is really not an issue. NHP A/B foam stops expanding in 20 minutes and cures in about 30-40 minutes. At which time you can shape as needed. Seal all wood to waterproof, then fill with foam.
I did a practice run using a thin plastic jug, it generated heat while kicking off, but did not distort the jug.

[Kmot]

Based on woodybobs recommendation I used the NHP 2-part expanding foam to fill an ABS hull. It was creating heat so I just set the hull in the pool to keep it cool. :D

[cyberhoops]

There is a second type of expanding foam - latex foam that only expands 10% while it sets up and cleans up with water. DAP has a version called DAPtex that you can pick up a a local hardware store. The final product is somewhat softer and more flexible after it has setup. I found it was simple to cleanup the little spray tube so it would be possible to use it more than once.

It looks like a pretty good choice for internal foam for floatation without the aggressive expansion and hull-busting risks of polyurethane foam.

I used it in the sponsons of an electric hydro and I think the results were pretty good and very predictable.

Jim

[mfr02]

The original query was "how to make the hull more buoyant". As Doc said, replacing air with foam will not work. The only way to increase the payload is to lose weight in the structure and/or hardware carried.

[Shaun Hendricks]

True, adding foam will not increase boyancy in normal running state, it will increase boyancy in swamped/flooded conditions.

The boat will NOT displace any more water than it would if you just add foam to the chambers. However, if the boat gets swamped, capsizes, etc., it will remain floating and boyant. With just air in the chambers, it could sink unless all the chambers are sealed to the deck and water tight.

By putting foam on the outside of the hull, you are increasing displacement and therefore creating more boyancy.

So, as has been said, if you want it to ride higher in the water, lose some weight in the boat. If you want to keep the boat floating in case of water incursion, use foam in those chambers.