Filling a rubber dinghy with foam?

[David_Jersey]

I have had an idea!

I have a very nice Avon Dinghy, although 15 years old it has no patches etc but it is still too nice to leave chained to a Pontoon 24/7.

Rather than bringing the dinghy back and forth from home every trip I need something to "float" across a very sheltered harbour and be able to leave on the mooring and chained to a pontoon 24/7.

For a previous boat I had a very cheap plywood pram dinghy which did the job, but I sold this with the last boat (and kept the Avon!) - the only problem with the pram dinghy was that after many years with Avons I did find it rather a tippy b#gger, I never fell in, but I had my "moments"!!

My options are:-

1) Another cheap pram type dinghy - too "tippy"

2) A plastic dinghy with built in buoyancy - hard to get cheap S/H

3) A cheap s/h inflatable - they require frequesnt (ish) pumping up (especially cheap s/h ones!) and keeping them afloat 24/7 doesn't do them a lot of good.

My idea is to get a very very cheap small s/h inflatable dinghy, doesn't matter if it only holds air for less than 5 minutes and has more patches than a quilt or more holes than a sieve, because...............I am going to fill it full of foam!

My questions are, has anyone done this? Would the usual expanding foam react with the Dinghy "rubber" (ie does it contain chemicals that would "eat" the rubber?). I was also thinking of coating the Dinghy with some form of Epoxy or similar (on the basis that anything I buy will probably not be water (air!) tight, and I know you gotta keep the foam dry).

I am not sure whether I patch the dinghy first, then coat it with epoxy and then fill with expanding foam (i figure this was way would give me a bit of "leeway" in case I over fill it!). Or fill it with expanding foam first, then epoxy it.

Perhaps this is not the cheapest route and the resulting "creation" may not win any beaty contests, but as long as it does the job I will put any resulting ugliness down to a cunning anti theft device!

Any thoughts / words of wisdom (I have not used epoxy or expanding foam before).

 

[bendyone]

Good idea, might work, but could be very messy if you use too much foam. Why not cover the filled dinghy in GRP? Be sure to have a vidio running when you fill it!

 

[tazzle]

I'm open to correction, but I have a feeling that standard Polyurethane builder's foam is not closed-cell - i.e. it will absorb water if the skin is punctured. Could be wrong.

 

[David_Jersey]

[ QUOTE ]
Why not cover the filled dinghy in GRP?

[/ QUOTE ] - I was rather hoping to get away with just "painting on" a coat (or two) of epoxy, rather than doing any laminating. Of course epoxy is not cheap, maybe I could get away with just the resin stuff that is used to "make" GRP???


[ QUOTE ]
Be sure to have a vidio running when you fill it!

[/ QUOTE ]

Actually that is not a bad idea, might pay for a proper dinghy!

 

[David_Jersey]

[ QUOTE ]
I'm open to correction, but I have a feeling that standard Polyurethane builder's foam is not closed-cell - i.e. it will absorb water if the skin is punctured. Could be wrong.

[/ QUOTE ]

I was assuming that this was the case, hence the covering of epoxy - but I didn't realise you could get any other sort. Anyone know? - cos it might save me messing around with coating it with epoxy (or similar) to make 100% sure it was waterproof.

BTW I will post up photos of the finished "creation"!!!

 

[Stemar]

I don't think the covering with epoxy bit would work, 'cos the whole advantage of a rubber duck is that it's flexible. Epoxy isn't. At least, not compared to a rubber duck which, even when filled with foam is still going to stretch in the sun and bend with waves and bumps against the pontoon or your boat.

Sheathing the beast in grp isn't such a daft idea as it sounds at first. I've seen an aluminium "rib" which, allegedly, adds rigidity and puncture resistance to the advantages of the rib. Cost and time would probably make it a non-starter unless you have nothing better to do for a few weeks and an unlimited supply of glass cloth and resin. If you have, please let me know when I can come and pick up a load /forums/images/graemlins/smile.gif

I wouldn't trust builder's foam, but Mr Sadler and M Etap seem to have found some stuff that might work. I think I'd want to know more about how it would stand up over time to the flexing of the boat before I spent much time or money on it though.

 

[Talbot]

This has been done, and IIRC there was an article on PBO- as a means of extending the life of a dead inflatable.

 

[VicS]

The builders foam works by reacting with moisture in the air, I believe, so it may not work in large confined spaces. The resulting foam is not "closed cell" so could absorb water. Closed cell foams are produced with a two component system. It should be possible to get them from glassfibre suppliers especially one that supplies materials for making canoes.

In either case it will be difficult to judge the quantity required to fill the compartments and impossible to actually get the mixture in unless you cut big holes in place of the valves.

IMHO your best bet is to find a tatty old fibreglass dinghy which is more stable than your old one. It'll probably be cheaper and last a lot longer.

 

[simonfraser]

i think it's a great idea, please let me know what foam should be used !

just make sure you never want to roll it up again )

 

[Blueboatman]

I have seen this done to a quite large RIB,sheathed comprehensively in grp..
The owner said it was a bir er heavier and a b--ger when it rubbed up against his topsides!
Using 2 part foam? Why not,it will prob cost you £100 in foam though-and if you dont get enough in there it wil be,er,lumpy?saggy?..I think the video and using too much foam is the way to go,.Hey at worst
you will get a bigger dinghy than when you started!
There was a short thread on here about 10 years ago where someone asked if it was possible to construct an inflatable dinghy from a kit or a set of plans....It ended with the one response''Are you mad?"
How about a forum whip round,say a pound a pop to ensure you buy enough foam for this enterprise,could be fun

 

[silver-fox]

I did something very similar a few years ago - but not with an inflatable.

A small group of us decided to build a raft of plywood and enter a charity raft race. Like all good ideas thought up over a pint it was flawed in that we had only 24 hours to build and launch the raft.

We built two Vee shaped hulls so it was more of a catamaran than a raft but we quickly realised it wasn't going to be watertight so we quickly took it to a friend of a friend who filled it with foam. It worked, the raft floated and as a result we were able to use the raft in the race every year for about 10 years. two small points though.

1. We didn't leave the raft continuously afloat
2. When the boat is filled with foam there is a degree of guesswork as it continues to expand for several minutes after it comes out of the dispenser nozzle. In our case this sprang a few joints. In the case of inflatable it might cause a bit of over or under inflation.

Good luck!

 

[David_Jersey]

Ok folks,

The consensus seems to be that filling it with expanding foam will be "interesting" /forums/images/graemlins/laugh.gif So OBVIOUSLY this is the route I will be going down!! I really want to see what happens...........

I have the most important part sorted up already - over lunch I lined up the camerman /forums/images/graemlins/grin.gif

I am probably going to try and fill it up with foam first, and then look at coating it with Resin / epoxy - possibly using GRP on the undersides. No firm plan, just going to make it up as I go along /forums/images/graemlins/smirk.gif

I hope to start next weekend, but no promises. Photos to be posted if succesful..........a video if not!

PS thanks to Richard from Jersey for the donation of an old Avon..........and linking my wanted advert to this thread!

 

[paul_williams]

thought about this one myself. think standing dinghy on end, hanging it? and pouring the foam in from the top would work. ie pour a bit in, let it expand and fill the void, pour a bit more in, let expand, continue till dinghy is full. worked on my floor of a fast fisher i built, so why not on an inflatable? please post the result!
good luck.
paul

 

[polwart]

don't do it - it will be a disaster. as already stated expanding foam is not closed cell -so any water that gets in will stay in and eventually it will sink.

I doubt epoxy will stick particularly well to hypalon/pvc - never minding the issues of flexibility.

expanding foam is expensive (as is epoxy) - for the cost you could easily buy a cheap fibreglass or moulded plastic boat. There are some rotomoulded plastic dingies with hull shapes similar to an inflatable that will have all the stability etc. you want.

 

[MichaelHomsany]

Hi,

Seen this done twice, once in Pago Pago, once here in Savusavu. The first time they used two part closed cell foam, the second open cell, but then they glassed the whole thing over using polyester resin (one of the two plastic sisters: Polly Ester and Ethel Acetate!).

The cautions on the expanding arent a joke. An engineer on a purse seiner told story abt putting in a new hold, they shored everything up with 4X2s and plywood and the expansion bulged the hull out!

In the above mentioned repairs, they put slits in the top of the tubes to allow for expansion during the process. A trick for mixing the two part foam is to get a bunch of alloy beer cans and premeasure about 2 fingers (horizontal) of the liquid of both parts into each can. As you work, yell for a helper to mix the next batch as the can in your hand starts to heat.

After the foam expands, it will continue to expand for around the next 24 hours, albeit at a slower rate, for a total of around another 15% increase in volume or so.

When I built our current dink, most of the floatation was closed cell foam, then I topped up the low spots with builders foam on the grounds that being at the top, it wouldnt get water logged.

Hope this helps,
Michael

 

[Guest]

I know a guy who poured in two part foam .... it worked - but life of dinghy was relatively short considering a) the expense of the foam, b) that it was a leaky patched job and the foam stressed the already weak structure / seams.

You may be luckier than my mate John was ...

 

[ShipsWoofy]

[ QUOTE ]
don't do it - it will be a disaster. as already stated expanding foam is not closed cell -so any water that gets in will stay in and eventually it will sink.

[/ QUOTE ]

Was that an order!

[ QUOTE ]
I doubt epoxy will stick particularly well to hypalon/pvc - never minding the issues of flexibility.

[/ QUOTE ]

Ever heard of finding out? It doesn't actually need to adhere, in the same way the gel coat does not adhere to the mold, do you see?

[ QUOTE ]
expanding foam is expensive (as is epoxy) - for the cost you could easily buy a cheap fibreglass or moulded plastic boat. There are some rotomoulded plastic dingies with hull shapes similar to an inflatable that will have all the stability etc. you want.

[/ QUOTE ]

Have you never tried something just to see, I bet you had daddy buy you a go cart rather than scouring the local tip with your mates for pram wheels for your own design MkIII as the last two snapped. It's how you learn to do stuff.

 

[David_Jersey]

mmmmm. /forums/images/graemlins/confused.gif

Seems to be two distinct camps here

A) those who have used expanding foam and strongly caution against it's use for this project;

and

B) those who want to see the video /forums/images/graemlins/ooo.gif

I would normally find myself solidly in camp B......... /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

Now that I have a dinghy to play with it would seem a shame not to go ahead, BUT given what folk have said here I will mull this over during the week.

 

[ShipsWoofy]

If you had a dinghy with pointy sponsons, what would stop you cutting the ends off for filling and then gluing them back on once full.

 

[bendyone]

Why not invite everyone over to watch, belivers in the front row and the rest in the pub.