Thanks guys.

Your comments above really made me wiser and also made me think this: What if a sealed compartment (in the boats front part) with or without expansion foam actually had some holes in it - with some soft expanding rubber membrane covering the holes to take extra pressure, and still keep the compartment watertight? The holes and the membrane should off course be placed inside the boat between the front compartment and the engine bay.
Well, just an idea. Maybe someone has comments about this?

Cheers!

Woodie.

Woodie,
There is a product on the market that works that way for your trailer wheel bearings. You fill the hub with oil - not grease - and close it up. The unit has a rubber expandable button that goes in and out with temp and pressure so water is not sucked in or oil vented out when the hub heats up or cools down. You could try and make some thing like that, however my deck bulged up quite a bit, so you'd need to use a balloon or condom!! (wouldn't that be interesting to explain) or similar to allow the expansion. When I drilled the hole, it blew out under pressure. Maybe a pushrod seal with a fatter than normal (short) pushrod installed. Would allow air to leak in and out, and in the even of a flip, would probably remain watertight.

Actually, I'm going to try that idea. Very short fat rod, washer soldered on at each end so it can't slip out. Smear a little grease on it. Under any sort of pressure air will seep in either direction - and no dodgy expanding rubber devices to explain.

Hi folks

Even though I opened the original topic for a bit of fun, you have all given me a lot of good ideas and things to think about. I thank you for that and for your contributions.

The condom idea made me laugh but I could consider a non latex version being useful (to avoid it breaking down).

Today my pool noodles arrived and I can see why they are often used for model boat buoyancy. I will be trying them out (thank you for your recommendations).

I’ve had another thought today for buoyancy in the side sections of my mono hull (suggested by my twin brother but with me taking the concept further):

What about taking a bicycle inner tube? Cut off the two ends and (use the latest weld type solution now available for puncture repairs) to seal the ends. Thus leaving a length of flexible tubing that can be inflated as required in situ. Thus enabling easy deflation of the tube for later removal if required.

What do you think?

Digressing slightly:

If the hollow sealed box expansion causes problems with hulls potentially splitting etc, what impact could that have on our sealed air tight radio boxes when left in full sun prior to running?

Could that explain why when on the water, the box in question cools and later appears to have condensation moisture ingress?

Cheers
Craig

Hi Craig.
I did laugh at my own comment afterwards.
The bike tube idea could be a good one.

Re the radio box. Probably right, although the rod seals would let air leak past them under pressure. Have not seen a radio box ever swell up under pressure. When hot (in the sun) the condensation will be the water in the air (humidity). Like a glasshouse. How often do you see them fogged up.

Hi Folks

On the bike tube idea, I decided to give it a go today.

I cut the tubes then clamped the ends together with solvent weld. Then I folded the end sections back and nipped them together tightly with two plastic cable ties at each end.

The big advantage for my shallow mono hull is that these are dead easy to install in the narrow side sections without having to remove the radio box. I need to remove them for access to the turn fin bolts. Also you can pump just the right amount of air in to have them held sufficiently secure in place knowing that unlike some types of foam, they won’t hold water.

I inflated one with quite a lot of air and did the dunk test. No air bubbles leaked out so it appears to hold its air.

The photo shows both tubes, one inflated and one not.

Cheers
Craig

Hi Folks
Just an update on this original topic for information:

The cut off bicycle inner tubes have delivered results in keeping my Lynx (Delta Force) horizontal after flipping it! However for my new build project the Prestwich Model Boats Thunder FSRV Gas multi boat, I have decided to use expanding PU foam again.
However unlike with my Lynx, this time the sealed compartments will be filled with a 2 part foam mix and never again the can spray stuff that relies upon moisture to make it expand and set.
The two part stuff I bought is what they use in full sized boats low density high expansion (catalytic setting so the mix sets properly all the way through) and sold as waterproof unless crushed. I figure that the Epoxy Glass hull combined with this stuff should give no problems. If my foam gets crushed the boat will be pretty much totalled by definition!

With mono hulls such as the Lynx/Delta Force or indeed my new Thunder there is very little freeboard towards the rear side sections. That for me makes it difficult to use things like pool noodles to give sufficient flotation. So for me boxing those sections off and filling with foam is the ideal solution.
Cheers
Craig

Craig,

There is one thing to consider with two part foam - expansion. unless you get the perfect amount (or less)the foam will expand as the chemical reaction takes place - sometimes warping the area of the hull it is applied to. I have seen many boats with this situation, and once it happens, for the most part, it is irreversible. I would craft various pool noodles and cut and glue or wrap them together to get the fit I wanted in place of two part foam. Besides, a single pool noodle will hold a small human afloat, and as long as the proper amount is placed in the hull and secured you would not have any issues.

Mitch

It is about twenty + years since I last used 2 part foam in a model boat.

I will use the same procedure again, 50/50 mix well stirred (warm temperature) and further applications sufficient enough to fill the voids with expansion holes to avoid any blow out or deck busting prior to the stuff setting.

Pool noodles for me simply don't cut it for me. Please bear in mind that I am talking of boats that have minimal flotation sections in their hind quarters.

Cheers
Craig

Hi Folks

I my last thread I said that I would revert back to the 2 part catalytic foam if I could source the right product.

I found a marine grade 2 part low density foam and it was so much easier to apply and unlike the lousy aerosol foam, this stuff set solid throughout within 15 minutes of pouring in the liquid mix.
The bow of my Epoxy Thunder hull now feels rock solid and thankfully with the vent holes in the bulkhead there has been no distortion of the hull during the process.
All that remains is to trim away the waste and seal the holes with fine mat and epoxy.






Cheers
Craig

I made the mistake of not researching foam and it's expanding times ECT. I ended up with the front of my cat hull having high points and low points WAVES in the fiberglass. I'm not saying dont use this stuff,but they make foam that expands slow and low this is what I use now and it works great. Here is the site....


Handi-Flow®