@ColRay

Hi Col, I fully endorse Jumpugly’s suggestion.

Here are a few general points that might be useful; I encourage you to look into them further and weigh them carefully.

1. Buoyant material is only effective if the total volume you add to the hull exceeds (even slightly) the volume of the submerged portion; otherwise, it serves no purpose—it is essentially useless.

2. By "buoyant material," we mean something significantly lighter than water, which remains impermeable and does not become waterlogged in the event of flooding. Furthermore, it must not undergo any physical or chemical changes upon contact with water.

3. While no one has suggested it yet, someone might propose using expanding foam. Although it is lightweight, water-resistant, and (to my knowledge) chemically inert in water, be very careful: it must never be placed inside a fully enclosed space! If it has nowhere to expand, it will deform or even burst the hull.
During the curing and stabilization process, the material expands to many times its original volume.
You are likely already aware of this, but it’s worth reiterating—many people have fallen into this trap.

4. The buoyant material must be securely fastened to the model. Its specific location—whether below or above the waterline—matters less than ensuring it remains firmly attached to the ship in the event of flooding, capsizing, or other incidents. If it detaches, it fails its purpose and becomes useless.

5. In a previous discussion, I explained why spherical shapes are not the most geometrically efficient choice for filling a space—whether for ballast or for providing reserve buoyancy. I would avoid them, but if you’d like to explore this further, we can certainly discuss it.


Regarding the choice of material, as previously mentioned, I agree with Jumpugly. It would be interesting to find a material that has these characteristics while also being fireproof—though I suspect that might be somewhat difficult.

N.B. Assuming point 1 is clearly understood, we still need to determine the practical method for applying the right amount to ensure it serves its purpose. I can elaborate on this aspect if necessary.

I have one slight concern with this project, it all started by using a very small sized model CAD file the boat was about match box size the wall where very thin, but after scaling up ended up a tad on the thick side , although not solid has a skin over a honeycombed core I feel the vessel could end up top heavy. I guess only time will tell.
As with all I do .. Always a 'Plan B' Col

Thanks once again for all the help with my project Col

He Col!
I love the Polyethylene foam packing material that comes in many electronic shipping boxes. It's designed for cushioning and is not rigid like styrofoam. It's easy to cut, doesn't create millions of loose styrofoam dust pellets when you cut it, is malleable, and stays in place.
😉

Table tennis balls work well I am told by the Buxton model boat club I bought a box of 50 for very little money and glue them in with a hot glue gun.

I have never used any and still have all of them.
I suggest when the model is finished you do the 'Upside down test'. As it says turn the model upside down and see what falls out and then go back and secure it.
Roy