Polystyrene (Styrodur) Hull ?

[Oliver Pischke]

Hi folks,

This is probably a faq or maybe even a stupid question ...

Would it be possible to mill the hull of a 21 ft Boat (Mini Transat class) from high density Polystyrene foam (Styrodur) and apply a few layers of glass or carbon ? I have access to a LARGE milling machine that would be able to mill the complete hull from a single (or rather glued together) block of high density extruded Polystyrene. Is this possible at all ?

cheers

Olli

olli@spring.de

[ErikG]

Kidding aside, I am quite sure you could use it for milling a plug to then make a mold to then make a boat, you could also skip the first step and just mill a mold at once. It all depends on the quality of the millingmachine and what your tolerances are.

What specific foam to use seems to be different wherever you go. I have not done it myself, but I just called around to see how it works and to get prices. Some just use a foam some first mill in foam then apply a layer of paste in wich they do the final milling and subsequent fairing.

Normally it costs quite a bit ( I was quoted 500 - 900 USD per square meter)
Prices depending on complexity of the shape.

To mill the boat itself sounds pretty difficult. The result would be extremely flimsy and probably useless. Maybe someone has done it successfully with some special technique, but I'd favour a plug-mould technicque. You could even sell more boats later on if you wanted to.

Good luck

[Jeff]

Hi Oliver,

First, what I really wanted to say is welcome to the Boat Design Forums! I hope you will keep us updated as your project moves forward.

Exactly as Erik says, I think it would be much more practical for you to mill the plug and then make a mold or mill a mold than to try and mill the actual hull. I have no hands on experience with CNC materials, so take the following with a grain of salt.

1.) CNC milling allows you to create a very accurately finished mold and thus a nicely finished accurate hull. If you mill the actual foam of the boat and then build as a one-off you lose some of the accuracy and have to do a lot more sanding with a longboard and fairing by eye.

2.) To achieve optimum weight / strength characteristics of the finished core, the foam would be too thin to not distort before the composite skin – core – skin were finished. I suppose you could mill, fiberglass one side, build a jig, then mill the other, then fiberglass the other side while still supported by the jig, then finish, but that seems like a lot of work. With that much effort, it would seem more advantageous to either mill a somewhat disposable mold or have a mold from a plug which could be reused.

3.) I have no experience with the foam used for milling, but I wonder if its properties would be desirable for a core in the finished hull – my guess would be that it wouldn't be the most desirable, but I could be totally wrong.

I was quoted 500 - 900 USD per square meter

Well, right now I can afford something the size of a canoe at least