Hybrid Aluminium/Steel Plywood Hard-Chine Hulls

Hi all

looking at some pictures of the Rm-Yachts RM 1260 I was asking myself whether combining an metal frame (e.g. all bulkheads) with a ply planks would be a feasible construction technique for a 11 meter one-off offshore cruiser.

http://www.rm-yachts.com/contenu/,home,1



My questions in particular are:
o How cost-effective are such constructions?
o Is a typical yard able to build such a boat in a good quality?
o How strong are Epoxy bounds between wood and a metal (coefficient of expansions are different, ...)?
o Are you aware of any other example/designers/stock plans for that kind of construction.

I am interested in having several metal structural components in a otherwise very simple constructed boat to provide support for bilge-keels and two unstayed masts (junk rig or cat-ketch).

Thanks for any comments
Babu

 

Citation from the German Book "Konstruktion und Bau von Yachten" H. Dieter Scharping, 3. Auflage

page 405
"Der Eintonner "Bremen", ein Schwesterschiff des Gewinners des Pokals 1978, hatte eine Sandwichaussenhaut aus Sperrholz und GFK mit einem Kern aus Balsa. [...] Die auftretenden Kräfte aus Kiel, Ruder und Rigg wurden von einer leichten Alu-Rohrkonstruktion aufgenommen, [...]. Bei diesem Ron-Holland Entwurf ist das Gewichtsoptimum nicht erreicht worden, denn um die äusseren Belastungen aufzufangen, hätte es keiner Rohrkonstruktion bedurft. [...] Es ist ohnehin problematisch, derartige harte Metallteile einzubauen, weil einmal die Ausdehnungskoeffizienten verschieden gross sind und zum anderen die unterschiedlichen Elaszititätsmoduln an den Berührungsflächen bzw. Verbindungslinien für harte und unelastische Stellen sorgen. Aber für ein kurzlebiges Regattaschiff sind diese Probleme zweitrangig. [...]

Der Einbau von Metallen - ob Stahl oder Alu - ist bei GFK- o. FVK-Booten oft zwingend geboten, wenn es um die Strukturfestigkeit geht: Aufhängung von Kielen, Befestigung von Ruderanlagen, Aufhängung der Wanten und Stagen. Es ist das kleinere Übel, wenn die Verarbeitung werkstoffgerecht erfolgt."

Stantments:
* A sister ship of One-Ton-Cup winner "Bremen" had a sandwich hull built of ply, composite with a balsa core. The forces induced by the keel, rudder and rig were transfered to a lightweight alu tubular structure.
* Prof. D. Scharping doesn't think that this construction has been necessary
* he further states that it is problematic to have such metal parts in the structure due to the different coefficient of expansion and Young-module
* But further down he states that it is often necessary to have metal structures in a composite boat for reasons of structural strength: keel, rudder, shroud ...
* He thinks that it is the "the lesser evil" when the construction is appropriate for the material

Still unclear to me what this means for modern (West) hard-chine boat building

 

Metal/wood construction has been used since the days of sailing ships. The Gougeon brothers have used their West Epoxy to bond metal fittings with success.

 

Its not real popular, perhaps because steel under epoxy can cause a rust problem ?

I have heard of quite a few aluminum tube frames encased in glass, builds.

I guess it would depend on what problems you are trying to solve with the combination of materials.

 

What problems should it solve

Thank you very much for taking the time to read my question and answering!

I was asking because I hoped, that the construction will have the following benefits for a 34 foot one-off go-anywhere sailing boat:
* Many different interior layouts possible in the same hull (like in a metal boat)
* Save the tropic forest by minimizing the amount of wood needed
* Have a rigid structure to connect bilge keels to
* Possibility to build the hull in economic ways (time,cost,quality) by buying the the metal skeleton as a pre-made Kit
* Fair hull (CNC cut) bulkheads, "self fairing" hard chine shell
* Wood where it belongs (water/interior separation: isolation, easy to repair,...)
* Aluminium where it belongs (electrical isolated, not in contact with seawater,...)
*...

I was thinking of a boat like Dudley Dix Didi 34/38 or the in Germany very popular Reinke 10M,S11 constructions.

Any thoughts on that?

 

Build a steel boat. If you want 'go anywhere' capability, there is no other material to choose.

PDW

 

Gotta agree PDW -

PS got the pumps and motor off the cylinder OK'

 

Not to argue but If built and designed for that purpose Aluminum, wood, fiberglass can be pretty tough also LOL

 

I would think going the other way would be a better option steel or aluminum muti chine frame less hull , partial frames where needed with plywood bulkheads to keep it simple and cost effective for an offshore cruiser