small boat

[mehdiaityoussef]

hello,

I am student in naval engineering, I work now on a small pleasure craft under 6 m, I need help to choose the material: wood, composite or aluminum.

thank you

[Olav]

I'd go for wood. Or maybe composite. No, wait: Aluminium!

Just kidding.

Let's get serious:

What's the intended use of the boat? What's its shape (developable surfaces or rather complex curvature?), who's going to build it (amateur home builder with limited experience and tools or professional yard?), what about the number of units that are planned to be made? Are there any weight issues, what about costs?

Without answers to the questions above (and probably others that I forgot to mention) it's not possible to give a proper statement on the "best" material for the project.

[mehdiaityoussef]

it would be a central console boat, the cost must be low, for forms i think of progressive v-shape but it is not decided yet, it is a boat designed for small output ,the category is C.
I think in aluminum to provide weight, resist facilities maintenance etc, but for a series construction I know that the composite aproprier So here I am hesitant.
Excuse my English

[FMS]

Small output = 5 or 10 boats?

[PAR]

If low cost is the driving consideration then aluminum is decidedly out of the picture. Composite is likely out as well, as the core materials are often quite costly, so this leaves wooden of some sort. I'd recommend sheathed strip planked as the least costly, of the hull material choices, though plywood will run a fairly close second. One of the most important things an engineer can do is work up materials cost effectiveness graphs, to help with various projects.

[liki]

I'd assume GRP to excel over the other alternatives already with surprisingly small production runs. All factors considered, including mold making. Somebody here can likely provide an example based on realistic figures?

[PAR]

Your assumptions would be incorrect Iiki. GRP builds pay for themselves in larger production runs, not small ones as there are a lot of associated costs, not to mention a mold. Even a small boat mold, could run into several 10's of thousands of dollars in man hours and materials. As a one off, low production run build, say foam over a jig, the materials costs as well as the fairing costs, are much higher then say a low production run, plywood over frame build or even a well jigged stripped plank build, even with it's tedious and man hour consuming planking schedule.

Providing an example would be difficult, as you'd need to compare apples to apples, in that it would need to be the same or very nearly so hull and accommodations build in both compared build methods, which of course is exceedingly rare.

[liki]

Without any real knowledge I won't start an argument over this but I welcome any insight on this subject. My view is also heavily influenced by the cost of labour in here, that puts emphasis on per-unit time savings earlier.

[PAR]

It wouldn't be unreasonable to have 500 man hours in a GRP mold for a small pleasure craft. I don't know what your average shop rate is, but this bounces the GRP build right out the window, unless it's a one off. As a one off, you'll have much more fairing to do, so the labor costs go right up again. Plywood is mostly fair if accurately cut and hung on a well made set of molds. Seams need to be faired, but broad expanses of planking are naturally fair with these sheet goods, reducing fairing time considerably.

[DCockey]

How would you compare aluminum for very low volume production? Material costs are may be higher than wood but I wonder if labor might be less, assuming the boat is designed for it with developable surfaces and so that little tooling is needed. I've seen some small shops in BC building small boats in aluminum.