Hi John,
I think the only reason to go any thicker than 3/16 or 1/4 would be for stiffness, and you can deal with that by welding on stiffeners were needed. As for material choice, I think you have the right idea: use whatever you're comfortable working with. Stainless is nice, but hard on cutting tools. Steel just needs more corrosion control (paint).
You may want to do a little homework on the forces involved, mainly torque. It's probably much less than you're thinking. I know I was surprised when I actually did a little math AFTER finishing my first installation. Your motor's spec sheet should give you a max torque or at least a torque constant. Multiply the T.C. by max amps to get max motor torque. Multiply that number by your reduction ratio to get max prop shaft torque, then add a little fudge factor for when you run over a log. Some may laugh at my "cave man" math. I'd welcome any refinements/corrections. Anyhow, I think you'll see well under 50 ft-lb at the prop shaft for any motor in the size range we're talking about.
I used 1/2 inch aluminum plate and 3/8 wall aluminum angle, bolted together with 3/8 stainless bolts on a couple of my installs. (see pics under "McMillan" for an example). That was extreme overkill but very stiff without adding additional bracing, and all that aluminum helps dissipate heat.
Regards,
Jim McMillan
--- In electricboats@yahoogroups.com, John Raynes <johncraynes@...> wrote:
>
> John,
>
> I used 3/16" plate for my inboard electric.
>
> John Raynes
>
> SEE: You Tube: "Johns Electric Boats"
>
> On Fri, Jan 14, 2011 at 7:14 AM, John Green <v_2jgree@...> wrote:
>
> > Hi,
> > As I intend experimenting, I wish to use steel for the main mounting plate
> > for the bearing, and the motor(s). This will allow oxy-acetylene torching of
> > slots for belt adjustment, as well as holes for decreasing the weight, and
> > easy welding for braces and mounts etc.
> > My overall expected electric power might be around 3 or 4 HP.
> > This would supply 50% of my hull speed power requirement.
> > It might be prudent to overbuild on this item though, up to the total for
> > my hull speed, 6 HP, plus a margin.
> > I would like opinions:
> > Would 3/8 inch plate work, or am I likely to need 1/2 inch?
> > Bear in mind I can add angle iron or ribbing to decrease flex.
> >
> > Thanks,
> > John
> >
> >
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