You could also inbed solid pvc.

Also, solid infused glass laminate, if it is strong enough.

Finally, aluminum might not be appropriate in salt water, or at all. Perhaps inbeding a stainless steel plate might be a better choice.

On June 19, 2018 8:40:00 AM UTC, "oysteinchina@yahoo.com [harryproa]" <harryproa@yahoogroups.com.au> wrote:
|Higher density PVC foam is available, like 200kg/m3 or higher used by
|commercial builders as backing plates. when combined with correct glass
|fiber / epoxy layers to ensure stiffness. Steel washers of appropriate
|size is also required.
|
|
| Oystein