Here's a picture I took this AM of some plate. Any thoughts?

Ice damage? but kind looks like a lifeboat or something.

Without a knowledge of where the material is on a vessel it is difficult.
The shape of these markings is of a beach mark similar to tidal marks on a beach. These markings occur when steel or other materials operate in the post yield stress area. There is an alternating stress present which puts the material into tension somewhere in the stress cycle. They are called beachmarks.

regards
jimmy

I am not quite sure where on the boat it came from, probably the bow area. It is a piece of cropped out plate we have kicking around the office from one of the smaller boats.
As you can see it is aluminum plate, marine grade 5086, 1/4" in thickness. I think a 6" timber end would probably fit in the groove quite nicely.
The black marks are from building.

Hi Jk,

The main damage in the picture loks more like impact damage, and striations/ scoring from a hard object to me.
The material would have to be a very ductile material, such as Mild steel ( 30% extension before it will fail) or Aluminium to enable it to stretch that much without breaking. A brittle / short material such as cast iron would have fractured long before it had strained/ yielded so much.
To me it appears that an object with a corner struck the plate, at an angle, moving from the top of the picture downwards, creating a steep indentation above the steel rule, with a definite scratch mark starting directly under the rule, the scratch mark and indentation becoming shallower as the object moved down the picture.
The thick layer of paint originally on the plate appears to have flaked off in the damaged area and been repainted, overall the paint finish looks very new and shiny.
Some of the new paint on the edge of the bare patch looks as if it has been "feathered / tapered off at the lower edge, possibly the bare patch was created by deliberatly scraping off some of the paint to reveal the surface for examination.
I wrote the above simultaneously with your last Post and didn't bother to re submit it but looking at the high shine on the paint has your office cleaner been spraying it with furniture Polish?
I am not sure about the comments about Beach Marks, I always understood that these were visible on the face that had cracked, not on the original face, and a quick Google of the term appears to confirm this.

BP