If you have added a console for radios, etc. under the factory installed shelf, you may want to see how secure it is. I noticed a flex in rough water and inspected the mounting. On a TC-255, the shelf is held in place with the 2 bolts that secure the roof rails. I noticed that the next 2 roof rail bolts were about 2" aft of the shelf. Here's the fix I came up with. It's now rock solid.
I started with 2 stainless straps similar the this and a flat headed bolt usually used on toilets!
With the flat plate secured by the roof rail bolt, the flat head bolt head is pinned to the ceiling and protrudes through the shelf. A washer and acorn nut secure the shelf.
You will have to loosen the whole shelf while installing these. Don't try this alone while your wife is at a meeting. Don't ask me how I know this part!

I started with 2 stainless straps similar the this and a flat headed bolt usually used on toilets!

With the flat plate secured by the roof rail bolt, the flat head bolt head is pinned to the ceiling and protrudes through the shelf. A washer and acorn nut secure the shelf.
You will have to loosen the whole shelf while installing these. Don't try this alone while your wife is at a meeting. Don't ask me how I know this part!