Marking harness line position?
 

On my old black gripped HPL boom the harness line position markers have rubbed off.

When I switch between sails, I need to move the harness lines. Is there a good trick for marking harness line position between sail sizes? I tried a silver permanent marker but it rubbed off.
Is there a particularly permanent marker that would last?
Any suggestions?

It burns quite a bit of time and energy to rediscover the perfect position for the lines and retighten them especially when sailing overpowered and in choppy water.

There are white felt tip paint marker pens that I have used to mark masts, mast extensions and booms. The paint doesn't last forever, but you can re-paint very quickly.

Try office supplies or hardware stores.

Mark the sails with a piece of electricians tape. (centre point of harness lines)