Condition of old paint
It's important to know what you will be painting over. If the existing paint is old and chipping off, your new paint won't likely stay on well. And if there are many visible layers of old paint on there it sometimes becomes tough to make the hull fair. In some cases all the old paint should be removed down to the gelcoat so that you can start over. Your new paint should also be compatable with the existing paint or your results may suffer so it helps a lot to know what type of paint was last used. If the old paint is good and you have a compatable paint all it might need is some sanding. Sanding bottom paint can be an awful and toxic job. You want to avoid breathing the dust. I remember 20 years ago seeing guys who did this for a living, their faces covered with copper paint dust with only a cheap paper mask for protection. I wonder if they are still alive. So be careful. If you can taste the copper then you are breathing it. Just don't inhale too much.
