As you say, it's veneer. One of the best ways is to replace the veneer with new veneer. If the chipped edges are jagged, using a straightedge score lines around the chip (you only need to go as deep as the veneer) and remove the old veneer so you have straight sides. Place masking tape over the area and use a pencil to mark your edges on the tape. Peel the tape off and place the tape on your new veneer. Cut the new veneer according to your lines. You should now have a new piece that fits the chipped area. Rough up the wood
where the chip is so the glue will have good adherence and be sure to clean the area good with thinner before gluing. Wait until dry and put the glue (definitely non-water based wood glue on a boat) in the chip area and place the new veneer in the spot. Clamp it until the glue is dry. If you can't clamp it because of the location, if it's on a flat/semi-flat surface place something on it (doesn't need to be supper heavy, only 1-2#s and use wax paper between your clamp/weight). If you can't place something on it, use the tape to hold it down as well as possible. Follow up with sanding
to smooth the joints and the varnish
Because of the wood grain, you need enough new veneer to try to match the flow of the grain as well as possible (so it doesn't stick out like a sore thumb when you are done). For bigger chips you may find it best to use a chisel by hand only to remove a larger section of the old veneer for better matching of the grain. And of course, if you currently have mahogany, use mahogany as the replacement.