Not many responses here. I subscribe to some boating forums as well and will offer up advice I have seen on them.



You might try Soft Scrub (if the stain is on the surface) or Sno Bowl toilet bowl cleaner (if you believe the stain has soaked into the gelcoat).



I`ve read that Sno Bowl will damage chrome if left in contact too long. Some of the old timers swear by it to remove fish blood stains though. I suspect it has bleach in it.



As always, YMMV. I would definitely try a test spot using an old toothbrush (or similar) before soaking down the entire stain.



Best of luck, TerryD