Used to reseal the keel on my brother-in-law's aluminum bass tracker boat.  Had been fighting leaks on this boat for past three years.  He had tried some of that infomercial rubberized spray, which was totally ineffective, and various epoxies, nothing worked.. Boat shop recommended this product.  Read the online reviews and everyone seemed happy with it. In our case, we had to spend a fair amount of time prepping the surface first to remove all the other unsuccessful products.  The 3M Marine 5200 sealant goes on easy with a caulk gun, although as others have said, you need to make sure you get it where you want it, or clean up the excess with acetone right away, because once it sets up it is permanent. The product comes in three formulations with different curing times.  The version we used was the long set up time one; 24-48 hours to skin over, then 7 days to fully cure, so you can't rush the job.  Took the boat out last weekend on a shakedown cruise around the lake.  When we came back in, there was barely any moisture in the bilge.  Before using this product, we could barely get the boat in the water before the bilge pump was coming on. So far, we are very happy with the result and with this product.  Will do a follow up later on long-term durability, but highly recommended based on experience thus far.