It might be wise to mention your idea to the vet. He/she may be able to give you some recommendations.
I think the worst problem would be if your dog was allergic to shellfish....and the second problem would be a too-massive dose for the dog's weight.
Otherwise, Glucosamine/Chondroitin supplements are generally without any side effects.
Most dogs are quite happy on these supplements with no change to their general health. They are natural substances normally produced in the body anyway, but their levels can drop in older age.
I gave it to my dog and she was fine on it. I gave it to her for a few years. Her weight was 30lbs so the dose for her was 500mg Glucosamine and 200 of Chondroitin (combined in one capsule once daily with food.) For a 47lb dog you would probably be looking at between 500mg (Glucosamine) and 700mg, and Chondroitin between 200mg and 300.
But do check with your vet first and maybe ask advice about that