Would you be concerned that a 5hp Johnson CD-12 might be too heavy or too potent for a 19’ Grumman single stern canoe? The boat is rated for up to 7hp, and it has a 5/8" piece of aluminum plate across the transom. Any and all thoughts appreciated.
If it was rated for 7 horse, and it had probably well over 50 years of aging on it, I wouldn’t put a bigger motor on it myself.
It has almost certainly lost strength over the years.
A CD 12 from the '50’s? It probably weighs as much as a modern 15 hp would. It definitely would not be too much power, but you will probably have to have a lot of weight in the bow. A newer 2.5 to 3 hp would probably perform better
If you have it already it would be worth trying. Just be careful and put some weight in the bow. Modern engines are mostly 4 stroke and heavier than the old 2 stroke motors. There is not much metal fatigue in an aluminum canoe if it has not been abused.
A 5 hp engine weighs around 58 pounds plus fuel. That is a lot of weight to all the way aft on a canoe especially if you run it from the rear seat. You might be able to use an extension handle and run it amidships. Good luck. Tell us what happens.