HP
I have a North American 23' in Texas that I use an old 1.2 HP British Seagull (175 model) on, and it makes hull speed with ease, how ever all of the new engines do not have a prop like the Sea Gull. I use a Feather weight 40 (British Seagull)long shaft on my Vn 23' in Michigan and it works fine too. My other Vn 23' has a 7 HP Evinrude and it works OK, but it's biggest problem is that it is a standard length shaft motor (20"). It has a 4 bladed 5" prop on it. The best new motor for your money I think is the Tohatsu. They make the Nissan and Mercs so they are all the same engine. For a 19', 4 HP (20")shoud be plenty, but I would go the 6 HP extra long shaft(25") if you want to be able to charge your batteries while on your way out of the ramp/docks, and while comming into anchorages. The longer the shaft the better. It will help keep the prop in the water when the swells come up. A problem on small sail boats using out boards. I think you may find that the boat is rated for 2.5-4 Hp Going up to a 4 stroke 6 might require a stronger out board bracket. When these boats were built, small out boards were all 2 stroke, so were much lighter than todays motors. I always find the best motor for a sail boat kicker to be a British Seagull. I know they are all old, but not as old as they look. But they run for ever, and are easy to repair. They will out last any of the new motors. My Vn 23' kicker is a '58 model. My grand son will probabley pass it on to his kids. If gasoline still exsists.