It's not the size
It's not the size that counts as much as the mounting, and prop. The others are right when they say get the long shaft. Keeping the prop in the water will always give you more thrust than having it comming out of the water. If you can't find a long shaft, consider moving the motor mount lower. Now the problem with most small motors is they were designed to be put on a row boat/dingy for the really small ones. The pitch on the prop they come with is too much when you mount them on a sail boat, so that the engine can't reach its full wide open throttle RPM's. This means that the performance of the engine is not at its peak. You will not get the full rated out put (Horse Power) and the prop will cavitate (no thrust). I have 2, New Port 23's. One has an old British Seagull, and the other a newer, but no longer made Evenrude. The Sea Gull is a 7HP and the Evevrude an 8HP. The seagull with it's 5 blade prop and lower RPM's along with it's longer shaft moves the boat much faster, and has much more pulling power than the Evenrude, despite that it has less HP. These are small boats, and the only reason I can think of for going to an electric starter is to get a small alt. on the engine. However my Evenrude does not have electric start and does have a small alt., about 4.5 amps measured with a meter, at 13.5 v. Extra weight especially hanging off the stern will slow down your boat, and can also make it harder to handle. A heavier motor is also harder to lift up on the mount. It may be easier to start, but would the wife or kids be able to lower the heavier motor? I have a custom 4 blade prop I just got for my Evenrude I will try this spring. It has 1" less pitch and of corse the 2 extra blades. I have done this before and know it will 1) lower fuel consumption, 2) increase speed, 3) lessen cavitation. and 4) give me more thrust for motoring into a wind or current. 5) give me more thrust for towing other boats. Maybe what you really need is to just have your old outboard rebuilt. After cleanning out all the carbon, a set of new rings, maybe new reed valves, and a carb rebuild, getting all the old carbon out of the exhaust system, new spark plug, and strater rope. It might work better than anything you could find new. To top it off, the savings could be used for a new custom prop.
