I put a Yamaha 2.5 hp 4 stroke on the Daysailer and it works just fine. Last year I was using an Evenrude 9.5 and that worked well too. On the bigger boat (Aquarius 23, 7.0) I have a Johnson 8HP Sailmaster with an alternator for charging the batteries.
The biggest problem with the Evenrude is that it needs an external fuel tank. I had a hose running into the cuddy where I kept a 6 gallon fuel tank. I used about a gallon and a half all last season and having a tank is just a pain. But I love the motor. It's a shorty from 1968. A lot of cool stuff comes from those late 60"s and early 70"s years.
The Yamaha came with a Dinghy that I bought for the big boat. The first time I tried the motor out was on the Daysailer. I laid it in the back of my Ford and trailered to the ramp. When I went to put the motor on the boat I found all the crankcase oil leaked out onto the rubber cargo mat from laying it on its side. I had to pack the boat up and go find oil. Later, once in the water, the motor started up just fine but felt like it was starving for gas. Damn ethanol, I was thinking as I hoisted the sails and set out. After an hour or so on the water I was looking at the motor and noticed a vent on the built in fuel tank. On the way back in I opened the vent and the motor started and purred like the day it was made. Next trip with the motor I had it stored properly in stern hatch on the Aquarius and I had the dinghy tied to our stern. (Our big summer trip.) When we moored at the Vineyard we set up the Yamaha on the dingy and took it to the dock. The vent was open but it seemed to be starving again. Damn ethanol. Later I went back alone to stow the motor and dinghy and take the launch. I was slightly smashed and the motor would barely run even with the choke on and vent cap open. Had to break out the oars, but it was farther than I thought. Finally, just before dark I got a tow out to the boat from a guy who thought I looked like the Tidy Bowl Man (Hawaiian shirt guy paddling a rubber dinghy). I wasn't amused. When I was putting the motor away I noticed that the fuel cutoff valve was only halfway open. I figured this must be it and would try again next time out on the Daysailer.
Next time was yesterday. The Daysailer was rigged and launched. No oil leaked out of the Yamaha and I'm keeping it clamped on the transom from now on. Fuel cutoff fully opened. Ramp crowded with boats. Single handing and stressed. Motor starts, gets me out and away and stalls out. A few pulls and some choke, running again but peters out. So I'm thinking that it wasn't the fuel cutoff after all. Ethanol. Out sailing for a couple of hours and looking at the motor and I realize that I had left the vent valve closed again. The winds died, I dropped the motor, it started right up and ran just fine. In fact on the return to the ramp the winds died altogether and I had to motor back about 2 miles maybe more.
So whats my point? I don't know. I work maintaining heavy machinery, Diesel Trains. About half of the problems we have with them are caused by operator errors. Part of my job is figuring out if it is operator error or if it's actually broke. And here I am sitting on the water thinking about taking a perfectly good carburetor apart to fix something that isn't even broken. Just saying. I'm a mechanic by nature and over the last couple of years I've had at least a dozen carburetors apart to repair ethanol damage. I've seen it eat away accelerator pumps, fuel lines, gaskets. had it turn to a corrosive jelly and eat away aluminum and cadmium. Cars, chainsaws, mowers, outboards (including the Sailmaster), wood splitter, weed whackers and leaf blowers. So why not the Yamaha?
My point is, I guess, is to not jump to conclusions. Stop and brain things out.
Oh, the motors? The 9.5 will plane the Daysailer if sailing solo. The 2.5 will get you to hull speed at about half throttle. And the 8 gets the Aquarius to hull speed with a full crew and provisions at about half throttle also.
I saw a guy and his gal in a dingy zipping around with a "Torketo?" electric. He was going ashore from his 35+' yacht. It's a sharp looking self contained motor and would work well on a Daysailer and there's no fuel to turn on or vent cap to open.
Carl