My '73 Midship 25, hull #65, came with a 5hp Petter which I replaced with a 10hp Faryman which I recently replaced with a 10hp air cooled Yanmar diesel..A little noisy, but works fine. Engine compartment is ventilated with a 12 volt automotive cooling fan. It's coupled to the old Farymann transmission with a simple Lovejoy shaft coupler. I still have the original Hallmark sails, plus a 150% Genny from a J-24..

I posted a complete description, with pictures, in the "modifications" forum..Come on boys, pay up! We need this site!

Yanmar model L-100EE (L-E series). Here is the data sheets for all 3 Yanmar air-cooled single cylinder diesel engines.

http://www.yanmar.com/industrial/pdf/L-E%20Series%20Specification%20sheets.pdf

I had already built a 4" high box replacing the original engine hatch when I replaced the Petter with a Farymann. The Farymann A-10 dissolved, and I was not going to spend $5000 on a $3000 boat. I was resigned to using an outboard when I thought of using an inexpensive air-cooled engine. A 16 horse Briggs V-twin Vanguard gasoline engine would fit nicely and can be had for $900. What makes it work, on the starboard side of the engine compartment I cut a 11 inch diameter hole and installed an automotive cooling fan (usually mounted in front of the radiator on most cars today) that size over the hole in the storage locker facing the engine compartment. I sandwitched some hardware cloth behind the fan so the blades are protected from the engine side. That fan pulls air OUT of the engine compartment and blows it out a Dorado type vent topside. The engine has run for hours with the hatch closed with no heating problems. The key to making this work is the fact that the Farymann transmission bolts to the engine bearers and formed the old rear engine mount. So the transmission is rigidly mounted and lined up with the prop shaft. Now all you have to do is get the engine output shaft to line up with the Farymann transmission input shaft. This is a lot easier said than done. I do not use the fuel tank that comes with the engine. The exhaust is dry, routed along the cockpit storage locker rear bulkhead and out the port side just below the rub-rail. I used 1" iron pipe wrapped with fiberglass insulation. The Yanmar has a balance shaft, so even though it's rigidly mounted, vibration is not too bad. This is an "auxillary" engine, so long periods of motoring are not undertaken. I might pull the engine and re-engineer the mounts to some sort of rubber cushion mounts to reduce noise and vibration. For the first time since I have owned this boat, my bilge is Bone Dry. The engine is electric start and comes with a 12 amp alternator. It also has a high quality recoil hand starter and it will start the first pull every time..The 7hp model would have been much easier to install but they are VERY hard to find. I think I paid around $1600 for it. The entire installation was less than $1900. A diesel supply house in Phoenix is where I purchased it. Most of these engines are used on pumps and generators. I hope this info helps you..There is always more than one way to skin a cat. I paid my $20 so maybe soon I can get into the other forums..Fairwinds..