model 21a
I own a H33, 1981 and the original engine had been replaced with a Westerbeke 21a. This engine is rated at 24 hp, not 21. I've found it to be a very sound engine but the maintance of this engine has been solid and timely. Your concern about the aft-facing impeller plate is not too big of a deal. It does take some fancy finger work to get two of the six screws out but I've done it a couple time. It would be a challange in any type of sea way, much easier at a dock or calm anchorage. Also depends on your engine compartment access, mine is fairly good. My biggest problem has been the heat exchanger. I had to replace it and considered rebuilding the old one vs. buying new. The cost was about $200 more for a new one ($500+/-). I spent many hours cussing in the lazzeret but all in all it went well with minimal problems. Actually, my main problem was getting the replacement hoses to fit, had to do some "rigging" to make all the hoses work correctly. I've found the parts are a bit more expensive than other engines but no more difficult to come by. The cost is not anything to worry too much about. I'm a HUGE beliver in PM, keep it working before it breaks down on you. Change your oil every 100 hours, fuel filters every 200 hours, etc. etc. I'm quite satisfied with mine but I'm also no expert in diesel engines.