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Wednesday, October 05, 2005
Thoughts on Engines...
I know it is WAAAYYY to early to seriously consider a brand and model for an auxilary power plant for the WestSail. But, I am in the midst of CAD work and I need some size reference based on suitable make/model of diesels for the W42. Horsepower... Rule of thumb says 1hp per 500lbs of displacement. A calculator I found says 32,000lbs of displacement with 40 feet of waterline will need about 63 horses to drive it up to a hull speed of 8.5 knots. Size... I want to make the engine room as tidy as possible and leave as much room for other mechanical accessories like genset, water maker, etc. etc. So, naturally, the smaller the better. Technology... Modern technology has definately come to the marine diesel industry. No longer do you have just "plain" diesels. You also have turbocharged, and intercooled turbocharged. Both give an increase in HP with the same cylinder displacement and physical overall size. Current thoughts are stay with KISS (keep it simple stupid). Going with a turbocharged engine seems to violate this prinicipal (at least to me). There MUST be increased maintenance with a T/C engine. I am sure turbo technology has come a long way (I remember when turbo's got a bad rap with autos in the 80's), especially on diesels. But, I dont know if I want to take a chance. I have read reports turbos getting their blades torn up, bearings going out, etc. etc. Do I really want to deal with that? Right now my feeling is 'no'. So, I am leaning toward naturally aspirated diesels. Ratings... Ratings (or duty cycle) is the latest ad craze with manufacturers. They post different HP specs based on duty cycle and list these under things like M1, M2, M3, etc. ratings. This typically means that the stated HP is only for a certain duty cycle, %100, %80, %50, etc. I dont know the full details, but suffice it to say my interest is in FULL CONTINUOUS 100% DUTY CYCLE. You have to expect, when cruising that you might need to run your engine for very long periods of time (no wind?). So what are ideal make/models? Yanmar? Well, I would prefer to go with Yanmar. We have a 3GM on our 28 foot sloop and it has been running great with nearly 700 hours on the clock. Unfortunately the low end of the 4JH series is short on horsepower until you go turbocharged. It is a nice size however, Volvo? We had an MD7A in our sloop and it served faithfully. But parts were VERY expensive. Despite the newer small volvo engines being Perkins blocks, I believe that if it is painted Volvo Green, it will cost 3x more as it would otherwise. Westerbeke? They have a low RPM 64 hp naturally aspirated engine (model 64A) that looks ideal. Just a bit bigger than the Yanmar 4JH series. And it looks like it could be mounted very low in the bilge. So, think I will use the Westerbeke as a reference. Anyone got some more thoughts? opinions? (I opened comments on this post). ...later!