I have a traditional cutter that weighs 9,200 lbs, 9' beam, 24' LOD, 31'LOA, and 21' waterline. My question is: Would the BD722, 20 HP overpower her or would I not be able to run the engine at optimum cruise RPM due to having too much engine for the boat, thereby possibly hurting the engine. I know diesels like to run at their recommended RPM. I'd like to have the 16 HP BZ602 with it's new quieter technology, but the BD722 should be smoother due to it's three cylinders as opposed to the BZ602's two. I appreciate all's opinions and thoughts. And thanks!
You are on the right track with your inquiry. I will ask for some more information before I answer your inquiry. I assume that your propeller is in a "cutaway" and thus you are limited in prop diameter. Can you please let me know what size propeller you can fit. Remember to allow for 15% tip clearance to avoid a lot of prop wash noise and cavitation. It is pointless buying a lot of horse power if you cannot get it to the water.
Quite often, with a smaller engine, the correct choice of transmission ratio and propeller can make an older traditional boat perform as well if not better than one with a large engine and inefficient drive system.
Stanley, sorry it's taken awhile to get back to you--working TOO much. The absolute maximum prop diameter I can use is a 12-inch, which it currently has with an 8" pitch. The problem I'm having with my current engine (Farrymann A30), despite it's age (30 years), is that it doesn't have a proper reduction gear like a 2:1. Presently, for every turn of the crankshaft, I get 1 and 1/4 turns of the shaft! Due to bad engine access and in order to change the transmission, the engine would have to be pulled out. If I go to all that work, a new engine is going in! The issue now is getting the best engine for my dollar. I think the BZ602 would be about right, but I've heard others say that a good rule-of-thumb is 1 HP for every foot of waterline? I don't want to ever be under-powered again should the need arise. Your opinion? Thanks. undefined
I think that the BZ602 with a 2:1 ratio will give you plenty of reserve. As you are limited to a 12" diameter propeller, you must use a three blade prop to get as much of your HP to the water.
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