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Fyfield, Ted, 2006-09-06 17:44:46 I was wondering if two Lugger 1276 are really being installed or is there a typo error somewhere in the specification etc.
Ted...
I can confirm that it is definitely two Lugger 1276a engines. Here's the little I know on this topic (I'm a software, not a hardware guy!):
Nordhavn gave me a spreadsheet, which represents their guess of the horsepower required to move the boat at various speeds. This spreadsheet takes into account lots of parameters, including the length/weight of the boat, the props, hull inefficiency, etc. Mine is the first 68, so the numbers are really just estimates. And, to put all the facts on the table, the spreadsheet I received was for the N64. Using various formulas I modified it to apply to my boat, reflecting the greater length, weight and twin engines.
The bottom line on all this math is that the maximum useable horsepower on my boat is somewhere around 440hp, or about 220 hp per engine. The engines are rated at 340hp continuous duty. However, full displacement boats consume an infinite amount of energy if you try to move them past their hull speed, which for the N68 is about 10.5 knots. According to my spreadsheet, at around 220hp per motor, this speed is achieved, and any more power is just wasted fuel.
Most cruising will be done at around 9 knots. This same spreadsheet shows consumption of only 110hp per engine at 9 knots. This represents only about 1,200 rpms on the engine. I like the idea of low rpms. Less vibration and noise.
Now, let's say I lose an engine. With my main engines rated at only 340hp, I clearly can't achive hull speed with one engine. However, 340hp will get me to almost 10 knots, and at 9 knots, that single engine (outputting all 220hp alone) will only be turning 1,700 rpm.
All of this shall remain an interesting math problem until we are able to put the boat in the water, early next year, and see what it does. My guess is that it will out-perform these numbers. I have spoken extensively with a N72 owner, with twin diesels, and he felt I was overly conservative on estimating the inefficiency on dual props. I hope he is right.
-Ken Williams
| Williams, Ken |
2006-09-06 18:24:00
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