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New Cummins/Mercruiser Project

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Old 10-30-2008, 06:57 PM
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Boat was at X Site today... Played with a lot of different props... The best they found with the time allotted was 69.8mph on the revlimiter - 18 second hole shot - 17x37 5 blades. They said the boat pulled hard - quiet - no black smoke. Overall we are very very happy. They left with 17x39 5&6 blades... Now en route to Ft Lauderdale.

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Old 10-30-2008, 08:43 PM
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I want this project to suceed in the worse way because I think you guys put this together right and would like to see a diesel boat with outdrives in production that can challenge a gas boat. I think this project can do that.

So, not to beat this to death, too much pitch, not enough prop speed. If it pops on plane fast it's under wheeled for a diesel boat. Your pitch is already too big which means they are not turning fast enough. Less pitch more rpm's.

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Old 10-30-2008, 11:13 PM
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sounds like the boat is coming together nicely

Last edited by obrien; 10-30-2008 at 11:16 PM.
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Old 10-31-2008, 08:33 AM
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They ran with a full load, 5 big guys and 240 gallons of fuel. Boat weighs in at 13k lbs dry. They ran 4-5 miles on good water. Best number I saw....24gph consumpton at speed.
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Old 11-03-2008, 05:04 AM
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Quote:
Originally Posted by shueman View Post
They ran with a full load, 5 big guys and 240 gallons of fuel. Boat weighs in at 13k lbs dry. They ran 4-5 miles on good water. Best number I saw....24gph consumpton at speed.

per side
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Old 11-04-2008, 10:26 AM
  #156
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How does she sound? Bad Azz!

http://www.youtube.com/watch?v=FqVMk...eature=related

Like a couple of heavily juiced dodge cummins.
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Old 11-04-2008, 04:42 PM
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The boat is staying at X Site for a few weeks for Cummins testing and some photo/demo runs. If your in the area, give it a look. Can't wait to get some lake video of it...
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Old 11-04-2008, 06:54 PM
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Demo rides were being offered and I was lucky enough to get a spot on one in Ft Lauderdale. It was enlightening to say the least, and overall, I thought it was a nice package. The installation looked very nice.

The drives are at 1.35 now, I think they're going to try a 1.25 this week with a stop by X site on the way back to CA. It should help a bit with allowing a reduced prop pitch. It didn't exactly jump up on plane though. Idle speed (boat, not engine) was higher than I'd expect though backing the boat into a tight spot posed no problem on this particular day. I don't think "no wake" would be possible without taking it in an out of gear. Like Joe said, too much pitch.


The ride was 95% 5-10 mph out of the marina/harbor area so I don't have much to go on, but it seemed that it needed CMD participation on the engine calibration side of things. He revved it up in neutral and no load speed was 3450 rpm, but it seemed to take for ever to get there. Might be some cal changes to let it ramp up quicker. I don't know if these had production calibration or something special for the application. It seemed to me that the engines had more in them. Maybe CMD is trying to protect the NXT drives with a nice soft torque curve?

480hp is only 740 ft-lbs at rated speed. Torque limiting to 750 or so would take a lot out of the mid-range power availability.
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Old 11-04-2008, 07:35 PM
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mthill,

My thought is 1:15 or something close to that. Those gears may not be avail, but that's the range you need.

The faster the prop rpm the smaller the dia of the prop and that helps idle speeds tremdenously because you have lots of slip with the little dia prop and a big heavy boat. Big prop, big bite can't idle slow.

Was CMD able to tell you how much power they were putting out with those props on?

That was always my first test on a boat (pre electronic days), record the boost at each 100 or 200 rpm and go back and put a similar engine on the dyno and load it to that boost at those rpm's. I could see right away how much Hp we had left.

That was always a problem with diesels, you run up against the governor and you don't now where you at. Props are expensive and time consumimg, you know how much HP is left and you know where to go from there with less guess work.

I'm sure with all the electronics they know exactly where that engine is at?

Joe Gere
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Old 11-04-2008, 08:28 PM
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13k lbs seems rather light. I think the biggest problem you will find is the lack of abillity to run a larger diameter prop. However if you go to the taller gear that will help some.
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