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Old 02-04-2011, 06:50 PM
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Howard Arneson runs one of his ASD16s on his 46Skater with a 5000hp turbine so I don't see a problem with big HP/TQ and surface drives. You see lots of express cruisers like Pershing that use shaft drives and big diesels.

Last edited by Catmando; 02-04-2011 at 06:54 PM.
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Old 02-04-2011, 07:16 PM
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Imagine the rooster tail with 12,500 HP and surface drives!!!!
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Old 02-04-2011, 08:56 PM
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Originally Posted by nautdesign1 View Post
Water jets are essentially ducted fans for the water. The large jets have their inlet geometry, blade configuration etc etc designed for a particular design speed and loading for maximum efficiency. As you might imagine, successful high end builders such as Pershing donít make this stuff up as they go along. A failure to meet the design speed for a $10-$15 million yacht can be catastrophic and thus extensive CFD and FEE studies are commissioned. For this size of craft and speeds near 50 knots conventional shafts and associated stern gear create untenable drag but also cause huge flow/cavitation problems. They are therefore generally excluded from anything in this class that runs over 45 knots. In the 40-50 knot range, water jets are often similar in efficiency to surface drives so in Europe we see the specification of both. However above 50 knots the water drag (and the increase in vessel displacement resulting from the mass of water entrained within the jet path) make surface drives the more efficient option. Nevertheless, even at speeds up to 70 knots jets are still utilized as they have a proven track record and can handle enormous power. The torque restrictions on existing surface drives still somewhat limit their application on sizable craft.

Hope this helps,

While some of the thoughts are spot on some are not exactly.

The efficiency of the jet pumps at a very specific point can be efficient, however, over a broad range the jet pumps are not as efficient as they have difficulty in dealing with speed and displacement changes. Typically the jets are used on 35 knot range boats and cease to be uses on things higher than this speed design.

This boat uses the jets for the simple reason that they can operate at a ram seed and this is relevant when the auxiliary power is turned on as they do not have to use a two speed transmission to allow the outboard motors to keep up with the inboard motors.

As for torque limitations, this is why we make 11 different sizes and the largest can handle 38,000 ft'lbs of input torque. Take the TF50 put a 20:1 reduction ratio in the ZF box and you can see why we make them so large..
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Old 02-04-2011, 10:57 PM
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Ive ran crew boats with jets and they are fast, but a pain to dock and hold position. And its the only time i've seen the fuel charge higher than the day rate per day haha. But when you are an oil company i'm sure fuel consumption isnt a big deal
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Old 02-05-2011, 02:00 AM
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38000 ftlbs torque???

Rik what drives will the new Magnum 100 use? I know the 80 uses your drives.
What did the Callan boat use, 10s or 12s?
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Old 02-05-2011, 11:47 AM
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