http://www.luxist.com/2011/02/03/per...15-superyacht/

But you wouldn't like to feed it!

Y? its only running 12500 hp

$3.5 million Vericor TF50 gas turbine - 5,100 hp

Total 12,500 hp

Wow! Maybe I'll see it at the Miami Boat Show?

that would look good at the Char Marina!!!!

Don't know what is so good about these big boats with the jet ski drives. I have a 10 foot Sea-doo with 185 HP and it tops out at about 57 with me on it and full of fuel.

If it had a surface drive for the size and weight, it would run well over 100. I fully understand from a safety standpoint why jet ski's need the pumps, but for these big boats, I have to wonder just what they would do with properly set up surface props?

It appears to be a fad, and not a very good one at that.

Another example, Jet boat with 1200 HP blown BBC, tops out at 80 to 100. Put a surface drive on it and look out, 150 to 190, if you could keep it right side up and on the water.

I started with a 25 foot rag-hauler at 4 knots; moved up to 60 feet at 32 knots and 96 gph; now I'm at 50 feet, going 50 knots, at 35 gph. Surface drives are working real nice for me.

I have not been around with a big jet drive boat was in port, so I have not seen one. I wonder how well they work in big, lumpy seas, when there are no backs to the waves?

From my experience working on the bigger boats is that I have yet to see a turbine in a yacht use anything but a jet drive. I do not know why they use jet drives, you would think that a surface drive would be a better choice.

One thought is that, and I have no idea if this is possible or not, but on pleasure boats that have turbines, they all seem to use some sort of caliper to break N2 (I think) which makes it possible to shift gears. maybe there is not a system strong enough for these 5000hp turbines, so the jet drive just skips that problem all together.

Why any yacht uses a jet drive is beyond me, I have spoken to a lot of captains and they all say that they are way more of a pain in the azz to dock, and they generally maneuver like crap, over a conventional twin screw yacht.

I just ordered two.

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 don’t 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,

ND1