What Propulsion unit?

[monrosm@shrewsb]

I was wondering if anyone could help me with advising me on what propulsion unit/ engine i would need for a boat i am designing.
Its a roughly 35meters in length with a beam of 7-9 meters and a draught of 1.3 meters 95 tonnes approx (at half load) cruising speed of approx 50knots. Can anyone advise me on what type of engine to use, i need it to be efficient, and size is important, if you give details could you give approximate dimensions of the engine aswell. Thankyou
Stefan Monro

[marshmat]

That's a large, heavy, insanely fast boat. No matter what you power it with, it will not be efficient.
Common power options in boats of this size and speed range often include twin diesels of two or three thousand horses a piece, plus a helicopter turbine or two in the 2000-5000 hp range. Waterjets are becoming a popular drive option for these large boats, partly because they can be pretty efficient at these speeds and also because they don't tend to overload the expensive engines.
Are you actually planning to build this, or is it just a concept study?

[StianM]

We have build some boats in aluminium 46m (not cats) with proppelers.

We have used MTU and caterpilar ZF gear and some localy made proppelers(not cpp)

We used 3 engines and 3 proppelers, you would probartly nead to go for a 4 engine setup if you don't want to get to large engines witch probartly weigh more than 4 smaer ones would do in the first place.

The boats we build was only for 35+ knots and not 50.

[monrosm@shrewsb]

Well it's still in the design stages at the moment, but could well go on to being built. To give you more of an incite as to what it is, it is based on the 'Wally 118' (as in similar sape and size, and weight) therefore needs similar propulsion. Now the Wally 118 has up to a maximum of 16800hp (which yes is alot) but this boat needs to be able to achieve 65 knots maximum, so the hp is probably somewhere in that order. This horse power is produced by gas turbines and water jets, having a look at the design on the Wally 118 i was also wondering if the air intakes on either side need to be so big? When you say helicopter turbine are you meaning gas turbine? StianM what is the limit with propellers? As in will they drive a heavy boat at 60 knots without cavitating or slipping too much?
Thanx

[monrosm@shrewsb]

The Wally 118

[marshmat]

There is no "limit" with propellers. They just end up being huge, heavy and very expensive. They can also be very hard to match to the boat on something like this, which is so rare that there's little hard data to base drive selection on.
Without doing much real math apart from plugging some guesses into a Savitsky-based planing resistance spreadsheet, I would think your hull alone would have at an absolute minimum 200 to 250 kN of drag at your 50 knot cruise. Say your propulsors (jet or prop, including drag on the propulsor hardware) give you a propulsive coefficient of 0.6, which is probably achievable with some good engineering, that's what, 8500 to 10500 kW at the driveshaft. Add some allowance for gearbox losses etc, how does 12-15000 hp sound as a minimum? Not easy to achieve, and absolutely impossible to achieve economically by any standards.
Your engine room will be HUGE. It would likely need to house twin 4,000 hp diesels and a 4000-7000 hp turbine (or pair of turbines), or three (maybe four) big diesels.... then you need the gas tank for them....
You'll need a really good engineering team if you want to actually build it, and an equally good financial advisory team.

[timgoz]

And "at least" several million $US. :)

Tim

[lazeyjack]

now why do I think someone is pulling legs here

[Guest-3-21-09-10-33]

I was wondering if anyone could help me with advising me on what propulsion unit/ engine i would need for a boat i am designing.
Its a roughly 35meters in length with a beam of 7-9 meters and a draught of 1.3 meters 95 tonnes approx (at half load) cruising speed of approx 50knots. Can anyone advise me on what type of engine to use, i need it to be efficient, and size is important, if you give details could you give approximate dimensions of the engine aswell. Thankyou
Stefan Monro

Considerations on propulsion by designer Albert Nazarov.

[RANCHI OTTO]

install :

3 x MTU 12V 4000 M93 (3140 bhp)
2 x MJP650 (steerable waterjets)
1 x MJP600 (booster)

Speed in excess of 50 knots with 95 t displacement

[Pericles]

As you are in England, talk to Yellowfin http://www.yellowfin.com/pr_shipnboat.pdf

This is their main page http://www.yellowfin.com/VSDTechnology.asp

They are looking for major projects with which to collaborate.

Pericles