Help Select BIG Propeller =)

[Hellbringer]

hi,

I am working on designing a ship that is 250' long an weighting in at 1000 tons (total) and i am looking for engines ( 2 most likely ) gearboxes and props to get it to travel 24 knots.

i have found this website

http://www.psychosnail.com/BoatSpeedCalculator.aspx

that calculates the powered needed and it comes out to 7837 hp

i also found these props

http://www.masson-marine.com/en/prop...ers_03_01.html

and these gearboxes

http://www.masson-marine.com/en/mari..._02_01_00.html

now the questions,

1. the charts that are listed for both the props and gearboxes make no sense to me what is P/n ratio?

2. this propeller

http://www.masson-marine.com/en/prop..._03_01_06.html

(if i am reading it correctly ) if it is spinning at 250rpm it will put out about 5026 hp (3750 kW) so if i stick 2 of them in my ship i should be good right?

3. on that prop it says to use gearbox MM W20000 so i go to the specs of the gearbox

http://www.masson-marine.com/en/mari..._02_01_27.html

and then the specs might as well be in greek. i need to know how much hp the engine needs to get a output of 250rpm and the hp to spin the prop listed above. then i can go to cat.com and find the engine =)

thanks in advance
Mike

[ryanonthebeach]

Mike

For a vessel that size, that little boat speed calculator of mine is not going to be enough, although it'll give you starting place. For more info go to Dave Gerr's propeller handbook. Some good step by step approaches to selecting a prop/engine. Also have a look at westlawn newsletter, they have some articles there but usually for smaller vessels.

[Adler]

Mike,

Could you please provide the following data of your project?
1. Vessel Type: Displacement / Semi-displacement / Planing / Catamaran / Barge
2. Service: Passenger / Commercial / Tug
3. Maximum Diameter of the Propeller that is able to operate at stern available space without to create turbulence's influence at the flow around the Hull.
4. Immersion of the Propeller's Shaft end from the Waterline Level (Static).
5. Length of the Vessel on Waterline Level.
6. Final Weigth of the Vessel (a good approximation).
7. Required Top Speed and Cruise Speed (Service Speed).

Through them we will be in position to have an idea regarding the matters you referred.

Waiting your reply.

[sbmar.com]

Some quick calcs from a pretty good estimator came up with this based on your input using a planning hull shape:

Power needed: 30,000 HP total

Props: (2) 130" x 115" 4B

Prop speed: 360 RPM at WOT ( about 25 Kt's)

Prop speed: 300 RPM at a 20 Kt cruise



Want to go faster? Up the HP & prop without increasing the weight to much (40,000 HP total ?) .. As to the engine choice and gear box, that would your call to find what meets the specs.. But I'd certainly be looking at a high speed, high power density diesel using #2 fuel ( if one is even made at those power levels) ..Or, a turbine may be all that would work weight wise.... Most medium speed diesels or heavy fuel engines may be too heavy?

[Tim B]

Ok, so ballpark hull-speed is 20 kts (1.3*sqrt(LWL)). so to get another 4 knots we have two options:

1) Planing regime
2) Improve expected hull speed

Now a 250ft hull weighing 1000 tonnes is not going to be easy to make plane. Even if you could get it to, consider the structural problems you'll have when planing in calm water; and the problems you'll have with impact forces!

So, the easier solution is to forget about planing and concentrate on controlling the wave pattern to reduce the wave resistance as far as possible. Of course, that is an altogether different question.

Tim B.

[daiquiri]

Tim, Sbmar - at SLR of 1.52 we are definitely not talking about planing regime here. This is a high-speed displacement ship, which requires some careful hydrodynamic design.

Hellbringer, provided (but not taken for granted) that you have already choosen the right hullform for that speed - what are the other main dimensions of your ship - like beam, draft, mid-section position, half-entrance angle, keel/rudder/appendages areas? And (possibly) some coefficients - like midship, waterplane, block, prismatic.

Cheers

[Tim B]

DQ,

Agreed. I was discrediting Sbmar's use of a planing resistance calculator. This is way into big ship territory.

Tim B.

[sbmar.com]

Big ship Territory--100% agreed


Planing hull form ??-------With zero really known about the hull spape or actual form, other than a couple of very basic parameters, everything else including my post is all up for grabs..

Cheers.........

Tony