searching for catamaran using waterjet propulsion

[tsuji_kenji]

hello all...im student from from malaysia that are searching catamaran using waterjet propulsion system..hope that 'old timers' can help me...

[Steve W]

many of the large catamaran ferryboats have waterjet propulsion, not sure why!

[Ad Hoc]

Originally Posted by Steve W

many of the large catamaran ferryboats have waterjet propulsion, not sure why!

More effecient than a prop and able to offer a lower draft and run in shallow waters too.

[Steve W]

Originally Posted by Ad Hoc

More effecient than a prop and able to offer a lower draft and run in shallow waters too.

I was under the impression that they were less efficient than props,that would make sense then but all the ferryboats ive seen dont need shallow draft as they operate from deep water docks.
Steve.

[Ad Hoc]

The crossover threshold is around the 20-25knots. Below, prop is best, above waterjet.
Typical effiiciencies around 0.65 for a waterjet, compared to 0.45-0.50 typ. props.

But most fast ferries are "generally" of a low length displacement ratio hull form which also lends itself to a waterjet propulsion too.

[masalai]

How does the performance in "water-jet drive" compare to "surface drives" in the 25 to 30 knot region?

[tsuji_kenji]

thanks for all corncerns...im very appriciate...my new question,what is the best method to calculate total resistance for catamaran?is it Molland and Insel or Holltrop..or both?

[keysdisease]

This one is for sale. I actually got to go on a sea trial on her not long ago, pretty cool. The manufacturer Sabre Cat in Australia has quite a few ferrys similar to this Cat running around with water jets.

http://luxurycatamaran.blogspot.com/...catamaran.html

[Alik]

Originally Posted by tsuji_kenji

thanks for all corncerns...im very appriciate...my new question,what is the best method to calculate total resistance for catamaran?is it Molland and Insel or Holltrop..or both?

Molland works for round bilge hulls only. For sharp chine hulls we use:

For semi-planing range:
- VMB 89' systematic series (Muler-Graf);
- Pham method based on regression analysis of CFD data.

For planing range:
- Savitsky with doubled resistance of one hull, pls additional factors such as extra friction (due to wetting of tunnel) and hulls interaction factor.