1:2 gear box?

[decamio]

I have a 30 foot catamaran with 200hp Cummings engines driving Hamilton jets through 1:1 gear boxes
Top speed is about 16 knots
The engines are never under any strain an I wondered if the impellors should be doing more revs
Is there such a thing as a 1:2 gearbox and if so would this be an improvement?

 

[Latestarter1]

I have a 30 foot catamaran with 200hp Cummings engines driving Hamilton jets through 1:1 gear boxes
Top speed is about 16 knots
The engines are never under any strain an I wondered if the impellors should be doing more revs
Is there such a thing as a 1:2 gearbox and if so would this be an improvement?

decimo,

More data please, exactly what Cummins engine model?

What engine speed are you making at WOT.

Jets properly sized can never overload an engine, however if improperly sized overload is constant, impeller sizing is critical.

What is make of transmission, suspect you do not mean 1.2:1 reduction.........

 

[BruceK]

Would it not be easier to change impellor pitch and or nozzle?

May be worth speaking with the suppliers:

HamiltonJet (U.K.) Ltd.
Unit 4A, The Birches Industrial Estate
East Grinstead
West Sussex RH19 1XZ
United Kingdom
Phone: +44 1342 313 437
Fax: +44 1342 313 438
E-Mail: sales@hamjetuk.com

 

[decamio]

Hi BruceK,
Thanks for that, I have sent all the relative information to Elliot at Hamilton Jets.
I had not considered this option and it would make more sense.
In response to Latestarter1, thanks for your input. It is a straight through 1:1 gearbox. I have had 3:1 and 2:1 reduction boxes in boats in the past and wondered if there was such a thing as a 1:2 or 1:1.5 to increase the revs at the prop but I'll see what sort of reply I get from the jet man.

 

[Latestarter1]

Hi BruceK,
Thanks for that, I have sent all the relative information to Elliot at Hamilton Jets.
I had not considered this option and it would make more sense.
In response to Latestarter1, thanks for your input. It is a straight through 1:1 gearbox. I have had 3:1 and 2:1 reduction boxes in boats in the past and wondered if there was such a thing as a 1:2 or 1:1.5 to increase the revs at the prop but I'll see what sort of reply I get from the jet man.

At the he risk of sounding grumpy may we have some data! What model Cummins engine CPL, current engine speed at WOT, without data nobody can even attempt to help you!