Discussion in 'Engines' started by gft, Jan 3, 2013.
Can anyone explain what 2 to 1 reduction gears means for a boat with 800 manns
engine turns 2x faster than the prop.......
or the gear reduces the engine rpm to the prop shaft in the ratio of 2:1
Is that a positive option on the man diesels
2:1, 800 hp, probably 56 to 64 footer. Usually a TD 5114 gear. Yep, sounds pretty standard.
So, gft, are you doing homework, daydreaming or just wondering about things?
Sold my 45 Viking looking to move up, looking at a 50 or 55, the 50 makes a large point that the boat is one of the few 50's built with the 2 to 1 reduction gear, as if to say it is a good feature, just trying to see if it is good or bad. The 800's in a 50 seems under powered
Generally the slower a prop turns the larger (in diameter) it can be and the more efficient it will be, with other benefits like reduced load variation in heavy seas and reduced vibration.
I assume that is an older boat with mechanical engines vs electronic controlled common rails. I was looking at a new Viking in 2007. The 45 came standard with 900 hp CRD's with 1100hp as the prefered option. Not that this answers your question.
I believe the 2:1 ratio would allow you to swing either a larger diameter or higher pitched prop. Under the right circumstances this can get you higher speed out of the same HP in the same hull.
I would suggest a lot more research. PM me if you want to talk to two people that are very expierenced with MAN and Viking running gear. They are both in NJ and may have worked on the set up of this boat.
When we built a 61 in 1998 with 900's everyone thought it was HUGE power! I'd say the 800's in that size should provide good economy with "decent" performance by todays standards, not a 40+ knot screaming battlewagon but a respectable cruise speed and a LOT more friendly at the fuel dock. Something we'll probably be seeing more of in the future.
2;1 gears let you swing a bigger wheel more slowly which can mean less cavitation and more efficiency (=less slip). As long as you have adequate tip clearance for the bigger wheels and suitable shaft diameter (deeper reduction puts more load on drivetrain), it should be fine.