Malta Fishing Forum

Marine => Engines/Drives and Electronics => Topic started by: busumark on January 25, 2010, 20:01:53 CET



Title: gear ratio
Post by: busumark on January 25, 2010, 20:01:53 CET
can someone tell what it means when they say that the outboard has a gear box ratio of say 1 : 85 ? and between 2 motors of the same HP which has more top speed one with a gear ratio of 1 : 85 or one with gear ratio 2.62 ?


Title: Re: gear ratio
Post by: Destination Sea on January 25, 2010, 20:33:22 CET
example 2:1 indicates two revolutions of the input shaft are required to rotate the output shaft by one revolution. ex engine connected to input shaft and wheels to output shaft .thus output torque is double to engine torque (turning moment)

example 2. Fisrt gear in a car is say 3.812 : 1   4th gear  1:1 direct drive and fifth gear .85:1.  (ex first ir revs tal magna huma hafna mixi ftit w fil 5th huma ftit w mixi hafna imma f'tela mhemx sahha w twaqa il gear..)i.e as torque inc speed decreases proportionally.


Title: Re: gear ratio
Post by: busumark on January 25, 2010, 20:44:04 CET
its a bit complicated destination sea.  so a motor  gear ratio 1 : 2 has less top speed than one with  gear ratio 1 : 1.5 or i didn t understand nothing  :D  :D


Title: Re: gear ratio
Post by: skip on January 25, 2010, 20:48:24 CET
On motors its usually expressed as a reduction ratio. 2.62:1 reduction ratio

at 1000 engine rpms your prop will be turning at 381.6 revs per minute. (I think!)

In simplistic terms, with a larger reduction ratio you can run a larger diameter and larger pitch prop giving your more theoretical forward thrust and def better thrust for trolling etc.

A 1.85:1 is usually aimed at engines that want to deliver more top end speed than low to mid range torque as you would run a smaller diameter propxpitch but have the prop spin faster.


Title: Re: gear ratio
Post by: Destination Sea on January 26, 2010, 17:58:05 CET
Yes that it. ex 4:1 = 4 times torque and 1/4 engine speed.
yes skip  its 381 .


Title: Re: gear ratio
Post by: kurtfalcon on January 27, 2010, 05:46:51 CET
What I can tell you is that the reduction on a mercury verado 300 is 1.75:1 while on their mercury racing outboards the gear ratio is 1:1.


Title: Re: gear ratio
Post by: skip on January 27, 2010, 08:50:42 CET
Top End Speed (Racing) is best achieved without much of a reduction ratio as the gearboxes are basically straight through.

Diesels on shafts usually have a 2.2+ reduction ratio allowing them to swing a bigger diameter and pitch prop. I don't think many of us in here are into racing with our boats we use for fishing. It's why Suzuki are doing so well with their newer engines that are built to run big diameter and pitch props.


Title: Re: gear ratio
Post by: busumark on January 27, 2010, 12:48:59 CET
what is the advantage of having a bigger and higher pitch prop ?


Title: Re: gear ratio
Post by: kurtfalcon on January 27, 2010, 15:16:35 CET
 ;D Skip I know that many of you are not into racing. I was just showing the differences between an outboard used for fishing and an outboard used for racing.


Title: Re: gear ratio
Post by: robby017 on January 27, 2010, 16:26:35 CET
well, lampuki season tends to become a race to the next FAD


Title: Re: gear ratio
Post by: LapsiBoy on January 27, 2010, 21:28:54 CET
when people race to the next fads they are the most immature and sellfish people. For many reasons,  and its not fair on the people who have slower boats (Most fads probably belong to the slower boats)