Can't imagine there would be much (if any) difference between them.
Does anyone know how the fuel consumption of the larger gear case variants of 60hp 4-Strokes (Mercury CT or Yamaha HT) compare with the standard models? I'm not after detailed numbers, just in general.
It has always been my private conviction that any man who pits his intelligence against a fish and loses has it coming. ~John Steinbeck
Can't imagine there would be much (if any) difference between them.
The motor will be running at the same RPM if propped correctly so it should use the same amount of fuel its when u run one heavy rig and one light rig say a fibreglass boat to a alloy boat u see the difference because of the boats over all weight and throttle position
when u change from normal to larger gear boxes that motor is still going to achieve the same RPM just u get a different output ratio at the propeller using the same throttle position all that will change is your speed from pushing a boat to pushing a barge or party pontoon
its not that simple
the gearbox ratios are different , so can swing a substantially bigger proper for controlling large cumbersome craft, house boats barges pontoons etc
the gear box casing is bigger but these dont generally see the same speeds as their normal gearbox models so drag doesnt matter as much
go up in horsepower before considering one as a overweight fishing boat isnt their real intended use
Steve the gearbox is not what burns the fuel tho the crankshaft would be designed to output so many NM of torque in either configuration at a set rpm, the gearbox just has a different output
Having owned both versions , i can confirm
1. both can obtain excellent economy
2 the engine with the larger gearbox is substantially more sensitive to proping correctly.
I have managed 3km per litre with both engine variants both on glass boats but the larger gear case required several props to get it on the money.
BigE
mate dont know if you reply just for the sake of replying but i didn't mention fuel consumption
i mentioned the two gearbox designs are for different purposes and if youve got a conventional planning hull go up in hp first if you can
gear boxes are a torque multiplier ie can swing a bigger prop with more load on it
in this care you will travel less distance per turn of the prop and burn more fuel to travel the same distance
but int he end doesnt matter as they are for different purposes
mate your like a rash, yes i read his post
a bigger gear case will always burn more fuel as has more drag, may be negligible but will burn more
thats before even looking at the gear ratio issue
Your of ya chops mate.
Bigger gearbox has more torque to push the forces easier which in return it will be easier to deal with any extra drag but whos to say a bigger gearbox going slower is anymore draggier than a smaller gearbox going faster?
outboards have a rated RPM they must be ran within if your within this area than u will see normal fuel economy now if u run the bigger gearbox its torqued accordingly by the propeller its called a load u use the right propeller to achieve this correct load and this will put u within the RPM range limit
when u run a engine at the correct RPM how on earth is the fuel economy going to change you have the same power head on both engines your have a different gear ratio however your still achieving the same "load" on the engine otherwise your RPM would be compromised
Some words to replace the content
not worth the effort of a reply
An easier way of seeing it, You have 2 outboard engines both running at 5000RPM you now have two different gearboxes and propellers, Your still going to use the same amount of fuel per hour run time just your distance is going to be different due to the gearbox output and propeller ratios
Your still running the powerhead at 5000RPM on both engines which burns the fuel not the gearbox
I think the point that Stevej is trying to get across is that the high thrust gearbox’s not only have a higher ratio and thus greater torque multiplication, but they also are often physically bigger, thus have a greater “frontal area” in the water and thus higher drag at any given speed. You can prop them both differently to get them to similar speeds at similar revs, but the bigger gearbox will always have more drag, thus a cost in power.
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Swof63 yeah but what produces more drag a bigger gearbox doing 40kph or a smaller one going 70kph? gearboxes are hydro dynamically engineered to use the lease drag possible so i think there would be hardly any difference