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diesel outboard Jump to page :12 Now viewing page 2 [20 messages per page]
Posted 1/10/2008 1:20 PM (#1921719 - in reply to #1921594) Subject: Re: diesel outboard
Posts: 920 Member Since: 2/28/2001
Location: Mobile, AL USA
Trav4011 - 1/10/2008 11:26 AM
The TQ figures are far more important than horsepower.. "horsepower", is a bragging rights term..
Look at the difference between a 150hp 2 stroke and a 150hp 4 stroke, on the same hull. Which one planes faster? Which one accelerates faster? Both have roughly the same top end speed.. Why is this? The 2 stroke makes 50-70% more TQ under the curve than the 4 stroke engine.. Diesels are much the same, but, usually make even more TQ. Top end speed is set by prop pitch/diameter, and is affected by TQ output. Horsepower isn't really even a "measureable" term. Horsepower is just a number, derived from TQ and RPM..
Travis
In your example you are comparing two 150 hp engines, so it is unsurprising that they would have the same top end. In this case they are comparing a 300 hp engine to a 160 hp engine, and they will not have the same top end, no matter how big a prop you slap on that sucker. Cruise speed may be roughly the same, but the gas engine boat will walk off and leave the diesel when you push the throttle to the stops. My boat has twin 200 hp diesels, and it does cruise at about the same speed as the twin 350 hp gas version, but I'm turning about 600 rpm off the top. The gas boat is cruising probably 1500 or more off the top so it will keep accelerating while I hit the governors. And the gas boat will get out of the hole faster than the diesel, because I have to wait for the turbos to spool up.
Posted 1/10/2008 1:47 PM (#1921749 - in reply to #1921060) Subject: Re: diesel outboard
Forum Member
Posts: 1595 Member Since: 2/4/2007
I agree that the motors are more like 160 hp and not a true 300 hp, but at least they are trying to make this work. Let's
not kick them in the balz before the motors are introduced. Certainly it will take some time to have good diesel outboards
but I'm glad somebody is stepping up to the plate.
Posted 1/10/2008 2:36 PM (#1921804 - in reply to #1921719) Subject: Re: diesel outboard
Posts: 988 Member Since: 6/27/2007
Location: Houma, Louisiana
285exp - 1/10/2008 1:20 PM
Trav4011 - 1/10/2008 11:26 AM
The TQ figures are far more important than horsepower.. "horsepower", is a bragging rights term..
Look at the difference between a 150hp 2 stroke and a 150hp 4 stroke, on the same hull. Which one planes faster? Which one accelerates faster? Both have roughly the same top end speed.. Why is this? The 2 stroke makes 50-70% more TQ under the curve than the 4 stroke engine.. Diesels are much the same, but, usually make even more TQ. Top end speed is set by prop pitch/diameter, and is affected by TQ output. Horsepower isn't really even a "measureable" term. Horsepower is just a number, derived from TQ and RPM..
Travis
In your example you are comparing two 150 hp engines, so it is unsurprising that they would have the same top end. In this case they are comparing a 300 hp engine to a 160 hp engine, and they will not have the same top end, no matter how big a prop you slap on that sucker. Cruise speed may be roughly the same, but the gas engine boat will walk off and leave the diesel when you push the throttle to the stops. My boat has twin 200 hp diesels, and it does cruise at about the same speed as the twin 350 hp gas version, but I'm turning about 600 rpm off the top. The gas boat is cruising probably 1500 or more off the top so it will keep accelerating while I hit the governors. And the gas boat will get out of the hole faster than the diesel, because I have to wait for the turbos to spool up.
A pair of diesel inboards, and a pair of gas inboards, I/O's, or even gas outboards are all totally different animals from one another... What size boat do you own?
I think on a outboard that's making 500ft lbs of TQ, you would be able to run a much larger prop than you would on a 2 stroke gas engine that makes 200ft lbs less at the prop. A larger prop can spin at slower speed, and run just as fast as a small prop spun at higher speeds.. Then there's the issue of gearing to take advantage of the extra grunt down low and in the midrange. You don't have to turn 6K RPM to run 60mph..
The TQ output from a newer, common rail, turbocharged diesel engine is insane, compared to what a gas engine (even a 2 stroke) could do with the same displacement.. Why do you think guys with 8K lb turbo diesel pickup trucks, with only 300hp can yank much harder than a 400hp gasser? The diesel truck is making 800ft lbs of TQ.. whereas the gasser may be making 400 lbs of TQ. Again.. Horsepower really isn't the "end all" when it comes to performance.. especially with diesel and 2 stroke gas engines.
Posted 1/10/2008 5:47 PM (#1922087 - in reply to #1921749) Subject: Re: diesel outboard
Posts: 4106 Member Since: 1/2/2006
Location: Way out west
If you click on the link at the bottom of the first link, you'll get the actual engine statistics:
Propshaft Rated Horsepower 185 (139 kW)
Full Throttle RPM Range 5000-5800
Cylinders V-6 (60" vee)
Displacement 185 cu. In. (3032 cc)
Bore 3.63" (92 mm)
Stroke 3.00" (76 mm)
Induction System 2-Stage Direct Fuel Injection
Ignition Digital Inductive
Charging System 60-amp (846 watt) w/Voltage Regulator
Gear Ratio 2:1 (FM)
Lubrication System Electronic Multipoint
Recommended Oil Mercury Premium Plus TC-W3
Required Fuel JP5, JP8 or Commercial Jet A fuel
Rotation Left or Right Hand
Shaft Length 25" (635 mm) or 30" (762 mm)
Weight 512 lbs. (232 kg)
Warranty One-year limited warranty for military agencies
At 185 HP with the torque they'll put out and weighing 512 pounds, I'd MUCH rather have a pair of them than my Yamaha 208's. You can bet the horsepower number on engines sold to the feds is not going to be as "optimistic" as Yamaha's. numbers.
Posted 1/11/2008 7:43 AM (#1922571 - in reply to #1921804) Subject: Re: diesel outboard
Posts: 920 Member Since: 2/28/2001
Location: Mobile, AL USA
A pair of diesel inboards, and a pair of gas inboards, I/O's, or even gas outboards are all totally different animals from one another... What size boat do you own?
I think on a outboard that's making 500ft lbs of TQ, you would be able to run a much larger prop than you would on a 2 stroke gas engine that makes 200ft lbs less at the prop. A larger prop can spin at slower speed, and run just as fast as a small prop spun at higher speeds.. Then there's the issue of gearing to take advantage of the extra grunt down low and in the midrange. You don't have to turn 6K RPM to run 60mph..
The TQ output from a newer, common rail, turbocharged diesel engine is insane, compared to what a gas engine (even a 2 stroke) could do with the same displacement.. Why do you think guys with 8K lb turbo diesel pickup trucks, with only 300hp can yank much harder than a 400hp gasser? The diesel truck is making 800ft lbs of TQ.. whereas the gasser may be making 400 lbs of TQ. Again.. Horsepower really isn't the "end all" when it comes to performance.. especially with diesel and 2 stroke gas engines.
My boat is a 28 ft, the engines are 3.6 liter Volvo diesels, 200 hp@3800 rpm.
I'm sure you can swing a pretty big prop with 500 lb/ft of torque, but there is just so much prop you can physically use without having to use extended shafts, and no converted gas outboard gears are going to be able to handle that much torque.
That diesel outboard is a 3 liter, and the claimed fuel burn indicates it is making around 160 hp at 4000 rpm. That would be 210 lb/ft of torque, peak torque is probably around 250. That's a bit short of 500.
The GM, Ford and Dodge turbodiesels make 620-650 lb/ft of torque. Trucks have the advantage of being able to use multiple gears to keep the diesel engine operating in its more narrow powerband, in a boat you have one. If you gear and prop it for top speed it's going to be a dog at low rpm. And horsepower does matter, it tells you the amount of work the engine can do over time. It takes the same amount of diesel hp as gas hp to make a boat go a given speed.
Look, I don't have a problem with diesel outboards, just don't bs me; tell me how much hp and torque it really makes. If you put that "similar to 300 hp" but actually 160 hp diesel outboard and an actual 300 hp outboard on identical boats, the gas boat will run away from the diesel.
Posted 1/11/2008 8:05 AM (#1922615 - in reply to #1921060) Subject: Re: diesel outboard
Forum Member
Posts: 513 Member Since: 6/13/2006
285exp - 1/11/2008 7:43 AM
Look, I don't have a problem with diesel outboards, just don't bs me; tell me how much hp and torque it really makes. If you put that "similar to 300 hp" but actually 160 hp diesel outboard and an actual 300 hp outboard on identical boats, the gas boat will run away from the diesel.
Exactly.
Same gear ratio as a 300hp Merc Verado, factory size 4 blade prop and a minimum of 1800rpm less than a gasser.
Performance data must be based on 3500rpm +/- and below....fuel burn the focus....
All for the emerging market, maybe there is a gearing package or prop package in the works for the lower unit.
.
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diesel outboard
