Powerplant question

[nightvision]

Why is boat powerplant so inefficient in comparison to a car?<br /><br />Here is an example:<br /><br />Toytota Tacoma 4cyl., 2.7 L, 159 HP, city 20mpg , highway 27 mpg<br /><br />Typical 18 foot bowrider, Mercruser + Alpha 1, 4 cyl, 3.9 L, 135 HP, at 3000 rpm about 5 mpg<br /><br />Why the large difference?

 

[QC]

Re: Powerplant question

Tires roll better on pavement than boats move in water . . . It is that simple. It is not the powerplants, it is the inefficiency of operating "in" something instead of "on" something. Try swimming as fast as you walk

 

[Limited-Time]

Re: Powerplant question

Co-efficient of drag, as QC pointed out. Try running in chest deep water compared to running on land. How much more energy would your body consume running a ¼ mile in chest deep water as opposed to a ¼ mile on land.

 

[TilliamWe]

Re: Powerplant question

Yeah, put that 2.7l Toyota in place of the 3.0l Merc or VP, and it would be rated at 170hp, and would have to turn 4000rpm to get on plane, and it would get maybe 5.1mpg, but more likely it would get 4.5mpg.<br />Think of boats as always going up a pretty steep grade, (5-8%)that's how the environment compares to a car.

 

[Reel Poor]

Re: Powerplant question

Good examples. Understandable too

 

[Silvertip]

Re: Powerplant question

What kind of performance and mileage would those vehicles get if they had only high gear to work with. Boat engines have no transmission.

 

[waterone1@aol.com]

Re: Powerplant question

You can also take a 5.7 liter engine and make it produce 600 horsepower ( dome pistons, cam, NOS, turbo charger, etc.) but I can guarantee that it won't last 100,000 miles or 2000 hours. When was the last time you drove your car at 4500 rpm's for hours at a time ? My point is that marine engines sacrifice some horsepower for reliability in extreme conditions.

 

[akriverrat]

Re: Powerplant question

a boat engine normally operates at about 75% of its rated horsepower at cruise. the car in your example is operating at about 25% of its rated horsepower at cruise. drive that car at 120mph for a couple of hours and then compare fuel usage.