What if you have 8 250HP motors?

This was a Mexican drug runners boat designed to out run border patrol and drug agents. Do you think it may be overkill?

Just a little overkill ... instead of measuring miles per gallons, you'd measure gallons per mile.

Overkill? Nah, he's just a very smart outboard motor smuggler.

RPMs dont equal speed! Thrust does, so double the thrust and you can of course go faster. Even though you roughly say a certain number of RPMs will get you x amount of speed with one engine if you ad another engine you may as well take away any RPM factors in calculating speed. If you want to get into thrust calculations, Good luck!

I guess they caught him at the dock!

Very well said prpjt.

In even simpler terms, the power of the boat is not determined by its horsepower, but rather the torque that horspower produces. The prop transforms the torque into thrust. The thrust of the motor is what pushes the boat.

In short, adding a second motor is like a buddy helping you push your car down the road. You may not necessarily go twice as fast with his help, but definately faster and further than if you were pushing alone.

Now in your origional question, if the two motors were somehow connected to the same shaft and turned only one prop, then I think your original assumptions would be correct. I do not beliece the second motor would have any effect if turning the same shaft.

I hope he has hydraulic steering.

Pretty simple answer. I did not read all the post but the overall horse power is not the main factor it is the fact you are pushing against twice as much water therefore the amount of thrust is 2 fold or some percentage of. Thus the boat will get moving faster at lower RPMS which means when you reach the max rpm for the motors you are going at a faster rate of speed and each egine does not have to work as hard to get to that top end speed and has more power left when the max rpms are reached. Think about this can you lift as much weight with one arm as you can two arms. Your arms are basically the same length and stength and you can only move them so fast. So why is it you can lift more weight with 2 arms instead of one arm. Becasue you have to points of thrust or lift against the weight thus reducing the load on each arm and allowing for a greater overall lift. I hope I made since.

Now I've read about more horse power & more torque equals higher speed, but all speed is from prop pitch. Take a 300hp at 5000 rpm with a 25pitch prop it moves 125000 inches of water. Take a 225hp at 5000 rpm with a 25 pitch prop it moves 125000 inches of water. the 300hp will have more torque to reach top end faster but once reached the 225hp will run just as fast top end. running twins just gives you twice the torque but without a higher pitch prop top speed is unchanged.

I'm with ya Dreamin. In your example the 300 moves 125000 inches of water. And a 25 pitch prop on any HP motor, if you can turn it, would move the same 125000 units of water at a particular rpm. Displacing 125000 units of water creates a measurable force, or thrust.

Now lets use 2 150HP motors to turn 25 pitch props. Each prop will displace 125000 units of water, for a total of 250000 units of water displaced and a corresponding increase in thrust.

The only way it would not go a little faster is if the addition of the second engine created enough weight and drag to to completely cancel the force of moving 125000 units of water.

This is all theoretical because there is so much more going on. Reality says that we wouldn't use the same props on the 150 as we would on the 300. However, because of drag coefficient and physical limitations, I would think you could ultimately displace a little more water with 2 engines than with 1.

yes it would be faster look at the boys doning tractor pulls they run one two four engine on there tractor and it gives alot of wheel speed

The two motors on tractors I understand, because they are in line with each other, and can create a large amount of torque and horsepower. They are both hooked up the same driveshaft.

The boat thing had me puzzled a little, but I did get a couple of good responses to my question.

HELL NA!!!!!!!
aint enough

It was like a jet ski on steroids. Oh, those are illegal. Don't tell Marion Jones.