I know the answer is probably simple, but it eludes me. Cars have less of a contact patch than boats, but water is a lot more forgiving than the street, so that should just about even out, right? Does it have something to do with prop slip through the water? I can see that when accelerating, but when cruising and up to speed???? I've thought about this for a while, i'm sure someone much smarter than me can give me an answer. What is it?

I would think the wheel has a bit to do with it.

I'd say it's all about drag force. Water is like 800 times more dense than air.

friction.
4 tires with little surface space contacting the ground
-vs-
entire boat hull contacting water

some boats have "steps" in the hull to ventalate and remove the contact. yellowfin= "steps"&"pad" in the aft most part of the hull there little secret

Well what about those wheel boats then!! Why don't they go so fast :wtf:

Boats have a lot of factors to deal with.

1. Prop slip- even if your boat is propped correctly, you're still looking at a around 12% slip.

2. Aerodynamics- Your beloved T-Top/center console acts like a huge parachute, add radars and antennas.....

3.Hydrodynamics- Although when a on a plane, most of the boat is out of the water, you still have some drag and now you have wind resistance.

4.Weight-Fuel,water,engines,hull,gear,people start creeping up, throwing the hp to weight ratio out the window.

5. Wind, current,tides,wave direction, all affect a boat independently.

6. Lack of a shiftable transmission. You're average lower unit is somewhere around a 1.87 gear ratio. Although shiftable sounds like a good idea, it would be too taxing on the tranny, due to lack of clutch. And how are going to shift,clutch,throttle,steer, while holding your rum and coke??

7. Technology- up until the introduction of EFI,DFI, and four strokes, everything was two stroke. Although incredibly easy to work on, they are by design, horrible at fuel efficientcy.

8. Boats are a luxury, if you gotta ask how much, you can't afford it;)

What FREEK said, plus boat engines are always(when going any decent speed or RPM) under full engine load. You would never load your pick up with as many tanks as possible, and tow as big a boat as possible, then go 4500 RPM for hours at a time, that is almost what a boat does. That is why you can have the same 350 chevy I/O as your truck 350 chevy, but the boat engine will need much colder plugs as the same plugs as in the truck would burn out in hours in the boat. Always under a load. Your car almost never is under any load. Also with new 4 stroke OBs and EFI the mileage is still maybe doubled at best from the old carbed 2 strokes, when both are loaded with same boat. But doubled or tripled, is better than 1 to 1 1/2 miles per gallon loaded heavily. But the 4 strokes dont have the performance of the 2 strokes, in speed mainly.

What FREEK said, plus boat engines are always(when going any decent speed or RPM) under full engine load. You would never load your pick up with as many tanks as possible, and tow as big a boat as possible, then go 4500 RPM for hours at a time, that is almost what a boat does. That is why you can have the same 350 chevy I/O as your truck 350 chevy, but the boat engine will need much colder plugs as the same plugs as in the truck would burn out in hours in the boat. Always under a load. Your car almost never is under any load. Also with new 4 stroke OBs and EFI the mileage is still maybe doubled at best from the old carbed 2 strokes, when both are loaded with same boat. But doubled or tripled, is better than 1 to 1 1/2 miles per gallon loaded heavily. But the 4 strokes dont have the performance of the 2 strokes, in speed mainly.

EFI motors such as the Mercury EFI get about the same mileage as a carbed 2 stroke.

Not even the motor manufacturers have made wild claims about doubling the mileage when going from a carbed 2 stroke to a 4 stroke.:eek:

I had a 1996 carbed 225 Johnson 2 stroke and went to a 2004 Evinrude DFI 225 2 stroke, and my mileage did not double, the DFI 2 stroke motors are almost as efficient and sometimes more efficient than 4 strokes, plus they have a lot more power, are lighter, have far less moving parts, and run at lower RPM's.

I have been on quite a few boats with 4 strokes and they are typically cruising at 5,000 RPM, while the 2 stroke boats I have been on are usually being run about 4,000 RPM.

Cars are under a load quite a bit, a car once rolling, does not take as much energy to keep it rolling.

A boat takes more energy to get it on plane and keep it on plane.

Your car analogy loaded with tanks is a bad one, my truck a F250 with a 5.4 Triton Gas motor has pulled a trailer with 17,000 lbs on it, once it gets going, the RPM range is around 2,000, I don't think it ever would go up to 4500 RPM, my truck weighs almost 9,000 lbs as it sits right now, and it cruises at 70 MPH at 2,000 RPM, there is quite a bit less rolling resistance on a car than there is on a boat, that is why boats do not have multi gear transmissions like cars and trucks do.

Your car analogy loaded with tanks is a bad one, my truck a F250 with a 5.4 Triton Gas motor has pulled a trailer with 17,000 lbs on it, once it gets going, the RPM range is around 2,000, I don't think it ever would go up to 4500 RPM, my truck weighs almost 9,000 lbs as it sits right now, and it cruises at 70 MPH at 2,000 RPM, there is quite a bit less rolling resistance on a car than there is on a boat, that is why boats do not have multi gear transmissions like cars and trucks do.
How many miles you got on that truck now? I think you are close to setting the record for mileage on a gas engine work truck.

How many miles you got on that truck now? I think you are close to setting the record for mileage on a gas engine work truck.

170,000 miles.

I started changing the spark plugs the other day because it was starting to miss, and I changed the air filter (the old one was probably 2 or 3 years old) and it runs like a champ again, I changed out 4 of the plugs so far, but with it running so good, I may just leave the other 4 in just to see how many miles you can get out of spark plugs.

It is funny my spark plugs have lasted for more miles than some vehicles have.

I do not treat my truck very well, and have had very little problems with it, I have always liked Ford's and this truck pretty much has me convinced the only truck I will ever drive is a Ford.

I have pulled a lot of weights in this truck that guys with the Diesels usually do, I pull a 9,000 lb generator with the truck and although you know it is back there, it doesn't seem to bother the truck.

When I had 17,000 lbs of asphalt in my dump trailer, you could definitely tell it was there, the truck handled it, but I don't think it is good to do it all the time.

I really do like the Ford Superduty trucks, my next one will probably be a F350 single rear wheel, if the 5.4 liter Triton Engine is still available, that is most likely what I will get again.

A friend of mine had the same truck as I do except he has the V 10, he had over 290,000 miles on it, before he bought a new one, I think his main issue was the front end was wore out.

Ford...yes.

'91 Exploder w/ 225,000 miles original engine/tranny (yes, it is an ugly truck)



On the boat question. Just compare the efficiency of hydroplanes to regular hulls. I think most of the difference comes from water resistance to movement. Throw in prop slip and wind resistance above water and it all adds up to 1-2mpg.

I'd like to stick a 250 outboard in a small vehicle...tricked out VW bug maybe?

I'd also like to have a bad ass boat with 4 on the floor and flames on the side...shifting gears, racing other boats for pink slips, pickin' up chicks, sippin' on my Natty light. :cool:

A good analogy would be to put a loaded truck in 4 foot of soft sugar sand with paddle tires on the back and try to drive 40mph.

170,000 miles.

I started changing the spark plugs the other day because it was starting to miss, and I changed the air filter (the old one was probably 2 or 3 years old) and it runs like a champ again, I changed out 4 of the plugs so far, but with it running so good, I may just leave the other 4 in just to see how many miles you can get out of spark plugs.

It is funny my spark plugs have lasted for more miles than some vehicles have.

I do not treat my truck very well, and have had very little problems with it, I have always liked Ford's and this truck pretty much has me convinced the only truck I will ever drive is a Ford.

I have pulled a lot of weights in this truck that guys with the Diesels usually do, I pull a 9,000 lb generator with the truck and although you know it is back there, it doesn't seem to bother the truck.

When I had 17,000 lbs of asphalt in my dump trailer, you could definitely tell it was there, the truck handled it, but I don't think it is good to do it all the time.

I really do like the Ford Superduty trucks, my next one will probably be a F350 single rear wheel, if the 5.4 liter Triton Engine is still available, that is most likely what I will get again.

A friend of mine had the same truck as I do except he has the V 10, he had over 290,000 miles on it, before he bought a new one, I think his main issue was the front end was wore out.

Just turned 160000 miles on my 2000 F-150 5.4L. Haven't done anything to it since I bought it at 103000 miles. I want a diesel next for the torque/efficiency, but I can't support those new head blowing powerstrokes. Pops and I have always been Ford fans with over a million miles between us, he just cracked and got the duramax/alison on a new chevy 2500. Runs good, but doesn't ride as well as a Ford. Test drove a Dodge and I swear they use 2x4s for shocks. I hope Ford gets their motors together before I'm in the market for another truck or i may have to go the gm route also.

BTW, pops was backin up my boat w/ his 2500 the other day and gets his wheels stuck in a little bit of mud(non 4x4). I put mine in 4wheel low and IDLED pulling both him and my boat out. I could do that V-10 but that MPG would kill me!