Fuel consumption compared to HP and distance traveled

[gilcarleton]

I am considering purchasing a 19' Bayliner center console with a 200 hp engine. I am a guy who likes to fish and have never owned an engine this large. I have moved to Gulf Shores, AL and will be fishing Mobile Bay and the Gulf of Mexico. I will probably do some trolling but most of my fishing will be to run out to an oil platform and bottom fish. I did a little research where someone said that in order to calculate the fuel burned per hour you need to move a decimal point one number to the left which seems about right at least from the engines I have had. Using that formula, the 200 hp would burn about 20 gal an hour.

Now here is my question: Would a 200 hp engine get me to where I want to go twice as fast as a 100 hp? If so, either would be a push and with the price of fuel these days, I am concerned. If I could get to where I want to go twice as fast and not burn any more fuel that would be fine but if the 200 hp would burn, say, 25% more fuel I will probably look for a smaller engine.

This one is above my grade level and experience so any help that anyone can give me would be greatly appreciated.

Gil

 

[Sea Rider]

Re: Fuel consumption compared to HP and distance traveled

Welcome to the forums,

Which 200 HP would that be : 2 strokes standard, 2 strokes TLDI, 4 strokes, Inboard Mercruiser style ? Each one has it's fuel consumption wot parameters, can't throw them all in same sack.

Happy Boating

 

[Chris1956]

Re: Fuel consumption compared to HP and distance traveled

A 200HP motor will not propel your boat twice as fast as a 100HP motor. It will push it faster and at max RPM, burn more fuel than a 100HP motor. What is the max HP the boat rated for? Rule #1 is that boats do consume lots more fuel than autos, due to friction and drag of the water. You can economize in certain ways, and a smaller motor is not always one of them.

 

[Texasmark]

Re: Fuel consumption compared to HP and distance traveled

I am aware of the decimal general rule that a lot of folks use. To me you cannot apply that in a boating situation due to many factors including but not limited to, engine condition, type, hp, prop, rpms, boat weight, hull type, sea condition, speed, load you are carrying, hull wetted area and on and on.

Personally I get excellent MPGs with my boats. Since 1989 I have run 2 cycle Merc outboards that were either Direct Charged (a modified loop charge at the time OMC had the loop charging patent in effect) or Loop Charged, engine sized to the high end of the recommended BIA rating for the boat. I prop them to run with the normal load right at or slightly above the upper published limit of rpm range for the engine at WOT (usually).

I select boats that have the ability to reduce hull to water contact which essentially means a padded hull. The pad is a flat patch of the bottom of the specially designed boat hull in front of the engine that functions much like a water ski. Getting everything setup properly allows all of the boat mass to rest on this ski or the rear part of it reducing the wetted area, and hence drag to a minimum.

My mercs have the timing setup (from the factory) whereby at about 3000 rpms the timing is at maximum advance. Any throttle above that just increases the fuel supplied to the engine (carb butterflies continue to open).

Since the throttle position where the timing ceases to advance further consists of only more fuel to get the HP, if in a fuel saving mode, I run at that throttle setting.

Power trim is a must and trim is tweaked for max rpm for a given throttle setting. I set the throttle to some point and then fine tune the trim for max rpm (and resultant mph) which really tells me how much drag the hull is costing me at that point. Obviously if you can set your engine up at some throttle setting, timing set, butterfly opening set, by increasing your rpms, you are running more efficiently. At least that's the way it works for me and I don't have a fuel flow meter. I just know how much gas I put in the tank and how long it lasts.

So, based upon engine size only, if weight doesn't hamper the numbers, I would take the largest engine that the boat can take/you can afford and run it as I said.

My 2c and everyone has an opinion. This is mine.

Mark

 

[Georgesalmon]

Re: Fuel consumption compared to HP and distance traveled

Assuming an outboard a 200hp probably won't get you there "twice" as fast as a 100hp. Your best fuel economy will be at planing speed with either motor. I would opt for the 200 and run at a nice planing speed for economy but still have the power for when I need it to outrun that unpredicted storm that always happens when you least expect it. Remember that the 10 or 20 gallons per hour is at the WOT speed and you don't have to do that unless you want to and/or water conditions will let you. Although there is extra weight involved I tend to think that if you ran the 100 at WOT and compared the 200 running at the same boat speed as the 100 they would use nearly the same amount of fuel. After all, isn't 100hp, equal to 100hp no matter which motor it comes from? Probably won't be trolling with either motor unless you use some trolling bags or 5gal cans or best bet is a kicker engine.

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

Welcome to the forums,

Which 200 HP would that be : 2 strokes standard, 2 strokes TLDI, 4 strokes, Inboard Mercruiser style ? Each one has it's fuel consumption wot parameters, can't throw them all in same sack.

Happy Boating

It is a 1987 so I am going to assume that it is a standard 2 cycle.

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

I am aware of the decimal general rule that a lot of folks use. To me you cannot apply that in a boating situation due to many factors including but not limited to, engine condition, type, hp, prop, rpms, boat weight, hull type, sea condition, speed, load you are carrying, hull wetted area and on and on.

Personally I get excellent MPGs with my boats. Since 1989 I have run 2 cycle Merc outboards that were either Direct Charged (a modified loop charge at the time OMC had the loop charging patent in effect) or Loop Charged, engine sized to the high end of the recommended BIA rating for the boat. I prop them to run with the normal load right at or slightly above the upper published limit of rpm range for the engine at WOT (usually).

I select boats that have the ability to reduce hull to water contact which essentially means a padded hull. The pad is a flat patch of the bottom of the specially designed boat hull in front of the engine that functions much like a water ski. Getting everything setup properly allows all of the boat mass to rest on this ski or the rear part of it reducing the wetted area, and hence drag to a minimum.

My mercs have the timing setup (from the factory) whereby at about 3000 rpms the timing is at maximum advance. Any throttle above that just increases the fuel supplied to the engine (carb butterflies continue to open).

Since the throttle position where the timing ceases to advance further consists of only more fuel to get the HP, if in a fuel saving mode, I run at that throttle setting.

Power trim is a must and trim is tweaked for max rpm for a given throttle setting. I set the throttle to some point and then fine tune the trim for max rpm (and resultant mph) which really tells me how much drag the hull is costing me at that point. Obviously if you can set your engine up at some throttle setting, timing set, butterfly opening set, by increasing your rpms, you are running more efficiently. At least that's the way it works for me and I don't have a fuel flow meter. I just know how much gas I put in the tank and how long it lasts.

So, based upon engine size only, if weight doesn't hamper the numbers, I would take the largest engine that the boat can take/you can afford and run it as I said.

My 2c and everyone has an opinion. This is mine.

Mark

Thanks for the great information. I just assumed that a 100 hp would get any 19ft boat up on plane and the question was would the extra 100 hp be a benefit. Good info also on the timing. I have to admit that I got lost in your paragraph of the loop charged and the direct charged. Would you mind explaining that a little better for me? I thought the engine was an 87 Merc since that was the year of the boat but I found it is a 92.

Thanks again.

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

Assuming an outboard a 200hp probably won't get you there "twice" as fast as a 100hp. Your best fuel economy will be at planing speed with either motor. I would opt for the 200 and run at a nice planing speed for economy but still have the power for when I need it to outrun that unpredicted storm that always happens when you least expect it. Remember that the 10 or 20 gallons per hour is at the WOT speed and you don't have to do that unless you want to and/or water conditions will let you. Although there is extra weight involved I tend to think that if you ran the 100 at WOT and compared the 200 running at the same boat speed as the 100 they would use nearly the same amount of fuel. After all, isn't 100hp, equal to 100hp no matter which motor it comes from? Probably won't be trolling with either motor unless you use some trolling bags or 5gal cans or best bet is a kicker engine.

Good point of the 100 hp analogy. On the other hand, a 426 hemi going 50 mph in a dodge will get less gas mileage than a 6 cyl going 50 mph. As I said, above my grade level. I agree that I will probably need a kicker engine for trolling and I would also feel safer in the ocean in case the big one dies on me. Tuna trolling is a high speed operation though so I thought it would work for that. This is my first post on this forum and there is a lot of great information here. As they say, "Experience is the best teacher but the tuition is prohibitive."

 

[Texasmark]

Re: Fuel consumption compared to HP and distance traveled

Thanks for the great information. I just assumed that a 100 hp would get any 19ft boat up on plane and the question was would the extra 100 hp be a benefit. Good info also on the timing. I have to admit that I got lost in your paragraph of the loop charged and the direct charged. Would you mind explaining that a little better for me? I thought the engine was an 87 Merc since that was the year of the boat but I found it is a 92.

Thanks again.

Back in '68-69 time frame OMC came out with a 3 cylinder loop charged engine. Look up the Evinrude 55 HP Triumph on the www. The 3 cylinders is significant as it was the number of cylinders required to make the loop function with the technology developed at the time. It was a fuel efficient revolution. There should be plenty of verbiage on the net as to what that consisted of.

One thing unique was that it used fancy porting, a flat topped piston and fine tuned exhaust chambers to resonate the exaust from one cylinder to help to retain the charge in another allowing better combustion. Merc was caught (my opinion but it surely has merit) with their britches down as the loop charging combustion process just about halved the fuel consumption of 2 cycle engines that could incorporate the design (3 cyl or multiples...like Mercs tower at 6 cyls...just used 2 sets of what a 3 cyl would use) and prior to that, on a 35 hp engine, you could go through a couple of 6 gallon tanks in a Sunday afternoon's boating with a lot of sitting on the bank breaks, only pulling one ski person with a 14' plywood light weight boat with one person in the boat.

Since OMC had the patent, Merc apparently (my vision of what happened) looked at the process. The result was that they incorporated the fancy porting and the 3 cylinder exhaust tube reverberation that assisted the process, but left the dome on their pistons like the older cross flow engines used. So, they named it Direct Charge, named after the ports in the pistons where fuel/air mix was injected. In my engine boat application, it worked like a dream. My fuel economy was stellar on my '88 manufactured 115 Merc 6 cyl (Tower of power) as compared to what it had been years before on straight cross flow combustion engines.

How's that? Supper's ready.

Mark

 

[steelespike]

Re: Fuel consumption compared to HP and distance traveled

Wot on any healthy motor will use fuel at a rate of"about"10% of the hp.
Whether pushing a runabout or a house boat 100 hp+ 10 gph.(gallons per hour).
Older motors a little more but still a good rule of thumb.
Todays motors are really close to these figures.
Take an aluminum and a glass boat of roughly the same configuration often times the glass boat will be faster even though heavier.

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

Thanks. I have seen the affects of this but I did not know what had changed. Great explanation. I can remember, in the late 60's, going out with a friend of mine water skiing. We had 10 gallons of gas and I was amazed that we were sitting in the middle of the lake empty after only being on the water for a little over an hour. I knew that 2 cycles had become much more efficient but I never knew why. I am going to do a little more research on this.

 

[Sea Rider]

Re: Fuel consumption compared to HP and distance traveled

I knew that 2 cycles had become much more efficient but I never knew why. I am going to do a little more research on this.

New 2 strokes TLDI, Etec inyected type are much more fuel savers than traditional new 2 strokes same HP engines. 10% fuel consumption at wot is very conservative, 12% is closer to reality. Nobody in their right mind will go boating at full wot, unless fuel cost is unimportant to you, you are in a real hurry being chased by a huge tornado or happen to work for a Oil Company. 3/4 throttle is opt for good speed and less fuel comsumption than going wot.

Happy Boating

 

[Home Cookin']

Re: Fuel consumption compared to HP and distance traveled

let's step back a minute.

200 hp is a big fit on a 19' CC. Are you sure it's within the rating plate?

I understand you want speed to cover long distances to the fishing grounds, but it's not like what the sparkle boyz do on a lake. You are crossing open sea in a 19' boat and it will be a rare day you go full speed. On a boat that size you will cruise 25-30 mph, maybe less, seldom more.

You need to consider how much fuel you carry and figure your effective range. Remember the 1/3 rule. So if your target is 20 miles out, you need fuel for 60 miles. If you do a lot of trolling or moving around once you are there, add more.

Maybe you'd be better off with a 200 on a 23' boat or a 115 on a 19.

 

[Chris1956]

Re: Fuel consumption compared to HP and distance traveled

OK, How about a little more clarity on Loop Charging, versus Direct Charging. Loop charged motors use flat heads and have several transfer ports that sweep (or loop) the exhaust out of the combustion chamber. All 2 cycle motors allow some unburned fuel mixture to escape the cylinder, in order to have a good exhaust action. A good loop charged motor will have a tuned expansion chamber which will cause a pressure wave to reverberate back into the cylinder, to force some unburned fuel mixture back into the cylinder. This plus the improved scavanging action increases power and reduces fuel consumption. Because loop charged motors require multiple transfer ports, they are hard to design and cast in multiple cylinder engines. Single cylinder motorcycles had 6 or 7 port loop charged engines in the late 60's. OMC poduced loopers before Merc. A Merc Direct Charge motor is a variation on a cross-flow engine, not a looper. It has one transfer port and one intake port. Some later IL6 motors had a power ported piston and an elongated transfer port, as well as the raised eyebrow on the piston. These produced a bit more power.

Over the years casting aluminum has evolved from simple sand-casting to lost foam casting. I would think this would allow more intricate castings, as are used on the multiple cylinder loopers. It should be said that looper exhausts can only be tuned for specific RPMs, so obviously a designer must make a choice.

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

let's step back a minute.

200 hp is a big fit on a 19' CC. Are you sure it's within the rating plate?

I understand you want speed to cover long distances to the fishing grounds, but it's not like what the sparkle boyz do on a lake. You are crossing open sea in a 19' boat and it will be a rare day you go full speed. On a boat that size you will cruise 25-30 mph, maybe less, seldom more.

You need to consider how much fuel you carry and figure your effective range. Remember the 1/3 rule. So if your target is 20 miles out, you need fuel for 60 miles. If you do a lot of trolling or moving around once you are there, add more.

Maybe you'd be better off with a 200 on a 23' boat or a 115 on a 19.

I was wondering the same thing about the hp. I have never seen the boat in person but found it on Boattrader.com. It seems like a lot of power for the size boat. Yesterday afternoon I found that they have sold the boat so I am looking again. I am looking for something in the 17'-23' range. In say, a 19' boat, wouldn't 125 hp be plenty?

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

This is a lot of great information that I have not heard of before. In buying a used boat, what is the earliest year you can look for that has the fairly sophisticated loop system? Do all outboards offer them now? The boat I was looking at sold and now I am looking at a 19' with a 2000 Johnson 115 hp on it. Two more questions, when did mfgs convert to fuel injection? Is a 4 cycle more fuel efficient than a 2 cycle?

 

[Sea Rider]

Re: Fuel consumption compared to HP and distance traveled

Regarding consumtion would say the best towards the least : 4 strokes EFI, 4 strokes carbed, 2 strokes EFi, 2 strokes standard. But probably a 2 strokes EFI guzzles less fuel than a carbed 4 strokes ? Who knows ? Seems loop systems is standard on 2 strokes carbed models and cross flow on 4 strokes carbed models, both systems not found on 2 & 4 strokes EFI engines.

Happy Boating

 

[Home Cookin']

Re: Fuel consumption compared to HP and distance traveled

I was wondering the same thing about the hp. I have never seen the boat in person but found it on Boattrader.com. It seems like a lot of power for the size boat. Yesterday afternoon I found that they have sold the boat so I am looking again. I am looking for something in the 17'-23' range. In say, a 19' boat, wouldn't 125 hp be plenty?

yes generally although it depends on hull design first and boat weight second. I use a 19' carolina Skiff with a 50 that does fine; my sister has a 19' Grady with a 150 that does fine; neither boat would work at all if you swapped motors. That's a 100HP swing on the same length boat. Each of us could go 20 hp up (for me) or down (for her). Mine is light and flat; hers is heavy and deep V.

But almost any 19' with a 125 will have enough power; it may be too much for some, though.

Look at the capacity plate. You want no less than 75% of the max. After that it depends on your use and whether you often need the top power/speed, and consider the trade off for weight, cost, fuel consumption and tank capacity.

Quality boats are packaged with the right HP, so if you bought a used Grady or Sea Hunt for example with the original motor it is probably matched correctly. Low end boats, often they underpower them to bring the price down. You see them in the color ads in the Sunday paper for big box sporting goods stores.

it seems that the smooth water (lake) boaters tend to focus on what the boat does at WOT while the open water (coastal, great lakes) boaters, who seldom run at WOT for long stretches (in smaller boats), consider more practical aspects of powering the boat. It's all about what you want to do.

That being said, it can be dangerous to underpower a small boat, depending on your use and conditions (for example, a jon boat with 3 duck hunters in tidal waters needs to be powered enough to be able to beat against a current and 25 mph wind to get home alive; the same boat on the municipal lake is fine with a 9.9).

that's boats for you: no simple answers!

 

[gilcarleton]

Re: Fuel consumption compared to HP and distance traveled

I am looking at a 19' Trophy now that comes with a 120 hp engine. It seems like a good boat for what I want to do and probably enough power. I see you can special one with 150 hp. One thing that threw me though is that is reading reviews by owners many said that one of the downsides of the boat is that it can only be used in salt water. Do you have any idea why you cannot use any boat anywhere you want where safety permits?

One unrelated question, is there a way to set up my account to notify me by email when someone responds to one of my posts?

Thanks again.

 

[dingbat]

Re: Fuel consumption compared to HP and distance traveled

Real world. Fuel flow monitored. 200 Hp stroke on a 22' boat.

Flat water, 27 kts. = 2.4 MPG
Moderate chop, 27 kts. = 1.9 MPG
Getting snotty, 20 kts. = ~0.9MPG