O/b vs I/b all things equal

[QC]

Re: O/b vs I/b all things equal

To me, composite data, over a bunch of examples is probably the most legit. The fact is that the OPs original post was (the OP's, OP?) impossible "all else equal", and noted by Silvertip I think. That's why I think composite info is important.

 

[frantically relaxing]

Re: O/b vs I/b all things equal

I know this much from experience (not only mine)--

Our Party Cruiser, 32' long pontoon boat, pretty heavy bugger at around 6000#, with a single 115 hp Mariner outboard-- The original owner's logbook showed the thing was burning 12 gallons of gas every 20 miles at 12 to 14 mph cruising speeds, which is 1.66 miles per gallon. My experience with the boat was almost identical. And I (it) went thru 2-stroke oil at the rate of 30 to 1 rather than the 50 to 1 is should've been (injector needs adjusting)

Our SkipperLiner, 53' LOA x 14' wide, near flatbottom houseboat, weighs in at around 35,000#, it's pushed around with TWO 120 hp Mercruiser 4-bangers. My cruise speed is only 7 mph, but my miles per gallon is typically 2 to 3 depending on wind.

2 completely different hulls are part of the reason too. The PC's toons dig into the water, the SkipperLiner only sits in the water 10", so it's like a large lilly pad...


Theoretically a 2-stroke should burn twice as much fuel as a 4-stroke since a 2-stroke sucks and burns fuel every time the piston hits TDC, But they don't use as much fuel per burn so that offsets it a bit. I believe that a 150hp 2-stroke will always use more fuel making that hp than a 4-stroke will, but the weight savings of a 2-stroke again offsets it...

so the answer is... pick one and have fun!

 

[S8861]

Re: O/b vs I/b all things equal

Here's a close comparison. Stingray 235 with 260 hp single prop vs stingray 234 with Yamaha 250 hp outboard.

Boat specs other than motor are very similar.

http://www.stingrayboats.com/products/models13/performance_options.pdf

 

[dingbat]

Re: O/b vs I/b all things equal

OK, I went through your math, Rick. Looked at the tests and the hulls, and I have to say they seem fairly valid. On the hulls I was pretty concerned about deadrise comparison, as a higher deadrise will eat more fuel. The fact is, the I/O was 22 degrees, and the O/B Whaler is 21. Conclusion being that the Whaler didn't suffer any simple penalty to explain the high fuel use in the comparison. The rest of the comparison between boats and power seems pretty valid as they reach similar top speeds.

I would say that's a fair comparison, and indeed a 200 hp OB vs. a 300 hp I/O which shows that you can do the same job with a smaller OB, but it won't always burn the same fuel.

With that said, what I do when I make these comparisons is I try any find data that contradicts my belief. If I find 10 examples that confirm my belief and 3 that refute it, I feel much better. Obviously 100 examples that confirm it vs. zero refuting is even better, but I think you get my point. Off to the data mines

Uhhhh... you over looked one little point, those numbers are for twin 200HP outboards "Mercury 200 hp Dual Verado (L-4)" The dead giveaway is the top speed. Who here thinks you can push a 24', #5400+ offshore boat at 54 MPH with 200 HP?

Something else I picked up. The listed weight of #4400 for the Whaler is w/o engines. Add another #1020 pounds for the outboard so your'e comparing #5400 and 400Hp to #4400 and 300 and wonder why such a big discrepancy?


Here is the same boat with a single, 300Hp verado on the back http://www.mercurymarine.com/enginetests/third_party.php?ID=105

You’re comparing an offshore boat to a lake boat. The hulls are completely different animals. The Whaler is running a mod-v. ~45 deadrise in the front. Also noticed that the lake boat carried 30 gallons of fuel during the test. The Whaler has a 150-gallon tank. If that tank was half full, you’re looking at another #500 pounds of fuel.

Fuel usage will vary considerably with conditions. I would also bet they did not test the Whaler on a lake with 5 MPH winds as they did with the lake boat.

 

[QC]

Re: O/b vs I/b all things equal

The fuel consumption alone should've been the clue :facepalm:

 

[UncleWillie]

Re: O/b vs I/b all things equal

...Theoretically a 2-stroke should burn twice as much fuel as a 4-stroke since a 2-stroke sucks and burns fuel every time the piston hits TDC, But they don't use as much fuel per burn so that offsets it a bit. I believe that a 150hp 2-stroke will always use more fuel making that hp than a 4-stroke will, but the weight savings of a 2-stroke again offsets it...

A 2 stroke WILL theoretically burn twice as much fuel at the same RPM if the engines are the same Displacement.
If they are the same Horsepower, they will "Theoretically" burn the SAME amount of fuel.

A 200hp 4 stroke will be in the neighborhood of 4 liters of displacement.
A 200hp 2 stroke will be closer to 2 liters.

The two stroke will give you the same horsepower in a smaller, lighter, simpler, engine.
Its downside is that it does not operate with cam controlled valves like the 4 stroke.
With a 2 stroke the intake port and the exhaust ports are both open simultaneously during a portion of the cycle.
Intake and exhaust takes place at the same time, and a small portion of the intake Fuel/Air mix can pass straight out the exhaust port and burn in the tail pipe.
Some fuel is wasted in exchange for simplicity, size and weight.

If high power and fuel efficiency is the overriding factor, think diesel.
If operating cost and fuel efficiency is the goal, the 4 stroke is preferred.
If simplicity, size and weight are the big concern. The 2 stroke is indicated.
If fuel efficiency is of No Concern but small size and light weight are required. The gas turbine wins!
That is why you will only see Turbines in unlimited racing boats where operating cost are not a consideration.

Don't expect to see a Turbine in pleasure boat or a private vehicle unless the cost of fuel approaches Free!
The Government/Military loves Turbines, but they don't pay for the gas!

 

[dingbat]

Re: O/b vs I/b all things equal

The two stroke will give you the same horsepower in a smaller, lighter, simpler, engine.
Its downside is that it does not operate with cam controlled valves like the 4 stroke.
With a 2 stroke the intake port and the exhaust ports are both open simultaneously during a portion of the cycle.
Intake and exhaust takes place at the same time, and a small portion of the intake Fuel/Air mix can pass straight out the exhaust port and burn in the tail pipe.
Some fuel is wasted in exchange for simplicity, size and weight.

This maybe true of 20th century 2 stroke, but this is the 21st century, by 10 years. A modern 2 stroke is just as efficient than a comparable four I/O stroke. The weigh to HP ratio isn't even close

 

[dingbat]

Re: O/b vs I/b all things equal

~5.3mpg

The lighter weight of the OB appears more significant in a smaller boat. It might be that a 300HP OB might compare more favourably with a 300hp I/O in a similarly sized boat.....

Any comments on the lastest development?:embarassed:

 

[dingbat]

Re: O/b vs I/b all things equal

Well lets use my example above, shall we?

Lets say you're a "Fishing Fool"! AND the KIDS are Skiers!

You have a favorite fishing "hole" that is precisly 27 miles away. So, it takes you an hour to get there and an hour to get back in those boats above. running that "optimum cruising speed around 27 mph...

You go every weekend during summer. (14 times this Summer JUN-AUG)

That would be 14 times 2x7gal (out and back)................. 28 hours (x7) for a total of 196 gallons With the I/O boat above.

Let also say that the other day of the weekend the kids want to ski (at approx 27 mph for the sake of argument) for a 3-4 hours AND for the same sake of argument you end up with a total of 2 hours of average running at 27mph..... (For another 196 gallons) (that's 392 gallons total for you math wizards!)

AND a total of only 56 hours of average running time for the entire summer.

With the other one running the 200hp OB, the same running would require 56 x 9.4 g/hr or 526 gallons.

At $5/gallon, you're spending (I/O) $1960.00 and (OB) $2630

For the same math challenged ones, THAT'S $670! MORE with the outboard!

If you operate 100hrs, then it's approx $3500 vs $4700 (or roughly $1200) MORE per year.



I don't know about anyone else but I'll take the little bit additional maintenance cost of the I/O.

Besides, the kids wouldn't want to ski behind a 4400lb boat with a 200hp outboard on the back because it would be a REAL DOG out of the hole!

ymmv......


Rick

EDIT: I wanted to look a tad further since some people don't just run at the most efficient cruising speed all the time..........


Just looking at running those same boats at APPROX 38MPH (NOT WOT)

The I/O boat above fuel flow went to 12.8 Gal/hr

and the OB boat went to 16.7 Gal/hr !

and at WOT, The 1.7L 200hp OB burned 38.4 galhr

and the 5.7L V-8 300hp Bravo III I/O burned 25 gal/hr

Any comments now that it's been brought to your attention that your comparing a #5400, 400HP boat to a 300Hp, #4400 boat?

Not only are you comparing 30% more HP pushing ~35% more weight, your comparing an agressive offshore hull to a lake boat under lake conditions. If you don't think the hull makes a difference, run both boats 40 miles offshore and back at 38 MPH and get back to us on the winner and their fuel consumption. After you call the chiropractor for the guy in the Larson.:lol:

 

[Campylobacter]

Re: O/b vs I/b all things equal

I gotta say I love the OB vs I/O threads, they seam to show up several times a year. Nothing is every settled, nobody minds are changed, but we do get some insight into the "other side".

As a completely biased OB guy, I love it when the I/O guys are reduced to "but...but..chicks love sun pads".

My smoking hot admiral loves outboards

 

[UncleWillie]

Re: O/b vs I/b all things equal

This maybe true of 20th century 2 stroke, but this is the 21st century, by 10 years. A modern 2 stroke is just as efficient as a comparable four I/O stroke. The weigh to HP ratio isn't even close

I agree. The 2 stoke will always beat the 4 stroke for power to weight ratio.
The 2 strokes have gotten much better over the years and can approach 4 stroke efficiency.
The nature of the design is against the 2 stroke for power efficiency.

Along with the problem in getting fuel into the cylinder and having it stay there.
The other issue is that the the exhaust port begins to open half way down the power stroke,
wasting the potential energy still remaining in the hot compressed gasses.
This is why the 2 stroke exhausts tend to be so loud. You are hearing that wasted energy.

It is just the nature of the design and there is no way around it. It is, what it is.
In some cases the weight saving of the 2 stroke can compensate for the lower power efficiency.
But the 4 stroke will always make more power per gallon of fuel.
And the 2 stroke will make more power per pound of engine.
Which one gets more miles to the gallon depends on the overall design of the vehicle.

They are just different. One is not "Better" than the other.
They both have their preferred uses.

 

[QC]

Re: O/b vs I/b all things equal

can approach 4 stroke efficiency.
The nature of the design is against the 2 stroke for power efficiency.

Yeah, no way to actually "catch" the 4 cycle for the reasons you note.

It is just the nature of the design and there is no way around it. It is, what it is.
In some cases the weight saving of the 2 stroke can compensate for the lower power efficiency.
But the 4 stroke will always make more power per gallon of fuel.
And the 2 stroke will make more power per pound of engine.
Which one gets more miles to the gallon depends on the overall design of the vehicle.

Direct injection has lessened some of the impact, but you are right. The only reason two strokes match MPG on a boat is the weight savings.

Still embarrassed about missing the twins, but I am gonna blame Rick :redface:

 

[dingbat]

Re: O/b vs I/b all things equal

Yeah, no way to actually "catch" the 4 cycle for the reasons you note.


Direct injection has lessened some of the impact, but you are right. The only reason two strokes match MPG on a boat is the weight savings.

Here is a manufacturer?s comparison between twin 4 stroke verado and twin 2 stroke Optimax on the same boat. Both running 19" props. Seems the 2 stroke has caught up, and passed the 4 stroke on the bottom and top ends.

Trolling for hours on end as I do, the fuel savings of the Opti is significant. Same if you had miles of no wake zones to navigate on a regular basis.

http://www.mercurymarine.com/engines/engine-tests/boat-house-bulletin/?ID=381&38319.04140617247

Engine Test | Mercury Marine

 

[QC]

Re: O/b vs I/b all things equal

I love that kind of data. Be aware, there is no guarantee that the Verados aren't PsOS I am so far from anti 2 stroke that you should consider me as actually pulling for them. But with equal technology 2 cycle gasoline are still off of 4 cycles from a pure efficiency standpoint. Again, not weight, and certainly not all examples. i.e. Super good 2 cycle vs crap 4 cycle is not a valid comparison. And I am not calling Verados crap, it's just that there are some serious laws of physics things that the 2 cycles are up against.

 

[dingbat]

Re: O/b vs I/b all things equal

I love that kind of data. Be aware, there is no guarantee that the Verados aren't PsOS I am so far from anti 2 stroke that you should consider me as actually pulling for them. But with equal technology 2 cycle gasoline are still off of 4 cycles from a pure efficiency standpoint. Again, not weight, and certainly not all examples. i.e. Super good 2 cycle vs crap 4 cycle is not a valid comparison. And I am not calling Verados crap, it's just that there are some serious laws of physics things that the 2 cycles are up against.

I agree on the Verado comment. You'll never find on the back of my boat. When my 2 stroke finally bites the dust I'm bolting a Yammie F series on the back

 

[UncleWillie]

Re: O/b vs I/b all things equal

I love that kind of data. Be aware, there is no guarantee that the Verados aren't PsOS I am so far from anti 2 stroke that you should consider me as actually pulling for them. But with equal technology 2 cycle gasoline are still off of 4 cycles from a pure efficiency standpoint. Again, not weight, and certainly not all examples. i.e. Super good 2 cycle vs crap 4 cycle is not a valid comparison. And I am not calling Verados crap, it's just that there are some serious laws of physics things that the 2 cycles are up against.

+1

Looking at the tests they appear to be about as equivalent as you'll likely ever find.

Some comments.
The 2 stroke is 130 lbs lighter despite it is a 3L compared to the 4 strobe 2.6L Supercharged engine.
This would be expected as the two stroke always wins in the power to weight race.

The wild card is that presumably it is Not the same Hull and different crews and equipment were on board as the tests were performed 10 months apart.
The sea conditions and atmospherics during the tests were certainly uncontrolled variables.

To make it a lab standard test you would need to run two or more equivalent boats side by side on the water and then swap engines on the hulls and run them again. Crews and equipment remain with the hulls.
I doubt any one would be willing to do that.

The tests are only a snapshot of how a particular engine and hull operated on a particular day in the local conditions.
It is representative of generally how you might expect your engine to perform.
Your result WILL vary.

 

[BrianCinAz]

Re: O/b vs I/b all things equal

Here is a manufacturer?s comparison between twin 4 stroke verado and twin 2 stroke Optimax on the same boat. Both running 19" props. Seems the 2 stroke has caught up, and passed the 4 stroke on the bottom and top ends.

Trolling for hours on end as I do, the fuel savings of the Opti is significant. Same if you had miles of no wake zones to navigate on a regular basis.

http://www.mercurymarine.com/engines/engine-tests/boat-house-bulletin/?ID=381&38319.04140617247

Engine Test | Mercury Marine

I love that kind of data. Be aware, there is no guarantee that the Verados aren't PsOS I am so far from anti 2 stroke that you should consider me as actually pulling for them. But with equal technology 2 cycle gasoline are still off of 4 cycles from a pure efficiency standpoint. Again, not weight, and certainly not all examples. i.e. Super good 2 cycle vs crap 4 cycle is not a valid comparison. And I am not calling Verados crap, it's just that there are some serious laws of physics things that the 2 cycles are up against.

Since the discussion has now turned to 2 stroke vs 4 stroke, we should look at the dirt bike industry since they went through this exact same transition in the past 10 years. They are essentially ahead of the boat engine manufacturers in this evolutionary process. Also, dirt bike engines are more similar in design to marine outboards than the car engine I/B or I/O.
The problems that they discovered are that the 4 stroke engines are not as durable as the auto engines for several reasons. The first and foremost is that they (dirt bike engines) are running much higher RPM's continuously as opposed to an auto engine. You don't see 4 cylinder cars running 4500 RPM non stop for the duration of the commute to work. Dirt bike engines and marine O/B's do run at those RPM's or even higher for extended periods of time. The 4 strokes were found to be far less durable than the 2 strokes. Did the 2 strokes use more gas? Yes. But when you factored in the much higher cost of NORMAL (aka COMMON) repairs, the 2 stroke won the "which is less expensive to run?" debate. Typical 2 stroke repairs include a new top end at a given number of hours. Typical 4 stroke repairs included frequent valve adjustments, frequent valve replacements due to stem stretching caused by the higher RPM's at which the engine would normally operate. Then the pistons and rings were also replaced at approximately the same number of hours as the 2 stroke (unless a valve stem snapped, in which case the piston would be damaged....), so the top end repairs were essentially a wash (between the 2 stroke and 4 stroke).
Interestingly, Honda had the worst history and Yamaha had the best track record in regards to the durability of their 4 stroke engines in the early years. Kawasaki and Suzuki also had fewer problems than Honda.

 

[dingbat]

Re: O/b vs I/b all things equal

Since the discussion has now turned to 2 stroke vs 4 stroke, we should look at the dirt bike industry since they went through this exact same transition in the past 10 years. They are essentially ahead of the boat engine manufacturers in this evolutionary process. Also, dirt bike engines are more similar in design to marine outboards than the car engine I/B or I/O./

They may be similar in design, but that?s where the similarly ends. The marine environment is murder on power plants. You' re talking apples and oranges w/o subjecting them to the same operating enviroment.

The problems that they discovered are that the 4 stroke engines are not as durable as the auto engines for several reasons. The first and foremost is that they (dirt bike engines) are running much higher RPM's continuously as opposed to an auto engine. You don't see 4 cylinder cars running 4500 RPM non stop for the duration of the commute to work. Dirt bike engines and marine O/B's do run at those RPM's or even higher for extended periods of time.

You hear this argument all the time, but the failure mode doesn't support the claim. By far, the leading cause of catastrophic failure in marine engines is mositure, followed by overheating. The number of marine power plants that die from wear and tear can be counted on one hand. It's just not an issue

The 4 strokes were found to be far less durable than the 2 strokes.

Maybe in dirt bikes but not in outboards. The average life expectancy of a 4 stroke outboard is almost twice that of it?s 2 stroke counter parts. Why, plain and simple. 4 strokes are much less prone to catastrophic failure from fuel contamination, fuel delivery problems and overheating that plague 2 strokes

Typical 2 stroke repairs include a new top end at a given number of hours. Typical 4 stroke repairs included frequent valve adjustments, frequent valve replacements due to stem stretching caused by the higher RPM's at which the engine would normally operate.

The number of 2 stokes in the outboard grave yard with melted pistons and rods sticking thru the side of the block is mind boggling. Most grenade from problems in the fuel delivery and cooling system long before they wear out. I can tell you from experience, the difference in cost between replacing a 200 HP powerhead and adjusting the valves on 200 HP 4 strokes every 1000 hours (10 years of use) is substantial. Also, If I'm not mistaken, dirt bikes are air cooled. Makes a big difference on the wear and tear issues

 

[dan02gt]

Re: O/b vs I/b all things equal

Since the discussion has now turned to 2 stroke vs 4 stroke, we should look at the dirt bike industry since they went through this exact same transition in the past 10 years. They are essentially ahead of the boat engine manufacturers in this evolutionary process. Also, dirt bike engines are more similar in design to marine outboards than the car engine I/B or I/O.
The problems that they discovered are that the 4 stroke engines are not as durable as the auto engines for several reasons. The first and foremost is that they (dirt bike engines) are running much higher RPM's continuously as opposed to an auto engine. You don't see 4 cylinder cars running 4500 RPM non stop for the duration of the commute to work. Dirt bike engines and marine O/B's do run at those RPM's or even higher for extended periods of time. The 4 strokes were found to be far less durable than the 2 strokes. Did the 2 strokes use more gas? Yes. But when you factored in the much higher cost of NORMAL (aka COMMON) repairs, the 2 stroke won the "which is less expensive to run?" debate. Typical 2 stroke repairs include a new top end at a given number of hours. Typical 4 stroke repairs included frequent valve adjustments, frequent valve replacements due to stem stretching caused by the higher RPM's at which the engine would normally operate. Then the pistons and rings were also replaced at approximately the same number of hours as the 2 stroke (unless a valve stem snapped, in which case the piston would be damaged....), so the top end repairs were essentially a wash (between the 2 stroke and 4 stroke).
Interestingly, Honda had the worst history and Yamaha had the best track record in regards to the durability of their 4 stroke engines in the early years. Kawasaki and Suzuki also had fewer problems than Honda.

I rode motocross bikes for a long time, and to add to this the at the top end of performance spectrum (where motocross bikes are) 4-strokes require dang near twice the displacement to be competitive with the 2-strokes. Also my friends 05 KX250F (4-stroke) required 2 twice the money and work to stay running as my 99 KX125 and my brother's KX250 (both 2-stokes). While this really has nothing to do with outboards or i/o's it's interesting never the less.

Also, all performance oriented dirt bikes have been water cooled since the early 80s.

All that being said count how many 4-strokes and I/Os you see here?

Awesome video if your into performance boating and the average guy can own one of these. I think I/Os, 2 and 4 stroke O/Bs all have their place and perform certain tasks very well, but I like 2-stroke O/Bs :joyous:

 

[buellwinkle]

Re: O/b vs I/b all things equal

One thing not considered is space. An outboard will give you much more room in the boat than an i/o or inboard. We feel our 18' OB has as much room as 20' or even larger inboard or i/o drive boats. So for example, you can get a 16' outboard like the new Glastron 160 with OB that has as much room inside as the 18/19' i/o drive boats you may be looking at.