O/b vs I/b all things equal

[CharlesRiver]

Ok, I know this is tough question, but I'm going to ask anyways! All things being equal, same boat, same load, same water conditions, same prop, etc etc... How do the fuel consumption compare with say a 150hp o/b vs a 4.3 I/b?
Thanks

 

[Silvertip]

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

No difinitive answer because all things cannot be equal. Not even the prop is the same. Hulls are different. Weights are very different.

 

[rallyart]

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

It takes a specific amount of horsepower to move a particular hull at a particular speed. Where that horsepower comes from does not really matter. It takes a specific amount of fuel because of the BTU content to make that horsepower with small variations based on efficiency
The answer is that it really does not matter if the engine and drives are similarly efficient.

 

[Don S]

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

You are also asking about a 150 hp outboard, and a 190 to 205 hp IO (assuming carbed). Might want to compare a 200 hp OB to a 4.3 carbed engine.

 

[QC]

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

Define I/B?

True I/B = slow and inefficient (don't beat me up, look at data). No way to trim.

I/O = same horsepower will be slightly slower and slightly less efficient than a modern 4 or 2 stroke OB due to weight advantage. Can get drive up for shallow water. Highest weight.

O/B = Ugly transom (I like OBs, but hard to argue that they are pretty despite most men's love of machinery) Better trimmability so faster. Able to get drive completely out of the water. Lightest weight.

 

[jestor68]

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

Here's an example from Mercury's web site engine tests:

4.3L(220) powering a 18ft Larson used 15.8gph at wot and 7.2gph at cruise.

150 Optimax on a 19ft Crestliner used 13.8gph at wot and 5.9gph at cruise.

 

[airshot]

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

Another thing to consider, are we refering to an new $15000.00 4 stroke outboard, or an older 2 stroke OB, are you refering to a straight inboard or are you refering to an I/O. The newer and more expensive OB are probably going to be as fuel efficient as any I/O and probably a little faster in the performance area. I/O are less than half the cost of the new OB and just as fuel efficient but a little more maintaince. A straight inboard is the least expensive but not quite as fuel efficient and more difficult to maneuver the watercraft and needs more water to run in. These examples are just a teaser to all the other possibilities that could occur.

Airshot

 

[UncleWillie]

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

Ok, I know this is tough question, but I'm going to ask anyways! All things being equal, same boat, same load, same water conditions, same prop, etc etc... How do the fuel consumption compare with say a 150hp o/b vs a 4.3 I/b?
Thanks

Reading the question closely...
This is a hypothetical question; Leaving reality out of it!

The same boat at the same weight, going the same speed, in the same water, is going to be (wait for it!) the same!
Power is power! THE I/O has an addition 90 deg bend in the power train.

The 4.3MPI makes 220hp and likely gets better gas efficiency than the equivalent 4 stroke Carbureted Outboard.
The same 4.3L motor is rate at 190hp with a carburetor.

A 2 stroke motor will have a higher output per pound at the cost of lower fuel consumption.
A turbine would be even worse yet! But much lighter!

So our theoretical 4.3 throttled back to 150hp will be just about the same as our theoretical 150hp Outboard.

Now, reading through the question, The 4.3 is going to burn more fuel (MPG, MPH) than the 150 OB at WOT, But it will be going faster.
They will similar if you slow down the 4.3 to the same speed as the OB.

All things will never be equal in the real world.
Your actual mileage will definitely vary!

 

[carribbean soul]

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

next throw in a diesel i/o then it swings the fuel burn back to the i/o side

 

[CharlesRiver]

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

I knew this was going to get way more complex than I had intended! lol

So, lets muddy it up some more! Im looking at a 1999 glastron 190, with a 4.3 merc. as well as a 2001 larson with a merc 150 2 stroke.

Same day on the water, playing cruising etc, which will cost more to run??

Im not going to base my purchase decision on which boat is less expensive, if I was going to do that, I probably shouldnt even be looking at boats, I know! Just curious thats all!

 

[mwe-maxxowner]

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

I had an 86 dixie hustler 188 with a 150 black max. Now I have an '87 dixie hustler 188 with a 4.3. The outboard had much quicker acceleration and higher top speed than the 4.3. I think fuel usage was about the same.

The difference I think would only be detected with a fuel flow meter hooked up to it. After a day of playing and a trip to the pump I have always had to put about the same back into either boat. But, keep in mind you have to pay for the oil you add to the outboard's fuel.

 

[SigSaurP229]

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

If it were me I would buy the outboard based on the simple fact of less and easier maintenance. Fuel is only one part of the cost of ownership.

 

[UncleWillie]

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

Assuming the Larson is the same size as the Glastron, you will enjoy the extra performance of the Glastron and the 4.3 much more. (All things being equal.) :facepalm:
Your skiers will thank you for the 4.3. Slow starts really Suck!
Very few people have ever complained about have a too big engine.
The difference in fuel usage pulling a Tube or cruising at Idle to 30mph will be a non-issue.

My 4.3 averages 15 gallons a day of mixed activities for 4-6 hours on the water.
$50 of fuel for a day on the water for 2 adults and 4 kids is way cheaper than dinner and a movie!

 

[tazrig]

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

:fencing:op2:

 

[CharlesRiver]

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

Now, if I do the math correctly, it seems the O/B has a better power to weight ratio... should count for something!

 

[JoLin]

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

Fuel consumption differences are minor relative to the overall cost of ownership of one over the other. Do you do your own maintenance, or does your marina do it all? If it's you, which are you comfortable with, 2-stroke or 4-stroke? Any way you slice it, the I/O will cost you more to maintain than a 2-stroke OB- the difference will be greater if somebody else is doing all the work.

Fuel cost is usually the tip of the iceberg when owning a boat.

My .02

 

[southkogs]

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

Assuming the Larson is the same size as the Glastron, you will enjoy the extra performance of the Glastron and the 4.3 much more. (All things being equal.) :facepalm:
Your skiers will thank you for the 4.3. Slow starts really Suck!
Very few people have ever complained about have a too big engine.
The difference in fuel usage pulling a Tube or cruising at Idle to 30mph will be a non-issue.

My 4.3 averages 15 gallons a day of mixed activities for 4-6 hours on the water.
$50 of fuel for a day on the water for 2 adults and 4 kids is way cheaper than dinner and a movie!

I like Uncle Willies reply on this one: I switched from a 2 stroke to a I/O about 3 years ago. The difference in fuel usage hasn't been all that noticeable.

 

[ezmobee]

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

Lots of extra stuff to wear out, break, or require maintenance between the crank and the prop on an I/O that just simply doesn't exist on an outboard. That being said, the engine itself is generally a little more complicated on an outboard (multiple carbs).

 

[spdracr39]

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

Which boat has a better layout? Which boat is in better overall condition? Which boat has a nicer trailer? Which boat has a better overall look to it. It's more about what you like and is better to meet your needs.

 

[dingbat]

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

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