Inboard vs outboard performance

[75-JOHNSON]

I'm just wondering how inboards and outboards compare with power? Like would a 140hp out board perform the same as a 140 inboard? What are the pros and cons of each. if there is another thread like this feel free to let me know.

 

[a70eliminator]

Re: Inboard vs outboard performance

I/O is quiet and you don't see it, but it takes up room in the boat.
Outboard is louder and you see it, but more room in boat, gets in the way landing fish.
I/O is basic iron horses compared to outboard that has a lot more tech engineered into them.
Winter layup is easy with an outboard.
No big hole in transom with outboard.
The pro's and cons go on and on.

 

[dingbat]

Re: Inboard vs outboard performance

A 140 HP outboard would run circles around a 140 inboard.

All things considered, a 140 HP inboard would be closer in performance to a 100 HP outboard.

 

[DuckHunterJon]

Re: Inboard vs outboard performance

I've seen this said before, that it isn't an apples and apples comparison - is this because OB's are quoting prop-shaft HP and IO's are quoting crankshaft HP (not accounting for geartrain losses)? Or is there some other reason I'm missing. Thanks.

 

[H20Rat]

Re: Inboard vs outboard performance

And outboard of equal HP will ALWAYS outperform a similar I/O. If nothing else, just the simple fact the outboard weighs less. If you can find a boat that gets faster as you add weight to it, you found the exception to the rule. (and in that case, you can always just carry another buddy or more fuel with anyway)

 

[wire2]

Re: Inboard vs outboard performance

The torque curve for an I/O rises much earlier than an O/B. If you're trying to pull skiers up, or get a loaded boat on plane, it makes a big difference.

Mileage is typically no contest, an I/O doesn't burn expensive oil along with the gas, and no smoking.

 

[haulnazz15]

Re: Inboard vs outboard performance

The disparity between the inboards and outboards begins when you get up in the 250+HP range. Outboard become prohibitively more expensive in the 250-300HP range, and place a lot of weight farther back on the boat. It's a lot cheaper to have a 300HP I/O than it is a 300HP outboard. The torque on the I/O will also be much better than the O/B.

The issue with drivetrain-type is what your use for the boat will be. Outboards can operate in much shallower waters and are self-draining for those winter outings. Very few people prefer the look of outboards hanging off of the boat to the smooth lines of an I/O. Outboards get in the way of watersports as well.

 

[45Auto]

Re: Inboard vs outboard performance

You will find it beneficial to do some research on similar boats powered by outboards and I/O's. If you compare a 1000lb 140HP outboard fishing boat to a 3000lb 140HP I/O bowrider don't be surprised if the outboard wins. You're giving up comfort for performance. But you'll find that in similar boats the HP doesn't know what kind of motor it's coming from, performance is the same.

It's hard to find a direct comparison, but for example, Boattest.com has tests on an 18' Sea Ray bowrider powered by a 115 HP Mercury outboard and a 135 HP I/O. They also have a 17' Glastron bowrider powered by a 115 HP ETEC and a 135 HP I/O.

http://www.boattest.com/boats/boat_video.aspx?ID=702

http://www.boattest.com/boats/boat_video.aspx?ID=968

http://www.boattest.com/boats/boat_video.aspx?ID=2312

http://www.boattest.com/boats/boat_video.aspx?ID=1233

 

[ezmobee]

Re: Inboard vs outboard performance

This was very interesting. Thanks for posting it.

 

[Snobike Mike]

Re: Inboard vs outboard performance

I've seen this said before, that it isn't an apples and apples comparison - is this because OB's are quoting prop-shaft HP and IO's are quoting crankshaft HP (not accounting for geartrain losses)? Or is there some other reason I'm missing. Thanks.

Dunno about older ones, but new I/O's are rated at propshaft HP, not crankshaft HP so they are rated the same as O/B's.

 

[Boatist]

Re: Inboard vs outboard performance

I agree the HP is rated at the prop shaft on outboards and I/O now. In the old day they were both rated at the power head.
Because of the difference of weight the same HP outboard will be faster because it lighter. In the old days fuel mileage was better on the I/O because they are four cycle.
Today the fuel mileage is the same or slightly better on 4 cycle outboards.
The 4 cycle outboatds are much heaver than the the 2 cycle outboards of the same HP but still lighter than the I/O.

As some have said already the outboard takes up less room in the boat.
While this is true it is not that big a difference on some boats.
Many outboards will have a big motor splash well that take up a lot of room.
I still like the I/O for several reasons. The ladies like to lay out on the back engine cover and deck.
I like the fact that the weight is farther foward and lower in the hull.
In big chop or offshore swells this makes the boat ride better.
Yes you can trim the ride with trim tabs and motor trim but just not the same.
When drift fishing tabs a and motor trim will make no difference but the weight farther foward and lower still reduces the rock and roll.
Offshore in large swell having the weight lower in the hull means the boat does not rock and roll as much as a outboard with weight higher in the hull.
I like that the motor is inside and any touble you can work on it.
My 1980 boat has never been towed in or had to come in on my kicker but I did replace the points one time offshore.
Took about 10 minutes to diagnoise and repair. If it had been an outboard would have had to come in on my 15 HP kicker.
I would also say the outboard lover are winning as fewer and fewer I/O boats built.

 

[H20Rat]

Re: Inboard vs outboard performance

I would also say the outboard lover are winning as fewer and fewer I/O boats built.

That really isn't from market demand though. Look up the brands that brunswick marine owns. When you make 30+ different brands of boats, and also happen to own mercury outboards, guess what, you are going to make sure you sell far more outboards! Yes, obviously they own mercruiser marine, but buying someone else's engine block and bolting on some marine equipment isn't nearly as profitable as an outboard.

 

[Fireman431]

Re: Inboard vs outboard performance

Have you seen all of the Homeland Security, Coast Guard, and Navy runabouts? All O/B powered.

I have had 20' boats with both I/O and O/B power and I'll take the O/B anytime, but my opinions are based strictly on personal preference and have absolutely zero data to back them up. Obviously, once you get to the bigger vessels, I don't think O/B engines are really in the mix any longer, although there is one poster who is putting O/Bon a 36' vessel. Should be interesting.

Was the OP also mentioning the difference between 2-stroke and 4-stroke O/B?

 

[Mike Robinson]

Re: Inboard vs outboard performance

....buying someone else's engine block and bolting on some marine equipment isn't nearly as profitable as an outboard.

I may be mistaken, but I'm pretty sure outboard manufacturers do something similar. I believe that certain models of Mercury's had Yamaha engine blocks.

 

[cribber]

Re: Inboard vs outboard performance

Most of the pro bass boats around my area are running 150 to 225 hp OBs or a little better. Those dudes can scream across the lake at 60 + on GPS.

 

[wire2]

Re: Inboard vs outboard performance

Most of the pro bass boats around my area are running 150 to 225 hp OBs or a little better. Those dudes can scream across the lake at 60 + on GPS.

That's getting into apples/oranges though. A bass boat is lighter than a deep V runabout, almost a flat bottom, and not deep enough at the stern to fit an I/O package. And at 60+ they guzzle gas. It's all about the competition in a bass tournament.

 

[dingbat]

Re: Inboard vs outboard performance

Obviously, once you get to the bigger vessels, I don't think O/B engines are really in the mix any longer, although there is one poster who is putting O/Bon a 36' vessel. Should be interesting.

With the advent of the 300+ HP outboards, 30' + boats with outboards are becoming common place. Most the major offshore builders, Grady White, Contender, Fountain, Regulator, Hydra-Sport, and Pro-Line to name a few, all build 34'+ outboard powered boats. The largest production outboard powered boat that I'm aware of at this time is a 44' model built by Concept boats.

 

[QC]

Re: Inboard vs outboard performance

There are plenty of 100+ MPH I/O boats where I boat . . . Agree, apples and oranges.

The hp at the propshaft thing changed around 1990 for I/Os. To be clear though the OP mentioned IBs and we should probably have three categories for this discussion OB, I/O and true IB . . . that's also getting muddier with Pod drives, so there you go. I do, however, assume like most of you that he meant I/O . . .

One more vote for data collection at places like Boatest.com. All of our speculation, and misunderstanding of torque curves, gear ratios, propshaft vs. crankshaft hp, fuel use etc. can be put to bed with data . . .

 

[Fireman431]

Re: Inboard vs outboard performance

With the advent of the 300+ HP outboards, 30' + boats with outboards are becoming common place. Most the major offshore builders, Grady White, Contender, Fountain, Regulator, Hydra-Sport, and Pro-Line to name a few, all build 34'+ outboard powered boats. The largest production outboard powered boat that I'm aware of at this time is a 44' model built by Concept boats.

That's correct, although I was picturing more of the aft-cabin or pleasure boat vs. the Contender/Everglades type awesome fishing machines. I regularly see 50+' houseboats with twin 200 HP O/B.

 

[riptide09]

Re: Inboard vs outboard performance

My 2 cents worth.

On a smaller boat, such as my 17', I like an O/B because there is more room in the boat. Put 7 people in a 17' bowrider and you will be glad the motor is on the back and not in the boat.

I have never really looked at performance compared to an I/O however I can tell you that with just me in the boat the top speed is 45 @ 5400 and with 7 people (max capacity) my top speed is 39 @ 5200. (Of course those speeds vary based on conditions) I have pulled skiers and tubers with 7 people (6 in boat, 1 being pulled) in the boat no problem. She is slow to get up on plane but once there no issues.

I prefer an O/B because there is less maintenance required and easier to winterize. Took me 30 minutes to get my Johnson ready for winter. I do most of my own work and I find working on an O/B to easier and also lots of room. You are not on your back or side half way down in the sump with your arm twisted around a corner trying to work on something you can't see.

And finally, I am 50 years old and had assorted boats over the years. Not by design or plan however I have always had O/B power. In my book the O/B rules.