OB vs. I/O - Fuel Economy Question

[packman35]

This is my first post so please be gentle!!!

I am hoping to purchase my first new to me boat next year. It will unfortunately be 2009 before the finances are right to allow me to buy a boat. My budget will likely be $5k or less. I am looking in the 18-19 ft bowrider range. Will be used for general cruising, some watersports (as the kids get older), and fishing. I live in central NC so the winters are not harsh and I can see using the boat almost year round, particularly for fishing. Fresh water only.

So my question is this. And I know it has probably been asked a thousand times in a thousand different ways but here goes.

I am trying to decide the I/O vs. OB thing. I have read all the comparisons and based on what I have read and what my situation will be, OB doesn't sound like a bad thing. I like that I don't have to winterize it. Due to our relatively mild climate here, I would hate to have a nice fall or spring day and not be able to go fishing because my I/O was winterized. Nice to be able to hitch up and go and then just drain the engine after with no worries. I also will be doing all my own maintenance/repairs (I am quite mechanically inclined - albeit no experience with marine engines - but I can learn) so I like the easier maintenance and access that the OB provides.

But I am also worried about fuel economy (who isn't). Given the age of the boat that will likely fall in my budget range, I doubt I will find one with a 4-stroke OB. So the question is, how much more fuel will a 2-stroke OB use compared to a comparable I/O. Say a 115 hp OB as compared to the 3.0L I/O?

Trying to look at all the angles here so I appreciate all the wisdom and experience you all can bestow on me!!

Sorry for the long initial post and thanks in advance!!!

 

[tashasdaddy]

Re: OB vs. I/O - Fuel Economy Question

actually about the same, when you run them wide open. i would go OB, must more user friendly.

 

[45Auto]

Re: OB vs. I/O - Fuel Economy Question

actually about the same, when you run them wide open.

That's generally true. WOT fuel flow is about 10% of max enginie horsepower. For example, a carbed Yamaha 115 burns 13.5 GPH at WOT (42 MPH) and a 135 HP Volvo burns 11.5 at WOT (44 MPH). Both on an 18' Glastron bowrider.

I've found that I very seldom run WOT for any length of time. At cruising speeds you'll find that the older carbed 2 strokes around 115 HP will be lucky to see 4 MPG. The 3.0 I/O's get around 6 MPG.

Figure about 50% overall more fuel usage with the older carbed 2 stroke. Trade that off against the winterization (pull 4 or 5 drain plugs) required for the I/O.

 

[Silvertip]

Re: OB vs. I/O - Fuel Economy Question

Don't forget the extra weight, less interior room, gimbal bearings going bad, rusted through manifolds, water injestion, oil changes and disposal on the I/O.

 

[ufm82]

Re: OB vs. I/O - Fuel Economy Question

Or the blown head gaskets from overheating, blown powerheads from oil-injection failure, steering cable replacement issues and the like on outboards. Plus they are noisier and stinkier. (A big concern for my family that hates the smell of the 2-stroke smoke.) While I run an outboard, I like I/O's as they are more like your car or truck engine and I think are easier to work on. Most people who are mechanically inclined in regards to their vehicles don't know much about 2-strokes. They know how to check oil and put gas in their cars and I/O's can be more familiar to them. It's all a matter of how much you can spend and what you plan to do with it. For a family cruiser type boat, I much prefer I/O's.

UFM82

One more plus for an I/O. Usually the L/U sits deeper in the water than does an outboard. In many cases, a swim platform is present on an I/O style boat as well. This makes them much more user-friendly as the swimmers are much less likely to hit the L/U with their feet when swimming around the boat. I know this from experience. :-(

 

[tashasdaddy]

Re: OB vs. I/O - Fuel Economy Question

One more plus for an I/O. Usually the L/U sits deeper in the water than does an outboard. WRONG, the AV plate are in the same position. 2 stroke smell can be over come with synthetic TC-W3 oil.

 

[109jb]

Re: OB vs. I/O - Fuel Economy Question

Or the blown head gaskets from overheating,

Last I checked I/O's have head gaskets too. They can blow just like a 2-stroke head gasket.

blown powerheads from oil-injection failure,

Oil injection is very reliable, and with premix engines this isn't even related. I/o's also have a lubrication system, and failure or mismanagement of this system is every bit as catastrophic.

steering cable replacement issues and the like on outboards.

And I guess I/O's are thought controlled since they apparantly don't have steering.

Plus they are noisier and stinkier. (A big concern for my family that hates the smell of the 2-stroke smoke.)

Noisier?? Have you listened to some of the I/O's out there?? How about a 2 stroke that doesn't smoke or smell. My 115 mariner doesn't smoke or smell except when choked for start. A synthetic TCW-3 oil eliminated most of the smell

While I run an outboard, I like I/O's as they are more like your car or truck engine and I think are easier to work on.

How do you figure they are easier to work on when they are burried in the bottom of the boat. The outboard is in the open and everything is exposed. On top of this, you can add in that replacing an outboard takes about an hour if you know what you are doing. How long does it take to just remove the I/O lower unit?

Most people who are mechanically inclined in regards to their vehicles don't know much about 2-strokes. They know how to check oil and put gas in their cars and I/O's can be more familiar to them.

So I show someone the oil resevoir once on an outboard and they then know where to both check and fill the oil. Big translucent tank that you can see through. As for the gas, it goes in the fuel filler whether it is a I/O or outboard.

It's all a matter of how much you can spend and what you plan to do with it. For a family cruiser type boat, I much prefer I/O's.

UFM82

To each his own.

One more plus for an I/O. Usually the L/U sits deeper in the water than does an outboard. In many cases, a swim platform is present on an I/O style boat as well. This makes them much more user-friendly as the swimmers are much less likely to hit the L/U with their feet when swimming around the boat. I know this from experience. :-(

Huh, the prop/LU are or should be at the same height relative to the hull. This is dictated by efficiency. Also, the outboard height can be changed by raising the motor on the transom. Can't do that with an I/O. At least not easily. As for barked shins, I've climbed into many an I/O and outboard and have hit knee's on both. With the outboard all you got to do is look at the motor hood and you know which way the lower unit is pointing. There are outboard boats with built in swim/boarding platforms. I have one and it works very well.

Some things you left out:

Forget to winterize:
I/O - buy a new block
Outboard - Oh, well. Try to remember next year.

Blow a coolant hose:
I/O - bottom of boat full of water
Outboard - what hose?

Break a belt:
I/O - lose water pump, alternator, dead in the water.
Outboard - What belt?

Bilge blower failure:
I/O - dangerous situation that could lead to explosion from trapped fumes
Outboard - What bilge blower?

Bellows splits open:
I/O - boat sinks
Outboard - What bellows?

 

[jkust]

Re: OB vs. I/O - Fuel Economy Question

I prefer the kick in the pants acceleration and ease of maintenance of my outboard compared to my I/O. I love the smell of 2 stroke but not all the time. Unfortunatly, there are virtually no newer bowrider type outboard boats to my knowledge that I saw used with few exceptions. It seems all I see are I/O's as I think they are less expensive for my size boat. I can attest the old fashioned two strokes perform great but really drink gas compared to the I/O. Mine requires mixing the oil and adding lead additive so not sure about the reliability of oil injection. I don't know the numbers but know the O/B required lots more fill ups for less than half the HP. I have said this before but my 24 year old outboard has cost three dollars total in maintence all its life for one set of plugs but my I/O will cost over $300 just to have winterized. Our outboard seems bulletproof to me while the jury is still out on the I/O since we just got it. I do like the full sunpad and hidden motor with the I/O.

 

[sickwilly]

Re: OB vs. I/O - Fuel Economy Question

Wow -- you guys went way beyond the original question to lay our your IO versus OB biases!

That is what is so kool about boats, there is a style that fits each of us.

Welcome to Iboats Packman!

 

[Dakota47]

Re: OB vs. I/O - Fuel Economy Question

I think I/0 are better

 

[jevery]

Re: OB vs. I/O - Fuel Economy Question

.
I wasn?t able to find a direct comparison between a 3.0 I/O and a 115 OB, but I was able to find this comparison between a 4.3 I/O (190 HP) and a 200 HP Optimax OB on a Tahoe 215

Performance is surprisingly close in top speed and fuel efficiency. The OB has the edge in acceleration and the I/O has the edge in fuel efficiency and noise levels. The I/O doesn?t have to spin up as much as the OB for a given speed. Hard to beat the I/O for a quiet, refined, and out of sight powerplant and hard to beat the OB for maintenance and frequent use. I?ve owned both, and while I miss the Bryant with the 350 V8 in my avatar at times, I currently own a Yamaha outboard powered boat and don?t regret it

 

[QC]

Re: OB vs. I/O - Fuel Economy Question

I love OBs, but chicks don't . . .

 

[BoatinFool]

Re: OB vs. I/O - Fuel Economy Question

What QC said ^^^^^^^^^^^^^^^^^^^^^^^^^^^^

If you wanna fish, get an OB and slick fiberglass seats and floor. If you want the babes to be smilin', go with a smooth running IO with upholstery and carpet.

 

[reelfishin]

Re: OB vs. I/O - Fuel Economy Question

....................
Bellows splits open:
I/O - boat sinks
Outboard - What bellows?

This is the one that really does it for me, the one part about an outboard boat that I like the most is having a secure hull with no boots, bellows or seals to fail that could cause total loss. If an outboard fails, at best your looking at a tow home, not a long swim or worse.

Fuel mileage wise, every I/O boat I have has gotten pretty fantastic fuel mileage compared to an equal horsepower outboard. Up until just recently I owned two Starcraft Capri trihulls, one with a 115HP Evinrude outboard and one with a Mercruiser 120 I/O. Both got run about the same. The outboard boat had far more room inside and was much easier to launch load and trailer simply due to it being about 450 lbs lighter. The outboard boat would burn about 6 gallons of gas during an average day on the river, the I/O would run all weekend on it's 12 gallon tank with no fear of running dry. The outboard boat was about 10 mph faster, handled better and needed little to no maintenance. The I/O over the course of two years needed two gimble bearings, a shift cable due to a shift boot leak, (fun job), and it had issues on cold damp mornings starting which turned out to be a distributor problem which I fixed with an aftermarket electronic ignition kit. Starting the I/O meant a several minute wait while the bilge blowers ran to purge the hull of any fumes, while the outboard was a start and go type of boat.

While there's no doubt the I/O was far better on fuel, the comparison can be suspect due to the different types of engines. I suppose they would be far closer if run on dead equal courses at their pace. An outboard needs to turn more RPM to make power and torque, but if propped correctly, this shouldn't be as big a factor in fuel economy. My I/O boat was able to turn a 15 1/2" x 19P prop, while the outboard ran only a 13 1/4" x 17P prop. The difference being mostly in the lack of low end torque in the 2 stroke outboard. The outboard would get on plane far quicker and I could back off the throttle for a comfortable cruise speed, but the I/O would need far more power to remain on plane and had to maintain more speed to stay on plane. The added weight of the I/O was its own downfall in that respect. I sold both boats this summer, both sans their powertrains, I kept the outboard boat's motor and sold the I/O for more than the boat would have brought.

Overall, if I were to be buying a new boat, with a warranty, I might consider the I/O, but only if I didn't have to deal with all the maintenance and repairs. I for one have had enough of gimble bearings, bellows, shifter boots, rusted, clogged, cracked manifolds and risers and various other maintenance issues found on I/O boats. I like the idea of being able to swap out a motor in a matter of minutes if something goes wrong. I can be back out on the water the next day after an outboard fails and I can keep several spare motors around taking up minimal room in the garage. If I blew a motor today, I could come home, remove and rehang another motor and be out fishing tomorrow again. No the case on an I/O boat. Lose a gimble bearing, bellows, motor whatever and it's a day or more of hard work.

If I decide I want more power, I can unbolt my current outboard and hang on more hp as well. That's not a simple undertaking on an I/O boat.

 

[marine4003]

Re: OB vs. I/O - Fuel Economy Question

Last I checked I/O's have head gaskets too. They can blow just like a 2-stroke head gasket.



Oil injection is very reliable, and with premix engines this isn't even related. I/o's also have a lubrication system, and failure or mismanagement of this system is every bit as catastrophic.



And I guess I/O's are thought controlled since they apparantly don't have steering.



Noisier?? Have you listened to some of the I/O's out there?? How about a 2 stroke that doesn't smoke or smell. My 115 mariner doesn't smoke or smell except when choked for start. A synthetic TCW-3 oil eliminated most of the smell



How do you figure they are easier to work on when they are burried in the bottom of the boat. The outboard is in the open and everything is exposed. On top of this, you can add in that replacing an outboard takes about an hour if you know what you are doing. How long does it take to just remove the I/O lower unit?



So I show someone the oil resevoir once on an outboard and they then know where to both check and fill the oil. Big translucent tank that you can see through. As for the gas, it goes in the fuel filler whether it is a I/O or outboard.



To each his own.



Huh, the prop/LU are or should be at the same height relative to the hull. This is dictated by efficiency. Also, the outboard height can be changed by raising the motor on the transom. Can't do that with an I/O. At least not easily. As for barked shins, I've climbed into many an I/O and outboard and have hit knee's on both. With the outboard all you got to do is look at the motor hood and you know which way the lower unit is pointing. There are outboard boats with built in swim/boarding platforms. I have one and it works very well.

Some things you left out:

Forget to winterize:
I/O - buy a new block
Outboard - Oh, well. Try to remember next year.

Blow a coolant hose:
I/O - bottom of boat full of water
Outboard - what hose?

Break a belt:
I/O - lose water pump, alternator, dead in the water.
Outboard - What belt?

Bilge blower failure:
I/O - dangerous situation that could lead to explosion from trapped fumes
Outboard - What bilge blower?

Bellows splits open:
I/O - boat sinks
Outboard - What bellows?

Yea,But..........Nothing sounds as sweet as a worked pair of 502's running @4700 RPM. To each his own.

 

[45Auto]

Re: OB vs. I/O - Fuel Economy Question

As you can see from Jevery's post, the carbed 190 HP I/O has about a 25% advantage in efficiency over the fuel injected 200 HP outboard. $5000 around here (original posters budget) will put you in a good condition 10 year old boat with an I/O or carbed 2-stroke OB. The carbed 2-stroke OB will get about 50% of the fuel efficiency of the Optimax (according to Mercury).

If you've decided you can live in the 3-4 MPG range, you might as well go to a big block in boat around 22-25 feet. As you can see, this 24' Baja with a 375 HP 496 gets about the same mileage as the 200 HP outboard in the 20' Tahoe.

I've had both, and I can't imagine going back to an outboard unless I want something less than 100 HP. Maintenance on an I/O is like your car. If you don't drive cause you're worried about your hoses splitting and belts breaking, an I/O's not for you. Check'em every so often and replace them if they don't look perfect. The bellows is analagous to a timing belt in a car, change it every 4 or 5 years and don't worry about it.

If you're not into maintaining your boat correctly, doesn't matter what you get it's gonna die. 2 gimbal bearings in 2 years (reelfishin's post above) doesn't say much for whoever installed the bearings (or maybe bellows) mechanical ability. Time to get a new mechanic.

 

[mhlbnghm]

Re: OB vs. I/O - Fuel Economy Question

Fewer moving parts = fewer things to go wrong. 2-stroke

JMB

 

[ufm82]

Re: OB vs. I/O - Fuel Economy Question

What WAS I thinking? You are so right OJB. Please forgive me and my opinion. Obviously I'm not nearly as intelligent as you regarding boat power. Silly me; I posted based on my past experiences. Please accept my apology. Next time I'll send you my replies first so you can proofread them and enlighten me when I err. Would that be OK with you?

UFM82

 

[45Auto]

Re: OB vs. I/O - Fuel Economy Question

Poor lubrication (mist lubed - IE 2-stroke) vs pressurized bearings (4 stroke) = even lower parts count in a 2-stroke when the internals weld themselves together !!

(check out all those broke-down unreliable 4-strokes on the side of the road vs all those super reliable 2-strokes (can you say Traubaunt ) going down the freeway next time you're out)

 

[109jb]

Re: OB vs. I/O - Fuel Economy Question

...I've had both, and I can't imagine going back to an outboard unless I want something less than 100 HP. Maintenance on an I/O is like your car. If you don't drive cause you're worried about your hoses splitting and belts breaking, an I/O's not for you. Check'em every so often and replace them if they don't look perfect. The bellows is analagous to a timing belt in a car, change it every 4 or 5 years and don't worry about it.

If you're not into maintaining your boat correctly, doesn't matter what you get it's gonna die. 2 gimbal bearings in 2 years (reelfishin's post above) doesn't say much for whoever installed the bearings (or maybe bellows) mechanical ability. Time to get a new mechanic.

I don't think anyone is arguing that I/O's can be relieable, but by the same token, outboards are reliable too. My post in particular was in rebuttal to a post that pretty much claimed that outboards weren't as reliable by naming some failure modes. I have had outboards for many years and have only replaced spark plugs in addition to routine maintenance. I have maintained it to the degree necessary to maintain reliability. The point here is that maintaining for reliability entails much less in regard to a 2-stroke outboard as opposed to an I/O.

I like all boats, and simply prefer outboards for my boats, which by the way are smaller boats (16' w/70 hp, and 17' w/115 hp).

I/O's are certainly cleaner looking boats, have better fuel effeciency (compared to carb'd 2-strokes), are more friendly to the environment, and have many other features that appeal. The decision is up to each individual and being able to read the opinions of others can help them make their decision.