I/O versus Inboard

[dogfish1]

I am sure this has been discussed but when I put this in the search engine nothing came up. I am having trouble understanding why people would prefer an I/B installation and why on larger boats that is what you see being installed. The outdrive has so many advantages, here is a quick list of the one I see:
Saves fuel, cruise and top speed are improved, gets boat on plane quicker and can maintain boat on plane at lower speeds, more maneuverable, less draft and drives can be raised to unfoul a prop easier.
I realize they are more maintenance, but the savings in fuel should allow for all maintenance to be carried out by yard personnel and you could still see a savings depending on how many hours a year you run, size of engines etc.
All this talk about pods and they still don't have all the advantages of stern drives. Finally why do they limit the size of outdrives? I don't think there is an outdrive that can accept more than 500HP and that is 500HP gas not diesel with all the torque diesels make. I realize there are some specialized outdrives for the go fast crowd that can handle big HP but 500 is a rough high end number.

 

[H20Rat]

re: I/O versus Inboard

The outdrive has so many advantages, here is a quick list of the one I see:
Saves fuel, cruise and top speed are improved, gets boat on plane quicker and can maintain boat on plane at lower speeds, more maneuverable, less draft and drives can be raised to unfoul a prop easier.

Finally why do they limit the size of outdrives? I don't think there is an outdrive that can accept more than 500HP and that is 500HP gas not diesel with all the torque diesels make

What??? Unless I misread every statement, almost every single 'advantage' you listed is actually in favor of inboards, not i/o's...

fuel: Simple physics, i/o's have alot more metal to drag through the water. Disregarding gearing and hull differences, an inboard will ALWAYS be more efficient.

cruise and top speeds: See #1. I/o's drag more metal. also, again, disregarding gearing.

plane quicker: nope... inboards allow all the weight to be moved forward, and again, drag... Competition ski/wake boats are inboards for a reason, this is one of them.

maneuverable: ok, I'll give you that one. single screw inboards can suck at times. Don't try to actually control them backing up.

draft: nope... A straight inboard will have about the same draft, although I do agree, you can't tilt them up. For some people that is an important consideration, for others is makes no difference. An inboard in a pocket configuration drafts far less than an i/o.

power: Because you have to have all the gears located outside the boat in a housing that causes drag. (seeing a theme here?) The larger you make the gears, the larger the housing has to be, and the more drag you get.

 

[smclear]

re: I/O versus Inboard

Why do some people prefer sail to power, 'tinnies' to fiberglass, outboards to I/O's, Pontoons to speedboats, fishing to skiing/tubing? It's all just personal preference. There is NO right or wrong. Don't try to understand it. Appreciate the diversity. We're all just trying to get out on the water and enjoy the day. Celebrate what we have in common. With that said, give me a straight inboard any day of the week. Maybe it's because I grew up with one. Maybe it's because I think they have a more 'classic' look to them. Maybe I like the sound of a 440 singing it's song. Maybe I like that I can pull 8 skiers with ease (my old I/O bow-rider could never think about doing that and yes, it had a 5.7 in it).

 

[Silvertip]

Re: I/O versus Inboard

Ever see an outdrive on an ocean going freighter? There comes a point where certain design features in any application become impractical. There is nothing more practical than a straight shaft drive. If you look at the physics in a "V" drive, the drive is actually trying to "lift" the hull whilst providing forward motion. They require a special trailer and because they use a rudder they are not as controllable at slow speed.

 

[dogfish1]

Re: I/O versus Inboard

What??? Unless I misread every statement, almost every single 'advantage' you listed is actually in favor of inboards, not i/o's...

fuel: Simple physics, i/o's have alot more metal to drag through the water. Disregarding gearing and hull differences, an inboard will ALWAYS be more efficient.

cruise and top speeds: See #1. I/o's drag more metal. also, again, disregarding gearing.

plane quicker: nope... inboards allow all the weight to be moved forward, and again, drag... Competition ski/wake boats are inboards for a reason, this is one of them.

maneuverable: ok, I'll give you that one. single screw inboards can suck at times. Don't try to actually control them backing up.

draft: nope... A straight inboard will have about the same draft, although I do agree, you can't tilt them up. For some people that is an important consideration, for others is makes no difference. An inboard in a pocket configuration drafts far less than an i/o.

power: Because you have to have all the gears located outside the boat in a housing that causes drag. (seeing a theme here?) The larger you make the gears, the larger the housing has to be, and the more drag you get.

No I disagree and the numbers from boattest.com confirm that a comparably equipped boat with outdrives will out perform an inboard boat, at least in the 30'-40' boat range. I am mostly looking at cruisers. Below 30' you almost never see inboards with cruisers, off shore fishing boats do come with inboards in that size range. When you step up beyond 30' you start to see a mix of outdrives and inboards and in that range you can really make the comparisons. The advatages of the outdrive is they put the thrust in the direction you want it and they have less drag. I know that you don't agree with that but look at the total amount of running gear. With an outdrive it is one hydrodynamic piece sticking out behind the boat vs the fitting where the shaft comes out of the hull, 10' or so of shaft with a strut, and then the rudder with its hardware. Beyond 40' you almost never see an outdrive, this was exclusively inboard terratory until recently with the new IPS drives.
Anyway I would invite you to look at boattest.com if you are still having trouble with this. Compare some of the boats they have tested, there are lots of sea rays that are comparable and you will see that the outdrive boats out perform the inboard boats.
I agree in small ski boats you see lots of inboards however that has to do with planing off and they put the engines very far forward to assist them in doing so. Those boats rarely go over 45MPH. All offshore racing boats are outdrives or in the extreme surface piercing drives.
It is a similar comaparison with the new IPS drives vs inboards and again IPS put the thrust in line with the motion of the boat better than inboards and are more hydrodynamic. With regard to performance the results are the same IPS beats inboards hands down.

 

[tpenfield]

Re: I/O versus Inboard

just grabbing a seat to hear what folks have to say about this . . . opcorn:

 

[RogersJetboat454]

Re: I/O versus Inboard

just grabbing a seat to hear what folks have to say about this . . . opcorn:

[Rogers walks up to seat next to Tpenfield's seat and asks] "Is this seat taken?"
op2:

 

[25thmustang]

Re: I/O versus Inboard

As someone who debated this before I will chime in.

I/Os are more efficient, faster, able to tilt the drives, easier to trailer and I'm sure have a lot more positives. With that said, I've found more robust parts with inboards, less moving parts, easier maintenance, less to worry about when wet slipped, offer more power options etc.

I went with inboards due to what I thought were the positives. This was with my 29' express. With my 34' there really aren't boats like it with I/Os.

FYI I think an inboard would be more maneuverable than an I/O set up (twins).

 

[smokeonthewater]

Re: I/O versus Inboard

I dunno twin I/O's will do some pretty cool things if you can remember which way to crank the wheel for which maneuver

 

[JoLin]

Re: I/O versus Inboard

I dunno twin I/O's will do some pretty cool things if you can remember which way to crank the wheel for which maneuver

Disagree, smoke- twin IB's are more maneuverable than twin I/O's. IB props sit under the hull, putting the boat's pivot point there as well. You can spin them on a dime. I/O's are trying to accomplish the same thing from a point 2-3 feet behind the transom. More torque is needed to muscle the hull around.

As for the OP's question, the only advantage I see to I/O's is shallow water running, which makes them good for where I boat. All other things being equal I'd much rather have IB's for their mechanical simplicity.

My .02

 

[mercrewser]

Re: I/O versus Inboard

My 2cents: Experienced boaters move to inboards. Straight Inboards. My Ride:


1979 17' Chris Craft Super Sport - YouTube

 

[Oshkosh1]

Re: I/O versus Inboard

One my skippers was a master shiphandler and more than once we got underway/tied up from/to a pier sans tugs...and that was on a destroyer. He could walk/pivot that thing away using differential backing/helm manuevers like it was a small 50' "Whale boat". Oh, and we had no bow thrusters either. I regulary drove single/twin screw I/B's and would take one all day over a twin I/O just based on manuverablilty. Head dead on toward the pier full speed, turn bow out, all back full, turn IN to the dock and viola! Parrallel parking...and the respect of your peers!

 

[haulnazz15]

Re: I/O versus Inboard

I/O's win in fuel efficiency, top speeds, and shallow water ops; all due to the ability to trim the drive up. They lose in the "potential" for expensive repairs/maintenance simply because there are a lot more moving parts. The bellows, while not a huge concern, is still a possible source for leaks in a moored boat, much more so than the propshaft seal on an inboard. While there aren't a lot of regular I/O drives capable of withstanding 500HP+, it's really not necessarily as most powerplants made by Mercruiser and Volvo don't go about 400HP. They are using I/O's on more commonly on bigger boats now (30-40ft) where they used to be inboard-only territory. Once you get into bigger boats (yacht-class) that have non-planing hulls, there isn't much advantage to use an I/O when your boat can't plane out, and the draft is deep enough that you better be in deep water anyway to avoid an expensive mistake.

There's probably a very slight advantage to I/B's vs I/O's in terms of maneuverability around the dock, but it's really small. Anyone with the Axius system can attest that they can pretty much perform the same maneuvers that an I/B can do.

 

[dogfish1]

Re: I/O versus Inboard

I forget what Merc and Volvo call it but they both have some system where you use a joy stick to maneuver your boat with stern drives. It moves the drives and shift them in and out of gear as needed this will allow the boat to go in any direction, even side ways. I think with these systems onboard they don't even use bow/stern thrusters anymore.

 

[haulnazz15]

Re: I/O versus Inboard

I forget what Merc and Volvo call it but they both have some system where you use a joy stick to maneuver your boat with stern drives. It moves the drives and shift them in and out of gear as needed this will allow the boat to go in any direction, even side ways. I think with these systems onboard they don't even use bow/stern thrusters anymore.

Axius (for Mercruiser) system I mentioned above, Aquamatic for Volvo.

 

[frantically relaxing]

Re: I/O versus Inboard

I dunno twin I/O's will do some pretty cool things if you can remember which way to crank the wheel for which maneuver

Disagree, smoke- twin IB's are more maneuverable than twin I/O's. IB props sit under the hull, putting the boat's pivot point there as well. You can spin them on a dime. I/O's are trying to accomplish the same thing from a point 2-3 feet behind the transom. More torque is needed to muscle the hull around.

As for the OP's question, the only advantage I see to I/O's is shallow water running, which makes them good for where I boat. All other things being equal I'd much rather have IB's for their mechanical simplicity.

My .02

As to this debate-- boats nearly always pivot near the middle, regardless of the drive. With the props closer to middle, maybe that helps with maneuvering, but I really don't know. But I DO know that since I got some props with a little bite attached to the Alpha's on our houseboat, I can turn it in circles within it's 53' length.

When the wind ain't blowin--

 

[southkogs]

Re: I/O versus Inboard

[Rogers walks up to seat next to Tpenfield's seat and asks] "Is this seat taken?"
op2:

"Hey guys, gotta'nuther spot? I brought drinks."

 

[Oshkosh1]

Re: I/O versus Inboard

Torque/Hp is transfered much more directly/efficently in an I/B setup...a straight propshaft, a couple of seals/bearings and a screw completes the drivetrain. Once you learn to drive it...properly(many commands are 180? opposite of I/O's/OB's with steerable props)...the advantages outweigh the disadvantages.

 

[JoLin]

Re: I/O versus Inboard

Axius (for Mercruiser) system I mentioned above, Aquamatic for Volvo.

Let's note that these systems are not common on low- and mid-priced boats. I'll bet even money that not a single iboater has a boat equipped with one of these. I doin't consider these a representative example for the 'IB vs I/O' debate, in the same way that I wouldn't consider a boat with a bow thruster to sway the debate one way or the other.

 

[haulnazz15]

Re: I/O versus Inboard

I wouldn't go as far as to say "no one on iboats", because I've seen a few threads about it. However, the system itself doesn't do anything that you can't do manually. It just simplifies it. If you know what your doing with either drive setup, you can do the same things as the other setup.