I/O vs. OB
 

Just a general nonsense question :D

Same boat same horsepower.

Would they both go about the same speed or would one be that much faster (I don't know the answer)?

I guess this would be a good trivia question.

Re: I/O vs. OB
 

Good question...
I'm guessing the difference would be minimal. On the Moeslyseacraft.com site Carla had some Mercury tests for the Bowrider and the 20' but they were like 125 O/B vs 140 I/O and a 100 O/B vs a 120 I/O.

In each case the greater HP I/O had advantage ranging from 1 to 2.5 mph top end... I guess you could extrapolate from that or just gather some of your southland buddies and go get some answers for us :D

Re: I/O vs. OB
 

Above all look at weight to horsepower ratio. Then consider drag if that may make a difference.

Re: I/O vs. OB
 

An outboard also puts weight further back, you usually get more boat out of the water trimmed out at higher speed with an outboard.

Re: I/O vs. OB
 

I think Eddie's right, a DI 2-stroke OB will have the edge on power/wt, and with the weight a little farther back, would be able to get a little more hull out of the water, so I think it'd have a little more top speed. With the heavy 4-stroke OB's, there might not be that much difference. The CG would be a little further forward with the I/O however, so it might ride a little better, and actually be able to cruise faster in rough water! So there are trade offs as usual - I guess it comes down to how you want to use the boat!

Re: I/O vs. OB
 

My father's 23' Sceptre OB (225 Yam OX66 carb on 6" manual jack plate) is within 1mph WOT of his best friend's 23' Sceptre I/O (260 Merc carb/Alpha drive). Their cruise speeds are similar too. The one thing I like better about the I/O is ride - all that weight down low gives it a bigger boat feel under way. The OB has a virtual dance floor in the cockpit so it's better for fishing.

Re: I/O vs. OB
 

Since there are a lot of 23 cc's with o/b here, I can chime in and say that my i/o's top end has been around 41 mph burning about 20 gph. My optimal cruise is right around 27-28 mph, getting 2.8 mpg. This is with a mercruiser 250/carbed/alpha.
It does ride like a tank when i need it to. The funny thing about fishing space on this boat is that I fish most often with two guys and the engine compartment makes an excellent casting platform in the back.

Re: I/O vs. OB
 

I have had a '72 20' Seafari with an inline 150 Mercury outboard (same motor was later re-rated as the Mercury 140, but rated at the prop)

I have also extensively used a '73 Seafari with a Mercruiser 3.0L 140 hp I/O.

The outboard accelerated faster, planing about 1 second faster. Optimum cruise speed on the OB was about 27-28 mph at about 9 gph. Top speed was about 40-41 mph. Fishing offshore while anchored in the OB had the problem of water coming in the engine well and then down into the bilge through the cable boot. On the other hand, the OB Seafari can comfortably fish 4 people.

The sterndrive (with a brand new '83 motor) had a slightly smoother ride in a chop, and cruised at 26 mph, getting much better fuel economy at only 6 1/2 gph, and had a slightly higher top end of 44 mph. Fishing while anchored in the sterndrive brought no water in due to the full transom, but was comfortable for 2, 3 or 4 was slightly crowded because of the engine box.

Does this answer the question?

Re: I/O vs. OB
 

I like that an outboard has its own little compact compartment(no engine box in the floor). Probably the best thing about an outboard(and most of you have been here). You go out in the boat(I/O or OB) and the son-of-a-b@#$h breaks down and leaves you strainded. While the towboatus guy is dragging you back to the ramp you can have the OB unbolted(no cherry picker required) and making a nice little artificial reef that you can go back and fish later. With an I/O it is pretty easy to blow you and your boat into a million pieces if you were to forget to turn on the blower. The only thing I like about the I/O is the ride. They do ride much better in a chop.

Re: I/O vs. OB
 

????- What's that about, or am I missing something?

Re: I/O vs. OB
 

I was just saying if you had to replace an engine an outboard is easy to remove and replace. I was just joking about dropping the outboard overboard although I do know someone that got so fed up with an outboard that kept leaving him stranded that he did unbolt it and drop it overboard. Gas inboards have always scared me a little because there have been two or three that have exploded when the people went to start them around here where I live. Those gas fumes can be pretty dangerous when they are bottled up in an engine box.

Re: I/O vs. OB
 

Most seem to feel an i/o or inboard rides better in rougher water. I've never seen this occur with 20', 23' boats. In my expierence that applys only with slightly rough water and/or at a crawl. Also any advantage the i/o may have the outboard could compete with with proper trimability at speed. When you get above a certain point in wave/chop height or speed of the boat you want the bow to have the tendency to stay in the air. Again I am speaking of the smaller boats like here, once you get a little more length on the hull then it seems to be more of a tossup. I have rarely been on a quality smaller boat that runs better with an i/o or inboard in comparison to an outboard at what most would consider a practical speed. Now if we are talking about drifting or feeling like a heavier boat then I could never argue about an i/o. Most of the guys I know prefer outboards on smaller boats even taking into account some people love closed transoms and some hate brackets. Then again I may be nuts which has happened before.

I will say the nicest running small inboard boat I have been on is a 25 Rampone with a single cummins, amazing but makes a seacraft seem drier than Arizona. It would cut the tops right off of solid close 4's on the nose and put it all over cockpit at 20knts.

Just my .02.

Re: I/O vs. OB
 

had a 74 scepter 20 with a 130 yamaha (91) outboard and now have a 71 i/o with a 4 cyl merc (circa 89).

The I/O rides better, gets better economy, cruises a little slower and tops out a couple miles per hour less... any day my family and I would rather have the IO. We actually like the IO box, it's great for sitting on while drift fishing, and the closed transom is nice...especially with a 1 and 3 year old. It's the best, most capable all around boat for us I feel like we could find anywhere.

Re: I/O vs. OB
 

outboards-only power designed strictly for marine use,anything else,is an after thought-hence,the term,"marinization"
stern drives,nothing wrong with a stern drive-my rig's stern drive powered-merc 5.7 magnum mpi with the horizon package and a bravo I drive-230 trouble free hours in 2 seasons-fantastic on fuel ! there's a little more upkeep on a stern drive boat-risers and manifolds every 4-5 seasons,pull the drive every winterization,30hr oil changes...but,it's got it's benifits,quieter,much quieter...engine box ?? not in the way at all,it's a center console,you fight a fish from the bow...

ride is better on a stern drive,but,the inboard has the best ride-low center of gravity...outboards on a bracket are the worst ride-leverage.the engine's sitting way behind the boat,acts as a lever,the boat has a tendency to porpoise,and ride "bow high",need alot of "down tab" to counter act...

Re: I/O vs. OB
 

Come ride on mine, I honestly don't get what most people expect their boat to do or how they expect to run them. These are small boats and a I/0 or inboard at any real speed in any sea condition worth talking about usually doesn't come close to an outboard. I have spent extensive time on 20sf's like mine. I/o, outboard, and bracketed. My and the two other bracketed boats I have spent time on far exceed the ride and capability at speed of an outboard on the transom or I/o. I just have a foil on it no tabs and no porpousing.

Re: I/O vs. OB
 

Let's be honest for a moment.

If you are looking for braggin' rights regarding WOT speed you'll probably favor an OB and maybe a bracketed OB with the cav plate 1.5 inches above the keel.

If your looking for a bit quieter engine noise at a lower less irratating pitch and are willing to give up 12-16 square feet of cockpit space that can double as a seat/"cocktail" table/ casting platform/ baiting station/ sundeck, with better fuel economy and a more "solid" ride, then you're going to favor an I/O. (guess which side I'm on?)

The reality is that this is why they make chocolate and vanilla!

Regarding speed I just did a quick calculation. If the distance is 20 miles and an O/B WOT speed is 43, then you get there in about 28min., if your WOT on an I/O is 39 then 20 miles is about 31min.

My question is: Whose wife has gotten mad at them for being only 3 minutes late getting home from a fishing trip?

Just a thought! :D :D :D

Re: I/O vs. OB
 

I assume the response is for me and thanks for the input. For me, I'm not looking for bragging rights, those days are behind me. As far as being honest, I am basing it all off real world expierence. I do though absolutely believe in a 2 to 4 headsea at 20 knots or most conditions worth saying how well a boat runs in a properly bracketed 20sf as compared to a non-bracketed, the boat will be a more enjoyable ride to most. I just can't let that go. I respect and appreciate everyones input but I have yet to expierence the contrary.

Re: I/O vs. OB
 

Bruce,

My response is not directed at any one. No configuration is better than another except to the respective user.

If I were to have to choose, I would answer based on my needs and personal preferences and circumstances. It is just terrific that these boats and the entire industry and country, for that matter, affords us the opportunity to choose for ourselves. Thus my point in saying, "That's why they make chocolate and vanilla!" We get to choose because there is a choice.

Re: I/O vs. OB
 

Properly set up, I would think there wouldn't be much difference. HP is HP. The lightest power source will be the fastest. What are the weights of a modern 250 hp outboard vs. a 250 i/o? Straight inboard is a different story because of inefficient drive angle. Not the fastest but probably the best ride.

Re: I/O vs. OB
 

A 300 HP Mercruiser with Bravo Drv.900 #

A 300 Yamaha 4/s 800#.

So hundred pounds lighter, I bet the speed would be insignificant.

Remember I asked which would be faster, not which would be better :D

It is interesting getting everyone's opinion.

Ford or Chevy...Black or White!

Re: I/O vs. OB
 

I had a 300hp Mercruiser (7.4L) which is a 454 ci Chevy block and a bravo 1 drive, It was way heavier than 900 #, all together it was close to 1300#.

Re: I/O vs. OB
 

I don't know the weight, but the current 300HP Mercruiser is a multi-port fuel injected 5.7 liter,(350ci) small block.
Dave

Re: I/O vs. OB
 

I'd say closer to 1300 lbs for the I/O myself...I think the 5.0 merc in my Hiliner and bravo 3 is about 1100 lbs. The new 300 Yamaha should be closer to 575 lbs not 800.

Re: I/O vs. OB
 

One site lists the complete package for a Mercruiser Magnum 5.7L 300 hp motor, transom mount and Bravo 2 drive at 1083 lbs.

Re: I/O vs. OB
 

A big block will always be heavier than a small block.

A small block will be heavier with a bravo 2 drive than a small block with a bravo 1.

My numbers come directly from Mercury (in brochure form).

Re: I/O vs. OB
 

Oldfielder,What's your WOT RPM?
I also have a 23 footer(Tsunami) with a 350 I/O with a Merc Alpha drive.I wish I could get 41 mph top speed.
I'm only getting around 36 at wot.
Maybe it's the weight difference and wind resistance,between the ctr console and Tsunami/Sceptre models.
It cruises nicely around 27 at about 3400-3500 rpms.

It was originally a 305 but the block was replaced with a new 350 short block.They transferred all the other parts to it,and I put a new intake and a 650 cfm Edelbrock 4bbl carb on it,so I'm assuming that I'm around 240-260 HP.
A mirage ss prop that seems perfect.Maybe it's the weight difference for the slower speed.
Also,the stand up canvas work,the radar arch,and some wet foam in the stringers may also be slowing me down.

Either way it rides awesome.It's stern heavy but it jumps on plane very fast,and the tabs easily correct any other ride issues.

Re: I/O vs. OB
 

I top out around 4400, which is really the bottom of my 4400-4800 range, so I may be slightly overpropped but I don't let it bother me.
As far as weight/wind resistance, you are probably spot on. I added a simple three sided enclosure this year to the t-top for a little break in November from the wind and I've lost a bit off the top. It's amazing how that little item changes things in the wind-even when docking.

Re: I/O vs. OB
 

Hit 39.5 today with the windscreen up, two big guys and about 50 gallons of fuels and 4 big fluke on board :)
Was burning exactly 20 gph and running in a slight chop(which the boat seems to like best)