I/O vs. OB

Islandtrader · #1 07-01-2010, 05:53 PM

Just a general nonsense question

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.

McGillicuddy · #2 07-01-2010, 07:45 PM

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

htillman · #3 07-01-2010, 11:46 PM

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

workinpr0gress · #4 07-02-2010, 12:02 AM

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

Bushwacker · #5 07-02-2010, 02:03 AM

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!

ScottM · #6 07-03-2010, 09:25 AM

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.

oldfielder · #7 07-03-2010, 10:05 AM

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.

Fr. Frank · #8 07-04-2010, 04:58 PM

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?

adamcannon · #9 07-05-2010, 09:39 AM

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.

BigLew · #10 07-05-2010, 11:43 AM

Quote:

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.

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