Inboard vs outboard performance

[dingbat]

Re: Inboard vs outboard performance

That's correct, although I was picturing more of the aft-cabin or pleasure boat vs. the Contender/Everglades type awesome fishing machines.

I understand, but a lot of these "awesome fishing boats" are now being built in Express and walkaround configurations that are being used as family "pleasure boats". They rival, if not exceed most of the "pleasure boats" in amenities, comfort and ride quality. One could say the SUV of boats.

The only thing missing is the indoor/outdoor carpeting and the particle board furniture.

Fishing or pleasure boat?

 

[jkust]

Re: Inboard vs outboard performance

Those stats expecially on the 18' Sea Ray are actually shocking especially the time to 30mph. The 45Auto chart flies in the face of conventional wisdom. Here's my take on I/O versus OB. I have similar sized open bow boats one with o/b and one with I/O. The OB is old school 2-stroke, it is smokey, smelly, extra loud, dismal on gas but is quick out of the hole and required zero maintainance (other than one set of plugs) over it's 25 year life. My I/O on the other hand just broke 100 hours on the engine, requires a couple hundred of annual maintainance/winterization and this year $800 of tune up, drive maintainance and winterization. The sport seating configuration (single bench in the rear) provides a lot of storage space and a ton of lounging space as does the tanning platform. We are loungers and so that set up was made for our needs. Under the tanning platform are amounts of storage I could only dream about on my O/B boat. Noone ever sits on the jump seats next to the o/b engine since I think you'd loose a little hearing and potentially suffocate from smoke inhalation if you did.

As for performance, if I ever complain about the performance on my I/O, I can only blame it on having the second cheapest power package since there were three optional engines above mine. In reality when you have a wife and a couple little kids, you rarely ever go WOT for long anyway. You have to cut the budget off somewhere and a v6 instead of a v8 is an easy way to get boating but do it for less up front $. Also I bought it a few years ago when gas was at its all time high which skewed my thinking a bit.

 

[QC]

Re: Inboard vs outboard performance

The 45Auto chart flies in the face of conventional wisdom.

That's the beauty of those charts and data, data, data. Conventional wisdom is often wrong, and I have personally found, with 30+ years in the engine business, that conventional wisdom involving engines in boats and wheeled vehicles, maintenance etc. is especially misunderstood . . . I have unlearned as many things as I have learned while being on the R and D side of engine technology. A lot of what we think and believe, and swear by, is in fact incorrect . . . Just is.

 

[haulnazz15]

Re: Inboard vs outboard performance

Ad nauseum, I will give my input on the powerplants. I like bothe the O/B and the I/O in different applications.

The O/B's are small and economical for boats under 20ft or so. They are very low maintenance and can be used at any time of the year with no though involved regarding water/air temps. I love them for any fishing boat. They are noisier and (imo) ruin the clean lines of most boats. The other major downside to them is that when they do malfunction, you don't want to be removing parts while on the water because dropped parts are forever lost. The other downside as far as maintenance/repair goes is that many of the parts aren't avaliable except through marinas/boat repair facilities so running to O'Reilly's isn't usually an option when something breaks and you want to get out on the water.

The I/O's are better in bigger boats where space isn't at quite a premium. The move the weight (in addition to weighing more) forward which helps in evening the load for planing vs the O/B setup. The I/O's also rule the water when it comes to large amounts of power. While it's always possible to stack 4-300HP O/B's on the back of a Cigarette boat, having twin 600HP engines is much more simple and doesn't ruin the lines of the boat. I also prefer the sound of an American V8 over the whine of a Honda any day.

It's true that when things go bad on an I/O, they can get expensive quick. But in my experience, the I/O's have been just slightly above the O/B's in maintenance costs. I have never had to replace an outdrive due to failure. I haven't had to replace cables or manifolds on a boat we've had for 18+yrs and it never failed on us. We replaced the bellows maybe twice in that 18 years as well. Our winterizations were done by us, so the cost of some fogging oil is really the only added "expense" come wintertime.

I rebuilt the 34 yr old engine this summer with new everything for $3.5K. It will be good to go for another 30yrs I'm sure with proper maintenance. If I had to replace a 225HP outboard it would have been easier and quicker, but 3-4 times as expensive. Each drive-type has it's plusses and minuses, but I have specific applications that I like for each. Runabouts/Cruisers get the I/O's, fishing platforms get the O/B's.

 

[45Auto]

Re: Inboard vs outboard performance

The 45Auto chart flies in the face of conventional wisdom.

As QC says, that's the advantage of looking at REAL data and making your own decisions versus accepting conventional wisdom.

For thousands of years conventional wisdom said that the sun revolved around the earth. Up till a few hundred years ago they killed people for claiming otherwise.

A Gallup poll taken a few years ago showed that now almost 4 out of 5 people realize that the conventional wisdom was incorrect. But there's still about 20% of Americans out there whose conventional wisdom says that the sun revolves around the earth. It's obvious to them that the sun revolves around them. They see the it come up in the east, travel across the sky, then go down in the west.

Four out of Five Americans Know Earth Revolves Around Sun
Probing a more universal measure of knowledge, Gallup also asked the following basic science question, which has been used to indicate the level of public knowledge in two European countries in recent years: "As far as you know, does the earth revolve around the sun or does the sun revolve around the earth?" In the new poll, about four out of five Americans (79%) correctly respond that the earth revolves around the sun, while 18% say it is the other way around.

http://www.gallup.com/poll/3742/new-poll-gauges-americans-general-knowledge-levels.aspx

Hopefully if enough people are exposed to actual data, within another few hundred years the OB vs I/O conventional wisdom will also come around to reality!

 

[JimS123]

Re: Inboard vs outboard performance

The trouble with statistics and statisticians is that they tend to publish only the data that will support their hypothesis.

I am not arguing or disputing the data and I admit that I did not take the time to read the 4 reports in detail. When I saw the short summary data my first thought was "I wonder if each boat in the test was propped correctly (i.e, to achieve optimum performance), or did they just test what the factory sent them.

An optimized little motor may very well do better than a poorly set up big one.

So, homework for someone that has the time and inclination to find out - are all 4 boats in the tests running WOT at the max engine rpm specs?

Since we're talking about the sun and moon, how about the 3 statisticians that went deer hunting. One shot and missed 4 feet to the right. The second shot and missed 4 feet to the left. The third got out his calculator and pronounced "We got him"!

 

[ingalp01]

Re: Inboard vs outboard performance

Outboards tend to transfer more of their listed HP to the water.

 

[45Auto]

Re: Inboard vs outboard performance

Outboards tend to transfer more of their listed HP to the water.

Interesting theory.

Since they're all rated at the propshaft, is their some magical attachment between the prop and the shaft on an outboard that transfers additional power to the water?

 

[Lou C]

Re: Inboard vs outboard performance

The OB has only one right angle change of direction, the I/O has two, maybe that makes a difference.

 

[45Auto]

Re: Inboard vs outboard performance

The OB has only one right angle change of direction, the I/O has two, maybe that makes a difference.

You may want to do a little research and understand what exactly a "propshaft" is .......

It's the thing the propeller is attached to. If power is measured at the propshaft, it doesn't matter how many changes of direction it takes to finally get there. It's the amount of power that is delivered to the propeller. The prop doesn't know if it's an inboard, outboard, 2-stroke, 4-stroke, Wankel, turbine, whatever attached to it.

You're confusing crankshaft power and propshaft power.

 

[dingbat]

Re: Inboard vs outboard performance

Here are performance figures from the exact same 21' hull of a #3300 fishing boat.

One is OB powered and the other I/O. Which is which and what HP are each?

RPM MPH Knots Total GPH MPG
2500 11.4 9.9 4.6 2.48
3000 22.3 19.4 6.3 3.54
3500 26.9 23.3 8.4 3.20
4000 33.4 29.0 10.8 3.09
4500 38.0 33.0 14.0 2.71
5000 41.9 36.4 16.4 2.55


RPM MPH Knots Total GPH MPG
2500 11.0 9.5 4.0 2.74
3000 17.3 15.0 4.5 3.88
3500 23.5 20.4 5.5 4.27
4000 30.8 26.8 8.7 3.56
4500 33.6 29.2 10.3 3.26
5000 39.1 34.0 12.7 3.09

 

[QC]

Re: Inboard vs outboard performance

Interesting challenge dingbat . . . I am going to guess the upper on is an I/O, say a 4.3 at 205 bhp.

The bottom one is the OB and I am going with a 150 4 stroke.

Although the hulls are the same, weight, weight balance and trim leverage are still very different between an I/O and OB which can explain the close top speed with 45 less horsepower.

 

[Wishiniwuzfishin]

Re: Inboard vs outboard performance

I'm guessing top is outboard, bottom is I/O. No guess as to actual hp but I'm guessing both are the same.

 

[Summer Fun]

Re: Inboard vs outboard performance

I'll take my inboards any day over outboards.

 

[Wishiniwuzfishin]

Re: Inboard vs outboard performance

And I'll take my o/b's over inboards any day. It's been sunny and getting into the 60's F during the day here the last week or so, but dropping as low as 20F at night. Been on the lake a few times the past few days.....I noticed what few boats were out were all o/b's. Just one of the many advantages IMO. But I'd take either over no boat at all any day.

 

[dingbat]

Re: Inboard vs outboard performance

Interesting challenge dingbat . . . I am going to guess the upper on is an I/O, say a 4.3 at 205 bhp.

The bottom one is the OB and I am going with a 150 4 stroke.

Although the hulls are the same, weight, weight balance and trim leverage are still very different between an I/O and OB which can explain the close top speed with 45 less horsepower.

The test claims the 4.3 at 210 bhp but that's close enough. Your outboard selection still needs some thought. I will tell you it's a 2 stroke.

 

[H20Rat]

Re: Inboard vs outboard performance

The test claims the 4.3 at 210 bhp but that's close enough. Your outboard selection still needs some thought. I will tell you it's a 2 stroke.

I'm guessing 150 hp Merc 2 stroke.

 

[QC]

Re: Inboard vs outboard performance

I'm actually going to go up to a 175 2-stroke, but the fuel use at WOT seems too good . . . craterboy is probably right and I almost went that way in the beginning, I can't see going down in hp with the close top speed to the 210 I/O.

 

[dingbat]

Re: Inboard vs outboard performance

The boat in question is a 21' Trophy W/A.

Length Overall 21' 7''
Dry Weight 3,342 lbs.
Beam 8' 1''
Fuel Cap 85 gal.
Draft 2' 9'' (max)
Deadrise/Transom 19 deg.

The numbers on the top are the Mercrusier 4.3L 210 bhp. The numbers on the bottom are for a 135 hp Mercury Saltwater 2 stroke.

 

[45Auto]

Re: Inboard vs outboard performance

The above is an excellent example of why you always want to look at real data. Here's another one, can you figure out what it is? Notice how the performance is slightly WORSE (both speed and fuel consumption) than the outboard that dingbat posted.

Hint: It's a smaller boat, 1000 pounds lighter, and has LESS power. You would think it would get better MPG.

RPM MPH Knots Total GPH MPG
2500 9.8 8.5 4.8 2.06 1.79
3000 21.0 18.3 6.2 3.39 2.95
3500 26.7 23.2 7.6 3.53 3.07
4000 32.1 27.9 9.0 3.57 3.10
4500 35.5 30.9 11.3 3.16 2.74
4800 38.0 33.0 11.9 3.19 2.78