3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would do?

[andrewbabich]

Hi I've only ever had outboards. I currently have a tri hull 15' with 50 hp johnson.

Last year I fell in love with my buddies 21 foot alum with I/O. I want something a little bigger then my tri hull now.

How much more economical is an aluminum boat than a fiberglass 21 foot.

How fast do you think you could go with the 3.0 in a 21 foot boat. 3.0 seems small but i don't know how much lighter aluminum boats are.

Is the 3.0 OMC a good motor? I know parts are harder to come by for OMC then the current brands.

 

[Silvertip]

Re: 3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would

OMC didn't build the 3.0 -- GM did and parts for that engine are readily available. Merc and Volvo also use the same engine. The bigger question is what outdrive does this rig have. You do realize OMC went out of business decades ago. It is the outdrive that parts will be harder to come by. If you have to worry about MPG on a boat then you probably should approach this entire deal with a little more thought. It will not be like a car I assure you. 3 - 5 MPG is probably in the ball park since we have no idea what this 21 foot boat is or what it's hull design is.

 

[airshot]

Re: 3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would

About as close to answering your question as possible is to give you an example of my own 22' aluminium boat. I have a Starcraft Islander with the mercruiser 3.0 140 hp I/O. With two adults and alot of fishing gear as well as a 10 hp kicker motor and 25 gal of fuel it will do 34 mph (GPS). At its optimum cruising speed 3000 rpm @ 22-24 mph I avg about 5mpg in fuel (5 gal per hour). At wide open throttle it jumps to 14 gal per hour. Total wt of the boat is about 3000 lbs compared to 4500-5000 for a glass boat with similiar equipment. Keep in mind a 4 cycle I/O is not designed to run at WOT for long periods of time, this is where a 2cycle outboard is needed if you want to run WOT all day. The trade off is the 2 cycle O/B is going to use at least 50% more fuel than the 4 cycle I/O. Rough estimates for fuel consumption is 1 gallon per 10 hp per hour at WOT. I have no need to run at WOT all day, on the big lake 24 mph is a very comfortable cruising speed and I really enjoy the added fuel economy of the I/O. Hope this gives you some food for thought.

Airshot

 

[andrewbabich]

Re: 3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would

Airshot! Thats the best info to a fuel consumpton question I've every got! Thanks.

I'm comparing a 22 ft 1986 sulivan aluminum cuddy with 3.0 gm I/0 (not sure of the outdrive) with a 22 ft Cruisers cuddy with v6 yamaha 150 hp OB.

You see I'm mainly a 75% buzz around the river/ wakeboard/ crusie type of boater that only 25% of time go 6 miles off shore (on my friends boat or mine on a calm day) . I am not a hard core fisherman. I'm a pleausure boater who'd like to have a little more boat for the occasional fishing adventures.

So I really just want a boat thats bigger then my 1972 tri hull 50 hp johnson, but doesn't need to be that much more ocean worthy, while incurring a minimal bump up in fuel consumption and towing weight.

If aluminum is that much lighter then glass, and fuel economy is that much better on I/0 it sounds like a no brainer for me since I'm not worried about the improved ride in choppy water and stability in wind that glass offers.

Plus my boat comes out of the water every day so no need to worry about outboard being better for staying on a dock.

Thats great info. Anything else I should be considering?

 

[jestor68]

Re: 3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would

The trade off is the 2 cycle O/B is going to use at least 50% more fuel than the 4 cycle I/O.

Airshot

A typical Mercruiser 3.0L(135 hp) burns about 4.7 gph at cruise and about 11.4 gph at WOT.

A 125 Optimax burns about 4.8 gph at cruise and 10 gph at WOT.

A 150 Optimax(V-6) typically burns about 4.3 gph at cruise and 13.8 at WOT.

Not sure where you get that outboards burn 50% more gas? You must thinking "in the old days". Modern direct injected 2 strokes are as fuel efficient as any I/O of similar horsepower.

The typical 200 Optimax on 20 ft boats burns about 5-6 gph at cruise and 18-19 gph at WOT.

The typical 4.3L I/O burns 7-8 gph at cruise and 15-18 gph at WOT.

I see virtually no difference in fuel consumption between MODERN direct injected outboards and I/O's.

Since modern outboard motors are available in power ratings of 300+ HP, and weigh half as much as their stern drive equivalents, it makes you wonder why anyone would want a stern drive.

 

[andrewbabich]

Re: 3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would

Not sure where you get that outboards burn 50% more gas? You must thinking "in the old days". Modern direct injected 2 strokes are as fuel efficient as any I/O of similar horsepower.

Thats a great point jester, but everything I'm lookign at is going to be most likely from between 1985 to about 2000 is my guess, so I doubt any outboard is going to have direct injection is it? Direction injection is from the last few years and you're looking at very valuable expensive motors when you are talking direct injection motors right?

I don't boat enough to justifiy an awesome modern boat yet, (gotta pay of the wifes massive debt first... hold your jokes, i agree I know how I could easily solve that problem and get the boat of my dreams......but...)

So if I'm looking in the 4-8k boat range do you agree I/0 might be better for me? How much can direct injection motors be found for used?

 

[crabby captain john]

Re: 3.0 omc on 1986 21 alum cuddy. What speed and mpg do you think this combo would

I've run both. Your gas mileage will not be that much less with an older 2 stroke and maintenance could be less. My current boat is MUCH heavier and with a 150 Yamaha 4 stroke will get better mileage than either you mentioned. You are going to have to run many hours to get a mileage return. Buy what suits you now as you will have another in a few years.

Thats a great point jester, but everything I'm lookign at is going to be most likely from between 1985 to about 2000 is my guess, so I doubt any outboard is going to have direct injection is it? Direction injection is from the last few years and you're looking at very valuable expensive motors when you are talking direct injection motors right?

I don't boat enough to justifiy an awesome modern boat yet, (gotta pay of the wifes massive debt first... hold your jokes, i agree I know how I could easily solve that problem and get the boat of my dreams......but...)

So if I'm looking in the 4-8k boat range do you agree I/0 might be better for me? How much can direct injection motors be found for used?