Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

[cptnmcluvin]

Howdy,

I'm considering convert my mercruiser 470 alpha one to a mercury outboard.

Question 1: will the alpha one controls and gauges be compatible with the mercury outboard?

Question 2: where can I get the best deal on an outboard bracket?

Thank you,

John

Richmond, VA

 

[shrew]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

This project would be cost prohibitive IMHO. Going from a IO to a an outboard would be a lot of material and labor.

 

[RogersJetboat454]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

Question 1: will the alpha one controls and gauges be compatible with the mercury outboard?

Nope. May be able to mickey mouse them to work, but more time and money would be spent screwing around with trying to make something work, than if you just get the correct controls in the first place.

Question 2: where can I get the best deal on an outboard bracket?

Dunno the answer to this.
You need to really consider the scope of this project though. It's not going to be as simple as pulling the I/O out, and hanging a bracket on the back. To do this right, the transom should be replaced so it is solid, especially if you are considering hanging a big honking outboard on the back. The outboard will be heavy, and with an outboard bracket, it will multiply the leverage on the transom. You also need to consider that the boat will now be stern heavy with an outboard so far back. You will also have a big hole (the bilge) to deal with once the engine is removed. Honestly, if you are really set on having an OB powered boat, I would be looking for a boat intended to be powered by an OB. If you really want to keep your boat, but aren't happy with the headaches associated with the 470, I suggest finding another donor boat with a 4.3L V6 and drive, and swapping everything over.

 

[kahuna123]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

So are you saying that the transom was never built to handle and outboard to start with? Having a bad transom has nothing to do with how the boat was built.
Its going to be more aft heavy than before?? If so how come outboards don't need the world famous smart tabs?
Are you saying that a 200 merc weighs more than the 4.3 with the outdrive.
Come on

 

[mrshake]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

So are you saying that the transom was never built to handle and outboard to start with? Having a bad transom has nothing to do with how the boat was built.
Its going to be more aft heavy than before?? If so how come outboards don't need the world famous smart tabs?
Are you saying that a 200 merc weighs more than the 4.3 with the outdrive.
Come on

Kahuna,

Its not as much a weight thing as a position of weight thing. The primary weight for an I/O is INSIDE of the transom (the engine) where as the weight on an Outboard is OUTSIDE the transom as well as being higher than the engine from an I/O. That changes the center of gravity WELL to the rear of the boat and will make the boat sit lower in the back.

 

[Sprky]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

If it is a weight placement thing then tell me why (for example) The 17' Larson with the 130hp 3.0 is a pig compared to the same boat with a 115 OB mounted aft on the transom. The 115 outboard is nearly 7mph faster with 15 fewer hp and a whole lot less torque. The outboard boat handles nicer and rides considerably smoother than the I/O. The boats are basically the same with minor differences to accomidate the outboard or the I/O.

Another question, why do boats respond favorably to set back? Even Mercury performance builds and sells stand-off boxes (set back plate for a I/O) for go fast boats. If a longer lever (moving the drive aft) were of no value then Mercury wouldn't be selling any transom assembly's that are three times the cost of stock ones.

Having a motor in front of the transom moves the horizonta CG forward. Moving the motor aft moves the CG aft which in turn act like a longer lever carring more of the boat out of the water. Less wetted surface=more speed............Which brings us back to the I/O vs OB larson. The OB runs better on less hp because the balance of the boat allows more efficient running.

Or you could just buy a set of "Smart Tabs" and bolt on 5mph for $100.........

 

[drrpm]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

It would be cheaper and easier to put the 4.3 V6 in the OP's boat than to try and retro fit it to be an outboard. If you really want an outboard sell the boat and buy one that was designed and built as an outboard.

 

[Sprky]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

It would be cheaper and easier to put the 4.3 V6 in the OP's boat than to try and retro fit it to be an outboard. If you really want an outboard sell the boat and buy one that was designed and built as an outboard.

But why, when he could just add smart tabs and gain 5mph. ..................................

Yes, installing a V6 would be way less work.

 

[kahuna123]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

There's not a low end boat around that was designed for an inboard. Hence smart tabs. Not enough boat to displace the weight until it reaches a higher speed to plane and forces the CG more forward. But the inboards years ago and still today were much cheaper to install. If we are talking about a 34 Fountain that needs twin 1000 hp that's different. Take any small bayliner with an outboard of equal hp and the outboard will plane better and ride better and have a higher top end. Outboards have a much more efficient hp to weight. MUCH less moving parts. And what doesn't get brought up much is that in I/O changes power direction twice and an outboard once. That's a huge loss difference. Now on a boat that has enough aft glass in the water to make up for the weight difference things change. But not on small lake boats.

The center of gravity is higher with an outboard. But not as much as you would think. The CG is ONLY relevant to the amount of water being displaced. At speed the CG MOVES. That's how boats plane. The more water the aft has to move per the weight it is displacing the faster it has to go to plane. The faster it has to go to maintain plane. Sitting still doesn't matter. That's why smart tabs greatly improve boats that are balanced to far back to start with.

Why the setback??? It because the outboard runs in much cleaner water a little further aft and can run higher out of the water. Hence MUCH less prop slip and MUCH less drag. Down here we call them jack plates.

Its like anything else. Everything is compromise.

 

[RogersJetboat454]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

So are you saying that the transom was never built to handle and outboard to start with?

Who knows? The OP has not posted what brand/model boat he is planning on doing this with. We don't know if his model was offered with an OB option. What we do know is that if his boat was offered with an OB, it would; A. not have a hole in the transom where the original stern drive would have resided. B. The outboard would have most likely been clamped directly to the transom with a splash well. Not cantilevered off the back by a bracket. C. May have had additional bracing, since all the weight and thrust of the power plant is on the transom rather than the stringers and transom.

Having a bad transom has nothing to do with how the boat was built.

Who said the boat had a bad transom? The boat could have a perfect transom if he intended to stick with an I/O. The fact remains that his current transom has a hole in it, and may not be built/braced heavy enough to hang a decent sized outboard off of.
This thread is a perfect example of what he may run into; http://forums.iboats.com/showthread.php?t=469836

Its going to be more aft heavy than before?? If so how come outboards don't need the world famous smart tabs?
Are you saying that a 200 merc weighs more than the 4.3 with the outdrive.

It's a simple matter of leverage. The engine doesn't need to weigh as much as a 4.3 W/ drive to make the boat transom heavy. Just the simple fact that EVERYTHING is now outside of the boat, with more leverage (A.K.A. the transom bracket) than a motor mounted on a splash well, it may be enough to upset the balance of the boat.

Come on

Come on nothing..... No offense to the OP, but starting off by asking if mercuiser controls will work with a Mercury outboard says to me the OP may not be fully aware of the task he is considering. I'm not going to paint a rosy picture by saying it's as simple as gutting the power train, stuffing the hole, bolting the transom bracket and mounting an outboard. A project of this magnitude requires careful consideration, with the results possibly being less than desired.

 

[JoLin]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

If so how come outboards don't need the world famous smart tabs?

From what did you draw that conclusion? My 21' Pro-Line with 175 Johnson and (factory) setback bracket was so butt-heavy in the water it was ridiculous. Smart Tabs made a fantastic improvement. A slew of OB users on this forum have had similar experiences.

I concur with Rojersjetboat's comments. Nobody's said it can't be done, but the OP is in for a much bigger and more complicated project than he realizes.

My .02

 

[Bob_VT]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

The 470 was phased out in the 1980's say 20 years ago........ you are entering a cost prohibitive change. Now everyone is saying go with a v-6 IO and even a good 140 4 cylinder I/o would serve you better.

Now there are many people still running 470's and the good news is.......used parts are plentiful .....what is wrong with yours?

 

[Sprky]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

Acutally when you replace the 140 or later 130 with the 470, there is a huge gain. Did a job on an old Glastron V168, removed the 140 which ran 38 on a good day and replace it with a 470. The boat with a 184 gear will pull a 27 pitch mirage to 4600rpm. You do the math............

 

[kahuna123]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

I wouldn't use Pro Line as an example. They are or used to be made here.
http://www.pensacolafishingforum.com/f21/opinion-pro-line-boats-35180/
http://www.thehulltruth.com/boating-forum/7963-proline-boats-2.html


Yes and my CVX 16 with a 1976 140 Evinrude ran 66mph all day on a 21 pitch and could pull two 200lb bare footers with ease. And with a 200 would have smoked those numbers.

I understand why you guys like I/0's. Easier to work on, cheaper parts. I was amazed on my first trip to Michigan. We went to a boat yard and I saw I/0's 20 years old still never been apart. That would never happen here. I see people move down here all the time and buy a cheap I/O boat because of their past experiences. They don't work here. I see it everyday. Some one moves down here, all excited to get a boat. They buy what worked up North head out and get beat up, the drive will fail. Its only a matter of time. End up with a 40k Sea Ray they can't sell. The Gulf is choppy rough and those small lake heavy aft boats have to go fast to plane and you get beat up. The water is not much more than hot acid and the out drives can't take it. You cannot leave them in the water. Look at ads down here for used Bayliners and Sea Rays with I/Os.
Poor riding boats get weeded out real quick. What holds value down here is what is sea worthy.
There's a boat dealer down the road that sells eggshells all day and is still making money. He sells a deck boat that can't take a foot chop and the wiring is non tinned. Way too many boats are bought down here cause of wife appeal.

 

[JoLin]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

Kahuna, you're moving off topic. I don't understand what these links are supposed to demonstrate, except that some people like Pro-Lines and some people don't? That isn't exactly an earth-shattering revelation. My P-L was a 1986 and, IMO, a good boat. I daresay that any 21' boat with a 400 lb OB on a 36" setback is going to have issues with stern-heaviness. Once I alleviated those issues with trim tabs the boat was fine.

The OP wanted some feedback regarding a conversion from I/O to OB. It's a big job, and the result may be less than wonderful.

Most of us feel that if he wants an OB boat, he oughta buy one. If he likes the boat he has, it'd be a lot easier/cost effective to swap out the motor.

My .02

 

[Sprky]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

One more off topic........... Kahuna, the only time your boat sees 66 is behind the truck. Your motor would have to turn 7700 with the prop and gear you have.

7700 x 21 x .5 x .0009469 - 13% =66.6

RPM x prop x gear ratio x constant - slip = speed.

Maybe with a V6 but not a Xflow 4cyl.

 

[shrew]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

It seems that a key point here is beign missed by many. The discussion isn't the merits of an OB over an IO. I don't think anyone is questioning WHY the OP wants to move from an I/O to an OB. The discussion is the feasibility of converting an exiting I/O to an OB. The fact is, you have a huge hole in your transom. This will need to be closed. Think of the force that an OB is going to place on a seam where the hole was closed. This will require a significant amount of transom work to make the boat seaworthy. Then there is the cost of an OB. It would be far less labor and cost to either replace the 470 with a suitable inboard, or buy a boat with an OB than it would be to perform this conversion.

 

[Sprky]

Re: Question: Converting Mercruiser 470 Alpha One to Mercury Outboard

Feasable yes, practical no.

The transom only becomes an issue when repaired by incompetents.

The thread got off topic because of stupid info about wieght and balance.