Converting Inboard to Outboard

[Meadie33904]

I am thinking of converting my 1994 Sea-Ray 20 to outboard power. The current config. is a 5.0 Mercruiser 200 HP inboard. My question is would 115 HP outboard be sufficiant to power the boat. I think it would be fine and would probably run a top speed of 30-35mph but I am not sure. I have located a 1984 Mercury 115 w/ Power controls no steering though. I am thinking I could use the existing trim pump.<br /><br />If you are wondering why I am doing this there are two reasons. Gas milage and freeing up room on the deck.<br /><br />My idea would involve removing all the inboard mechanicals, close up the transom hole with fiberglass and marine board and mount a outboard bracket and new steering controls. Thoughts on the matter would be greatly appreciated.

 

[Mark42]

Re: Converting Inboard to Outboard

Did you use the search button? If not, do a search on "convert inboard" and read the posts. Lots of info directly related to your questions. I found 6 entries on converting inboard to outboards using that search.<br /><br />The short answers are:<br />1) Yes you can do it.<br />2) It requires a lot more transom work than you think.<br />3) It may change the handling of your boat.

 

[ondarvr]

Re: Converting Inboard to Outboard

The other thing is the cost,It would be much less money to sell yours and buy what you want, plus you will be back on the water in a few weeks, not next year. I can say this because I've done it, it took about 4 months to finish, 2 of those months were between jobs so I could work on it all the time.

 

[Meadie33904]

Re: Converting Inboard to Outboard

Originally posted by ondarvr:<br /> The other thing is the cost,It would be much less money to sell yours and buy what you want, plus you will be back on the water in a few weeks, not next year. I can say this because I've done it, it took about 4 months to finish, 2 of those months were between jobs so I could work on it all the time.

OK, The motor is out already (redoing floors in some spots and rebuild of outdrive and motor outdrive is done waiting on motor)the transom currently has a built in fiberglass platform that offers an L-Shape to work with. The transom is in perfect condition with a 2'X 2'x 2" inch thick buildup. I am thinking when I plug the hole I could add another 1" for mounting the bracket. I am pretty sure the strngth for the bracket is there. My biggest concern now is the 115 HP VS the 230 HP. When the four barrels kick in I am consuming a bunch of fuel now. I am not in need of going real fast but I want to get on plane at least. The boat is used for canal cruising or for day trips around Sanibel and Captiva with the wife and kids as well as fishing inshore with my buds. Freeing up the space taken up by the motor will also add 3-4 feet of rear deck space. <br /><br />Cost is minimal as far as the purchase of the new motor and controls and bracket ($2000 to be ofset with sale of newley rebuilt outdrive and 5.0 motor) I just don't know if the 115 hp will be enough.

 

[ondarvr]

Re: Converting Inboard to Outboard

115 hp would be at the very low end of enough, you might not be happy with it, and I think your fuel bill will go up. When I talk about cost, there will be many odds and ends that will need to be fabricated or purchased that you won't know about until it's being put together, they will add up to many hundreds of $$. If you can get a 115hp outboard that runs good and the bracket for $2000 then you're doing very well. I was going to do the same thing on another boat, minimum for the 2 was going to be around $8,000 used. On the boat that I did convert, I already had all of the stuff to do the job and it was still a drain on the wallet. It can be done, I don't want to scare you away from it, but it's a big costly job and more time consuming than you may think. Next time I will just get the right hull to start with.

 

[Mark42]

Re: Converting Inboard to Outboard

Sounds like your moving right along. Can you post some photos of transom, bracket and areas?

 

[tashasdaddy]

Re: Converting Inboard to Outboard

just sold a 96 18' Aquatron for the reason you are wanting to make this change, i bought and older 18' Bonita and put a 135 Merc on it i get the same performance, as with the 190hp 4.3L V6 i/o. gas is about the same. just a lot more usable room.

 

[b.gagnon]

Re: Converting Inboard to Outboard

I doubt there will much of a difference in fuel economy. As far as power goes, I think the 115 would do, but it will be working hard! Have you considered looking for a used Sea Drive?

 

[Always Broke]

Re: Converting Inboard to Outboard

I don’t know about the other people on here but my ’73, 135 Evinrude is a real pig on fuel compared to my 252 Buick V6 on a 16’ Correct Craft , I would guess it uses almost twice as much, but the 252 is a strait inboard, with a high performance cam and a four barrel. They came a long way on outboards and I know both of mine are antiques but I would do a lot of research before I went to far if it were me. The 135 is on a 17’ Bonito deep V, it’s been bored 90 over and does 35 to 37 GPS MPH depending on current and load, I usually have two people on board. The 252 Buick will rip a skiers arm out of their socket if your not careful on take off and has more torque then it can ever use!

 

[KaGee]

Re: Converting Inboard to Outboard

This question pops up occasionally in the I/O forum. Some of the things have been addressed here. One thing touched on slighty was performance. <br /><br />Your hull was designed around the I/O setup. Weight displacements, center of gravity were all figured in. You can't just simply throw an outboard on it and expect the boat to get up on plane and perform properly under WOT conditions. Others may have done it and got lucky, no guaruntee it would be the same with you.<br /><br />With regard to the transom, simply making it thicker will not increase the strength to which it is tied into the hull. In an outboard, the power load and engine weight is bore by the transom. In an I/O, the stringers bear not only the engine's weight, but also the power load. So, lesser regard is given to the joinery of the hull to the transom.<br /><br />Bottom line, the advise given to most over in I/O is, if you want an outboard, sell the boat and buy another designed for use with an outboard.

 

[recess]

Re: Converting Inboard to Outboard

Meadie, shoot me an email and I can discuss what it takes. I am just finishing up the conversion on my 20' Grady White from 4 cyl 140 I/O to 175 Yamaha. rfshould@verizon.net

 

[Mark42]

Re: Converting Inboard to Outboard

Recess and Meadie,<br /><br />Would you guys mind keeping the discussion on the forum so the other forum members can follow the project. Taking things offline via emails defeats the purpose of being able to share information, and denies us the ability to follow the project and add our comments.<br /><br />Just because some members do not agree with your plans does not mean you have to discuss it away from the forum. Stand your ground! Show defiance! Continue to post in the face of adversity! <br /><br />Plus, I just want to know how you do it and how it comes out.

 

[recess]

Re: Converting Inboard to Outboard

Sorry Mark42, didn't mean to offend ayone. I've been watching this topic for 3 years now getting ready for this conversion and as you say "Stand your ground". Well, here goes. <br />The conversion, while time consuming, is actually much easier than I ever thought. Yes, it does take more time and dollars than originally thought, and every now and then something jumps up and bites you in the butt, but they can be resolved and worked through. I spent about 1 week building up the hole in the transom. Fortunately, the Grady Whites from the 70's were rock solid. Even though, I still screwed and expoxied in a 3/4 ply to cover as much of the transom internally as possible. Then, being as anal as I am, I glassed, smoothed, and then gelcoated the entire inside as well as the out. Note: I am not in the business of boat repair, just a school teacher who did a lot of reading on this great site. Every thru-transom penetration was coated with epoxy and then used 5200 to seal the bolts for the bracket and any other attachment. The part I didn't anticipate originally was the rigging components for the switch from an i/o to the outboard re: shift control and cables, new guages, rigging tube etc. Fortunately, I had all winter to slowly gather the parts needed so I guess I really don't know how much I spent, and guess I don't want to know. But, it really wasn't as bad as you might think. Some non-critical parts can be picked up on auction on another site very reasonably if you're not in a hurry. Now I'm in the final stages of rigging the new hydraulic steering system and rigging up the electrical. Again, watching this site for 3 years now and reading every post that seems remotely connected to my project has been a god send. <br />So, to sum it up; I am a proponent of the conversion. It is something an individual with comon sense and some handyman ability can do. But, as the most common response in all these threads say; if you're going to do it, do it right the first time. Don't put yourself on a timeline that says "I want it done by ......" There will be problems and setbacks, but do it right and it will be worthwhile.<br />Mark42, what do you think? Did I hold my own?<br />By the way, when growing up, had the best summers of my life in Ocean City and Somers Point.

 

[ondarvr]

Re: Converting Inboard to Outboard

A Grady would be a good candidate for a job like this, they hold their value and this would be considered a plus for this type of fishing boat. It's a little different for a 20' runabout, changing it too much may reduce it's value. Plus there are so many boats around of the age and style that he wants, he should have no problem getting one for a good price. If Meadie decides to do it, then there is no problem answering questions or helping him through it. I think people just want him to know what problems he may run into and not to think he will have it done before this summer.

 

[Mark42]

Re: Converting Inboard to Outboard

" ... Mark42, what do you think? Did I hold my own?..."<br /><br />I think you did it with style and class, my friend.

 

[KaGee]

Re: Converting Inboard to Outboard

Pictures would be great as well as an honest opinion of how the boat runs in open water. <br /><br />I'm not trying to poo-poo on anyone's idea... just pointing out some things maybe not considered. <br /><br />As Recess found out, though he studied the project long and hard, there were a few ticks that he did not anticipate. <br /><br />Good Luck!