I have been doing a bit of reading in here and it looks like people favor doing this conversion. I am thinking about doing it myself. Are there any tips or tricks to it? I love Marks restoration page. It would be nice to have a similar page for an I/O conversion. I would also consider trading my boat for one setup for outboards if anyone is interested.
Hi there Monzarati I'm glad you like the restoration section. Most of the restoration stuff applies whether it is an outboard or I/O. The expert on the I/O to outboard convision is "jim" on this website. Indeed, he likely one of the most knowledgeable members overall on Hydrodynes - he helped me a lot on my restoration. You might try a PM to him. He has not been on the site for awhile. I think he might be away from home visiting family right now but he will likely check in soon. He did a great conversion and there are some sticky points that have to be addressed so if you do it you'll want to touch bases with him. Good luck. Let me know if I can offer any help. Markbano
Hi monzarati, My boat was a 77 I/O with the Mercruiser 198 drive. That is the 305 cubic inch Chevy V-8. I estimate the boat lost at least 600 pounds in the conversion. I chose a 1995 Johnson Fastsrike 150 which only weighs 370. Needless to say a 600 pound weight reduction in an 18 foot boat gives a significant performance gain even with less HP. Every aspect of the performance and interior room got better. As far as I know, I am the only member that has done this. If you are going to hire this work done and depending on how much repair your boat needs, you might be better off just buying another boat, even a new one. The I/O can be made into a nice outboard. The nice thing is that you can design your own aft deck because it will have to be fabricated. That is the major part of the job and it requires that the deck either be gel-coated or painted. That is the most difficult part of the conversion. If I did another one, I would do it slightly differently from mine. The rest is pretty straight forward. I will be glad to answer any questions. jim
Thanks for the responses. It may be a while before I get up the courage to do the conversion. I'd been thinking about doing a pretty good restoration, so then would be the time to make the change. As far as the gelcoat, it is cracking some already, so I think that might have to be done anyway. I have a line on a 97 mercury 150 efi that I was thinking about using. Would that be a suitable engine? What about putting 2 of those on an 18 footer?
The '97 Merc is a good choice. It has plenty of power and is fairly light. Look at the picture of my boat and you will see that the motor well is the same width as the engine cover was. I do not believe there is room for two V-6's without some further cutting. I will measure it if you like. I would not recommend putting two V-6's on an old 18 for a bunch of reasons. However, if you think you cannot live without a twin V-6 18 then it needs to be done. As far as performance the single 150 has plenty of power for family skiing, and the boat is nicely balanced. An 18 with two V-6's is a testosterone trip in my opinion and would be a beast. I have seen one in action. The V-6's are much heavier than the inline 6's. Just my opinion, and there are some members here that do not agree. edit: I should add that there are members here that can afford and could handle such a conversion. They have $$, Dyne experience, and understand the issues. jim
So, in your conversion, did you separate the halves of the boat like Mark did in his restoration? I'm assuming that you'd have to if you're going to replace the transom. What did you do for reinforcement for the aft deck?
I did not replace the transom because it was sound. They filled in the hole where the outdrive was and added aluminum plates that wrapped up over the top of the transom. I think replacing the transom is a good idea especially if there is any sort of problem with it. If I ever do another 18 for myself, it will be a new one. I would not remove the deck to replace the transom unless you are doing a complete restoration as Mark did. He essentially has a new Hydrodyne and it cost big bucks. I would do it like Tom Miller does. He cuts the aft deck off and gets access that way. That creates an issue of how to repair the joint where the deck was cut and there are several ways to address that. If you keep the I/O pylon like mine, you need to address the pylon loads that go through the aft deck and motor well. The vertical angle iron that goes from the deck to the floor under the pylon attach point needs to stay or be replaced. I also placed a wood beam from the same deck area to the transom at the same level as the lower motor mounts. This piece addresses the loads that normally go through the motor well on an outboard. My motor well is much shallower and more modern looking. I also added another wood beam that acts like a transom knee. It lines up with the stringers and is attached to the transom at the same level as the upper motor mounts. This piece is probably not necessary, but my engineering mind is always thinking about how to make it stronger without adding too much weight. This area is difficult to take pictures in, but I will try if you are not understanding my description. jim
I'll take a little closer look at the transom area tonight. I was thinking about doing this as a winter project after the ski season. I'll tear off the rubrail and carpet to see how thorough of a restoration it needs. Is there a way to fix a cracking gelcoat more easily than a new paint job?
