convert ib to ib/ob w/ jackshaft

beached · #1 02-19-2003, 05:46 PM

Has anyone converted a straight inboard to an ib/ob with a jackshaft? I like the idea of having the motor in the center of the boat allowing more room on the deck, but don't want a straight ib, and might prefer not having ob's hanging off the rear.
I'm considering all options, advantages, costs, etc. for my future (hopefully 23'classic CC)project.
Any thoughts?

Rich · #2 02-19-2003, 07:58 PM

Do you have an inboard now?

rudders_midship · #3 02-19-2003, 09:18 PM

Naval rhibs are set up that way the 2 that are on DDG's are about 23' with cummings 220 turbocharged inline 6 b model set up with a jackshaft to an outdrive I belive its a odd outdrive I can look tommorow I do know they use a huge prop like a 19 square

deepsushi · #4 02-19-2003, 10:20 PM

Converting a straight inboard to a jackshafted I/O outboard I think would be a very difficult project. The inboard seacraft has a prop pocket or "tunnel" where the running gear /prop sits. If you look take a look at either Craig Miles or Capt. Skip's inboards you can see the half moon curve of the tunnel which runs from the transom up approximately 1/3 of the way up the keel. The bottom of the v of the keel is in reality "missing" as this is where the shaft /rudder/skeg sits. I would think that this tunnel would create cavitation which would prevent either an I/O or an outboard from getting enough clean water for the props to get a good "bite" on the water. However, like the saying goes "anything is possible" and I guess it could be done with a a huge amount of hull modifications.

If your looking for a jackshafted seacraft, they do in fact exist, however, they are as rare as hen's teeth. A while back I believe there was a thread called "seacraft trivia" and if I remember correctly Trayder posted that the number of jackshafted I/O Potter seacrafts numbered in the single digits (3 total?).

If you are determined to undertake such a major project, it would seem to me you would be better converting a hull that was all ready an I/O and figuring out how to move the engine forward under the console.

However, as a wannabe seacraft inboard owner I think it would be a crime to convert a straight inboard into either an I/O or outboard.... [img]images/icons/shocked.gif[/img]

edit: you can see the prop pocket here:

http://www.theboatzone.com/gallery/miles01

[ February 19, 2003, 09:37 PM: Message edited by: deepsushi ]

Briguy · #5 02-20-2003, 01:22 AM

When I thought about repowering my '78 23' cc I first looked at doing a Jackshaft 260hp inline 6 Yanmar. I spoke with a naval archatect and we agreed it could be possible mounted like an Albermare. Our thoughts were to NOT mount it under the console but to make a box starting at the leaning post. That way the transom would be clear and the 1100lb diesel would be far off the transom allowing an even weigth distribution. My problem. COST. 5k to do the transom work and install the motor, 23k for the motor and outdrive. Gas tank? Where the heck that would go was a mystery. I really wanted to have a CC with a full transom and open console. No dice. My twin 115hp suzuki's were the best decision as they were about 15k fully installed and ready to run. Oh well, I'll save the Diesel project when I retire or win the lotto or when Amazon goes back to 300.

Briguy · #6 02-20-2003, 01:24 AM

As an added comment. The Silverhawk comes with a 230 hp yanmar io diesel as an option for not much more than 55k brand new. Check it out as its a copy of a seacraft 23 and its actually 24'. I would consider it over a new sc 23'.

catman115 · #7 02-20-2003, 10:16 AM

beached...as an added comment to briguys post, check out the "True World Marine" boats located in jersey city. They have ib jack-shafted boat with the motor located under the leaning post. I like their larger ib set up.

John R · #8 02-20-2003, 02:37 PM

Beached - here are some links to some previous Jack Shaft talk but it doesn't sound like you would want to do it to an inboard, maybe to a former stern drive or outboard boat but the inboard's running surface is significantly different...

http://www.classicseacraft.com/cgi-b...c;f=1;t=000218
http://www.classicseacraft.com/cgi-b...c;f=1;t=000268

Miles Offshore · #9 02-20-2003, 06:38 PM

Iagree with all of the above- if you want that set-up, use an existing i/o and instaed of the leaning post I would stillput the engine under the console My boat originally came with a deisal under the console as did the other 2 the police bought here and talking to the former "officers" who ran them they rode well. The reason I say this is that there is not all that much room anyways between the console and the stern, and (personally) I like a lot of room to work when fishing/trolling.Anyways good luck with your project. My neighbor had one of the original jack shafted i/o's and if I recall correctly he had some problems with universal joints, mainly because there are a whole lot required (At least 3?) between the motor and the outdrive.

Jon G · #10 02-20-2003, 06:48 PM

I'm with deepsushi on this one, the tunnel is too deep the drive would be to high if you could do it at all, and if you could, it probably would not run in "clean" water. I remember seeing on jackshafted boat on the BT a year or so ago it was claimed that it was Bill Potters "show Boat" that hit all the boat shows. It was a 23' CC jackshaft diesel. It sounds like a CC I/O is a good starting point and with a lot of effort you could put an engine under the console. I think that the 23 inboard [img]images/icons/grin.gif[/img] is one of the cleanest looking boats around, nice lines nothing on the back. Good luck [img]images/icons/smile.gif[/img]