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Old 17-10-2011, 12:34   #1
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Adding Inboard Auxiliary

I have a theoretical question about installing an inboard auxiliary into a boat that did not have one previously. I know that the cost may be greater than what it would be worth so I would like the thought of money to be removed from the discussion. I am just interested in the possibility to take a hull that has no stuffing box or mounts for an engine and add the required components to have inboard power. Also assuming that the space is available below decks to install everything.
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Old 17-10-2011, 13:29   #2
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Re: Adding Inboard Auxiliary

On a 22 foot boat,this would be a poor choice. The cost and time reenforcing the hull and building a block to act as a shaft log would be worth a whole new boat. The hull of an O'day would require a strut to keep the prop away from the bottom of the boat. Lots of reengineering. If you have the time, money, and ability working with fiberglass, do it, but I wouldn't bother. You'll do better with a long shaft,8 h.p. outboard. If you're planning to do this with some other boat,it might be worth it.
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Old 17-10-2011, 13:53   #3
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Re: Adding Inboard Auxiliary

I should have indicated that it was not for the O'day. I just was looking for information to see if it could be done if one had a larger boat. Lets say I find a larger boat that did not come with an inboard but wanted to add one, and if money was not a factor.
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Old 17-10-2011, 13:58   #4
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Saildrive...

Adding a small saildrive may not be really difficult.
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Old 17-10-2011, 14:42   #5
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Re: Adding Inboard Auxiliary

sort of related: about 7-10 years ago, there was a CA (?) company marketing a 9.9 Honda saildrive system designed to convert an outboard powered sailboat to a gas inboard or replace the obsolete OMC 15 hp two-cycle saildrive that was installed in S-2's, etc. Those OMC's had a serious problem with the saildrive leg corroding away, requiring most owners to hang an outboard on the transom. As I recall, the Honda had an upgraded alternator and was priced around $8k. Seemed like a good idea, but may have been too pricey for their targeted boat size market since I have not seen an ad for them in years.
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Old 17-10-2011, 15:22   #6
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Re: Adding Inboard Auxiliary

Good time to look at electric drive/portable alternator? Electric outboard or modified old outboard would be good. (no prop drag)
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Old 17-10-2011, 15:53   #7
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Re: Adding Inboard Auxiliary

I believe a frontal lobotomy is required FIRST!
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Old 17-10-2011, 15:55   #8
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Re: Adding Inboard Auxiliary

You can do damn near anything if money is no object.
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Old 17-10-2011, 16:01   #9
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Re: Adding Inboard Auxiliary

With price out of the equation and with the assumption that everything fits internally, I don't see any significant problems although I agree a sail drive would probably be a better retrofit choice. Otherwise an inboard engine would require bearers for mounting and a suitable shaft log and bearing carrier - the configuration ultimately dependent on the shape of the underwater hull at the blunt end. The greatest challenge would be in the glassing up of the bearers and shaft log, along with the alignment of the engine and drive system.

The one caveat for a conventional inboard would be the angle of the engine installation required in order to allow the prop to sufficiently clear the hull. On some smaller hulls designed for outboards this may mean that the clearance is unachievable without exceeding the specified maximum allowed static inclination of the engine. Although there are uni-joint type solutions to this problem these are expensive both in terms of cost and installation space required.
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Old 17-10-2011, 18:11   #10
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Thanks for the information. I had not even considered the profile of the hull in relation to drive line and its affect on inclination of the engine.
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Old 17-10-2011, 18:31   #11
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Re: Adding Inboard Auxiliary

I've replaced and upgraded a few myself but usually a boat large enough to take an inboard already has one. It's the space that's important. If there's no room to keep them clean & work on them, then they become bad fast.
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Old 17-10-2011, 19:00   #12
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Re: Adding Inboard Auxiliary

Your proposal is quite common in UK boats. Small Westerlys and Cornish Shrimpers and Crabbers are regularly fitted with small diesels. Those who say it can't be done, dont know how to do it.
I fitted a Swedish 7hp Vire to my 21ft Friendship sloop 41 yrs ago.
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Old 17-10-2011, 19:47   #13
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Re: Adding Inboard Auxiliary

There have been a few books written on the subject so research in a local library or through the internet might be a good idea. I've found "From a Bare Hull" and "This Old Boat" to be a couple of good resources but there are many more.
kind regards,
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Old 18-10-2011, 00:22   #14
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Re: Adding Inboard Auxiliary

I don't see any fundamental reason why this couldn't be done...in fact, it sounds like a great project.
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Old 18-10-2011, 05:18   #15
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Re: Adding Inboard Auxiliary

Of course it can be done -- but why???

A long-shaft outboard and be done with it. Outboard motors have a number of spectacular advantages over inboard motors. One of them is almost trivial installation -- compared to major surgery and enormous expense for an inboard where none was provided before. Another advantage is no drag when sailing -- just tilt the engine up out of the water. Yet another advantage is weight -- which will have a huge effect on sailing performance of a boat that size.

A small sail drive would be easier to install than a shaft drive, as someone suggested. See this: http://www.frenchmarine.com/DataSheets/1gm10c.pdf

But again -- why?????
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