Repower with outboard?
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kthoennes
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Well, I've seen that done at our marina at least a couple times, bolted to the swim steps or even on sailboat transoms to replace dead inboards. I know it's done, but it always seemed like a -- hideous jury rigged? -- okay, I'll be nice, an in-elegant way to replace dead engines. I'd be interested if anybody did it on purpose though, in other words, to actually improve efficiency and maintenance access, rather than as a lower-budget means to replace dead engines. But then I have pretty limited exposure to boats here, maybe that's much more common than I think. Fuel lines, steering lines, ignition cables, beefing up the swim step struts or transom, conversion of a diesel fuel tank to more likely gas for the outboard(s). Hard for me to envision that it's cheaper or better in the long run. I'll be interested in the responses to your post though, maybe I'm out to lunch and it's commonly and neatly done.
Gdavid
Guru
It is quite common for boats that plane where weight savings is important. Classic boats in the 20-35' range converted from inboards to bracket mounted outboards. There are varying degrees of thought and design that go into these projects and some handle better than others. I would be concerned about changes to stability, especially when fuel tanks are partially filled and you no longer have the inherent ballast of inboard engines.
Another important consideration is that diesel boats do not require the same ignition protected devices that gasoline vessels do. If you switch from inboard diesels to outboard gas, you need to very carefully inventory all electrical devices to ensure you aren't creating a risk for explosions. There are diesel outboards of course but these are pretty rare.
For operating at displacement speeds, a slow turning diesel engine just makes a lot of sense, the prop is deep in the water you don't run the risk of the prop cavitating in rough weather. A planning boat runs with the bow up and the stern stays planted (unless you are running really fast) so the props will stay in the water, a slow-moving boat with an outboard pitching in waves is much more likely to have problems.
This is far from all considerations, but just a couple things to consider.
DennisB1
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I have seen diesel outboards at the boat shows. They are expensive, but have the advantage of using a diesel engine the benefits on efficiency that diesel provides. Works best when replacing gas outboards with a diesel. Becomes viable if you use the boat many hours/year. Horse power I saw was 200hp. They said that larger were in developoment.
This store has 7 of these turbo(!) bad boys in stock:
https://www.outboardisland.com/yanm...11-turbo-diesel-outboard-engine--50-hp---sale
Comodave
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You also would have to look at the weight movement and balance of the boat with outboards.
psneeld
Guru
Yes and no.
It really depends on so many factors like boat size, weight, desired speeds, range desired, etc, etc that a simple answer can't really be had.
Name a boat and you might start getting definitive (realistic) feedback.
Advice saying what you would need to do is just a shot in the dark without putting the whole project together.
Old Sea Dog
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Think I can get 4 of those diesel outboards on the transom of my GB 36. They are massive. Need to contact Armstrong brackets with measurements.
Nomad Willy
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The problem w OB’s on trawlers is their small props that can only offer small amounts of thrust.
Best to look for OB engines w lowest lower unit gear ratios and most radial room for biggest propeller.
The last time I shopped for OB’s the mid sized Suzuki’s had the best numbers re the above.
Best to look for OB engines w lowest lower unit gear ratios and most radial room for biggest propeller.
The last time I shopped for OB’s the mid sized Suzuki’s had the best numbers re the above.
SteveK
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Can you imagine 4 of those on the back of a trawler, yahoo
O C Diver
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Don't know if they're still offered, but some outboard manufacturers offered a sailboat model with a longer length and a bigger diameter lower unit and propeller to push sailboats out of the marinas and mooring fields.
Ted
Ted
Pete Meisinger
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Maybe you have been sleeping under a rock or just have not been paying attention.
Big boats with lots of outboards on them are everywhere. Although center counsels seem to be the most popular right now, just about any cruiser can be factory ordered with outboards.
Those big Mercure V-8s come in at over a hundred thousand a copy, so cost is a consideration if you need to buy three or four of them.
I think until the outboard manufacturers get the diesel issue worked out it will never be very practical.
pete
Big boats with lots of outboards on them are everywhere. Although center counsels seem to be the most popular right now, just about any cruiser can be factory ordered with outboards.
Those big Mercure V-8s come in at over a hundred thousand a copy, so cost is a consideration if you need to buy three or four of them.
I think until the outboard manufacturers get the diesel issue worked out it will never be very practical.
pete
psneeld
Guru
There are all kinds of larger boats being powered by outboards.
More and more boat types are being built lighter and lighter due to engineering both in design and materials.
Even some pretty good sized sportfish (not CC style) traditionally in the inboard gas/diesel range are either outboards or inboards these days.
Because boats are often compromises on many levels, traditional design/engineering is going out the window every day.
Being tuned into these new advances causes one to ask about fitting new tech/concepts into used vessels to save money, enjoy the asset more.
More and more boat types are being built lighter and lighter due to engineering both in design and materials.
Even some pretty good sized sportfish (not CC style) traditionally in the inboard gas/diesel range are either outboards or inboards these days.
Because boats are often compromises on many levels, traditional design/engineering is going out the window every day.
Being tuned into these new advances causes one to ask about fitting new tech/concepts into used vessels to save money, enjoy the asset more.
I'm not involved with that world but it seems that Mercury, Cox, OXE and Yanmar
all are selling diesel outboards today and have been, in Yanmar's case, for years.
heysteve
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800 HP Detroit Diesel "outboard"? Been done... https://youtu.be/Z7OkhLu53UQ
Not sure what the benefit would be, although if you give us a specific boat you would get better replies.
As others already pointed out, you can find a wide choice of boats up to 40ft, at least, being built with outboards, but they have been designed that way
I have seen diesel outboards from Yanmar and OXE, which seemed to cost around twice what an equivalent-HP inboard diesel would be. Once you add in the cost of a mount for a 700lb motor on a transom not designed for it, moving fuel lines, controls, and a raft of other stuff, not to mention what to do with your existing prop, shaft, transmission.....
Why wouldn't you simply replace your existing diesel with a new one, and save all the extra expense and headache?
PNK
As others already pointed out, you can find a wide choice of boats up to 40ft, at least, being built with outboards, but they have been designed that way
I have seen diesel outboards from Yanmar and OXE, which seemed to cost around twice what an equivalent-HP inboard diesel would be. Once you add in the cost of a mount for a 700lb motor on a transom not designed for it, moving fuel lines, controls, and a raft of other stuff, not to mention what to do with your existing prop, shaft, transmission.....
Why wouldn't you simply replace your existing diesel with a new one, and save all the extra expense and headache?
PNK
