stability issues by modifying - SailNet Community

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Old 01-21-2012
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stability issues by modifying

I truly tried the search engine....I am sure that this has come up before...so forgive me in advance if I offend anyone. But can any one direct me to or tell me how to determine if a vessel's stability is altered by removing the inboard engine and replacing it with an outboard. Does one simply install the equivalent weight or is this even a consideration? This is for vessels in the range of 22-35 feet. Thank you very much.
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Old 01-21-2012
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Yes, the stability is changed. the critical question is by how much.

There isn't a simple answer, because it depends on the weight of the boat versus the weight of the respective engines, plus one would like to know distances the load is moved both in the x and y dimension.

If you give some specifics, people here could help you or at least give a rough idea.
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Old 01-21-2012
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This has been done numerous times.. probably most often on boats originally equipped with the OMC saildrive gas units, which are notoriously difficult to keep healthy.

Aesthetics aside, the outboard is going to be weight where it's doing the least good. However there's no point in dragging the deadweight of the old engine and drivetrain around - that space can be put to better use. The other issue is removing the drag of the saildrive/shaft&strut and structurally filling in those holes.

On most boats I don't think the weight redistribution is going to be worrisome, esp if you're not trying to race competitively. If you must go this route, then cleaning up the old and doing a proper job of mounting the outboard mount on the transom are of more concern, along with the limitations of a transom mounted outboard vs the inboard installation.
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I wish I could be more specific. I am in the process of looking at boat to buy and have come across quite a few that have gotten rid of their inboard and replaced it with an outboard. Now that I am aware that it is a major factor...this will be an issue that I will take into consideration and perform significant research before buying. Again, thank you very much!
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Forgive me for alarming you - it is likely not a big stability issue for the vast majority of weekend inshore sailors on overweight cruising boats.

It will effect stability, but usually not very much.
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Not so much alarm...but I usually find that there is a very good reason why things are designed the way they are. Since, I have no knowledge in this area.....well....I know others do...and they can share their concerns and experiences. Again, thank you all very much.

AKscooter in Asia...........
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Old 01-22-2012
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22-35 feet.

At 22 feet about 1% of the boats might be inboard at 35' its about 100%

BUT boats like the Cal 29 and J29 were built in inboard and outboard models at the same time
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