Outboard Snowmobile engine

I think I have seen it before, even though I still haven't been able to find it online, an outboard engine that has snowmobile type treads on it.

The advantage is if you have a flat bottom skiff you can use a regular marine outboard in the summer and then change it to the tread engine for the winter. I think I have only seen it as an antique or in an old advertisement. If it was around, and it isn't now there might be a good reason for it, boats flipping over or something like that.

Has anyone seen or heard of such a thing, and if you have what would you call it so I could look up more information about it.

Thanks

 

have you read the modern paddlewheels thread? my guess it its in the "still to come" catagory, dont think i've ever really seen such a system

 

thank you very much for the reply