The WR250F is one of the best dirt-bikes available & is on my shopping list, but will be kept in my brother's garage to ride with him when back home.
But at it's heart, it is a competition bike capable of landing 30/40/50ft jumps etc and as such needs to be very tough, that toughness comes at a cost... weight! Ok, yes its less than 100kg (220lb) dry weight but that is too heavy to think about keeping on a small boat and you would need to crane it on and off etc
The little FX is light enough that it could be lifted onto the dockside without a crane, and (i think) put onto a tender safely, as long as some care was taken to protect the tender.
Any use abroad is going throw up problems regardless of what you were to take with you.
as long is the FX is properly road legal then it shouldn't (in theory) be a big problem.
Initially however it will be used as a commuter tool and play thing around the UK, if for example I decided to sail up to Scotland and explore some of the Scottish islands then I can do so on the little FX without needing to hire a car etc.
Here is a picture of the 'paps of Jura' for you all to enjoy, I lived on the west coast of Scotland in 2010 and fully intend to go back that way sooner or later and explore some of those waters in my little boat...