Are you sure you are at the right house, or haven't had a real bad day on the turps. I have never heard of such a thing and I have been around for a few years now, does the replacement boat have a hin plate fitted to it, if so this may help find out what has happened to the "other boat"
Maybe a hot cup of tea a bex powder and a little lay down may make the situation become a little clearer.

Hope you get the right boat back.

100% sure brother inlaw was down there and took pics of the boat in its place no hin on it no number plate on tralor either

Does seem kinda strange. So have you called the ranger to report the glass boat being dumped on your property? I hope you Ali boat was insured  

 Sounds like they are upgrading, they reckon your ali was better than their glass jobbie and decided to do a swap.

 Round here, thats pretty common with bikes being stolen and upgraded,

never heard it with boats though.

not good at all. 

im guessing the other boat may have been stolen and found its no good so they stole yours and dumped the previous. 

sounds like your boat was kept in a yard or similar yes ?

if thats the case , then your might be nicked , but the replacement may have just been parked there in the vacant spot by its owner after your boat had been stolen from that space ??

thats more likely a probability than some random thief upgrading imo

but nowdays you never know lol truth can be stranger than fiction as they say