Hi Chris,
Most of my boat & aeroplane designs which were free plans, are available on ebay, Glynn's Fireboat Elliot is for £5.00 and the article should be easy enough to get copied by somebody as Lindsey suggests.
The copyright of the design stays with the designer actually, especially as in recent years they haven't been passed to SARIK which used to be the case.
Not sure if there was a physical archive passed on from myhobbystore who published MB's back in 2011.
Glynns latest design does carry a Morton copyright, but the plans such as my White Marlin don't ! Maybe Mortons will revert to passing the designs to SARIK ?
In reality there is no practical way to stop people copying the plans, this is not the case when you buy plans to build a fullsize boats, as those plans include a royalty to build 1 nr boat
Regards Ray