Mike,
Nice fish indeed - however, they have both been recorded as Thornbacks. I presume from your notes that the smaller one was an Undulate ?
I am still sceptical that an accurate estimate can be made by lifting the fish. ( I know I couldn't perform such a feat - and that fact alone would mean weighing "by hand" is not feasible).
Of interest - in the Utopia report on here there is a picture of my friend Steve holding an Undulate Ray - how heavy does everyone estimate this fish to be ?
Another dilema which I would have, assuming your Rays - sic. Skate were accepted for prize giving purposes with estimated weights, would be that as standing the larger Thornback would actually be Fish of the Month, just beating Gnasher's 5lb 2oz Bream by a fraction. ( A fraction which is easily within the error of your estimate ).
Happy to leave in the book as (est) weights, but I cannot put these forward for prizes, which is a shame, but those are the rules.