Yes there is a lot of differing opinion about this definition, I think it means different things to different people depending generally on their age. It seems that the older blokes take into account the technical attributes vacuum tubes and so on, whilst younger people generally go by physical weight and age of manufacture.
This topic led me to a search of the Net for possible explanations and I came across a very useful website accredited below, that wrote the following:
ORIGINS OF BOATANCHOR
THREE VERSIONS -- Opinions From The Internet.
Version I -- During World War II, Military Radio Techs used the term BoatAnchor as they struggled with the huge, heavy, electronic equipments of the day -- full of transformers, tubes etc. Also the US Navy frequently marked electronic gear with an anchor. After the war -- tons of the equipment appeared on the surplus market and was dubbed BoatAnchors due to the reasons above - one or both.
Version II -- After WWII a national magazine editor answered a query "As what to do with an outdated heavy, large, surplus electronic instrument?" and answered "Tie a line to it and use it as a BoatAnchor"
Version III To all those who expressed interest in the CQ magazine reference to boatanchors, I found it after only an hour or two of skimming. And I also found that some of my recollections were a bit hazy after all those years. The original letter to the editor (not to the "Surplus Editor" as I incorrectly recalled) appeared on page 16 of the October 1956 issue of CQ and was as follows: Gentlemen: I recently acquired a "Signal Corps Wireless Set. No. 19 MK II Transceiver." Are there schematics or conversion data for this rig? Any info will be appreciated. David J. Wilke W3LSG Pottstown, Pennsylvania The editor replied: The only conversion we seem to have on the files here at CQ calls for 100 feet of 1" Manila line, one end of which is to be tied securely around the MK II Transceiver.
This then converts the unit into a fine anchor for a small boat. If any readers have better conversions we will be glad to hear about them. Ed. This letter apparently generated a lot of interest and in the February 1957 issue of CQ there was a follow-up from CQ''s editor, another letter from W3LSG and several pictures. If I find the time I will scan them and post links to them here.
The expression "boatanchor" may have originated earlier than 1956, as Doug Hensley pointed out. I found no earlier references in amateur radio than these CQ''s, but there may be some. However, there was no reason to call amateur gear of that era "boatanchors" since almost all of it fit that description. It wasn''t till later when smaller, lighter gear became popular that there was reason to categorize some gear as boatanchors. And it is also interesting to me that a word originally used to denote something of little value, useful only to anchor a small boat, has taken on a more affectionate meaning. We love our "boatanchors". Roger K6XQ
And then there is this one from a News Group. "The true determination is generally made by your spouse. If you can walk in the front door with it, without your spouse asking "and what are you planning to do with that?", it is not a boat anchor. Boat anchors are brought in during the night or on long weekends. That is CLASSIC! :-)
Reprinted without permission from
http://ac6v.com/73.htm#ba 
