I have written a summary (with lots of detail) of how to extract information about a shipwreck from surface magnetometer measurements.
Magnetometers are well known as wreck finders (indeed I have used proton magnetometers since the 1980s) -- what is less well known is how to deduce more about the wreck from the detailed data. In particular, for wrecks mostly under the seabed, some useful information can be extracted.
For the detailed discussion, see Magnetic imaging of shipwrecks , or arXiv:1105.3136 [physics.geo-ph], which includes examples of imaging of ship wrecks in Liverpool Bay. Examples are given of the wrecks of YSTROOM and BOUBOULINA (ex COLONEL LAMB) among others.
Contact me via Liverpool Marine (email: firstname.lastname@example.org) to discuss options, if you would like my assistance in extracting maximum information from magnetometer readings. (Also if you have any useful comments on my report)
If you don't have a precision magnetometer but do have a smartphone,
you can still have a go at detecting a shipwreck - see here.
Some notes on evaluating PMI RM3100 magnetometer on a chip here.