I went to this site : http://inland.agc.army.mil/enc/echar...ileRequest.cfm
, filled in information, selected the charts I wanted, then hit "submit" button on bottom of the page. When the download completed, I unzipped the file(s), then copied the folders under ENC_ROOT (one of mine was U37TB001 ) into my "charts directory". When I next opened OpenCPN, I went to: options, charts and selected "scan charts and update database". Using the cursor, I moved my boat onto the outline of my new chart, then selected the chart from the status bar. It took about 5 minutes the first time I selected the chart to convert from ENC
to SENC but since then all has worked well.
BTW, I cannot use these (or any ENC) charts with my linux installation
on my tablet. I don't think the issue is with the charts but most likely a memory limitation in the tablet.