I've been using these plotting sheets to find the one which can be used most easily with SH3 and SH4. The 4 pics at the bottom are all usable in RL; but the easiest to use in the "games" and most conforms with the F5 chart are the first two, immediately below. It requires that you use the center horizontal line as the Nearest Latitudinal parallel to your in-game position.
Latitude is obtained by drawing a line from point "A" in the lower-left corner to the nearest vertical line to the right. Now you draw short lines, one above and one below to designate the whole degrees above and below your present whole latitude. Individual minutes of latitude are obtained by placing one point of a pair of dividers at point A and the other point along the diagonal, drawn in, line.
Longitude is represented by the vertical lines placed every two minutes apart. These longitudinal lines are always equidistant. I've shown two examples here:
These Plotting Sheets all work and are free to copy and use.

This is for close in work near shore. Small scale.

This is used for normal use at sea in open water.

This is the form where the longitude stays the same, but the latitude varies.

This form is from the US Coast Guard, dated 1941.
Cheers,