http://www.edsonmarine.com/faq/#q10

Q10: I would like a larger/smaller steering wheel, will it effect my
steering system?
A10: In most cases, moving up or down in wheel size a few inches will have
little effect. However, you should not go much smaller than 2-4 inches in
diameter than the originally specified wheel size or the effort required to
turn the wheel may be excessive. Moving up in size is not as critical, but
you may have less feel, as less effort is required to turn the wheel. The
best way to determine if another size of wheel would work for your boat is
to borrow a wheel of the size you would like from a friend at your marina or
yacht club for a day and try it out in varying conditions and circumstances.