Any (1kw,2kw,3kw) FCV295 transducer running 50 khz or lower should be able to manage those depths easy enough. If you are not going any deeper than 700m, you might want to consider 50khz because the higher the freq the better the target resolution (yet you want it low enough to reach your target depth). Yes, 38khz will work for sure, but it really is a bit low freq considering you don't need to go deeper than that.