Hi Don,
I read all the posts so far and it's nice to know that there are others out there with some good advice.
The maximum shooting distance for our strobe is about 8ft depending on water visibility and the reflectivity of the subject. Using two strobes instead of one will not increase your shooting range, it will just better illuminate the subject from both sides and prevent shadowing.
When shooting beyond the range of the flash, try taking a couple of shots with the strobe turned off. Also try another few shots with the strobe(s) turned on but directed to the outer edge of the picture frame. Set the camera to FAR FLASH (i.e. pushing the flash button when you are in Ext Flash mode will toggle between FAR flash, MACRO flash and NORMAL flash)
Bjorn