I had to measure carefully here. My keel guard goes up front a bit more than usual, because I also built that stainless steel guard at the bottom of the step. I didn't want to drill through the keel guard, so I found I had to cut a bit out of the battery platform, to get to exactly where I needed to drill. I don't know why, but the manual called for a 1/2" hole drilled for this. I found that 3/8" was perfect.
Cut battery box and drilled 3/8" for bow eye
Installed, inside view.
Installed, outside view, right in front of the keel guard.
