If you have such a boat take a measure of
length, width, and depth of the cockpit. if the cockpit is wider at on end than the other measure bout ends and take the average. With all of the measurements in inches multiply the length times the average width times the depth and divide that sum by 231 the result will be gallons. Then you can count the drains and measure those.edited to add:Place a straight edge across the cockpit at the companion and see if the threshold is above or below the coamings. That will make a big difference. if the companion threshold is lower than the coamings and you get pooped you will get some of that water down below.