On a 16' cruiser, you need all of the space you can get 
We bought this childrens potty a few months ago, and I had the need to try it out this last week. We have a regular porta potty, but for day trips, which is all that we do, it just takes up too much space. This was excellent for me - I'm about 5'1" and 130 pounds, so it might not be so great for bigger people. I just set it between the port seatbox and the vberth, and voila!! Would be great for kids, too, it's only 13' by 15", and the "cup" comes out so easily to clean over the side, or for when it's too rough for the guys Took the overseat out, and what's left is this pic. Very sturdy too, you can easily use it for a step. Here's the amazon link..
https://www.amazon.com/gp/product/B00674RWC2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Here's a pic in the boat...
We bought this childrens potty a few months ago, and I had the need to try it out this last week. We have a regular porta potty, but for day trips, which is all that we do, it just takes up too much space. This was excellent for me - I'm about 5'1" and 130 pounds, so it might not be so great for bigger people. I just set it between the port seatbox and the vberth, and voila!! Would be great for kids, too, it's only 13' by 15", and the "cup" comes out so easily to clean over the side, or for when it's too rough for the guys Took the overseat out, and what's left is this pic. Very sturdy too, you can easily use it for a step. Here's the amazon link..https://www.amazon.com/gp/product/B00674RWC2/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Here's a pic in the boat...