I have a oday 302 and it does not have a raw water strainer. A Scoop install installed in reverse was all it has. I am in the process of installing a Groco strainer. It is a tight fit. I did check the heat exchanger and it was clear so seems like the scoop is working. The boat is on Lake Michigan so not too much of a concern.
Your boat likely does not have one. My O'Day 322 went 30 years without one, apparently.
I liked the Vetus strainer some of the new boats I deliver have installed, so I installed one for my own boat a year or two ago. Very easy to check and clean out. See pictures.