With this above type you end up with two lots of hose, one from the pick up and the other from the pump.
If you use the type I use the pump sits on the bracket where by cutting a hole in the bottom of the rule plastic base the water gets forced up through the pump. When the boat drops off the plane the pump can be turned on as the pump drops bellow the waterline. A simple on off valve somewhere easy to reach is needed to stop water flow when not needed.
As you can see from where we place them they would be extremely hard to get fouled by ropes or tackle, Ive never had anything wrap around mine.
If needed I could quickly reach over the stern to unclip the pump then place on the floor inside the boat to pump out any water on the floor (self draining means I dont need to bother but this may be worth a thought for those without self drain).
Not quite sure why anyone would want a timer as 500- 750 lt pumps draw very little power and to keep 20 -30 mackerel in prime condition a constant water-flow is needed (keep it simple).
JonD