Water strainer hiviz level indicator?

[Dellquay13]

I have a water strainer with a clear plastic lid, at the normal seawater level. I’d like to pop an indicator float in to have a quick visual check it is working properly when I start up.
My first thought was a ping pong ball, but probably a bit too big, it would be pressed tight against the lid with only a minimal water level. Something wide, flat and buoyant, and obviously waterproof would be ideal. Has anyone else done this?

 

[Roberto]

Small fishing floats (they come in all sort of shapes/colours); for something "flat", there are small foam tablets which are used -again- to wind the end of fishing lines, they can easily be cut they shape one prefers.

 

[Dellquay13]

Small fishing floats (they come in all sort of shapes/colours); for something "flat", there are small foam tablets which are used -again- to wind the end of fishing lines, they can easily be cut they shape one prefers.

I thought about cutting foam sheet, but wasn’t sure about the waterproof state of any cut edges, and being absolutely sure no bits would detach and get stuck somewhere in the engine.
I’m wary of fishing floats which are often polystyrene, again for the risk of bits detaching and getting up to mischief.

 

[Minerva]

A Neoprene donut cut from old wetsuit?

 

[Roberto]

I thought about cutting foam sheet, but wasn’t sure about the waterproof state of any cut edges, and being absolutely sure no bits would detach and get stuck somewhere in the engine.
I’m wary of fishing floats which are often polystyrene, again for the risk of bits detaching and getting up to mischief.

Some are rigid plastic, sort of oval shape. I put one in my Vetus water strainer but my filter level was that either I really saw water bubbling in, or the filter was totally filled and the float rested without moving against the lid, so I eventually took it off. Maybe your filter position is different.

 

[Crazy-Diamond]

As you suggest, the risk is that anything you put in there will in time become detached and cause mischief! The movement of the raw water through the strainer will move whatever is in there around, indeed this is the point as you want to see if moving to be assured the water is flowing. This movement has the potential to wear the float away over time and cause it to break off or break apart. Whatever you added may be best to be bigger than the outflow pipe, to stop if getting sucked into the engine, but then again of course this would mean it would block the raw water flow if it came lose.
How much of an air gap is there under the lid when the engine is off?
Can you not see the exhaust discharge easily from on deck?

 

[Jokani]

I use a red ping pong ball (40cm), it's very easy to spot whether the water is flowing or not.

 

[Dellquay13]

As you suggest, the risk is that anything you put in there will in time become detached and cause mischief! The movement of the raw water through the strainer will move whatever is in there around, indeed this is the point as you want to see if moving to be assured the water is flowing. This movement has the potential to wear the float away over time and cause it to break off or break apart. Whatever you added may be best to be bigger than the outflow pipe, to stop if getting sucked into the engine, but then again of course this would mean it would block the raw water flow if it came lose.
How much of an air gap is there under the lid when the engine is off?
Can you not see the exhaust discharge easily from on deck?

My exhaust is underneath, and it’s sometimes hard to see the splashes from exiting water.
I am hoping for a plastic none friable float that is a quick confirmation of water in the strainer, but doesn’t hinder closer inspection of water flowing through when needed.
It also needs to be too large to fall down the inlet hole in the base of the strainer but small enough to have a meaningful rise and fall with varying water levels.
Normal external sea level varies a lot on a 7m lightweight boat depending on crew and loading for both displacement and fore/aft balance.