I have the same problem. In fact this past summer I found a couple small jellyfish and all kinds of debris in my filter. My air conditioning unit draws water through the same filter. I have resolved to check it about once a week and clean out all of the foreign objects, it's not a big deal.

My 81 Catalina 30 has a strainer of sorts over the seawater intake port. Is something like this strainer available for other newer, larger boats.

Knock on wood, eel grass doesn't seem to be a problem with my Catalina 36. And here in the Pacific Northwest there is a LOT of it.

I theorize that the eel grass rides on the surface, but the intake on the C36 (the Mk II, anyway...not sure about the Mk I boats) is so far beneath the surface that surface junk doesn't get near the intake. I check the strainer fairly frequently and rarely find eel grass trapped there...maybe three blades of grass in a year.

When I can see an area of eel grass ahead of the boat, at a tide rip say, I throttle to idle and let the boat glide through it. Usually this suffices.

[QUOTE=LCBrandt;4299]

When I can see an area of eel grass ahead of the boat, at a tide rip say, I throttle to idle and let the boat glide through it. Usually this suffices.[/QUOTE]

Even if you're on idle, shouldn't the engine be drawing in sea water anyway? Or are you thinking that if the prop isn't turning it is less liable to stir up the grass and get it to clog the intake?

At idle the engine draws a lot less water, but yes, it is still drawing. In my experience, finding so few blades of it in the strainer, it must be that the eel grass is on the surface, while the raw water intake is well below the surface.

It isn't unusual to come across a patch of eel grass 30 ft or so in diameter, usually at a tide rip, but if I see it ahead all I do is throttle to idle, sometimes shift to neutral, and glide through it. Or a large patch, I motor through it at idle.

I recently had my raw water intake clog up at the hull inlet.  Vessel assist dove and cleaned it out.  If it had not been a calm day and a good location, it could have been a bad situation.

If this happens again, how can I blow air out the inlet to clear it from inside the boat? 

Bardo #828
1988 Tall rig
Shileshole/Seattle, WA
 

John-
I think you have the same strainer as on my former 1986 C-30. I experienced the same issue cruising around the Cape and Islands. My remedy was to shut down the engine, unscrew the clear strainer cup, remove eel grass and then clear the eelgrass  from the hull by poking a wooden dowel through the strainer base and thru-hull (It was a straight shot and the grass seemed to wad into a tight ball in the thru-hull). When completed, I closed the thru hull valve so I wouldn't panic with the water gushing while reattaching the mesh screen and strainer bowl. I got this whole preceedure down to about 2-3 minutes because I encountered it so frequently- including a Cape Cod Cannal transit with a freighter bearing down (maybe less than minute for that clean out).  We have not had the problem with our MKII- not sure if it's luck, design or the fact that we don't much  eel grass north of Boston.  

I used to have the same problems in the same areas. Problem solved by the following:
* replaced small strainer with a Grocco about double the size
* eliminated 90 degree elbows - this was the root cause
Never had a problem since