Blocked raw water thru hull

[Ken Heyman]

The Chicago harbors have engaged in a "weed kill" causing massive amounts of vegetation to float on the water surface and cause much mischief. The stuff is so thick that it took 15 minutes to navigate thru 20 feet of the stuff in our dinghy. The mess is supposed to be skimmed and cleared away but-------Chicago.
So against my better judgment, I picked up a guest that required me to power through the mess.I returned to our mooring and immediately noticed that I was not pumping water(also an age related problem).
I unscrewed the bowl at the seacock and it was completely fouled with crud. Only a slight trickle of water was coming up thru the thru hull fitting .After finally getting a bend in a hanger that I could insert down through the open sea cock I managed to clear The blockage and we were on our way. I have a robust impeller and there was no damage to it.
I wonder that if one can't avoid debris on the water, if it's okay to simply shut the seacock for a few minutes until you're clear of the nuissance and then reopen it. Suction will be stopped and nothing should be sucked into the cooling system. For just a few minutes , the engine temperature shouldn't get dangerously high and my impeller is "guaranteed" to run dry for 10 minutes.
-----curious as to some opinion on this.
Thanks,
Ken

[Ron Hill]

Ken : You can try shutting off the thru hull for a minute and hope that boat speed and lack of suction will clear the crud.  But remember that impellers are lubricated by the water they are pumping and don't like to run dry.

I installed a round strainer on the outside of the hull to protect ingestion of sea grass and hydrilla.  Used a 4 points of caulk to hold it in place and if necessary I could poke it off with a 3/8" wooden dowel if necessary.  
The strainer worked great for 20 years and never had to "poke it off" nor had another ingestion of weeds.

A thought

[Stu Jackson]

Ron's had good experience.

Here's another point of view:

Why External Strainers are a Bad Idea 101 (Maine Sail)  http://forums.catalina.sailboatowners.com/showthread.php?t=124964

[Ken Heyman]

Thanks Ron and Stu,
I did have an external strainer  on my C27 years ago and the zebra muscles seemed to have an affinity for it although it never was so thoroughly blocked that it obstructed flow. The situation I described is so rare that I probably will stick to my method of clearing a blockage which in fact was very similar to what was described in the link that Stu provided.
Thanks again,
Ken

[Julian Elliott]

For those of us that don't normally carry a plumber's snake as standard gear, I found that the air hose from my dinghy foot pump fit perfectly into the disconnected strainer hose as described in the above link.  A hard couple of pumps blew out the clog.  I discovered this while overheated in a busy shipping channel in fog.  Emergency averted.   

Your mileage may vary, of course.

Julian

[Ron Hill]

All : Remember that if you do put on a strainer that the inside of the thru hull and strainer needs to be painted with bottom paint.  
Also the best way to keep the nasties from attaching is to run the engine periodically and have a flow of water thru that system.

A few thoughts

[Jeff Tancock]

I too have used the footpump blast out solution three times over the last 15 years. Works great! I have a 4" piece of hose that is the correct size to adapt my dinghy footpump to the through hull fitting so it's quick and easy.

[Stu Jackson]

http://c34.org/bbs/index.php/topic,6733.msg44679.html#msg44679

[RV61]

I use dinghy foot pump method first however if the dinghy foot pump will not blow out the clog and you do not have far to go to get out harms way  up you can use a bucket and fill bucket with the head water faucet for water and put intake hose in bucket as long has water tank lasts.  next would use bucket and grab water sea water over board. I once could not clear a clog and used this until I could safely address. Had to take strainer off thru hull and used coat hanger now have dowel rod ready too. Another option is make an hose adapter  to fit engine hose on the sink drain or head intake thru hull until you get unclogged.  

[Roland Gendreau]

When we experienced a thru hull blockage, I found that an air horn fit the opened the raw water strainer nearly perfectly so a couple of air horn blasts blew the blockage out quickly.