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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel > Cooling water - to screen or not to screen?
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Thread: Cooling water - to screen or not to screen? Reply to Thread
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Topic Review (Newest First)
10-27-2011 03:17 PM
Capt Len Several thoughts on this. I'm on the 'screen is good' side. It should be positioned so that the screen is aft facing.Mine is easily removed when hauled. Six bronze screws thru the matching copper washer/plate installed before the thru hull was in. I have never had a marine growth problem in 30 years . I picked up a plastic bag once and the engine exhaust sound gave instant alarm .My anti syphon U has a hose fitting on it which can be quickly connected to my engine room wash down hose.This has a lot of fresh water at 25 psi behind it. Quit enough to blow the bag out. winterize the heat exchanger or act as emergency water supply if the raw water pump were to fail at a very inconvenient time .
10-13-2011 10:17 PM
Classic30 Thanks for the examples, MS.

Quote:
Originally Posted by Maine Sail View Post
And that is why I no longer use external screens.
.. and, given that I'm the sort that pay someone else to dive on the hull, why I won't either.
10-13-2011 10:17 PM
Classic30
Quote:
Originally Posted by T37Chef View Post
An interesting idea.. but, nope. Not for me.
10-13-2011 09:11 PM
Maine Sail
Quote:
Originally Posted by Rick486 View Post
I have owned two boats over the last 30 years with external strainers. With the first boat I removed the strainer each spring and painted the interior surfaces with antifouling, after removing last year's paint, and never had a problem with growth at all. When she came out in the fall the strainers were clean. When I took delivery of my current boat new, there were no external strainers on either the generator raw water inlet or the main engine inlet. Strangely, however, the A/C inlet did have a strainer external. The first weekend I used the new boat the generator shut down twice for temperature when the inlet became clogged with floating vegetation and I dove twice in 50 degree water to clear the clog. Suffice it to say the following week I had her short hauled and installed screens on both the main engine and generator. Since then I simply spray the interior of the exterior screens in the spring with the same anti-fouling stuff I use on the prop. No problems. Here's the thing, sure you can clear a clog internally if you don't have an external screen but I guarantee you will not want to do that on a dark and stormy night making harbor under power when you suck up a bunch of grass into your main engine inlet and she begins to overheat. When I need my engine I want it to be there, period. BTW, when I was installing my screens I was debating screen forward or screen aft. I was aware of the ABYC standard of screen aft on sailboats, but I wanted to see what boats on the hard had. Naturally I looked at Hinckleys and they all had external screens facing aft for the main engine. Good 'nuff for me. That said, it is critical that the screens be maintained, like everything else on our boats.

And that is why I no longer use external screens.

In 1988 on a Post 50 Sport Fisher the generator sucked in eel grass and shut down. Took over an hour at 1:00 am to get it running again. Impeller had been toasted and the eel grass clog, even with full dive gear, took nearly 40 minutes to get free with coat hangers.

It then plugged up the next morning at about 7:30 am again..

In 1996 on our Cape Dory I experienced the same type of clog heading up into Robinhood cove. Not a good time to lose the engine. Again, it took over 35 minutes with coat hangers to free the clog while diving in 3+ knot currents.

In 1999 on our Catalina 30 we suffered the same fate only this time drifting towards ledges with no wind. Got the drifter up and missed the ledge by about 30 feet. Spent over an hour getting my head banged on by the hull trying to free the eel grass. Took over 35 dives holding my breath to clear it.

In 2006 I experienced our first and only intake clog since removing the screens. Had it free and clear from inside the boat in under 4 minutes. I can't even put my we suit on in four minutes... With our current set up the eel grass makes it into the large internal strainer which I can open and clear in well under two minutes....
10-13-2011 09:10 PM
T37Chef Another hinged strainer...

STRAINER SCOOP HINGED PL BRZ 138276

http://www.go2marine.com/search.do?q=hull+strainer
10-13-2011 08:21 PM
Rick486 I have owned two boats over the last 30 years with external strainers. With the first boat I removed the strainer each spring and painted the interior surfaces with antifouling, after removing last year's paint, and never had a problem with growth at all. When she came out in the fall the strainers were clean. When I took delivery of my current boat new, there were no external strainers on either the generator raw water inlet or the main engine inlet. Strangely, however, the A/C inlet did have a strainer external. The first weekend I used the new boat the generator shut down twice for temperature when the inlet became clogged with floating vegetation and I dove twice in 50 degree water to clear the clog. Suffice it to say the following week I had her short hauled and installed screens on both the main engine and generator. Since then I simply spray the interior of the exterior screens in the spring with the same anti-fouling stuff I use on the prop. No problems. Here's the thing, sure you can clear a clog internally if you don't have an external screen but I guarantee you will not want to do that on a dark and stormy night making harbor under power when you suck up a bunch of grass into your main engine inlet and she begins to overheat. When I need my engine I want it to be there, period. BTW, when I was installing my screens I was debating screen forward or screen aft. I was aware of the ABYC standard of screen aft on sailboats, but I wanted to see what boats on the hard had. Naturally I looked at Hinckleys and they all had external screens facing aft for the main engine. Good 'nuff for me. That said, it is critical that the screens be maintained, like everything else on our boats.
10-13-2011 02:57 PM
apogee1mars This is the way..
Quote:
Originally Posted by downeast450 View Post
I replaced my thru hull strainer with an open thru hull last winter when I replaced my thru hull valve. I also added a large strainer and mounted it well above the WL. Finding space and building that mount was a challenge. The original thru hull was a flush bronze surface filled with small diameter holes. There was no strainer on the raw water side of the pump and I had added a small plastic one when I replaced the engine two years ago. It worked, stopping some grass. The new arrangement seems to work well. The strainer I now have looks large but it is easily serviced and is doing its job. I did push a small brush with AF paint up into the opening of the thru hull when I painted the bottom this spring.
10-13-2011 02:50 PM
mbsl98 Some years back, I acquired a used Dufour 35 with an external strainer installed. The yard I used then was a high quality shop in Marion, MA, and the first thing they hounded me about was removing that external strainer and replacing it with an internal Groco. I did on ocasion, have to open the Groco and clear weed, etc, but very infrequently. Never had to actually rod out the through hull in the following 18 years with that boat.
10-07-2011 12:13 PM
ilikerust I removed an old one of those external strainer through-hulls and replaced it with a larger diameter bronze mushroom-style Groco through hull, and added a nice large Groco strainer inside the boat.

Haven't had the boat back in the water since then (hopefully will be re-launching in the next couple weeks, after 10 months on the hard), so we'll have to see how the new system works (along with all the other many changes I've made...).
10-07-2011 11:30 AM
lancelot9898 I put an external stainer(the round type that can be opened) several years ago on the intake of the air conditioning thinking that might help with the jelly fish around here, but even with coating both inside and outside surfaces with bottom paint it has a tendency to clog with marine growth. Next time out of the water, I'll remove the hinge if there continues to be problems with the marine growth.
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