Intake Thru-Hull, Screen or Not?

[toddbrsd]

OK, this is kind of last minute but here goes. My boat is currently on the hard. The engine intake thru-hull is being replaced (amongst other things!) The one removed had a screen similar to the one here:

http://store.hamiltonmarine.com/bro...plain-bronze-with-screen-103632-/4,17829.html

I have been able to google the pros and cons on whether or not to replace it with a screen or not. So I know the issues relative to clogging and flushing the line associated with having the screen.

I do have an in-line filter. It almost seems to boil down to a regional issue, so I am probably more interested in So. California experiences but would welcome any and all. I have the hull cleaned monthly. I am aware that the marina does have some eel grass, but it is not pervasive.

BTW, I visited the shipyard today and the replaced thru-hull does not have the screen on it and I didn't think to inquire. I was too busy pumping the bildge out (more on that later!) Because of the rain here, it is likely not to be ready until next week. So I want to make a decision relatively quickly.

I will give a full report on the maintenance and associated costs once everything is done, because I know that is always an interesting topic.

 

[mherrcat]

I would think the screen/grate over the intake beneficial. Without it if you suck up a piece of plastic bag or one of those deflated Mylar balloons I regularly see floating around it might get jammed in the ball valve or hose, requiring disassembly for removal.

While your boat is out would be a good time to remove hoses from your through hull valves and lubricate them. I wish I had remembered to do that when my boat was last out.

 

[Loren Beach]

http://forums.sbo.sailboatowners.com/showthread.php?t=124943&highlight=strainer
Good thread on reasons not to use an external strainer. Note the photos in reply 14.

I would rather clean out my Groco inside strainer than have to dive and clear something (or sea growth) clogging an outside screen.

Loren

"Straining for an Answer" and "Screening all Responses"

 

[bayhoss]

I'll go with Loren, clean an inside strainer and you stay inside the boat. Clog an outside strainer and you go for a swim. There's a CO2 injector made to clear lines that I posted before. It will blow any clog from a line in an instant.

Best,
Frank

 

[Emerald]

No external strainer would be my vote. I agree I'd much rather shut a seacock and clean an interior line or my interior Groco strainer than go overboard in who knows what sea state or traffic situation to mess with an external strainer.

 

[Frank Langer]

But it may not be so easy....

I agree that cleaning an internal raw water strainer would be much easier, but if the clog is due to a plastic wrap or something similar that has been sucked into the seacock and gotten stuck there, the solution doesn't sound nearly as easy.

I'm guessing one would have to close the seacock, remove the hose, then open the seacock and fish a wire or something into it to remove the clog, which would result in a significant water geyser into the engine compartment before one could get the seacock closed again, especially if the raw water intake is in an awkward place, as they often are.

I don't have an external strainer, but have considered adding one, to avoid the situation described above.

Frank

 

[Joe]

Will a CO2 injector clear a clog on an external strainer?

 

[Guy Stevens]

No Strainer

If you do get something stuck IN the thru hull of the hose leading to the seachest you can generally blow it out with a garden hose and a few fittings!

However much more common is something that grew inside the exterior strainer that you can't get out without removing the strainer cover etc etc... Basically no fun to try when under water.


Guy

 

[Emerald]

I had an external strainer clogged with growth. I cleared it by taking the line from the seacock off at the engine side, lifting it high, connecting it to the bellows pump for the Avon, and keeping the bellows above the water line, gave a nice firm slow push on the pump, and woooshh, it cleared the junk out. I then removed the external strainer on the next haul out not wanting to repeat the growth issue, and have never had a problem since.

 

[Glyn Judson]

To strain or not.

Todd, I'm just up the road from you and experience the same waters pretty much. Given that we don't ever have clam, mussel, grass or other crud issues as can be found in other regions of the country, I have chosen to have an outside strainer but not the slotted type. Mine is a Buck Algonquin peppered with 1/4"(?) holes that I decided upon reasoning that if a plastic bag were to get "sucked" up, it would go no farther than the strainer. At the first sign of an overheating issue, one would almost naturally kill the engine and odds are that would allow the bag or whatever to float away. Here's a link to their web site http://www.buckalgonquin.com/downloads/Cat_108.pdf scroll down to page #107 to see the type I installed. So with that design strainer and given the waters we sail in, I think that outside strainer delivers the best of both worlds. I might add that in the 15 years we've owned the boat, I think only once did I see a single strand of grass through the sight glass of the internal Groco strainer I also have. Of interest, there was no sign of there ever having been an internal strainer in the boat fitted at the factory. I guess almost everything was an option. I can honestly tell you that of all the E31's I have documented, 71 in all, no two of them are identical for the above reason and taking into consideration the depth of the pockets of the first owners. Cheers, Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[cimarronE35]

When I did the bottom back in june we spent 2 weeks fairing the bottom. A lot of hard work. Because we were spraying the paint, it was also expensive. There was a screen on the intake thru hull, this was not fast so I did not replace it. I have a strainer so I wasn't to worried. After 6 months, I check the strainer everytime I start the diesel and nothing. No grass, Happy boat.

 

[mherrcat]

I have only cleaned my internal strainer once in the three years I have had the boat and there was nothing in it.

The "painting over" illustrated by many of the pictures is an issue. If you have the bottom painted by a yard it would be a good idea to check the exterior strainer and clean out any accumulated paint before dropping the boat back in. I noticed that when my bottom was painted and had to clean out a few of the holes.

Not having the external strainer is appealing except for what Glyn mentions. If the seacock and hose are easily accessible and there is no 90-degree fitting it might be easy to clean out from inside the boat. My intake is pretty inaccessible for a cleaning operation. There is a lot of kelp floating around here in the Channel Islands (large leaves) and I regularly see balloons from birthday parties and the occasional plastic bag.

I have my bottom cleaned every other month and have not noticed a lot of growth in between. I have seen some boats that look like they have not been cleaned in at least a year; in that case, I don't think it would matter whether you had an external strainer or not...

 

[Maine Sail]

Seeing as my post was referenced earlier I thought I'd share it here so folks don't need to "click" and be taken elsewhere.



Over the years I have really grown to distrust and dislike external intake strainers of either the scoop type or the non directional round type. The real danger in these devices comes when you have a blockage and can't get to the crud to clean it. They often require a dive over the side with a coat hanger but that does not always work.


In areas with high barnacle or muscle growth these creatures know no bounds and often take up residence in the "no mans land" hiding behind the screen. After spending nearly three hours one day, in really, really cold water, even with a wet suit, trying to get eel grass out of one, I vowed to never, ever have one again. Any time you dive in your risk goes up.

The harsh reality of external strainers is that they can become can be a safety hazard, if they have not already. I find when intakes are plumbed properly there is little to no need for one, and there better straining options. You can far more safely ream out your intake from INSIDE the vessel if you don't have an external strainer and this can be a huge safety margin when you don't have to physically get into the water. In just one season here in Maine I was in the water three times with a coat hanger...:cussing:

To ream out an intake from inside some good pre-planning can make this a dry and easy task. It can be done in under three minutes if done right. All you need is an intake hose that can be held up higher than the static waterline and a snake. Close seacock, remove hose from strainer, hold hose above water-line, open seacock and ream out with your snake, done!

Some reasons why I don't like them....

Beyond these photos many boat yards, some builders:doh:, and DIY's install the scoop style strainers BACKWARDS on sailboats. Many a sailor have actually caused their engines to become hydrolocked and dealt with water in the cylinders because of the improper installation of a scoop style strainer. If a scoop strainer faces forward you risk physically scooping sea water up and over the siphon break then filling the exhaust and eventually the cylinders of your engine with sea water. This is not healthy for the engine or your own piece of mind.

This strainer, like many out there, is another potentially expensive mishap waiting to happen. All it takes is some rough weather and a good surf down a wave to fill your engine with salt water. Facing them backwards is better but can also add unnecessary vacuum on the raw water pump. Sailboats should ideally have round, non-directional strainers, not scoops, or my favorite, none at all.

If you feel you absolutely must use one please make sure it can be opened. This one is made by Groco and Hamilton Marine stocks them.

External strainers are absolutely not clog proof or growth proof. If they can't opened it may be next to impossible to clear without removal of the external strainer screen. The worst of the external strainers are where the strainer is actually integral to the thru-hull fitting, and can't be opened, or even removed, without physically cutting it apart......:doh:

 

[Poco A Poco]

SoCal = tubeworms, hard for the diver to properly cleanout when they are behind the strainer.

 

[bayhoss]

One more solution!

Another solution (and on my to do list) is to go to another thru hull (in my case a raw water flush valve) and then to a "Y" valve and then onto the raw water pump. If you clog your thru hull on the orginal, then move the Y valve to the aux. Keeps the motor running cool until you get the other unclogged.

Best,
Frank

 

[bayhoss]

P.s.

A CO2 injector will not clear the line if you have an external strainer. the debris will just sit there and be sucked back into the line.
Best,
Frank

 

[stuartm80127]

Water intake screen

When I got my E27 one of the first projects was to replace all thru-hulls and to install real seacocks. On the raw water input I am glad I replaced it with a 3/4" input that feeds into a Groco Strainer and from there to Engine and Sink raw water. Much easier to pull kelp fragments, sea grass, jellyfish parts... from the strainer which has a much larger filter surface area than the pictured external cover.

 

[toddbrsd]

Boat Yard Decided For Me

Well based on my previous research, I assumed that I would get both sides on this issue. Given the aquatic life in this area (or more accurately, lack thereof), I had decided to go with whatever the boat yard decided to do, especially given that I have an internal (inline) filter and I have the hull cleaned monthly.

I visited the boat yard when I got back in town on Saturday and was somewhat surprised that they had installed a clam shell type screen (not the flush screen type which was on previously). I had no previous conversation with them regarding the screen.

I am going to leave it on. I will ask when I go back to pick up the boat, but I am hoping their decision was to put that type of screen based on "local" preference, which is what I was looking for in my initial post.

Thanks again,