Sea Strainers

[Jasper]

When I purchased my 53 Convertible in 2010, one of the first things I noticed was that there were NO sea strainers servicing the raw water intakes for the engines. When I asked why, I was told the rise of the the intake (almost 3 feet) from the hull and the outer screen were usual in Florida and no sea strainers were necessary, since then I have found many US boats do not have sea strainers on their Raw Water intakes.
My engines run beautifully and I will do everything possible to maintain this, hence I am about to give the go ahead to add Sea Strainers to the raw water intakes to prevent the odd plastic bag or even large jellyfish causing an issue. This is the only boat I have owned without some filter between the ocean intake and the HE, other than the bronze hull fitting.
Am I right to be concerned or is this being over cautious?

 

[Pascal]

It depends on what you have outside. I if you have slotted scoops then yes you should have sea strainers inside. on the other hand, if you have what is known as South Bay strainers with a stainless steel mesh you don't need anything else.

 

[Diver Down]

Three years ago we removed the large raw water strainers for our 8v71 engines and replaced these with external Algonquin scoops. We've had zero problems with these hull scoops and freed up considerable space at the rear end of each engine. Fouling of the screens has not been an issue.

 

[Angela]

I did the same things on my mains a few years ago, except I got the ones with the little hinged trap door at the back so that if I needed to get in there for some reason, I wouldn't have to remove the scoop. That sure did free up some space in the engine room when I removed the huge strainers.

At the advice of someone here (Boatsb, I think it was), I bought extra screens so that when I might need to replace the screen with one that has fresh bottom paint on it, I can just unscrew the old one and put on a new one, and then strip and repaint the old one so it's ready to go next year if it's not a year that I'm hauling out. That said, the screens I put on nearly 5 years ago, were still well covered with bottom paint.

At my recent haul out, I put these on my air conditioner intakes. Pascal says he did that a few years ago and has had no problems with it. So, I'm giving it a try, too. I kept the air conditioner strainers in place for now, but removed the basket inside, so I can see how it goes. If I like it, then I'll remove the strainers entirely at my next haul out. There are some things I just don't like to torque down on in the water. If I don't like it, I can simply call it a failed experiment and put the baskets back in and just remove the screens from the scoop which will put me right back where I was.

 

[Jasper]

Three years ago we removed the large raw water strainers for our 8v71 engines and replaced these with external Algonquin scoops. We've had zero problems with these hull scoops and freed up considerable space at the rear end of each engine. Fouling of the screens has not been an issue.

View attachment 14712

Thanks to you all!
From memory these are the external strainers I have. Going through all the photos I have of the last haul out to confirm and will dive under the boat when I get the chance. I have never seen them in Australia before, hence the question.
Cheers.

 

[Diver Down]

Ang, when was your recent haul? Please keep us posted about how the A/C scoop works out. I'd like to do the same if it works OK.

 

[saltshaker]

Ang, when was your recent haul? Please keep us posted about how the A/C scoop works out. I'd like to do the same if it works OK.

I put an external wedge strainer on my AC intake for my 46C over 13 years ago. Never had an issue and when we've had the basin load up with jellyfish, my AC kept on going while others kept shutting down because a jellyfish got sucked into their strainers.

 

[seasalt]

I put these on my air conditioner and generator intakes after my first visit to the Keys. I had to clean the grass out of the old strainers every few hours.

A word of warning, however, is that the generator does not like positive water pressure when it is not running but the boat is moving. It will fill the engine with water. What I did was drill about 20-30 small holes in the back end of it and install it backwards. Plenty of water if you need to run the generator while underway and no sea grass when stopped.

 

[Angela]

My recent haul out where I put these strainers on my AC intakes was just last month, so the jury is still out, but I'm confident all will be well based upon others' experience. Oddly enough, in the 8 years I've had the boat, every time I've checked the genny's strainer, it has always been empty - completely empty and clean. So, I'm not touching that one.

 

[rwetherington]

What broker sold you the boat? He does not know the correct answer to your question. Hatteras took the internal sea straingers out of the boat to have a clean looking engine room. If you look where the thru hull is in the bottom of the boat you will see that there is a boss in the bottom of the boat. That is the sea chest that the engine get its water from. On the bottom there is a screen at covers the sea chest. everytime you haul the boat you need to remove the screen and clean the sea chest. also when diver is cleaning bottom make sure he cleans the screen. the screen is held on with some bolts that can be removed so that it can be cleaned or replaced.

I wish brokers would learn a little bit about what they sale.

 

[Pascal]

On the 70 footer I run, I put an external strainer on the watermaker about 4 years ago as a test. The year before, in Nantucket, the strainer had to be clean almost daily because of grass. The external strainer solved that issue 100%

Two years ago at the next haul out, I had them installed on the 3 air con intakes and again, no more strainer cleaning...

As mentioned above, you have to be careful installing them on generator intakes as the scoop could force water up the exhaust of the generator at speed. May not be an issue for single genset boats where the Genset runs at all time but it could be if you have two gensets. I considering switching the intake on our next haul out but will drill holes in the back to make sure there is no pressure up the exhaust.

 

[Vincentc]

The external strainer sounds appealing. Our 43 has large strainers for the engines mounted close to the shaft / gear coupling and are very difficult to access and block access in that area. replacing them with the external strainers would be helpful. However, we moor in some shallow silted water and rub the bottom and occasionally run aground getting to and from the dock.

We used to have a 43 Gulfstar MY, and occasionally the internal sea strainers would fill with mud after a shallow experience. In 5 plus years, Lillly Marie's strainers have never had anything significant to empty. ( and if they had it would be very difficult to access and clean them.)

Any information on replacing internal with external strainers where you have to deal with silt?

Pondering what I have written has almost convinced me to make the change at the next haul out.

Regards

 

[RT46]

My boat with 671TIBs came with the external South Bay strainers.

I was talked into adding internal strainers because small mussels were found inside the raw water
gear coolers.
How they got through the external strainers is a total mystery.
The mussels in the gear cooler were approximately 1/4 inch long.

I gave the green light for the strainers, and I think it cost something like $3K.
(Im not exactly sure about the price, I could check, but I seem to remember 3in strainers costing around 1k each)

With the external and internal strainers I have not had to empty the internal ones.

However, my AC and genny have the slotted through hull and internal strainer.
They need constant attention depending on the water quality.
I have had to clear the slotted ones sometimes twice a day in some anchorages.

 

[LBDboater]

Any information on replacing internal with external strainers where you have to deal with silt?

I would like to know this information as well, if anyone has any experience. We're on an inland lake, and while we don't have to rub the bottom, the prop wash, when the water is down, will stir up silt and mud. Will the external strainers do anything to keep the silt from making its way through the impeller and into the heat exchanger?

 

[Angela]

The external strainer sounds appealing. Our 43 has large strainers for the engines mounted close to the shaft / gear coupling and are very difficult to access and block access in that area. replacing them with the external strainers would be helpful. However, we moor in some shallow silted water and rub the bottom and occasionally run aground getting to and from the dock.

We used to have a 43 Gulfstar MY, and occasionally the internal sea strainers would fill with mud after a shallow experience. In 5 plus years, Lillly Marie's strainers have never had anything significant to empty. ( and if they had it would be very difficult to access and clean them.)

Any information on replacing internal with external strainers where you have to deal with silt?

Pondering what I have written has almost convinced me to make the change at the next haul out.

Regards

Whether this helps or not, I can tell you that the same perforation that is on the baskets inside the strainer are the same perforation pattern/size as are on my screens on the hullside. If anything can get beyond those external strainers, it will get past the internal strainer's basket, too. So, it probably is a non-issue. Perhaps the silt contains small enough particles to pass through the entire system, anyway.

 

[Mike36c]

I installed external strainers on my mains and A/C then removed the internal strainers. That was 11 years ago with zero issues. The genny has been another story since it still has the original set up, grass in the Bahamas clogs the internal strainer at least once a day when fishing.

 

[jim rosenthal]

Same here. I have had the external screens for at least ten years, probably longer, with no problems. The one caveat I'll mention is this: I tried the stainless screens using bottom paint on them and they fouled almost immediately. I think my external strainers are Buck-Algonquin and they have bronze screens as well, with about 3/32 holes in them. Those do not foul and they work fine. I'd recommend bronze screens based on my experience. I don't think that you need internal strainers with screens on outside wedge strainers.

There is another liability to inside strainers, besides cluttering up the engine room as Roger mentioned; when they are full of seawater they weigh a lot and unless properly secured they can tear loose when the boat is moving around a lot in rough weather. My boat has two-inch seawater intakes- those of us with large Detroits have even bigger seawater intakes, so the size internal strainer that you would need is quite big and the weight of it filled is significant. And you need something robust to secure it to, so the use of inside strainers has its complexities.

 

[lisaann]

I do not have any internal strainers on all 5 thru-hull intakes 2 main, 1 gen, 2 a/c the ac's have clogged probably once a year on the great south bay with grass or seaweed while in the slip it would have been nice to be able to clean them without getting wet I would leave them on the a/c's and gen never a problem on the mains

 

[fissioneng]

It seems like most have the Buck Algonquin strainers. Groco makes one with a door that can be opened in order to clean the thru hull as Angela mentioned. Does it make any difference which one?

This solves part of my accessibility problem to the strainer. The other problem is access to the seacock which is just as impossible. Groco just announced a motorized valve that would solve that nicely, but way too much $$.

 

[lisaann]

south bay strainers on all 5 with removable screens the screens are what gets clogged