Which Thru Hull Strainer Screen Design for A/C?

[ThirdHatt]

I have had enough fun with picking 4"-5" fish out of my A/C intake sea strainer basket about once a week. I noticed when the boat was hauled out on survey that there was no screen on the outside of the hull. The survey noted that it was "missing", so there was one there at one time. At any rate, I plan to add a screen when I haul out this fall for a bottom job.

Although this has been discussed here before, but there was no real conclusion as to which type works best. Right now there is just a 2" intake flush with the bottom of the boat. There are no issues with flow or priming at high speed and I do not want to introduce any flow or priming problems with whatever style screen I install. I am not sure about the pros and cons of the angled "scoop" style that will force water while underway, and may just go with the round style that should work just fine. Which of the three styles pictured below are preferred?

THANKS!

 

[saltshaker]

I have the wedge strainers on the AC intakes and never have an issue. Before I installed them I was cleaning out the strainers 2-3 times a day when the jelly fish got bad. 10 years and no problems. I have them on the engine intakes and have never found anything in the internal strainers. Just make sure no one loads them up with paint and you'll be fine. The slotted strainers let the jellies get in and on occasion will trap and hold debris like a plastic bag.

 

[Walter P]

Jack,

As I understand it you have both the wedged screen outside as well as the typical strainer with the basket for clean out. As you know the jelly fish are really bad this year, particularly at Patten Point which is a few minutes from your club. I have needed to clean out the air cond basket a few times this year already and have never had this issue before. Did you experience any restriction problems with the use of both systems?

While we're on the subject, what about your mains.

Walt

 

[saltshaker]

Jack,

As I understand it you have both the wedged screen outside as well as the typical strainer with the basket for clean out. As you know the jelly fish are really bad this year, particularly at Patten Point which is a few minutes from your club. I have needed to clean out the air cond basket a few times this year already and have never had this issue before. Did you experience any restriction problems with the use of both systems?

While we're on the subject, what about your mains.

Walt

No problems at all. A lot of the boats here had problems with the jelly fish. There were times when I think you could have walked across them. My engines are running 180 with no problem, even at WOT. I had different thermostats in before this season and would run 165-170 even with water temps in the 80's. The newer Vikings don't have internal strainers, only the external wedge ones like I have. I thought that there might be a problem with barnacle growth on the screens but again no problem there either. I've had the boat for over 11 years and have never had to clean out the internal strainers for the mains. Before I added the wedge strainer for the AC intakes, I would have to clean out and sometimes back flush the jellyfish out of the intakes. I hauled the boat mid season, put on the strainer and haven't had a problem since.

 

[ThirdHatt]

Jack,

I assume that you mean the pic on the upper left with the removable screen when you say "the wedge"?

I have found the strainer basket half full of jelly fish occasionally as well. I am ready for some type of screen on the outside of the hull, but I am just looking for opinions on which style has worked the best with no issues while running.

Thanks guys.

 

[saltshaker]

Jack,

I assume that you mean the pic on the upper left with the removable screen when you say "the wedge"?

I have found the strainer basket half full of jelly fish occasionally as well. I am ready for some type of screen on the outside of the hull, but I am just looking for opinions on which style has worked the best with no issues while running.

Thanks guys.

Yes that's the one. That one looks a bit small. Mine are more rectangular.

 

[34Hatt]

I use the wedge on all my thru hulls and nothing else I never have ANY problems. Clean and simple might just might be to simple for some

And yes I agree that one looks a little small bigger is better in this case!

 

[ThirdHatt]

Most are rectangular and larger, but I thought they are more for engine intakes. I thought the smaller one would be good for an A/C, but maybe not.

Believe me I am all about clean and simple, hence my thoughts about the simple round one with holes. Once you add a wedge, then add the removable strainer screen, then add the choice between stainless or bronze screen material....that seems to get complicated to me!

So you guys recommend something like this one.........

 

[saltshaker]

Most are rectangular and larger, but I thought they are more for engine intakes. I thought the smaller one would be good for an A/C, but maybe not.

Believe me I am all about clean and simple, hence my thoughts about the simple round one with holes. Once you add a wedge, then add the removable strainer screen, then add the choice between stainless or bronze screen material....that seems to get complicated to me!

So you guys recommend something like this one.........

Yeah that's what I would go with. You have a 2" intake which is pretty big for the smaller ones. I have the round one on my genny and it also works fine. I like the wedge because it it less likely to suck up debris while running. I've hard problems with the scoop strainers sucking up plastic bags. One of my neighbors just replaced a 4 year old C32 Cat for the same reason. Sucked up a bag at 30+ knots and cooked the engine. I don't think that could have happened with a wedge strainer.

 

[Paul45c]

Byron, if you do the wedge with the "cheese grater" removable screen, you don't need your sea strainer inside. I don't know about you, but given the near-constant use that system undergoes down here in the south I was having to really clean out that strainer just from mud and growth about every month and a half. Went to the external strainer with no inside Perko strainer and life is good! Whenever the bottom gets scrubbed, just pay a little extra attention to that strainer and you have tons of flow. I've got a big old Oberdorfer that's driving a huge volume of water to four different units and it's never strained from inadequate flow.

 

[DCMY #92]

Those of you using the cheese grater wedge strainers:
What material grate do you suggest? Bronze or SS?

I am considering replacing the original slotted scoops on the mains with wedges.

I relocated one of my A/C intakes to an unused head discharge fitting mounted further forward on the hull. The A/C pump sometimes looses its prime underway. I was going to install the slotted scoop strainer over the intake in hopes that the positive pressure generated underway by the scoop will reestablish the pump's prime before high head pressure shuts the unit down. Do you guys think the wedge will generate positive pressure underway as well as the slotted scoop?

Also, the round non-scoop strainer is appropriate for the gen-set. Scooping water in can flood the exhaust manifold and fill a cylinder when underway with the gen-set not running.

 

[ThirdHatt]

Byron, if you do the wedge with the "cheese grater" removable screen, you don't need your sea strainer inside. I don't know about you, but given the near-constant use that system undergoes down here in the south I was having to really clean out that strainer just from mud and growth about every month and a half. Went to the external strainer with no inside Perko strainer and life is good! Whenever the bottom gets scrubbed, just pay a little extra attention to that strainer and you have tons of flow. I've got a big old Oberdorfer that's driving a huge volume of water to four different units and it's never strained from inadequate flow.

Hey Paul! Thanks for the reply. That is what I was hoping. Cleaning this strainer every week is getting old, especially when I have to remove whole fish. Did you go with the wedge type with the removable screen? Stainless or bronze screen? I doubt I will go trhough the trouble of removing the inside strainer as it is out of the way. It will serve as a place to hold chlorine tablets to keep the growth down. I have an Oberdorfer 1/2hp 70gpm pump cooling 12 tons of A/C that really doesn't like the flow restricted. If all I have to do is install a wedge type screen under the boat at the next haulout to relieve me of these inside strainer cleanings, WOW! It almost sounds too good to be true.

So Paul, please tell me that you will make it to FLIBS this year? It has been too many years since we have had too many beers together. I've already made my plans and will get in town Wednesday and leave Tuesday, so I won't miss any of the fun. Hope to see you there!

OH Paul, I would like to say THANK YOU for taking the time to talk me out of that big Broward last year. Too many big boats were getting too affordable to buy. JUST SAY NO to big aluminum boats. I had no idea at that time that my fantasy boat was on the market in Ft. Lauderdale just waiting for me to find her!

 

[Paul45c]

To answer both your questions, the bronze wedge body with stainless removable screen is pretty much all that I've seen around these days (not to say you can't find one with a bronze screen -- I just haven't seen one in a long time); regardless, it works great. That's what actually came on my boat over the a/c inlet thru-hull. Oddly enough, the original setup had a big Perko strainer inside; it actually had a few issues with maintaining prime even at the dock. I guess I was snoozing through that part of the haulout pre-purchase survey and didn't remember, but much later when I was diving the hull I noticed it had the cheese grater, thus not needing that Perko strainer inside! When I put the lowest-rise street elbow on the seacock and just had straight hose going to the pump, I've never had a single prime problem.

Yeah, Byron, I'm going to FLIBS this year pretty much for sure. My wife and I moved my terminally-ill brother-in-law into my house for most of this last year; understandably, that's been taking most of our available time. Sure hasn't been much time left for boating.

Barring something unforseen with his condition, I'll be there with bells on. And hell yes, I'm glad you didn't own up to the motto, "Don't be a coward -- buy a Broward!" Your new trophy looks much nicer.

 

[Pascal]

we put one of these on the 70 i run, for the water maker. so far so good, up north we used to have to clean the strainer every few hours of run time (there was nothing on the intake, jsut the TH). We kept the strainer inside the boat has a back up but didn't have to clean it so far, the outside strainer does its job.

the AC TH have scoops and dont' foul as fast as the WM did.

 

[Walter P]

Two things......

Be careful of putting chlorine tablets into your strainers. The chlorine will play hell with hoses and impellers real fast.

Number 2 is more of a question to the experts.... Why use stainless or bronze screens on the "wedge"? It seems logical that the screen should be made of copper. Copper is the main ingredient in anti-fouling paints and in historical times sheet copper was actually fastened to ship bottoms as an anti-foulant. Granted it would probably need to be replaced frequently as it wears away, but as I said, logic tells me that it should be the material of choice. Comments please?

Walt

 

[ThirdHatt]

Two things......

Be careful of putting chlorine tablets into your strainers. The chlorine will play hell with hoses and impellers real fast.

Number 2 is more of a question to the experts.... Why use stainless or bronze screens on the "wedge"? It seems logical that the screen should be made of copper. Copper is the main ingredient in anti-fouling paints and in historical times sheet copper was actually fastened to ship bottoms as an anti-foulant. Granted it would probably need to be replaced frequently as it wears away, but as I said, logic tells me that it should be the material of choice. Comments please?

Walt

I think you answered your own question there Walt. A copper screen would erode away and you would have NO screen! I have heard from a marine A/C expert that a piece of copper pipe works wonders in a strainer basket instead of chlorine tablets. Without a screen on the outside of the hull my basket catches too much crap so I don't feel like sifting out a copper tube each time I clean the basket.

It turns out that if you use the mild version of chlorine, Calcium Hypochlorite or even Bromine tablets, it does not attack hoses like the much more agressive Tri-Chlor.