Thru-hull fittings with external strainers...... why?

[NYSail]

So at first glance these may seem like a good idea, however in real life are they really worth it? My boat has a few.... one on engine intake and one on a/c intake. At the end of last season I took a few minutes to pull all the debris out that was trapped inside the strainers from under boat. Fast forward.... The past few weekends we have been staying at slip so we can run the heat. Sunday found my heater having troubles and saw interior strainer was full of sea grass... emptied it... all good. However before closing things up I blew into the intake hose and could barely get air through meaning the external strainer was completely blocked. Now what?? I took the hose completely off and found it clear then opened the valve and the water trickled in... obviously blocked. Now if it were a simple skin fitting without a strainer on outside I could have blown and cleared the debris. After finding a solid copper wire and working it down through the 90 degree fitting I managed to get enough grass out to get a steady flow. I am considering removing these as they don't appear to be worth the trouble.... If this were the engine intake I would have to dive down and spend a lot of time under water to fix. Am I missing something?

Thanks

Greg

 

[Captain Larry-DH]

I think your concern is justified. Even more because LIS is such a nutrient-rich environment for fouling growth. I’d change those intakes to open ones.

 

[Ward H]

Sounds like your thinking is on the right track.
Here's the link to Maine Sail's article on external strainers.
https://marinehowto.com/external-strainers-omg/

 

[NYSail]

Thanks Ward....... exactly what mine looked like last season and sure they look like that now!

 

[RoyS]

I do not know. I removed my engine intake strainer this spring, replacing it with a standard thruhull mushroom. I already had an internal strainer on that line. While winterizing I found the internal strainer full of sea grass. This had never happened before in probably a decade of use. I never noticed an overheating problem with either set up. It appears that the external strainers do prevent sea grass from entering the thruhull. I suppose I will just check the internal strainer more frequently.

 

[Charlie Jones s/v Tehani]

They also help prevent jelly fish and sea nettles from being sucked in.

 

[RoyS]

Had a jelly fish plug up my toilet raw water intake this summer. That line also has an internal strainer. Jelly fish was in the hose before the internal strainer. Had to reverse flush that with the dock hose. Might add an external strainer there.

 

[NYSail]

I do not know. I removed my engine intake strainer this spring, replacing it with a standard thruhull mushroom. I already had an internal strainer on that line. While winterizing I found the internal strainer full of sea grass. This had never happened before in probably a decade of use. I never noticed an overheating problem with either set up. It appears that the external strainers do prevent sea grass from entering the thruhull. I suppose I will just check the internal strainer more frequently.

My engine and a/c interior strainers get eel grass... more from the a/c because we are sitting in the harbor sucking up the floating debris. I have cleaned the a/c strainer 3 times (full) this year and engine strainer 1 time (not much)... so the grass does get through. Think I would rather have a traditional mushroom to at leased be able to clear a blockage from inside as Maine Sails article shows. Also, my first year with the boat I cleaned my a/c strainer out and had a jelly fish in there... again they get sucked through the slots.

Greg

 

[Scott T-Bird]

Well, I do not have an external strainer, but I still get clogs in the thru-hull that I sometimes have to dive on to clean. I've been told by dock neighbors that an external strainer is the only way to keep the eel grass out. In the middle of the summer it is basically a daily occurrence. My internal strainer is always filled with eel grass, too, and needs to be emptied almost daily. (I may be doing too much motoring ) I think the problem may have more to do with the 90 degree angle at the top end of the thru hull. I try to use a stiff wire to navigate the bend but it is very often unsuccessful - the stuff usually just forms a plug at the entrance that I can remove when diving on it. The most luck I have is with something like a dental pick that pulls the stuff out after I remove the hose. This is easily the most vexing problem I have in the summer. It's worse than the green heads!

 

[Gunni]

At the dock, backwash the system by removing the hose from the system and forcing a water hose with municipal pressure back through the thru-hull.

Off-shore you can do the same thing with your RIB air foot pump. Have a section of hose that extends above the waterline to facilitate this process.

There is no perfect answer. I have found fish stuck in my A/C raw water hose, stopping the system. The little critter had lived and grown himself into a very tight plug. My A/C thru-hull is an open mushroom like the one you seem to want. My engine and shaft thru hulls are screened.

Go sailing on a rowdy day, the thru hull screens will get a good scrubbing.

 

[NYSail]

I did the same using my dinghy foot pump.... that cleared a bit but ultimately I was able to use a small solid electric wire (home stuff) to snake in and clear enough for the heat to work again while water came in..... Bet the water pressure would work better. Engine seems much better because I am moving while running.

 

[Ward H]

A bit past mid season I cleaned a large chunk of eel grass from my strainer but hadn't noticed a reduction/improvement in water flow. I've been expecting a plugged thru hull based on Scotts issues but I've been lucky so far.
@Scott T-Bird , Maybe you can replace that 90 with a T fitting with a ball valve on top. That may give you a straight shot to knock out a plug of grass?