thru hull fittings

[sailaway]

I want to change my  thru hull fitting for my engine intake.  I would like some pros & cons of brass intakes with the grating or slots protecting them. I have a 1986 34 and sail in lake Erie. My old thru hull is flush with the hull. I want to replace it with a larger dia maybe 3/4 in. The problem I have is seaweed in some marinas, have  plugged the intake.  I am not sure who the new thru hull will fit in the counter sunk hole of the old thru hull . Charlie

[Roc]

By putting a grate or strainer outside the hull, when it clogs, you have to dive overboard to clean it.  I see very few boats with that type of grating on a thru hull.  Most seem to be flush.

[Stephen Butler]

Agree with Roc.  We had a grate over our engine intake and removed it after the first year of picking up seaweed and and constant cleaning.  Suggest you stay with a flush intake and no screen or grating.  You can still clear seaweed from the interior is needed.  Just a thought.

[SeaFever]

Alternatively one could install an engine flush arrangement and use it to flush out the seaweed etc. From the thru' hulls with the grill. Just a thought.

Perhaps we are lucky where we are and are not troubled much by seaweed, eh, Stu?

[Stu Jackson]

Don't know why you'd want to enlarge the hole, just makes more space for the critters to gather.  See Reply #2, here: http://c34.org/bbs/index.php/topic,4635.0.html

From the earliest Mainsheet Tech Notes from 1987 onwards, this has been a recurring theme:  big bump outside intake thru hulls or not.  The general consensus was that it is not a good idea, because it makes another barrier to cleaning the thru hull itself.  If you've rearranged your intake strainer with a T that you can use a dowel to clean it out, then the extra outside barrier simply gets in the way.

So, redo your strainer to have a T with the straight run to the hole, put a pipe or hose up to above the waterline and you can even open the thru hull and not sink the boat and rod out the stuff in the hole.  Much simpler than the dinghy foot pump, which still works for me, but we don't have the build up you get where you live.

[mainesail]

Don't know why you'd want to enlarge the hole, just makes more space for the critters to gather.  See Reply #2, here:  http://c34.org/bbs/index.php/topic,4635.0.html

Stu,

I actually increase the intakes on the boats I have owned to a min of 1". This allows for some "growth" while still allowing plenty of flow. It also makes clean out and passage of weeds to the strainer basket significantly easier. Small ID's plug faster and easier before the junk hits the sea strainer. On my C-30 she had a thru-hull ID of less than 1/2" about 3/8" actually. Even a minnow turd would plug my intake. 

Up here in Maine we get TONS of vertical floating eel grass and weeds due to spring tides that grab all the junk back off the islands and bring it into the bays and ocean. This is NASTY stuff and it will clog an external strainer grate in no time, been there done that. It also tends to bunch up between the thru-hull and the screen making clean out nearly impossible from inside the boat. Even diving requires a sharp knife and a coat hanger between the slots. If you use an external screen be sure it is of the opening hinged type so you can actually clean it out.

I refuse to use an external screen on my own boats as I have been the "dive master" on far to many occasions and it is NOT fun.

Benefits of enlarging the intake.

1) Water will still flow if a barnacle grows inside the 1" thru-hull and from what I've seen they are not picky on the intakes ID size.. I have physically seen a barnacle taking up nearly the entire thru-hull intake of a 1/2" thru-hull.

2) Easier to clean out from both above and below water. I can actually run a snake through mine from inside the boat. I could never do that with a 1/2" intake and when it plugged it almost always required a dive with a coat hanger.

3) Weeds and crud will more easily pass through the 1" seacock and hose and into the strainer where it is easily removed and cleaned.


Things to minimize restrictions and plugging.

1) Use only sweeping elbows on the intake before the sea strainer and large radius bends on the hose.

2) Use only full flow seacocks.

3) Remember that a 1" intake with one inch hose will still only yield an opening on the hose barb of about 3/4" and a 1/2" will yield about 3/8".

4) Avoid the use an external screen or scoop unless it opens.

5) If you do have an external scoop it needs to face the stern of the boat, NOT forward.

6) Do not idle your engine when seaweed is present..

7) Clean your strainer basket regularly or junk will back up and get stuck in the hose as opposed to making it into the strainer.

Eel grass stinks!!

[sailaway]

Thanks guys for all the help. I want to upgrade my seacocks. I will stay with the flush thru-hull and put a tee on it. Now I have to take the strainer basket off, and use a coat hanger to clear the problem. I think my intake is 3/8 and I will up the size. Charlie

[Ron Hill]

Charlie : Sorry to be so late offering an openion.  I've mentioned this in the Mainsheet Tech notes a couple of times.  I've also posted this on this message board at least once!!

I've had three cloggings of the engine raw water intake between 1989 & 1997.  Two were with hydrilla and one was with eel grass.  I had to take the strainer assembly off of the raw water thru hull and poke out the stoppages with a 3/8" wooden dowel.  To counter future clogs I put a 3 inch round bronze strainer over the intake on the outside of the hull.  I was concerned that if I got a clog that the strainer would make it impossible to get it unclogged.  So I didn't screw the strainer to the hull, but rather "lightly" caulked it to the hull so a 3/8" dowel could easily unseat that strainer.

I've never had a clogging since I put on that strainer and probably put an additional 3000 hrs on the engine running at 160F.  
The 1/2" thru hull is adequate and I'd strongly recommend a round bronze strainer.  I did make 4 or 5 of the holes slightly larger.  Just make sure that you put bottom paint on the inside of the strainer.
A few thoughts.  

[mainesail]

 To counter future clogs I put a 3 inch round bronze strainer over the intake on the outside of the hull.  I was concerned that if I got a clog that the strainer would make it impossible to get it unclogged.  So I didn't screw the strainer to the hull, but rather "lightly" caulked it to the hull so a 3/8" dowel could easily unseat that strainer.

But then you lose the strainer..

These work well and the screw is captive so you don't lose it when opening it underwater..
http://store.hamiltonmarine.com/browse.cfm/plumbing/strainers/strainer-round-hinged-----pl-brz--------------------138281/4,19407.html

[Ron Hill]

Mainsail :
The hinged strainer looks nice and I thought about one, but has to be released from the outside and I don't like to go swimming, just to unclog a strainer.

The whole point of my story is that in the past 12 years with a fixed strainer I've never had a clog nor have I had to poke off the strainer !
A thought.

[mainesail]

Mainsail :
The hinged strainer looks nice and I thought about one, but has to be released from the outside and I don't like to go swimming, just to unclog a strainer.

The whole point of my story is that in the past 12 years with a fixed strainer I've never had a clog nor have I had to poke off the strainer !
A thought.

You're very lucky! In one summer I had to do it about six times. I do think the external strainers with holes work vastly better than the slotted ones like I had. Vertical floating eel grass is tough stuff to combat. Once it gets sucked in between the slots it tends to accordion, bunch and plug stuff up even before it gets into the thru-hull. I now handle it with the ability to ram a snake through from inside the boat clearing the entire intake in seconds. I suppose different areas have different weed problems and types of floating debris. I would not be opposed to an opening one with the holes like I posted, or your method, but if I can ream it out from inside I don't really have a need for one. If you can;t ream out from inside then one with the small holes might make sense if you've not up-sized your intake..

[Hawk]

I had a plug twice in one week last summer in two different sailing locations without ever a problem previously.
I still like the dingy pump attached to the intake hose idea of Stu's.....worked well for me.

Merry Christmas.

Hawk

[Ron Hill]

Guys, Susan & D.Gill : Maine had some good points and maybe the reason that I'm lucky is that my 3" strainer has 3/16" holes and not slots.
However, it's been my experience that if you can do a task from the inside of the boat it's much better than going into the water and doing it from the outside.  I've found that things "go to crap" at the most inopportune times, water temp is very cold, sea nettles(jelly fish) are present or there some wave motion (with the hull threatening to konk me on the head) etc etc.  Poking off the strainer from the inside (if necessary) is a simple and fast task

Hawk mentioned the dink foot pump to blow out a line or thru hull as another option.  De Winchell sent me that idea which I published in the Mainsheet Tech notes back in about 1997.  She came up with that remedie because a jelly fish had stopped up the head intake line and hose!!  What a great idea for getting out a clog that was "unpokeable".  She's probably looking down on us right now and smiling.
 
Great stuff in those old Mainsheet tech notes and they are there for the reading.  A thought