Disconnect the hose from the through hose. Have a bottle brush ready. Open the seacock and insert the bottle brush - wash the heck out of it. Pull it out and close the seacock.

Three things I do before this: 1. Be sure the seacock is in good condition. 2. Have some wax toilet gunk on hand. If you have a problem it can stop any leaking. You should always have this stuff on board anyway for emergency leaks. Also have wood plugs ready in case things go bad on you!! 3. I always have a person there with me when I do this - just in case.

The first time(s) you do this it's kind of scary. Water is coming in! I've done it and never had a problem.

 

Rashly assuming you've got any kind of the usual intake guard on the hull over that intake? You'll still need to get in the water to clean them off the outside. No need for snorkel or scuba, just get in wire a wire bbq grill brush and scrub 'em off.

If they're INSIDE and there's a guard on the intake? You may have to unscrew the guard to get in and get all the debris out. From the inside, a bottle brush might not do much, you might need a piece of metal bar stock (a blunt chisel) to twist around and smash 'em out. All depends on what you've got and how it can be accessed.

Maybe a "lunch haul" or overnight haul and get whatever you can done, while it is hanging in the sling?

 

Once had a small cape dory cutter. Thought I was cool . So I sailed it off and on to its mooring. Engine was never on. When it came time to motor over to the ramp to load on to a hydraulic trailer to take home,disaster. Some water came out the exhaust at idle so I thought things were fine. But under load at high rev the diesel immediately over heated. Ended up having to replace the whole wet exhaust system. The thing was totally clogged with mussels and barnacles.
Please start you engine and if you get a good strong exhaust stream at all revs maybe clean out the barnacles. If not you may need to make other plans.

 

I have used bleach pool tablets to aid in keeping them clean, filling the sea strainer with them, however they are pretty bad for the environment and they won't remove the shell, even if the barnacles are dead. With most modern sailboat thruhulls the strainer is not removable, so it's difficult cleaning and painting in there. I've even considered cutting away every other bar on the strainer to facilitate access, or grinding away the built in grills (strainers) on the outside and replacing them with the power boat strainers that do unscrew.
If you have a strainer outside, diving is the only way I know of, and it is time consuming and tedious work, using screw drivers and picks. Working from the inside it is quite possible to plug the thruhull completely, jamming shell and growth against and into the strainer on the outside of the thruhull.
I talked to the maintenance people at the Charleston Aquarium and they use ozone to keep their lines clean, but again it won't clean out the shell, only prevent growth.
A haul out is the best way. Moving to fresh water for a bit will kill what's alive, but again won't remove the shell.

 

Looking around for something to clear the intake once I noticed my cheap Rachet wrench had a round knurled handle that was just the right size to ream the wildlife out a little, as an added bonus the head was too big for it to fall all the way thru. I've used wooden dowels for the same purpose and managed to loose them by getting carried away and launching them like a torpedo.
Scotty's bottlebrush is probably a more appropriate tool for the job.

 

One good reason to close seacocks when not in active use is to kill growth; with no oxygen, they cannot live.

As for the few that will grow between the valve and the sea, they are easily removed with a screw driver or similar while snorkeling.

On the other hand, if you have them up the pipe because you left the valve open... there is disassembly in your future.

 

do you hookah?

if you cant dive or snorkel are you willing to hookah? there is just no way to clean them out from the inside.

most engine intake systems have a screen or bronze cap with holes to block the big stuff...on haulout I would always take those screens off then use bristle brushes to clean them out.

I also dove on them a million times using picks, to clear at least the cap...

screw drivers first to dislodge the barnacles and then a thick nylon brush like a barrel cleaner they use for guns...

cheers

 

Thanks to all. The thru hull is one piece with a slotted screen on the outside of the hull. There are probably no critters up stream of the ball valve and the raw water filter is always pretty clean, an occasional crab or shrimp, but no barnacles.
The marina just deep sixed the travel lift and the replacement won't be in place until the end of February, which probably translates to April or May. The nearest lift is about 20 miles away up the ICW which I'm not happy to navigate without an engine as the last time I was up there, there was a barge straddling the ICW blocking passage.
Still no diver to do it for me, so I guess I'll have to give it a go. Brrrr.
I'm just not going to take the hose off the thru hull and open the sucker while I'm in the water.
John

 

I'm just not going to take the hose off the thru hull and open the sucker while I'm in the water.

Choosing between diving in frigid water with a wet suit or removing the hose I would remove the hose. It is really no big deal. Probably takes an hour to sink the boat that way. Have a rag and a plug handy. Work the screwdriver (or whatever cleaning tool) thru the rag plugging the seacock. It's really no big deal. You might ship 5 gallons of seawater. Plus it builds character and confidence.

Alternatively you can have someone outside slip a soft plastic bowl over the thru hull. On a stick or something. Or just by reaching from the dinghy or dock.

Really no big deal. I pull the speed transducer out. Frequently. Underway. That hole is big and probably deeper.

 

John. I've done a lot of diving, so I have some hints. Go down to a sport store and get a wetsuit. You can also get them on Craigs list or rent one at a surf shop. I carry a light wetsuit on my boat just in case. Wear fins. Likewise get a mask and snorkle. Get a wetsuit hood if you can. If not, use at least the heaviest bathing cap you can buy. You'll be surprised at what a temperature difference it makes, and keeps yucky stuff out of your ears!! Put a dab of tape above the waterline at the location of your through-hull fitting. It's really hard to find just on your own. Have a person with you to hand you stuff and to help out. Especially if you have any problems. Remember to have an easy way out of the water. If you're in good shape and comfortable in the water you can do this, otherwise it might be a job you can farm out.

 

Just after my last post I found a diver that does this work. We set a date for the following week. I was happy, ready to go sailing. The night before our appointment the diver called saying he was going out if town until the end of the month and would reschedule when he returned. Grrr.
So I waited until favorable winds were forecast and sailed up the ICW, into the harbor and into the lift slip. It turned out to be a nice day of sailing, one of those big dolphin days and while the wind was not only not what was predicted, it wasn't even what was being reported all around me, but dead on the nose and very light until the midway point.
When they hauled the boat the engine water intake was completely crusted over with a robust colony of barnacles and other creatures. Plus there were quite a few critters inside the strainer, but before the valve. Clearly it was time for a bottom job. Two and a half years on Trinidad SR is not much, but I'm in the water 24/7/365, so what are you going to do?
Nonetheless, I'm happy this problem ran this course as I found the gudgeon had movement and was beginning to leak.
One thing I noticed beneficial; on my last bottom job I used Petit zinc spray anti fouling paint on the propeller, strut and shaft and only had barnacles on the shaft. The propeller was pretty clean.
So that raises the question, should I use this zinc antifoulant on the engine water thru hull?
Your recommendations will be appreciated.
John

 

Somewhere I read that you can merely disconnect the inlet hose at the engine, hold the hose above the water line, then open the sea **** and pour oxalic acid in, about two or three cup fulls, and it will dissolve the critters. Then it has to be flushed with fresh water before reconnecting the hose to the engine.

Now, the trick is to keep them out. Just a light electrical charge, 9-volts, across the inlet and nothing will attach to it. That's what the power companies to do keep zebra mussels out of their intake pipes in some of the great lakes. The critters sure don't like getting an electrical shock. They also don't like bleach, so a Y-valve on the inlet hose that would allow you to dump some Chlorox down the hose when you return to the dock would do a good number on them as well.

Gary -cool:

 

I may be facing something of the same sort as I resurrect a yanmar 3qm30 that is in the water but run since 2010.she starts and runs well but only steam comes out and she jumps to 220 in about 5 minutes. I had divers do the hull so am free down there. Which by the way, why can't you get divers. We got them everywhere here in Chucktown.

I will be working on a diagnosis this week starting g with cleaning strainer and changing impeller... Then maybe some saltaway or rydelime... And check mixing elbow... Hoping...

 

You can also do the same equivalent procedure as is done with power plants, etc. that have mussel blocked intakes: Plug the inlet (w/ plumbers putty, etc.), pour in a commercial inhibited boiler descaler to dissolve the shells, let soak, reverse blow-out the 'plug' when done; repeat until clear. Works on head discharge lines and holding tanks too for the removal of uric acid-carbonate + toilet paper buildup. RYDLYME Marine: The Ultimate Biodegradable Marine Descaler! | RydLyme Marine www.rydlyme.com

 

Rich H,
Any ideas on how to use this product on a thru hull of a boat in the water?
John

 

I would suggest using a small temporary plug of paper toweling or toilet paper ... plus a quite small amount plumbers putty smeared onto the OD of the plug to help it 'stick'. The descaler will soak through the cellulose. Make the 'paper plug' as small as possible. Pour the descaler into the emptied/drained strainer body and let it drain back to 'the problem' to 'let soak'.

No need to remove the small plug, as it will eventually 'digest' and fall out all by itself. Any paper fragments still adhering should be captured by the strainer .... you may want to wrap the strainer screen with an open weave cloth at startup to lessen the input of digested cellulose. A wee bit of leakage of the descaler through the paper plug should be inconsequential.