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Discussion Starter #1 (Edited)
Many times this season, the bilge in my '73 C27 has had 1-2 inches of water in it. I would pump it out and sponge dry, but by the next weekend, the 1-2 inches had returned.

At first I suspected the companionway hatch, as I sometimes failed to pull the hatch completely over the drop boards, leaving small corners for rain water to enter. But more recently I began doubting this as the core problem due to the amounts of water involved.

Now the boat has been on the hard for 2 weeks during which we had very significant amounts of rain and wind. If the hatch were the majority source for leakage, then I would expect the same 1-2 inches. But the bilge was dry except for maybe a 1/4 inch at the low end near the pump, which I do attribute to the hatch.

Does this all suggest that I had seawater entering while afloat? I suspect this impeller, but when I think about the fluid dynamics, I wonder if it's even possible. I mean, isn't this impeller well below the water line? Can this impeller even slow leak without a major malfunction? (I cannot bring myself to use the 4 letter S-word).

BTW the bilge pump works fine using the manual switch, but it does not have a float switch or if it does it is broken - I tested this. Sorry I should have taken a pic of the pump. Yes, I will be replacing the pump with a new one that has a working float.

I am truly afraid of what you all have to say about this :eek:

Thanks
 

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Many times this season, the bilge in my '73 C27 has had 1-2 inches of water in it. I would pump it out and sponge dry, but by the next weekend, the 1-2 inches had returned.

At first I suspected the companionway hatch, as I sometimes failed to pull the hatch completely over the drop boards, leaving small corners for rain water to enter. But more recently I began doubting this as the core problem due to the amounts of water involved.

Now the boat has been on the hard for 2 weeks during which we had very significant amounts of rain and wind. If the hatch were the majority source for leakage, then I would expect the same 1-2 inches. But the bilge was dry except for maybe a 1/4 inch at the low end near the pump, which I do attribute to the hatch.

Does this all suggest that I had seawater entering while afloat? I suspect this impeller, but when I think about the fluid dynamics, I wonder if it's even possible. I mean, isn't this impeller well below the water line? Can this impeller even slow leak without a major malfunction? (I cannot bring myself to use the 4 letter S-word).

BTW the bilge pump works fine using the manual switch, but it does not have a float switch or if it does it is broken - I tested this. Sorry I should have taken a pic of the pump. Yes, I will be replacing the pump with a new one that has a working float.

I am truly afraid of what you all have to say about this :eek:

Thanks
What type do you have? is it mounted in a well? if so it will have O ring seals. a picture would help
 

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Would it be possible to identify the type of knotmeter that is on your boat? That would make it easier to determine whether or not the leak could be coming through the impeller. If your knotmeter is like most, it won't be leaking through the impeller itself, that is completely sealed. The only way it sends speed information is through a magnet, no part of the impeller breaches the sensor casing.

I have had a very small leak between the knotmeter sensor's thru-hull and the hull itself (due to the age of the sealant). It just slowly wept before I rebedded it, and it would probably account for a couple of inches of water over the course of a week. Rebedding was a very easy process. I popped out the thru-hull, cleaned off all the old sealant, and rebedded with 3M 4200. It hasn't leaked a drop since.

It will not be as easy for you to find the culprit now that it is out of the water, but if you think it is the knotmeter, there's no reason that you shouldn't inspect it and rebed it while you're on the hard, it should be pretty easy.

Is the knotmeter your only thru-hull on the boat?
 

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Discussion Starter #5
jhock: I failed to attach my pics when I first posted but they are there now. Im not sure If you saw them or not, but basically those pics are all I know about the type. I hope they help.

Regarding other thru-hulls, there are 3 others that I know of and they appear to be OEM. They were all bone dry throughout season. You may be interested in this thread for pics and more info: http://www.sailnet.com/forums/gear-maintenance/174138-how-do-these-seacocks-look.html
 

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Sorry, I was writing my response while you were busy attaching pictures.

It is possible that the seal to the sending unit is leaking.

It strikes me as odd that there is sealant on the threads above the large plastic nut on the thru-hull. There doesn't need to be any sealant there if the thru-hull is bedded properly, and if someone put sealant there in response to a leak, I would highly suspect that is your culprit.
 

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Discussion Starter #7
It strikes me as odd that there is sealant on the threads above the large plastic nut on the thru-hull. There doesn't need to be any sealant there if the thru-hull is bedded properly, and if someone put sealant there in response to a leak, I would highly suspect that is your culprit.
My thoughts exactly.
 

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Either way, if it is the thru-hull or the seals for the sending unit (there were some o-rings around the black plastic, right? It is too hard to decipher from the picture.), you have no reason to be worried. Both are an easy and cheap fix.
 

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Most likely the O ring. But the whole unit should be rebedded or turfed. Can't imagine the only moving bit moving and if it did be accurate. There's a caping plug available to replace the impeller unit but a cedar plug would be just as safe as what you got.
 

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bricka :

Now that the boat is out of the water, you might try re-fitting the water speed impeller and flooding the bilge with a water hose up to the level of the water speed impeller.
It should be easy to see if water is coming out of the water speed impeller mount when viewed from the outside.
It is not an absolute test but if you can get the water level right above the top of the impeller, then you can have a decent leak test, albeit from the inside.
Be careful with the amount of water you put in there that it does not add too much to the weight taken by your boat cradle.
You might get a bucket of known volume and see how long it takes to fill it against a stopwatch, then weigh the bucket (or calculate its volume). A litre of fresh water weighs a kilogram.
Then you can time how long you run the hose for before the level reaches the impeller and get out your calculator to estimate the weight of water in there.
.
 

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Am I the only one who thinks the plywood against the hull isn't helping things here? Granted if it's leaking it has to get around the mushroom flange first (which it should not).. but using plywood there isn't really the right way to do that either.
 

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The plywood backing doughnuts are old, and should be replaced with G-10 or epoxied wooden doughnuts.

Replace the gate valves, re-do the knotmeter. I like the idea of filling the bilge with water to see if any leaks out of the knotmeter through-hull.
 

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Rather then fill the whole bilge...for a little more work you could put a small container with the bottom cut out around the unit and fill that with water ...temporarily sealing around the base...
 

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Just pull everything off. build new backing plates rebed the new thruhulls and apply real valves and hose clamps .Gain some self respect knowing you're not just another screwup.
 

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Many times this season, the bilge in my '73 C27 has had 1-2 inches of water in it. I would pump it out and sponge dry, but by the next weekend, the 1-2 inches had returned.

........

Does this all suggest that I had seawater entering while afloat? I suspect this impeller, but when I think about the fluid dynamics, I wonder if it's even possible. I mean, isn't this impeller well below the water line? Can this impeller even slow leak without a major malfunction? (I cannot bring myself to use the 4 letter S-word).

.....
Since the knotmeter sensor is well below the water line it's entirely possible that it would leak into the boat. While it was in the water the 'taste' test would have told you if it was salt or fresh (assuming you're in salt water) Water leaking past the seals of that removeable transducer would probably not affect it's function - it's a sealed unit.

Can see some rust in that general vicinity, so salt water ingress is a possibility for sure. Not crazy about the ordinary 'silicone' remnants you can see in your pics either - not the right sealant for that kind of scenario.

Does the instrument work? This would be a prime time to replace it if not, with something you can properly bed and that would have a better seal.
 

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I would doubt that a cup or bilge-full of water inside the boat would exert the same force on the O-rings that sitting in the water does. But in any case, those O-rings and the tube around them are in nasty shape, they should be replaced, the hole cleaned, and a little lubricant used in future.

Many impellers come with plugs these days, you might also look into getting one to match the fitting in your boat. The idea is to pull the impeller, routinely, whenever the boat is secured. Then clean it and replace it only when you need it again, making it clean and accurate all the time. Pulling it while the boat is in the water, shouldn't be an issue. Really, only a quart or two comes in while you're popping the plug in.

The water could be coming in the shaft log or someplace else as well. Check what you can while it is in the yard, but assuming you don't find anything, before the launch you can take some "children's washable markers" from Crayola or other companies, and draw a big fat circle around whatever you think is leaking. If it is leaking? The washable marker gets washed away, leaving prominent traces.

Or you can clean the area and sprinkle it with talc, plain unadulterated talcum powder. Same thing, the powder will be washed away by any water leaking over it, and eventually washed away. No sticky mess, no problems with allowing that.
 

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Ironically I too had a leak on my CS that I just COULD NOT FIND. Even pulled the boat to check it over. The yard accidentally got the strap right on top of the knotmeter paddle wheel, crushing it. Turned out the leak was the thru hull for my knotmeter. The hole for the knot meter thru hull was right where the liner started to lift up and away from the inside of the hull and there was a very small (1/16" wide by maybe 1") gap there. Water would leak in around the thru hull and then was squirting into the hull, but under the liner. Absolutely no way to see it and water was not leaking into the inside of the hull liner (where you put the knotmeter plug in) Only happened to find it because the thru hull loose enough to the point that when trying to put the dummy plug in the thru hull was actually turning.

I'm guessing your thru hull is just forward of the mast and keel and you may find the same issue. I'd pull all your thru hulls and re-bed them.
 

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Discussion Starter #19
After a long winter I finally got to the boat yard yesterday and resumed work on this knot meter. My intention was to re-snug the original paddle wheel, fill the bilge with fresh water, and look for a leak through the sensor.

Well I put a pipe wrench on the outer nut to snug it up and the wooden backing plate spun with it :eek:

Honestly I cant say I was surprised, and neither were you guys. Clearly the recommendations to replace were accurate.

I decided there was no point continuing the inspection of the thru hull and promptly removed it. By promptly I mean the time it took to decide to remove it, not the time it took to actually remove it. But it really only took tedious grinding, and not without the required flesh offering, as you can see.

Now I need to identify a good replacement. I would like to interface a new knot meter with my Garmin 50s plotter/finder (8 pin NMEA183). Reusing the existing dedicated instrument is an option, but it's old and I dont know if it works or even how to test it (yet). A new instrument is also an option, if it can be economical.
 

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That's not an ideal location for a speed transducer... Far better on/near the centerline ahead of the keel. This would be a good time to re glass that hole and put the new one in a better place.

Airmar makes a depth transducer the 'talks' NMEA (DST800?)
 
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