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Old 04-06-2018, 20:57   #1
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Sea Chest draining

Hi there, I have a Tayana 48 and I have an issue with the sea chest. When sailing and heeling for a long period of time, the sea chest empties to below the outlets that service the engine and genset. As a result, I need to "bleed" it in order to get the water back up to the top.
Any ideas as to the reason and a possible fix.
Cheers,
Harry
S/V Eleni
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Old 04-06-2018, 21:13   #2
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Re: Sea Chest draining

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Originally Posted by harpon View Post
Hi there, I have a Tayana 48 and I have an issue with the sea chest. When sailing and heeling for a long period of time, the sea chest empties to below the outlets that service the engine and genset. As a result, I need to "bleed" it in order to get the water back up to the top.
Any ideas as to the reason and a possible fix.
Cheers,
Harry
S/V Eleni
It is not so much that it "drains" as air bubbles entrained under the hull when sailing fast or rough bubbles up into the thru-hull and displaces the water. Unless you closed the seacock, there is not much you can do to prevent this from happening.

Your engine and genset impeller pumps should be able to self prime that air. If they can not, there is something wrong with them.

The raw water system on my boat includes a tiny little electric diaphragm water pump, designed for feeding a single galley tap, that is self priming, so it can pull that air out and re-fill the system.
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Old 04-06-2018, 21:40   #3
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Re: Sea Chest draining

Could you not fit a small vent line, lead to a point well above the heeled waterline? If I understand your problem correctly, that should bleed out the entrained air and allow the chest to fill with water reliably.

Jim
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Old 04-06-2018, 22:24   #4
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Re: Sea Chest draining

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Could you not fit a small vent line, lead to a point well above the heeled waterline? If I understand your problem correctly, that should bleed out the entrained air and allow the chest to fill with water reliably.

Jim
One suggestion- Google 'Automatic Air Vent' Commonly used in fuel installations on top of filters to purge air out of them.
Simply a float valve on the top of your (usually fuel filters). The vavle is open, allowing air to vent when fuel, in this case water, level is low. When water level rises the float shuts the valve.

I see there are cheap brass fleabay ones listed around $22. No garauntees how good they are.

I would plumb it with its outlet connected to a hose that loops up above all water levels in case it fails.
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Old 04-06-2018, 22:52   #5
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Re: Sea Chest draining

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I would plumb it with its outlet connected to a hose that loops up above all water levels in case it fails.
You mean for WHEN it fails...

And, no you can not put an open vent on a seachest. It is under a small amount of suction when several users are pumping out of it. Air will be drawn in the vent.

Trust me.
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Old 05-06-2018, 03:24   #6
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Re: Sea Chest draining

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You mean for WHEN it fails...

And, no you can not put an open vent on a seachest. It is under a small amount of suction when several users are pumping out of it. Air will be drawn in the vent.

Trust me.
Yes absolutely correct. Every mechanical device is going to fail. Its only a question of when.

I guess the general theory is that its given reasonable service in the mean time.

In fact as a maintenance guy I have made a comfortable living from that fact. The more gagets the more failures. Which is exactly why I suggested the loop.

The valve is shut in operation when full of water.

As for 'trust' you, I generally dont trust anyone I dont know, especially who tell me to trust them. However in this case luckily I do agree with what you are saying about suction.

Fuel filters, which I have seen these on can also create vacuum when in the upstream configuratuon. They only let air out. They dont let anything in. As you say having a big air leak in your filter would be a silly idea.

Of course if you dont like the idea its your choice to not use it.
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Old 05-06-2018, 04:14   #7
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Re: Sea Chest draining

Greetings and welcome aboard the CF, Harry.
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Old 05-06-2018, 19:22   #8
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Re: Sea Chest draining

Thank you all for your feedback. I agree that a mechanical valve that opens and closes will eventually fail. Perhaps the best way would be to have a hose looped above the waterline. as the sea chest is below water line, I gather that the water level in the tube would stop any air from coming in the sea chest.
As to the self priming pumps on the engine and genset, they do not seem to fill up the sea chest once they are operating. The water level, if below the pick up point just stays there.
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Old 28-07-2018, 12:02   #9
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Re: Sea Chest draining

I also have a Tayana 48 with a sea chest, and I am having the exact same problem. When motor sailing to weather (and running hard) the sea chest will gradually fill with air. I have to bleed off the air every 45 minutes or so, or leave the top seal on the chest cracked, but this allows a small amount of seawater to slash around the engine room - not a long-term solution.

I've watched the air bubbles coming up from the inlet into the chest and initially thought the inlet hose had a pinhole leak. We changed the hose, but the problem didn't go away. My next thought was an issue with the welds (it's a stainless steel chest), but when we pressure tested the chest we couldn't find any leaks. The idea of entrained air along the hull is very interesting. Any thoughts on how to prove that, other than process of elimination?

We've thought about the idea of venting the air, but I didn't want to just fix the symptom if it means ignoring a growing problem. But, if it is in fact entrained air then this solution is a good fix. BTW, thanks for all of your thoughts. They are incredibly helpful.

Chris
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Old 29-07-2018, 04:26   #10
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Re: Sea Chest draining

Had the same problem on a charter boat I ran. Seachest and engine would fill up with air if we were sailing for more than an hour or so at speed. I always suspected it was bubbles accumulating from outside the vessel. A right pain, especially since the main engine didn't self bleed due to a worn water pump.

I would have liked a bleed valve to save having to crack the raw wqter filter every hour or so while sailing.
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Old 29-07-2018, 04:51   #11
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Re: Sea Chest draining

It's about the shape of the bottom around the intake and the grate. Any air bubble will rise against the hull and straight in the seachest if there's nothing on the way. A V-shaped guide in front and a bit on the sides of the intake could do the trick..
Could easily try if there's a possibility to dive under boat and glue a kind of wooden wedge there.

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Old 29-07-2018, 04:54   #12
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Re: Sea Chest draining

Greetings and welcome aboard the CF, Chris.
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Old 29-07-2018, 19:16   #13
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Re: Sea Chest draining

Hi there all,

This issue is not uncommon at least with Tayana 48s!!!! I have finally taken the "plunge" and fitted a fitting with a manual shut off valve and a hose on the top of the sea chest. I have sailed 3 times now hard upwind for about an hour each time and no issues with the sea chest draining.
I have secured the attached hose well above the water line. Unfortunately I am not on the boat at the moment so no photos. It seems to work well and talking to a few people they seem to also think that this will be a good long term solution.
I have considered the option of a wedge of some kind on the hull but that means taking the boat out of the water as well as the added issues of fouling and its effects on the intake area.
Hope the info is useful.

Cheers,
Harry Pontikis
S/V Eleni
T48 DS
Whitsundays, Australia
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