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Old 04-08-2022, 14:48   #1
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Loud Bang!

Hi Cruisers,

I'm hoping someone here has experienced something similar and has some advice.

We've noticed a periodic loud BANG on our 2005 Saga 43. It sounds low in the boat, and as if the hull was stuck hard by something like a mooring ball or log. It is only a single bang never multiple closely timed together. My wife pointed out that it seems to correspond with flushing the toilet or using the sink in the head. At first I thought she was crazy, but it does seem like it may be correlated. It happens so sporadically though its hard to track. Could this be some sort of water hammer? Or maybe somehow the tank is building a vacuum until it pops back into shape and equalizes, and that reverberates through the hull?

We have two 65 gallon plastic tanks, one under the port and one under the starboard settee.

Thank you for any ideas or advice on how to best investigate further!
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Old 04-08-2022, 15:18   #2
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Re: Loud Bang!

Kellmic5 the only time we have a loud bang in our boat is when my jaw hits the deck after being presented with another boat bill.
Have you checked your tank air vents? You should really take them of and blow throw them. Here is Australia mud wasps build nests in the smallest crevices.
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Old 04-08-2022, 16:03   #3
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Re: Loud Bang!

Is it a freshwater head? If not, then it's hard to relate to it happening when the sink is used or the head is flushed.

If so, it certainly sounds like pressure release in the freshwater system.
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Old 04-08-2022, 17:42   #4
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Re: Loud Bang!

The Saga 43 water tanks do not vent through the hull. They vent to open-ended hoses in the cabinetry above the tanks.

This question might get good answers on the users forum at
(Note, I am the moderator there.)

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Old 05-08-2022, 00:54   #5
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Re: Loud Bang!

Sounds like tank flexing
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Old 05-08-2022, 01:14   #6
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Re: Loud Bang!

Accumulator tank?
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Old 05-08-2022, 01:57   #7
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Re: Loud Bang!

Originally Posted by goboatingnow View Post
Sounds like tank flexing
Would second that. My fresh water tank does that when almost full and filling
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Old 05-08-2022, 03:32   #8
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pirate Re: Loud Bang!

Lift your seats/hatches and one of you eyeball the port tank while having one hand on the tank as the other flushes, repeat on the stbd side.
If sight does not tell you, the vibration of the tank will tell you if that's the cause.

It was a dark and stormy night and the captain of the ship said.. "Hey Jim, spin us a yarn." and the yarn began like this.. "It was a dark and stormy night.."
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