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S&S Swan General - swan 36 smelly water in keel
13 October 2021 - 20:48
Join Date: 16 November 2020
Posts: 8

swan 36 smelly water in keel

The Swan 36 has a deep keel. Plugs left and right offer the possibility to drain the keel once the boat is lifted. But before the yearly shore maintenance this water smells terribly. Does anyone has experience how to solve this issue: maybe by filling this area with foam ? 

15 October 2021 - 10:00
Join Date: 20 July 2017
Posts: 115

Hi Robert,

when you say the water 'smells terribly', are you  refering to the bilge water that drains when you open the drain plugs i.e. at the end of the season?

Or does your bilge water smells all the time i.e. also during the season?

If only it's only smelly when you drain via the drain plugs and the water has sat for quite a while in the bilge the smell might just be caused by the water going 'off'/foul over time? Possibly the limited air flow in the depth of the bilge would be an ideal environment for this, especially in warmer climates. 

We have a similar problem with our toilets depending where we sail; as you can't get them completely empty the remaining sea water goes moldy when Kairos is moored for a few weeks e.g. in the Elbe River. Not a big issue and it doesn't smell, just looks rather horrible. We try to remember to flush some fresh water before we leave.

If the bilge water smells all the time it might be worth checking if you have a leak somewhere in the waste water system of the toilets or waste/grey water tanks (if you have any). Or the kitchen sink or washbasin drains/shower bilges? I'd think it wouldn't take much of a leak of waste water to make a bilge smelly ...

Personally, I would not amend/filling the bilge to make it shallower; I think the problem is elsewhere and not caused by the depth of the bilge. Also, you might cover up an underlying problem if you can't find the source and a very good clean doesn't fix it...

Also, the bilge was designed by S&S hence is probably nearly perfect; a deep bilge tends to make pumping water out easier and the drains from other areas probably rely on a certain depth (plus you might lose access to the drain plugs). And I would think it would be near impossibel to achieve a water-tight fill e.g. with foam unless you laminate the whole lot; imho foam is likely to make things worse with water seeping into/behind it, which you won't be able to get to. 

Not sure if this is helpful, just some thoughts.

Good luck and fair winds,


Kairos 57/043


15 October 2021 - 10:25
Join Date: 16 November 2020
Posts: 8

Hi Stefan


thanks for your reply. Yes I refer to the bilge water that drains when opening the drain plugs at the end of the seaon.


The bilge has 2 parts: the upper part approx 50 cm below the cabin floor. And the lower part which is accessible via a round barton screw inspection cover. The lower part has again 2 depths following the shape of the keel. 

Water in the upper part is drained via a bilge pump.

Water in the lower part(s) is drained via the plugs in the keel. This water is smelling after a year. Of course we could try to pump it out every month but its difficult to access via the inspection cover.

tx,  Robert

15 October 2021 - 11:47
Join Date: 02 January 2008
Posts: 1547

Dear Robert

Appended a detail showing the aft part of the bilge. The bottom of the upper bilge apparently allows water to leak into the lower part, where it begins to smell.  
This may be a bad sign - if osmosis is going on in the lower part, and causing the smell, it has to be stopped.
Access from above may be very difficiult, and he recommendation is to cut an inspection port from the side, so you can look into the space, and do what is required.
Kind regards

15 October 2021 - 11:51
Join Date: 20 July 2017
Posts: 115

Hi Robert,

this is interesting - I didn't know the 36 had such an arrangement. Is there a particulary reason for this feature?

Our 57 just has the one bilge, probably over a metre below the floorboards...

If the water in the lower section is in there sloshing around for a whole season with very limited oxygen I'd think it's not too surprising that it smells; maybe you could dry leaving a little bilge cleaner in there?

Fair winds,

Stefan - Kairos 57/043

15 October 2021 - 12:15
Join Date: 02 January 2008
Posts: 1547


At the time wooden boats were still the norm, and they have straight keel planks.
I think this influenced the thinking

15 October 2021 - 14:00
Join Date: 20 July 2017
Posts: 115

Hi Lars,

always good to learn something new!

Thank you,


26 October 2021 - 21:41
Join Date: 28 May 2019
Posts: 7

Hi Robert,

A feature of the 36 is indeed the spectacularly deep bilge. As Lars notes, this was common in wooden yachts with a deep hull profile and external ballast keel. Having (salt!) water in the bilge of a wooden boat is normal, and not a problem at all.

It sounds like yours has had a false floor fitted in the bilge at some stage. If the water collecting in the deepest part isn't accessible to your pump/s it will certainly become anaerobic over the course of the season, which would explain the bad smell.

We're still completing the refit of our 36 so we haven't finalised the bilge pump setup, but it will be arranged to pump out from the deepest aft part of the bilge, to try and keep it as dry as possible.

The previous setup was a high flow Gulper type electric pump mounted just below the cabin sole under the companionway. The pickup pipe - with a strainer and an electronic water level sensor - was mounted in the deepest part, on the end of an aluminium pole. The pickup pipe for the manual bilge pump was also mounted in the deepest part. These could completely empty the bilge, leaving just a couple of cm of water under the pickup pipes, so very effective.

It would also be possible to fit a submersible electric bilge pump in the deepest part - mounted on the end of a vertical pole under the floor.

However the best electric pump setup I have seen was on Shaytana (36/066). She has two parallel electric Gulper pumps mounted under the cockpit, with the pickup pipes and air pressure switches mounted in the deepest part of the the bilge:

That system has nothing electrical submerged in the bilge, and gives high flow with two redundant electric pumps (plus manual backup).

I would not consider filling the space in the bilge with foam or anything else - as that will prevent future access to the aft keel-bolts. They are difficult enough to reach!

Good luck!


Lofna, 36/021


01 November 2021 - 20:19
Join Date: 16 November 2020
Posts: 8

Thanks for all your replies. Nice to have this forum.... I chose the gulper pump solution now. Now winter series regatta in Scheveningen but in summer it will be warm and the proof of the pudding will be in the eating )))

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