New Exhaust for Swan 38 I have recently fitted a new Volvo D-130 30 hp engine and gearbox to my Swan 38. I want to fit a new improved exhaust system as I am getting some sea water coming back through the water lock in rough conditions. Can anyone recommend a good solution/design that prevents any possibility of sea water coming back up the system?
Mnay thanks,
Patrick
Dear Patrick
It appears that the exhaust has been changed in some way if water enters, perhaps Swan 38 owners could confirm.
For improving the system the suggestion is to lead the hose from the water lock up to cockpit bottom level as far forward as feasible, i.e. near the forward end of the cockpit, and from there sloping evenly aft to the thru-hull connection. How much slope can be achieved?
The hose location sideways is decided by the position of the thru-hull, the hose should be run from there parallel with the centerline all the way to the highest point forward.
The water lock should have a drain valve which can be opened in rough conditions.
There are also two other uses for this valve
- if the engine does not start and is cranked for a considerable time the cooling water pump will convey water into the exhaust, which then needs to be drained
- before winter arrives with freezing temperatures it is good to empty the exhaust
Kind regards
Lars
Many thanks Lars
Are there any diagrams of a recommended solution, maybe we should try an exhaust exit on the stern above the waterline even though this may look untidy?
Kind regards
Patrick
Patrick,
a nice historical drawing of what Lars clearly described is here:
http://www.sparkmanstephens.com/yachtdesign/design_typeplans/typeplans_M12.php
Dear Daniel
Thank you for the very helpful contribution.
I would like to comment the S&S plan on three points:
- The high point on the exhaust hose should preferably be forward, as the stern wave at speed is highest aft, at times close to deck level, and lowest midships.
- Branching off part of the cooling water reduces back pressure in the exhaust system, which is very good, but this has to be approved by the engine supplier.
- The cooling water by-pass also functions as a siphon break, even if this is not mentioned. Therefore the height is specified. The by-pass can also be taken out through the topside, or led into the cockpit drain, gives a visual warning if water stops flowing.
Best regards
Lars
Many thanks Lars &Daniel for your advice. I have the standard exhaust tell tail on the port top side which indicates if cooling water is entering via the impeller by "peeing" out water. I would be interested if anyone has got a modern Vetus type exhaust and water lock that works well with modern Yanmar/Volvo Penta engines. I have a feeling the previous owner had the same problem with the original exhaust system but simply ignored it.
Regards,
Patrick
Dear All,
Having thought about this it struck me that the water lock must be the original fitment as per the attached photo's. The original Swan 38 engine was a BUKH 10hp so this water lock is not suited to the typical 30 HP Yanmar/Volvo type engines. The original water lock is shaped like a pudding bowl with a diameter of 23cm and depth of circa 11 cm. IE circa 2 litres capacity: therefore, allowing for the S&S instructions of a min water lock capacity of 2 litres and 1 litre per 10 HP - I should be looking at fitting a water lock of > 5 litres capacity.
The issue, I think, is not with the vent or swan neck being high enough, but with the actual original small water lock getting flooded in operation. When the engine is switched off, the residual water in the lock is flooding back into the engine causing contamination etc. I cannot see any solution other than fitting a bigger & better water lock- taking into account that the exhaust outlet on the engine (see photo) is lower than the inlet on the water lock what type of waterlock should I be fitting?
Regards
Patrick
