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S&S Swan General - Exhaust system swan 41
22 January 2023 - 17:29
Join Date: 22 January 2023
Posts: 2

Exhaust system swan 41

Dear all am jnstalling a new engine, craftsman 4.52 to replace perkins 4108, however noticed there's no air breather nor waterlock, only overboard muffle/ check valve.The coolingwater injection used to be at the top of the stainless vertical pipe chamber on top. Am wondering how the internal looks like.. anyone? New engine injection is at the exhaust, instead of the chamber.. Main query is if i need to install a waterlock at the bottom in combi with air breather.. kind regards swan 41 spica

Check valve


23 January 2023 - 15:57
Join Date: 30 January 2007
Posts: 461

Maybe you already know this drawing but in case you don't...

Your old system seems something like a dry exhaust system although I am not sure.  As Lars Strom explained in one of his messages, there is an hystorical reason for dry exhaust systems in the first produced Swan's but, as you can see in the drawing, Rod Stephen himself soon changed idea.

In my 411, which is almost like your 41, there is a system very similar to the one shown in the drawing; I am pretty sure that you can design one like this for your boat.

There are a few notes regarding the difference between the system on the 411 and the drawing.

In my boat there is a short piece of stainless steel pipe approximately midway between the mixer and the water lock with a temperature sensor; its presence is very important to check that the cooling effect of the water is indeed ok and to avoid the burning of the rubber hose.  Lately I found that there are temperature sensors with a "stinger" to be inserted into the rubber hose; this is a good idea because you can avoid the piece of s/s pipe which tends to corrode.

Instead of what is defined 50% thru by-pass in the drawing, in my case there is a small copper pipe whose main purpose is anti-siphoning. It is probably not more than a 10% by-pass and goes overboard at the shortest point, not at the transom.

The water lock is a standard Volvo waterlock/silencer made by two s/s end pieces and a large rubber hose in between.  The only variation that Nautor made following Rod Stephen suggestion, was to insert (weld) a "drain lock" in the output end.  It is a very good choice, I think.

Daniel, 411/004 Luna Menguante

Rod Stephens Type Plan M12, Water Lock Exhaust System

23 January 2023 - 17:15
Join Date: 02 February 2007
Posts: 202

Dear Jantijs and Daniele,

The original exhaust of a SWAN 41 is indeed a dry exhaust.

I hope I will be able to send you a copy of an original Nautor drawing.

This means that the exhaust gases are completely separated from the outlet of the cooling water, and that they only mix at the top of the muffler.

If your engine is a modern one, i.e. mixing exhauste gases and cooling water directly as they come out of the engine, there is no other solution than a waterlock, and installing one on a 41 is not easy, as there is very little space available.

You may find these solutions in older thread in the forum.

On our 41/022 we still have a Perkins 4108, and the orignial dry exhaust, as I explained in the oldest thread, but the flexiple pipe has to be changed regurlarly, which I am not too happy about...

Hope this helps.


28 January 2023 - 11:12
Join Date: 30 January 2007
Posts: 461

I looked at the plans of the 411 and of the 41 and I fully understand the problem.  In the 411 there is an almost-two-places bunk in the left side of aft cabin which allows the exhaust pipe to go under it, straight from the engine without problems.  Please notice that it goes indeed under the bunk totally hidden but it is confined in the lower right corner where, laterally and heightwise, it occupies only a small part of the space.

The main point, different from other solutions seen in this forum for the 41, would be the use of the in-line Volvo waterlock/muffler whose height and thickness is limited.  I would suggest to put it, in the 41, where the dry pipe is now and I am pretty sure that it would need an additional rather unobstructive cabinet which will act as a step to the bunk.


Daniel, 411/004, Luna Menguante

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