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S&S Swan Maintenance - Exhaust advice
22 April 2021 - 06:38
#1
Join Date: 21 April 2021
Posts: 13

Exhaust advice

hi everyone,

i am looking for some advice on one of my ongoing projects

i am replacing/reconditioning the exhaust on our swan 44 since it has a small leak

the current exhaust is either the original (unlikely that it lasted 48 years) or a good replacement made to follow the original which is part dry and part wet, routed athwartship under the floor, through the port hanging locker and exits through the port side just above the waterline

i should be able to have a replica made from scratch at a local engineering shop

has anyone undertaken a similar project?

i have seen that some similar boats choose to change to a more modern system with rubber hose running fore-aft and an exit on the transom but i would like to keep the original design as far as possible

thanks in advance

dav

22 April 2021 - 15:55
#2
Join Date: 02 January 2008
Posts: 1528

Dear dav

The choice of material for the exhaust is an interesting question.
The original exhaust was of AISI 316, which in contact with hot sea water develops pinholes after roughly 25 years. If you prefer a longer life, either a material having better pitting resistance is needed, or using rubber hose instead of metal.
Titanium would have excellent corrosion properties, but is expensive, and welding requires shielding with an inert gas. 
Alloy 625 Inconel or alloy 825 Incoloy are possible alternatives.

If you choose to make a new similar system in AISI 316 it is important to choose AISI 316 Grade L, otherwise the welds may develop a problem called weld decay.

Some 44s have changed to rubber hose led out through the side. Then it is important to make sure that water from the water lock can not run back into the engine even if the boat is knocked down
Kind regards
Lars

23 April 2021 - 16:33
#3
Join Date: 21 April 2021
Posts: 13

Dear Lars,

Thank you for your reply; I am honoured that you chose to give advice on my specific requst; I have followed your replies on other threads and value your insight.

My concern is mostly about water running back and flooding the engine; the original design seems to have proven its siutability and am reluctant to deviate much.

The situation I can see with the original design which could result in flooding the engine is as a result of corrosion in the dry part of the exhaust which is covered by a water jacket. Pinholes here could remain undetected until they form in an area which allows enough water to drain out of the water jacket and back into the engine.

Corrosion anywhere else will not be catastrophic so 25 year expected life seems reasonable to me.

I will look into the availability of the other alloys you recomended.

Warm regards,

dav

23 April 2021 - 17:04
#4
Join Date: 02 January 2008
Posts: 1528

Dear dav

If you make a new water jacketed system, you could add a tiny drain at the lowest point of the dry part, enabling you to check if there is water inside.
If it is possible to fit in a big enough water lock right aft of the exhaust bend, the rubber hose alternative would be safe.
Kind regards
Lars

24 April 2021 - 21:16
#5
Join Date: 21 April 2021
Posts: 13

Dear Lars,

The drain at the bottom of the dry part is a good idea, thank you.

I have looked closely at the Nautor drawing of the exhaust and with the help of google translate i have realised that there are two drains in the system; one in the lowest point of the water jacket and another at the bottom of the mufler. Both of these are not present in my current exhaust.

I would like to ask for your advice about the flexible coupling between the elbow at the engine and the elbow on the exhaust; i currently have what seems to be a mild steel bellow. Do you think it would be ok to change to a braided stainless steel fitting as used on motorcar exhausts?

Warm regards,

dav

25 April 2021 - 07:18
#6
Join Date: 02 January 2008
Posts: 1528

Dear dav

The two mentioned drains have been added later. They can be used to drain out the water when freezing conditions are expected.

The bellows are a critical part of the system, as the engine must be able to move around a little. Braided stainless would work well.
Kind regards
Lars
 

02 July 2021 - 17:17
#7
Join Date: 21 April 2021
Posts: 13

Hi everyone, just an update to this post.

I had a new exhaust made following the original drawings, i introduced a flange between the waterjacket coverd pipe and mixing chamber to make it easier to remove and install so that i can inspect the condition periodically.

Here are a couple of photos before i covered the uncooled parts with insulation.

Thanks for all the helpful advice, the forum is an invaluable source of information, hope to be able to help if anyone else needs any further information about my experience.

horizontal section below the floorboard and the new elbow and flexible coupling

new flange to make removal and inspection easier

02 July 2021 - 17:34
#8
Join Date: 29 January 2007
Posts: 878

Dear Dav,

excellent job!

Maybe you want to double the stainless steel clamps, and if you find ABA (quite common in Italy), they are good quality.

Fair winds!

matteo (47/069 Vanessa)

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