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S&S Swan Maintenance - Stringer Rot
09 April 2010 - 14:56
#1
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milo
Join Date: 26 March 2008
Posts: 69

Stringer Rot

We have our engine out at the moment replacing worn gaskets. The engine normally rests at four points on stringers covered in fibreglass. I am concerned that there is some rot of the stringers, particularly the forward ends. Does anyone have any experience with treatment options, both short and long term? A general description of how the stringers are designed, construction material, and access would prove helpful. It is particularly the access that worries me. Ours is a Swan 47, though I sense the concept is similar for other boats. For clarity, I have added a photo with the area of concern highlighted. Sometimes terminology varies from country to country, but a picture paints a thousand words. Cheers,

Milo

s/y The Last of the Normal People

47(048)
10 April 2010 - 20:49
#2
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matteosalamon
Join Date: 29 January 2007
Posts: 1022

Dear Milo

there are steel plates inside the stringers.

When I had the new Yanmar engine installed onboard Only You I had to lower the engine bed, and build a new one, you can see from the attached images how the plates are (and the original ones are quite similar as these).

Fair winds!

Matteo (38/067 Only You)
10 April 2010 - 22:07
#3
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milo
Join Date: 26 March 2008
Posts: 69

Hi Matteo:

Thanks for the info and pics. However, it doesn't feel like steel plates inside. I can stick a screwdriver in one of the holes and it feels like rotten wood. Certainly not like steel. Could the 47 have wooden stringers and the 37 have steel?

Milo
11 April 2010 - 08:32
#4
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matteosalamon
Join Date: 29 January 2007
Posts: 1022

Dear Milo,

I think Lars Strom will give us a right answer to your question!

Fair winds!

Matteo (38/067 Only You)
11 April 2010 - 16:45
#5
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the professor
Join Date: 02 January 2008
Posts: 1547

Dear Milo and Matteo

Swans have back-up plates of steel inside the FRP engine bearers. They are put in on the underside before the bearer module is attached to the hull.

The original engine was a Volvo MD21A. The records say that there is another engine now, and the bearers have probably been modified in connection with the engine change. The picture you sent indicate that the bearers have been cut down at the forward end.

Suggest you drill small holes in the engine mount area to determine the composition of the top flange. If there is no steel inside it is recommended to put in at least short lengths of it where the engine mounts are located.

One way to do this is to cut slots through the vertical side of the bearer, slide in the steel piece, make sure it stays attached to the top flange, and add a laminate over the slots with appropriate overlaps in all directions. If the slots can be cut in the forward or aft ends of the bearers this is preferable, these areas are less loaded than the sides.

Kind regards

Lars
13 April 2010 - 22:11
#6
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milo
Join Date: 26 March 2008
Posts: 69

Dear Prof and Matteo:

Many thanks. It looks like we have steel. Whew.

Cheers,

Milo
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