Mast and steel frame repair
Dear all,

just a brief note here: I started a thread on February 7th (G10 or G11 on a mast foot) to describe the problems a corroding steel frame caused on our 48. I have just uploaded a description of the repairs with some pictures to the same thread. So now everything is in one thread -- however, as the thread was started some time back, I thought I'd alert you to it, particularly as mast and frames become topics again ...

Best regards, Martin
Age of Swan, 48/039

Dear Martin
Thank you for posting this interesting information.
I would like to check the buckling safety for one part of the new steel frame - the vertical plate right under the mast, as it takes the whole mast compression. This plate is visible in the middle of the picture showing the frame before galvanization.
If the safety is deemed insufficient it can be improved by adding sideways support to the forward edge.
Could you give the thickness, width, and height of this plate, and confirm it is welded also to the top flange?
Kind regards
Lars

Great catch, Lars - good eye. It sure does look like it needs to be beefed up. Even if the math says no, it would be a good idea, but my guess is the math will say yes. We are very lucky not only that you answer all manner of questions and help us all as you do, but that you look at things like this and alert us to possible problems before they become dangerous.

Thanks to you Lars, and all the best to you Martin on this nice repair.

Geoff, Corazon, 411 #41

Thanks for the caveat, Lars ... and sorry for the delay. Here are the data:

- the vertical supports are welded both to the bottom and the top plate;
- the top plate, the bottom plate, and the forward and end plates are 16 mm thick;
- the cross-section is I-shaped (the top plate has two vertical bars left and right);
- the thickness of these bars as well as of the center plate is 10 mm;
- the center plate under the mast is 15 cm wide and about 30 cm high (but slopes).

I hope they don't need to be strengthened as they are stronger than the part we cut out ... which looked original, at least.

Best regards,
Martin

Hello Martin.
I would definetely try to beef out that 10mm plate.
Think of that big mast tube resting on top a 10 mm plate! Of course I know there is a 16mm thick "bridge" in between, but I will never forget that Eric Tabarly lost a mast on Pen Duick 6 during a Whitbread round the world race because of the buckling of an H shaped support the middle part of the H being vertical and the side bars of the H supporting the mast foot on one side and bolted to the keel. About the same arrangement we have on our Swans.
On our 41 I checked that the mast was supported by a cross rather than a plate (below the horizontal plate), and its not higher than 10 cm...
All this is probably not easy to do I expect, but I wwould personally go for it.
Sorry to disturb this huge project.
Wishing you all the best.
Philippe 41/022

Dear Martin
Thank you for the additional information.
The 10 mm thick 150 mm wide and 300 mm high vertical plate under the mast has insufficient buckling strength, but this is not difficult to improve.
If I interpret the picture "Detail of the base plate..." correctly the aft edge of the vertical plate in question is supported sideways by bolted angles connecting it to the transverse floor plate both sides.
Similar angles could be added to the forward edge for support, and to avoid drilling holes they could be bolted to the plate edge as sketched. A strip of 10 mm plate is required outside of the bolts to ensure the jamming action, and further it is recommended that epoxy glue is used between angles and plate to secure them in position.
The angles should be full height, and it is recommended that also the aft edge angles are replaced and extended down to the bottom plate for added safety. It is suggested that it is checked after hard weather sailing if the 10 mm plate is compressed, causing the angles to bear part of the load.
You can buy angles of 8 mm plate with 60 mm sides, this would be suitable for the new angles forward. Same size bolts spaced abt 50 mm.
Hope this explanation is clear
Kind regards
Lars

Sketch

Dear Lars,

thank you for the valuable input! Your explanation (as usual) is perfectly clear ... even laymen as I am one can follow.
I have attached a picture of the old frame from before the repair. Now that you mention the strengthening angles I see that there are remains of an old welding line -- so the frame must have had that enforcement until it was repaired twenty years ago.

Best regards,
Martin