Do you want to be informed on new Posts on this Thread? (members only)

S&S Swan Maintenance - G10 or G11 on a mast foot
07 February 2013 - 19:03
#1
Join Date: 05 August 2010
Posts: 164

G10 or G11 on a mast foot
Dear all,
got quite a shock today after having the mast pulled out ... the shock mainly due to the fact that virtually no outward corrosion was visible. After unstepping the mast, things looked different.

The second owner of our 48 had discovered galvanic corrosion on the mast foot in the early 1990s. The mast was then treated by cutting the bad part off (about six centimeters) and by fixing a wooden plate inside the mast as a water stopper (water would not run through to the bottom but would drain out of the mast through holes above the shoe collar. I am not sure whether the lowest part was reinforced -- what remains in substance is still inconclusive.
Cutting the mast results in a shorter mast, obviously. To address this problem and in order to use all the existing rigging, a steel pedestal was welded on the steel frame, thereby lifting the mast shoe to compensate for the missing length of mast. Unfortunately (or, speaking after pulling the mast, fortunately) this steel pedestal showed massive corrosion. A pic of the mast foot is attached.
The space between the stainless steel mast shoe and the aluminium mast was filled with grease or vaseline, the rationale being, in the words of the former owner, "where there is grease, there is no corrosion". Sounds logical but actually is a bad idea!!
As you can see on the picture of the mast pedestal, the mast itself -- as far as it was visible -- looked pretty good; the yellowish stuff is the grease. However, after we pulled it, we discovered that the inside of the mast was filled with a mushy substance which I take to be moist aluminium oxide, in other words, what used to be mast material before it converted. I have attached a second picture showing the mast from below. I guess we are fortunate it did not come down underway. That is what I meant by saying that fortunately the pedestal was corroded: this fact forced us to unstep the mast this year -- which we might not have done otherwise, or not yet.

What we plan now is to cut another piece off the mast (sigh) and build an extension that will be fixed inside the mast with a sleeve. The extension should be long enough to make the pedestal obsolete, giving the mast its original length back. In addition, I would like to have the mast base plate made of G-plate (G11 or G10) so there will be no more corrosion in this area. Twice is enough. The steel pedestal will be removed, the affected areas of the steel frame cut out and replaced, and the stainless steel shoe brought back down to the steel frame. I hope we do not find that the damage in the frame is already so spread that we have to replace the complete frame -- that is yet to be determined.

Long text, no question? Well, any comments on the procedure are highly welcome. In addition, if anyone knows what the required G-Plate thickness would be, I would be grateful for this input. Lars has also commented in an earlier thread that on one (larger) Swan the complete steel frame has been replaced by a G10 frame. Lars, do you know the specifications or have any further information?

In any case, I will post further details once we are underway with the repair.

Best regards,
Martin and Age of Swan (48/039)

07 February 2013 - 21:48
#2
Join Date: 01 March 2007
Posts: 147

Hi Martin,

Only sharing my experience - and I am not an expert. My 47 Sarabande ( 1977 ) had her mast reduced due to fizzing - 50mm? /the mast heel was compensated with a nice galvanised fabrication, and the standing rigging was replaced/adjusted at the same time. This work served her well for 15 years, a few transatlantics and some tough offshore racing. I have since replaced the whole rig with Carbon which is a different story, but it seems that good workmanship at the mast base can work and last. It is not that scientific, just good basic engineering!. Best of luck, Rob. Sarabande 47/029

08 February 2013 - 15:59
#3
Join Date: 27 January 2011
Posts: 140

This is our solution to a similar problem: the mast was corroded at the bottom and could not be unstepped anymore. It was cut, and a sleeve was added.

Christian IF 411/028

08 February 2013 - 17:48
#4
Join Date: 30 January 2007
Posts: 462

Hi Christian,
very nice indeed, do you know of which material is the large plug made of?
I have only one question: the shipyard decided not to keep the two transversal big bolts that keep the foot of the mast fixed to the floor. Do you know their rationale?

Daniel, 411/004

08 February 2013 - 20:35
#5
Join Date: 02 January 2008
Posts: 1547

Martin
You could also consider to make the mast shoe out of aluminium, and thereby eliminate further corrosion. Then it would be appropriate to put the G-plate between the shoe and steel mast step, and make big ventilation holes. 5 mm G-plate or so would be fine here.
Actually it was another 48 where the mast step of steel was replaced with G-plate. I can dig out the required thickness which was calculated to be strength and stiffness equivalent to the steel. Could you pls confirm the steel thickness?
Kind regards
Lars

08 February 2013 - 20:35
#6
Join Date: 02 January 2008
Posts: 1547

Martin
You could also consider to make the mast shoe out of aluminium, and thereby eliminate further corrosion. Then it would be appropriate to put the G-plate between the shoe and steel mast step, and make big ventilation holes. 5 mm G-plate or so would be fine here.
Actually it was another 48 where the mast step of steel was replaced with G-plate. I can dig out the required thickness which was calculated to be strength and stiffness equivalent to the steel. Could you pls confirm the steel thickness?
Kind regards
Lars

09 February 2013 - 16:27
#7
Join Date: 27 January 2011
Posts: 140

Hi Daniel,

I looked at a number of photos before and after the repair, and there were no additional bolts before. Thank you for the hint though, I will look into this.

Christian IF 411/028

09 February 2013 - 21:08
#8
Join Date: 05 August 2010
Posts: 164

Lars,
just a quick reply today ... I am working on the drawing of the possible solution. - The thickness of the steel frame / mast support seems to be 10 mm in most accessible places. I am not totally sure if the current construction is original, so let me describe it:
the visible part looks like a big T in cross section. The stem of the T is 10 mm and is upright on the keel, running fore-to-aft. I cannot measure the crossbar of the T (which is the platform that the mast shoe rests on), but the "hands" of the arms of the T (or the serifes of the letter T) are 12 mm. I don't yet know exactly how much of that is metal, rust, or paint.
I strongly suppose that there is a second plate sitting below the laminated bilge bottom, making the steel frame a double T shape. We have not dug that deep, though.
More tomorrow,
Martin

21 February 2013 - 17:30
#9
Join Date: 02 February 2007
Posts: 202

Dear all.
May I bring in my own experience. On our 41 born in 1974 we only unstepped the mast for the first time in 1999, and there was indeed some corrosion at the bottom: this was mainly because there was no isolation between the aluminium of the mast and the stainless steel shoe, and also the drainage was rather poor.
So we did cut about 20mm of the mast, and added an aluminium plate roughly 15mm, isolated by a 3mm piece of tufnol (thanks Lars!) to isolate it from the stainless steel of the shoe. All this compensates for the lost mast height. We also increased the size of the draining holes.
The tufnol sheets aroud the bottom of the mast have also been kept.
As an adititional safety device we glued with epoxy and bolted an aluminium sleeve at the bottom of the mast. (Too strong has never failed as would probably agree our Master Olin?)
We unstepped the mast again last year to replace the standing rigging, the electric cabling, and check in for corrosion under the stainless steel at the spreaders, and here is how it looked before painting again.
We also beleive that rinsing with fresh water through the halyard passages is important to get rid of the salt and make sure the drainig holes are unobstructed.

21 February 2013 - 18:52
#10
Join Date: 05 August 2010
Posts: 164

Dear all,

thanks for your input! After lots of long discussions with the rigger, some backup information from Lars and some nights with bad sleep, we have decided on a repair that will hopefully get rid of this problem.
The steel frame has been cut out of the boat in the affected areas. A new insert will be made of galvanized steel and be connected to the remains of the old frame. The connection will be made with bolts, both because welding inside the boat is not a favored option, and because that way we can remove the complete frame if we ever have to access the keel. By the way, the keel bolts look great, and the nuts can still be turned. -- We have decided on a steel frame instead of G10 partly because of the available knowledge, as there is no one here who had any experience with it.
The mast shoe will be made of aluminium, with an isolating layer between shoe and frame. Draining will then be straight down into the bilge, not sideways out of the mast and into the shoe as we had it before. As a matter of fact, the complete foot design will have to be changed. This is the second time our mast has to be cut, and the mast builder strongly advised against constructing a 12 cm extension to get the mast back to the original length. So the mast will be extended a bit, but not fully, and the steel frame will be slightly higher than before. Once we are underway, I will post more pictures.

Martin
Age of Swan (48/039)

23 May 2013 - 20:25
#11
Join Date: 05 August 2010
Posts: 164

Dear all,

as you will perhaps recall, we had to undertake a major repair this winter, as we found the steel frame supporting the mast badly corroded. Unfortunately, the frame was not the only problem - the mast foot was also severely corroded where it had been standing in its stainless steel shoe for two decades. In addition, we found more corrosion beneath the wooden halyard cleats -- actually something that worried me a lot, since they are all on the same level and seemed dangerously like a perforation line ...
Anyway, here is a description of the repairs, split in two posts, one for the mast and one for the steel frame.

We addressed the mast problems with custom-made aluminium parts. A ring cut away from the damaged mast part gave us a clean edge to work on as well as a template of the mast profile. With this template ring, two half-sleeves were made. Together they form a sleeve that sits underneath the halyard cleat ring. The sleeves are bolted into the mast (see pics) so that the aluminium thickness at this point is twice five millimeters now so I am less nervous about the perforation line. And the halyard cleats are bolted through both mast and sleeve.

For the corroded mast foot, we had a new foot made -- in solid aluminium, bolted into the cut end of the mast. The new base plate (yes, aluminium!) is a solid plate with two massive bolts that go into corresponding holes in the mast foot. Water can run out along the bolts, and as the base plate has no rim, it runs right down into the bilge.
With the bad repair of twenty years ago, that has been the second time the mast needed to be shortened. The mast top is still at the same height, but the steel frame needed to be made a bit higher to compensate for the missing mast section. The cables running inside the mast now exit exactly on the level of the floor boards instead of below. But that is a small price to pay.
And now for some pictures ...

Martin
Age of Swan, 48/039

The corroded mast foot after cleaning

Corrosion beneath the halyard cleats

Mast foot after cutting

23 May 2013 - 20:27
#12
Join Date: 05 August 2010
Posts: 164

More pics of the repair ...

The sleeve halves for the cleat ring

Sleeve ready to be fixed inside

23 May 2013 - 20:30
#13
Join Date: 05 August 2010
Posts: 164

Pics of the new mast foot ...

New foot and shoe (or base plate)

... in detail

23 May 2013 - 20:58
#14
Join Date: 05 August 2010
Posts: 164

The other problem was the steel frame. As a replacement of the complete frame (which is rather huge) was neither necessary nor very tempting, we just had the bad part cut out of the frame. Sounds much easier than it was, actually.
For this cutout, a new frame piece was made -- this is not aluminium but galvanized steel. We considered G10 but found nobody experienced enough with the material so went for the steel solution. In retrospect, I would still have preferred the G10, perhaps even more. One reason is that we did not want to weld the steel frame, as the welding areas would have been only centimeters from the fiberglass hull and we feared the heat would cause new damage.
The other reason is that G10 would have been much easier to fit to the irregularities of the boat shape. The steel frame now is bolted to the old frame, but there are some pockets of air underneath the base. In consequence, the complete frame sits on a bedding of a kind of concrete ... something that could have been avoided with G10, so if I ever have to address this area again ... hope not.
Nevertheless, the steel frame sits in the cutout and is bolted to the the old frame.

to be continued in the next post ...

The damaged part of the frame cut out

... and the new part, fitted before galvanization

Detail of the base plate of the new piece with keel bolts

23 May 2013 - 21:01
#15
Join Date: 05 August 2010
Posts: 164

The last pictures show the steel frame in position. As the new aluminium base plate does not have the adjusting screw of the old stainless shoe, the frame has two extensions at the front and back ends. To position the mast, we placed a hydraulic press against the extension and slid the complete base-plate-and-mast ensemble into position.
As the frame is bolted into place instead of welded, it is also possible to remove the complete frame insert if the keel needs to be worked on. As the mast is right above some keel bolts, keel bolt take-offs require a removal of the mast, but again: that is an acceptable price to pay.
Because what matters is: the mast is back in position. And I don't think the frame or the mast foot will cause any further problems any time soon.
The work was done on Sardinia, the aluminium parts were made in Genoa -- feel free with any question you might have.

Martin
Age of Swan, 48/039

The new steel frame

... and everything assembled!

29 August 2014 - 23:32
#16
Join Date: 27 August 2014
Posts: 17

Hello Martin

 

I'd like to get a copy of the templates for the Swan 48 mast step.    Can you put me in touch with whoever built yours?

 

Larry

26 September 2014 - 21:47
#17
Join Date: 27 August 2014
Posts: 17

Lars and All:

Can you suggest a process to remove corrosion from the mast step in my Swan 48 without removing it from the boat?  

Also, my mast step has a plate passing under and bolted to the forward side of the bulkhead forward of the mast.   Is that how these boats were built?

 

Larry

27 September 2014 - 12:29
#18
Join Date: 02 January 2008
Posts: 1547

Dear Larry
There are many products able to remove rust, from household stuff to strong chemicals, and it is suggested that the choice be related to the person doing the job.
The recommendation is to lift the mast step so also the underside can be inspected, this requires removal of all keel bolt nuts and can be done when the yacht is on the hard.
Particular attention should be paid to the stiffness of the support taking the mast compression, the proper connection of the forward end to the bulkhead, and the continuity of the transverse floors connected through the mast step.
Referring to your question about the forward end, there may be a keel bolt close to the bulkhead causing the bottom plate to be attached to the forward side.
There is not much difference if this is done on the forward or aft side, the important thing is that it is well attached.
When the step is out it would be a good time to check that the keel bolts are properly sealed where they come up through the keel plank.
Kind regards
Lars

27 October 2014 - 21:12
#19
Join Date: 25 July 2008
Posts: 30

Dear All,

Other examples of mast corrosion and of solutions were described in threat 504:

http://www.classicswan.org/forum/post_thread.php?thread=504

Since I did the refit of the mast (and participated to the forum) I have not seen any corrosion but I wanted to ad that I have made two holes in the mast shoe (see picture) and that often I fill the mast with fresh water and get my finger below the shoe to unblock dust and small particle and to check if the water is flowing or if there is a blocage.

The other main mast corrosion problem for our 47's is the goosneck. At the swan cup I looked at other boats and saw that for the 44 the goosneck in on a rail (see picture). In this case the corrosion is on the rail and not the mast so you can change the rail when refiting the mast.
Does anybody have experience of changing the original gooseneck (staneless steel directly on the mast) by this rail. I was thinking of this solution for the next refit.

Ludovic
From Rumtrader (47)

System on 44 with a rail

situation of RUMTRADER after sanding the mast

28 October 2014 - 10:35
#20
Join Date: 30 January 2007
Posts: 462

I cannot say anything about the feasibility of changing the gooseneck support from the large flange to the rail because it is a matter of mechanical strength difference that only an expert can judge. For sure I can affirm that no stainless flange is ever put in direct contact with the aluminum of the mast; there must be always an isolating layer between them and, as far as I know, Nautor always complied to this basical rule.
It is normal that the isolating layer needs to be checked and possibly replaced every once in a while.
Daniel, 411/004

28 October 2014 - 18:44
#21
Join Date: 02 February 2007
Posts: 202

Hello dear Swan fans!
I have a question (for the professor?) regarding the general arrangment of this mast step repair.
Should not the steel support of the mast shoe be also be considered as a sort of longitudinal backbone for the center section of the hull?
In other words I was wondering wether, or not, it would be wise to bolt its lower plate to the keel, so as to spread the weight of the keel on the longest section of the hull possible?
One also has to make sure that there will be very good drainage for the water coming from inside the mast: VERY IMPORTANT!
Kind regards.
PhilippeV 41/022

  • Threads : 1710
  • Posts : 10244
  • Members: 822
  • Online Members: 1