Two small keelbox cracks
We have discoverd on our Swan 44/038 two small (8cm) cracks on the afft side of the keelbox. The two cracks ends just at the lower side off the crossbeam.

Has someone seen the same damage, and if so how did it get there?

Maybe the professor can give us some repair advice.

Dear Ice
Unfortunately the photo is not very clear, but it appears the edges of matting-in are cracking.
A better picture would be appreciated, or arrows showing the beginning and end of each crack, as well as the position of the crossbeam in reference to the keel attachment
Kind regards
Lars

Hi Lars,

Many thnx for the quick response.
On the second picture below you see the arrows showing the beginning and end of the biggest crack.

This crack is about 10cm after the last two keelbolts and just in front of the crossbeam that's in front of the dieseltank.

Kind regards,

On saterday i will make a picture with a keel attachement overview. If you need more pictures just let me know.

Dear Ice
This looks like an old repair, badly done because of the uneven surfaces. Suggest the cracks are opened, dried out if wet, and repaired.
Kind regards
Lars

We had similar cracks on or Swan.  Long story but...

Worth investigating the cause thoroughly to understand what type of reapir is needed.

Are these the only cracks; eg are there any fwd for the keel sump, any on the aft side of the transverse stringer they are on?  Are they new/old?

I found with ours cracks that they were really just a sympton of something else.  I would recommend a bit more investigative work.

Cheers

Adrian

Hi Adrian,

Good idea. I will have a look at the complete keelbox next weekend. I have to take out the dieseltank to have a look on the other side of the springer. Keep you all updated here. Regards,

Dear Ice, I had cracks develop in the area of the aft most keel bolt on my 47 Sarabande. For a few years I experimented with topical repairs, but last year I removed the keel which exposed the problem. If you are talking about the single aft most keel bolt, it joins the hull in a narrow area, largely filled with filler with poor lateral support. This bolt is twice the length of all of the other bolts. Therefore it has more leverage, and able to compromise this section of the join! I have good photos if of help! Best regards, Rob. Sarabande 47/029

Thnx Robmably for the comment.
I'm going to search the last single bolt this weekend because i have not found it yet. Mayabe he is under the dieseltank on the other side of the springer, or a 44 has no single last bolt. Can anyone clears this out? Pictures would be handy Robmably, you may send them to ice[at]clubracer.be. Many thnx in forward.

Dear Ice

Here are the 2 aftmost bolts you are looking for, underneath the fuel tank. You should find 2 more forward, just under the bulkhead.

Good luck

Tonyh 44/04 Hatha

Dear Ice,

Here are a couple of pictures showing the aft most keel bolt which is longer than all the rest and is NOT bolted through the matrix which forms the bilge box. The narrowness of the hull and keel at this point makes it difficult to strengthen. We removed all the cracked areas of the hull, refilled the deep narrow section and fabricated a steel plate which was faired to fit the internal shape of the hull.

Rob. Sarabande.

Dear Ice, Here are a couple of pictures showing the aft most keel bolt which is longer than all the rest and is NOT bolted through the matrix which forms the bilge box. The narrowness of the hull and keel at this point makes it difficult to strengthen. We removed all the cracked areas of the hull, refilled the deep narrow section and fabricated a steel plate which was faired to fit the internal shape of the hull. Rob. Sarabande.

Dear Rob, your pictures are quite interesting, it is for me the first time I can see the keel of the 47' disassembled, thank you
As far as I can see there are 7 bolts at the fore, 6 in the deep bilge and three abaft. Do you remember where is the nut of the most abaft bolt located? on the cross stringer under the engine? Maybe the professor can check if there exists a design from Nautor in which we can see from the profile of the boat the exact location of the bolts.
When in 1995 I bought Grampus I observed from the boat ashore that there was a craze of around 6 inches at the aft junction of the lead with the fiberglass. The owner showed to me immediately a letter to him (or) a document in a release from Nautor in which it was explained that these cracks might arise because of the different thermal expansion coefficients of lead and fiberglass; it was therefore suggested to deepen the craze and fill with an elastic glue, polyurethane or whatever silicon. How then to apply the antifouling? it might be a problem...
So, almost every other year I fill with epoxy this crack, with an exception about ten years ago in which the job was better done covering a couple of bands of glass tissue on that area and with the boat suspended so that the bolts were in tension, but this remedy was good for 3-4year
This fact is annoying, does the professor think that I should undo the fiberglass covering the last bolt aft and try to strengthen the nut? I am not much worried from the fact that I will loose the keel and sink the boat but they might come from that area some leakages that would come from the cracks. Anyway the boat is until now very dry in the bilge when it is not raining.
I would much appreciate the comment of lars, thank you
Matteo
Grampus II 47/016

Dear Matteo
I would agree with your thought to dig out the last bolt, and attempt to reinforce the area so the crack closes.
Rob's pictures should help you to find the bolt.
If you then send me pictures of the inside and outside recommendations can be made.
Kind regards
Lars

Dear Matteo,

Yes your numbers are correct. The section aft of the keel box reduces in width very quickly, hence single bolts as opposed the pairs in the wider sections. The aftmost bolt is the most accessible of all of them on my 47'. It is situated just forward of the athwartship stringer supporting the cabin sole at the base of the steps. As aforementioned, it is the only keel bolt which does not go through a steel matrix - it is simply through fiberglass only. The steel matrix which forms the keel box extends forward and in turn bolts go through the frame which forms the heel of the mast. Aft of the keelbox it stops short of this final longer bolt. My theory is that there is excessive leverage from the keel at this point and with the longer shank of the bolts, the through hole (largely fiberglass filler) gets stretched easily, and in my case cracks developed from there and extended toward the keelbox, similar to the pictures posted by Ice. The bolt itself was absolutely fine - as were all the others - I have not replaced any of them. Rob. Sarabande

Hi Robmably,

Can you post some pictures of the repaires, please?

"We removed all the cracked areas of the hull, refilled the deep narrow section and fabricated a steel plate which was faired to fit the internal shape of the hull."

Regards,
Ice

Hi Ice,

Yes of course I will do this - it will be next week.

Best regards

Rob.

Hi all,

I think luck us on our side, yesterday i managed to cut out the lose polyester with the crack in and it looks like it was fabricated afterwards. Under the cracked polyester there was pure and solid laminate without any evidence of cracks anymore.

At first it looked like a bad repair job but after close examination it looks like a support that partly removed(maybe a battery holder).

Next job: drying, epoxy primer, and bilge paint.

Dear Matteo, Yes your numbers are correct. The section aft of the keel box reduces in width very quickly, hence single bolts as opposed the pairs in the wider sections. The aftmost bolt is the most accessible of all of them on my 47'. It is situated just forward of the athwartship stringer supporting the cabin sole at the base of the steps. As aforementioned, it is the only keel bolt which does not go through a steel matrix - it is simply through fiberglass only. The steel matrix which forms the keel box extends forward and in turn bolts go through the frame which forms the heel of the mast. Aft of the keelbox it stops short of this final longer bolt. My theory is that there is excessive leverage from the keel at this point and with the longer shank of the bolts, the through hole (largely fiberglass filler) gets stretched easily, and in my case cracks developed from there and extended toward the keelbox, similar to the pictures posted by Ice. The bolt itself was absolutely fine - as were all the others - I have not replaced any of them. Rob. Sarabande

Dear Rob,thank you. It looks like this bolt is positioned under the container of the main set of batteries.
I observe from your pictures that this longer bolt is not parallel to the other bolts, that is it does not look really vertical. Did this happen when the keel went down in the shipyard?.
I have an opinion,which might be wrong, too, because it is too many years ago that I made my exams in construction science. The fin keel of this boat has in the aft section a pronounced slant aft. Splitting the vertical charges into the various bolts, there is a much higher stress for the most aft bolt.It is clear that the baricenter of the keel does not coincide with the baricenter of the bolts, and the most stress is aft. Second, but not last, in case of pitching, which is quite common in the sea, the stress on the bolts at the extreme areas is much more relevant. Third, the constraint on this bolt is much more flexible compared to the others because the nut is positioned much higher. Probably setting much more tension through a higher torque on this nut would help very much, but I do not know if in this case the thread will break. Dear Lars, thank you, I will surely check this when the boat will be ashore.
In my previous post I have mentioned that there should be an old position of Nautor regarding this matter. If I remember properly the letter sent from Nautor to the previous owner contained an alleged article of the company with regards to this topic. Do you remember, after so many years, or can you trace a similar argument? Thank you very much,
Matteo, Grampus 47/016

Dear Matteo and Rob
The longitudinal center of gravity of the keel is below the forward end of the bilge recess, and there are roughly the same number of bolts forward and aft of this point. Further the three aft bolts are bigger, 30 mm, and when pretensioned to the recommended level of 70% yield strength i.e. 76 kN, each one of them alone is carrying more load than the total weight of the keel.
The hull area around the last bolt is stressed highly in case of grounding, and it should be checked whether this area has softened, or if there are old repairs not well done.
Tapping the area and comparing the sound to that from a known healthy area is a simple test, but there are more sophisticated methods available, and they can determine internal damage quite in detail.
It is important that the laminate here is sound throughout, and does not contain filler as Rob indicates. Further a large steel washer under the nut would improve the situation, and laminate can also be added on the outside in the hollow area above the narrow end if the inside is inaccessible under the engine.
Rob, before attaching the keel to the hull again beads of mastic are usually put around the bolts, but this is not sufficient alone. When the keel is in position against the hull the slots in the keel plank around each bolt should be filled completely with mastic from the inside, right up to the top of the steel plate before the nuts are put on.
To do this for he long bolt is not easy, suggest that a thin tube that goes down to the bottom of the slot is used for pressing in mastic.
Matteo, I remember that a difference in thermal expansion is mentioned in the keel section of the Owner's Manual text, could it be the reference?
Kind regards
Lars

Dear Lars, thank you very much, it is great to know that one single 30 mm bolt can carry the total weight of the keel!!

With regards to the baricenter of the keel I still have a different opinion, it looks like the baricenter is more in the aft area of the low bilge box. I have checked on a profile plan of the boat, unfortunately I am not able to load this file on this post, I will try to send later the link

I will check on the owners book, it is very possible that I might find something there related to the topic of the cracks, thank you
Matteo, Grampus 47 /016

here is the link of the profile plan of the 47' where it is possible to see the location of the deep bilge:

http://3.bp.blogspot.com/-gn2RWKQG7rQ/TiB_VBh415I/AAAAAAAAIRc/xXHp552ESRw/s1600/2201%2BSwan%2B47%2BGA%2Bhi-res.jpg