Hull bulging
My 47 S&S #33 1978, we have sailed this boat round the world for the last 9years and after leaving her in Trinidad June to Dec 2010 on our return I noticed that the rib halfway down the hull was bulging out from bow to stern horizontally about 12 cm wide , on both sides and right at centre ship a big bubble the size of a dinner plate on the starboard side ,I have knocked on it and it has a hollow sound .The boat has original gelcoat and I had it polished in Trinidad .It seems like osmosis look alike.If you rub your hand over it you can clearly feel that it is raised .Has any Body have had a similar experience and if so any ideas will be welcomed !Philip Strauss Gypsyduo3@hotmail.com

Dear Philip
This would indicate that the weather in the area has been extremely hot.
The temperatures in the sun have exceeded the Heat Deflection Temperature of the polyester resin in the hull laminate, and have probably been in the order of 80 deg. C (176 F). For white topsides this is surprising, and would suggest that there have been some additional effects concentrating or reflecting the sunlight towards the topsides.
The topside longitudinal stringers are now showing through as you say. The stringers are foam filled, this works as insulation locally and prevents heat from dissipating to the inside like in the single skin areas. The stringers therefore see higher temperatures than the adjacent areas.
It is possible to determine whether the structural integrity of the resin has suffered by employing scientific methods. The recommended method is Fourier Transform Infrared Spectroscopy, for short FTIR, and portable equipment is available.
It is very likely that the problem is purely cosmetic, but to restore the appearance filling, fairing, and painting is required.
Kind regards
Lars

Interested to hear the recommendation of FTIR.  Fully support the use of this, having used it on our Swan two years ago to help diagnose some hull/keel issues. 

Have also seen it used on an Oyster 70 to define extent to osmosis.  Interestingly it also highlighted they had some grounding damage at the leading edge of the keel/hull joint; something they were not aware off. 

Very quick and cheap process.

First picture is a nice healthy looking hull with longitudinal and frames clearly visible.  Second picture is extend of delamination on the aft STBD hull keel joint green area, with significant water ingress showing in the blue area.    Last picture is damage to an internal frame; this is interesting as there was no visible sign of damage here.

What you show is extremely interesting and I wish I could understand more (I am pretty familiar with FTIR spectroscopy of microscopical samples under laboratory conditions).
Can you please indicate some literature I could read? The closest reference I was able to find is a Master thesis in Metallurgical and Materials Engineering (http://ethesis.nitrkl.ac.in/2049/1/thesis_renu.pdf) but it does not treat extensive surfaces like the ones you show and this makes a big difference.

Daniel, 411-004

All,

I must offer my apologies to the Forum.

 The above images/survey was not undertaken using FTIR, but thermographic.  It was carried out by Graham Connor, www.intys.co.uk.  (The case studies on his website are interesting.)

If anybody has a basic understanding of the differences between the two techniques and the relative pros and cons I would be most interested.  Unfortunately various commitments have not allowed me the time to investigate.

Many thanks to Lars for pointing out my error.

All the best,

Adrian

Tiderace II

Dear Adrian,

thanks for your message!

Fair winds!

Matteo (38/067 Only You)

I gladly accept the request to explain the difference between thermography and FTIR spectroscopy and I promise I will try to be as clear as possible without being too technical. I am afraid it will not be a short explanation so I need the permission/advice of Matteo before going ahead.
My suggestion is either to publish it somewhere else different from this forum or to split it into two or more parts.

While waiting for further indications I start working on it off-line.

Daniel, 411-004

I gladly accept the request to explain the difference between thermography and FTIR spectroscopy and I promise I will try to be as clear as possible without being too technical. I am afraid it will not be a short explanation so I need the permission/advice of Matteo before going ahead.
My suggestion is either to publish it somewhere else different from this forum or to split it into two or more parts.

While waiting for further indications I start working on it off-line.

Daniel, 411-004

Both techniques mentioned above are passive radiometric measurement techniques which quantify emitted radiation. So it would be the case that the FTIR method is not per se optimal to reveal structural characteristics such as delamination, expect to the extent these structural characteristics are well correlated with the thermal properties of the structure.  Whilst this correlation is logical to expect, it's unknown specific value assures significant uncertainty in any inferred structural assessment.