Surveyers Hammer

Always used a hammer to find studs and joists behind the plaster board in houses or locating the extent of rot in wooden structures without even marking emulsion paint so I would hope it could be used on a GRP hull. Guess some of the comments on here are why there is miss understanding and traditional skills are lost. Although I can see a tap test being far less useful on a thin skinned cored boat. But for solid laminate or wood if the surveyor did not hammer test at 6"(150mm) intervals I would consider he had not done his job.

Strikes me a forum would be a good place to learn from other peoples knowledge and preconceptions and as such a good way to review one's own position on a topic. Therefore it can be a rewarding experience and if this is not the case what is the point of participating.
 
G Connor said:
Sorry gents but using a hammer is hit and miss and not accurate .Use a hammer on most builds today and you would be kicked off the job. Thermography or Ultrasound are the tools to use.Sheerography for aerospace.http://http://intyachts.co.uk/thermalimaging.aspx;)
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Ah - the sexy techniques of thermography, ultrasound, and shearography........

All involve very expensive equipment, lots of time to do properly and specialist knowledge and experience to interpret what has been seen. All are costly to the client. These techniques are used widely in aerospace where the quality of the laminate is much higher than production or custom boat building. Using aerospace grade techniques on boat hulls will reveal countless defects that do not matter on boats, that may be a problem on the higher stressed aircraft - so need to be interpreted with care.

Each has their own types of material they work on, and defects they can find. If you spend the time talking to the practitioners (such as Roby and Felix of Marine Survey Bureau in Palma, for example, one of only a handful of companies who have calibrated and applied these techniques successfully to boats), you will find that the hammer is one of their preferred diagnostic techniques in appropriate circumstances. Defects can often be found faster and more accurately than by the other techniques.

Having watched them working, it is clear that they are neither simple or quick to apply. Trying to apply them to all boats would result in pre-purchase survey fees being in the thousands of pounds rather than hundreds for most boats!

The techniques have their limitations: Ultrasound does not work well on some GRP constructions using any chopped strand mat. Kevlar can affect a number of the techniques. The defect orientation can affect the ability to detect it for given techniques.

Roby recently wrote an interesting article on use of all these techniques on a carbon mast subjected to a lightning strike in the Dec/Jan 2011 edition of Professional Boatbuilder Magazine. On page 52 is an interesting chart of applicability of these methods on boats.

For high tech yachts, made from exotic materials, you are right about use of the hammer.

But around here the vast majority of boats are still GRP or GRP/sandwich construction, where careful, sensible use of the hammer is still more applicable, reliable and affordable to the client.
 
stav said:
Although I can see a tap test being far less useful on a thin skinned cored boat.
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Tap testing is used to detect delamination of the skin from the core in a cored boat. The tone and bounce changes noticeably when you reach an area of delamination.

stav said:
Strikes me a forum would be a good place to learn from other peoples knowledge and preconceptions and as such a good way to review one's own position on a topic. Therefore it can be a rewarding experience and if this is not the case what is the point of participating.
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I agree whole heartedly with you on this.

Martin
 
Good luck using a hammer on a cored boat. Costing clients thousands that is rubbish and misinformed .Extensive tests were carried out on core testing and delamination . The problem with using a hammer is the core saturates in different areas when curing as does honeycomb core .This would give a different sound when tapping.Its not accurate . As to Ultrasound speak to Olympus on composites .Your comments on that are also missinformed. The use of visible data or a hammer.mmmmmmmmmmm no brainer. I often come across comments about Thermography ,Ultrasound and sheerography . Just out of interest what do you use out of the three ? I use all three on yachts and composite built structures. ;)
 
G Connor said:
Good luck using a hammer on a cored boat.
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I use it without problems on powerboats built of GRP, with cored construction up to 50ft regularly. It is not just the tone it is also the bounce of the hammer which helps to locate defects.
The ASA detail tap testing as an acceptable form of NDE for a wide variety of defects on aircraft. (Ref ISBN 1560277521)

Standard methodology, well documented, used by numerous surveyors wordwide. The methodology is taught on a number of course including the IBTC course, and the IIMS practical course.

We serve different markets in our own equally valid ways offering two different ways of getting to the same point.

If I need to have these types of advanced NDE undertaken, I find someone who is experienced in undertaking the work and in interpreting the results to undertake it for me.

My comment on cost was for a full hull survey of an average sized boat. As I understand the process for undertaking a thermographic survey to find defects in a boat is:
1 - spilt the surface of the hull into a grid of approx 1m2 rectangles appropriate for the camera.
2 - Take an image of the surface before heat is applied
3 - apply heat to the surface of each of the grids to provide an even thermal gradient by lights or other heat source
4 - Either video the heating/cooling process with a IR camera, or take stills at appropriate times when the defects are visible
5 - Post process the images to eliminate the original differences in temperature caused by environmental factors such as trees, telegraph poles etc. and to ensure that the defects can be found.

If this can all be done within a normal survey fee in the lower hundreds of pounds, for a 40 ft boat, then I am impressed given the additional work load required. My cost statement was based on my understanding of the workload.

Don't get me wrong about these techniques. They have their place and are very useful for identifying defects. In the right hands they are very powerful.

However the tap test (hammer test) if carried out properly is still valid and should not be dismissed completely.

I am interested to know about the research relating to use of hammers to which you refer. If you could PM me the details I would be grateful.

As I understand it your expertise is with advanced composite construction where your comments are very valid.

I wish you all the best with your business, and look forward to meeting you in the future.

Cheers

Martin
 
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