Glass and utrasound

I am looking at buying an Aloha 34. I am told by the designer (Ted Brewer) that the hull has a balsa core from the deck all the way to the keel (unusual!) and the 'outer' layer of glass is thinner than the 'inner' one which is the structural one. (unusual also) I am trying to think of a way to check the condition of the balsa core. I thought that maybe an ultrasound machine may work. Can it? Has it been done?
This is my first posting for a long time and I hope I have done it right.

 

The three situations I have run into with balsa core FG hulls are:

Delamination -- skin pulled away from core which can be detected with a tap hammer
.
Moisture in core -- blisters in skin are one indication. Can be found with a moisture provided someone knows how to reliably read a moisture meter.

Rot -- in areas around mounted fittings. Obvious when you see it but the fitting must be removed first.

Have no experience with untrasound for this purpose. Ted is an honest sort and can give you pointers and past experience with the boat.

 

I would believe you would only get a measure of either the inner or outer layer of the laminate, IF you suddenly can measure the full laminate Inner, outer + balsacore, is probably only when it is fully saturated with water.... I would not suspect that you would get any useful reading with regard to delamination against the balsa core with a ultrasonic thickness gauge, not better than you can get with careful knocking with a small hammer...

 

glass and ultra sound

Since ultra sound is out and hammer is in (done that!) maybe I can asked if any of you had a Aloha 34 and had good or bad experience with the hull? I am trying to get a handle on this as I am thinking of buying the boat. But the last thing I need is a project for the rest of my life. I am sure you understand.

I have found some evidence of water leaking in the deck around the chain plates / deck surface. When I push with my finger, a little water will show itself. So at least there are repair to be made on the deck. I can handle that but not so sure if I can handle the same in the hull.
Vinay

 

Pro Boat Builder had a story on this subject. I think it was about using an heat sensitive camera. You might search their index.

 

http://www.proboat.com/digital_issues.html

 

http://www.sailingbreezes.com/sailing_breezes_current/articles/Feb00/cored_hulls.htm

 

While not calibrated or scaled to read Balsa core, Could not an indication of "something" abnormal be gained by adapting the meter?
A thin sheet of metal, (heavy foil perhaps), would be laid on a spot., higher up, where known to be dry. A "constant" would be noted. Based on this, the test would move to suspected areas. Wet Balsa should give a different indication. A variance from the constant would indicate "something" different. Then an exploratory hole could be made for a sample & explanation of the variance. If it was found to be a reliable method, then the test would reveal other areas of a like reading.
An accurate scale or value is not necessary, only an indication of "something" different.
What do I know. Just a laymans thought.

 

Glass and ultra sound

Thank you for all your postings. Ted I think has something usefull and experimentation on that particular hull may prove a big asset. Thank
you.

 

Perhaps so, but you will probably be left with more questions on how to interpret the results than when you started. Such as, how do you know where a "dry" spot is for a reference? I guarantee that there will be varying results from any meter testing. If it's my hull you are thinking about drilling into, forget it. I can tell you that simple moisture in balsa core looks just like dry balsa when you core it. That is, unless its really wet which is unlikely. The tap hammer is a pretty foolproof method for finding the location and extent of delamination from balsa core. The fix for delamination is not too difficult either.

 

Infrared thermography is a pretty reliable method of finding any of the described issues. I don't know any surveyors on your coast that do it but I am sure they exist. If you can't find one out there it is worth your time and money to fly one in. Take the time to check it out carefully...it may save you a sea of tears later.