Re: Older boat osmosis


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Posted by Bengt Blomberg on March 20, 2002 at 17:08:48:

In Reply to: Older boat osmosis posted by Dennis Kenney on March 16, 2002 at 10:29:09:

: I have a 1976 Buccaneer 270. I'm not sure if I have osmosis in my hull. There are small indentations in the hull but they look like barnacle damage.

: 1. Could a hull 26 years old have osmosis? I would think it would have delaminated by now if it did.
: 2. What is the best way to test the hull for osmosis? I would think, drilling a small core sample and testing it for moisture.
: 3. What moisture tester is best?
: 4. Is there an acid tester for this purpose?
: 3. Is there any way to adapt the HotVac process for the average boat owner who cannot afford professional HotVac, i.e. buy a vacuum pump and make your own heat vacuum pads. It seems the heat control is the hardest thing to achieve.

Hello Dennis, Here are some answers:

1. If the laminate delaminates or not mostly depends of if it contains any layers of woven roving or not. If there are such layers, each will mostly delaminate on the under side before the hydrolysis proceeds deeper. A chopped strand or sprayed laminate in severe cases can become totally soft without showing any delaminations.

2. You don't need to brick drill through the laminate. Just use the tip of a 1.5" drill bit to make a conical hole through about 3/4 of the laminate. Buy a packet of blue lithmus paper strips in a drugstore. Wet the hole slightly (not with saliva) and press a lithmus paper strip against the side of the hole for a few seconds.
Remove the strip and check thee colour. If any part of the strip has become orange or red you have an active hydrolysis. Check the walls of the hole with a magnifying glass. If you can see any black or brown layers, delaminations have started.
If any of those layers leaks fluid it is fully delaminated.

3. As I have mentioned many times in this forum, it is not excess water or moisture which causes the hydrolysis. It is the hydrolysis which causes cavities where the watere can enter and cause the abnormal readings. An old hull can have a moisture content of between 0.2 and 10% without any sign of hydrolysis and 5% already causes most meters to reach the top of their scales.
However an eventual hydrolysis never proceeds totally even along the hull and if a meter instead of fairly even readings shows large differences when moved along the hull a hydrolysis process must be assumed. The only meter I have found so far with suitable sensivity cales is the Tramex Skipper. Note, that the percentages noted on the scales are not the actual percentages of moisture in the laminate but a relative percentage of the total amount of fresh respective salt water pine wood can absorb. If you want to know an estimated percentage of moisture in the laminate you must use tabels provided by the manufacturer.

4. Answered at 2.

5. There is no way to use any "home made" equipment for this purpose. There are equipments in the market used for postcuring of quality polyester laminate parts like for instance helicopter prop blades. There a temperature span of 75 - 85 degrees C. is sufficient and not near any dangerous levels.
When it comes to remove the dangerous hydrolysis products, the polyester must become plastic which means temperatures of 100 degrees C + - 3 degrees. A few degrees too much might cause hull deformations and below 95 degrees means risk for dangerous substances to remain.
Further, there can be foam filled or otherwise insulated areas on the inside which calls for a very sofisticated arrangement of temperature sensors in the mats.
Actually it took a long time for the inventor to overcome all problems and you might have observed, that I refused to accept the system for a couple of years until all problems were solved early last year.

Regards Bengt




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