Welcome Aboard Shipmates

This is my blog which I would like you to follow, comment on, and use as another method of collaborating with me and your classmates, if we can all learn together that is the aim, don't leave anyone behind and if you are unclear on something you need to ask.

The first session is Tuesday the 28th of February 2012 12:30 to 4:00 we will talk about what the assessment is all about, the Field trips we do, your expectations and mine from the course
This is the opportunity for you to understand what the assessment instruction is telling you to do

http://www.yachtsurvey.com/maitenance.htm

http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook%20061205.pdf

Osmosis Repair

Osmosis avoidance, detection, treatment

Osmosis-Is a problem with fibreglass hulls built from polyester resin... The problem is that water is, able to make its way through the gel coat and in to the fibreglass laminate. Gel coat is not completely waterproof, water penetration does occur. If the water is able to find its way into any air bubbles or small voids that have been left behind from the laminating process it will mix with chemical residue (styrene, MEKP, etc) to form a dense acidic liquid. Because that liquid is more dense than the seawater on the outside of the hull water is drawn from the outside into the void in an effort to equalise the pressure difference, the result is that the void pressurises and forces the outside layer into a blister which shows on the outside of the hull often when the hull is removed from the water a dark liquid can be seen forcing its way back out through the laminate, or gel coat. The blister is actually a small delaminated section of hull, sometimes just under the gel coat but often into the outside layers of CSM depending on the lay up. The process of water penetration is called osmosis and is the same process used in nature by plants to transmit water from roots to leaves.

Avoidance-FRP boats these days are not as prone to osmosis as they were some years ago. Boat builders have realised that they put their product and company name in jeopardy by using cheaper materials and taking shortcuts in production. Hulls that don’t have osmosis problems have a sealed laminate, they use vinyl ester, or isothalic polyester resin rather than orthothalic Quality control the temperature, the humidity, and take good care to lay up using proven techniques. The underwater surface should be sealed with a good thickness of epoxy paint prior to antifouling

Detection- Is not always straight forward, the best way is to view the bottom of the boat when it is first hauled out, and by looking along the wet surface the raised blisters will show up and should be marked. Often as the hull dries the blisters quickly disappear. This is because the surface has been softened and the liquid is allowed to escape as the water is no longer pressuring on the outside of the hull. This will happen quite quickly as the hull dries and often only one hour after haul out the blisters have disappeared. The problem is still there it’s just difficult to individually locate them. Sound tapping with a hammer will find the blisters as they are just small delaminated areas. Often so small that it’s difficult to cover the entire surface with a hammer and feel confident all the blisters have been located. Antifouling should be removed to be sure of finding the full extent of an osmosis problem.

Repair-There are only two proven methods of repair. The first is to remove the affected area of each blister individually, dry out and epoxy fill which is considered as damage control rather than repair. Or the second method is to plane the surface of the hull down to a level where the laminate is healthy (sometimes that is not possible), dry out and re laminate with a resin rich matrix back to original thickness. This is often done with vinyl ester resin and sealed on the outside with a good thickness of epoxy paint.