Checking For Bad Core/ delmaniation 101?

[barrelroll]

My '82 has had some neglect and has some rot and possible delmaniation, the question is how much. What are your methods for checking for bad core or delmaniation?


I bought a General combo pin/ pinless moisture meter, it didn't work great outside in the rain. In pinless mode it just gives a range of LED's, not a number. Now that the boat is inside and out of the weather I plan on giving it another try.

I've been going through and drilling out old no longer needed screw holes to 1/2". I'm getting some holes with dry shavings, some wet though solid shavings, and some with black mush. The black mush holes I know need more investigation. What would your plan of attack be for the wet though solid holes?

I've been trying the tapping method though my ear hasn't quite picked up on the differences yet.

I'd like to get it all in 1 shot while the boat is inside in the heat, it's a half day ordeal to get it in the shop and Southeast Alaska isn't great for working outside. It's currently in a heated shop drying out.

[thataway]

Unfortunately the surveyor's models are in the 19th century--tap and moisture meter. Using a plastic (phenolic so they say) screw driver handle or hammer. It is both the sound and the resilience of the fiberglass. Light taps and work out from a known bad area to the good, and then visa versa.

A friend who is one of the World's top NDT instrument experts adapted one of his ultrasonic devices to check for delimitation and voids in cored boats. Surveyers didn't want to pay $2,000 for an instrument which costs $15,000 to NASA, Boeing etc;. So it never went into production.

With ultra sound it will measure the depth as long as you have a solid conductive material, such as saturated core. If the core is delaminated from the inner hull surface, then only the thickness of the inner glass layer is measured. For a single project I would not invest in an ultrasound. But if a friend has one, then use it.

Moisture meters are helpful, but often misleading. I also use one of the cheap ones, but it gives % on a LCD screen. It is a relative value in comparison with other areas in the hull bottom. I would dry the boat at least a few days--week is better. Then map out areas which seem moister. There may not be any differential between the "mush" and wet plywood core.

I would start with areas of the known "mush" and work out radially to see what the rest of the laminate is like. Same with the wet plywood. You don't have to go all of the way to the bottom in each hold--but estimating where the screws from the runners come thru the outer hull will be helpful for test drilling.

You will probably never completely dry out the wet plywood. I have seen foam cored boats which still are not dry over a year's treatment, using heat, and vacuum to remove moisture. However if it is not delaminated, and the boat will not be subject to prolonged freezing temperatures, I would be tempted to not replace the wet core, before this summer, if time is a constraint. I realize that you do want to rebuild the furniture. Also probe the test drill holes outward with a sharp small pick to give some idea of the core. Often you can hook behind bad core and pull it out for some distance from the test hole.

I would start working on the transom and let the core dry before doing a full assay, depending on your schedule. Start by working out from the known bad areas. You certainly want to check the integrity of the bottom next to the transom before doing any lamination of the new glass onto the transom. .