Hull coring

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    We are replacing a thru hull in our D37 Calypso and the coring is fairly soft. I cannot find a source on the hull coring. Does anyone know if it goes just to the waterline or if the coring continues further down. The boat was built in 1983.

    Fleet Captain

    I’m sorry you are not getting any responses here–come on folks, somebody really knows the answer. I am of the opinion that the end-grain balsa core stopped at the waterline and from the waterline down it was solid glass and mat until you get to the keel where core is reintroduced—but I could be very wrong.

    Mike, how would you attack the soft core?

    Al Sampson

    “Wanderlust” a D37 has coring through out. If done properly you should not see coring when a thru hull is removed. The core is balsa wood, very soft. I would suggest with the thru hull fitting removed. Dig out some of the core all around the hole, approx. 1/4-1/2″ deep. It should not be wet! fill the entire hole with epoxy. Then re bore the hole. No core will be exposed. FYI, some owners have water in the coring below the waterline, big problem!

    Al Sampson

    Mike Aitken

    I’m going to agree with Al….dig out as much as you can……

    If Al says Balsa, I’ll defer to him…..

    Wet core presents huge challenges. If its “end grain” basa (BALTEK), hopefully the water only compromized the squares adjacent to the thru hull…end grain balsa “tends” to not allow water to tranfer throughout the whole deck, unless it travels along the inner/outer skin. Wire “digging” tools and chisels & anything you can use to “reef” ot the core…If its a 1 1/2 inch thru hull you can use a dremel & wheel Or (my favorite) a high speed grinder & disk that’s 1 1/4 inch dia. gets you 3/4 inch all around the hole pretty quick. spins at 22,000 rpm…so care is needed.

    I’d mix up a blend of chopped/milled glass fibers, cabosil & epoxy to a “peanut butter” consistency & use that a filler….use the edges of the existing hole as your guide & fill to the edge of the hole tillfull….This will be a very strong compression ring of epoxy/glass ……. Then just sand the hole sides, and reinsert thru hull…..

    Also, after you “reef” out the junk, throw a 100 watt light on it for a day …perhaps 8 inches away…to see if there is any moisture the heat might drive away…..Makes the area “dry” for epoxy too……

    A plastic hammer “tapping” ( tap fairly hard..) around the hole will give you a decent idea on wet core…the sound does not “ring” like good core…more of a “thump”….Try it and listen for “sound” differences……

    Never fun…..

    Me……I use 5200 on all thru hulls….I bevel the hole edge to hold more sealant. To remove…Bronze with a propane torch….plastic I cut off with a big chisel……I don’t want leaks….

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