Luna's foam cored decks

[Chris Campbell]

When I bought Luna (then just Hull #70), one of the things that drew me to her was the fact that her decks had been recored. Yankee 30's are notorious for soft decks, and she had had that dealt with. See below for an aside (read: rant) on the Yankee's soft decks.

Her decks were recored with divinycell, professionally by a yard somewhere in Maine - presumably near her previous home in Addison. I've got pictures of the job on my site - they look good:






I think they used polyester resin, and doubt they used biax, but otherwise it looks like a good job.

Here's the thing, though - the decks move underfoot! As I walk around the decks - these freshly, professionally recored decks, they squish a bit with each step. I don't know, but I assume that this is a result of the foam compressing - but it feels funny, especially for a boat with freshly cored decks.

Does anyone have any suggestions as to: a) why this is happening, and b) what I might do about it?

I've been pondering sanding off the paint they put over the decks and putting an extra layer of 'glass. I've also considered adding thickness to the decks from underneath, since I know the bottom skin is skinny on this boat. But I don't really have any idea what is going to bring me satisfaction, and would rather avoid trying things at random until I hit it.

As always, any and all suggestions greatly appreciated!

Cheers,

Chris

A note on Yankee 30 soft decks: Turns out that while the Yankee Yachts company had some great ideas about how to build boats and do it well, they did miss the boat (so to speak) on a number of issues. First and foremost of these is how to build a cored deck. They correctly sandwiched balsa between sheets of fiberglass. They correctly layed it up with good resin in controlled conditions with expert workers. They then left the edges of the balsa core exposed, covered only by a teak toe rail, with bedding compound between the toe rail and the balsa core. Sigh. Of course I write this with the usual 20/20 hindsight, but even so - I've never seen this anywhere else - all that has to happen is the bedding fails, and there you are with your decks rotting out from under you!

[Tim]

Divinycell is very hard and firm and wouldn't give an impression of "squishiness" even if you walked on it without benefit of a laminate over the top.

Do the sidedecks "give" in the manner you're describing, or is it more the foredeck? Wide foredecks, even cored, tend to flex underfoot slightly when trod upon. This is normal and OK. If the narrow sidedecks are flexing, though, it seems something doesn't seem quite right. They should feel firm and solid underfoot, as the span is too short to really allow flexing with a properly cored structure.

First step: sound the decks with a steel hammer. This will help you determine how well (or not) the top skin is bonded to the core. If the skin were not well bonded, you would get the sort of give and "squishiness" you're describing.

Depending on your sounding findings, you might want to drill a core sample or two--easy to fix, but very instructive in terms of showing you what's going on inside. Just drill through the top skin and into the core, not all the way through. Only do the core samples if you find something during your sounding test to indicate that the structure is not all it should be.

Beyond this, more information is needed, I think. Not being able to walk on the deck myself and feel what you're describing is quite a handicap. Let us know what you find out.

[Chris Campbell]

Thanks, Tim. I tried sounding the decks with a hammer, and with the plastic end of a screwdriver, and they sound alright to me, but I'm no expert. They do change sound in some places - like near the edge - but I'd expect that since the structure is different there.

I started to doubt myself as I was doing it, and walked the decks in bare feet to see if I could feel more that way - and they felt fine. I think I'll have to get someone to dance on them while I observe from below, and from beside - with no toe rails I should be able to spot any deflection as they put their weight on it.

Maybe I'm just being a boat hypochondriac.

Anyway - thanks, and I'll keep this thread apprised of any new information - including, perhaps, a recording of me tapping the decks, to allow more expert ears to impart judgement.

Thanks again,

Chris

[Rachel]

Chris,

One time when I was boat shopping I walked the decks and was dismayed to feel them "giving" beneath my feet. Boy, did they feel spongy. Then I took my tennies off (in this case, Adidas running-type shoes) and they were fine. It was amazing the way the shoes made them feel completely springy.

Maybe that is what happened on Luna (great name, by the way!)

Rachel

[Bluenose]

Chris,

For all intents and purposes, the stiffness (and deflection) of sandwich panel is determined by the core (biggest effect) and skin thickness. Only in areas of concentrated loading would the core strength become a factor. So I would think that if your new divinycell core was laid up to original thickness, and replaced with an equivalent outer skin, and was repaired to formed a proper sandwich panel then the stiffness and deflection should be similar.

For me, a proper sandwich panel repair would ensure that all of the core pieces are well bonded to each other along their edges and that the inner and outer skins are well bonded to the core.

The only other thought I had was have you walked an any other Yankee 30s to have a comparison? And how much curvature do they have on the foredeck? If they were on the flat side compared to other designs that would come into play.

Cheers, Bill