I'd say this is not an accurate test.

  Boiling the cells creates excess pressure, which eventually will find a way out.  Putting the now hot honeycomb into cold water will then create a partial vacuum inside the cells, which will do what they can to suck in water.

  Those conditions will never be replicated in a sailing boat.  Surfaces in the sun may get hot, but not boiling, the surfaces that do get hot aren't likely to then be submerged in cold water, and even if they are, they'll be protected by layers of either vinylester or epoxy, along with either a gelcoat or lpu paint, and then perhaps a layer of barrier-coat epoxy if it's below or near the waterline.

  I imagine that most foams would not be ideal, either, if boiled and then submerge.

  Of course, you could argue that Derek's test is meant to accelerate what would happen if you were to have a deck penetration, such as for a chainplate, that develops a leak and is then exposed cycles of sun, rain, and salt water over a period of years.

  In the end, though, edges should be well-sealed, period.  No core material will perform properly forever if water is inside the skins.  Soft/heavy spots in foam cores are less common than in balsa cores, but they still happen just the same.

  Nidacore and Polycore both have great strength-to-weight ratios, and both do noticeably better than foam with respect to internal fractures in response to collisions.  Practical sailor did a test a year or two ago, and while impact could produce long internal cracks in the various foam core products, the honeycombs had very localized damage.

  Foam will be easier to shape, and will have other advantages.

  I'd pick a core material according to its weight, stiffness, response to impact, and easy of shaping.  Both foam and honeycomb will have their own advantages in each category.  The boiling immersion test wouldn't even earn a spot on my list.

       - Mike

Gardner Pomper wrote:

Hi,

I don't know if anyone is watching the KSS forums, but I got Derek to give a little more detail on the test he did where he sees water infiltration into honeycomb. It was a sample with unsealed edges, put in boiling water for a minute, the doused in cold (not ice) water. He immediately got water in 3/4 of the cells. He let it sit for a day, by which time all except 3-4 cells had water in them, meaning that water migrated between cells even after cooling.

This seems to be a test of what would happen if the skin was broken, or some cut (cleats, hatches, etc) was not sealed completely. If water does migrate in honeycomb, might we be better to restrict its use to the hull sides and maybe the bridgedeck, which does not get as much water exposure or hardware mounting?

Derek didn't specify a manufacturer he tested. I have a sample of Nidacore I am going to try this on. Maybe we could see if it is true of all the different varieties.

Any thoughts? Is this serious or just a reason to be extra careful sealing holes in the honeycomb?

Thanks,

- Gardner Pomper

York, PA