I don't think the test is particularly scientific, but I would be interested to try it myself, although I don't think that boiling the water is quite correct. I would use steaming hot, but not boiling. I think I will also immerse a piece of honeycomb in room temp water for a week to see what that does.
I think your explanation of why the water migrates in this test is probably correct. The question is how susceptible is the honeycomb compared to balsa, for example. Water migration is not an all or nothing thing. That is why I am looking for feedback from people who know more than me about it.
Btw, Derek says that this is the test he uses on all his core materials, so apparently the foams he uses pass that test.
You also did not mention the biggest factor for me.. the price of honeycomb vs foam. From what I see, honeycomb is about 1/4 the price, and since the core is the most expensive material in the boat, that make a HUGE difference in the materials cost.
I don't see Dereks test ruling out honeycomb, the way he does, but it does raise questions for me about whether I should use it everywhere. I have already been thinking that it might be good to use a flexible airex foam for the keel sections where the big flat panel needs to bend, with honeycomb for the hull topsides. Now I am wondering if maybe I should use foam on some or all of the decks, like where the various cleats are mounted, just in case.
- Gardner
On Thu, Feb 5, 2009 at 8:23 AM, Mike Crawford <jmichael@...> wrote:
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?
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 ...
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...
Hi, I don't think the test is particularly scientific, but I would be interested to try it myself, although I don't think that boiling the water is quite ...
That sounds like a good compromise. Use each material where its strengths will matter the most. Since I won't be making my own hulls, I don't care about the ...
Oh, and while this may be redundant for most on the group, I thought I'd add a comment on sealing techniques for anyone who hasn't been using them. There are...
Hi, I am also drifting a little from the topic, but how do you join full sheets of honeycomb when making a big panel? Do you route out the edges and epoxy in a...
-I have been thinking of that also. Whatever you do will make some kind of discontinuity. I would simply butt them up possibly with hot glue providing you have...
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