Airex Cored Decks
My husband and I recently looked at a 1983 Kelly Peterson 46. According to the old brochure, it has an Airex cored deck. Originally, an Airex core seemed a real advantage over a balsa or plywood core, since foam doesn't rot. However, doing a little research, I've seen a couple of negative comments that said that Airex can get spongy in hot climates. Furthermore, it's not clear to me that "spongy" foam would ever really return to its original strength. Anybody got any experience and/or knowledge of Airex cored decks they'd care to share?
Airex core is pretty good stuff. It is relativly good at NOT absorbing water (it is not completley water tite however). The same procedures for examining balsa core can be applied to airex core. IE: whacking the snot out of the laminate with a rubber mallet to find delamination. This ia a good job for a competent marine surveyor.
I have not seen heat related softening due to high temps and I have seen a number of vessels return for the south Pacific. This doesnt mean this can't happen. I have seen delamination due to impact stress in airex cored hulls, and rarely (but have seen it) seen water intrusion making the hul spongy.
I have not heard of any major deck problems endemic to the KP 46. This vessel was built at the queen long yard and was a serious upgrade from the origional 44. If I recall correctly the 83 was one of the early 46's built.
If you really are considering the vessel, get someone heavy to walk around on the deck, if you don't notice any springy spots the vessel (other than other obvious problems) would be worth a survey.
The KP 46 sails very well indeed and you should find it a comfortable craft. The joiner work from the queen long yard really sets it apart from the earlier 44 and the streched 44 (Spindrift 46).
Most of the Ureathane-foams can lose significant amounts of strength when they heat up...however, as far as I recall, the strength loss is not permanent—however the deformation may be. I would highly recommend that you paint any foam-cored boat a light color, as most of the foam lose strength at temperatures far lower than end grain balsa, which is still IMHO a superior core material.
Foam as a core material has some strong disadvantages over end-grain balsa. Water tends to migrate along foam cores relatively easily, plywood cores have the same problem. Balsa cores tend to resist water migration. Foam can also have bonding issues with the laminates on either side, as the foam does not wick the resin and create a strong bond, as does end-grain balsa. Also, most foam core materials have a much lower shear resistance than end-grain balsa. Lastly, most of the foam core materials have a much lower deformation temperature than end-grain balsa.
I have been on boats with foam-cored decks, where there were foot prints left in the glass when the glass was very hot from exposure to the sun and then walked on by a very large crew member. This boat was a fairly dark navy blue however. I don't know if the same thing would happen to a white boat under the same circumstances.
Plywood is an inferior core material as it does not have the advantages of either balsa or foam. It wicks water along the core, can have the bond formation problems of foam, and is significantly heavier than either. However, it is an excellent core material for areas under heavy loads, as it resists compression loads and shearing loads far better than either the foams or balsa.
However, the foam cored boats have a few significant advantages over balsa-cored boats. One, they're usually lighter. Two, foam cores resist rot. Three, in some cases, the foam core materials can be cheaper than balsa.
Thanks to Dewey and sailingdog for the prompt and informative replies.
Dewey- Unfortunately, we liked the KP46 very much. I say "unfortunately", because it is significantly more $$$ than we want to spend. (Silly us, we had to go look.) I'm also concerned about the draft, which I'm sure works just fine in the deep Pacific, but we're more interested in the Atlantic. It's all about compromises, of course. What's one more year of work?:-)
sailingdog - Did this boat with the footprints have a navy blue deck or just the hull? Was it unusually hot weather, or a standard island sunny day?
Thanks for your time and thoughts.
The deck and topsides were navy blue. It was pretty brutal weather, about 98 degrees and very sunny, and had been for about a week or so when the foot prints happened. The crew member in question is about 300 lbs. and 6' 5" or so, and was carrying a 100 liter cooler at the time. However, I don't believe the boat was cored with Airex specifically. I do know it was cored with foam though, as I had been working on installing a new winch earlier in the week.
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