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Go Back   SailNet Community > On Board > Boat Review and Purchase Forum > old glass hull v. new glass hull
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Topic Review (Newest First)
10-30-2003 11:20 AM
sailingfool
old glass hull v. new glass hull

>>with the rebirth of sandwich core hulls
I''m not sure what rebirth you refer to. The big three sailboat manufacturers, Hunter, Catalina and Beneteau, have stayed with solid glass hulls. Given their expertise with cored construction in decks and the fact that cored laminate hulls could reduce their build costs (and boat weight), they must think all glass delivers benefits despite the cost (and weight).

Meanwhile over in the powerboat world where some volume builders have adopted cored hull construction, complaints and lawsuits about hull problems apparently abound. You heard it here, the class action lawsuit will show up soon...

I guess hull construction is one of the numerous choices we all make in deciding what boat is right for us, a buyer needs to understand the tradeoffs and then make an informed choice about the risks he/she is willing to take for what benefits..
10-30-2003 09:22 AM
Jeff_H
old glass hull v. new glass hull

With all due respect, I disagree with the statement "cored hulls ...are weak and do not resist impact as well as a heavy lay up." In a properly designed and constructed cored hull that simply is not the case.

In actual testing performed by the US Naval Academy (from a paper presented at the 2002 SNAME Chesapeake Bay Sailing Yacht Symposium), non-oriented fiber reinforcing fabrics were found to be the primary mode of failure in point impact situations. This paper outlined that Naval Academy cutters, which are used in training exercises, are subjected to frequent collisions, but the Academy cannot afford to take them out of usage for long repair periods. As a result, impact resistance was very critical. In order to test the impact resistance a large pendulum with a massive weight was constructed. On the leading edge of the pendulum was a steel replica of the bow and stem fitting of a Naval Academy cutter. Test panels were constructed that matched both known (prior cutter lay-up schedule and J-24 topsides) and conjectural hull panels. The panels were aged and then tested warm (some resins lose strength when warm). The tests consisted of retracting the pendulum with a forklift and then releasing the restraint cable. The results were very dramatic.

To begin with. Solid hulls did far worse than cored hulls. In examining the panels after the collisions, the failures almost always occurred in the non-direction material being used and not in the core materials. The test sample that faired best used an oriented glass laminate, NO non-oriented materials, vinylester resin, and a high-density foam core. The pendulum never entered the outer laminate and microscopic analysis further destructive testing showed that core was still fully adhered to the skin and that the deformation was within the elastic (memory) properties of the core.

Jeff
10-30-2003 07:36 AM
sailnaway
old glass hull v. new glass hull

All of the information here is on the mark from what I can see. Fiberglass also had a history of from good to not so good in the seventies when we had the gas chrisis. The formula for fiberglass changed to make up for the rising cost of the materials made with peteroleum and glass was not as good in say 1977 as it was in 1974. This I am sure is also a choice of quality made by the manufacture of diffrent boats and if they were willing to cut back on quality. I have found the glass in some boats to be mostly mat and not much on roving and cross ply materials. Mat is just a filler and really adds very little in strength but is also needed in some phases of the layup. Also boats that were laid up in wet climates have more problems than boats in dry climates for reasons that can be seen in the humidity levels affecting the laminates.Now with the rebirth of sandwich core hulls new and maybe better materials being used below the waterline a new set of problems arise from this process.I dont like cored hulls they are weak and do not resist impact as well as a heavy lay up. They may have a place in racing but then if you don''t find your self in that nitch why bother.
10-24-2003 07:20 PM
Jeff_H
old glass hull v. new glass hull

I see statements like "they didn''t always know how thick to make them so they were conservative." From talking to early fiberglass boat designers and from reading early fiberglass design texts, I think that early fiberglass boat designers understood the limitations of the fiberglass that they were working with quite well. While the udertood the material they did not understand how to over come its short comings. Dispite their heavy layups, I would not say that early fiberglass boats were all that conservative from an engineering standpoint.

To explain, even early fiberglass was quite strong but fiberglass is a very flexible materal. Because fiberglass is so much more dense than wood and so much less stiff than wood on a pound for pound basis, they could not achieve the stiffness of a wooden boat at anywhere near the weight of a wooden boat. Early designers also understood that fiberglass is a very fatigue prone material and so flexure would ultimately rob the laminate of much of its initial strength. In order to come close to the stiffness of a wooden boat, they built these early boats heavier than they needed to be strickly for bending strength. The irony is that these heavier hulls actually increased loadings and thereby stress on the hulls and were not all that effective in reducing flexure.

It is only in the 1970''s that designers began to realize that they could achieve stiffer lighter boats by using more sophisticated internal framing and through the more extensive use of cored components.

Jeff
10-24-2003 04:01 PM
pblais
old glass hull v. new glass hull

I would say a whole lot more is known about fibreglass and the assorted other asspects of building boats now vs. 20 years ago.

In your question you ask "everything being equal". It''s never that easy. There are a host of tradeoffs when comparing even two new boats. On any boat you need to know is the hull damaged, in poor condition or suffering any of a multitide of diseases.

Newer boats can have problems just as well as old boats. They all need a carefull examination by a surveyor.

I have an older boat with an excetionally thick hull. It''s heavy! Some old boats have very thick hulls and it''s not that they are "better" it''s more like they didn''t always know how thick to make them so they were conservative. I would not mind if it were lighter but there are a lot of other things I find desirable for the price I paid.

10-23-2003 07:20 AM
shmangasarian
old glass hull v. new glass hull

one would assume that over the last 30 years or so there have been changes/improvements in the methods and materials used in laying up fiberglass hulls. Inasmuch as there are numerous opinions about quality of construction
(Beneteau vs. Hylas for instance) are there less subjective criterea for judging whether one should buy newer over older (everything else being equal - rigging, power plant etc.). In other words, have the chemical and/or physical properties of fiberglass and how it is used to build boats changed dramatically since 1980 or so. Thanks in advance.

 
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