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john232 01-05-2004 10:46 PM

Cored or NOT cored?????
Which is better in your opinion....
1)Cored hull and cored deck?
2) Cored deck but all glass hull?
3)Cored hull only above the water line with a cored deck?
4)Cored hull above waterline and all glass deck?
5) All glass all the way?
6)Glass deck with cored hull?

I think I covered most of the different ways you can get a boat built with fiberglass. feel free to add other varied ways that you desire. This is just to see how people differ in there ideas of the perfect built boat. Also explain if you think the size of the sailboat would determine your picks. John.

john232 01-05-2004 10:56 PM

Cored or NOT cored?????
I prefer an all glass deck because I seem to here alot of horror stories about deck corings rotting, leaking, and idiots adding hardware to them and causing major problems later on down the road. My hull pick would be cored only above the waterline because I worry about de lamination and osmosis/blisters, but want coreing for insulating and noise reduction above the waterline. any Sailboat under 32 feet I would like an all glass boat because I am not concerned about weight as much with a smaller boat.

Jeff_H 01-06-2004 03:18 AM

Cored or NOT cored?????
To begin with, whether a hull is cored or not tells you far less about a boat''s strength and durability than how that boat is framed. You are also ignoring the choices of building materials and methods. For example there are huge differences in strength and durability between a thatis vaccuum bagged and laid up with vinylester resin, no non-directional fabrics, a moderate to high density foam core and a boat laid up in polyester resin, high non-directional cloth ratio with or without a glued core. But to answer your question;

I strongly prefer a cored deck but especially on smaller cruising boats. On boats under 40 feet the design loads are determined by the weight of people walking and jumping around on the deck and the framing spacing is very similar between a large boat and a small boat. As a result the deck lay-up schedule does not vary much between a 20 footer and a 40 footer. In either case, to achieve the necessary stiffness, a glass deck without coring would weigh over double what a cored deck would weigh. This is not the end of the world on a 40 or larger footer where it would represent perhaps a 5% increase in the weight of the boat but on a small cruiser this can add 15% or more percent to the weight and since small boats are much more weight sensitive to begin with and have a harder time carrying sufficient stores etc.,on a small boat a deck without coring would be a really bad idea.

If durability is a concern, the ideal solution is a cored deck constructed using vinylester resin and no non-directional or cut fiber reinforcing with a moderate to high density closed cell foam core. While a moderate to high density closed cell foam adds cost and is roughly 10%-15% heavier than Balsa (adding something in the neighborhood of 1% to the weight of the boat), it is inert and can withstand the presence of water without delaminating. In long term and impact testing this has generally proven to be the most durable and impact resistant construction form of fiberglass construction.

As to hulls, I strongly prefer a similar construction to that described above, (i.e. vinylester resin and no non-directional or cut fiber reinforcing with a moderate to high density closed cell foam core) that comes with some caviats. Areas of the bilge and along the centerline, areas near the keel and support, areas where thru-hulls and rigging hardware pierce the hull, the core should be left out and these areas have a extra layers of laminate built up. This should be done by tapering the core at the edge of the un-cored area so that the inner skin can be directed bonded to the shell skin, and then the area is further built up with additional tapered laminates.

If I were designing a boat for durability and strength I would add kevlar to the outer skin. In testing, vinylester resin and no non-directional or cut fiber reinforcing with a moderate to high density closed cell foam core proved to have a much greater impact resistance than any of the materials tested (including an uncored hull). Adding kevlar to the outer skin greatly added to the localized impact resistance.

Another issue is how the hullis laid up. Vaccuming the hull during ly-up produces a denser, stronger, more durable, and lighter layup. Vaccuuming the core and adhering the core with a higher strength, lower permiability resin like vinylester greatky increases the likelihood of a trouble free hull.

More important than whether the hull is cored or not is how it is framed. Ideally any FRP boat has a series of closely spaced longitudinal and athwartship frames supporting the skin. This has a far greater impact on the durability and strength of the boat than whether it is cored or not.


WHOOSH 01-06-2004 06:43 AM

Cored or NOT cored?????
Jeff, I''ll admit to a small secret. I saw the post explaining a preference for a solid fiberglass deck on a smaller boat, winced a bit, and then decided to wait for your reply...''cause I just knew it was coming and also knew you''d do a better job than I could at correcting the misunderstanding.

In fact, your answer was so thorough I''d like to pose a follow-up question based on its content. I think you are generally referring to chopped strand mat when you carefully denote "non-directional or cut fiber reinforcing". For folks not familiar with boat building, some builders use a vacuum- or pump-fed gun that sucks up supplies of resin and chopped strands of fiberglass (one would hope, in the right ratio!) as they are building up large areas of e.g. when they are building the hull of your boat. This is a quick, not labor intensive method to build up laminate thickness but it results in a weaker glass-resin matrix. sum up: using "non-directional or cut fiber reinforcing " is not, when generally speaking about the major components of a glass boat, good news for the owner/buyer, relatively speaking. (Hope I qualified that sufficiently. They used chopped strand mat when buiding the shower stall for my boat, and I don''t have any gripes about it!)

Jeff, my question is based on the hope that you might be familiar with the ever-popular, relentlessly-reviewed, high-volume boat builders most often discussed on this BB (and others) - let''s include the following altho'' please add those I''ve missed:
Specifically WRT the hull lay-ups, do you happen to know which of these builders use "non-directional or cut fiber reinforcing " in building their boats'' hulls? Knowing would be one basic, helpful data point for folks shopping for their next boat, I would think...even tho'' it''s a complicated, complex equation that produces an end product we call a boat.

BTW based on my limited experience, I surely do agree with your comments about closed cell foam as a preferred core material on decks. I notice it being a favorite of northern European builders and I assume it''s partially because of its insulating benefits. Were I a Northwest, Great Lakes or Northeast sailor, that would rank relatively high on my list of preferred boat characteristics.


Fishboat 01-06-2004 08:04 AM

Cored or NOT cored?????
Good question. I think another thing that should be tossed into the choice decision is whether the choice is relative to a new boat or a used (maybe 10-12 years) boat.

With a new boat that will likely be sold in 3-5 years I''d lean more toward coring in any area where it''s beneficial to what I want from the boat in terms of performance, comfort, quality... If the boat is new(and from a reputable builder) then it should be fine & after it''s sold it''s no longer a concern for me.

With an older boat, from a time when closed cell coring maybe wasn''t used as much as balsa & plywood, my choice with regard to coring would be much more conservative. In that case I''d go with an all glass hull and accept (with a rigorous survey) that the deck will be cored with balsa or plywood as (I think) most were.

As always, Jeff''s comments regarding how the boat was built are right on, but on an older boat, even though it was built perfectly, you can never rule out the previous owner punching unsealed holes or not maintaining the ones that existed originally.

geohan 01-06-2004 08:53 AM

Cored or NOT cored?????
Jeff H.: I certainly appreciate your posts and must say you?ve tweaked our interest in the Laser 28 that you are so fond of. By way of introduction, we are 76 years old, have been sailing on Puget Sound for the last 38 years, and managed a second and a third plus 5 firsts out of the 7 club races last fall, in a slow (PHRF 235) boat. However we are getting weary of short tacking the 420 sq ft genoa with the sheet strumming like a bass viol. (Hopefully this shameful brag helps set the stage, if not we?ll just have to claim senior privilege <grin>). In light air we do fairly well (I?m a great fan of Frank Bethwaite?s ?High Performance Sailing?, especially the micro-meteorology portions), but when the wind pipes up over 15 knots the two of us can no longer really manage the 30-foot, 9800# boat competitively. Hence, the attraction of the Laser 28 as you have described it, particularly the easily driven hull and the ability to stand up to a blow. When cruising, we occasionally cross the Straits of Juan de Fuca and too often get caught in the ebb current against a fresh westerly. Confidence in the boat?s integrity is a must! We don?t mind the rail dipping if it must, but we don?t want it to stay there.

You have mentioned its superior construction features, but that the boat requires considerable skipper skill. Was this in regard to getting the most out of the boat in competitive performance or to insure safety in challenging conditions? Also will the boat heave to and behave itself? And lastly, will hull strength allow it stand, laterally secured, on its keel against a seawall for bottom maintenance without ''oil caning''?

Thanks for any opinion and Happy New Year, George

Stede 01-06-2004 09:35 AM

Cored or NOT cored?????

I can''t answer your questions concerning the Laser, but I just wanted to let you know that I appreciated your post. Wow! 76 years young, and still going strong! You certainly deserve the right to claim "senior privilege" for bragging rights! To a "youngster" (46 yrs.old) like me, your post is encouraging.As I get closer to retirement, I sometimes wonder how long I''ll be able to sail after I retire.I look forward to a long "close reach" as you all are doing. Fair winds to you!

Sailor-man 01-06-2004 01:04 PM

Cored or NOT cored?????
Does anyone have any opinions on the Injection Molding Process Dufour Yachts is using on their new Performance 34, 40 and 44 boats? They claim a weight savings of 30% with better structural strength as a result of better resin saturation. Are any other builders using these techniques?

Refer the following:

Jeff_H 01-06-2004 03:33 PM

Cored or NOT cored?????
I think that a lot of the better builders (and some high production companies like Beneteau and I believe Hunter) have gone to infusion molding. (I believe that the ''I'' in J-Boats ''SCRIMP'' system is for infusion.) This technique has been around for a long time and has been used in all kinds of industrial applications. (Subway seats for example.) My former boat (a Laser 28) was constructed this way and so had almost no liners.

It is a very good method of laying up a hull or deck with a proper resin/fiber ratio. It really is an excellent way to go. It allows more exotic laminates such as kevlar to be incorporated more easy. Properly done it eliminates a lot of labor and results in a boat that does not need liners.

The down side is that it is a comparatively expensive process. The molds are expensive to build since they need to withstand being pressurized. Precision alignment of the parts requires more expensive quality control. Infusion actually uses more resin but less of it ends up in the boat.

Many companies have gone to infusion molding for environmental and worker safety reasons.


Jeff_H 01-06-2004 04:30 PM

Cored or NOT cored?????
Sorry, I missed the other items in this thread. For Jack, in using the term "non-directional cut fiber reinforcing", I meant both mat and chopper gun applied laminates. I have mentioned before the research project performed at the U.S. Naval Academy on fiberglss composites, and in particular the component that addressed impact resistance. One of the most significant findings in the course of the study of impact and impact resistance in FRP was that non-directional fabrics (in the NA study they used mat) dramatically decreased the impact resistance of the laminate and served at the failure zones in almost all cases. Other earlier studies found similar results in studying fatique in FRP.

The bad news is that virtually all boat builders use some amount of non-directional fabrics. In the best cases it is only present in the form of a ''veil coat'' below the gelcoat to minimize print through. Most production hand laid up boats still use mat as a ''bridge laminate'' to level out and bridge between the uneven surface layers of roving. One of the reasons that older 1960''s and 1970''s era laminates were found to be more brittle and fatigue prone than modern laminates is that very large percentages of the layup which were non-directional materials, generally in the form of mat.

As to the Laser 28, I really loved my boat, but I felt that it required a little more skill to handle than a more heavily ballasted and perhaps lower SA/D boat might have required. We generally cruised with a 105% lapper which was a great sail, easy to tack and quite versatile in winds from maybe 3 knots to up to 20 knots. I kept my boat rigged for both a single and double reef lead back to the cockpit (two line reefing)and when cruising would typically at least use the single reef as winds approached teh high teens or so. Over 20 knots the boat was most happy with small 90% blade and eventually a second reef.

The boat gave you a lot of tools to deal with changing conditions, all from the cockpit and most from the helm. The boat would hove to under bare poles and generally under sail as well although oddly enough there were times when I could not get her to stay hoved to (but I also occasionally encountered that same thing with the 1939 full keeled Stadel cutter that I owned in the 1970''s). All of that said, in hindsight I think that the boat required a certain level of athleticism. My father and stepmother recently sailed with me on my current boat, (He''s 76 or 77 or so also and in very good shape). We were thrashing to windward in gusts in the mid-twenty knots range and a pretty steep chop. The boat and I were loving life.

After a while my father volunteered that "He and Betty (my stepmother) generally do not experience that kind of vigorous sail very often." When I stopped and thought about it it was a pretty good work out to drive into a chop at the speeds we were moving. I think that I tend not to be all that aware of the amount of sail trimming and effort that I expend pushing a boat. It is only when someone else comes along and comments that I realize that I am playing things as much as I do. I don''t know how else to explain my comment that these are pretty athletic boats to sail.


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