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Cored or NOT cored?????

4K views 19 replies 11 participants last post by  sailingdog 
#1 ·
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.
 
#2 ·
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.
 
#3 ·
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.

Jeff
 
#4 ·
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 fiberglass...as 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. So...to 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:
Bavaria
Beneteau
Catalina
Hunter
Jeanneau
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.

Jack
 
#5 ·
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.
 
#6 ·
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
 
#7 ·
geohan,

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!
 
#8 ·
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:

http://sailingsource.com/dufour/readingroom/injection_mold.php
 
#9 ·
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
 
#10 ·
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.

Regards
Jeff
 
#11 ·
WOW!! I like all the discussion on this subject. I guess I was really thinking about the older boats in the late 70s to about the late 80s as far as building materials concerning fiberglass lay-ups. I know I will probably never be able to buy a new 36 to 42 foot boat, brand new, for 300K, so I would want my used boat to be as trouble free as possible concerning spongy cores and osmosis problems. If I was buying a late model boat (or a new one) I would most surely want something like a SCRIMP process as its done at TPI for J Boats or the system they now use at Tartan/C&C, and kevlar sounds like a great idea also.
 
#12 ·
The early 1970''s through early 1980''s was the worst period for glass work. The resins during this period went through a redesign and were brittle and blister prone. Manufacturers and designers alike had begun to lighten boats but most had not yet learned how to properly engineer these lighter craft. Better fabric and fabric handling techniques were becoming known, but most big manufacturers were still doing things the bad old way, lots of roving and non-directional fabrics, folding the cut fabric for storage, large volume useage of accellerators, manual resin mixing techniques, and so on.

Jeff
 
#13 ·
I hate to bring up amature methods, as I know that alot of amatures screw up perfectly good materials in the first place, but what about C-Flex planking? It''s lighter than conventional glassed hulls of similar thickness and is composed of unidirectional fibers properly infuesed, so in theory (and according to it''s fans) it should have most of the plusses with a bit less weight, and easy to use (as any boat building is "easy" ;)) for amature construction without need of any mold at all.

So... What''s horribly wrong with that picture that I missed? I''m sure there''s something, but for the life of me, I cant put my finger on it.

-- James
 
#14 ·
I am not sure where you came up with the idea that Cflex is lighter than conventional construction. Cflex generally ends up being significantly heavier and not as strong because of the large amount of fillers required to fair the hull. Voids at the rods are fairly common as well.

Cflex is but one approach to constructing a one off fiberglass hull but there are much easier and lighter ways to go. Fairing a CFlex hull is a real bear. While the stiffening rods are pultruded fiberglass, the actual fabric is wet out just like any hand laid up hull except that Cflex makes vaccuum bagging nearly imposible.

Is that what you could not put your finger on?

Jeff
 
#15 ·
Thanks for the information Jeff. I just got done reading "The Worlds Best Sailboats" The first book and then the 2nd volume. Ferenc Mate is the author who went around to some of the best Sailboat yards in the World in the late 80s and again in the early 2000s and wrote some pretty interesting info about how each individual yard produced and engineered their yachts. All the things you have been saying about the subject of laminating hulls has been discussed in His books and you seem to know alot about the subject. Thanks. Also I was wondering if you wouldn''t mind doing a little boat reveiw on some of the various yachts you are familure with and have sailed in the past years. It seems like it would be infomative to get reveiws from not only you but others also who own particular models of boats and can share there pros and cons on there experiances with different models of boats.. Just a thought. Later
 
#16 ·
I have owned over a dozen boats in my life and my family members have owned dozens more. Over the years I have sailed on, raced on, coached on, commissioned, done repairs or consulted on repairs on, rented, and delivered probably something between fity and a hundred different model boats. I try to provide commentary based on my experience on these boats but to write a list and analysis of each would be a full time job for a while. I already have one those running my architectural firm. 8^)

Regards,
Jeff
 
#17 ·
Look into Tartan and C&C Yachts. They are both built by Fairport Yachts in Ohio.

I strongly suggest you arrange a tour to see how these boats are built with Epoxy Hulls. They are lighter and stronger than any Glass boat. Each boat is assigned one team of craftsman who build and supervise all aspects of a specific hull number from start to finish.

I am sure that at some point in the future, other manufacturers will follow Fairport with the epoxy Hull and carbon fiber spars. I don''t own either C&C or Tartan but perhaps someday will be be a pround owner of a Tartan 4100!!
 
#18 ·
Paul:

A couple of quick clarificaction points here:

-"They are lighter and stronger than any Glass boat."
Actually C&C''s and Tartans are glass boats, they just happen to use epoxy resin. While I love epoxy resin for many applications, Vinylester resins (as used in military and motorcycle helmets) actually produces a higher strength and more impact resistant laminate.

"Each boat is assigned one team of craftsman who build and supervise all aspects of a specific hull number from start to finish." That is how most Oriental boats were built in the early 1980''s and it is no guarentee of a high quality product. In fact having laminating specialists do the hull and carpentry specialists do the interior and electrician specialists do the wiring, and etc. generally results in a better quality overall at a lower price.

Hopefully, someday Tartan and C&C will follow the current ''best practice'' and go to Kevlar/ E-glass laminates with vinylester resins and eschew using non-directional fabrics. Then they really will have the are lightest, strongest, most durable boats for a lot less money.

Don''t believe everything that you believe in Tartan/C&C ads. 8^)

Respectfully,
Jeff
 
#19 ·
Kevlar in boats

This is an old thread and I am new to this forum (in fact it is my first post) but I believe that I have something of credibile interest that could be added here. To the non-technical this post will be tedious and boring!!!!

I recently retired from an "advanced composites" business and I am seriously considering the pruchase of a boat. In my business I used Kevlar (and Twaron) for several balistic applications and I used fiberglass a lot (I always spelled it that way)! I even used carbon fiber in many applications (in fact my spelling is generally bad and I rarely use spell check for blogs).

When it comes to boats I believe it is important that one considers carefully blending advanced materials like Kevlar and Twaron (aramid) and Carbon fibers with fiberglass and resins. From a physics and applications perspective one has to be particularly concerned about the aramid group of fibers.

These fibers typically have a wetting characteristic that repels the resin that is trying to bond to the fibers (it is of little consequence whether it is vacuum bagged or laid up by hand/this is a matter of physics/surface energy) . Sort of like oil and water! There will be those of U that may choose to challenge me on this one but I suggest that U tell that one of the larges aircraft manufacturers in the world that had to replace the leading wing edges of a popular model that they made with aramid fibers and resins to cleverly survive abrasive and impact failures in this area encountered on runways (they replaced them).

The leading edges of the wings failed from freeze-thaw cycling of absorbed moisture (not abrasion or impacts) and much sooner than their life expectancy. Simply stated water expands and contracts as it freezes and thaws. It turns out that the fibers repelled the resins during vacuum bagging (physics relating to surface tension mechanisms) and as the resins shrank on curing they pulled away minutely from the fibers. The resulting emply space provided a capillary space for moisture ingression at an atomic level. The freeze-thaw cycle thereafter can be a very destructive process (and was) to composites as the aircraft manufacturer discovered. Water expands when it freezes. This is a huge force. It can split steel barrels!! Resins and plastics have relativly little strength.

Aircraft parts experience multiple freeze-thaw cycles during take offs and landings. The effect was that the aramid fibers delaminated from the matrix. The laminate puffed up (a bit like pop corn) and took on more moisture (compounding the problem) and resulted in laminate failures.

I believe that some waterlines on boats experience this same cycling but at a slower pace albeit that there is more water present for obvious reasons (certainly not when the boats are parked where freezing never occurs). I would be very mindful of this potential problem in boats if re-inforced with aramid fibers!!! IMHO they will not be as strong as intended in a few years as they were engineered and tested to be when constructed!

Aramid and carbon also have another characteristic about them that is purely physics (that is to say that clever design cannot outsmart Einstein completly)! This is called CTE (coefficient of thermal expansion). Fiberglass is a very elastic material (sort of a perfect spring) - (it also intimately wets out and can bond elemently with the resins with no separation space (elemental or otherwise) between resin and fiber). Carbon and aramid are very strong and rigid when compared to the reisn that they are embeded in. In plain english these fibers have a relatively neutral CTE - close to 0 - (effectivley they do not expand and contract in a meaniningful way when compared to resins and fiberglass). What does this mean??

They can add a lot of stress to the internal matrix (the resin to fiber bond/if there is one at all) when compare to fiberglass when variable temperatures are encountered. This is probably not a huge effect in boats but internal stresses in the laminate do take away from the ultimate strength of the laminate during temperature fluctuations.

Polyester and vinylester resins shrink while they cure to varing degrees but the fibers do not. Epoxy, on the other hand, expands while curing and shrinks during the cool down after cure (the shrinkage is small and has very little effect because the bonds with the fibers are formed during the expansion pahase of the cure cycle. The effect is that epoxy bonds very well to the glass fibers (and other fibers as well) when compared to polyester and vinyl ester. The expansion of the epoxy during cure forces the resin at a molecular level into the fibers (in a mechanical way) such that it produces physical properties substantially greater (upon cure) than most other resins by far!

Finally carbon fibers are a galvanic material. That is to say that they contribute to galvanic corrosion. Most boaters already know a lot about galvanic corrosion so I won't embarrass myself by attempting a technical description of the pitfalls of such.

Coming back to aramid fibers in my summary I would personally be cautious. I do like their impact characteristis and their outstanding resistance to penetration failure. I simply don't know if they bring a bigger problem than they solve with them. The galvanic corrosion properties of carbon fibers can be engineered around but when it comes to aramid pure physics is a more dominant player that cannot easily be engineered around!
 
#20 ·
Coldandhardy-

Thank you for your post. Although it may be a bit more technical than most of the users would appreciate, I am glad you posted it. If someone were looking to reinforce a fiberglass hull for additional abrasion and impact resistance, what fiber would you recommend be used? I've been looking at using some of the UHMW PE fibers for doing such a thing, and wanted your feedback on it.
 
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