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Old 10-24-2004, 08:23 PM
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kes
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Default balsa core

What is balse core? is it bad to use in certain areas of boats? thanks for you help
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Old 10-24-2004, 09:00 PM
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Default RE: balsa core

Balsa is a type of wood. Core is a filler used to add strength. Think of a boat with a cored hull or deck like a sandwich. The fiberglass is the bread and the core material is the baloney. Core is fine as long as it doesn't get wet. If it gets wet (from a fitting that wasn't installed correctly) then it can delaminate and rot. Hope this helps.
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Old 10-24-2004, 09:02 PM
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Default RE: balsa core

Balsa core is Balsa wood sandwiched on each side with fiberglass. It reduces weight, may help keep down vibration and often rots from water intrusion.

Hatteras made balsa cored 41's in 1986 (below water line) and most failed and they changed the manufacture of these. Balsa is O.K. in hull sides and decks, etc. but, in my experience, poor for hulls below waterline.

The failure mode is for water intrusion to turn the balsa into mush and then you have air and mush sandwiched with glass, hit something and it squishes.
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Old 10-24-2004, 10:24 PM
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Default RE: balsa core

Sea Ray's use of balso*has been in the boating news quite a bit lately.* Check out Powerboat Reports findings, etc.* I don't think others will follow.
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Old 10-25-2004, 01:51 AM
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Default RE: balsa core

IMPO there absolutely nothing wrong with boat builders using balsa below the water line - balsa gets a bad wrap. The problem of rot isn't the balsa's fault, it's the fault of the glass work around the balsa. If the glass work sealed in the balsa properly in the first place, the balsa would never get wet = never a problem. IMO if the balsa or any other hardwood gets wet, rot is inevitable - fix the surrounding glass work and balsa is a great material to use.
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Old 10-25-2004, 04:47 AM
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Default RE: balsa core

As Garrett said, the fiberglass work around the balsa is what causes the problems initially.The only real way to solve that is to quit taking the cheap and lighter way out and just use solid fiberglass on the hull. That's what you bought, a fiberglass boat, that is what it should be made of.
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Old 10-25-2004, 06:56 AM
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Default RE: balsa core


Balsa make for a very strong but light hull. The strength makes it seaworth and its light weight makes it more fuel efficient, thats why boat builders have used it. You are correct that the glass work must be done properly, and since thru-hulls are major source of water intrusion, the boat builder should have built-in bottom areas with no balsa for the thru-hulls. If I looked at a balsa core hull and the thru-hulls were installed thru the basa, I would not buy that boat.

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Old 10-25-2004, 08:04 AM
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Default RE: balsa core

I agree with all of the above comments, and to summarize, balsa is as good a core material as any of the space age composits if used properly. Putting it below the waterline, is risky, and only time says it was done right. If you are gonna buy a cored hull either it needed a very good hand laid job, or proper vacum bagging to ensure the resin gets all the way*into the core and glass. My preference is to avoid coring in the bottom (wet surface) all together. I've got 2 things to add,*the first of which*I learned from reading Pascoe:



1)* While rot is a problem, Pascoe states the biggest problem with any type of coring/cored hull is that once water gets in between the glass and the core on a surface that regularly flexes (all do to varying degrees), the core disintegrates from pressure (like a constant diaphram pump action)*rather than rot.

2) "Strength" is a tricky word.*Sharp impact**resistance, shock dissipation, torsional rigidity, tensile strength,* compression resistence...are all different types of strength. If you want to talk about strenghth to weight ratio, then you need to talk about what kind of strength. Depends on the stimulus. A cored hull will be lighter, and very rigid, and dissipate shock better (if done right w/ glass designed to let shock travel and dissipate correctly), but impact resistance, is not a core strength which is another reason to avoid it in the running surface. Also, lighter is NOT always better, especially in an offshore hull.



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Old 10-25-2004, 11:00 AM
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Default RE: balsa core

You can have just as big a problem above or below the water line if the holes are not sealed properly. Delamination can also happen to your deck and cause it to feel spongy over time.

Bruno and Stillman built beautiful down east fishing boats but gave balsa core a bad name. They used bedding compound to seal fittings. Commercial fisherman don't baby their boats and some of them developed serious delamination problems. B&S was sued and eventually went out of business.

Balsa core has the highest strength to weight ratio of all the core materials. It is an excellent material to use but you have to be especially careful of fittings, like thru hull transducers, installed by someone other then the builder.

I have a balsa cored hull and it had some leakage due to my installation inexperience. The problem is that a little water will get into the core. Water does not go across the grain but under it like a spider web. The web gets bigger every time the water freezes and expands the gap between the fiberglass and the core. I had to cut out sections around the rudder, strut bolts and aft stern rails. The rotten core was removed from the inside and replaced. All the new holes were oversized and filled with epoxy/high stength filler and glass strands before redrilling. This can be a major project unless you have access from the inside.

Most fiberglass repair books have a section on fixing delamination with epoxy resin.

Best insurance is to get a good marine surveyor who knows how to check for moisture and buy the WEST book on fiberglass repair so you know how to install anything which requires a drilled hole.

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Old 10-25-2004, 11:27 AM
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Default RE: balsa core

Water freezes in and around boats? I haven't seen that down here!

Balsa as used in the boat building industry is layed up with the grain on end, so water doesn't migrate very far in a puncture incident, but it can travel along a bad laminate between the wood and the glass, then down the grain. So, if the laminate is done properly and doesn't fail, balsa is great for a hull stiffener. Lots of racing sailboats use balsa for that reason and the weight savings. They can put the extra weight in the keel and still have a stiff light boat. It is not as important in an offshore boat that needs weight to punch through a head sea.
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Old 10-25-2004, 11:48 AM
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Default RE: balsa core

I am not so sure that I would own one, but I do know of a couple of old B/S hulls from the 1970's and early 1980's that are still going very strong.
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Old 10-25-2004, 12:51 PM
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Default RE: balsa core

Top yachts such as Viking, as does Tiara, and Pursuit use blasa above the waterline. These three limit the balsa coring to the hull sides and decks. The key is to seal the end grain of every hole and thru hull, using epoxy resin.
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Old 10-25-2004, 04:19 PM
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Default RE: balsa core

There's an article - "Cored Hull Bottoms" - on David Pascoe's website.
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Old 10-25-2004, 04:46 PM
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Default RE: balsa core

Viking is using balsa in their bottoms on certain models from an ad I read a few years ago. Like many have said, if done properly and maintained properly, it is an excellent building material. Vacuum bagging should be considered manditory for cored layup to ensure full bonding. The hull at all thruhull locations must be decored, making it a solid hull at those points. Also, not all cored hulls are lighter than the comparable solid glass hull. Many times the same amount of glass is used, but cored construction is employed to yield a stiffer hull.
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Old 10-25-2004, 06:51 PM
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Default RE: balsa core

thanks for the help. great site for information.
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Old 10-25-2004, 07:06 PM
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Default RE: balsa core

Quote:
Eric S - 10/25/2004 5:46 PM ... Also, not all cored hulls are lighter than the comparable solid glass hull. Many times the same amount of glass is used, but cored construction is employed to yield a stiffer hull.


Most boat Mfgrs, that bother to mention that a hull is cored, market it as a lighter, better, more fuel efficient boat. For the same thickness, a cored hull will be lighter, and it is probably be stiffer, and may or may not be better. Coring doesn't require the same amount of resin for bonding, as*does a*comparable thickness of soaked glass layers. I think the resin is the majority of the weight vs. the glass. In comparing 2 identical hulls, it is probably more the exception than the rule that the cored boat would use the same amount of glass as its all glass predecessor/competitor.

Does it*save the Mfgr's money (materials or labor), or time in the mold etc. to build a cored boat instead of a solid glass boat? When is coring mandatory for the function/design of a boat?
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Old 10-25-2004, 08:21 PM
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Default RE: balsa core

Laying up a cored hull is definitely more labor, and more costly in materials compared to a solid glass hull. In my particular boat, the manufacturer doesn't have a molded grid system, so with just longitudenal stingers and bulkheads, the coring is very effective in making the hull stiffer. I don't think coring is as useful if there is a molded grid system that can be bonded in, or if the builder spends the time to glass in a grid.
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Old 10-26-2004, 06:22 AM
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Default RE: balsa core

I agree that a tight structural grid will make a hull stiffer, as less surface area goes unsupported, but I don't think you mean to say that a stringer/bulkhead boat should be cored, and only grid boats should be without coring. Stiffness can be built into an all glass hull in many ways: thicker glass, and well thought out stringer and bulkhead placement and attatchment. It usually will make it heavier, but like I said in an offshore boat weight is not*usually a bad thing if its balanced right.

Despite what you*said about the coring materials costing more, and the labor being more, I don't have any evidence to support this, but I would*guess that some,*not all,*cored boats are made that way because of some advantage the Mfgr gets, rather than the consumer: cost, materials, labor, time in mold, less defects, etc.. I would think that coring becomes a requirement when the hull is too big to have as much structural stuff and stiffness to make it solid without it weighing too much. I also think that a heavy solid bottom and cored sides*helps*to lower the center of gravity a little*which is an advantage especially on smaller boats.
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Old 10-26-2004, 07:56 AM
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Default RE: balsa core

is it cheaper to go with balso core or a solid fiberglass hull. what percentage savings are there with going with balsa core. thanks for the help.
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Old 10-26-2004, 09:21 AM
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Default RE: balsa core

Whether or not to have a cored hull, and what coring to use depends on who is building your hull, how the hull layup/stringer/bulkhead system is designed, how that particular builder does things. Most production boats don't give you options, they just build them how they build them. I'm not sure about mass produced boats, but on most all hand laid hulls, if available, coring is an option that costs extra. My experience is with the lobsterboat hulls from Maine. If you look at pricing sheets or pricing on websites like Wesmac's website, you'll see that coring is an added cost. Coring a hull by hand definitely adds significant labor especially when done properly by vacuum bagging the core to the outer laminates in the mold. Besides the vacuum bagging process, when the core is installed it must be laid into bedding compound (similar to laying tile) which must be troweled onto the outer laminates prior to installing the core. Also cutting the core material to fit the hull is more time consuming than cutting fiberglass cloth sheet to fit the hull. If you have a particular boat you are interested in and you trust their work, your best to bet is to let them do things the way they are accustomed to, unless discussions with the builder yield an acceptable alternative. This probably isn't even an issue if you are talking about strictly production boats.
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