Soundness of balsa cored hulls

[bendriver]

I’m looking at purchasing a premium built cruising sailboat built in 2003 with a balsa cored hull. The coring goes below the waterline. Most boats I have owned were solid hulls excepting my Tayana which is PVC cored and very solid. What I’m looking for here is anyone with experience owning a balsa cored boat. Also opinions from all, especially surveyors or builders would be appreciated.

[SailingHarmonie]

My opinion is any cored hull does not belong on a world cruising boat that expects to cross oceans.

A cored hull can be lighter, and stiffer than a similarly designed solid glass hull, which is of course is all for the better. The issue I have is that they are much more susceptible to impact damage, especially point impacts.

The sum of the thickness of the inner and outer skins is much lower than a solid glass hull (that's where the weight savings comes from). The core does and to stiffness, but does not add to the impact strength.

If you are sailing a small boat on inland and very near coastal waters that's not a big deal. If you are 200 miles offshore, surfing down the face of a wave at high speed and hit a deadhead, piling, or other relatively pointed object a hull puncture is much more likely with a cored hull than a solid hull.

If you are a racer, that risk is part of your game. I am very conservative with the lives of my family and crew. We routinely have long passages far offshore. A hole in the hull violates the first rule of sailing, "Keep the water out of the boat." I simply do not consider the added performance benefit to be worth the added risk.

[Foswick]

I'm kind of with SailingHarmonie, on this. Understand that my perspective is skewed by my love of older heavy displacement boats that are overengineered. I don't mind the decreased speed and responsiveness in favor of having six inches of solid fiberglass between me and the bottom of the sea. (I know it is not literally six inches.)

But, I would add that there is another more insidious reason you may want to think twice about balsa core. It is possible to damage the outer fiberglass and not know about it for a long time because the inner fiberglass remains intact. When water gets into that balsa layer, you have a problem that could make itself known at the worst possible time.

There are quite a few ways water can get in there, actually. So, you need to be just a bit more vigilant with things like through-hulls and such. Also, repairs are generally more difficult and therefore costly. I do not know this from experience, so others might verify or dispute this claim.

I will grant that pound-for-pound, the balsa core is stiffer. Therefore, it isn't fair to say that solid fiberglass is "stronger". It is more resistant to puncturing, but also more prone to flexing. So, the kind of sailing you plan to do affects the suitability of one or the other.

I would definitely not say that balsa core is bad. It just needs to be weighed against the kind of sailing you plan to do and how much time, attention, and money you are willing to devote to maintenance/inspection.

[JPA Cate]

Hello, bendriver,

Our previous boat to this one had an Airex foam core hull and balsa cored deck. It had been built in 1974, when people underestimated the strength of the coring, and so, its fiberglass was a lot thicker than it needed to be. We sailed thousands of ocean miles in her, and did have a couple of issues with the deck. We got water intrusion at the chain plates, and Jim fixed those by spooning out the mush that the balsa had become, and filling with epoxy with filler in it; and there was a deck delamination issue that we fixed by pumping it full of epoxy. and weighting it .

We (obviously) did not perceive the boat to be either unsafe or particularly vulnerable to puncture, however it did have a flaw that we discovered following a hard grounding [on a reef in northern Fiji] that eventually became major repair, replaced a floor, added two stringers, supporting the hull at the aft end of the keel, which Jim also accomplished, after consultations with shipwrights. The coring works as sound insulation--the boat was quiet, and cool. Jim's history includes employment both as a race car builder and driver and as a physicist, so he has varied skill sets, including confidence approaching repairs. We sailed and were aboard her for 18 yrs.

As it happens, for our next boat, we did consider cored boats, and this one is coved strip planked western red cedar, epoxy and glassed in and out--nature's own carbon fiber, as it were.

If the boat you are considering now makes your heart go pitty-pat, and the hull is balsa I'd probably sadly give it a miss, and it is because when the water gets at it, the balsa does turn to mush, over time, and could be a boat sinker over time. A penetration injury, left unfound and unfixed, could be a boat sinker, as Sailing Harmonie suggests. Most penetration injuries have the potential to be sinkers, and many of them are small, and the sinking is slow and the bilge pump can keep up with it. But we had friends with a sinking catamaran who had to pump the boat full time to keep it afloat, for 15 hrs., with no rest, to get their boat to where it could be repaired. If they'd been penetrated at sea, they might have been lost, and the boat sunk.

I hope someone with a balsa cored hull comes along with some input for you that is more encouraging. Your choice will ultimately depend on risk avoidance/risk tolerance, of you and whoever else is involved in the decision.

Ann

[BenBowSirocco]

I have to voice some cored hull love here.

Cored hulls have been around since the 70's and have generally proven themselves indistinguishable in durability to their solid glass brethren.

Of course we have all heard of the older balsa cored decks having trouble because early on, builders didn't know to seal the holes they drilled for stanchions and other deck features. But this has been solved for 40 years.

Think about powerboats. Basically most offshore powerboats since the 80's are cored: with 1,400+hp bolted to the transom, traveling at 40-50 miles an hour and smashing waves with immense force hugely in excess of what a cruising boat would ever see and yet they live on. Repowered over and over and used for many decades, with plenty of classics hulls coveted by owners.


Its also VERY rare to see a any modern sailboat made without coring. It has become the very standard of boat construction.
Would you choose to NOT sail a modern boat if you had the resources to have one made?

I think the fear surrounding a cored hull is based upon very early mistakes that created a reputation. As Foswick pointed out: you need to be more careful with penetrations: but in the hull, changing through hulls is incredibly rare. Its also something builders learned how to properly handle about 40-50 years ago.

I believe cored hulls are the progression of composites. They are much more efficient in terms of weight and cost. They are also generally still highly overbuilt. The coring provides great stiffness to hull as well as the lighter weight, which is desirable as it reduces creeks and groans as well as adds sailing efficiency.

If I were looking at a balsa cored hull, I would hire a surveyor who has experience in cored hulls and verify it was done properly: like any other boat I would be shopping and then move forward based upon what I learned.

There are thousands and thousands of cored hulls sailing the worlds oceans and while yes, some have had problems, the majority have not. I dont think you should be prejudice to them. Lighter boats with more modern bigger rigs sail faster and on more points of sail than their older solid core brethren.

[deblen]

Avoid cored hulls in freezing temps-especially hauled out.
Never drill a hole in a cored hull or deck until you have learned how.
Cheers/Len

[Wandering1]

W3 have a cored hull and deck. It's built using Airex. The hull is 1.5" thick in the topsides. The grp skins are 1/4" inside and out with 1" Airex core. The hull was built in 1980. Its bone dry. The insulation from 1" Airex is fantastic. Quite and a great thermal barrier.
Lots of negative comments on core construction but with no real evidence as to why. US builders never really got sophisticated with boat construction and believed that lots of glass was better. If you compare a 1/2" solid glass hull that has the same amount of glass as my boat[ 2x1/4" grp skins) my hull is 37 times stiffer for the same weight of glass.
I don't see a downside.

[coopec43]

Originally Posted by SailingHarmonie

My opinion is any cored hull does not belong on a world cruising boat that expects to cross oceans.

A cored hull can be lighter, and stiffer than a similarly designed solid glass hull, which is of course is all for the better. The issue I have is that they are much more susceptible to impact damage, especially point impacts.

The sum of the thickness of the inner and outer skins is much lower than a solid glass hull (that's where the weight savings comes from). The core does and to stiffness, but does not add to the impact strength.

If you are sailing a small boat on inland and very near coastal waters that's not a big deal. If you are 200 miles offshore, surfing down the face of a wave at high speed and hit a deadhead, piling, or other relatively pointed object a hull puncture is much more likely with a cored hull than a solid hull.

If you are a racer, that risk is part of your game. I am very conservative with the lives of my family and crew. We routinely have long passages far offshore. A hole in the hull violates the first rule of sailing, "Keep the water out of the boat." I simply do not consider the added performance benefit to be worth the added risk.

Well that's your opinion but the fact is most production boats have cored hulls above the waterline- Beneteau, Bavaria, Halberg Rassy, Bertram, Oyster yachts..... Are these yachts "Ocean going?

A lot of the extra weight of solid glass is the result of internal stiffeners required (They are not required with cored construction)

I bet you drive a 4WD off road vehicle as it would be able to handle rough conditions better when off the bitumen?

[malbert73]

My 1987 Tartan 40 has a fully balsa cored hull. The outer skin is not nearly as thing as newer boats - almost like an hull- and the entire laminate is vinyl ester resin which they were early adopters of, and is relatively impermeable to osmosis. Tartan also eliminated core in the midline and anywhere there was a through hull.
So, my hull is strong, stiff, and quiet. No downside, but my boat was extremely well built it seems.
But, I’d be careful with an old boat particularly if it has a polyester hull- as that could be more of an issue with water ingress to the core, which can be a big issue

[boatpoker]

I've done over 5,000 surveys and would not offer and opinion, regardless of core material without knowing model, year and mfg. but I do have some thoughts to offer regarding inspecting such a hull ... Moisture Meter Mythology and Flir thermal imager

[Wandering1]

Originally Posted by deblen

Avoid cored hulls in freezing temps-especially hauled out.
Never drill a hole in a cored hull or deck until you have learned how.
Cheers/Len

Not all core is the same. I think what you mean is balsa core as that core will rot.
Plastic foam cores dont have that problem with their closed cell structure. Every modern boat uses a cored deck. You have to go back a very long way to find a boat that doesn't core the deck. The only issue is how good the builder was and what core he chose.
Any DIYer can lay up glass panels. It's not a skilled job but introduce core and you need to know what you are doing.

[Fore and Aft]

Boat poker we both know any balsa core hull is only one badly installed skin fitting away from being a nightmare.
Cheers

[deblen]

Originally Posted by Wandering1

Not all core is the same. I think what you mean is balsa core as that core will rot.
Plastic foam cores don't have that problem with their closed cell structure. Every modern boat uses a cored deck. You have to go back a very long way to find a boat that doesn't core the deck. The only issue is how good the builder was and what core he chose.
Any DIYer can lay up glass panels. It's not a skilled job but introduce core and you need to know what you are doing.

The type of core material makes little difference.If water gets between the outer hull skin and the core face,it works it's way outward from the "crack",causing the core to "un-glue?" from the hull skin. The rigidity in that area is now severely decreased.
Over time,at the least,gravity will cause the trapped water to move downward.Eventually it will get under/around/thru the closed cell core and attack the inner hull/core face joint in same way.
The only difference in closed cell cores is that they don't soak up water or rot.
In freezing temps,out of water,the water between the hulls freezes,expands,freezes,etc-crushing the closed cell core.
Same is true with cored decks.
I have drilled enough cored hulls-& had to wait several minutes for the water stream to subside,in order to install a fitting. I have seen them left to drip for several days,trying to get core area "drier".
I agree 100% cored hulls have come a long way & proper cored construction requires very technical expertise.
My point is that cored hulls can be susceptible to "massively expensive" damage from things that would only cause cosmetic,DIY repairs to a solid hull.
A cored hull needs to be tested regularly & only worked on by knowledgeable

people.


Cheers/Len

[Wandering1]

Originally Posted by deblen

The type of core material makes little difference.If water gets between the outer hull skin and the core face,it works it's way outward from the "crack",causing the core to "un-glue?" from the hull skin. The rigidity in that area is now severely decreased.
Over time,at the least,gravity will cause the trapped water to move downward.Eventually it will get under/around/thru the closed cell core and attack the inner hull/core face joint in same way.
The only difference in closed cell cores is that they don't soak up water or rot.
In freezing temps,out of water,the water between the hulls freezes,expands,freezes,etc-crushing the closed cell core.
Same is true with cored decks.
I have drilled enough cored hulls-& had to wait several minutes for the water stream to subside,in order to install a fitting. I have seen them left to drip for several days,trying to get core area "drier".
I agree 100% cored hulls have come a long way & proper cored construction requires very technical expertise.
My point is that cored hulls can be susceptible to "massively expensive" damage from things that would only cause cosmetic,DIY repairs to a solid hull.
A cored hull needs to be tested regularly & only worked on by knowledgeable

people.


Cheers/Len

You make a lot of assumptions but present no evidence.
My experience is very different. Where do you expect this water to come from and where is this 'crack'. Why do you think a core hull would experience massive damage and a solid hull would suffer little damage? No evidence for that. The ultimate hull construction to resist penetration is a cored hull with a layer of kevlar on the inner skin. The outer skin and core absorb impact very well. The kevlar catches everything and resists penetration. This won't happen with a solid laminate.
You need seperate cores in to types. Not all core is the same. Honey comb cores will hold moisture. Balsa will rot. My own cored hull was thoroughly surveyed and moisture checked before awlgrip. NO moisture. 44 years old and in great shape

[boatpoker]

Originally Posted by Wandering1

You need seperate cores in to types. Not all core is the same. Honey comb cores will hold moisture. Balsa will rot. My own cored hull was thoroughly surveyed and moisture checked before awlgrip. NO moisture. 44 years old and in great shape

Please tell us what type of boat you have.

Wet Balsa Core in Boats