Soundness of balsa cored hulls

[boatpoker]

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

Deblen, I think we are pretty much on the same page except that I have seen quite a few foam cored rudders where the foam has disintegrated. I have also seen a number of saturated and disintegrating foam cores in Boston Whalers that weighed in 3-4 times their advertised weight.

[Wandering1]

Originally Posted by boatpoker

Please tell us what type of boat you have.

Wet Balsa Core in Boats

She is a Van de Stadt Trintella 44. Built by the Ane Weaver Shipyard in the Netherlands.

[smj]

Originally Posted by boatpoker

Deblen, I think we are pretty much on the same page except that I have seen quite a few foam cored rudders where the foam has disintegrated. I have also seen a number of saturated and disintegrating foam cores in Boston Whalers that weighed in 3-4 times their advertised weight.

Would the Boston Whaler foam be considered a foam used as a structural core or a foam used for flotation? If I remember correctly the Boston Whaler foam has no similarity to the structural foam cores used in sailboats and was well known to become saturated.

[boatpoker]

Originally Posted by smj

Would the Boston Whaler foam be considered a foam used as a structural core or a foam used for flotation? If I remember correctly the Boston Whaler foam has no similarity to the structural foam cores used in sailboats and was well known to become saturated.

It was advertised as both and claimed as "closed cell" just like the cheap foam used in many sailboat rudders. To have it act like a cheap Chinese sponge below the waterline was idiocy.

A friend bought a 12' , four people could not lift it (no motor). We drilled holes in the transom and stood it up (used a fork lift). It took 6 months to drain.

https://continuouswave.com/whaler/re...ullDesign.html

Take a look at the first minute of this video it clearly shows the the foam supported the entire deck and center console (for a while). Not shown is that it was also to support the transom and the weight and stresses of the outboard.

https://www.proboat.com/2019/03/unsi...boston-whaler/

[deblen]

Originally Posted by Wandering1

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

I am glad your experience is different from mine and others.
I am glad your 44 yr old boat has no core problems. Obviously your boat was designed,built & maintained correctly.That is wonderful!


My experience has been different than yours & the evidence was sprayed all over me when I drilled into some cored hulls. This bad experience has prompted me to recommend that owners & technicians be aware of possible problems that can happen in some cored structures & treat them differently than solid structures.

Cheers/Len

[boatpoker]

Originally Posted by deblen

I am glad your experience is different from mine and others.
I am glad your 44 yr old boat has no core problems. Obviously your boat was designed,built & maintained correctly.That is wonderful!


My experience has been different than yours & the evidence was sprayed all over me when I drilled into some cored hulls. This bad experience has prompted me to recommend that owners & technicians be aware of possible problems that can happen in some cored structures & treat them differently than solid structures.

Cheers/Len

Yup ! I am pretty comfortable that I can predict which brands/model years are going to have serious bottom core issues before we even arrive for the survey. There are also some uncored hulls out there so badly designed and are so weak that care has to be taken when lifting and blocking.

[Wandering1]

Originally Posted by boatpoker

Yup ! I am pretty comfortable that I can predict which brands/model years are going to have serious bottom core issues before we even arrive for the survey. There are also some uncored hulls out there so badly designed and are so weak that care has to be taken when lifting and blocking.

I wonder if the Sailing Uma Utube channel brought some home truths to the state of boat building in the USA. The quality of that boat construction was truly shocking and no cored hull.
Can you image if the builder had used the same quality approach and used core!

[Dockhead]

Originally Posted by 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

That's completely false as a blanket statement.

There are a number of different ways to execute balsa cored hulls.

If it's just balsa planks, like cheap boat builders used to do in the 70's and 80's, then yes -- any water intrusion can migrate through the core and destroy the whole thing.

But no quality boats have been built like that since at least the 90's.

The best way to do it is with fully encapsulated balsa blocks, vacuum infused with resin. This is pretty much bulletproof. Any local water intrusion stays local.

Quality cored hulls have solid glass pads where the through hulls go through, so no risk to the core there either.

Balsa is immensely strong for its weight -- better than titanium -- especially in compression. So a balsa cored fiberglass panel is many times stronger and stiffer than a solid glass panel of similar weight, or even double the weight. Concerns about point impacts are misplaced -- a cored hull is better than a solid one for that.

Foam coring materials have been improving and some now approach balsa in strength, so they are gradually becoming the predominant coring material.

Uncored fiberglass is an unsuitable material for any application where you need strength without excess weight, or when you need a lot of strength regardless of weight. Cored hulls are the way to go. The only real drawback of fully cored hulls is cost, as a properly done cored hull is quite a bit more expensive than a solid one. That's why expensive high end cruising sailboats (and ALL racing boats), like Swan, Hallberg Rassy, Contest, Discovery, etc. have fully cored hulls (with only a couple of exceptions), whereas cheap mass produced boats like Beneteau and Bavaria, have solid hulls.

[Wandering1]

Originally Posted by Dockhead

That's completely false as a blanket statement.

There are a number of different ways to execute balsa cored hulls.

If it's just balsa planks, like cheap boat builders used to do in the 70's and 80's, then yes -- any water intrusion can migrate through the core and destroy the whole thing.

But no quality boats have been built like that since at least the 90's.

The best way to do it is with fully encapsulated balsa blocks, vacuum infused with resin. This is pretty much bulletproof. Any local water intrusion stays local.

Quality cored hulls have solid glass pads where the through hulls go through, so no risk to the core there either.

Balsa is immensely strong for its weight -- better than titanium -- especially in compression. So a balsa cored fiberglass panel is many times stronger and stiffer than a solid glass panel of similar weight, or even double the weight. Concerns about point impacts are misplaced -- a cored hull is better than a solid one for that.

Foam coring materials have been improving and some now approach balsa in strength, so they are gradually becoming the predominant coring material.

Uncored fiberglass is an unsuitable material for any application where you need strength without excess weight, or when you need a lot of strength regardless of weight. Cored hulls are the way to go. The only real drawback of fully cored hulls is cost, as a properly done cored hull is quite a bit more expensive than a solid one. That's why expensive high end cruising sailboats (and ALL racing boats), like Swan, Hallberg Rassy, Contest, Discovery, etc. have fully cored hulls (with only a couple of exceptions), whereas cheap mass produced boats like Beneteau and Bavaria, have solid hulls.

I couldn't agree more. Cheap boats don't have well cored hulls

[Fore and Aft]

Dockhead you have an optimists view of Balsa/foam core resin infusion. Just this year two Fountaine Pajot cats I sueveyed had core issues. Fountaine Pajot even proudly claim on their website resin will fill any gaps. I have no idea about the science of water entering between a core and fiberglass skin but when it does the results can be very interesting.

Cheers

[Wandering1]

Originally Posted by Fore and Aft

Dockhead you have an optimists view of Balsa/foam core resin infusion. Just this year two Fountaine Pajot cats I sueveyed had core issues. Fountaine Pajot even proudly claim on their website resin will fill any gaps. I have no idea about the science of water entering between a core and fiberglass skin but when it does the results can be very interesting.

Cheers

Wouldn't FP make the list of none quality boat builders? I have seen lots of horrible details on these boats. They are built to a price not a quality level. You get what you pay for.
Core done badly will end in tears. Core done well is a remarkably effective construction

[geoleo]

Originally Posted by 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.

I have seen 2 Kadey Krogen Trawlers having the entire below waterline outer skin removed and all the Airex foam core removed and replaced because it rotted out . Huge cost on a otherwise great boat.

[boatpoker]

[QUOTE=Dockhead;3896765]That's completely false as a blanket statement.

There are a number of different ways to execute balsa cored hulls.

If it's just balsa planks, like cheap boat builders used to do in the 70's and 80's, then yes -- any water intrusion can migrate through the core and destroy the whole thing.

But no quality boats have been built like that since at least the 90's.

The best way to do it is with fully encapsulated balsa blocks, vacuum infused with resin. This is pretty much bulletproof. Any local water intrusion stays local.
/QUOTE]

I have yet to see an infused hull where the kerfs have been truly infused so that a breach in one will not reach another block of balsa such as two brand new infused Bertrams that disintegrated on their delivery voyages (see photos).One sank and one made it back to harbour.

I have dozens of such photos of failed balsa core in hulls built over the last over 15 years. I have dozens of photos of balsa hulls saturated in water after only one season in water.

I agree that if installed properly, infused Balsa can last an extremely long time but ... After thousands of surveys I cannot name a single builder that can consistently be relied upon to install balsa core properly every single time.

As someone once said - Trust, but verify.

[Foswick]

The bottom line is, if not done well or maintained appropriately, a balsa cored hull is subject to host of minor and serious problems. If done well, it is fine, provided you understand and work within the benefits and limitations of that design choice. Same with foam core. Same with solid fiberglass. Same with anything.

To me, blanket statements on the subject rarely hold true enough to be very helpful to anyone trying to make up their mind about a particular boat.

[Wandering1]

Originally Posted by geoleo

I have seen 2 Kadey Krogen Trawlers having the entire below waterline outer skin removed and all the Airex foam core removed and replaced because it rotted out . Huge cost on a otherwise great boat.

Build quality not a core problem. Airex doesn't rot out. It's a plastic core.
My Airex cored boat was built by a reputable yard that knew how to build boats. In addition, the designer Van de Stadt knew how to spec the construction. The boat was built to Lloyd's 100A1 standard. 44 year old and perfect core with no moisture. Don't blame core for bad build quality. The boatmhasnt had an easy life either. 37,000nm in thr last 10 years. Another Atlantic crossing in the next week. There will be another one next year.