Shocked by hull material catamaran

[44'cruisingcat]

Originally Posted by Moody Mike

My old Moody54 was balsa cored . Very strong boat but had much thicker lay up than what I see on this cat. I had some wet balsa around a poorly fitted transducer. It only penetrated about 3 inches into the balsa. Easily removed & solid glasses.

You're wrong, obviously! Your balsa cores were pounded to dust, rotted away, turned to mush etc etc etc...

You need to listen to the forum experts!

Meanwhile, the first boat to ever have a balsa core is still sailing, still hasn't rotted away, more than 50 years after launch. Of course it's only a matter of time, right? Any 50 year old foam core boats around?

[Marc_H]

If the Technical specifications are correct,
Balsa core hull, solid laminate under water line.

[Jim Cate]

Originally Posted by 44'cruisingcat

You're wrong, obviously! Your balsa cores were pounded to dust, rotted away, turned to mush etc etc etc...

You need to listen to the forum experts!

Meanwhile, the first boat to ever have a balsa core is still sailing, still hasn't rotted away, more than 50 years after launch. Of course it's only a matter of time, right? Any 50 year old foam core boats around?

Not quite 50 years, but our previous boat, a Standfast 36 built by Palmer Johnson in Sturgeon Bay, WI was Air-x foam cored throughout the hull. She was laid up in 1974 and has been in salt water her whole life... that makes her now 43 years of age and no problems with the coring. She's done a hell of a lot of miles, too! Her current owner did a huge refit a couple of years ago, and the shipwright had a careful look around with the interior stripped right out... no worries. Interestingly, there had been a problem with the hull, but it was at the root of the keel stubby... the only part of the hulll that was not cored, but was solid laminate!

Oh... no blisters, ever!

Jim

[arsenelupiga]

Originally Posted by barnakiel

Nothing wrapped in plastic btw as the balsa cubes must be glued well to both skins. Otherwise there is no sandwich laminate benefit.

Wrapping the core in plastic would induce delamination at the very start. A NO and NO.

If they build something like this or that it is nearly always saving on labour in case of mass produced boats. Keep the costs low, get a higher margin. BAU.

b.

thks. No, I do not know if wrapped. Just my uneducated guess. From what you say, and from the pics of L57, likely not.

So, vacuum construction sucks out all (most?) air. And only fiberglass and balsa remain and balsa is impregnated with fiberglass glue. Even water intrusion would not do much harm then and will not spread ?

[Night_Sailor]

Originally Posted by arsenelupiga

hahahaha, guys normally badmouthing lagoon, suddenly defend lagoon building method

because they use the same method.

Of course lagoon has no clue after 3000 cats built and they were just lucky this time.

I was interested in a Priviledge 65 that was for sale for a long time in Port San Antonio. It sat in the water for seven years. I was on a fence about looking at it, and ultimately decided it was not worth the expense of a trip to see it. A short while later a few yacht brokers, sparked by my interest, decided to buy it. It was found to have extensive core damage. As I recall it was balsa. Now, one issue with water is if there is a path for it to propagate it can spread far. I've seen this on a deck I recored. Both foam and balsa are cut to lay in a curved mold. That leaves gaps which if not filled create pathways for water to propagate. If however, these are filled with epoxy or some other filler, that created mini I beam type structures and make the laminate stronger and resist water propagation. So much depends on how well the voids are filled. Good prep can make a sound hull, and avoiding core near thru hulls helps, but one crack can lead to extensive rot--eventually. The big cat I was looking it needed a crazy amount of money poured into it for this, and that took away money for other things it needed. The owners made a day charter boat out it--it was not worthy.

So the bottom line for me, is how long do I expect to keep my boat, and what effects re-sale. A solid glass bottom is a huge plus to me. It may have less impact resistance, but at least I know it won't need a crazy amount of repairs in the future, or be a worry for a buyer.

[UNCIVILIZED]

Originally Posted by arsenelupiga

thks. No, I do not know if wrapped. Just my uneducated guess. From what you say, and from the pics of L57, likely not.

So, vacuum construction sucks out all (most?) air. And only fiberglass and balsa remain and balsa is impregnated with fiberglass glue. Even water intrusion would not do much harm then and will not spread ?

Vacuum bagging draws the layers of reinforcements (fiberglass, carbon fiber, kevlar, etc.) tightly up against the core on both sides. And if the boat is built with a resin infusion system, then the vacuum used for this also pulls the resin into the reinforcements, & holds the now wet reinforcements tightly against the cores until the resin cures.

Said vacuum goes a long way towards moving the resin into the kerfs cut into the core, in efforts to fully fill all of these gaps with resin. Thus isolating each small square of core via thin barriers of resin. However rarely do 100% of these kerfs get filled. Since infusion is still a bit of an art, despite the huge amounts of testing done in order to eliminate as many glitches as is possible.

The resin doesn't saturate the balsa persay, rather, it just bonds the ends of the kerfed blocks to the skins (reinforcements). Particularly as when balsa is harvested, & processed into thin sheets to be used for things like boat construction, a proprietary coating (like Baltek's Al500) is applied to it's end grain so as to limit the uptake of (excessive amounts) of resin by the balsa. Thus the resin that's sucked through the bagged part penetrates at best a mm or two into each end of a block of balsa. Not all the way through it's cells, such that if that were to happen, then it would pretty much be fully protected from rot, even were it to get wet. But a resin soaked piece of balsa would be hugely heavy, & of course resin's expensive.

In order to use balsa (or other cores) for the construction of curved parts like boat hulls. After it's sawn into thin sheets, with it's end grain facing vertically, a coating like AL500 is applied to the ends of the sheets, so as to limit future resin uptake. Then the sheet has kerfs sawn into it. Kerfs being akin to 0/90 deg notches as are formed in ice trays in your freezer. And then a thin scrim is bonded onto one side of the sheet. The scrim's purpose being to keep all of the blocks together, as otherwise they'd be somewhat prone to seperating from one another thanks to the partial depth cuts kerfed into them when the sheet was processed. And the scrim also serves to make it easier for workers to handle full sized sheets of kerfed cores like balso.

In order to build the boat, composite fabrics are laid down in a mold. The cores are laid on top of them, followed by more layers of fabrics, & then the top half of the vacuum bag. After which manifolds for the distribution of resins are connected to the mold/vacuum bag. And once it's determined that all's in place, & the bag is airtight, resin is introduced into the bag, where by the vacuum pressure pulls it through the fabrics, & onto the ends of the cores in the mold/bag. And the vacuum pressure is maintained until the entire part is cured. Which, in this instance is most likely a hull.

Hope that helps, & you can learn more at;
composites world (online, gratis)
westsystem.com
systemthreeresins.com
lbifiberglass.com
youtube.com
proboat.com (Professional Boatbuilder Magazine)


And believe it or not, the above is a gross simplification of how the process works, & is/can be done


PS: The only real way to ensure that 100% of the kerfed cuts in a piece of core get filled, is by having a human hand butter & fill each one with thickened resin, prior to putting a piece of core into a mold for a part. Whether the part is to be vacuum bagged, infused, or just laid up by hand. So it's pretty labor intensive, & also time sensitive, as you don't want the resin used for buttering the cores to cure prior to the resin used to bond the skins onto the cores. So, yeah, semi rocket-science (at first glance anyway).

[saltydog47]

Years ago many boat builders were using coring materials above and below the W/L.
This is a bad practice on a cruising boat mono or multi . All should only be solid below the W/L.
After 45 years of boating , I have heard and seen many horror stories of cored hulls soaking up water . One was a million $ classic mono , just absolutely stunning , apart from her lower outer skin had to be stripped off , core cut out then reskinned in solid laminate.
Cruising people generally cannot not afford or risk this type of structure .
Of course there is always the case where one has lasted many years , just like smoking and cancer .
Lagoons and others built this way many years ago , as in the photo of the 57 . But today they build them solid . And I am glad they do .
A few years ago while coming down the Chesapeake in my HR 53 , very solid hull, we hit a 20ft long Log about 15’’ in diameter, at 8knots . It tumbled along the bottom of the hull , then shot out the back , not a scratch . Try doing the in
A cored bottom.
A cored hull is a problem waiting to happen .

[BigBeakie]

Uncivilized,

Good description of the VIP process. However one thing to add is that commonly the balsa kerf cut core is laid in the bilge with the kerf cuts facing the mould surface. This opens up the cuts as they bend to the tighter radius of the bilge curve. Why do the production manufacturers do this? Because it makes the core easier to fit, of course. The alternative of facing the knife cut kerfs "inwards", away from the mould surface is more labour intensive. You have to fit the core better, take more care that there is not separation of the sheets and that the core is flush with the mould surface. And they can't be bothered with all that, so they just lay it in, knife kerfs down!

The result is that there are large triangular wedge spaces in the blocks of balsa that fill up with resin. Resin on it's own, without glass fiber, is not strong. It cracks under load and impact. But whats more, because there is no solid core there, the glass gets pulled down ( by the vacuum) into the wedge space and you get a "cordaroy" effect of the glass fibers bent at all the edges of the balsa blocks. This substantially weakens the glass fibers as the effect is cumulative.

Good composite technique pays attention to details like this, knowing that straight fibers are strong fibers and kinked fibers are much weaker. That's why stitched cloths are better ( stronger, tougher ) than wovens. And why sharps bends in layup are avoided if at all possible.

But, it sure is important to save that time in production layup so the Lagoon customer can save a couple of hundred bucks on the sticker price, cuz THAT's what matters. "They'll probably never sail in winds over 20 knots anyway". I actually heard that from a company rep. Oh dear.....

At boatshows I look in the bilge at the latest production cats from the big 3, and it isn't confidence inspiring. Some of the infusion work is laughable. I guess the phrase "Built to a price" comes to mind?


Sent from my iPad using Cruisers Sailing Forum

[Lance]

Build method , quality and then design for a smooth ride in a rough sea state are my first criterea .
Thanks for showing that dodgy looking lay up .
As mentioned imagine an un noticed skin breach soaking up water , but I suppose the owner would not notice the resultant performance loss from a max of 8 knots to 6.
I recently sold my very well built Whitehaven .
It became frustrating trying to convince potential buyers that the build method of WRC Strip planking with West System Epoxy fully encapsulted inside and out was absolutely super strong and yet light and was a desirable feature .
I believe longtitudinally glued strips of wood provide a flexing moment that is resilient to stress and also provides a forgiving feeling to the ride when hard pressed.
The enquirers needed the extra bathroom , the laundry and the galley with oven .
I dont even think they considered where the helm was located on their first choice of production type boat .
Each to their own leisure I suppose and with charterers taking these floating apartments out regularly it is only to be expected to see the odd one come to grief on the rocks .
If repaired the process needs to be fully documented and shown to any new owner .yeah right ??

[danielamartindm]

I researched the issue of balsa cores before my purchase of a cat WITH balsa cores. I saw no red flags in terms of insurance claims data or online reviews. Several industry mavens I spoke to on the subject also agreed. Balsa is light, a prime requirement for catamaran substrate.

[Mr B]

My beefed up hull after it had encountered 10 tide changes sitting on rocks,
Its gone from about 5 mm thick to about 13 mm thick,
The original hulls were very thin,
These are the plugs from the thru hulls I cut out of the bottom of the hulls,
I am happy with it,
It has removed my original fear of just how thick are my hulls and will they withstand sitting on a beach with out punching a hole in them,

Cheers, Brian,

[drewm3i]

More concerning to me is the obvious dry glass in the laminate that wasn't wetted out.

[Mr B]

Originally Posted by drewm3i

More concerning to me is the obvious dry glass in the laminate that wasn't wetted out.

Its the marks from the circle cutter, Is what your looking at,
Its extremely solid all the way thru,

[CaptRehab]

I saw an old CT ketch in Tortolla after Irma/Maria. It was scarred, mast-less, and the railings looked like some kind of sculpture but the hull was intact. Heard it was driven onto the beach but had to pound its way through 3 other boats before it got there. I personally do not want to compromise performance for this level of strength but I also prefer solid glass below the WL for smaller collisions