Cored Hulls

I was researching a hull described as "composite" and I came across this David Pascoe article. As usual, rightly or wrongly,Pascoe seems well researched but takes no prisoners. The article was of marginal help to my inquiry but may help someone.https://www.yachtsurvey.com/core_materials.htm

Reads like a kid in second grade explaining why the moon is made of cheese. Hard to understand why he has any credibility. Article has a fair amount of factual inaccuracies. Hard to take seriously a clown who goes from cored hulls to boffing Marylin Monroe. Sadly there's no peer review for crap like that.

Ted

He certainly has strong opinions and maybe he is correct. I know that I don’t want a cored hull boat.

A cored hull below the waterline is a big no no for me. I guess I’m just old school.

I agree with very little from Pascoe, but even giving him credit, he's comparing low end builders to high end and he's using very old information. The article was written in 1998. That's over 20 years ago. The coring materials used today didn't exist then and they certainly weren't in the boats he'd examined and based his article on.

One can certainly choose not to have a cored hull or one cored below the waterline. To say there are no builders who were successful with it is ridiculous. One only has to look at Kadey Krogen or Bruno & Stillman to see numerous examples of sound hulls.

Ted

O C Diver said:

One can certainly choose not to have a cored hull or one cored below the waterline. To say there are no builders who were successful with it is ridiculous. One only has to look at Kadey Krogen or Bruno & Stillman to see numerous examples of sound hulls.

Ted

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We really like the KK 42.

We looked really hard for a Krogen 42 to purchase in the first half of the 90's all over the US. Most had issues with the bottom. Either a concave distortion of the bottom between bulkheads or water in the foam core.

The water in the core is more a previous owner or yard installing a thru-hull without adding a solid spacer to prevent core crushing.

The hull deformation was attributed to the foam core deflecting under water pressure. The fix was heating the deformed area, pushing the hull bottom down with jack's and laminating additional layers of reinforcement. The deformed areas were under tanks which had to be removed before starting the hull repair.

The hull deformation would not have occurred had two more layers of roving been applied to the top of the coring in the larger spaces between bulkheads.

Coring is not used exclusively to save money as the author alleges.

Balsa and foam coring is used in high performance power and sailboats for weight saving. Those boats are not budget boats.

Most high end yacht builders utilize coring in furniture, countertops, floors, bulkheads and any place weight can be reduced.

They use balsa, foam and honeycomb.

He makes it sound like every boat ever built is about to fall apart.

Benthic2 said:

He makes it sound like every boat ever built is about to fall apart.

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He did, rest his soul. Not a man to pull punches, I read his reviews with a grain of ground up osmosis blister, instead of the more usual salt. But I thought the article added something to an old discussion.

Both the 21' Dovekie we cruised for 12 yrs and the 28' Shearwater we cruised 18 yrs had Airex foam cored hulls which served us very well, making for very strong and very light displacement promoting easy, no hassle trailer transport. We probably logged 60,000 miles towing that pair of Edey & Duff boats all over the USA and Canada. Both boats are still in service with subsequent owners.

Our present Albin-25 has a foam cored deck that is now 43 years old. Built in Sweden, I do not know the brand of the core material, however, it is sound.

Like everything else time changes both the materials and methods of boat building.

A good foam core 40 years ago like Airex is a delight , above or below the water.

A sheet of house plywood with a layer of GRP might be called "composite" but its hardly cored construction.

With todays vacuum infusion techniques ,cored construction is desirable if light and strong are needed.

The big question now, is how they can be repaired and maintain their integrity.

Benthic2 said:

He makes it sound like every boat ever built is about to fall apart.

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And TF collectively makes it sound like every boat not up to ABYC standards will sink, catch fire, explode, crumble...etc...etc...

In terms of numbers of boats built the Bayliner 4788 built from 1994 to 2002 has the most hulls in the water of any model in the 45-50’ range.

These boats were built with a below the rubrail construction consisting of a thick outer hull, a foam core and a thinner inner hull.

Remarkably there has never been a delamination or hull failure of one of these hulls, and again this is the most popular boat of it’s size ever built in terms of production numbers.

This practice continued when the boats were rebranded Meridian in 2003 and continued until the economic collapse stopped production in 2008

The same constriction was also used in the 52 and 57’ models

His predictions were way off. Boats didn’t sink, fall apart, or burn up. Just imagine if he reviewed RV’s

A cored hull can be good or bad. It depends on materials and methods. I worked with a high end builder during construction of a one off sailboat. The hull and deck were foam cored. In that case the outer skin was laid up, the foam was applied using a vacuum bag and then the inner skin was laid up using a second vacuum bag. Both skins had the same layup schedule. The only difference between the inner and outer skins was that the outer skin used vinylester resin for the skin coat and the first layer of 1708 before switching to polyester. Where thru-hulls were to be located the foam core was removed and replaced with solid glass. Stressed points were solid glass. A boat built in this manner will have few if any problems. If the hull had been resin infused (properly) it would be even better.


In contrast, a boat built using a chopper gun and balsa core is a disaster waiting to happen.


Foam coring is not cheaper than building from solid glass because the foam itself is very expensive. Coring does not make the hull stronger, it makes the panels stiffer. Finally, a cored hull is only as good as the bond between the skins and the core material combined with the shear strength of the core material.

So not being very smart I look at a cored hull as having an advantage in weight with other obvious disadvantage That being said in a trawler of displacement speed do you really want to save weight and take on the disadvantages?

Just my SSO!

One possibility that could be an advantage...with enough coring and additional flotation, a positive buoyancy number could be obtained. I didn't say unsinkable.. but may float when flooded.

May be true in an outboard but our boats are loaded with extra weight. My boat is over 80K pounds, it would take all the balsa in Florida to float her.

You would be surprised Irv, quite a few boats have been engineered that way.


Most boats start with the assumption floating will never happen so weight doesn't come into consideration. But start with it as a possibility, shave weight and it is possible.


Some weights can be calculated after immersion, so total boat displacement changes significantly.

While overall weight in a displacement hull may not be a big advantage, consider the balance center (wrong term). If the entire hull and super structure are solid fiberglass, the balance point necessarily becomes higher. This either requires more ballast or more draft. Clearly, making the hull below the waterline solid fiberglass and everything else cored, puts the weight where you want it and reduces the need for ballasting to lower the center of gravity.

Ted

Scott. You may have a new career in boat designing, large unsinkable trawlers.

Ted. I agree 100%. Weight is one factor, placement of that weight is more important. So that’s the reason you don’t have s bridge.

ksanders said:

In terms of numbers of boats built the Bayliner 4788 built from 1994 to 2002 has the most hulls in the water of any model in the 45-50’ range.

These boats were built with a below the rubrail construction consisting of a thick outer hull, a foam core and a thinner inner hull.

Remarkably there has never been a delamination or hull failure of one of these hulls, and again this is the most popular boat of it’s size ever built in terms of production numbers.

This practice continued when the boats were rebranded Meridian in 2003 and continued until the economic collapse stopped production in 2008

The same constriction was also used in the 52 and 57’ models

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Something Orin Edson remains very proud of. He built Bayliner from nothing. Later in his career, Pacific Mariner, and then, Westport. All PNW companies. The naval architect he was closest to was Bill Garden who was a pioneer in lightweight, good performing boats. Even today the heritage continues as while most large yacht builders build displacement and have cruise speeds around 12-14 knots, all models of Westport have WOT speeds around 25 knots and fast cruising speeds around 20 knots. Now, admittedly 20 knots on a 130' will use close to 120 gph.

After reading that I feel like I need to sell my boat to the first person that has cash. It's a good thing I have been studying boat building for the past 23 years. That article would scare me from ever wanting to be in the water with boats around.

Bigsfish said:

Ted. I agree 100%. Weight is one factor, placement of that weight is more important. So that’s the reason you don’t have s bridge.

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I have a bridge. Mine is just enclosed, heated, air conditioned, further forward, and less steps up from the galley and the head.

Most of my cruising is inland. So, air draft (bridge clearance) was a major consideration. A 15' air draft is really nice!

Ted

Ted by your standards I have two: one open air and the other under AC.

I've mentioned this in other threads, but the one thing that concerns me about cored hulls is lifting and transporting them solely on the pads of certain hydraulic trailers. I'm convinced the pressures exerted on the hull is enough to crush the core material and thereby debond the area around where the pads are applied. A keel support trailer that only uses the pads as supports is fine.

The Great Lakes have a very large number of these pad lift contraptions. I would not consider purchasing a cored boat that has been on one of them. In fact, I'm going to contact ABYC about this on Monday.

Rufus said:

I've mentioned this in other threads, but the one thing that concerns me about cored hulls is lifting and transporting them solely on the pads of certain hydraulic trailers. I'm convinced the pressures exerted on the hull is enough to crush the core material and thereby debond the area around where the pads are applied. A keel support trailer that only uses the pads as supports is fine.

The Great Lakes have a very large number of these pad lift contraptions. I would not consider purchasing a cored boat that has been on one of them. In fact, I'm going to contact ABYC about this on Monday.

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I think this could be a valid concern depending on coring material and fiberglass thickness. My old Bruno & Stillman was built back in 1975 when they still didn't fully grasp the strength of fiberglass. The outside fiberglass is a lot thicker than most 35' boat hulls today. I sure it can't even flex. But there are a lot of cored boats built in the last 30 years with only a few layers of cloth on the outside.

Ted

Well since I am not into fast planning boats anymore, I would not get a trawler style boat with a cored hull. The main upside is weight savings and I really don’t care about a bit more weight in my boat. There are huge downsides to cored hulls so I don’t think that it makes sense in the trawler world.

ksanders said:

In terms of numbers of boats built the Bayliner 4788 built from 1994 to 2002 has the most hulls in the water of any model in the 45-50’ range.

These boats were built with a below the rubrail construction consisting of a thick outer hull, a foam core and a thinner inner hull.

Remarkably there has never been a delamination or hull failure of one of these hulls, and again this is the most popular boat of it’s size ever built in terms of production numbers.

This practice continued when the boats were rebranded Meridian in 2003 and continued until the economic collapse stopped production in 2008

The same constriction was also used in the 52 and 57’ models

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Exactly right Kevin. But one thing you need to remember is that Bayliner used ATC Core-Cell, an extremely tough closed-cell foam specifically designed for below-the-waterline applications. Other foams used for coring will still soak up some water and are known to deteriorate/delaminate over time due to hydro-shock.

Pacsoe reviewed Core-Cell here and compared it to other foams: www.yachtsurvey.com/ATC_Core-Cell.htm


Talking specifically about the Bayliner/Meridian motoryachts (only), it always seemed to me they had some of the best hull technology, this is one example. To my knowledge, Bayliner/Meridian is the only production builder that used ATC Core-Cell, and they did build thousands of them.

That said, I think Bayliner was an exception.

I would never buy any boat with a balsa cored hull bottom, and I would be very wary of any other foam-cored bottom unless I know what kind of foam was used and how much experience the manufacturer had with it.