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Old 02-18-2019, 07:50 AM   #1
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Hulls - My Brains Exploding

So my brain is about to explode. Technology has changed and we grow to accept certain things. That includes hull technology.

Infusion is pretty normal. Coring is pretty much accepted above the waterline. Then it got weird for me. Even some very high-end boats like Hatteras are now cored below the waterline!

I'm looking at the Absolute Navetta. They have a very cutting edge, new, high-tech factory. Their boats, all 19 of them, from yachts to trawlers have solid fiberglass hulls.

Additionally, they hand glass in a computer-designed stringer system, then the bulkheads as well.

I'm thinking I'm in an alternate universe here. All this is very old school. What the heck is going on?
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Old 02-19-2019, 06:07 AM   #2
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I'm thinking I'm in an alternate universe here. All this is very old school. What the heck is going on?


A cored hull can be very light weight , but for boats that do not require light weight solid laminated GRP has far fewer problems , especially longterm.
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Old 02-19-2019, 07:26 AM   #3
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Just because a technology is there dosn’t mean it’s best. In the 50’s gas turbine cars existed and I think doable in mass production but as we all know they were determined to be not best.

For trawlers I’m with FF. Don’t need that much lightness. High tech available? Certianly. Is it best? That’s where we run afoul. It’s a mental attitude of late. The latest thing is almost always viewed as best. Like lube oil. Full synthetic lube oil is available even at 5w50 viscosity. Is it best? Depends on what yeo’re going to do w it. There’s lots of options other than 5w50 oil. The’re there on the shelf andat lower prices. They are there because they are the best for many applications. I’m think’in the Navetta people are looking at boatbuilding objectively. And using the appropriate materials for the job at hand.

People tend to buy the latest things thinking it’s best and all things that came before it is “old school” and inferior so olny fools use things that seem to have been superceeded. Often the new thing is best though. Remember when radial automotive tires were the latest. I do. And there was all kinds of awful tales about what would happen to people that used them. But they were best as history shows. But re the radial tires the safe route was the route most people took. Run my adequately good bias ply until the radials became proven.

But there are still lot’s of people that always go w the new thinking anything else is old school and stupid. They made plywood boats for many years. Had advantages .... and disadvantages. They sheathed them w FG and the sheathing had problems. But fiberglassing was the newest and latest and many many did it. Then there was FG boats and “anyone was stupid to buy a plywood boat now that you could get FG. ...........

But in your case the cored hulls are probably still just the “brand new latest” and time will tell if it’s best. But from cored hull history a trailer boat kept in a heated garage may be fine. But so would a hand layed boat. And the hand layed boat would probably fair much better anywhere. Old school .. and good.
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Old 02-19-2019, 09:21 AM   #4
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A well-done cored hull can be ok. One quality check is to see if the builder relieved the core around all hull penetrations. Easy to verify from the bilge side. Vacuum bagging is labor intensive but would increase the adherence of the core to the fiberglass skins. My main concern would be all the through hulls and penetrations installed by yards later. They almost never replace the core with epoxy filler around the penetration and simply rely on caulk. I cringe when I see multiple underwater lights simply caulked into a cored hull. This pretty much guarantees water in the core down the road.
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Old 02-19-2019, 09:55 AM   #5
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Depends on how fast you want to go. Coring definitely lightens up the boat. My 35' Bruno and Stillman is cored with balsa through out the hull. It's still dry and going strong after 40+ years of heavy use.

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Old 02-19-2019, 10:16 AM   #6
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Quote:
Originally Posted by markajh View Post
I'm looking at the Absolute Navetta. They have a very cutting edge, new, high-tech factory. Their boats, all 19 of them, from yachts to trawlers have solid fiberglass hulls.

Additionally, they hand glass in a computer-designed stringer system, then the bulkheads as well.
That reads like their marketing materials. There is nothing any more cutting edge about their factory that the dozens of others near them. Everyone is using computer designed systems and what many would label as traditional with hand glass and solid fiberglass is one of the least high tech approaches. On the other hand, it's a good, solid approach to boat building. It's a very good approach for those who aren't cutting edge.

Infusion and carbon fiber and Kevlar and "space age foams" and all the other things you see tossed around, especially in high performance boats, is more cutting edge in some ways but also more dependent on perfect execution and, if not done right, a more risky and perilous route to take. There are builders who have been doing many of these things well for decades, but their investment and commitment to technology is extensive. For those not in that position, and those not dependent on maximizing speed or performance, using what you call "old school" or what I label "traditional" methods makes sense.

They're a very interesting builder with a modern facility, interestingly enough located nearly 100 miles from the coast which is blanketed with Italian builders. However, Italy has builders throughout. Riva, for instance, is located on Lake Iseo in Sarnico and is far from the coast and their boats are very traditional in build methods. Meanwhile they also build in La Spezia in a huge Ferretti yard located on the coast now.

As it happens, we're going to Italy for a brief stay of 9 days in a couple of weeks and while most of the trip is going to be seeing Rome, Florence, Milan and Venice, we do have a day devoted to Viareggio, the epicenter of Italian boat building. While our primary emphasis is AB, we may also visit Sanlorenzo while there. In addition to Maiora/AB/CB Navi and Sanlorenzo, there are many other yards in the same port including Cantiere Navale Francesco Del Carlo, Azimut Benetti, Perini Navi, Mangusta, Rossinavi, VSY, Gianetti, Rossi Navi, Fipa, Codecasa, and Ar.pe.ca.

It was interesting that the Turkey press referred to the Absolute yard as "German disciplined." I interpreted that as being meant as a very fine compliment to the yard. Photos I've seen have certainly supported that. I compare to some yards I've seen elsewhere that look completely void of any discipline and organization. I applaud smaller independent builders such as Absolute, especially in Italy where everyone is owned by someone else it seems and a few huge builders predominate.
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Old 02-19-2019, 10:44 AM   #7
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Unless high tech means fully automated layup the quality is only as good as the worst worker on your hull.

I well understand th arguments for cored hulls and have seen and owned may hulls and would only buy solid. That is just my opinion
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Old 02-19-2019, 10:51 AM   #8
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The extent of reconstruction of cored hulls is similar in difficulty to replacing the bottom on a wood boat. Admittedly it doesn't happen often but to the owner of that boat it is a catastrophe.
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Old 02-19-2019, 01:07 PM   #9
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I'm appreciating the feedback, thanks. To some of the comments - yes I referred to their marketing video - which is terrible. I've been in marketing all my career. Absolute seems to get high marks on their products. If you can read through the reviewers who say everything is great - it appears they have a clean factory that's pretty well-run. It's odd to me that they would promote CAD. LOL. I"m very familiar with cored hulls. Clearly, when done right it's a good product - I can't imagine Hatteras would compromise. That said, it's interesting to see a company still doing a hand-lay up fiberglass hulls. Nordhaven has solid fiberglass hulls below the waterline. Outer Reef is the same. I can understand why mega-companies like Benateue with multiple brands and high volumes do cored - it's a matter of efficiencies and economies. But it seems to be a common theme on trawlers to be solid fiberglass.
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Old 02-19-2019, 01:31 PM   #10
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I'm appreciating the feedback, thanks. To some of the comments - yes I referred to their marketing video - which is terrible. I've been in marketing all my career. Absolute seems to get high marks on their products. If you can read through the reviewers who say everything is great - it appears they have a clean factory that's pretty well-run. It's odd to me that they would promote CAD. LOL. I"m very familiar with cored hulls. Clearly, when done right it's a good product - I can't imagine Hatteras would compromise. That said, it's interesting to see a company still doing a hand-lay up fiberglass hulls. Nordhaven has solid fiberglass hulls below the waterline. Outer Reef is the same. I can understand why mega-companies like Benateue with multiple brands and high volumes do cored - it's a matter of efficiencies and economies. But it seems to be a common theme on trawlers to be solid fiberglass.
It requires less investment in the facility and technology to do solid fiberglass, no new training of personnel. On a boat designed to go slow, there's no disadvantage and many advantages, especially over poorly done coring. No reason not to stay solid fiberglass in a full displacement trawler.
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Old 02-19-2019, 01:57 PM   #11
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Originally Posted by markajh View Post
Nordhaven has solid fiberglass hulls below the waterline. Outer Reef is the same. I can understand why mega-companies like Benateue with multiple brands and high volumes do cored - it's a matter of efficiencies and economies. But it seems to be a common theme on trawlers to be solid fiberglass.
I don't think it's about efficiencies and economies. I think it's about performance. The weight reduction from composite construction allows the high speed performance that is (I think) a large part of the Beneteau appeal.

It's not really fair to compare the ST and their ilk to LR voyagers. The design requirements are quite different IMO, and construction decisions follow.
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Old 02-19-2019, 02:42 PM   #12
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I have owned a balsa cored boat for many years now as well as my solid Willard. Both boats are quite similar (length, beam, accommodations, layout and so on)

But one is full displacement and designed to go at 6K with 20 HP and making it light weight would just make it roll more and it would not go faster by much. The other boat is cored to the keel, is 1/2 the weight of the Willard and designed to go at 12K with 150HP.
There have been some core issues over the years mostly on the fore, side, & transom decks and the trunk cabin overhead but not the hull. These have been easily repaired and if not for the freeze/thaw cycles in New England may never have gotten large enough to even find.
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Old 02-19-2019, 04:32 PM   #13
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I have seen several discussion on cored vs solid hull on this forum.

Boats are built with the new buyer in mind. My guess is that most buyers of new boats don't really care, and that they may even prefer a cored hull as they likely would be lighter and give better performance.

On the other hand, a potential buyer like me is looking at a used boat (15 - 30 years old). My preference would be a solid hull, as I would have to concerned about a soggy bottom. It would take time for any problems to develop in a cored hull (and they may never develop), and many new boat owners wouldn't still have the boat if and when that happens.

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Old 02-19-2019, 05:37 PM   #14
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I have seen several discussion on cored vs solid hull on this forum.

Boats are built with the new buyer in mind. My guess is that most buyers of new boats don't really care, and that they may even prefer a cored hull as they likely would be lighter and give better performance.

On the other hand, a potential buyer like me is looking at a used boat (15 - 30 years old). My preference would be a solid hull, as I would have to concerned about a soggy bottom. It would take time for any problems to develop in a cored hull (and they may never develop), and many new boat owners wouldn't still have the boat if and when that happens.

Jim
That's a very valid point. We are highly unlikely to keep a boat long enough for it to be a problem. However, I'll use an two examples with which I'm very familiar. A major yacht builder was a pioneer in foam. They've been doing so in various boats for 20 years and never a known problem. Also, a high performance builder of jet boats. Clearly in their world weight is an issue and they've used foam for a similar period. Now, why do both do so? Speed. The first builder has always had cruising speeds in the 20 knot range with 25 knots WOT. It's like Sportfishing boats where they're all seeking an edge. Now the jet boat builder targets top speeds over 50 knots in boats from 60 to 140 ft. That requires a lot of special materials, coring and even some unique build methods to reduce vibration with typically three very large engines.

So, it's possible to do it extremely well. I've never owned a boat cored with balsa, only with foam. We've had boats that are solid and others cored.

Now, I'm also aware of some very poorly built cored boats. They would have been poorly built with solid glass too though. There are many solid glass boats that have had water infiltration and other problems.

So,

1. I wouldn't hesitate to go cored with the right builder.
2. There is no reason to core a full displacement 6-7 knot trawler. It's a waste of time and effort.
3. Coring has a place in the so-called fast trawler world. It's part of the methodology of gaining speed without simply doing it all with larger engines. Some of those who have done so have done so for decades in various boats and have an excellent track history. Some would scare me because their workmanship in other areas is so weak and I'd be afraid their coring was the same.
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Old 02-20-2019, 05:35 AM   #15
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A solid GRP boat of 35-50 ft would have a hull thickness of 1 inch to 1 1/2 inches over most of the bottom.

This would weigh about 3 to 6 lbs per sq ft.

With about a max of 1000 sq ft the hull below the waterline could be 3000 to 6000 lbs of GRP , or perhaps a max of 3 tons (2240lbs/ton).

With a engine burn of 3hp per ton at LRC reducing the hull weight by half might result in a reduction of half the fuel burn just for the wetted surface.

A saving of 1 1/2 tons could mean a saving of 4 1/2 HP required to propel the boat.

With 15HP per gallon an hour produced from diesel , that would roughly be 1/3 of a GPH at cruise.

Trawler folks seem happy with an extra dollar an hour underway , to avoid the terror of a bad "composite" hull.

Even doubling the hull skin thickness does little to the fuel bill.

All my numbers are rough "rule of thumb" but close enough to get the idea.

Very light weight is a requirement to go fast , so the extra costs and risk are unavoidable.

For a buck or two an hour , think of it as sleep well insurance.
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Old 02-25-2019, 02:45 PM   #16
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Cored Hulls

I would not buy or reject a boat solely on the basis of cored or solid hull, unless it was balsa core below the waterline - that would be a deal breaker for me.

Next we have to talk about closed cell foam core above or below the waterline. I have built boats both ways. Most cored hulls are cored above the waterline and solid below (I have built a number of boats that way and prefer that approach).

But the most critical and most overlooked question for the builder is this: "how do you protect the core around each penetration?" Most sales people don't even know. Unless the builder is removing core and filling with epoxy or making the area solid FG, the risk is elevated. I have seen 50' foam cored hulls with elevated moisture content down the length of the hull, from a poorly installed chain locker drain at the bow.

On the used boat side, that is where the survey is so critical because even if the builder did it properly, what about the hack who later installed a fitting and simply wiped the core with some sealant?

We all know that every boat has compromises. In my view you have to look at the whole picture and in my case, I would not rule a boat in or out based on whether or not the hull is solid or cored - unless cored below the waterline with balsa Plenty of people can chime in that their balsa is fine after x number of years, and that's good news. But they are the exceptions.

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Old 02-25-2019, 03:37 PM   #17
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Some common thoughts

Lot's of great info.

1) The manufacturers' reputation counts. Obviously, if Hatteras is cored it's less of a concern than Bills discount hulls.

2) There's a difference between balsa and foam core. Surveyors have opinions on both, it seems. A problem with either is a pain and needs repair. The major issue is that if the fiberglass is too thin on either side of the core, it can be compromised easier. That goes back to the reputation issue.

3) It seems like everyone agrees on solid hull below the waterline if they have a choice. Coring above, in superstructure (when you can't afford all that kevlar), are ok.

4) Most importantly, regardless of coring type - there HAS to be solid material wherever any opening or hold will be. That's easier for the manufacturer - and makes it really critical for the uniformed DIY guy after the sale. Buyer beware on used. Get your own surveyor - not the sellers!!! And pay for the best survey possible.

So - that's what I have distilled from all the input. Through all this, I've found the company I'm interested in has solid fiberglass below the waterline and a great reputation.

I had been interested in another large company. Coring aside, and number of units produced, the interiors and appliances aren't much better than a high-end RV. That's good on land - but for me - not at sea.

Thanks
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Old 02-25-2019, 04:26 PM   #18
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We just hauled our 58 Westbay (cored hull) in June. With 3/4 fuel (carries 1000 gal. full) and full water (300 gal.) she weighed 77,000 lbs. in the straps. obviously not the standard over 100,000 lbs. for a full displacement trawler but not a "light boat" by any means. Long range travel up and down the outside of Baja Mexico always at 8-9 kts. In 7 trips over the last 10 yrs. she has been in some dicey weather and did well.
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Old 02-25-2019, 05:13 PM   #19
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There are two reasons to core a hull. One is to make a lighter hull with equivalent stiffness and the other is to build a much stiffer hull with the same weight. A cored hull is generally more expensive than a solid hull to build because of the cost of the core material Closed cell foam core is quite expensive relative to fiberglass. For a trawler there is no particular reason to build the lightest possible hull. In fact two boats built to the same design, one cored, one solid glass will displace the same on their lines. In that case the cored hull would be much stiffer than the solid glass hull, since the hulls would be built to the same weight. Coring above the waterline is often used to save weight above the center of gravity to increase stability just as lighter materials are often used to build the cabin house.



There are additional advantages to cored hulls including better sound and thermal insulation.


A properly executed cored hull (solid glass at all hull penetrations, ideally resin infused, high shear strength closed cell foam core, etc.) is, in my opinion, preferable to a solid glass hull particularly if puncture resistant fabrics (kevlar) are used in the outer layers below the waterline.


A disadvantage of a well built cored hull is cost. That is particularly true if the hull is resin infused and post cured.



A hand laid solid glass hull is generally quite resin rich (not as strong) as a vacuum bagged or infused hull. In that case the extra weight of excess resin is a disadvantage.


Just my opinion based on watching quality hull construction and building a few hulls.
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Old 02-26-2019, 06:01 AM   #20
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cored hulls

Hi you may want to read this before getting a cored hull !!


https://www.yachtsurvey.com/bad_news_for_Bertram.htm
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