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      • TT35 Ad Campaign: The Un-Tug
      • Coronavirus Song: 'Drone Shot of My Yacht'
      • Smuggler's Run: Florida's Own 'Mini-Loop'
      • Virtual Tours of Old Ironsides
      • BoatUS to Gulfport, Don't Break Law
      • Luperon's Swimming Robber or Maybe Not
      • Georgia Begins Undoing Anchoring Ban
      • Gulfport Joins the War Against Cruisers
      • Video on D.R. Consulting Gig
      • Reward Increased in Hunt for Dolphin Killer
      • Our Favorite Fugitive Arrives in Mexico
      • Humungous Crane To Slice Up Wrecked Car Carrier
      • Avoid Getting Screwed by Georgia; Just Go Around
      • Radar Detects 'Fowl' Weather in Keys
      • Old Abe the Naval Architect
      • $20,000 Reward in Dolphin Killings
      • Great Lakes Search for Sunken Planes
      • Great Harbour Advises D.R. Boatbuilder
      • Despite Sewage Apocalypse, Mayor Blames Boaters
      • Loopers Will Need NY Certificates
      • Dorian Dog Story 'Spiked'
      • $209,000 for 61-Foot Hatteras MY
      • Refloating Effort Progress
      • Free Bahamas Cruising Guide
      • New Florida Anchoring Bans
      • Propane Fire
      • Psychedelic Fibers Advance Knot Theory (Video)
      • Wanted on the Waterways 1/4/2020
    • Ken Fickett's Blogs
    • Cruising in the Time of Covid: Think Outside The Loop
  • Owners
    • Moving Aboard
    • The Odyssey Begins
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  • Home
  • About
    • A Family Affair >
      • Ken Fickett
      • Becky Fickett
      • Travis Fickett
      • Jessica Fickett
    • Mirage Manufacturing
    • Factory Support
    • Careers
    • Contact
  • Boats
    • TT35 >
      • TT35 Specifications
      • TT35 Key Features
      • TT35 Design Discussions
      • Towing Resources
      • PRESS
    • N37 >
      • N37 Specifications and Layout
      • N37 Photo Gallery
      • N37 Brochure
    • GH37 >
      • GH37 Specifications and Layout
      • GH37 Photo Gallery
      • GH37 Brochure
    • N47 >
      • N47 Specifications and Layout
      • N47 Photo Gallery
      • N47 Brochure
    • GH47 >
      • GH47 Specifications and Layout
      • GH47 Photo Gallery
      • GH47 Brochure
    • GH74
  • Great Design
    • Trawler Truths >
      • Trawler Truth 1
      • Trawler Truth 2
      • Trawler Truth 3
      • Trawler Truth 4
      • Trawler Truth 5
      • Trawler Truth 6
      • Trawler Truth 7
    • Design Discussions >
      • Twins vs Single
      • Shoal vs deep draft
      • Stability vs Ballast
      • Fishtail Rudders
      • Space Age Core
      • Core Materials
      • Unsinkability
    • Economy
    • Our Naval Architect
  • Construction
    • Lamination
    • Interior
    • Rigging
  • Trawler Times
    • News >
      • California Humpbacks Perform Rare 'Triple Breach' (Video)
      • Betrayal in Georgia? Anchoring Rules Appear Worse Than Ever
      • Ga. Wreck Removal Delayed Again: Anchor SNAFU
      • Chesapeake's Tangier Island: Enjoy it While You Can
      • Robert Peek, Beloved Deep Creek Lockmaster, Has Died
      • U.S. Agency Warns of GPS Interference
      • Rudy and Jill's ICW Tips
      • A TT35 Day at the Sausage Factory
      • Cat or Monohull Sailboat Versus a Trawler (Images, Long)
      • Loopers Warned To Linger Post-Sally
      • Coast Guard Shallow Draft Navigation Survey
      • Forget Lithium for a Moment: Why Old-Fashioned Batteries Explode
      • Tracking Hurricane Laura Live (Streaming Video)
      • The Downsides of Cruising (Comprehensive)
      • Circumnavigator Who Eschewed Instruments Dies at 104
      • Maritime Liens: Don't Let Your Boat Get 'Arrested'
      • Gulf Stream Is Slowing Down
      • Attention Cruisers, Perseids Meteor Shower Peaks Next Week
      • Ladies Publish Great Loop Tell-All
      • New NOAA Model Forecasts Another Sahara Dust Cloud Arriving This Week (Animation)
      • TT35 Demonstrations Set for Next Week
      • Prep for a Busy Hurricane Season
      • It's a Marina! It's a Mooring! No, It's a French Design (Video)
      • Giant Floating Chain Saw To Rip Up Wrecked Car Carrier off ICW
      • Lock Sked Final: Great Loop Doable, But...
      • Georgia Caves, Defangs Draconian Anchoring Law
      • Heads Up, Boaters: Here Comes the Red Dust from Africa
      • Bahamas Changes It's Mind: Keeps Covid Test Requirement
      • Insurance? Tell All or Risk Claim Denial
      • Gulf 'Dead Zone' Bigger Than Connecticut
      • GPS Spoofing Mystery: AIS Crop Circles & Ghost Ships
      • Yanmar To Install Fuel Cell Propulsion in Boats
      • Bahamas To Boaters: Welcome Back, Wear a Mask
      • Covid Concerns Fuel Coast Guard Retention Drive
      • Birthday Gift for Her 70th, a TT35
      • Above Average Hurricane Season Forecast
      • Foreign Boaters Get Some Relief as Restrictions Eased
      • Catalina Island Reopened for Arriving Boats
      • When a Boat Isn't: Supreme Court Decides
      • Coast Guard Adopting 'i911' for Your Location
      • Makeover: Storm Early Warning System Explained (Video)
      • The Reality of Quarantine in Paradise
      • 92-Footer Sinks Off California
      • New York to Loopers: You May Be Out of Luck
      • Badass Origins of Boating Law
      • Can Cannabis Save Florida Waterways?
      • Tale of a Terrible Boat
      • Boating and Social Distancing (Video)
      • Powering Through a Mexican Gale
      • Bahamas Says Stay Away, Get Out
      • Composting Heads Are a Good Option
      • TT35 Ad Campaign: The Un-Tug
      • Coronavirus Song: 'Drone Shot of My Yacht'
      • Smuggler's Run: Florida's Own 'Mini-Loop'
      • Virtual Tours of Old Ironsides
      • BoatUS to Gulfport, Don't Break Law
      • Luperon's Swimming Robber or Maybe Not
      • Georgia Begins Undoing Anchoring Ban
      • Gulfport Joins the War Against Cruisers
      • Video on D.R. Consulting Gig
      • Reward Increased in Hunt for Dolphin Killer
      • Our Favorite Fugitive Arrives in Mexico
      • Humungous Crane To Slice Up Wrecked Car Carrier
      • Avoid Getting Screwed by Georgia; Just Go Around
      • Radar Detects 'Fowl' Weather in Keys
      • Old Abe the Naval Architect
      • $20,000 Reward in Dolphin Killings
      • Great Lakes Search for Sunken Planes
      • Great Harbour Advises D.R. Boatbuilder
      • Despite Sewage Apocalypse, Mayor Blames Boaters
      • Loopers Will Need NY Certificates
      • Dorian Dog Story 'Spiked'
      • $209,000 for 61-Foot Hatteras MY
      • Refloating Effort Progress
      • Free Bahamas Cruising Guide
      • New Florida Anchoring Bans
      • Propane Fire
      • Psychedelic Fibers Advance Knot Theory (Video)
      • Wanted on the Waterways 1/4/2020
    • Ken Fickett's Blogs
    • Cruising in the Time of Covid: Think Outside The Loop
  • Owners
    • Moving Aboard
    • The Odyssey Begins
    • The Search For Adventure
Great Design  Trawler Truths  Design Discussions  Economy  Our Naval Architect
Twins v Single  Shoal v Deep  Stability v Ballast  Fishtail Rudders  Space Age Cores  Core Materials  Unsinkability

Space Age Cores

Why PVC and two ‘polys’ have eclipsed wood as a coring material

by Ken Fickett
​

My 50-year-old, 20-foot fishing boat sits in the tall weeds behind my barn waiting patiently for its turn at restoration. It has been in the family since it was built, and not only was I the first person to drive it, as a very young kid I did demos with it at the 1966 Miami International Boat Show. It sported twin 50 hp Chrysler outboards and absolutely flew by standards of the day. Built by Raleigh Stapleton, it was one of the very first production boats designed to fish the flats. It also was one of the forerunners of a whole new breed of boats that folks were calling center consoles.
Not only was this a fairly revolutionary boat for the day from a design standpoint, it also set itself apart when it came to construction. The hull was hand-laminated fiberglass with the bottom and sides cored completely with half-inch thick end-grain balsa. The transom was cored with two layers of plywood and the stringers were 2" x 6" fir, encapsulated with heavy laminates of fiberglass. This boat was the proverbial brick outhouse, and, with the exception of the transom, which is rotted and needs to be replaced, still is today.

Meticulous construction was the key to this extraordinary longevity. Had my brother and I been more careful on subsequent engine, transducer and ladder installations, the transom would have likely held up too. When I get around to replacing the transom, the likelihood of my using wood will be zero. I want my son to be able to give it to his kids in another 40 years without having to rebuild yet again. Like many of today’s builders, I will use a synthetic core.
cutaway view of honecob coring useid in great harbour trawler
Synthetic cores are certainly not new and have been in use for more than 60 years. In fact, I have been using them since the mid-1960s. They do the same job as wood cores by stiffening a part, but with the added benefit of providing flotation. Boston Whaler became famous for its foam-cored hull decades ago, and other manufacturers followed suit, injecting their vessels with a relatively low density polyurethane foam between pre-laminated inner and outer shells to gain U.S. Coast Guard required flotation and improve overall stiffness.

Many people have heard of “water logged” boats, and the technique of injecting an expanding foam to fill a void has caused a lot of heartache over the years when done poorly. This is not the kind of coring we are talking about. This discussion is about sheets or blocks of core that are bedded carefully onto a laminate—usually skins of fiberglass and resin—and then skinned over on the inside to seal the core, making a sandwich in which the core is the meat.

Today the major non-wood cores used by boat builders are PVC, high-density polyurethanes, and polypropylene. The PVC cores are probably the most common of the synthetic cores and fall into two categories: cross linked and non-cross linked. While the merits of both are bantered about endlessly by builders and designers with too little to do, the short story is that the cross-linked stuff is a bit cheaper, easier to use, and thickness for thickness will build a stiffer part. The non-cross linked foam is more expensive, harder to use, and not as stiff. But when it is designed as a component of a complete laminate, a non-cross linked core can take one heck of a whack without nearly the catastrophic damage you might see in other cores.

I remember racing a J24 sailboat in the late 70s in Key West for the annual winter regatta, getting hit hard in a port/starboard incident and being shocked to see a basketball sized piece of hull knocked completely out just above the waterline. These were balsa-cored hulls and very well built. But when they got hit, it could be a bad deal. On the other hand, a good friend of mine hit a piling that was floating offshore. He was in his fully foam-cored sportfishing boat running close to 30 miles an hour at night when he hit. There was no major damage and the hull only shows a minor dent today.

Hard hits to hulls made with non-cross linked cores are more akin to impacts to a piece of metal, in that the failure tends to be what engineers call “plastic.” We might call it “more forgiving” because the material tends to bend rather then break. Probably the toughest hull structure available uses a non-cross linked core such as Airex, with the laminates on either side being a hybrid mix of fiberglass and a man-made aramid fiber such as Kevlar or Spectra. While that combo is going to be considerably more expensive than conventional structures, it’s used on many of the leading high performance racing powerboats, and by all the smugglers that have to run offshore at night.

There is a new synthetic non-rotting polypropylene core that looks like honeycomb and is making huge inroads in boat construction. It is used everywhere but mostly above the waterline. This core has some great benefits and represents the best bang for the buck in the way of a core in areas that are not highly stressed such as decks, cabin sides, and roofs. It has great sound deadening characteristics and has received a good reception amongst builders for use around and over engine compartments.

The big drawback is that it almost always has to be vacuum-bagged into place. Vacuum-bagging is a technique used to insure the proper bonding of core to its substrate. Vacuum-bagging is time-consuming and expensive, but it can make a big difference in the bond quality for all cores. The most popular of the polypropylene cores is Nida Core, which uses a resin-absorbing material that is heat-bonded to the honeycomb cells to form a nonpermeable bonding surface. Nida Core is the least expensive core with the exception of the polyurethanes.

Polyurethanes are typically high-density and are the heaviest of all cores. In many ways they most closely resemble wood, except they will not rot. They have the highest resistance to compression (being squished) and can be an excellent choice in isolated areas that have bolts holding components on to the boat. A good example? Transoms that have outboards bolted on. Many transoms today have pre-molded, high-density polyurethane transoms bonded into their structure to avoid just the problem that I have with my old boat.


Picture
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