Negatives of full Fibreglass hulls/decks?

[Rucksta]

I did some penetrative testing on solid and composite panels at the firing range.

Small holes in composite, large chunks out of solid.

Counter intuitive but my anecdotal observations over the years suggest cored boats fair quite well being dragged over the reef - salvage not grounding - and are easily repairable.

No input regards hitting containers, ice bergs or whales

[Lucky Luke 1]

Thanks for all the reply's so far.
I'm under the assumption that a full fibreglass hull is less likely to be holed in the advent of a lightning strike than glassed over ply. True or false?

[Benz]

Originally Posted by Lucky Luke 1

Thanks for all the reply's so far.
I'm under the assumption that a full fibreglass hull is less likely to be holed in the advent of a lightning strike than glassed over ply. True or false?

I'm not sure there's a difference for lightning strikes, unless your ply is wet and thus conductive, which also means the boat is worthless, or soon will be.
Despite differing opinions, you'll notice that nobody here had advocated a ply-cored hull. That's because it's a bad idea. The closest to that you can safely get is a cold-molded timber-and-epoxy hull, which are quite strong and durable, if built right and maintained well (best sea boat I ever sailed was one of these).
But if you're asking which method of construction is better for lightning, perhaps you don't know yet what questions to ask.

[Benz]

Originally Posted by Rucksta

I did some penetrative testing on solid and composite panels at the firing range.

Small holes in composite, large chunks out of solid.

Counter intuitive but my anecdotal observations over the years suggest cored boats fair quite well being dragged over the reef - salvage not grounding - and are easily repairable.

No input regards hitting containers, ice bergs or whales

This testing is meaningless to any but yourself unless you publish the dimensions/materials/testing parameters of the panels you shot up.

[Benz]

Originally Posted by zstine

Well, this is an opinion and one I take exception to. You want a strong hull especially below the waterline. But if you want 'heavy' just for weights sake, then steel and fero-cement boats would be much more popular. Heavy does not equal comfort. Comfort, or the boat's motion, depends on where the weight is located as inertia is primarily what determines period & amplitude of motion and weight high, like a deck, is no bueno. Heavy also means slower, which means you are subject to worse weather on passages as you have 1) less ability to get out of the way and 2) will spend more time at sea 'waiting' to get hit. Heavy also means more fuel consumption, and therefor more cost and more pollution. I also believe solid glass layups are more prone to cracking/failing at hard points compared to a cored hull but it really depends on design. Heavy hull to some extent means a bigger sail plan to push it. That means bigger lines, bigger winches, bigger everything (unless you want to go slower)... that means higher cost of maintenance and replacement and more difficulty in handling the bigger rig.

I didn't say you wanted heavy decks--I said you wanted a heavy hull. The thing is, for a cruising boat, which is what we're talking about, you need a design that can be loaded with all the cruising gear and supplies you need and still get up and go. For a given waterline length, the heavier, fuller boat will always be able to take a greater amount of loading and still move than a lighter, smaller design. It's just physics.
The amount of load I put in my full-keel, solid FG-hull 31' boat to cruise with a family of five would all but sink a Catalina 31. Thing is, the boat was designed to be heavy, to carry a big payload, and to do it well. Strangely enough, even loaded to the Plimsolls, my 8hp outboard can still get her up to 5kts. And with 12kts of breeze she'd do hull speed. You can't ask more of any boat than hull speed, unless you're somehow cruising in a planing hull with barely a change of undies, which I get that some people do. But most of us, regardless or initial boat design, are not planing in our cruising boats, and certainly not in smaller ones.

[Rucksta]

Originally Posted by Benz

This testing is meaningless to any but yourself unless you publish the dimensions/materials/testing parameters of the panels you shot up.

I appreciate your view of test validity as the only objective was to satisfy my curiosity.

Only did this once with one set of samples so a non scientific test.
Additionally each panel took three rounds with increasing impact 9mm 7.62 50 Cal.

Hope this is enough to pique your curiosity.

Panels

-20 mm Airex 3 & 2 x 27 oz E glass woven roving hand laid in polyester
-18mm Divinycel 3 & 2 x 450 gsm E glass bias weave hand laid epoxy
-20mm Nomex 600gsm Kevlar epoxy prepreg over 450 gsm S Glass vacuum
bagged and autoclaved

-3/4' solid layup in 27 oz woven roving hand laid wet layup in epoxy
-3/4' solid layup in 27 oz woven roving hand laid dry layup in poly
-1" chopper gun in poly

All panels were 12" square edge clamped.
Range 20 mts

Ordinance
9mm parabellum
7.62 NATO
.50 Cal BMG

Results
9mm
Entered all the composites with no exit except the Kevlar which showed
surface distortion.
Cratering the solid roving no exit.
Radial fracturing of the chopped layup no exit.

7.62
Entered the Kevlar/ Nomex no exit.
Low energy exit on Airex & Divinycel. Shards attached Airex was cleaner. Solid roving showed non cratered exit with delamination.
Chopper layup showed cratered exit.

50 Cal
Nomex /Kevlar delamination over a 32 mm exit area.
Airex delamination over 25 mm exit area.
Divinycel delamination over 40 mm exit.
Woven layup Cratering 20 mm and delamination 40mm on entry. Cratering 45 mm and delamination to 75mm on exit
Chopper layup Cratering to 25 mm and fracturing to 75 mm on entry Cratering to 125 mm on exit and fracturing to the clamps.
Debris field showed large chunks on the chopper layup



The Kevlar layup showed the best resistance to penetration where the Airex core seems to absorb more energy.

After evaluation of the first three rounds in each panel we just let loose and had some fun blowing the **** out of all panels.
The solid layups disappeared first but in the end they were all dust, chunks and shards.

If I was a smuggler I think I would go Airex Kevlar S Glass for my cigarette boat.

[Copacabana]

Originally Posted by Rucksta

I appreciate your view of test validity as the only objective was to satisfy my curiosity.

Only did this once with one set of samples so a non scientific test.
Additionally each panel took three rounds with increasing impact 9mm 7.62 50 Cal.

Hope this is enough to pique your curiosity.

Panels

-20 mm Airex 3 & 2 x 27 oz E glass woven roving hand laid in polyester
-18mm Divinycel 3 & 2 x 450 gsm E glass bias weave hand laid epoxy
-20mm Nomex 600gsm Kevlar epoxy prepreg over 450 gsm S Glass vacuum
bagged and autoclaved

-3/4' solid layup in 27 oz woven roving hand laid wet layup in epoxy
-3/4' solid layup in 27 oz woven roving hand laid dry layup in poly
-1" chopper gun in poly

All panels were 12" square edge clamped.
Range 20 mts

Ordinance
9mm parabellum
7.62 NATO
.50 Cal BMG

Results
9mm
Entered all the composites with no exit except the Kevlar which showed
surface distortion.
Cratering the solid roving no exit.
Radial fracturing of the chopped layup no exit.

7.62
Entered the Kevlar/ Nomex no exit.
Low energy exit on Airex & Divinycel. Shards attached Airex was cleaner. Solid roving showed non cratered exit with delamination.
Chopper layup showed cratered exit.

50 Cal
Nomex /Kevlar delamination over a 32 mm exit area.
Airex delamination over 25 mm exit area.
Divinycel delamination over 40 mm exit.
Woven layup Cratering 20 mm and delamination 40mm on entry. Cratering 45 mm and delamination to 75mm on exit
Chopper layup Cratering to 25 mm and fracturing to 75 mm on entry Cratering to 125 mm on exit and fracturing to the clamps.
Debris field showed large chunks on the chopper layup



The Kevlar layup showed the best resistance to penetration where the Airex core seems to absorb more energy.

After evaluation of the first three rounds in each panel we just let loose and had some fun blowing the **** out of all panels.
The solid layups disappeared first but in the end they were all dust, chunks and shards.

If I was a smuggler I think I would go Airex Kevlar S Glass for my cigarette boat.

A while back, JeffH (is he still around?) posted an interesting study comparing solid and cored panel resistance to impacts. The study included a number of hull materials including fiberglass, wood and steel, if I recall correctly. I don't remember all the details, but clearly the cored panels absorbed shocks much better and fared better than solid panels. I think you also have to compare the type of impact (narrow point of impact like hitting the edge of a dock or a broader impact like hitting a sand bar).

I have a solid fiberglass hull, but I can certainly see the advantages in a foam-cored hull above the waterline.

[Polar Opposite]

[QUOTE=redneckrob;3503075]

Originally Posted by BillKny

I'm not actually aware of any over 30', are you?

I've owned two 30'+ boats with solid fiberglass decks...a Contest 32 ketch and a CSY 33 cutter. Both were/are rugged cruising boats. All CSYs were solid fiberglass decks, and defined the concept of "overbuilt". I'm not a marine architect, but I don't notice any more vertical support on the interior than any other production boat, and I don't notice any more condensation either. Nor did either deck ever noticeably 'flex". I would guess that the reasons to not do it are more driven by reducing construction costs, complexity and topside weight than by any other considerations.

[rslifkin]

Originally Posted by Benz

I didn't say you wanted heavy decks--I said you wanted a heavy hull. The thing is, for a cruising boat, which is what we're talking about, you need a design that can be loaded with all the cruising gear and supplies you need and still get up and go. For a given waterline length, the heavier, fuller boat will always be able to take a greater amount of loading and still move than a lighter, smaller design. It's just physics.
The amount of load I put in my full-keel, solid FG-hull 31' boat to cruise with a family of five would all but sink a Catalina 31. Thing is, the boat was designed to be heavy, to carry a big payload, and to do it well. Strangely enough, even loaded to the Plimsolls, my 8hp outboard can still get her up to 5kts. And with 12kts of breeze she'd do hull speed. You can't ask more of any boat than hull speed, unless you're somehow cruising in a planing hull with barely a change of undies, which I get that some people do. But most of us, regardless or initial boat design, are not planing in our cruising boats, and certainly not in smaller ones.

A hull doesn't necessarily need to be heavy to achieve that, although a light hull shaped to carry a lot of weight may not be happy if loaded too lightly. Having too large a portion of your weight as variable weight is a challenge.

[bailsout]

I like reading about these plastic boats and their sailing properties and construction drawbacks. Feeling very smug and happy with my double planked wood hull and wood everywhere else. And throw in being more environmentally friendly.😁

[onestepcsy37]

i owned a csy 37 which had no coring - hull or deck. i had to drill a hole in the deck to install the holding tank pump out fitting and was amazed at how thich the fiberglass deck was.

only had one problem - when the boat was already 30 years old. spider cracks around the mast thru deck fitting. mast was keel stepped and there was a massive mountain of fiberglass where the mast passed through the deck. so big no ordinary mast boot would fit it - had to make my own. but on the deck just around the 'mountain' there were some small spider cracks which i filled and patched and never saw a problem again.
not having coring was one of the reasons i bought that boat.

[onestepcsy37]

Originally Posted by Lucky Luke 1

Thanks for all the reply's so far.
I'm under the assumption that a full fibreglass hull is less likely to be holed in the advent of a lightning strike than glassed over ply. True or false?

we took a direct hit by lightning in the sea of abaco. evaporated the antenna, came down the mast - i watched it happen - and left the boat who knows where. i'm not grounded.

not a single problem to the solid fg deck and hull. none. did suffer some erratic equipment loss.

[onestepcsy37]

Originally Posted by bailsout

I like reading about these plastic boats and their sailing properties and construction drawbacks. Feeling very smug and happy with my double planked wood hull and wood everywhere else. And throw in being more environmentally friendly.��

the only real problem i have found with wooden boats is that you have to dry the wood a year before you can use it in the fireplace.

[boatpoker]

Originally Posted by Lucky Luke 1

Thanks for all the reply's so far.
I'm under the assumption that a full fibreglass hull is less likely to be holed in the advent of a lightning strike than glassed over ply. True or false?

Please tell me the make of a production boat with a glass over ply hull.

[Benz]

Originally Posted by Rucksta

I appreciate your view of test validity as the only objective was to satisfy my curiosity.

Only did this once with one set of samples so a non scientific test.
Additionally each panel took three rounds with increasing impact 9mm 7.62 50 Cal.

Hope this is enough to pique your curiosity.

Panels

-20 mm Airex 3 & 2 x 27 oz E glass woven roving hand laid in polyester
-18mm Divinycel 3 & 2 x 450 gsm E glass bias weave hand laid epoxy
-20mm Nomex 600gsm Kevlar epoxy prepreg over 450 gsm S Glass vacuum
bagged and autoclaved

-3/4' solid layup in 27 oz woven roving hand laid wet layup in epoxy
-3/4' solid layup in 27 oz woven roving hand laid dry layup in poly
-1" chopper gun in poly

All panels were 12" square edge clamped.
Range 20 mts

Ordinance
9mm parabellum
7.62 NATO
.50 Cal BMG

Results
9mm
Entered all the composites with no exit except the Kevlar which showed
surface distortion.
Cratering the solid roving no exit.
Radial fracturing of the chopped layup no exit.

7.62
Entered the Kevlar/ Nomex no exit.
Low energy exit on Airex & Divinycel. Shards attached Airex was cleaner. Solid roving showed non cratered exit with delamination.
Chopper layup showed cratered exit.

50 Cal
Nomex /Kevlar delamination over a 32 mm exit area.
Airex delamination over 25 mm exit area.
Divinycel delamination over 40 mm exit.
Woven layup Cratering 20 mm and delamination 40mm on entry. Cratering 45 mm and delamination to 75mm on exit
Chopper layup Cratering to 25 mm and fracturing to 75 mm on entry Cratering to 125 mm on exit and fracturing to the clamps.
Debris field showed large chunks on the chopper layup



The Kevlar layup showed the best resistance to penetration where the Airex core seems to absorb more energy.

After evaluation of the first three rounds in each panel we just let loose and had some fun blowing the **** out of all panels.
The solid layups disappeared first but in the end they were all dust, chunks and shards.

If I was a smuggler I think I would go Airex Kevlar S Glass for my cigarette boat.

Thanks for taking the time to post this.
If you have some spare ammo and materials anytime, could you do a solid panel: 1/4" S-glass woven 10oz cloth; 1/2" Kevlar biax; 1/2" 1708 hand-laid in vinylester? That's the schedule I'm after for the hull of my dream expedition schooner.

I'll bring a case of beer and ear protection.