Lighter weight boats ??

At least you know PVC foam won't rot. I'd be confident a lot of sleep has been lost by owners worrying about rot in balsa.

 

In any event, lightweight construction only works if the hull design suits it. It is hard to imagine a 24 degree vee planing hull being successful if it doesn't float on its design waterline because a stack of weight has been saved with composites.

 

Stating the bleeding obvious ! If you don't design any hull with the correct displacement, its always a failure - be it heavy or light.

The lightest weight design always works better. You can always add weight as ballast or cargo on a light weight boat. You cant take weight off an overweight, overbuilt boat. Also, heaviness and strength are not always closely related in plastic boats.

a 24 degree vee planing boat doesn't work any better if its overweight.

 

But it has to be somewhat heavier than it needs to be in terms of structural integrity, made using modern materials, is the point I am making. So, it makes limited sense to say building lighter is advantageous in this kind of boat, the deadrise will have to be reduced, and it will no longer be the same kind of boat. The only advantage I can see in lightweight, but strong build would be in giving greater freedom to instal heavier, particularly diesel engines.

 

Thats nonsense. Building a boat hull heavier than it needs to be maintain its water line is the work of an amateur. For a start, if the NA wants the boat to run at its lightest, its simply a case of adjusting the hull design.

... what ? only 1 advantage ?

Bigger engines is a considerable advantage. I already gave you two other reasons
extra cargo, extra crew

now lets name a few more obvious ones

greater fuel capacity, greater speed, less fuel consumption, less hull pressure under speed, more supplies, more water ....

there is no way anyone would let a boat float higher than its designed lines, there is always ballast if you cant take advantage of the very desirable lighter weight feature.

 

Using the example of the type of boat I mentioned, no-one seems to be in a hurry to switch to lightweight advanced composites, reason being it creates as many problems as it solves. For displacement power cats however, it opens up new possibilities.

 

Tell me something about the hull of my boat.
It is wooden carvel planked
Weighs 17000 pounds
Has 15 tons net carved into woodwork near the USCG number
It is a 1970 Eggharbor 37 sedan cruiser.
basic shape is 37 foot long 13 foot wide
The hull profile reminds me slightly of a guppy in profile, with a deeper front part and a slight hook at the aft part.
It seems to have a fair amount of deadrise at the transom. It has round bilges.
I totally redid all the screws and new framing. Coated everything with sanitred permaflex ( a polyurethane waterproof coating) and it rides slightly higher on its waterline ( looks at least 1 inches higher) so I think the wood is drier so less weight.

I find it to be a smooth comfortable running boat. It will roll around if a big deep wake comes and your moving slow.
How does my hull compare weight and shape with a typical FG hull today?

 

Is there a 'typical' FG hull ?? I dont think so.

You would need to compare your hull shape in wood with a similar one in glass.

 

How about

http://www.ellisboat.com/hullDesign.php

"With the exception of the solid fiberglass keel and skeg, the hull is cored with vacuum bagged ATC Core-Cell® structural foam core to provide exceptional seaworthiness, impact resistance, sound deadening, strength to weight ratios and insulation properties."

http://www.compositesworld.com/articles/composites-take-the-hit-in-us-navy-patrol-boat

"The Mark V Special Operations Craft (SOC) is the U.S. Navy SEALs' high-speed, medium-range insertion and extraction vehicle, also used for limited coastal interdiction"

Dolphin Boats
http://www.dolphinboats.com/backcountry_pro18.php

"10 yr. Structural Hull Warranty (transferable)
All Closed Cell Foam & Composite Construction (no wood)
High Density Closed-Cell Foam Core Transom"

do some searching yourself, and be surprised

 

You just need to have enough glass around it - you dont need the fibres in the foam at all. Its just there for compression

You just given the answer like every one thinks put enough glass around it!!! thats what you need to trying to get rid of is the glass and resin Thats where the weight is glass fibres in foam has a due purpose of holding the foam to stop the shear and adding to compression strength !! Its shear and peel ability after the shear that the biggest down fall with using foam . large areas of foam are really scary in a stress and pounding situation !! the panel size and inside framing is very important . just one point of shear or let go and its history .
We were making large panels for the inside framing of a mega yacht and saw a panel get caught on the edge of the bench as it was being lifted off and it peeled the whole glass layer off one side ,as in total the panel used 50 mm H 80 foam and Had 4 layers of 800 gram double bias glass on each side !!! its was the foam that let go !!! not where it was stuck , so back on the bench sprayed a coat of resin, rolled it with a mohair and sucked and pressed it back together again untill 6 hours later .panel got used as a bulkhead eventually !!

If you want see and learn all about what works and what dosent go do boat repairs for a year or two you will see things that will make you hair stand on end . i know what i have seen and what the causes were and what materials will take serious punishment and what is totally useless .
I dont have any exsperiances of using Core cell foam but it sounds like the only foam core to use , but thats only from what ive read !.
The old saying "dont believe anything you hear and only 10% of what you read" .

Ok a question! whats your take on Core matt ??
what is it ??
where can you use it ??
where should you never use it??
why should you never use it in that situation ??

 

i knew id find it given time !!

http://www.iccm-central.org/Proceed...lications/SANDWICH STRUCTURES/B6.26 Aktas.pdf

I remember seeing this principle long time ago and it to me totally makes sense fibres running through the FOAM core to hold the skins on each side . I could see something like this happening in the future thin skins a thickish core and resin infused inside and out in one hit !! dont hit me with all the problems look beyond them and think about what you would have at the other end . Now this is light weight !! the skin coming off the core and shear are greatly reduced but the strength is there . nothing is impossible
Was more than 15 to 18 years ago i saw something like this !!

 

Interesting article, thanks, Tunnels. The way I mentally picture it, a foam-cored panel with no strong tensile attachment between the two skins would be like an I-beam with no strong web between upper and lower plates. The two surfaces would be more likely to go their own separate ways with the tension skin more easily bent and the compression skin more likely to buckle. Foam cores are good at resisting distributed compressive forces but not so effective on point intrusions.

 

What both Wayne and Tunnels have forgotten, is that the two fiberglass sides of a panel are joined around the edges.

Its not like a ham sandwich with separate layers unconnected layers, its like a 'pie', where the edges are sealed.

The filling of a ham sandwich has no hope of holding the two bits of bread together.
Likewise, the filling in the pie doesnt have to have a terrific bond to the upper and lower pastry layer, but the edges are strongly bonded, so the two layers cant move across the filling.

If you hold a ham sandwich by the edge, the rest of it will flop as the layers separate- its a two handed job. A pie on the other hand, can be held by one hand.


Another analogy to foam construction, it works like a tent does. The tent poles dont need a tight fastening to the top ( to the tent top ) and the bottom (standing on the floor of the tent) because the tension on top and bottom ( trying to compress the tent pole ) keeps the pole in place.

The foam acts like a tent pole, to hold the two layers apart, held their by their apposing pressure.

For the upper or lower layer of a foam sandwich (better think of it as a foam 'pie' ) the edges of the panel would have to break so that the top or bottom layer could slide across the foam. The same goes for peeling. The edges have to be broken before any peeling can happen.

this is why the strength of the outer layers is the critical thing.

 

The thing that i dont like about foam is how easy you can peel the glass layes off foam!!, off like at a point it just falls off its not the glass to foam its the foam its self . The density specified in my veiw is always way to low simply it has not guts !!!and as for mr watson saying it needs more glass thats apart of why we use core ,to elliminate the use of thick glass !!
Some people have strange ideas of the materials we have to use .
Tell me whats you take on Corematt ?? how should it be used and what are it limitations ???

 

If you think all panels are flat you are not looking properly !! panels can be all shapes with curves and shape in many places . Even in the case of a side of a cabin with a 200 radius at the top and a gentle curve of the roof
In our case the roof supports a fly bridge and although the cabin has a foam glass framing inside the roof could have to carry the weight of up to 10 people . The bonding of the flybridge to the deck is critical as theres a inner and a outer panel of the flybridge that are in contact with the roof so its becomes a intergral part of the frame work . The radius in the corner of the roof is the weak point and if the core had been foam its possible for the foam to delaminate and shear and peel in all directions !!!. Peel because it dosent have the strength to stop its self from peeling . This has nothing to do with what you eating for lunch pie or sandwich (but i do like your discriptions) plain and simple its not good enough . In the begining we speced foam for this whole boat but after sitting and looking at the possabilities of panels comeing apart i shelved that idea and went 100% balsa every where .
Foam in panels that have bending happening on a regular basis has a limited life span . The thicker the core the more likely its is of letting go !! Panels sizes need to be smaller and there has to be more places where theres glass to glass all round (Like a pie )Big panels is why panels come apart .
The racing yachts we made 8 of where the motor and sail drive were mounted it was onto a glass to glass part where the core was kept away . because the sail drive went down through the hull the foan was kept well away because of motor vibration and in the event of the propeller stricking a floating chunk of wood and getting a sudden shock loading . It was speced on the plan that we simply mount the engine bed ontop of the foam core and dig out round the hole and epoxy fill ,then sand and gel coat . its the way most companies do it . and its not the proper way Oh but that the way its been done for whoe knows how long !!! i hear the cry's !! these were boats being build from brand new in a mould all the framing in the boat wereglass foam glass panels egg crated and glassed as it was assembled so if there was stress and strain its carried over a wide area . If Balsa had been used then would have been motor on top of the inner skin and dig out the core and epoxy filled . Foam has its place and have use square kilometers of it over the years but the density and the stick and stay of the glass to the core is my biggest concern .
So untill i see first hand with my own eyes the merits of corecell and how well the glass sticks and stays i am not changing my mind !!