non-cored fibreglass panels instead of ply

Panel construction of solid 'glass laminates isn't light, nor especially efficient, compared to more conventional methods of acquiring a solid laminate hull. Solid 'glass panel construction is inherently weaker and of course limited to developed shapes as well.

This type of panel construction becomes light only if it's used as part of a cored structure, which is precisely what the original poster is attempting to avoid.

Your images of the powerboat appear to be cored panels and Derek Kelsall's work is surely in cored panels.

 

I would suggest that the foam is the weak link in the strength equation. A PVC foam core you may use only has a tensil strength of a few hundred pounds. It simply is used to make a "stiffer" panel. Yes, most all of the panel boats were cored, but some were not, including a 71' long liner. Tommy Dreyfus, most notably built many single skin IOR racing sailboats in the 1970's. All of the Swans were single skin for many years. Light is relative as the shell is only a modest portion of the total weight.

 

1.- Glassfiber reinforced resin as a building material has ONE, just 1 advantage over all other common boatbuilding materials = it follows every curvature, shape, form without much effort. That makes it possible to produce a structure with non skilled labourers and get a product >sufficient< for the use intended!

So, why would one be so unbelievable stupid to use a material far beyond its capabilities? A flat panel has to be metal, plywood or (in some cases) wood, but never a glass layup! And there is not a single one argument possible why it should be.

2.- Cored material is well known for having serious issues, even when layed up by very experienced yards. Although it CAN be a excellent boatbuilding material if extreme lightweight (and extreme short longevity) is the goal. In the hand of a amateur builder, in the construction of a cruising vessel, it is the plain nonsense!
BTW it is impressive to see, that the claimed weightsavings never happen in a cruising design! (compared with ply for example)

Yes, but according to that :- "you can soak a dry boat quickly, but you cannot dry out a soaked core that quick" ! (and replace of course!)

please do´nt mix up the methods here! Swans have NEVER used a prefab. panel!

Regards
Richard

 

So, why would one be so unbelievable stupid to use a material far beyond its capabilities? A flat panel has to be metal, plywood or (in some cases) wood, but never a glass layup! And there is not a single one argument possible why it should be.

Strengths of modern glass laminates can be readily achieved in the 45,000 psi range, right there with Aluminum. Would you argue that while aluminum is a metal you would not build a boat out of it? Someone should have told Bob Derecktor or Burger. Hull panels while developable are not actually flat. They can incorporate arcs of a circle or cones, and can be compounded to some extent. the curvature stiffens the panel right up. Wood, glass and aluminum. They all have their merits.

The duribility of single skin glass with no maitenence is legendary. I own one of the first glass boats (1947) ever built. Single skin hull (original) and wood deck (3rd one).

 

All nice statements, all well known, all way off topic! Rest was blabla....
FLAT PANELS was the question right?
So, opinions, rumours and wrong info (like the Swan related) are no replies to the original question.
My oldest boat is built 1910, riveted steel, what does that mean? right, nothing...
As mentioned here several times: a flat panel GRP is heavy, weak, and by NO MEANS a boatbuilding material of proper characteristics period

Richard

 

Richard, I reckon that the solid glass could be good to meet your objectives, solid glass cops some knocking these days as to weight but some of those old solid laid boats have & will last a "really" long time. The "melamine" table flat panel molds are used for heaps of stuff in boatbuilding like bulkheads, cabin sides etc, If the boats designed for it & laminated/built well which should be your intention then go for it!. All the best from Jeff.

 

Thanks Otseg. I've heard that a lot of the problems found in fibreglass applications are partly due to inferior techniques used in the past - not just old age. And a lot of single skin frp boats we see today, were built in the past, with bad technique. I've heard that both single and sandwich skin frp is usually better now with more attention to proper epoxy curing and differing layers of fibre etc. etc.
This means I'm not so sure that a ply boat is necessarily the better choice for lazy old me. I'm still thinking!! lol. My design is done on Freeship. Transferring it to a CAD cutting machine wouldn't be a problem.

 

oops I missed a whole page. Didnt see all those other comments. My boat can be round - not necessarily flat panel. Sorry

 

single skin technique is not too heavy for my purpose. Stiffness can be improved by adding more supports between the frames and stringers, and reducing skin thickness slightly. These are mathmatical certainties.

My biggest concern is durability. Don't care too much about weight.

Thanks for all the comments so far. Every has a good argument.

 

So I can have someone lay up the frp sheets at full length, cut them out, and all I have to do is wrap them around my round bilge framework? And bending the solid frp panels won't weaken them? Wow....I like that idea. I could design the hull to be rounded but with no tight radiuses.

I will send a few pics of my design soon.

 

I guess full length prefabricated frp panels will only bend in one direction?

 

Nonono,

our fellow member mixed up single skin and flat panel prefabricated crap!
The former is the usual and valid boatconstruction in GRP, if done right, they last quite a while. (cores are another world)
The latter is nice to enclose your dog kennel, nothing else. Even for bulkheads it is a poor choice and therefore not common.
Bending those panels does´nt weaken them, it makes them structurally stronger! But the same is valid for ply, and ply is twice the strength of those panels, if not more!
But a round bilge design has to be made of a homogenous material, not panels! So you can either choose a solid glass layup or a strip plank method, or cold moulded veneer (thats plywood again), or a combination of strip and veneer (the cheapest, fastest and easiest method).
YOu mention Epoxy. The common material for GRP composites is polyester resin (the panels are made from poly too). If you would use EP for a glass layup, you do´nt have the poly related issues with water ingress, but a slightly heavier (and much more costly) hull.

So, again, I did never compare or even mention a single skin grp layup here! And that was not the question.
Any method you can think of, using these flat panels is a waste of time and money and will never, NEVER end up with a boat of ANY value! Nor a structural sound vessel you could rely on. Just forget about that stuff! Nice thoughts but wrong direction................

You mentioned "Freeship". Designing your own boat is not possible! Believe me it is NOT possible. You may be able to draw something that floats, but that would be as much a yacht as my Hayabusa can transport a cow! Apart from the lack of knowledge in boatbuilding methods and materials, the lack of knowledge in hydrostatics, hydrodynamics, a novice is completely unable to calculate and draw structures and structural joints in a sensible and sound manner. Building some 1000 tonnes of yachts per annum I claim to have a rough idea how one can make a boat, but I would not make my own design! Again, just forget about that.

Go for a proven design in what material so ever, there will be more than enough problems to encounter and to solve, you must not invite serious trouble before you even started the whole process!

This was not meant to disencourage or offend you! But what you are planning is a desaster not a boat.

Regards
Richard

 

Please read the thread before you contribute! There was no solid glass layup mentioned!

The fact that old glass boats are existent does´nt mean that is the way to go! A good made glass boat is not bad but needs the same or even more maintenance than other materials.

The statement that flat panel moulds are used in boatbuilding is wrong! Moulds yes, but flat no! And again that is out of topic: "prefabricated flat panel grp" was the stuff in question! And that is nowhere in the industry used in quantities worth talking. For a good reason: by far too weak for the weight.
Richard

 

Lets try to dispel some of the myths. In spite of what has been said or common misconceptions, fiberglass isn't especially stiff nor very strong. In fact it's kind of wimpy and bendy. This is fact, not speculation or conjecture.

To overcome the inherent weakness of these physical attributes, it's common to use sandwich construction methods or thicker, heavier single skin laminates with localized reinforcements (bulkheads, stringers, etc.). If designed properly, you can have a strong, durable structure.

Can 'glass be used in flat panels, then bent to form a chine boat or radius chine boat? Yes, but it's not the most economical method in materials, will generally be considerably weaker and likely quite a bit heavier then more conventional single skin and especially sandwich construction techniques. Again, this is fact, not speculation or conjecture.

Bending cured flat panels around a mold then edge bonding these together will require some pretty fancy engineering and design work ,though it can be done, you have to ask yourself why, when other techniques will use less materials and labor.

As a general rule, for a hull you want the whole thing to be formed into the hull shape, THEN cure so it forms one giant resin molecule (no kidding, literally a single poly or epoxy molecule). This monocoque, homogenous hull then can be made thinner, for the same strength, which will also be lighter for the same strength.

If you bend cured panels over a mold then bond these together to form a boat shape, you run the risk of laminate rupture, because it wasn't formed in the shape it finally ends up being. To compensate for this, both the seams and panels would have to be made thicker (more material and labor again).

For some reason you seem to think the additional weight isn't an issue, but you're kidding yourself. As a designer I work around the weight issue constantly, in fact the first few things I do in a new design, is calculate the weight or displacement I have to work with, so I can get a handle on boat shape.

Please do yourself a favor Richard and contact a designer or NA with your ideas. You'll find that most existing designs are quite weight sensitive and alterations to scantlings and building materials or methods have to be balanced against the volume the hull has to offer.

Maybe it would be helpful if you told us a little more about this design you're looking to convert (I assume), because some shapes (designs) can tolerate alteration better then others.

 

Ahh, ja. That was it the polite way round....................................