non-cored fibreglass panels instead of ply [Archive]

PAR

07-13-2009, 07:21 AM

Actually weight is a prime consideration in regard to the abilities of the yacht.

Adding 50% more to the build just isn't reasonable frankly and quite dangerous.

If you're looking to use 'glass panel construction, in replacement of the plywood on a hard chine design, you'll have to engineer the replacement 'glass panels to have similar physical properties as the plywood or re-engineer the structure for the new panel material.

In answer to you question about G-10, yes, it's nuts. In general reply to the concept, it's feasible, but unless you have specific plans arranged around developed 'glass panel (or what ever) construction, you'll have hire out a conversion. This of course is based on the nature of the original question.

You certainly don't have to use cored construction in the hull if you don't want to and there are many plans available that offer just this.

apex1

07-13-2009, 07:21 AM

Richard Atkin

07-13-2009, 08:32 PM

Thanks Par and Richard.

The boat is my own amateur design (with a lot of help from Gary Baigent and other experts). It's a trailerable twin masted coastal daysailer. No furniture/luxuries - just a couple of mattresses in the cabins. My design process is a bit unusual. I have designed the boat to be slightly 'underweight' with a transom that sits well above the waterline. The hull can afford to sink to some extent depending on the final choice of materials and construction, and will be 'good enough' as long as the boat stays within about 1.7 tonnes (including crew weight and equipment). The two freestanding masts will be professionally designed and built AFTER the hull materials and weight have been decided. The final boat performance is not actually important to me, as long as it stays within reasonable safety parameters - and it will.

I want to steer away from ply or any kind of water absorbant materials that could be exposed to water from any imperfections in the hull. I know that recent foam core hulls are more reliable than the older ones that suffer from delamination of the core, but they still require a lot of time and expertise to get it right. Even so, I don't believe in claims that a sandwich skin construction has better resistance to point impact than a thicker single skin. That just doesn't make sense. I like the idea of compromising with extra bracing to support a not-so-thick single skin. This method is lighter than the old thick single skin boats, and any water leaks are easily spotted and repaired with no concern about rot.

Plywood is strong and easy to work with - but my lazy attitude towards boat care and maintenance means I would probably end up with rot in the years to come.

I haven't ruled out the possibilty of buying about 500 kg of G-10 wholesale, but perhaps I should do some strength testing before I do anything stupid :)

PAR

07-13-2009, 09:46 PM

What's wrong with one of the few different single skin one off methods? G-10 would be ridiculously heavy.

gonzo

07-14-2009, 11:15 AM

If you have experts help you design, what did they say about the skin calculations? If the claims about cored construction don't make sense to you , maybe the best thing would be for you to spend some time looking at testing results. Also, look at stiffness differences between plywood and solid fiberglass. The design is obviously for flat panels which is a poor use of fiberglass

Richard Atkin

07-14-2009, 07:43 PM

The boat is never going to be left in the water for long periods. It'll be on the trailer most of the time. Maybe I should be less paranoid about rot and just build the damn thing out of ply.
I owned a tiny ply boat when I was a kid and could never keep the water out of the ply - I think it was due to tiny cracks from thermal changes. I became hooked on the idea of plastic fantastic, but I guess a ply boat can last if you take care of it.
It would be way easier to build. My boat design is still in the early stages. It could be rounded or flat chine.
I really hate the idea of spending hours in the garage working with chemicals. I will study ply construction in more detail.

Thanks guys for the comments.

apex1

07-14-2009, 07:59 PM

Well, a wise decision imho!
If you manage to encapsulate the ply properly in Epoxy (not too hard to achieve), and give it the same attention you would invest in a GRP boat you have a better one at possibly lower cost.
Look our cold moulded boats are nothing but ply done with EP and have proven thousand times to stand the test of time better than most of the GRP competitors. And on top, they are lighter and therefore perform better.

Regards
Richard

shugabear

07-14-2009, 08:16 PM

ply is good and if it wont sit in the water than go with that yet if it does stay wet then the epoxy may work better but its your boat i dont think its so crazy

PAR

07-14-2009, 10:34 PM

Build it in 'glass if you want, though you will not escape the chemicals thing as this is worse then coating plywood.

Again, there are several single skin, one off 'glass building methods, which don't have cored construction. Why not one of these?

Richard Atkin

07-15-2009, 10:03 AM

I havent ruled out the possibility of solid fibreglass.

Would a thoroughly encapsulated birch plywood last as well as solid fibreglass?

If ply is encapsulated with epoxy, it can't dry out on the trailer can it??

Solid fibreglass can become less stiff with age, but the boat will still be good enough to go sailing, even if it is a little 'soft'.

Rotten ply can leave you with a boat that is too costly to repair.

But....I would enjoy building with ply. DAMN!! I need to think about this

apex1

07-15-2009, 11:18 AM

>>>Would a thoroughly encapsulated birch plywood last as well as solid fibreglass? <<< longer, much longer....

I would´nt recommend Birch ply as material of choice, use a hardwood marine ply (just marine ply).

>>>If ply is encapsulated with epoxy, it can't dry out on the trailer can it?<<<

No, it does´nt. But you have to make sure that no freshwater finds it´s way into the hull. (same is valid for ALL other materials too)

>>>Solid fibreglass can become less stiff with age, but the boat will still be good enough to go sailing, even if it is a little 'soft'.<<<

EVERY boatbuilding material has a fatigue related weakness after some years. GRP has the worst rate!

>>>Rotten ply can leave you with a boat that is too costly to repair.<<<

Rotten GRP can be much more of a prob. (and it does "rot" if there is water ingress)

Think about it, it is worth to keep a eye on plywood construction! Or go a even easier and sometimes cheaper way, make a strip planked, cold moulded combination. Very common, easier than sheet ply, probably stronger than sheet ply (if designed to that method i.e. round bilge).

Regards
Richard

otseg

07-16-2009, 03:43 PM

80% of my fiberglass repair in my repair side of my buisness was somehow core related, and that experience comes from running 80,000 man hours a year for 10 years.

Go for the single skin. Think of all the Roberts and Colvin chine steel or aluminum amateur built sailboats built, and a high quality laminate is a great substitute.

A good cad guy can turn your lines into developable panels that can be laid up full size, full length, Then just "stich and glue" them together.

Coincidentally I have a 20 x 80' heated flat vacuum molding table that all of the panels could be infused with glass/epoxy in a week. This is shameless self promotion and I resemble that remark.

rwatson

07-16-2009, 07:09 PM

Hi Otseg and Richard.

This technique is of great interest to me, as I am considering a similar build in a 28' trailer sailer. I have asked my NA to do a developable version, with sort of constant radius bilge turn.

In my case, I am planning to to flat sheet FG with the 'inside' having a foam layer.
Then the one sided glassed foam gets placed stitch and glue style in a 'basket', and the inside gets laid up by hand.

I was re-assured by the web site Manie placed on the 'board'
http://www.voile.org/trimaran/progre...ber11_2005.htm

I did discuss this technique without using foam (just straight FG layup inside), but my NA assured me it would be way overweight, and not very stiff without the foam.

I have read all the talk about foam being problematic, but so is every other material, so I have opted for problematic and light.

Whats the saying - "you can sail a fast boat slowly, but you cant sail a slow boat fast"

otseg

07-16-2009, 08:12 PM

I have built a dozen Harry Schoell designed powerboats from 16' to 85' over 25 years in exactly the way you describe. Concurrently Derek Kelsal has been doing the same thing. Google him, and surf his site. It is an excellent method. Its all about good secondary bonds, prep the surface to be bonded with grinding just before lamination.

PAR

07-17-2009, 06:41 AM

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.

otseg

07-17-2009, 07:55 AM

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.

apex1

07-17-2009, 07:57 AM

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)

Hi Otseg and Richard.
I did discuss this technique without using foam (just straight FG layup inside), but my NA assured me it would be way overweight, and not very stiff without the foam.
I have read all the talk about foam being problematic, but so is every other material, so I have opted for problematic and light.
Whats the saying - "you can sail a fast boat slowly, but you cant sail a slow boat fast"

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!)

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.

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

Regards
Richard

otseg

07-17-2009, 08:50 AM

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).

apex1

07-17-2009, 09:59 AM

Strengths of modern glass laminates can be readily achieved in the 45,000 psi range, right there with Aluminum. 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.

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

waikikin

07-18-2009, 02:33 AM

Richard Atkin

07-18-2009, 03:47 AM

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.

Richard Atkin

07-18-2009, 03:52 AM

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

Richard Atkin

07-18-2009, 04:01 AM

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.

Richard Atkin

07-18-2009, 04:37 AM

Richard Atkin

07-18-2009, 04:53 AM

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

apex1

07-18-2009, 06:19 AM

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.

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

apex1

07-18-2009, 06:30 AM

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.

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

PAR

07-18-2009, 10:59 AM

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.

apex1

07-18-2009, 03:56 PM

Lets try to dispel some of the myths.
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.

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.

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

Richard Atkin

07-19-2009, 06:52 AM

The cabin lines look a bit awkward but I don't care because it has great functionality. The boat will look very good when you are sitting on it - nevermind how it looks from a distance. This is a party boat. Can be rigged much faster than any other trailer sailer. Less than 5 minutes with a few helping hands. VERY low centre of effort. Narrow BWL and centralised crew weight gives nice performance through waves and there will be no transom drag. This is especially important during California's notorious combination of light air and chop.

Boat weight plus crew currently guesstimated at 1.5 tonnes but will probably end up being more. Performs very efficiently at 6 knots boat speed. Will be a very smooth ride. Very low freeboard to create a small boat feeling. Rigging is kept well away from children. Unsinkable with huge reserve buoyancy below central cockpit.

This is my original design. Gary Baigent gave me some tips which led me to this design concept, but he might not like to have his name associated with it - but I am very grateful to him anyway. I will be taking this design to a NA when I am in LA for final calculations.

Still not sure which materials I will use for the hull. :p

apex1

07-19-2009, 07:16 AM

Hmmm, canoe shape hull, strong and easy made in strip plank, veneer. The superstructure looks alreaydy like ply sheets (and would be a perfect match if).
So, why did you waste one moment in thinking of sheet material to make such hull?
I do´nt want to talk you into any method, but this shape is easiest, cheapest and strongest (apart from exotic fibres) made of strip, veneer.

And I completely disagree with your former statement that weight does´nt matter. That low freebord will not forgive overweight!

(it seems you are very skilled in using Freeship)

Regards
Richard

Richard Atkin

07-19-2009, 07:21 AM

Has balanced transom hung rudder. Steering system uses large cogs for lower resistance.

Richard Atkin

07-19-2009, 07:24 AM

hi Apex. My only concern about ply is the fact that fungus eats it even when it is on dry land. I think I will have to make my decision closer to the time I commence the build. It might be a financial decision. I am waiting to see how far the American economy will implode before I move there!

apex1

07-19-2009, 08:11 AM

hi Apex. My only concern about ply is the fact that fungus eats it even when it is on dry land. !

Thats a myth Richard! My boats would´nt exist if not! They are all just cold moulded plywood, completely encapsulated in Epoxy. There are cold moulded boats in service built during second world war (before Epoxy was available).
A proper treated piece of wood / ply has far less issues than a perfectly made piece of GRP ! The flat panels you mentioned are worlds away from being just good, let alone perfect.
In terms of maintenance you will hardly find another material that is easier to handle than wood / epoxy !
And I never ever use the word plywood without meaning a fully Epoxy encapsulated material! That cannot rot, nor does it allow fungus to build up.

Regards
Richard

PAR

07-19-2009, 11:21 AM

I can't tell much about that hull shape other then it being a round bilge, but panel construction on that shape, would prove quite difficult.

You can have your cake and eat it too. I understand your desires for a durable hull shell, one that will not delaminate or rot it's core.

If it was me, I'd build station molds, then space furring strips over this on fairly tight centers, say about 9". Over this I'd lay cheap foam, open cell crap stuff, just wire tying it to the firing strips. Once the whole hull was covered with this foam, I'd then cover the foam with polyethylene plastic and begin 'glass layup. Just keep applying fabric until the desired thickness of hull shell was achieved. Fair, paint and pop off the jig. The foam, plastic sheeting, molds and firing strip stringers wouldn't be part of the finished structure. You'd just have a solid skin 'glass hull shell, ready for reinforcement, stringers, bulkheads, etc.

Another option is C-Flex planking.

This is one of the advantages of using a real designer, instead of attempting to make these decisions yourself or inventing a new construction method. We're familiar with the majority of techniques, likely including ones you've never thought of.

I can tell you, one thing designers don't like to do is "reconcile" some one else's work, especially if they aren't a trained designer. You must understand, from their point of view, every calculation and decision must be scrutinized. If these decisions have been made by an amateur, then all must be considered suspect and preformed over again to insure correctness. So, not only does it become a custom design, but one with considerable limitations and additional work, from the beginning.

mitiempo

07-19-2009, 02:34 PM

I would build this design in strip plank with diagonal veneer over - all encapsulated in epoxy. Lightweight glass cloth and epoxy coated for abrasion resistance. After the hull is finished you are left with a clean interior with just the main bulkheads and inner keelson showing. A few clear coats of epoxy inside leaves a good looking interior and this method is very durable, self insulating to a certain extent, and very light for its strength. Any attachments should be overdrilled and thickened epoxy filled before redrilling. Water ingress is an issue with any non metal structure and polyester absorbs more water over time than epoxy. Wood/epoxy is also pretty easy to work with in my opinion. I believe this method would also be the least expensive. Ultimately whatever the material durability is at least partially dependant on maintenance. This method should give you more durability than polyester in any of its methods and be as maintenance free as any other method if not more so. I suggest you see "Gougeon Brothers On Boat Construction". Good luck.
Brian

PAR

07-19-2009, 04:32 PM

If you'd read this thread from it's inception, you'd have noted that the original poster isn't interested in wood or wood cored construction, for understandable reasons.

As much as I tout epoxy use, polyester hulls can be easily found 40 and 50 years old, still quite sound. I even know of a few 60 year old 'glass production boats, that have faired far better then their wooden or metal counterparts, given the same level of up keep negligence and neglect.

apex1

07-19-2009, 05:13 PM

If you'd read this thread from it's inception, you'd have noted that the original poster isn't interested in wood or wood cored construction, for understandable reasons.

Thats not the full story Paul! Look here:

Maybe I should be less paranoid about rot and just build the damn thing out of ply.
I owned a tiny ply boat when I was a kid and could never keep the water out of the ply - I think it was due to tiny cracks from thermal changes. I became hooked on the idea of plastic fantastic, but I guess a ply boat can last if you take care of it.
It would be way easier to build. My boat design is still in the early stages. It could be rounded or flat chine.
I really hate the idea of spending hours in the garage working with chemicals. I will study ply construction in more detail.

And I have seen boats of any kind and material one can think of, in pristine condition after half a century of daily use! Which is one of the secrets the boater is´nt told too often: the more it´s used the better it will stand the time.

rwatson

07-19-2009, 05:28 PM

Richard -

Check out

http://www.f-boat.com/pages/construction/index.html

have a feeling this method would suit the your design.

Basically, if you want curves - you must suffer. I choose to suffer only moderately around the bilges.

People who recomend strip plank like to charge for their work - I wouldnt wish it on anyone who wasnt a masochist - especially cleaning out the female side of the hull. Plan on 10 hours per square metre.

Otseg - I am very familiar with Kelsalls work thanks. Your illustration were very usefull to me.

The main point - Flat panel on a smooth surface, whether one skin or two, does away with the most arduous part of boatbuilding - the exterior finish. Plywood is just as hard to finish as any other method, because you have to glass the outside - and thats where all the sanding, filling, more sanding goes on.

Plywood will last a long time - IF mantained well. Maintaining a ply or wooden hull is tiresome - every ding, nick and bump has to be attended to quickly as moisture spreads through the wood, and is really hard to get rid of..

Foam DOES NOT absorb water if you use the correct material.

The other point is that fibreglass panels are not 'floppy and weak', unless you use very little material. Fibreglass strength for the equivalent weight in steel is over ten times. Fibreglass made to the same thickness as ply, will bend exactly like the ply. Its just physics. Sure it will be heavier - hence the use of a core to maximise stiffness. It will bend exactly like PLy, in two planes.

Richard - , my feeling is like PAR said so well, CARE about weight - care a LOT about weight. Weight is $, and time and effort.

PS - since you are a New Zealand type person, I found www.high-modulus.com to be good value for materials.

apex1

07-19-2009, 05:47 PM

People who recomend strip plank like to charge for their work - That was a bit perky, yes?

Plywood will last a long time - IF mantained well. Maintaining a ply or wooden hull is tiresome - every ding, nick and bump has to be attended to quickly as moisture spreads through the wood, and is really hard to get rid of..

Exactly the same is valid for every Glass layup, with no exception!

Foam DOES NOT absorb water if you use the correct material. That is just wrong!

The other point is that fibreglass panels are not 'floppy and weak', unless you use very little material. Fibreglass strength for the equivalent weight in steel is over ten times.
That is valid only, when you compare a proper glass layup!

.

Rwatson, the material in question is a prefabricated flat panel! That is commonly not the best quality of glass and resin. And has only disadvantages compared with a hand layup.

A proper made strip plank vessel is less hassle than a glass layup and needs less maintenance than GRP. Thats not a guess, thats fact! And my products are proof of that every day.
Please avoid discriminations like the one above! I cannot see how I would charge a Forum member! Strip planking is one of the best methods for amateur building, and one of the strongest too.

Regards
Richard

PAR

07-19-2009, 06:50 PM

Rwatson, fiberglass is without question pound for pound the weakest of the bunch, in regard to hull material choices. So much so that engineering tricks have to be employed to make it successfully compete with other materials (well okay, except ferro).

Look, a single skin hull can work fine, eliminates the need for a core, potential core sheer or rot and multiple skin layups. C-Flex will require multiple face layups, but issues associated with cores don't exist.

I don't see any reason why this poster should settle for anything less then what he wants, a boat that doesn't have a core (and it's associated potential issues), no wood to rot, an easy way to lay it up and minimize fairing.

I disagree in that strip planking is less maintenance then a GRP layup. The facts do not bear this out. In fact, wood cores and wood construction of any type will require the most maintenance of all the other material choices. More importantly, wooden structures (any type) can tolerate the least amount of neglect before damage occurs. This is the primary flaw of wooden anything in the marine environment.

On the other hand, I agree that for home built craft, strip planking has much to it's credit. It's fairly easy for the novice to work with and less then top shelf planking stock can be used. It does require a good bit of fairing and the planking process is quite tedious, so if paying for labor, not the best choice of methods (as has been pointed out).

Some forms of strip planking, of which very few builders actually employ, can be the lightest of structures, only rivaled by high tech fabrics, foam cores and vacuum bagged hulls. I know of very few using these strip techniques, but it's possible.

As a rule, strip planking in it usual form, is one of the heaviest forms of composite building, if the wood is a true core. It's about middle of the road (in terms of weight) if just a wooden structure with a light 'glass sheathing.

I'm reasonably convinced the original poster has been persuaded from flat 'glass panel construction.

apex1

07-19-2009, 08:15 PM

Strip planked, cross veneered, glass sheathed Paul! Done with the accurateness (and time) of a ambitious homebuilder, to a well engineered design, and the comparison looks quite different.

PAR

07-19-2009, 08:53 PM

I don't consider strip plank with additional diagonal veneers as a reasonable backyard alternative for a novice. The strip planking is easy enough, but fitting veneers can challenge the beginner, let alone getting good bonding contact between the two surfaces. Yes, this is a strong and durable construction method, but not well suited to amateur efforts, mostly because you have to be fairly precise about cutting and especially bonding the veneers.

Now think about it Richard, remember the first time you applied veneers?

rwatson

07-19-2009, 09:03 PM

Rwatson, the material in question is a prefabricated flat panel! That is commonly not the best quality of glass and resin.

No its not - I raised the question of principle of flat sheets in this discussion, and if you re-read, I planned to lay them up on a flat surface, and then hand layup the inside. I dont know where you got the idea that it was some kind of inferior product.

Foam DOES NOT absorb water if you use the correct material. That is just wrong!

Dont argue with me then- argue with the Product Spec sheets. This applies to marine quality foam, Epoxy and to a great extent to Vynelester.

I have seen foam cored surfboards used day in, day out with big chunks missing, and no absorbtion. Try doing that with any kind of timber.

And, if you get any damage to a wooden hull - what do you have to use to repair it ???? More wood ? Nooooooo - you use some kind of Epoxy and Cloth !! Yes - even you do !

Strip planking is one of the best methods for amateur building, and one of the strongest too.

"best" in what way ?. Its hugely time intensive compared say to 'stitch and glue'. You need to have a carpentry savvy amateur - there is quite a degree of skill involved with it - and a *lot* of finishing work.

Please avoid discriminations like the one above! I cannot see how I would charge a Forum member! Strip planking is one of the best methods for amateur building, and one of the strongest too.

I wasnt referring to you personally, but it sounds like I hit a nerve. I was talking about boat builders in general - there is a lot more money to be made in labour intensive hull construction.

A proper made strip plank vessel is less hassle than a glass layup and needs less maintenance than GRP. Thats not a guess, thats fact! And my products are proof of that every day.

Aha - now we see where the strong opinions come from. So then Apex - why do more than 80% of all commercially built small boats get built in anything but timber. Its NOT because they are lower maintenance - and your biased view doesnt stand up to the real world practices. As Par says -

I disagree in that strip planking is less maintenance then a GRP layup. The facts do not bear this out. In fact, wood cores and wood construction of any type will require the most maintenance of all the other material choices. More importantly, wooden structures (any type) can tolerate the least amount of neglect before damage occurs. This is the primary flaw of wooden anything in the marine environment.

Yes Par I DO agree that "wood cores and wood construction of any type will require the most maintenance ". I DO agree that GRP is "strip planking is more maintenance'. I DO agree that wood tolerates the " the least amount of neglect before damage occurs."

I'm reasonably convinced the original poster has been persuaded from flat 'glass panel construction.

I know - and mostly by some very erroneous statements, which I am attempting to rectify.

Richard, I have been around and around this material business for the last two years. I even built several smaller craft before my big project, and have been using them on a day to day basis. I have owned steel, canvas and commercially built fibrglass larger boats.

I love wood, I love welding and I hate building in Fibreglass. But - I am convinced that the 'flat table' FG technique yields a high quality, much much lower effort product quicker.

waikikin

07-20-2009, 06:35 AM

Would it be insane to consider using prelaminated fibreglass panels (maybe g10 epoxy glass panels) for the shell of a 33 ft hard chined monohull, using plywood construction technique?

I want it to be an easy build (I have no boatbuilding experience) and don't want cored hull below the waterline.
Extra frames and stringers can be added for stiffness. I don't mind if the boat ends up weighing about 1.5 times more than foam core FRP.

Could I expect off-the-shelf prelaminated panels to be stronger than hand-layed solid FRP?

In Australia the process of flat panel constructions is fairly common although mostly in cored construction especially for the making of say- connective bulkheads for catamarans, hull bulkheads, deck panels, sole panels. Variations such as rebates for tabbing(the joining tapes) panels together for neatness & also door jambs & locker recesses easily added onto the table tooling, also upstands for capping returns & the like quite simply added as a few examples. the table will often be simply constructed from melamine faced particle board through to composite gelcoated tables, plate glass & polished aluminium. Melamine sheet is also used in temporary tooling as a form for contact molding of fiberglass components much the same as forms are used in concrete but of coarse detailed to a much greater degree for finish. These techniques could be adapted to your intentions, even curved forms can be skinned with products like 4.5mm poly faced ply for the creation of hulls. The downside is that you get to build everything twice:) once insde out for the form & again to build the part in it, the upside is so long as you work neat on the forms you can get gelcoat finished parts from them. Check out the likes of Kelsal, Sayer yachts for some inspiration, dont be discouraged, some top end builders use techniques such as this, the key is accuracy & neatness as this reflects the finished product. All the best from Jeff.

apex1

07-20-2009, 10:12 AM

Now think about it Richard, remember the first time you applied veneers?

It was a challenge, you are right! But the design was taylored to fit that method and the material specifications were exact to the single strip of veneer, so, it was within the abilities. I agree it´s much more effort for a homebuilder than strip / glass but the result is a much stronger and lighter than every glass layup, as you know.
The method though usually still named strip planking should be better called cold moulded over plank.

To the maintenance issues. A cold moulded, glass sheathed vessel, professionally executed needs LESS maintenance than a GRPoly one! Of course every dent has to be repaired soon, but the same is valid for every other material. With just steel as a excemption, where there is a larger time window.
Just look at the problematic gelcoat. Chalking, cracks, water ingress, blister due to hair cracks etc. We do´nt have that with cold moulded.
The fact that many of the wood epoxy vessels in the US have been poorly constructed, and given the method a bad name, does´nt mean it is a poor method!
One of my shops does only steel alu btw. and the large yard does GRP (Epoxy/glass/carbon) from 105ft upwards! And we ALL agree that the finest (though most labour intensive) method up to 30 meter is cold moulded (Mahogany) over lightweight strip (Paulownia tomentosa), using a premium formulation and post cure tempering.

Regards
Richard

apex1

07-20-2009, 10:50 AM

[QUOTE]Dont argue with me then- argue with the Product Spec sheets. This applies to marine quality foam, Epoxy and to a great extent to Vynelester.

You know the articles by David Pascoe!? That means you argue against your own knowledge. If a core (which one so ever) is encapsulated in Epoxy (not vinylester), we have a different view, but the foam itself is a weak point, and remains to be.

I have seen foam cored surfboards used day in, day out with big chunks missing, and no absorbtion. Try doing that with any kind of timber.

You could, no doubt! How long is a surfboard in the water? Compare apples and apples please.

And, if you get any damage to a wooden hull - what do you have to use to repair it ???? More wood ? Nooooooo - you use some kind of Epoxy and Cloth !! Yes - even you do !
No, never! You cut out and repair using the same material that you cut out. Then you sheeth with glass / epoxy.

"best" in what way ?. Its hugely time intensive compared say to 'stitch and glue'. You need to have a carpentry savvy amateur - there is quite a degree of skill involved with it - and a *lot* of finishing work.

The simple strip plank method is LESS time consuming than stitch and glue, and requires the same skills.

I wasnt referring to you personally, but it sounds like I hit a nerve. I was talking about boat builders in general - there is a lot more money to be made in labour intensive hull construction.
That again is not true, the average customer does´nt value our extra labour too much, he compares mainly by length or volume, not by method. But is willing to pay a bit more for the feeling "it´s real wood".

Aha - now we see where the strong opinions come from. So then Apex - why do more than 80% of all commercially built small boats get built in anything but timber. Its NOT because they are lower maintenance - and your biased view doesnt stand up to the real world practices.

That was unpolite and very naive but I will reply. The average boatyard uses GRP for one single reason only! It is SUFFICIENT (not good) to make a boat with low skilled labourers, in higher numbers! No manufacturer worldwide would use it if there was a competitive low cost high output stuff. And none of them really asks for the maintenance efforts you will have.

Richard, I have been around and around this material business for the last two years. I even built several smaller craft before my big project, and have been using them on a day to day basis. I have owned steel, canvas and commercially built fibrglass larger boats.

Well, rwatson, so your view should be a broader one. Not to make it a comparison, but I owned and sailed vessels from 48ft to above 48 meters, made of every common material including concrete for about 42 years now. And I produce vessels from 20ft to 43 meters, made of every common material, excluding Ferrocement, for about 30 years now. My next vessel is a metal one! Why? No doubt I would choose my favourite method if it was´nt a true bluewater boat for lifelong cruising after retirement, and if pounding on a reef or rock would´nt be a issue. But that happened to me in the past, so I calculate it can happen in future again, and wooden or glass composite structures are not good on that. But less than one out of 10,000 boaters uses his boat in passagemaking, so it´s not worth talking about.

Regards
Richard

PAR

07-20-2009, 01:25 PM

There are several different strip plank methods (I can think of at least a dozen). Your technique Richard, the diagonal veneer/strip plank is about the same, from a structural stand point as heavy biax external sheathed/strip plank. These two forms of strip planking are more akin to hand laid GRP construction scantlings, then wooden core. In fact, I use GRP scantling arrangements with these types of builds, in regard to bulkhead placements, etc. This type of building doesn't need a keel, nor a stem or stern post, a true monocoque shell results.

Again, the above techniques aren't the lightest of the strip planked methods, in fact are "middle of the road" (toward the lighter end) in regard to weight. The lightest is the Lindsay Lord method or my Lord/PAR method, which is just a modernization of the original. These are the lightest of the wooden cored composites, by a fairly substantial margin.

From a maintenance angle, GRP is well above all other materials. If you parked a 30' single skin GRP hull at a berth next to any other 30' build, then left for 10 years, with nothing done, except the bilge pump kept clear of obstructions. The GRP hull would need to be buffed, cleaned and possibly some bedding renewed, that's it. All the other build materials would have developed issues after a decade of neglect. Of course this assumes the GRP boat didn't use cheap resin and blistered, but those days are long since past anyway. Insurance companies, marina owners and Coast Guards around the world are well aware of this and it's one of the reasons wood is being "taxed" heavily as a boat building material. It's also why you're now seeing the delineation between wood, wood/glass and composite construction on insurance and registration forms. There is a difference and in some cases a huge difference.

The bottom line for a home builder is they just can't perform some of these methods. It would be very difficult for a novice to build a diagonal veneer/strip with sheathing hull. An especially skilled, perseverant builder might, but the average wouldn't. It would be unlikely an amateur would be able to do a Lord build too. On the other hand a traditional strip plank build with a light sheath is about as easy a method a novice could ask for. In this regard we should probably be talking apples and apples, rather then what a pro shop can do, verses what's practical for a shade tree build, because the two are vastly different in every way we measure (weight, labor, materials, costs, etc.).

apex1

07-20-2009, 03:18 PM

The bottom line for a home builder is they just can't perform some of these methods. It would be very difficult for a novice to build a diagonal veneer/strip with sheathing hull. An especially skilled, perseverant builder might, but the average wouldn't. It would be unlikely an amateur would be able to do a Lord build too. On the other hand a traditional strip plank build with a light sheath is about as easy a method a novice could ask for. In this regard we should probably be talking apples and apples, rather then what a pro shop can do, verses what's practical for a shade tree build, because the two are vastly different in every way we measure (weight, labor, materials, costs, etc.).

I can agree on that Paul.

Richard Atkin

07-20-2009, 08:08 PM

These figures are based on a 40 ft sportfisher. All hand lay up - not prefab panel. 'Panel Span' refers to space between stringers. Not sure if hull is curved or flat panel. The 3 sandwiches represent different core materials.

otseg

07-20-2009, 10:57 PM

One of my all time favorite boats was "Slithy Tove", a Michael Pipe design and build that competed in the 1978 Round Brittain two handed race. Warren Luhrs was his crew incidentally. Slithy was a "panel" boat made of ply that was a pioneer in using "space frames" to transfer loads from rig to keel. Tuesday and Thursday's Child were developements from that. If you can dig up old issues of the Amateur Yacht Reserch Society publications, Slithy was featured. At one time I had every issue and if I can find them will scan a picture. She looked alot like your proposed design.

From some testing I did 35 years ago, one layer of 10 oz glass on the face of 9 ply 1/2' mahagony plywood will double the failure loading in a three point bending test. Gee, glass can't be that bad after all.

Nice to finally see some numbers posted.

The attached data sheets are 2008 tests of a stiched 0-90 32 oz e glass/epoxy flat panel. These were shop made the same as the parts we produced.

avg 32,000 psi compression and 54,000 psi Tensil strength.
I can live with that.

Richard Atkin

07-21-2009, 12:05 AM

Thank you for all these very good posts. Everyone is very informative.

Just a quick note about WEIGHT: Solid frp skin is heavy because it is not porous. Not porous means poor ability to absorb water. The 'weight' in that sense has an advantage.

Ply has much better strengthh to weight ratio, but nature has designed it to utilise the osmosis effect! Without osmosis the tree will die.

Provided a single skin EPOXY fibreglass has enough extra ribs betwwen the frames and stringers, it will have the required stiffness, but more importantly for me, it will be more durable to the effects of abrasions and fractures. I will have plenty of time to fix something without the concern of rot. I believe the extra weight required to achieve the same stiffness will be well within my design limits. I am prepared to adjust the design to be suitable for single skin if the engineer decides it should be done.

I'm glad I recieved such good arguments for using ply. I think ply is a good choice for people who are not so lazy.

Another point: My design is complete conceptually, but will need a LOT of work done by a NA/NE.

So now I am sure I will use single skin FRP and I am leaning towards a round bilge hull - but I haven't ruled out the possibilty of using a hard chine shape but with 'bulging' panels (know what I mean?). If frp prefab panels can bend in 2 directions, I can get SOME multi-direction curve, but could keep the sharp angled chines so there will be no tight bends. Just glue and screw to the frame.

If I decide on hand layup, I will pay someone else to do that part of it.

I also like the idea of using CAD cutting machines for as many parts as possible.