flatpanel construction

Ilan Voyager wrote. "The resin won't harden on the very surface of wood."

Hi Ilan sorry about the delay but I wasn't following the thread closely. You seem to be having trouble with those phenols, was it something you said?
Seriously FRP(for P read polyester) has been successfully laminated to wood for longer than I can remember and I've been doing it for 60 years. The popular "stitch & glue" method of construction was invented for FRP NOT FRE(E=epoxy) For a clincher Jim Brown's range of home built tri's featured chines that were moulded in situ WITHOUT thru' fastenings using FRP. According to your theories those chines MUST fail. Instead "Searunners" have circled the globe, won tough ocean races and carried their owner builders many hundreds of thousand miles in the past 40 years.
No one disputes that epoxy is superior. But it's expensive, toxic and difficult to use under certain conditions. For flat panels on a houseboat it seems like serious overkill.
Regards Harry

 

Polyester can be used on wood, but it takes a lot of it, doesn't seal the wood, you end up with a heavier structure, plus the additional materials and resin don't offset the epoxy costs, when all things are considered (pound for pound, dollar for dollar, strength for strength).

Simply put, you need twice (~) the laminate for the same modulus if using polyester over wood. This means twice the resin, and heavier laminates, just to get the same panel. This tends to counter any resin cost savings using polyester. Now, in this vain, most manufactures don't use enough resin or material on wood, which tends to cause issues down the road. This is well documented and recorded with rotted out soles, stringers and transoms. Yes, some have used polyester to good effect, but this is the exception, not the rule and as mentioned produces a heavy structure of the similar cost.

Most shops shy away from epoxy because they think it's toxic (it's not as toxic as generally believed or as much as the styrene based resins), but more importantly because they're set up for a different resin system. This is why vinylester is so prevalent. You can still employ the same chemicals and control systems currently in place, with the switch from polyester to vinylester. The shop doesn't change much and techniques and personal can make a quick adjustment.

Many Searunners have had issues and structural element repairs, some of which could have been avoided with an epoxy resin system in place. We can always find examples of each system, siting it as proof it works, but the real indication is industry trends and call backs. Many custom builders are switching to epoxy, after using vinylester for several years. This is partly driven by elongation issues with vinylester, compared to epoxy, particularly with modern composite materials, but also the weight issue. These, typically high preformance structures, need to be light and strong, so many custom and semi custom builders are tossing vinylester in favor of epoxy, just to satisfy client desires, but also partly to insure they don't have call backs and repair reputation issues.

I've found the only folks that find epoxy difficult to use, are those with limited experience with it. It's cost is comparable, given all the costs associated with each resin system and it's toxicity is more easily controlled the styrene based resins. In fact once fully cured, it's essentially inert. So inert that medical implants have their electronics and umbilical cords embalmed with epoxy to prevent rejection and corrosion problems.

In your defense Harry, admittedly on flat panels, in a low budget houseboat, a very reasonable argument could be made for something other then epoxy. The original poster was interested in straight plywood panels, which he figured he's sheath to get some abrasion protection. Then the thread digressed into some contention, with a few posters well known for speaking about things they don't fully understand, but as a rule the thread has remained where the original poster was thinking. If I was doing a low budget houseboat, I wouldn't bother with sheathings, just taped seams and call it a day. Saves, cost, labor, weight and any JimBob or JoeLarry can fix it reasonably.

 

After trials made by the French Navy. These trials lasted one year with complete physical, chemical and stress data, before and after accelerated ageing. A part of the trials was made by the CETIM (a scientific institute of strength of materials). Many different sorts of woods, resins and fibers were tried, and also solutions for the adhesion problem. In short terms by serious and reliable persons...The budget was a pricey one but no Navy wants to spend money on a no-fool proof method. Warships are expensive, even if the hulls are a very small part of the total price, and planed to last 30 years with a lot of miles.

With a lot of mechanical "key" and on a small boat with very little stresses on the joints maybe... it's a bet.

Polyester is far more toxic than epoxy! Polyester contains heavy metals like cobalt as accelerator, peroxides and mainly the solvent styrene which makes a lot of vapors. A lot of solvents are needed also as it hardens fast and you have to clean the tooling. You'll have to prepare the wood with solvents, and cobalt naphtenate for minimizing the adhesion problem. It's difficult to be protected from vapors unless an expensive equipment.
Epoxy is eventually toxic by contact (and it's easy to wear gloves...) and emit almost not vapors. When cured epoxy is almost inert. Polyester never totally ends the curing and continues to release vapors; the noticeable smell of the polyester boats is the proof...
As naval engineer I have seen a good number of boats using polyester/wood and I never saw in Europe one being structurally sound after a few years. Here in Mexico I have seen a big bunch of USA made deep V motor boats using polyester/glass/plywood webs, decks and sterns with wood/glass/polyester inboard engine bases on polyester/glass hulls. After five years all have delamination problems. At ten years none is structurally sound.

That's a direct experience after almost 40 years of seeing the results of this ill fated combination.

The lone Sea Runner I've seen at Puerto Aventuras was nicely made in plywood epoxy...Trying to race with a Sea Runner is like trying to race with a 1980 Chrysler station wagon...I would like to see a 40 years old plywood polyester one...

On a house boat is simpler to use Nidacore and Matline (or Coremat) for the panels if polyester is to be used. Nidacore is lighter than plywood and rather cheap. Matline has a density of 600 kg/m3 (roughly the same as meranti plywood), is cheap, is very easy to use and the easiest thing to ship (simply rolls...). Nidacore and Matline are designed for polyester resins and glass fibers...It's impossible to use polyester on extruded polyestirene (it dissolves it). I have used it for my 18 m2 with good success but with epox. A little problem with extruded polyestirene, the dioxyde (carbonic) gas used sometimes for the expansion/extrusion is hygrometric...

But I would never marry polyester with any plywood, specially the low quality so called marine fir plywoods so common in the States. Nope that will last. If using plywood, just good screws, maybe taped seams, and a good paint is enough for a low budget house boat. And like always Par is right...

 

Point taken fellows. If you want to see a 40 year old Searunner go to www.outrigmedia.com and Jim will take you on a personal tour of Scrimshaw.
Here in South Africa most of the stuff you talk about is either unobtainable or carries a large price premium. Even plywood which is so readily available in the US is scarce and expensive. That's why I'm interested in low cost composites.
Regards Harry

 

The Searunner serie is designed mainly to to be made in Constant Camber. That calls almost automatically for epox. In third world countries like South Africa and Mexico you have to use the local materials ie polyester. Marine Plywood and Epoxy are simply too expensive. The better price/quality combination is to use a isophtalic polyester resin, glass :300 gr./m2 mat, 500 gr./m2 cloth and a core bulk like Coremat or Matline. It's basic polyester boat building. Coremat or matline are very common or can be imported at a decent price because it's a polyester-microballoons felt sold in 100 meters rolls. If not possible use an all glass stratification.
Polyester FRP can be used in flat panels for hard chine boats. The method is called in France Placo Plastic. It saves a lot of work on finishing the boat as the primary panels are "molded" gelcoated on a flat long table so the outside will ask for very little job (some gelcoat at the chines) and a paint job if wanted. These primary panels are generally 3 to 4 mm thick and are placed in a female jig so you obtain a kind of female mold. After the panels receive the further plies of cloth/mat to obtain the final stratification thickness.
It's the simplest and cheapest one off method for polyester boats.

 

Hi Ilan,
I have an origional Searunner construction manual, circa 1971. It called for douglas fir ply and polyester glass chines. Jim didn't develope constant camber until much later. Epoxy was only available as an adhesive at that time. The Gougeon's didn't publish until 1979.
I have used flat panel FRP also a system in which cloth is stretched over a frame(skin on frame) and is then covered with FRP. The result looks a little starved but produces a strong light boat. You're not likely to find any examples because it dates back to the 50's and they didn't look good against the sleek shiny boats that were beginning to come out of the factories.
I have been out of touch since my retirement in '98. So I am not au fait with the latest methods. I will check the availability of coremat etc but the main boatbuilding area is CapeTown and I am near Jo'burg. The other end of the country, a mile high and over 400 miles from the sea.
Regards Harry