Help choosing building method

I think about 2 parts mold for the facility of laminate with the mold open and finishing the keel after when the mold is assembled. With two parts mold open you dont have the problem to work with the feet soaked in resin and with too rich resin laminate in the bottom.

About Epoxy. If I well understand, it is possible to laminate epoxy over poly and vinyl resin but you can't do the opposite. Poly and vinyl resin are compatible one over the second and vice versa

 

Epoxy can be used to repair very old polyester boats, but the styrene(?) gas is a problem on newer boats for a long ime, I think. I wouldn't try to mix the two at all.

The idea of laminating on a flat surface and then bend the whole panel over frames requires an developable surface. This can be checked in Rhino for example.

 

I don't think you should mix polyester and epoxy in a new boat. Epoxy may be used to repair very old polyester boats but you can read many places in this forum about epoxy that delaminates because of the styrene gas from underlaying polyester. If you use some polyester inside the hull you have allready made sure the boat will smell for some years

The idea of laminating the outer skin and the core on a flat surface and then bend the whole panel over frames requires a developable surface. This can be checked in Rhino for example.

 

C-Flex has been around for decades, but has not gained a big following among amateur builders. The few rumors that I have heard suggest that it is difficult to get a beautiful and fair surface, and that the final layup is likely to be heavy. C-flex requires support every 12-18 inches, I believe, so there is a substantial amount of woodwork in building molds for that method.

You should get opinions from builders with C-Flex experience.

 

Epoxy V.S. Polyester

I first read that epoxy will bond to almost anything, including polyester. Polyester will not bond to epoxy base. I did that and it delaminated completely after two years.

Now the paint guys are telling us that epoxy and resin will not really bond as epoxy is base and polyester is acid.

They are also reccomending polyurethane based paint over fiberglass as they share the same flex characteristic. They told me to stay away from acrylic paint as it is brittle and works best only with metal.

 

I have also been pondering boat construction techniques for some time. The fundamental problem is that we are trying to build a prototype everytime we decide on a unique design and the problem with that is the labour component. Therefore this is the thing we have to minimize so that we get to enjoy our boat before we are too old to do so. I like the Bateau Boat plans concept (male mould) as the majority of your labour is actually retained as parts of the boat and the concept whilst they design in plywood composite the technique could easily be altered to "duracore" or "Klegecell" foam should you wish to go that way. I probably would as, here in Australia, long term surveying of timber boats for insurance purposes could be difficult and costly.
There is a delayed reaction epoxy on the market which allows you to obtain a good relatively smooth finish prior to starting the reaction might be worth looking at and may help with your comments on external finish ( don't know the product name though.)

 

Epoxy/Polyester

I said good bye to polyester resins already more than 30 years ago. A chain of friends used it (epoxy) who were working in aircraft- and related advanced industries. They were gluing the F4 together and when the steering housing of my Lambo broke, it was glued at Fokker Aircraft. (And after that heatcured)
Mixing poly resins and epoxy is not recommended, you destroy the process and therefore your product.
2. Using epoxy on a fresh poly surface is an even bad idea - as previously is pointed out - further, do keep in mind that polyester over wood is a bad idea too. Although it will show after a long time, delamination is an inbuild security in the process. The only remaining question is: when?
Yachtbuilders must know this phenomenon. You are toyning around with expensive materials so make beforehand a plan - a lamination schedule - as it is done in any professional outfits.

C-flex: using c-flex - long strands of fiberglass stitched together; is a very old techniqiue, useful for certain applications but not a very weightsaving solution. Fairing is VERY difficult and an uneven thickness of the laminate is mostly the result. Lot's of fairing compound is needed to get a flat and smooth surface so this is no feasible solution.

Before working with epoxy materials and foamrelated products like Airex, Klegecell, Divinycell and the like - make sure your brand of epoxy and the chosen core material do not interact on each other.
Airex is attacked by SP epoxies, as I found out long time ago. Airex can dissolve in SP or will partly dissolve. Just an example that you won't find in your books. However only experience will tell. If you don't know: test!
Ask your supplier in case you are in doubt and do it in writing. If soemthing goes wrong along the project, you have something in hand when making your complaint.

 

Don't forget to consider strip planking. It is easy, cheap and strong - then just sheath it in a couple of layers of glass at +/- 45 degrees.

 

(With two parts mold open you dont have the problem to work with the feet soaked in resin and with too rich resin laminate in the bottom.)

The problem with split mold, or two parts molding is the secondary bond. it is weak. Although there are techniques, we discourage it. The keel is the strongest and thickest part of the boat. it is too risky.

Never step on the mold after it has been prepped or waxed. also you do not step on the dry or wet glass when laminating. You will contaminate it. Use suspended scaffoldings.

We discourage our guys from holding the fiberglass as the oil in their hands is enough to cause contamination. The worst enemy is sweat falling into the glass. Moisture is the worst enemy of fiberglass and resin. It will not cure. a drop of sweat will show as white spot in the laminate. it will delaminate in the future.

Glass is coated on the surface with a "sizing" or chemical treatment to make it absorb resin. Washing it away will not make the resin stick to fglass.

 

Probably that next week will be male mold one...

 

Indecisions

Confused? Based on my experience this might help.

Your design will conform to a developable surface. Curvature is not much.

Foam core over male mold is the easiest to construct. You must plan carefully as there are different laminate and core thickness for the keel, bottom, and sides.

Male Mold
Construction- Easiest to construct
Lay up- Glass and foam conforms better to convex surfaces
Sharp Edges- You wont get sharp edges as fglass wont bend over sharp corners. You can fair the edges and lay up a thin glass over it but it will chip easily.
Fairing- Hardest to fair and time consuming. Blister will be a problem in the future.

Female mold
Construction- a little difficult to construct and correct curvature.
Lay up- easy to lay up. Foam might be a little difficult to bend. Use a vibrator and lots of sandbag.
Sharp edges- Fiberglass still wont conform but the trick is fill the corners with cab o sil and resin (bog) then lay up prewetted Rovings(strands of fibrglass) to reinforce. Then lay up the skin glass. Possible to get razor sharp edges.
Fairing- None to moderate depending on how good your female mold is.

my fair assesment is that since you are an amateur, female mold is the best. That way you can spend time perfecting the mold even in the stringer stage before you make an expensive lay up.

If you use a male mold, it will go up easily but i am afraid you will burn out and lose interest once you are into the fairing and sanding stage. In our shop only one or two guys can fair a boat from a crew of 50. It takes skill.

 

I'm definitly going FEMALE!!!

Rxcomposite is absolutly correct...that's why I'm more of the female mold idea.
If you build female and you loose interest, find out the job is too difficult etc. you can throw everything in the garbage loosing 2000$ worth of wood and cut from cad files...if you are able to obtain a fair mold then it makes sense to invest another 5000 $ to finish the hull and by that time (mold finished ) you will be able to know if the hull is coming out good and it's worth to invest that money.
Going male mold is risky, you spend for the mold, for the foam/c flex/balsa or whatever, then you spend for the fiber and resin then you get to the end ,spend 2 years fairing (heard of amateurs actually building the boat in 1 year and fairing for 2 more) if you don't have the guts to get to the end well...that will be very very frustrating and expensive!
I decided to go female, is a less risky investment,and I think much easier.
The only problem with female mold is the building process...I was thinking about building two half molds then put them toghether and laminate a monocoque hull in a single piece.

 

Thanks a lot RxComposite and Fede
You reconcile me with female mold. But I'm affraid with dust and water drop during laminate. Considering that I will make a small boat (6.7m x 1.8m excluding 0.4m collar) and that I can find somes friends for the lamination Day and that I live in a cold country, I think that I can make all the lamination in the same day without over temp (including the setting together of a two part right and left female mold) can I assume that all the lamination will be first bond? If I laminate bulkhead the second day after a cold night (heating shut down), is it first or secondary bond?

Joint a two parts mold of 350Kg (175 + 175 Kg) (mold plus laminate included) is not too hard. I will constructe the mold inside on concrete floor and before my boating love story, I had a woodworking love story, so I have a good skill and many woodworking tools.

Does I really need a core (foam, balsa or plywood), I'm not so low weight addict because I calculate that all FRP will weight 500Kg (included deck, console) (all the boat with pass and fuel 1500Kg) so with core I maybe save 50 Kg. Remenber that I want to build a RIB rigid inflatable boat philosophy.

 

Oups!! I forgot the transom

How can I split the mold at the transom?

 

Well...just cut 2 half transoms!
....may be i did not get the question eheh.