please advise on making a male mold?

Hi- this is where I have little knowledge since I am a steel guy-
after further consideration I will make a standard single skin frp hull rather than go with core.


I am hoping some on here could help me by informing me on how to go about skinning a male mold for a single skin frp hull? are there any threads on here that have ways to cheaply cover a male mold? what materials can be used that are cheap and nonstick and able to form to complex shapes?

I have considered a few layers of clear tape or some type of wire mesh that I can then make a single skin of csm over? but not sure what others have done-
I could make a female mold but again - not sure how to go about doing this?
could I build a half hull mold then join with epoxy? would that be strong enough?

the boat (if you know me ) is my tugboat which has lots of curvature.
I understand how to get the basic shape in building the male mold...
but don't want to fully strip plank the mold- that makes no sense or I would build a strip plank boat which I don't want to do.
so any clear precise directions on how to do this would be helpful... could the tape idea work?

thanks
Doug

 

I the design happened to have developable surfaces then the portions of the mold for the developable surfaces could be built using plywood. And if it had constant radius chines and the radius of the chines happened to match the radius of PVC pipe then the PVC pipe could be used for the chines. I remember seeing an article by J. R. Watson of Gougeon Brothers describing how he used PVC pipe as the mold for rounded chines on his sharpie. The chines were fiberglass and the rest of the hull was wood.

 

Hi David- I think you've seen my boat pics that I want to build. the trouble is the curvature. I wanted steel but that's too difficult, core was next- the stuff I can afford cannot be formed to compound curvature, and now I'm back to good old fashioned single skin...I know how to get the shape of a male mold and reduce the size to accommodate the stringers and the shell, but I'm not sure what would be best to skin this mold to form the frp to?

i.e. the mold surface; styroFoam? tape? paper Mache? (seriously), I've even toyed with a thin layer of concrete, bondo or packing tape, duct tape or even tuck tape. that's where I am at...

cheers!
Doug
p.s. strip planking the mold is an option. Slightly more expensive though. and not sure it will take to the compound curvature?

 

You could use C-Flex and pretty much skip the mold.

 

Would it form to the curvature? if so it might be an option...

 

Yip C flex just need a frame to build over and once its wet out with resin it pretty much supports its self to add the rest of the layers of glass, that way you have your solid glass hull without a core !!:idea:

 

thx Tunnels!

looks like I found my method- I have been researching it all day,- do you really need a casting resin or could low shrink gp resin work?

 

What you start with ,you should carry on with !!

Remember what ever resin you start with you should use all way through the job .
Mixing different resins with different properties is not a good idea !
Each one is designed for a reason and mixing is not matching .
A skin only on the outside of a different resin is not so much of a problem . But you could look at using Vinylester for your hull and poly for the deck there wont be a problem .
Vinyl has lower shrinkage and is a tougher stronger resin used in combination with good glass and its as strong as it comes !!
Poly is strong and costs less and is ok for the upper structures of the boat !

 

How many hours/days/weeks/months are you willing to spend fairing the hull?

 

Good question- My thinking is that its a workboat hull, and as such it doesn't need a production level finish on it. having said that - I will sand it to reasonable finish...how long that is- who can say. But I don't know of another material that is going to do the job.

my options for the R.B. hull are: Ferro cement, Fer-a-lite, core frp, and single skin frp.

out of those- c-flex single skins seems to be on the money.

of course not many boats are NOT going to require sanding.

maybe ill sand for a few hours...I like the workboat look to a hull, with its non-production look to it.

 

thanks Tunnels...

in Canada - sadly- vinylester is not much less than epoxy. the initial coat on the c-flex is -according to the manufacturer, supposed to be a low shrink resin such as a casting resin. but I want to an iso resin. the resin must have a viscosity within 800-1000 cps...

 

Vinylester is classed as a ester based epoxy anyway !! should be more expensive than poly but less than epoxy . its a hell of a lot easier to work with than epoxy . Personally I don't like epoxy at all for glass work , and if you fairing have to use epoxy for ever more including the deck as well ! so Vinylester would be my choice even it is a little cheaper in the end will be easier to work with and you will be able to use poly without to many hassles !!.

As for fairing its starts with the first layers of glass that get wet out and if you keep a good eye on what you are doing all the time then fairing at the end is just a minor job never a major .I always used wide rollers and a steel rule and faired the wet glass bit like a metre long squeegee just held on a slight angle off flat . At the end with 2 sacrificial layers of 450 csm and just carefully went over the hard glass with a 7 inch hard disc and 24 grit and after a quick check and a steel trowel applied a fairing layer of compound and long boarded it . I was doing 23 foot race boats and all were male moulded and could fair to a primer coat stage in a couple of day by myself no problems . But it all begins with the first layer of glass you wet out !!

 

Vinylester is not classed as an epoxy (just ask any shipper) and is not easier to use then real epoxy, though it might be for you, considering your (Tunnels) inexperience and dislike with epoxy. Vinylester is part of an epoxy molecule that is "esterized" with carboxylic acid, which then gets reacted with a styrene. This one small portion of the molecule, which gets chemically discombobulated, is all they have in common. In fact, many (most) thermoset resins are developed this way, but they're still not epoxies, nor classed as an epoxy. At the molecular and mechanical levels, they have very little in common. Vinylester is a catalyst instigated, thermoset resin, while epoxy is an activated (very distinct difference) resin, particularly in physical attributes on the molecular level.

It's one thing to not like a material or process, but another to misrepresent it to folks, who looking for information and options. Lastly vinylester isn't much cheaper (if at all) than epoxy, unless you buy the name brands of epoxy, at full retail. Epoxy can be had in small quantities for less then $60 a gallon, including hardener. If you buy larger quantities, you can reduce this price considerably (30%), which is competitive with the better polyesters, let alone vinylester.

C-Flex will cause you to use resin (regardless of type) by the 55 gallon drum and you'll spend years fairing it, just to have a really heavy laminate. This is why it's never really caught on with one off builds, like yours.

There are several ways to make a single skin hull, again regardless of resin system used. The simplest is to just use cheap furring strips over station molds, on a fairly tight spacing. This is covered with plastic sheeting and you layup your fabrics over this. Another way, that offers a slightly fairer surface is to use widely spaced stringers or furring strips (over molds), but cover these with cheap foam, which again gets skinned with plastic sheeting and the fabrics go over this. The foam is much easier to pre-fair then the nearly solid furring strip method, though usually costs a bit more.

Tug, think hard about the choice of vinylester over epoxy. If you want your project to stink to high heaven, requiring you to respirate up every time you open a can, go with vinylester. Every person for a mile around, (literally) will know what you're doing. No so with epoxy. This doesn't mean you still don't take respiratory precautions (a small fan on the work area will do), but there's no odor and you don't have to play with gallons of solvents either. Lastly, epoxy is better in every regard and in every way you measure things about a laminate. So if you want stronger for the same thickness, more waterproof, high modulus of tension, elongation, etc., etc., etc., epoxy is the hands down choice. Do you NEED epoxy - no, but in this vain, you don't NEED vinylester either, when polyester will do. I recommend you buy a quart of each product and play with laminates, on some test samples and come back and report about the experience. While doing these test samples, picture yourself in an enclosed space, surrounded by fresh laminate, because this will occur often in the build.

 

Why do you keep doing this ??

Derakane™ epoxy vinyl ester resin .
Perhaps you should check out what is written in old writing on the top of this page !!http://www.ashland.com/products/derakane-epoxy-vinyl-ester-resin.
I have used this resin by the truck loads of 44 gal drums during the total build of a 147 foot super yacht a few years ago . we were always told it was a epoxy buy the chemist that formulated and made the stuff so back off buster !!
I take the word from the chemist and manufacture as being pretty close to being the truth!!

Yes it is true I don't like epoxy and only use it when skinning a wooden boat or making glues etc that's all !!
its highly over rated and have found polyester and Vinylester resin ARE much easier to used than sticky smelly epoxy's. Have used a few brands and they all have the same bad habits!! I don't dislike just don't like the stuff .
There's many more people allergic to epoxys than poly or vinyl resins .
Had one cobber that if he gets just the smell he would have to get up and go and get away . even some one with epoxy on there cloths coming into the tea room and he was gone straight away his allergy was so bad ,but esters could work no problem at all ,all day long !!.

 

A foam core boat under construction

http://cernyyachtdesign.com/larche-dinghy-under-construction/#more-707