"female plug"

Hi guys, I'm thinking of building a 25/27 powerboat, and I would like to try building it starting from the mold and skipping the plug stage so that the first lamination will be the actual prototype/plug.
I know somebody does it, but don't actually know what's involved,is it more difficult? do you know any text book you can suggest that tells about this?
Thanks for your help
federico

 

There are some Slovenian builder from who I know use this method, the female plugs they use are made in Italy.

Only problem one of them had, was a leak in the plug, so setting up for infusion took some time. But if you do not vacuum of infuse your first layer(s), then you should be fine.

Building is pretty straightforward: set up frames, and plank the frames with wooden strips or plywood, of any kind. A quick coat of epoxy will fill most of the small gaps that are left, and a second coat will give you a sufficiently glossy surface to succesfully pull some parts from the mold.

 

Thanks Herman!

 

My question is. How do you intend to shape it accurately. We us a 5 axis CNC to make very large hulls/decks etc (80ft). We still get a slight waveliness. Not being funny, you asking the impossible. Well not impossible. Its uneconomical and practical.

It will come out pissed as a fart. You will never be able to so the surface and curvature.

Buckle

 

I've heard some old cat stories telling about this kind of "female plugs" expecially for off shore one off making.
And those farts won a couple of races...

 

Buckle, thank you very much for your most positive reaction.

If you tried the method of simple negative molds (negative plugs) and your products came out pissed like a fart, then you should reconsider your career. as always, it is most important to work true and fair, with the highest accuracy possible. The product, as pulled from the mould, will still need some sanding to remove minor blemishes, and of course a paint job, but to call it "pissed like a fart", no, absolutely not. Last project I have seen at a customer was a 48ft deck, in a one-time plank-on-frame mould. To create a smooth finish that would not have the used epoxy stick, he used regular brown packing tape after one quick coat of epoxy.

 

Hi Herman, I have no direct experience on this topic but from what I heard it sounds more like you describe it rather than how Buckle does...
Can you explain this better ? it's not very clear...but sounds interesting!!
"To create a smooth finish that would not have the
used epoxy stick, he used regular brown packing tape after one quick coat
of epoxy.

 

Pretty simple:

Start with the bare wood, coat it once with epoxy, then after curing, apply brown packing tape.

It does not give you a class A finish like a decent negative mould would, but it is more than perfect to start directly with the paint system.

 

The use of brown parcel tape is a cheap substitute for flash tape. However you cannot be serious about making full production moulds using this method. No serious GRP company would want to own moulds which produce moulding's which need serious cosmetic finishing. It would be far too uneconomical and labour intenstive. Plus also if you have to knock out between 300-500 moulding from this mould in its lifetime, you would be throwing your profits down the drain. Then you would have to question you career, thankyou.

Plus also, dont you have any concern for quality! Anyone would an eye of detail would know that you can't rub gel coats. Well not if you want a good finish. The resultant would leave serious porosity in your moulding, leading to a poor surface finish and release problems/break outs later down the line. The days of rubbing moulding's need to be eliminated as porosity in a dark blue moulding is not a pretty sight. If you have a method of rubbing your moulding without the need for spraying afterwards, leaving a good gelled surface, you hold the answer to many resin company dreams and prayers.

Thats why my friend, all GRP mould builder, put all their efforts into making a plug of excellent surface quality, therefore allowing a mould to be made which needs no rubbing, perhaps a fine polish. Remember, you cant rub a poor quality mould into a good mould. Its impossible.

Buckle

 

I think were on different lines then...

For a full-production mold, there is no excuse for not using top-notch materials, and demand the highest quality possible.

However, for various reasons people want to build only 1-3 products, but from a negative mould. To build a top-level negative mould would be a waste of time and energy. Especcially if the end product will be epoxy, and will be painted anyway. Many people over here use a temporary negative mold for these purposes, coated with a layer of epoxy, then brown packing tape. To use a much more expensive flash tape would also be a waste, as epoxy will not attack the brown tape, and will not stick to it either. (polyester won't stick as well, but can possibly attack the glue of the tape)

So to be short, for every purpose there is a solution. But one needs to know the parameters:
-size
-material (epoxy. polyester)
-no of products
-desired production method

Only then a right molding option can be chosen.

 

Styrene Attack

In my experience, I have known uncured/partically cured polyester and vinylester resins/gel coats to attack various surfaces and products. The cause for this is due to styrene in the product still being given off, even after its cured. I have experience with polyester moulds resulting in attacking variously waxes and chemical release agents leading to a poor first release. Afterwards, the mould matures and behaves itself as the styrene has been removed from the surface with the first pull.

Styrene has also been known to affect gelcoat cure. Most lamintors treat gelcoat like cheap paint. Slapping it down thickly aint good as a coat which is too thick does not allow styrene to escape. Likewise, if the gelcoat has been applied to thinly, an in-sufficient cure will not be reached.

Therefore I would perhaps recommend giving you mould a light abrasion with some polish just to remove any uncured styrene partials left or perhaps give you work a light post cure (leave it out on a warm sunny day in a greenhouse or inside you car. Dont leave it in direct sunlight). Then if you still wish to use your brown tape, cover the mould. I would therefore believe this would eliminate the styrene attacking you brown tape.

For the record, AeroVac supply a very good range of flash tapes, which are often better quality than brown parcel tapes, and also cheaper. You also get more on a roll.

Can I ask? Why do you use epoxy? Is it for the mechanical performance advantage or another reason?

 

Hey guys, keep an open mind to simple 'one off' solutions. They might work. Herman is right.
Though I do not see the advantage of building a female mould for a 'curved' hull the way you have been discussing - (it will take just the same amount of work (may be even more) to fair the hull after releasing) - for smaller parts and/or decks which are often mostly flat panels for the most part it might do. On the other hand, building the mold female takes at least the same amount of time and care as building it male. It is easier working outside your product than having to climb in and out all the time. Besides longboarding inside a curve is absolutely not ideal ....
When building inside out (male) you can pay extra attention to laminating your outerskin, resulting in easier fairing (less filler = less expensive)

Having said this .... since powerboats often have less curvature in their hull panels this female mould idea might work for a one off, I think. So, I would say it all depends on hull shape.

The brown tape or others like it do work (with epoxy anyhow) but an alternative would be ordinary sticky foil that people use for covering their cupboards at home (see attachment; we also waxed this plug to be on the safe side) Check your local DIY shop. Remember, we are talking a one time use only now.

Lucas

 

I still wanted to reply on the epoxy-polyester thing.

There can be several reasons for diy builders and small boat builders to opt for epoxy:

less smell, many builders have either neighbours (Holland is a dense country) that can complain, or their environmental permit does not allow polyesters.

for many one-off building projects, people tend to opt for the highest quality achievable (within limits). In Holland there are many, many of those small scale projects going on.

However, it is not my intention to create a "polyester - epoxy" discussion here. If one wishes, we can open a new thread for that.

 

My idea

hi there,

I think it can be done the same way as making the male shape. But instead of creating the outside you cut the inside transverse wooden forms you get them well alingned and fixed, then you put some thin 3mm MDF wooden panels in it. The large parts are easy, for the smaller(more curved) parts you first put in some carton-paper you can easyli cut to the exact shape and the copy onto a wooden pannel.

The seamings and staple holes need to be filled-up with an polyester paste and sanded, the same for all other impurities. Also don't foget to break sharp edges with an adequate radius 2-3cm.

It is less easyer to get the female mold made then the male one, but for a one of it's more economical than making first a male one and than the female?

Work will be more complicated but I thingk it will amost be the same as making first male and then female...

I didn't start building yet but I am occupied in designing a 7.42m daycruiser and that's the way I would do it.

Greetz,

Daniel Peeters

 

Hi fede,

I have read through the thread quite briefly. I am not sure wether you are going to start production or this is a one off. Would like to know

your reasons for considering this kind of technique.

However, I am currently building two direct female moulds. One together with my brother for a couple of 66' high performance sailing proas and

one for a smaller beach proa a'la tornado or hobie cat. For more information and some pictures please visit www.harryproa.com (updated

today....)

The big one is a custom proa and the smaller is an Elementarry.

Both boats are designed by Rob Denney Perth Australia and I am using his recipe for the moulds. Rob has used this technique on several of his

own boats. Wether he will use his finished boats as plugs and make production moulds from them or use the moulds as they are I am not sure. I

suspect he will use them as they are.

For the big one we chose to build a mould because we belive it will save finishing work as we will build two boats. For the smaller one I need

a mould in order to save som kgs of foam... Stripplanking 4mm divinycell is not easy..

Wether direct female is good or bad business for you depends on what you are planning to do afterwards and what kind of material you will use

in the hull. Anyway, a hard chine mould should be pretty straight forward as far as I can see.

So far the actual building has not been particularly tricky (we are building double curved)
Unfortunately, none of my moulds are finished yet so I can not tell you how succsessfully (or disastrously) it went. However, the first mould

for the smaller one will be finished within a week or two and moulding will take place somwhere before xmas.

The recipe for double curved surfaces is as follows:
striplank with, say 15mm, cheap timber. Knock off any obvious bumps with a machine sander with a coarse disc. Do minimal work on wood. Fill

screwholes and knotholes with bog. Seal the mould with a layer of 200gsqm woven glass. A cheap high viscosity epoxy works well on this kind of

surface with a lot of bumps.

(This is an important step. If you do not seal it off completely you may have serious trouble if you get humidity changes. Strips will swell

and print through your glossy finish. Happened to us and was frustrating as hell. Hours and hours and hours of hard work down the drain. Do

not cut corners!!!

Instead of woven glass you can also use csm, but since it soaks up more resin it is not cost effective.

Apply a thick layer of bog. We used a mix of epoxy and microballoons. Extreemly easy to sand if composed correctly- a nightmare if too lean

on microballoons. Read instructions if you are an amateur like me.....

to make sure the bog is evenly spread you may apply transverse strips (2mm high) first and then fill up between. You can also make the strips

higher and do some sanding on them to get rid of the largest bumps before you fill them up.

PLEASE NOTE:
We do not know if these srips will print through and be visible on the finished product. Don't think so but Will have the answer when first

one comes out of the mould.

Use 40 grit paper. For a sanding pad for double curved areas you can use a 150mm pvc pipe. Cut it longitudinally to desired stiffness. Move pipe +45/-45 degrees. One

metre per person is about right. I have found it useful to do some sanding transversely with a pad of 4mm plywood before I start with the

pipe. This will remove any ridges running longitudinally which the pipe has a tendency to jump over.

When the entire area has had a touch of the sandpaper the mould should be pretty fair. Go easy and see what happens.

Apply a coat or two of epoxy primer and sand to desired finish. If you are going to paint the boat you may stop at 320-400grit. I do not know

what is required for a good gelcoat finish.


I hope this is of some help for you. Will know a lot more in about a month or two.
If you have ideas, comments, questions please let me know. I need to learn as well.



Kind regards
Terje