The process of molding?

[andreasmehlin]

How does the process of molding a hull looks like? (If using a negative mold).

Is it first topcoat, then gelcoat and then starting with the fiberglass?

Is it a must to mold a whole mold at once or can it be devided up?

Do all layers have to be applied at once? If using a foam (like divinycell) as core can the last layers of fiberglass above the divinycell be applied "the next day"?

Why I am asking is just to figure out if one man could mold big items by him self.

[rwatson]

Does "negative" mean a "female" mould (inside of the hull is the desired shape) ?

Assuming its "female", then Gelcoat first (no need for a topcoat of you use Gelcoat.), then layers of wet out cloth.

If you use Foam, and the previous coats have cured (like the gelcoat) , then you must lay saturated chopped strand matt on the cured material, then make sure the foam is well and truly held against that layer till it cures - usually with a vacuum bag and pump.

For anything over dinghy size, one inexperienced man is advised to do it in stages. In fact, best to build a dinghy first before the big one.

I appreciate your nervousness. I will be attempting my largest project soon, and I will be doing it in stages,

What size boat ?

[andreasmehlin]

rwatson:

Can I use a topcoat instead of a gelcoat if using polyester resin?

If I do it in stages. Let say a 46 ft hull mold. Can I do 10 ft the first day and do another 10 ft the next day? Will the strength be the same as if I did the whole at once?

Yeah I will first fo a dingy sized boat before I go for the big one. The big one is a 46ft cat. The good thing is that there is a very modern and nice mold for this cat not to far from me and it just seem so much easier to mold it than building it from "scratch without a mold". There is also molds for carbon mast and bom

I crossed the pacific in a 30ft catamaran last year and really enjoyed the cruising life. My dream is to start a business doing boat charter.

Edit// Yeah, negative mold = female
/Andreas

[rwatson]

If you are only building one catamaran to start with, doing it with a female mould is three times the trouble.

As I understand it, a "topcoat" is too thin to apply successfully in a mould - it will have to get sprayed on after.

Even thin gelcoat is problematic.

Have you seen the Kelsall method (and others similar) where you lay flat panels on a table, and then assemble the panels later. http://www.kelsall.com/methods.html

or this method
http://www.amateurboatbuilding.com/a...rrier_f39.html

I am using a similar method for my boat. It is most successfull on Catamarans.

Doing staged layup is very common. When you do laying of fibreglass in stages, its best to ensure (by using Peel Ply) that the exposed surafce is kept as smooth and even as possible to avoid gaps on the next layer.

[andreasmehlin]

Three times the trouble?
Why?

I can only see advantages. The mold is owned by a private person and he let other people rent it to build. Most of the boat will be build by hand-lay-up.
Some parts is recomended to do vacum bagging (like the bulkheads and interior,etc.)

Where is the most problematic scenario molding like this?

Yeah I am familiar with Kelsall.

[Herman]

Topcoat is nothing more then parafinated gelcoat. Topcoat should only be used on top of a laminate, to protect it.

You can safely do a staged layup of layers, but please ask your resin supplier for the "open window time" which could be surprisingly short. After that a good sanding is recommended, but means extra work. Peelply could solve that, but even then careful planning is needed.

For installing foam:
Many builders just squish some scored foam in a wet layer of chop.

If you want to do it correctly, the foam needs a wetting coat, and should be installed in a bedding compound, then vacuumed down.

Another option for large scale, low manpower boat construction, is resin infusion. there is no time pressure for laying up the whole stack of materials. Vacuum testing can be spread over a nice amount of time. Only if everyting is 100% ok, the resin is mixed and infused. I have seen people building 50 ft boats, without any help from others.
There is a small leap in knowledge, however. This knowledge can be bought, or can be gained by reading and experimenting.

[andreasmehlin]

Herman: Thanks for your reply.

What is good with "short window"? Doesnt it means I have shorter time to work with it?

The sanding you did mention. Didn´t really get it, but what should be sanded?

And what do you mean as a "bedding compound"?

newbie questions

/Andreas

[rwatson]

Originally Posted by andreasmehlin

Three times the trouble?
Why?
.

What I said was "If you are only building one catamaran to start with, doing it with a female mould is three times the trouble."

Assuming you be using a current design.

There are very few catamaram designs that call for a mould to be built first.

If you find a design you like, then you can take a mould off one of the hulls, but very few people are willing to invest the time and energy to build a plug, then a mould then finally run off their first hull.

The economics of moulds means you have to be very sure it is a popular seller.

[andreasmehlin]

rwatson: Ah, now I understand what you ment and totally agree.

The mold is already in use and have produced 6 boats so far. It is a modern design. See photo: http://www.2shared.com/file/7548395/2d58efaa/1111.html

Best Regards
Andreas

[Herman]

Let's put it this way: After applying a layer of glass, the resin cures. Within a certain time frame you could apply another layer of glass, without the need for sanding (open window). This timeframe can be shorter or longer, depending on the resin. After that time, you would need to sand (thoroughly) before applying another layer of glass.

[andreasmehlin]

How long is the longest time frame for resin?

If using a female mould and glassing in stages, what is most common to do.
1) Glassing sections of the mould by laying all its layers. As I understood it, doing it like that and there is no need to sand it.

2) Glassing the whole mould, one layer at the time. As I understood it, doing like this and you have to sand.

What I know is that the construction consists of:
Gelcoat
one layer of 10oz fiberglass
two layers of 25oz fiberglass
divinycell core/airex core
two layers of 25 oz fiberglass

[rwatson]

I would like to be corrected if I am in error anywhere - because this is what I plan to do, so all advice welcome.

1) Layer of Gelcoat. I have heard it can be usefull to do that in two layers, as an inexperienced layer may may have "thin spots". Let it cure fairly well, but it wont matter if its not fully hardened (green)

2) You will need a layer of chopped mat next, with the first layer of the cloth. The chopped mat is required to fill in any voids on the gelcoat layer. After wetting out and laying the next two layers of cloth, apply peelply and roll it smooth. This will save a lot of sanding and prep after. Lay the peelply in sections of 1 or two square metres, overlapping.
You can do this in sections in the mould.

3) Once all this has been done, remove ALL the peel ply. Now lay and wet out the final layers before the core. using peelply on the final layer is a great idea.

4) Then comes the core - as stated previously
"For installing foam:
Many builders just squish some scored foam in a wet layer of chop.

If you want to do it correctly, the foam needs a wetting coat, and should be installed in a bedding compound, then vacuumed down."

You have problems vacumming in a female (negative) mould if you dont allow sufficient "slack" on the vacuum bag, so that the bag over the fibreglass can be pushed firmly down.

The big challenge is to make sure the core is firmly mated with the underlying layers. Airex make a core with perforations so that you can see the resin ooze out of the holes .

5) Layout the remaining layers of cloth over the core.

The time you have to do the wetting out is very dependant on temperature and the ratio of catalyst. The other consideration is to make sure you use the same ration of resin/catalyst for every layer. If you use different ratios then you risk the layers not bonding fully.

The method I have found usefull, is to try a conservative "layup" area, and see how much time it takes you. So, suppose you lay a 5 x 3 metre sections, and it takes you an hour. Observe how long it takes to "gel". If it takes an hour to "gel", then you could have done double the area.

Dont forget, you can do a progressive layup. So you start at one end and work towards the other end. By the time you get to the last end, the bits you laid two hours ago will have gone "off", but the last sections will still be liquid.

There is nothing like a few trial runs on a smaller project to get the feel for the process.

[andreasmehlin]

About the Peel ply. Is it making an even and smooth surface?

Is it most common to spray the gelcoat, or to to apply it by hand?

What is the drawback vacuum bagging? How strong vacuum pump do I need for let say a female mould, 15ft long

If doing hand lay up. Do I have to wait til the first layers of glass has cured before applying the core? Or is it better to use peel ply and wait it to cure and then put on the core?.

/Andreas

[rwatson]

Originally Posted by andreasmehlin

About the Peel ply. Is it making an even and smooth surface?/Andreas

Yes - absolutely. It prevents all that fine fibres standing up, and compresses the cloth into a much tidier and more level shape. Once again, try a small test section, and you will see what a difference it makes.

Originally Posted by andreasmehlin

Is it most common to spray the gelcoat, or to to apply it by hand??/Andreas

Big production places will spray it, but you would be surprised how many shops and people lay it by hand. Lookup some gelcoat laying tips in these forums. There is some really good advice.

Originally Posted by andreasmehlin

What is the drawback vacuum bagging? How strong vacuum pump do I need for let say a female mould, 15ft long

I have just finished the West Systems guide to vaccumm bagging where they specify the pump capacities, and they were surprisingly
"low end". I would get this technical advice from your local g/f supplier and books.

Originally Posted by andreasmehlin

If doing hand lay up. Do I have to wait til the first layers of glass has cured before applying the core? Or is it better to use peel ply and wait it to cure and then put on the core?.

There is nothing wrong with doing the core straight away on top of the previous layers, but I think the size of boat might make this a bit tricky for one man.

If you are doing it by yourself, you are probably better to let the first layers go off under the peel ply before applying the foam You will have to wait a few hours before the peel ply will release easily.

As you are using pre-used moulds, you may be able to contact some of the users who did other hulls, and get some usefull advice

check out

http://www.sportfishingmag.com/techn...65-page-1.html

Originally Posted by andreasmehlin

NO it makes the opposite! Though rwatson was right, it holds down single fibres of glass. The reason using it is to have a as rough as sensible surface to get the next layer sticking without sanding!

Absolutely your choice

The pump is not the issue, the mould is. In a female mould it is very tricky to get a perfect result. And anything less than perfect could mean thousands of € wasted in one go.

Again your choice!
/Andreas

But.........................
Why all the effort of bagging, sanding, peel ply? All unnecessary!

You have to understand why in the commercial boatbuilding we try to make pieces in one go. The chemical bond between the layers of resin is much, much stronger than a mechanical bond. A chemical bond you can achieve only when you do it in one go. (or at least within a short time window as mentioned before)
Once the resin is fully cured you produce a second shell in the former shell, but not one big molecule as it would be working in the green resin.

So now, before you go buying expensive crap like peel ply, vac bags, kilometers of tape and all the stuff to waste after one use, you are a clever guy and buy workforce!
Get some helpers for the layup party! Pay them in wine, beer or Kroner (for optimal results the latter is preferred), and do the layups up to the core in one go (including the core).
Then you can relax a few days (or month) and do the inner layers again in one go.
Does it harm you when you cannot say " I did it ALL myself" ?
Take care with the core! As mentioned above, you should apply a thin layer of resin and let it kick, then aplly a layer of thickened resin and mat as a glue between the glass and the foam. Make absolutely sure that there is perfect contact! This is the weakest point in all your boatbuilding task!!!!

Regards
Richard