Direct female mold construction...

[Brant Williams]

My first post at this great forum...so take it easy on me.

Looking toward my first boat construction project. The concept I'm leaning towards is a small (1-2 person) fast day sailing boat in the spirit of the JS9000...but probably a little smaller (about 24' LWL & 4.6-5.0' beam). This is a small boat...very skinny, light, and quick.

Construction technique will be vacuum infusion, with secondary bonding (vacuum bagging) of core, and vacuum infusion of internal skin.

There are two key requirements for doing a vacuum infusion project.

#1: You must have a professional quality female mold which has been designed with VI in mind. It must not leak!

#2: You must have a well engineered infusion configuration. (Luckily, recent efforts in software modelling have made the planning of an infusion process like this much less of a risk IF you are willing to pay a consultant to model and engineer your infusion process and set-up....or if you get the software yourself and learn to use it through experimentation.)

My question has to do with direct female mold constructon techniques. I have found past references on this board where direct female mold construction was protrayed as being inferior, etc. Yet there are people out there using CAD/CAM and CNC cutting to make the effort involved in a one off female mold more reasonable. [See pic below for reference] This is what I have in mind...though the scale of my project will be about 1/50th of the mold in the pic!. By putting all your time into the design of the mold frame structure, and then having it all CNC cut, building a precise mold is a very realistic project. (I already spoke to a CNC cut shop about having 5/8 die cut quality plywood section templates water jet cut. Total cut cost was estimated at about $1200-$2000...less if I give them total freedom on scheduleing so they can fit it in when they are slow)

Any opinions from the experienced constructors here on this general concept?

Also, I have been playing with the Maxsurf demos...and I really like it. It seems, however, that the tools in Workshop for plate developement (metal hull boats) are much more well developed than the tools for bulk head and stringer construction. This makes sense of course, since real ships (commerical) are welded together...not pulled from a mold.

With most naval CAD/CAM packages is it best to simply output all the station plans as simple 2D drawings (sections perpendicular to a common datum/baseline) and then engineer the stringer insert notch configurations yourself? After all, there is a lot to properly locating stringers in a mold section than meets the eye (ie avoiding twist, matching stringer surface to section template surface, minimizing skew bending etc.). Opinions are welcomed.

Thanks in advance.

[CDBarry]

1) Go to www.shipconstructor.com for a professional level package.

2) Lots of female molds are built in fiberglass -they are easier to seal.

[Raggi_Thor]

Stringers: You can use Rhino to place stringers on the hull surface. If the stringers are "high", I mean large in the moulded side, you can unfold them to a 2D shape so that they only bend in one direction during the building process.

[Navaldesign]

Hi Brant,


Take a look at www.navaldesign.it/My_Homepage_Files/Page59.html and then click on the 23 mt boat images.
As you can understand it is a 23 m LOA boat for net fishing in the Mediterranean Sea. It has a 650 Hp Guascor Diesel engine with 6:1 reduction ratio and 4 blade pro.
It took us 40 days of 3 persons and 25000 Euros to build the mold and we had the sections hand cut in plywood. It was quite easy for us to do so because the boat is a hard chine one. CNC cutting is perfect for round bilge hulls and sections may come out from any CAD program like Rhino, Autoship, Maxsurf or other. Since i usually work with steel i prefer to model the hull in such programs and then export the sections, waterlines and buttocs in Autocad for further work and nesting, because manual nesting minimises material loss when irregular shapes are involved. In your case the same procedure should be fine for nesting the various pieces of the sections on the plywood panels. For the planking we use 10 mm MDF. Alternatively you can consider the use of PVC panels which will give you a fine finish.
Such a mold is relatively cheap and sufficiently resistent for the construction of up to 5 - 6 boats.

Don't know where you are in the US but this company is located in Florida( http://www.vectorworks.com) and while a big company they don't mind taking on small projects-particularly sailboats. They have a process that makes a quickie female mold suitable for laying up several boats.They use a 5 axis machine and carve the shape in a short time.
If you're within traveling distance you might consider them. Talk with Matt McDonald...

[Brant Williams]

Naval...thats one big boat. Looks like 100x times the size of my little project! I think my construction method is definitely workable.

As for getting the mold directly machined...that will simply drive up cost too much. True, my time is worth $, but doing it yourself (to some degree) is part of the fun. Im going to stick with section templates and inserted planks/strips.......