Build question

[BigYeet]

What is the advantage of using a male mould to make a lightweight cheap carbon boat?

 

[Mr Efficiency]

what kind of boat ?

 

[BigYeet]

International Moth

 

[Mr Efficiency]

just single skin ?

 

[DCockey]

Advantage compared to what?

 

[gonzo]

Cheap and carbon do not belong in the same sentence. There is no advantage. If you are going to spend a huge amount of money on materials and time, it makes no sense to cheap out on the mold.

 

[bajansailor]

Are there any professional Moth Builders in New Zealand?
If so, maybe you could get them to build you a hull - or maybe you can rent a mould?
Are you looking to build an extreme Moth that has to be on foils when sailing, or a more conventional type that actually has enough buoyancy to support it's weight?

 

[wet feet]

Its a great deal easier to make a male mould than a female mould.The advantage is even more pronounced when you need to produce an acceptable surface at the bow.Its very tricky to get inside a fine bow such as a Moth's but fairing the male equivalent is quite easy.

The cost of carbon for something of a Moth's size isn't huge and the amount of effort to apply fairing compound is comparatively modest.The challenging part of the whole process is to think ahead and determine all the details of joining the hull to the other significant parts.You have to be certain that the parts which are intended to keep the water out can be joined soundly and you have to engineer in enough strength to keep the boat and all attached items secure.For some areas that require access you will have to be sure to leave surfaces that will accept an inspection hatch.

 

[TeddyDiver]

Dunno what the International Moth rules say about the construction but, why a mould? Just do it one-off, the core being the "mould"..

 

[fallguy]

I don't know much about the Moth, but if you really want carbon, I'd probably lean toward stressed or tortured plywood as the two make more sense together in my brain than the foam and carbon. Then, you are still sort of technically in a male mold, but also have very little movement of the hull after flip versus foam which might move a bunch with a single skin. The idea of building a stressed ply carbon Moth sounds rather fun and I am not even a sailor. Rumor has the rest of the moth would need to be built from carbon prepegs and such. Way above my experience level.

 

[ziper1221]

Build the first one out of tortured ply sheathed in carbon (or even glass) as fallguy suggests. The length to beam ratio is high enough you should be able to use one of the quick manufacturing processes they use for catamaran hulls. Check out gugeon's book or Kurt hughes' cove molding. It will be heavier and therefore slower than you would like, but if you like the design, you can use it as a plug to make a proper female mold. Then you can swap all the actual important and difficult parts (rig, foils, controls,) over the new, lighter hull.

 

[BigYeet]

Sorry for not replying for ages. Thanks for all you suggestions and advice. I know I started this thread about the advantages of a male mould but is it possible to get a CNC machine to cut out a female mould? And also what do you think about 200gsm carbon inside and out with nomex foam inbetween for the materials?

 

[fallguy]

Sorry for not replying for ages. Thanks for all you suggestions and advice. I know I started this thread about the advantages of a male mould but is it possible to get a CNC machine to cut out a female mould? And also what do you think about 200gsm carbon inside and out with nomex foam inbetween for the materials?

I had female stations cut on CNC. It doesn't do the bevels, but pretty accurate ftmp.

This is a female bow shape iirc. If I did it again, would probably finish the female bow as a nose and attach the nose to the hull... It would be nicer to lay the nose down on a table to complete. I spent a lot of time shaping two hull bows to match and work in the bow was really fairly tough..

 

[fallguy]

22" wide on the bottom to basically zero for'd

 

[wet feet]

You would have a great deal of difficulty machining the surface of the mould in one piece.It could be done by making sections and bonding them together once machined.The problem that isn't easily overcome is that the body of the machine won't fit inside the fine bow of a Moth.You could probably deal with about 80% of the boat from the transom forward in one piece and you would ideally need to find a 5 axis machine.You could then add on a series of vertical transverse slices to complete the bow.It could be done as a series of slabs if you could only find a 3 axis machine and it isn't that difficult,just time consuming to have to bond a stack of slices together and then tidy up the glue lines.With either of these approaches you would need to include spigots and recesses or locating features of some kind prior to bonding the mould together.

If you have a decent 3D CAD model of a hull,you do a Boolean subtraction from a large enough slab of tooling block to create the female surface and then divide it to suit the machining process available.