boat building

[brokenrinker]

A reliable source on another forum I frequent made a comment that boats of the day (sailing, beach catamarans, 1990s and later I guess) were made the same way as surfboards. I took this to mean that the master was basically hand carved and then molds were made from the master. Does that sound right?

It strikes me as amazing that molds for a boat that required two, perfectly symmetrical, mirror image hulls, that are going to be manufactured in pretty high numbers (thousands) would be made from hand carved masters.

Am I totally misinterpreting his comments or does that sound about right? How else might you go about doing it? I'm talking about hulls ranging in size from 16 to 21 feet.

[Al_The_Man]

I would have thought that the molds would be laid up or lofted just as you would in a wooden vessel with allowance for hull thickness etc.
There would be very little carving involved in this process?
Al.

[tulsaturbo]

Am I totally misinterpreting his comments or does that sound about right? How else might you go about doing it? I'm talking about hulls ranging in size from 16 to 21 feet.

You may want to check out this free cad program called FREE!ship.

"FREE!ship is a surface modeling program for designing ships yachts and boats."

http://sourceforge.net/projects/freeship/

[brokenrinker]

I would have thought that the molds would be laid up or lofted just as you would in a wooden vessel with allowance for hull thickness etc.
There would be very little carving involved in this process?
Al.

I'm a little dense. Can you clarify? Does that mean you would make a negative (female mold) without the use of a positive (male) model?
I'm still wondering how you would get mirror image molds with the level of accuracy that these hulls have.

[ger21]

I've seen video of a mold being cut with a 5 axis router.

[Al_The_Man]

I'm a little dense. Can you clarify? Does that mean you would make a negative (female mold) without the use of a positive (male) model?
I'm still wondering how you would get mirror image molds with the level of accuracy that these hulls have.

As in any boat building the accuracy would be in the lofting of the dimensions from a table of offsets and the production of the frames, this method has been done extremely accurately, probably for centuries, in order to produce the full size model.
I would suspect that for production a shell would be constructed over the frames just like you would in a Ferro-cement or wooden boat building in order to produce an inner core or plug model for which the final hull is built over.
Or conversely a female mould could be made with this method for constructing from the outside gel coat in.
Al.

[brokenrinker]

As in any boat building the accuracy would be in the lofting of the dimensions from a table of offsets and the production of the frames, this method has been done extremely accurately, probably for centuries, in order to produce the full size model.
I would suspect that for production a shell would be constructed over the frames just like you would in a Ferro-cement or wooden boat building in order to produce an inner core or plug model for which the final hull is built over.
Or conversely a female mould could be made with this method for constructing from the outside gel coat in.
Al.

That helps but I'm still struggling a little with the terminology. When you say frames are you talking about something that would reproduce the cross section at various points along the length of the hull - the way a bulkhead does on the inside of a finished hull?

[Al_The_Man]

Basically , yes, Frames are like sections taken at different points along the hull, these traditionally have been constructed by 'lofting' or laying out on a 'loft' floor these section details are derived from a table of offsets, these are then used as formers that provide support for whatever method is used to construct the hull.
Google should show some practical examples.
Al.

[Master of nun]

The process to build a mold for a production boat will start with a plug, as Al has pointed out, either built with materials with the intention of being thrown away when finished or built as going concern and finished to a final useable wooden boat. These days they are generally cnc cut from foam, light frp tissue laid down and machinable paste/urethane tooling material sprayed over (there are probably half a dozen different techniques and materials) to be re machined and then preped to pull a production mold from.

Yes you can build a female mold straight up, but this will not last the many pulls a production mold will have to last.

Surfboards, as far as i'm aware...I have made a few, are shaped individualy either by hand or dedicated surfboard cnc machines and then glasses over. I don't believe production surfboards come from a mold, someone correct me if i'm wrong the surf fraturnity luv the hand made by some legend thing anyhow!

as for being perfectly symmetrical etc. don't be fooled, I'm sure the people( I was one of the once upon a time) that have put hundreds of these boats together will be able to point out many missgivings (like anything there are good ones and bad ones). Although the age of CNC has changed things a lot.
It's a bit hard to make any measurements when fully assembled....and you can only see one side at a time.as long as they look ok and are nice and shiney no one will measure it anyway unless they are ripping of your design!


Cheers Liam