Hull Mould

[OPJ]

Hi guys,

I know someone who's making a small catamaran. This one isn't the same but, you get the idea; it has twin identical pointed bows:

Firstly, I'm having trouble drawing this in SketchUp. I've just watched a video on YouTube but, it doesn't clearly show you how to draw one to exact dimensions.

This is the side view. Top edges will remain square, with a gentle curve at the bow. Lower edges will be given a 10mm radius:

Next, the plan view, where you can see the radiused point at the end of the bow:

And how to bring these two together? Everything I've tried so far with the Follow Me tool just leads to disaster! :?

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I would also appreciate some advice on accurately making a pair of these - he's asked for them to be identical to within a tolerance of 1mm... He thinks something soft would be ideal for the moulds, which is why we're going with softwood - unless you can convince me otherwise?

I guess it's a case of making a couple of MDF templates, a bit of bandsawing with the fence tilted, rounding-over with the router and spokeshaving by hand?

Thanks for reading and for your ideas,

Olly.

 

[SketchUp Guru]

Olly, try this. Push the top profile down and the side profile through the top extrusion. Select the whole works, right click and choose Intersect>Intersect Selected. Then delete the stuff you don't need. Oh, and to start with, you should probably move the top profile up a little bit and the side profile left a little bit so they aren't touching. You'll probably have to copy them to move them without distorting them and then delete the originals.

 

[SketchUp Guru]

I shouldn't have replied before I got my first cup of coffee in. You'll also need to do a follow me thing with the radius on the stem.

E-mail the file to me and I'll see if I can put it together to show you.

Does your friend have anything better than side and top views of the hull? Does he have stations, buttocks and waterlines for it? Is there any sort of naval architect involved or is he just designing it by the seat of his pants?

 

[Chris Knight]

I don't really understand your dimensions the 20mm looks wrong. However, as a general case, does something like the thing below work for you?

 

[OPJ]

Thanks, Dave, that's got me pretty close to the right shape. As you say though, the lower edges still need rounding over - I'll e-mail you shortly. :wink:

Chris, don't worry, that actually says 70mm!

Yours isn't bad either, though he did specify a 10mm radius in his drawing - I might quiz him on that once I've figured out how to draw this properly myself!

 

[SketchUp Guru]

I was just doodling and did this in a few minutes. I wasn't paying any attention to dimensions though.

 

[Chris Knight]

Here's another way
http://www.youtube.com/watch?v=TbacLHiOo7U

And another:-
http://www.delftship.net/delftship/inde ... s&Itemid=4

And another
http://forums.sketchucation.com/viewtop ... ll#p220418

 

[SketchUp Guru]

The challenge would be to do a hull like these in SketchUp using that method.

This one was done in SketchUp before rendering it.

 

[SketchUp Guru]

Good links Chris.

Delftship would be a good alternative to SketchUp and it is capable of doing the hydrodynamic calculations. I haven't looked at the free version to see what limitations there are but it is better than SketchUp for boat hull design.

 

[Chris Knight]

Dave,

Do you mean a hull like this:=

With a few sections perhaps?

 

[SketchUp Guru]

Yeah. that's kind of the idea. Now how about a little hollow in the ends?

 

[would not]

OPJ I have and you can have it if you pay the postage pattern makers foam. You can cut the sections out and then use sand paper or file etc to shape it. It's a lot easier than wood. You simply cover it with fibreglass and you can make a mold from it.

PM if you're interested or want more info