Half Scale

Sorry.

A Millimeter is a miniature America's Cup boat.

http://www.millimeter.org

I want to build a wooden boat that size, but I want a "mini" Dragon or Skerry, not a mini- whatever-the-Millimeter-is boat.

Do any of you know of such a boat design?

That's my question.

 

Suppose someone says yes. And then what?

 

10 foot overall? That's 1/3 not 1/2 That would be a big model that would not carry a grown man. Even 10 foot waterline would be so small that the usual scale rules would break down and then there is the mass of the crew. You know the meter rule toy boats -you could follow the lines and modify the overhangs and deck to your preference. Otherwise you are looking for a complete new design.

 

Half would be fine, twelve, fifteen feet. No design like that?

 

that's the H 12.5 -classic daysailer

http://www.herreshoff12.org/specifications

There are many slight redesigns, plywood, lighter, chined...

Or are you looking to try and make something that LOOKS like the 30 ft proportions. That would be intentionally distorted.

 

Looks. Absolutely. Want to build beauty.

 

But it carries one human?

I think what you want then is to literally straight scale the canoe body of your chosen hull. Place your body in it (no small task). Replace the keel design with a deep bulb. You will be limited by the displacement so to have any chance of carrying enough sail to look like the original you will need all the remaining displacement in lead down low. Then it is just a mater of calculating how much sail you can carry in the shape of the original. The lower the bulb, the taller the sail.

The advice you have been getting is for how to design a boat 'right'. You want 'looks right'.

 

Ah, I see.

Thanks, I didn't even know that I don't even know the words.

"Straight scale the canoe body of your chosen hull..."

You mean choose a canoe body, or the Dragon?

 

Canoe body is the term for the boat hull without the keel. Old meter boats have lots of volume in their keel. "deadwood"

I was not suggesting you use an actual canoe. But if you are not fixated on the old meter rule hulls with their slender overhangs I would suggest you consider canoe stern designs. Double enders scale down well so you will have nice performance as well as looks. It's a matter of opinion but I think the canoe sterns are beautiful.

Robert Perry recently did a 62ft design he called sliver that is pretty amazing.

https://www.flickr.com/photos/nwswb/5752764162/in/set-72157626665955617/

The proportions look just like a good kayak hull.

 

Ah, I see.

So you're suggesting I scale the body without the keel to where I want it, figure out how to sit in it, then add a keel and bulb, and figure out from there how much rig I get. It sounds like getting the enormous, mile-high rig the Skerrys have would take a keel that would be large, relative to the scale of the rest of the boat. And it also sounds like it will want more keel anyway, to go to weather.

I should have stayed in school... but no. I joined the army to get away from home and stop taking orders.

P.S. I was up at Port Hadlock two weeks ago, taking the tour of the school. Came very close to signing up!

 

There are wooden 2.4 meter class boats. It is NOT a one design, therefore you couldvery loosely scale a Dragon to the measurements. The fact that most of the boats are FRP should not put you off. As far as I am aware they (hulls) may be manufactred from timber or glass, but not carbon.

If you want to you could try the Norlin 3 design, Stradivarious or a couple of others. You should be able to contact the designers via the website (2.4 class) or at least contact someone from the US part of that organisation.

My own take on these craft is they are quite good but more suited to sheltered water. If you want a fast one, either use one of the two designs mentioned above or design your own. Best wood construction method is strip plank cedar with glass/epoxy sheathing. A 'scaled Dragon' at this size with appropriate corrections would not be as quick as the current boats, even if it would look nice!.

 

That is the basic plan. The key to being happy with the result is understanding what it will be. You can build a smaller hull exactly proportional, but when you put your body in it and take up a large portion of the scaled displacement you will need to place the rest of the displacement very low to have the righting to carry sail. The point you might have missed is that the hull design has a design waterline that is critical to performance and looks. The scaled hull has a specific weight it will float and your body will be a huge portion of that and can physically only fit a certain way which is higher than it should be. To carry sail the center of mass needs to go close to the original design so the less weight that is left for the bulb, the farther down it must go. Some light weight racers can't be scaled down because the crew weight takes too much of the displacement -there is nothing left for structure and ballast. When you look at candidates for scaling, think about the placement of your 2X size body that weighs 8 times as much.

The other note is to consider performance -specifically hull speed. Those long overhang boats have short waterlines ex dragon LWL=19 half scale 9.5ft that means the boat will be hard pressed to do more than 3.08 knots. A double ender LWL 30 scaled to 15 would do 3.87 knots 25% faster.

So what I am suggesting is we (this forum) can do some calculations to show you the result. I think other posters have been telling you bits of this along the way.

 

Try this link, it gives some idea of the shapes developed from a sort of 12 meter rule scaled down. No bulb keels. These things exceed 4Kn displacement and get there very easily.

http://www.24mr.se/

 

Great resource for build technique at least. If the OP was satisfied with the look they have lots of good designs for performance.

 

The problem has been explained many times previously and all you need to do is look up the "law of mechanical similitude" and you'll quickly realize you can't half a yacht proportionately, without huge adjustments.

The boats that seem like scaled down versions of others (universal rule, 12 meters, etc.) aren't scaled down versions. These boat are wholly different in most every regard, except they've been styled to have the "flavor" of what they're trying to mimic. One look at a successful model pond yacht shows the extremes you need to incorporate into scaled down yachts.



This is a classic example, though not as extreme as others. It's sort of a 35' looking boat, but has a 10' deep keel. In reality, the 35' boat would have about half this amount of draft. It is just one aspect of the difficulties in scaling a design dramatically.

If you want a Dragon, just smaller, then design a boat that works in the smaller size and attend to the aesthetic considerations, so it looks like a mini Dragon. A 15' long Dragon (INT) will be a difficult thing to live with, as it will literally be little more than a canoe, with a huge rig, so you'll want to cheat on the beam a bit to get some bearing area. Ditto the ballast/displacement ratio. The Dragon works because of it's almost 60% ballast ratio. On a 15' boat getting this much higher (you'll need to) will be difficult, without really exotic materials (carbon, Kevlar, etc.) so use beam and build her light.

Given you're asking about this sort of thing, you'd be best advised to purchase a set of plans that have most of the attributes you like (in a 15' boat) and style her up to look like a Dragon.