Boat Hull gone wrong

Bryan K

Can someone help me figure out where I went wrong with this boat hull? I have some idea it's due to the shape or number of polygons, but I am not sure.

This is the starboard side of a catamaran.

Thanks!

catamaran.skp

Roger

I didn't open the files because I am still running version 6, but from what I can see I will share some thoughts. If the front of a hull is too narrow and sharp it will not raise from a sea. If you have a big wave coming at you, you will want enough buoyancy to ride over the wave and not sink under it. So the bow needs to be fuller. Second, the stern should not cut off square. A square stern creates a vacuum which will result in turbulance and result in slow speed.

Keep in mind that a catamaran operates in two modes. At slow speeds it pushes a bow wave in front which it trys to climb over. However at slow speeds it can't. Once it gets to a certain speed it comes up on plane and skates on the surface and scoots looses most of that bow wave so it no longer pushes a wall of water. That's when things get fun and the boat screams over the water. If you are running before the wind with a following sea you can easily overtake the ocean waves from the rear and the go screaming town the face into the trough. If you do this too fast and bow is too narrow you shoot right through the surface toward the bottom. And with the deck diving down at a sharp angle and the stern high in the air, you go ass over tin cups and you catamaran comes to rest in its most stable position -- upside down. Perhaps the mast breaks, sails tear, rigging parts, people get smashed against hard objects and thrown overboard--none of which is good.

Also in a cat when you are on a broad (also known in performance boats as a screaming reach, there is a lot of side pressure so you upwind hull may come completely out of the water. As far as the ocean is concerned the entire shape of the hull changes relative to the water. Think of a motorcycle versus a car. When you corner a motorcycle you are driving on the side of the tire and not the bottom. In other words as the boat picks up speed and heels over onto its side, you no longer have a deep keel down in the water to provide lateral resistance. The boat starts to slide sideways and loose forward speed and you crash back down into the water as you quit planning. To counter this you need a deep keel to penetrate far down into the water to counteract the sideways slide. In a big mono hull this can by a sort of shark fin shape at the bottom of the boat. But those are wide and slow. In a performance cat, they often take the form of a dagger board (a knife-like shapes that slide vertically through the hulls. Why do they side? Well the great things about cats is you can run them up on the beach. However, to do that your keel has to retract into the boat so you can slide through the shallows or run up on the beach. So the dagger boards have to go up and down depending on what you are doing.

Have I lost you, Are you still there?

Now the shape of everything under the water has to work with the shape of everything above the water. Where you mast(s) and sails are and how big they are has a great effect on what happens in the water. Your aerodynamics and your hydrodynamics have to complement each other. This is why there are so few really ugly sail boats. Good looking boats sail well and ugly boats often don't work well.

When designing a boat you have to consider the center of effort, the center of bouyancy, and center of gravity (along with a thousand other things. The center of gravity needs to stay under the center of bouyancy. If the two get switched or are too close together -- well hold your breath because the boat will turn upside down. Can't remember the rock star that was into sailing, but durign heavy weather the lead keel fell off and the boat flipped over and would have even with zero wind. You want that center of bouyancy to be lifting the boat so it floats. You want the center of gravity (great mass of weight) at the bottom so the bottom stays down and the top stays up. On a mono hull that is well designed the boat will right itself even if it flips completely over because in a flipped position she center of bouyancy will be tring to climb to the top and the heavy keel will be trying to roll back into the water.

I could go on all night, but maybe this will begin to show you how complex Nautical Architecture is evern before you start worrying about where to put the bunks, how to keep rolling and pitching to a minimum in the galley, and whey the head and the shower are all in the same tiny space.

--the Jolly Roger

Crazy Eyes

I like Rogers suggestion, but I would peronally just Google Catamaran Hull and go from there

Tobobo

Sorry not being nautical, what's the problem?

(Edit: I was too slow, I hope Roger sorted the problem for you)

(Edit: Wow Roger you know your onions! I had to read it in pieces so that I could do some work, Do'h here I go again! Must work must work must....)

MALAISE

EcoFeco,

Try this :http://sourceforge.net/projects/freeship/
You may then import file.obj into SU. Hope it can help.

MALAISE

pilou

Don't yet exist! It's now Delftship free!

Bryan K

Thanks for the great answers, especially Roger, though I am familiar with boat and ship basics. I'll be honest and tell you by not a lot, though.

First, I should apologize. My question was related to the problem with the lines that are still showing in the model. When I try to erase them, it also erases the 2 adjacent faces as well. I think this is due to bad polygon placement.

I'm sorry if my question was vague. I do very much appreciate the valuable information I did get.

The current shape of the hull is not complete as I stopped when I ran into the showing lines problem.

Here is an example:

ely862me

u should erase the inside geometry and later smooth it(u have some rests inside)

Bryan K

@ely862me said:

u should erase the inside geometry and later smooth it(u have some rests inside)

O.K. What's a "rest?"

ken

Roger

Will I have been working this Saturday and Sunday and I needed that laugh. As I read, I just kept seeing those visuals.

Thanks for the chuckles

Ken

ely862me

The rest is used to refer to all the parts of something or all the things in a group that remain or that you have not already mentioned. QUANT 'of' def-n

* It was an experience I will treasure for the rest of my life. + 'of'
* I'm going to throw a party, then invest the rest of the money.
* He was unable to travel to Barcelona with the rest of the team. + 'of'

* Rest is also a pronoun.
      o Only 55 per cent of the raw material is canned. The rest is thrown away.

in my sentence i used it like residue

Sorry for my english!

here ur model ..i cleaned up the inside geometry wich was useless

catamaran.skp

Bryan K

Thanks ely862me. I understand now.

So it was the geometry? Hmmm. Good to know.

I'm still learning this program and this boat is just another exercise. When this is done, I will attempt a car.

As always, everyone's help here is very appreciated. You guys truly are the best.

Roger

When connections like that do not work, they are probably not really connected.

Zoom way in. As in really extreme and you will probably find that your triangles are not connecting at one point. I fight this kind of problem all the time. I find the only way around it is more care and getting in a lit closer than you might think is necessary. Always bad perception or workflow on my part.

Bryan K

Thanks Roger.