Godzilla and hard chines

[marshmat]

Figuring out exactly why a file won't run can be a bit of a pain, yes. But you can usually sort it out in a few minutes, or if not, one of us can usually find the problem.

As Rick says, it sure beats spending piles of cash and several years to build a series of boats, just to get you to something not quite as efficient as what Godzilla finds in five minutes.

[Kudzu]

OK got this to running but there is one thing I still can not understand. I looking for an explination in the manual but I have not found it.

# Shape Factors: Minimum, Maximum, Seed.
0.0, 0.1, 0.1
0.0, 0.1, 0.1
0.0, 0.1, 0.1

I don't understand these numbers. This is something I just input playing and I ended up with a cardboard box. Can you explain the numbers? I am just not grasping what I am reading in the manual.

I have a pretty good looking hull to start with and want to keep something similar, just improve on it. That is my goal here.

[Guest625101138]

I have attached an in.mlt file for a mono hull. Rename it to in.mlt once you delete your in.mlt file from the Godzilla folder. It is a large model boat I was playing with. Displacement just 15kg.

It has the 7 shape functions and this gives greater flexibility on the shape. There is also an 18 shape function but you need to know what you are doing to use this otherwise you get something that looks really odd.

The manual lists the influence of each factor in the hull shape. I have placed remarks on a couple of the ones I often limit.

Rick W

[marshmat]

Originally Posted by Kudzu

OK got this to running but there is one thing I still can not understand. I looking for an explination in the manual but I have not found it.

# Shape Factors: Minimum, Maximum, Seed.
0.0, 0.1, 0.1
0.0, 0.1, 0.1
0.0, 0.1, 0.1

I don't understand these numbers. This is something I just input playing and I ended up with a cardboard box. Can you explain the numbers? I am just not grasping what I am reading in the manual.

I have a pretty good looking hull to start with and want to keep something similar, just improve on it. That is my goal here.

Hi Kudzu,

The "shape factors" are basically a numerical way of saying what the shape looks like. The first row (f0) is for waterline shape, the second row (f1) for cross-section shape, and the third row (f3) for the profile view of the keel line.

A value of 0.0 for any of these gives a rectangle. A value of 0.5 gives an ellipse, and a value of 1.0 gives a parabola. Values up to 3.0 can be used to produce hollows and reverse curvature. Values in between give shapes somewhere in between. In the 7- and 8-parameter series, you add parameters f3 and f4 for afterbody waterplane and sideview, f5, f6 for forebody and afterbody relative lengths, and f7 for the afterbody cutoff (ie, at what point the hull is cut off and a transom glued on).

When you enter the shape parameters for Godzilla, you give it a minimum and a maximum, within which it will vary the parameter to find an optimum. The "seed" column just tells it where to start, which except in a few odd cases doesn't really make much of a difference if you have a large enough population.

[Kudzu]

Thanks for the input. It's starting to make better sense now. It raining here. Shop project are on hold so I have the morning at least to play around.

[Kudzu]

Got this to work but I am just not getting practical results. Granted the resistance figures are great, much less than what I started with. But the hull shapes I am getting are just not practical for a kayak. Most are unstable and by the time it transforms them some of the things I designed in are long gone.

By the time I reshape them to get close to what I wanted I have lots what it did.

I know part of the problem is I don't know how to use it well. What i wanted was it to improve on my hull, not redesign it. And so far I have not been able to do anywhere near that.

[marshmat]

Hi Kudzu,

If you want Godzilla to make tweaks to your initial hull, use hull series 0. This will restrict Godzilla's tweaking to simple scalings of your initial hull in each of the three dimensions.

If you use one of the mathematical hull series, ie. Godzilla optimizing the shape as well as the dimensions, your initial hull serves only as a sort of "dummy" hull to initialize the program, and is thrown out when iterations begin.

[Kudzu]

OK, read that and forgot it, running it now. Powerful program for sure! Just a bit overwhelming to learn.

But hey, last time I couldn't even get it run Godzilla before I gave up!

[Kudzu]

You have been more than helpful and patient with me! I have stopped it running a few times just to see what sort of output I was getting. A couple of times the hull was far from fair. It would be irregular and lumpy looking.

Would I be correct it assuming that is because I did stop it after just a few minutes? That if I had let it run longer it would have found the versions with a straight line to be better and save that instead of the lumpy one?

What would be a good number of versions on average to let it run? I have no problem letting it run for hours if needed. Just wondering at what point was enough.

[Guest625101138]

Firstly you can set a stability constraint (GMT Minimum) if you want it to have a certain stability. Like I said earlier. There is only one optimum (maybe two as Leo points out) and it is unlikely your starter hull will be even close so you should just start with a basic hull form and set the constraints to get the result you want. You are wasting the power of the program if you use it just for scaling. You need to understand what all the constraints mean.

Godzilla always has some lumps and bumps. Some will be based on the number of water lines and stations set - basic resolution. Some may have something to do with wave cancellation but they will not have much impact on the end result. I always fair it out in Delftship before I build the boat. I do a check on drag once I have faired it to make sure it has not changed much. Sometimes I have got slightly lower drag doing this than Godzilla arrived at.

Rick W

[Kudzu]

I am willing to keep trying because I can see what it is capable of. But the fact I can't get a hard chine is limiting. My boats typically have one chine, near flat bottoms.

I just finished up letting it run to maximize an existing design I just about ready to build. By the time I got it changed back to hard chines I had much less stability and slight more resistance. I know it can work, it's just frustrating. I have a design I really like. It falls with in the norms or boats it size and I was hoping that Michlet could help me improve it. And it probably can. So far no luck though. There isn't a lot of room to improve this design and stay within the design goals, but there is room.

This is going to be a traditional boat. Nylon skin over a wood frame. So I can't produce a hull like it is showing.

I am going to keep playing with it. But I need to start this boat soon.

[Guest625101138]

What are your constraints:
Length
Displacement
Stability (GMT 0.3 is tolerable in a canoe 0.43 is very secure)
Single hard chine (or can you get multiple chine)

What power level are you capable of - will set the design speed.

Does it need to turn easy - might force some rocker.

Does it have to be a single hull canoe? Would a sit-on twin outrigger be a better choice?

Rick W

[Kudzu]

Originally Posted by Rick Willoughby

What are your constraints:
Length
Displacement
Stability (GMT 0.3 is tolerable in a canoe 0.43 is very secure)
Single hard chine (or can you get multiple chine)

What power level are you capable of - will set the design speed.

Does it need to turn easy - might force some rocker.

Does it have to be a single hull canoe? Would a sit-on twin outrigger be a better choice?

Rick W

15 foot
Looking for a stable but not extreme.
Single hard chine. (I have played with a multi but that is not our design goal)
Cruise speed is 3.5 mph
Thinking 2" to 2.5" rocker
Single hull

[Guest625101138]

You have not provided displacement - I assumed 100kg. Also 3.5mph is very slow for a 15ft boat.

I did the attached. It will be quite stable- KMT is 0.466. The unfaired version has a drag of 9N at 3.5mph. I have not chexcked this one but it will not be a lot different.

A chicken in a bit of flurry could produce the 15W required to move it at 3.5mph.

Rick W

[Kudzu]

Originally Posted by Rick Willoughby

A chicken in a bit of flurry could produce the 15W required to move it at 3.5mph.

LOL, you obviously don't kayak much do you? Yes you can paddle faster, but most recreational kayakers I have found paddle in around 3.5 to 4 mph. Sure most can paddle faster but not for an hour. I know some younger and stronger ones that probably average 4.5 mph. But the average person that this boat is aimed for doesn't.

I keep coming up with something similar to what you show. I didn't go flat bottomed though so I had some round chines. By the time I would change to hard corners I was back about where I started. No real improvement over my design.

I have a job to get to this morning. I may play a bit more this afternoon.