wave anatomy in relation to hull design

[gonzo]

The keel is the horizontal lower part of ther hull. The stem is the vertical part where the sides join. The forefoot is where they join. It can be a sharpe angle or a gentle curve. A curved forefoot digs in less.

[aquafiend65]

Originally Posted by gonzo

The keel is the horizontal lower part of ther hull. The stem is the vertical part where the sides join. The forefoot is where they join. It can be a sharpe angle or a gentle curve. A curved forefoot digs in less.

o.k. i think i understand. but it really just brings me back to my original dilema. only now i can kinda sound like i know what i am talking about, which i don't, when i ask how do i establish the longitudinal keel rocker with the intent of creating the longest water line possible but to keep the forefoot from digging in/plowing and thereby avoiding the broaching as much as possible?

[gonzo]

You need to consider other design parameters too. For example, displacement/length ratio, shape for and aft, center of floatation, buttocks, etc.

[aquafiend65]

Originally Posted by gonzo

You need to consider other design parameters too. For example, displacement/length ratio, shape for and aft, center of floatation, buttocks, etc.

is there a simple/laymans way to figure it all out?

[gonzo]

I think that if you look at designs for similar use and evaluate their performance it will give you a head start.

[aquafiend65]

i am doing that but i am not sure why one type of hull does what it does, or why another rocker does what it does. in other words why does a wide, flat bottom with lots of rocker surf well and narrow, long, round bottom suck in the surf? but the long narrow round bottom is fast in the flats but the surfing hull is a dog in the flats? and how do you look at a bunch of different ideas and try to find a happy medium and say o.k. lets do this rocker and this width and this length for the overall best all around in all conditions boat?

[Thunderhead19]

If you don't mind my two cents worth, I believe you're starting at the wrong point. I find that boats should be designed with a purpose in mind. Initially you would begin with what you're using it for, what your hull length limit is, how much internal space you'll need for your gear and passengers and rough in your requirements for machinery. Then you'll have a decent idea of what your hull's rough perameters are. Be aware that wide flat bottom boats without a keel wander all over the place, especially in the wind, and that long skinny round-bilge boats can suck up a lot of water too. Casting spray away is usually taken care of by the use of some kind of spray strake or chine. Also there are stability considerations to putting rocker in the bottom, racing kayaks have almost circular section hulls, but they're tippy like a log. Even if you have lots of reserve buoyancy, it might still feel tippy.

[aquafiend65]

Originally Posted by Thunderhead19

If you don't mind my two cents worth, I believe you're starting at the wrong point. I find that boats should be designed with a purpose in mind. Initially you would begin with what you're using it for, what your hull length limit is, how much internal space you'll need for your gear and passengers and rough in your requirements for machinery. Then you'll have a decent idea of what your hull's rough perameters are. Be aware that wide flat bottom boats without a keel wander all over the place, especially in the wind, and that long skinny round-bilge boats can suck up a lot of water too. Casting spray away is usually taken care of by the use of some kind of spray strake or chine. Also there are stability considerations to putting rocker in the bottom, racing kayaks have almost circular section hulls, but they're tippy like a log. Even if you have lots of reserve buoyancy, it might still feel tippy.

i totally appreciate your two cents. in a sense the design perameters have been set already. the gunnels need to bo about 17" apart to allow the paddler to lock in at the hips and get the vertical stroke at the side of the boat seat height is already determined as well as gunnel height. we will continue to use six paddlers, one of which is the steersman. the distance between the paddlers is already predetermined which to some degree has established a minimum boat length. etc. etc. it seems to me that really it comes down to tweaking what already exists. i had hoped to come up with some kind of formula or something that says this does that but i am beginning to think everyone just guesses. is this true?

[Thunderhead19]

Actually there are formulae that can give you some fair direction. There are scantling rules ...somewhere...that have been based on experimentation, and there is the full-on engineering approach which can carry you to the most disturbing reaches of fluid physics. Hard core engineering is time consuming and skill intensive, and scantling rules only work for specific ranges of perameters. Educated guessing keeps you from having to use someone elses perameters and saves you the real cost of engineeing the thing. If this is a money making proposition do engineer the boat. You can use the basic formulae from naval architecture texts or you can use massive computing power and the essentials of fluid dynamics and open-channel flow etc...

[icetreader]

Hi,
I just noticed this thread...
You may be interested in looking at this new concept:
http://www.wavewalk.com/SURFING.html
This new (patented) twinhull design offers the following advantages:
1. The ability to lean sideways which improves lateral stability as well as maneuvering capability (you can lean into the turn)
2. The ability to distribute your weight along the boat's longtitudinal axis thus controlling the bow's height as well as its CG's height, to some extent.

Yoav