planing hull

what is the difference between planning hull and displacement hull ?

 

http://www.boatdesign.net/forums/open-discussion/its-planing-people-not-planning-34631.html

 

Not if it's planning to be built.

Then it's my planning hull.

So, to answer the OP: The difference is, one is not yet built and the other is already built.

Easy.

Next question please...

-Tom

 

Abdo, you seem to be looking for an easier method to gather up information the studying your text books. There's no short cut, just years of study. Purchase the appropriate titles on the subjects you have interest/difficulty with and pour over them with your heart and soul. If you can't do this, then your career choices should be questioned.

 

After everyone has a little fun, the first obvious answer to your question is:

Get Dave Gerr's book "The Nature of Boats". This in a primer from which you can learn about the basic differences that make boats do what they do in the conditions they are put into. After that book is read and understood reasonably well, there are many other books that will fill out your knowledge of those parts of the subject you wish to follow up on.

 

oh, and don't forget -semi-planing hull - just to really confuse you.

 

...and hydroplanes, hovercraft, SWATH, foils, submersibles, ground effect plane/boats, etc, etc, etc.

Have fun.

Study hard.

-Tom

 

A displacement hull is a bit like this forum, pretty slow and short on excitement !

 

So Mr "Efficiency" likes fast and exciting

Everything... To broad brush it, planing hull must generate lift to rise over the hump and ride on top of the water at speed. Most are pigs at slow speed cause they're designed to run on top of the water on plane. Displacement boats need to run through water with minimal drag - long and very narrow beam is faster and short and fatter displacement is slow. Look at the hulls at your marina. Curved displacement hulls with transoms contoured to not drag water with them. Sharp v planing hulls that break clean and plane on top of the water. Try and get rides on as many as you can and study them close in and out of the water.

 

It is a rather arbitrary distinction. Planing hulls tend to be of flatter sections and have a wider stern and are designed to run at three or more times hull speed. Displacement hulls are designed to be efficient at hull and below speed and tend to have long curved lines.

 

Shapes, forms and edges have little bearing on the differences between planing and displacement craft. It's much easier to describe these differences in terms of speed. Displacement hull forms travel at 1.5 times the square root of the LWL or less (in most cases), while semi displacement craft travel from 1.5 to 2.5 times the square root of their LWL. Anything above this can be considered in full plane mode, regardless of chines, shapes, B/L ratio, sectional preferences, etc. This is such a basic question, it makes one wonder what Abdo is actually studying. Hull forms and S/L options are some of the very first subjects covered in any course.

 

Right, so, planing hulls require lots of Hp and gobs of fuel while displacement hulls require much less Hp and a fraction of the fuel.

Got it.

-Tom

 

Not necessarily so, it's more a function of power to weight ratio and hull form efficiency. How much HP does it take to get a Laser to plane? About 1 HP in a 10 knot breeze.

 

"Power to weight ratio and hull form efficiency". Those are the keys. Of course that efficiency must be in the form of planing efficiency and not wave making efficiency. That requires a low bottom loading in weight per sq area of hull/water contact surface. Planing boats can make similar miles per gallon but not gallons per mile as displacement boats and they can often do better. Where most planing boats fail is in the weight category.

 

ABDO, let me help you. Go to www.castlemarine.co.uk and download the program PROPCALC. Calculation of a propellor. Keep the same horsepower and play with the various hull shapes. It will give you an idee.
Bert