Draft effect on Resistance

Mr Efficiency · Dec 10, 2015

Looks like philSweet said something that did the trick, I thought jesdreamer was gonna be like a dog with a bone, not let go of it in a hurry !

pietermariof · Oct 1, 2017

Ad Hoc said: ↑

Hmmmm..one last attempt. Futile I know..but what the heck!

So, here i stated:

Do you understand this? From your replies, it appears not.

So very over simplistic basic hydrodynamics for you. All in one simple graph, well two actually.

Here, is the change in resistance with a varying LD ratio.

View attachment 104572

You'll see the more slender the hull the lower the resistance.

And here (graph number two):

View attachment 104571

You can see the effect of beam to draft ratio. The reason why there is a waffer thin mint's difference between them is...yup...the LD ratio.

But then if wish to start deviating away from pure numbers/theory and go into real practical hydrodynamics, then beam is the key to a successful boat, shown here:

View attachment 104573

So as the beam increases the stability of the boat increases. Ego, the more narrow the hull the greater the propensity to capsize. Not good!

If you wish to look into the theory of "something" related to a singular discipline of hydrodynamics, then feel free to read up and the voluminous amount of material. It gets heavy but explains all and it is not a 5min read either.

However, if you wish to delve into practical hull design with the end results a vessel on the water, not on paper alone, it is a holistic approach. Since not one single discipline related to a design is perfect. A successfully designed vessel is greater than the sum of it individual parts. Ergo it is all a compromise - often because each discipline is working at variance with the others. Focus on one issue...and you'll get lost, totally, and not understand comments like those from Leo et al. Take a step back and look at the whole picture....then the light starts to shine through...or should!
Click to expand...

Hello. From what books are those graphs from?

Ad Hoc · Oct 1, 2017

pietermariof said: ↑

Hello. From what books are those graphs from?
Click to expand...

The resistance graphs are from any paper by Professor Molland et al.

The stability graph any naval architecture book will show this. But this particular graph was taken from "Ship Stability for Masters and Mates" by Barrass and Derrett.

pietermariof · Oct 1, 2017

Thank you. Actually I've been struggling to find those L-D resistance graphs.

Ad Hoc · Oct 1, 2017

pietermariof said: ↑

Thank you. Actually I've been struggling to find those L-D resistance graphs.
Click to expand...

All the data is taken from here.

Log in or Sign up

Draft effect on Resistance

Mr Efficiency Senior Member

pietermariof Junior Member

Ad Hoc Naval Architect

pietermariof Junior Member

Ad Hoc Naval Architect

trim, draft calculation for counter ballast calculator

Optimum sail draft for wind speed

shallow draft redesign for older 24 Morgan center console

Craigcat Cat, options for shallowest Draft

Drag for Small Shallow Draft Displacement Boats

Weight effect on trim

How to compare effect of hull form (only) on motion?

The effect of a flat transom.

Gap between luff and mast, effect on efficiency?

Scale Effect at Low Reynolds Numbers