Advanced learning material on hull shape design?

[Dolfiman]

1. Hull shape optimization for reduced resistance in displacement mode;
For a sailboat, the main issue is the heeled hull drag versus the righting moment it provides : here the hull shape is of first importance, all other parameters being equal. And there is less published information on this issue, it lacks a compilation of the cumulative tests data and best advices on this. For example like the one of Jacques Fauroux, I quote : »When the boat heels, the centers of the area sections must form a spine that does not invert."

For a sailing dinghy, the main issue is different : it is to deal with both the displacement and the planing modes, because the wind force and/or the wind angle and/or the weight and the hiking posture of the crew. Here again, the hull shape is of first importance. The main guideline in my opinion is : the more the planing mode is developing, the less the curvature (in the longitudinal view) of the hull shape remaining in contact with the water.

2. Application of the fluid compression and particle deflection theory for hull design.
CFD simulations are great, top naval architects use them but I think more to confirm and fine tune their design options than to discover new ones

3. CAD techniques for creating parametric hull designs and linking them with CFD simulations.
Parametric approach for hull designs, when it is discoupling of the geometrical input data and the adimensional parameters typical of a hull shape, can be powerful to go fast and safe in a new project.

 

[starcmr]

Hi laukejas,

Hmmm…I think you have fallen into the trap that most armatures do. Assuming there is some magic or black art related to hull design and aspects related to it, because it feels so far away from what you know, or have seen.

Sorry to burst your bubble, but there is no real magic to it.

One can break id down to simple length-displacement ratio (LD). This is the mass/weight of the boat as a ratio over its waterline length. It is a non-dimensional value that is:
L/(displacement)^1/3

L in m, displacement in tonne

If you have a ratio that is low, i.e. around 4-5, as can been seen in the graph below, the drag, and hence resistance is high. Whereas if the LD ratio is high, the resistance/drag is less.
View attachment 201684

There is a plethora of data out there all stating the same…it is not rocket science…just data.
And the same whether a mono or a catamaran as also noted here:
View attachment 201685

And when you investigate hulls of the same LD ratio, and alter the basic parameters, such as Beam to Draft ratios (B/T)….the change in resistance is also minimal - just very minor 'sweet spots'. In other words, hull shape plays a very minor role, compared to the LD ratio.
View attachment 201686 View attachment 201687

So, it really depends upon whether you think there is some magical black art that awaits and is explained by the use or enhanced by computers, and waste hours/days chasing that rainbow….or just want the basic facts and accept there is nothing magical, except the simple fact that the more weight there is for a fixed length, the greater the drag.

Does this mean changes to hull shape etc do not have an influence, no, but the effect is less and less to being almost non-existent when you have a high LD ratio notes ai, but has ‘some’ influence when you have a low LD ratio.

As for CFD...unless the CFD is validated against known data and the hull you are analysing is also within the narrow range of the validation, the output of the CFD is highly questionable at best.
Pretty looking colours though!

thank you so much for your suggestion

 

[CarlosK2]

1. Hull shape optimization for reduced resistance in displacement mode

---

Residual resistance in Displacement mode (Fn < 0.40) is a corner of a small corner.

In this case, Total Drag (A16) is 845 Newtons

Residual resistance (A23) is 81 Newtons ca. 10% Total Drag

By completely destroying the design, we could perhaps, with a lot of luck, reduce it 10%, which would be 1% of the total. A narrow, dead-end street. And the Drive force (A15) would fall

 

[CarlosK2]

Certainly to illustrate this i have chosen an exaggerated case: Upwind against 30 knots (at 10 meters high, TWS_10)

 

[CarlosK2]

Ratios determine speed

Downwind

square meters of sail hoisted / Displacement

Upwind

square meters of sail hoisted / wetted area

and

Sailing carrying power: GZ / h

h: vertical distance between the lateral force of the wind and the lateral force of the water

 

[CarlosK2]

(Frank Bethwaite, High Performance Sailing)

Back to the Question

In Displacement Mode, the variable that can be adjusted is the bow angle.

 

[CarlosK2]

...

Racing dinghies, Motorboats, Royal Navy destroyers from the late 19th and early 20th centuries, the bikini and summer holidays in the Mediterranean ...

are the cosmic forces that have destroyed the design of offshore sailing boats.

 

[CarlosK2]

Back to the Question, 2

Half of Frank Bethwaite's book is dedicated to the Wind

Reading the Wind is The fundamental skill in a regatta/racing

 

[CarlosK2]

The order of priorities

1) Being able to read and understand the wind, a difficult skill that is key to racing

2) A rig that produces force lower, at lower high (C1 and C2)

3) A rig that can adapt and adjust/trim better to wind variations

4) Reducing (A24) drag induced by the centerboard and rudder

These are the four main topics

 

[CarlosK2]

A extreme case of the big, very big Power and Versatility of a low "h"

---

It seems absurd to make a sailboat from the hull of a rowboat ...

and yet the combination of low wetted surface area and ability to lower "h" is a powerful and versatile combination

 

[BoothBoatworks]

2. Application of the fluid compression and particle deflection theory for hull design.
CFD simulations are great, top naval architects use them but I think more to confirm and fine tune their design options than to discover new ones

This is spot on. We only use CFD when we are confident in fairness and shape of the hull form we are designing.
CFD can be useful for analyzing appendages, steps, chines, etc. but it's only as good as the info you put into it and it definitely comes with a high computative cost.

 

[tdem]

I'm no expert but I find the most insight comes from what designers write about their own designs. I think books, articles and interviews by and with people that have produced great designs are super valuable. The Bethwaite books are a good example, Bolger and the Atkins have great writing as well.

 

[tdem]

If you want to take some "professional" courses navalapp looks very promising. https://navalapp.com/ . You can sign up for just the courses that interest you, but the modelling is focussed on Rhino (which is very popular for boat design). But it's not parametric software like SW. I don't think any software is going to answer the questions you have though.

 

[Doug Halsey]

The main subjects I'm interested are:

1. Hull shape optimization for reduced resistance in displacement mode;
2. Application of the fluid compression and particle deflection theory for hull design;
3. CAD techniques for creating parametric hull designs and linking them with CFD simulations.

What's the meaning of subject #2?

If you mean CFD calculations, both fluid compression and particle deflections are irrelevant.

 

[CarlosK2]

Windex (1964-)

https://windexdevelopment.com/product-category/products/

The best invention since cold beer

Zig - Zag Upwind

We know there are three Upwinds: 25°, 30°, and 35° AWA

A Windex vane and a magnetic compass to see if the wind is blowing us outward make a great team

- ready to tack
- tack (!)