Hypothetical beam vs draft question

Purely hypothetical and out of curiosity, the class 40 has a max beam of 4.5 metres and a max draft of 3 metres. What if you removed any beam or draft restrictions and allowed designers to build the fastest boat possible within class 40 rules, minus beam or draft?

Would a boat with a 2 metre beam and 6 metre draft be faster, or a boat with a 6 metre beam and 2 metre draft? (Both are completely off the cuff measurements, again, hypothetical). What would the sweet spot be?

I've always wondered as I've heard some people argue narrow is faster while others have said wide is faster.

 

Welcome to the Forum Curiousa.

All else being equal, the boat with a 2 metre beam and 6 metre draft would be like the Victorian plank on edge yachts - she might be faster upwind in rough conditions, as she would probably slice through the waves that would stop the beamy boat.
Whereas the beamy boat would just run away from her as soon as the sheets are eased, and they bear off on to a reach.

 

Without changing the hull length and displacement...I think the boats would get both wider and deeper...if sail area is allowed to change. Without changing sail area or displacement I doubt that the general max beam and draft will change much...there is no real need to.

Personally I don't think you are asking the question you seem to want to be asking. I think you need to change your focus to the canoe hull dimensions....i.e. the part that is actually in the water, not the box dimensions.

While Hugo Boss is a IMOCA 60, the sailing hull shape is what you need to consider...

 

Thanks for the interesting replies, I must be oversimplifying it but I thought it would basically boil down to stability, weight, wetted surface area and sail area? Surely you would get more stability per unit of wetted surface area from a deep keel than a wide hull, and probably lower weight, which would make for a more efficient hull with less drag and weight while carrying the same amount of sail. Again, probably completely wrong and would love to be taught otherwise.

 

Rather than take up a lot of bandwidth and time explaining all the terms and concepts, I would advise you to get a copy of Aero-Hydrodynamics of Sailing by Czeslaw A. Marchaj and read it (it is a very approachable book). Then if you have questions come back and I'm sure the forum would be happy to answer them. Because the answer is always..."it depends..."

From the wikipedia page (after Merchaj)... Forces on sails - Wikipedia https://en.wikipedia.org/wiki/Forces_on_sails

 

"Surely you would get more stability per unit of wetted surface area from a deep keel than a wide hull"

Yes, but this is true Upwind

The sailboats are determined by (A) the course of the race and by (B) the rules - limitations.

It is a matrix of 3 columns (Upwind, Reaching, Downwind) and a handful of rows, at least four or five: F3, F4, F5-6-7, F-8.

 

SailBoat Velocity depends on

(1) Length at Flotation, Water Line (LWL)

(2) Sail hoisted / Wetted surface

(3) Displacement x (GZ / h)

h: vertical high: Wind Force - Wáter Lateral Force

(4) parasitic Drag / Drag

(5) Sail Hoisted / Displacement

Upwind, low Wind: 1 + 2
Upwind, high Wind: 1 + 3 + 4
Downwind: 1 + 5

 

The design of a sailboat depends on three Fundamental issues to begin with:

(1) The intended sailing: for example a sailboat to sail in summer (Upwind) from the South to the North of this coast would be different from a sailboat to sail this coast Downwind, and a third sailboat would be one that wanted to go up and down.

(2) The second question is the Matrix and what is the first box we choose: what is the privileged box, what is the bias of the design or where is our main obsession or what part is non-negotiable

(3) the third issue is the rules and limits we set for ourselves or the ones we accept.

And of course

(4) if it is a sailboat for High competition and we are going to sacrifice everything to Speed or not.

 

For example

This is my bias, the order of my preferences and which box has priority over the next one:

 

Box N 2

This autumn a Portuguese navy ship rescued and evacuated by helicopter a Polish sailor injured ... injured for not Stopping

It would have been much better to take the rudder blade out of the water like Robert Manry and anchor in the Sea:

 

(Transcuadra, Bepox 990, Alex Ozon)

It is true that Beam has been greatly exaggerated and that it is worth reconsidering Wet Surface: Alex's victory with a Bepox 990 is a good example.

 

I think the most reasonable limitation (besides Length) is "Beam / Hull Depth =< 2"

This simple rule would have limited many excesses leaving freedom of choice.