flat vs convex surfaces

[redreuben]

Cost.

 

[gonzo]

I don't agree with that. It is too generic. A small boat may have a few sits and a sink. Propulsion can be a small fraction of the cost, of more than 50% in the case of a high speed boat. I have never heard of that rule of thumb. However, rules of thumb only apply to similar systems.

 

[redreuben]

Obviously

 

[BlueBell]

I believe the T-bird is made of flat panels.
Thunderbird 26 - Wikipedia https://en.wikipedia.org/wiki/Thunderbird_26

 

[cavalier mk2]

Yes the Thunderbird is sheet ply with a Star keel. They sail well, often a bit faster than a same size molded glass boat. Is this about developed panels or literally flat no curved shapes?

 

[TANSL]

It is about curved developable panels.

 

[gonzo]

The OP wants to design a boat made of flat panels, not developed.

 

[TANSL]

Are you sure?. Maybe you are right and I am misunderstanding it but, from my humble understanding, with flat panels, you can only build a parallelepiped hull.

 

[DogCavalry]

A tetrahedron boat! All the work, no advantages

 

[DCockey]

The OP in his first post asked about a boat with flat panels similar to the "flat surfaces that make up the airframe of stealth jets". The F-117 is a first generation stealth aircraft with an outer surface of flat panels. It is definately not a parallelpiped.
https://www.nationalmuseum.af.mil/V...lay/Article/198056/lockheed-f-117a-nighthawk/

 

[cavalier mk2]

Geo dome corracles! Set up that beach cabin when you arrive.

 

[Barry]

I realize that your answers will start with "It depends ...". I am only after a sense of proportions.

Given that flat surfaces that make up the airframe of stealth jets cause a loss of aerodynamic efficiency of about 20-30 % within their flight envelope, compared to their more aerodynamic counterparts, is it safe to roughly estimate that a sailboat built from flat surfaces

For clarification, can you explain what you mean by "flat" surfaces. Completely flat over their area like Post 40 or made from flat surfaces which are curved/ developable?

 

[Barry]

STEEL sailboat plans, STEEL sailboat kits, sailboat building, steel boat kits, boat kits https://www.bruceroberts.com/public/HTML/STEEL_SAILBOATS.htm

The above link shows several Bruce Roberts plans. Without in depth inspection, they all appear to be built from developable surfaces. The easiest being 2 bottom plates and then 2 side plates

I have seen a few sailboats that use an additional side plate, or rather narrower side plates so as to more closely replicate a compound curve boat. So three side plated from the keel up each side to the gunwale

 

[TANSL]

The OP in his first post asked about a boat with flat panels similar to the "flat surfaces that make up the airframe of stealth jets". The F-117 is a first generation stealth aircraft with an outer surface of flat panels. It is definately not a parallelpiped.

You're right, I hadn't understood it well. Now that I understand it, it seems absurd to me to think of making a hull like that. It may work in air under certain conditions, but in a fluid the density of water, I don't think so.

 

[Rumars]

So the question is how far can one push the traditional shapes of a 40+ cruising cat to keep manual labor to a minimum. I understand that building the body of a boat is only about half the labor, but still. So, how to compromise while maximizing straight, flat and perpendicular. For example, going for a shunting drua-like design eliminates the need for rocker; the loss of light wind efficiency may be worth a simplistic brick shaped bottom; a plain rectangular wedge for a bow ? etc... This no-curve bias will dictate its own design spiral.

You can push manufacturing very far, the question is how much money do you spend for automation and how are you going to get it back. Some machines like welding robots and automated tape laying you have to buy, so it's only profitable for big series production. On others you can rent time on, for example portal cnc routers, or adaptive molds.
Then there's another tradeoff very few people like to talk about, with automation you trade floor time for office time, and that's something that also works mostly for series production. 3D modeling the entire boat to the last assembly detail so it can be cut by machines and assembled without any hand fitting is very expensive for a one off. The best analogy is building a female mold for fiberglass construction, the money you spend on the tooling is more then you spend on sanding something done on a male mold.

Compromising the shape to the extreme is the wrong way to go, there is no need for it at all. The biggest labor savings are in finishing not in the construction itself, and that's mostly a question of personal esthetics.
Can you live with unpainted aluminium and ugly welds? Do you like carpet glued over sprayfoam or raw fiberglass as an interior finish? How about oiled raw edge plywood furniture? That's where the real savings are in both labor and money.

Some labor saving possibilities depend entirely on the hull material and building choices. To give some examples: for metal there is a difference in welding hours between thin skin with extensive framing and thick skin with minimal framing. The money you save on welding you loose on handling, because thick plate is heavier and you need lifting equipment. The overall labor time between shaped plates and multichine isn't that great, the big difference is in having the expertise to use a powered english wheel. That's one reason plenty of "round bilge" metal boats are actually designed to use plates bent only in one direction, using straight rollers.
Other materials have their own pitfalls. High grade plywood doesn't need fiberglass, just a coat of paint, but today few owners are willing. Both cold molding and strip planking allow full shape freedom and building speed depends entirely on worker skill, good initial design and time vs. money decisions. Fiberglass can be done in a number of ways, all equally "good", because it's all about the SOR not what's "best". A chopper gun layed hull can't compete on strength and weight with one made from prepreg carbon with carefully aligned unis, but the question is do you need the later or is the former sufficient.

The simplest shape for a catamaran hull is the triangle, commonly called a "deep V hull". Rocker is obtained by cutting the keel profile into the plates. All the required bending usually relies on the natural flexibility of the used materials (some designers do prescribe some additional shaping).
The hull form is known, and you can find all the advantages and disadvantages listed and argued about in the literature or in forums.