boats that are designed with car aerodynamic method?

I think that "rigid" is a concept that doesn't exist in reality. Any engineer would probably talk about modulus of elasticity, etc. Not every boat can be designed as an inflatable, even though they are good at surviving hard bumps. Most decks can't be like the trampoline on a HobieCat either. Good design takes into consideration many aspects and requirements. Making an argument for only one of them is either lack of understanding of the design process or facetiousness.

 

Ok --getting out of hand here --its not my thread and Ive said what I want but there isnt one boat out there like this and Im sure im not so ill hinged that I would be the only one. I can feel designers shuffling uncomfortabley in thier seats so therefore I think Ive made my point.

 

What is your point?

 

Have you ever ridden in a boat that twists and flexes ?? its amazing absolutly amazing how much better it is to ride in in rought water and i mean rought water Its what the old vikings had long time ago !!
Its possible to make small runabout boats as soft riders by using the right glass and running it in the right direction in the bottom and the placment and construction of foam glass stringers inside ,
The differance is like a car with low profile tyres and another with more balloon type tyres .Boats that have a element of twist also track well in seas

 

Im just waiting to see how long before one completely looses the plot and completely falls of his chair !! i notice a few have settled down to watch and wait !! the old saying "many a true jest has been spoken in words" !!!

 

nihon dont have a western sense of humour so this could be hard for you to understand !
I notice money is something that worries you ! well sorry to say money does not feature much im my life at all . theres more to living and life than worrying about money !! I had a greedy theiving Japanese wife the used to dream about money all the time and will die with her hand stuck in her purse !!
There are people do things for others and donot exspect any payment at all teaching ,showing and working with young people gives enjoyment and from places i worked i have many people that have become friend with and we keep in regular contact . giving encouragement and know how is helping them and will get better jobs the more knowledgable they become and help there families as well .
Live a simple life and enjoy the time you have ,pass on knowledge to help others .There no good taking all youve learned to the grave !!wont do you any good and keep cool when you find yourself in a hot place !!!

 

Frosty, if you are serious about offering a design assignment for a boat you intend to build, many designers would be glad to talk about it and to discuss the technical aspects of your desires.
I've compared your SOR in this thread with the one in the other you have mentioned. Two completely different boats.
So, two things are necessary in order to start making calculations and preparing a preliminary design for you:
1) a precisely written SOR, or a wish-list, which will alone probably take several iterations before arriving to a well-defined one;
2) a real intent to engage a designer for this job, expressed through a design contract.
Only after you have gone trough this process with a right designer for the job, and got the shape and tech specs of the boat, you (and tunnels) will be entitled to judge designer's work and competence. Whole this discussion would have been much nicer and civilized without continuous spitting on the whole category just because you have met few bad designers through your career.

Now that I think about it, I have seen some real pigs at work out there, glassing the moulds. With terrible results - bubbles, delamination and stuff like that. But does it allow me to conclude that fiberglassers are the ruin of the boatbuilding industry?

 

So, after endless rants and not supplying any answers to simple questions, your justification for....its cheaper, is no longer make it thinner..or makes lots of cups of tea, or tell the mother-in-law, it is now this:

It isn't about how much money I have or whether I worry about it. It is about the client and what s/he wants to pay, i.e. their budget.

I'm sure if you went into a shop and said i'll buy a Ferrari..but hand them just $/€/£ 50, they politely tell you to sling your hook. Wants/desires/needs are generally at variance with ones actual budget.

So....just rants, and hot air. Nothing else. Great Stuff

 

I dunno AH....I can look back to quite a number of our more exotic ship projects over the last 25 years and claim that some were completed without regard for profit. Clearly.

(Maybe "regard" is not quite accurate....)

 

I'm jumping in here against my better judgement because I know you dudes [AdHoc in particular] to be knowledgable. So I just want to make a couple points and get your reaction.

I once calculated a rudder stock spec both ways, aluminum and stainless, and was impressed that the thinner walled stainless actually came out lighter (though very close). Then I did the same for a mast and again found that, in theory, a mast could be made in stainless at about the same weight as and aluminum mast. The problem is that a very thin walled mast is subject to denting an dimpling, and once dented would be subject to buckling at that location.

But there are ways to achieve a stainless steel finish without excessive weight. The DeLorean automobile is a case in point. There are also a lot of effects and finishes that can be achieved by a good faux painter. Since this thread is predicated on comparisons to automobiles I'll note that auto paint jobs improved dramatically in the early-mid 1990s, in quality, in color selection, and in rust inhibition. Also, companies started going to stainless steel exhaust, improving the longevity of exhaust pipes & mufflers dramatically. The difference was particularly dramatic in American cars. My impression is that GM led the way and the others followed in short order. It did a lot to close the gap in public perception about American vs Japanese cars. The change was across the product line, with the high end cars (e.g. Cadillacs) getting some fine metalflake in the paint and an additional clear coat.

Frosty, did you see my link to Fabio Buzzi's Code-X? Once at the opening page you'll see more information and images if you click on the right arrow. What do you think? Is the recent popularity of silver-gray paint jobs in Europe an answer to your criticism of the industry?

 

In fact, rods and other slender objects subject to compression loads are often made with low-strength (and lower-cost) materials when buckling becomes a primary dimensioning criteria.
If you consider Euler's equation for buckling load: http://en.wikipedia.org/wiki/Buckling

You see that the max load is proportional to the quantity (EI) / L^2 ; where E is Young modulus, I is the Area moment of inertia around the neutral axis, L is the length of the rod (or column).

But, since I is proportional to S^2, where S is the cross-sectional area of the rod, you have that the maximum compression load is given by an equation
F = K E (S/L)^2 ; where K is a coefficient.

The equation tells you that if you have a high compression load acting on a rod, you have to increase the cross-sectional area (or wall thickness) in order to avoid buckling. It means that a high-strength material will be wasted for that use, because the main purpose of using high-strength materials is to decrease the wall thickness and hence mass.

If you try to develop the above equations and include the mass of the rod into calcs, you will discover that the choice of materials, for compressed rods, is governed by the ratio density/sq.root(E) (or density^2 / E), which has to be minimized if you want to minimize the weight of the rod.

Now, see this:
Aluminum:
E = 69 GPa ; density = 2800 kg/cu.m ---> density/sq.root(E) = 0.0107
Steel:
E = 200 GPa ; density = 7800 kg/cu.m ---> density/sq.root(E) = 0.0174
so the right choice for that application would be aluminum, not steel.

One curiosity - let's check how a pine wood compares to the above two:
E = 9 GPa ; density = 400 kg/cu.m ---> density/sq.root(E) = 0.0042
- apparently the best, if you want to minimize weight for a given compressive load.
However, the resulting cross-section of a wooden rod would be very big when compared to the above two, due to a very low compressive strength of the wood - around 10 times lower than aluminum. It is not a problem if you have to use it for house pillars or similar, but becomes a source of unwanted aerodynamic drag in case of a sail mast.

Cheers

 

Frosty
the dreamliner is 1000nm short of flying from London to Sydney without ferry tanks
A 747 400 can just do it without passengers and bags
so maybe the industry is not ready for your boat yet??

 

Really good - THANKS! FYI I was looking at hollow tube in all cases on the assumption that section / OD remain same while wall thickness and ID vary. I could see the result I got for the stainless mast violated a rule-of-thumb concerning wall thickness.

 

After reading this page I wonder if Carrol Shelby's AC Cobra design is allready discussed
Aero dynamicly later a fastback was fitted to win Le Mans but by puttin a big blok
into the lightweight sport the chassis gave so much swing it actually improved cornering
Given today's price for such a car I only wish I had a boat like that

 

Oh to have a client lacking such 'regard' as a budget...ain't the military m/c great

Mind you we had one client many years ago...same, wildly extravagant. Only because he also owned the company thugh and 'we' couldn't say no

Not at all. Everyone has an opinion...just that some like to keep it in the hot air mode whilst others, like the excellent reply to your Q from Daiquiri, is supported by factual engineering and is objective, rather than subjective. Never be afraid to ask a Q

If you don't ask the Q, you won't know the A!!