old or new school?

curious;20 years ago most were18-21-24 or32-41 now adays it seems like you can get a boat any size in incramants of inches. I thought the old sizes were proven best through atrition? example24 footers rode good because in most rough weather ,the seas were 24ft apart? the us coast uses 41fter patrol boat ,also im seeing higher sides were as older boats are low to the water with a good portion below the waterline,,,less wind resistance in foul weather so what are the new rules of thumb?

 

There are no rules.

20 years ago or so, before the prevalence of computers, boats were designed in easy multiples of 10 units or 20 units on the waterline--so you had 20' Lwl, 40' Lwl, etc., plus the overhangs. The reason for this was to simplify the calculation of submerged volume using Simpson's Rule, which depends on an even number of station spaces--10, 12, 20, etc.

With the advent of the personal computer and the power of hull design programs, we are not restricted to the requirements of Simpson's Rule, because the computers use a modified form of the Trapezoidal Rule which does not depend on any particular number of stations, nor that they need to be equally spaced. Free of these restrictions, designers have become more free with their handiwork, and design parameters go all over the map.

The idea that a 24' boat rode well in rough weather because the seas were 24' apart is quaint but not true. There is no such correspondence. Seas are random, they vary with the weather and geography.

So, as I said, there are no rules.

Eric

 

thank you Eric,,,yes I understand that seas are different in differant places.so you are saying that todays builders can build the perfect boat for the individual,? still I see designs that are less than good ,but not all that bad.my personal theory is to have a boat that can take a good gale ;because sooner or later your going to get caught in it. thankyou again Eric.

 

No, I am not saying that builders are designing perfect boats, nor are designers designing perfect boats. Some are good, some not so good. There are a couple of elements at work here.

First, of course, is computers that give designers and builders a tremendous amount of computational power and 3-D design capability. One has only to look at the print ads or on the internet, even here on this forum, to see the broad spectrum of design that is around.

Second, there is the talent available--young people raised on computer graphics who have the knowledge to operate these programs, but who do not necessarily have a clue about naval architecture and marine engineering.

Third, there needs to be a directing talent that keeps control over this computational capability to direct the design into safe, workable yachts that perform, speed and stability wise, as they should. Sometimes this third element is there, sometimes not.

Fourth, the owners themselves have the most influence over the yacht design--always have, always will. We design to owners requirements, not to our own requirements. In the superyacht end of things, there are ever more wealthy individuals who can afford large yachts, and who leave the stamp of their personalities on the design. If they are willing to pay for it, they usually get it, and never mind about the safety or operational aspects of the design. That part depends on how much control the designer can exercise over his client to produce a safe and secure boat. Like I said, sometimes it is there, sometimes not.

At the smaller sizes, boats less than 60' (18 meters) say, there are fewer and fewer clients, I think, available. There is not an interested population in the smaller sizes, who are willing and able to pay for custom yacht designs in the smaller sizes. You can get these boats out of a production shop, so the custom side in these sizes, 60' and smaller, is shrinking. It is easier for a designer to design, or a builder to build, a smaller yacht, but the profit margins are less, and the custom market does not seem to be very big, never mind the growth in our population here in the US, and world wide.

I think you are right that sooner or later, some people are "going to get caught in it." Look at the Volvo Round the World Race going on right now and discussed on this forum and on Scuttlebutt.com. There are 7 boats in the fleet, and most of them have major structural problems. This comes, I think, from trying to do too much with the design, simply because we as designers and owners can do it. The Volvo 70s are designed to be best at round the buoys racing, with their canting foils. But the problems has been survivability out in the ocean. What is going on here? Why are the yachts breaking apart? Did the designers and engineers not take into account the loads and engineering properly? Or are they just so far beyond the leading edge that they are in a realm never tried before? It is probably a little of both--somewhere in between. We won't know the answers until a full review can be done of the race, the boats, and the crews.

There will always be people willing to play on the leading edge, and that's fine. But I personally believe that in those efforts, and in every yacht design and build, there needs to be doses of reality and downright good common sense put in the mix so that the boats perform properly and safely.

Eric

 

its a race and records are broken, safety may be second. not that i'm a big fan of these keels but the problems here may strange enough be in the rules that left little room for proper engineering.

back to longliners45 original question i recall reading bout old PT boats beeing resized to better fit seastates or something similar as to what longliner45 was saying. exept for the obvious there are no such rules on boat size at all?

 

OK guys;Im not an engineer .but I was a commercial fisherman ;and then I became a journeyman millwright and journyman machine repairman even I thought the volvo 70s were bad design. .........large weight on an extended keel .dont know about carbonfiber. salt water . long term effects ect,but I understand physics.also exposed rudders ;on this matter if I were building a race boat it would be for this perticular race ,,,,,money invovled ect. but I would plan for long run durabuility,the time down for repairs is costly.Eric and Yipster are right ;the cutting edge is a good tool to explore .also people with some seafaring expieriance need to do the heavier designing for the rest of us. thanks guys

 

I liken

The Volvo 70's ocean race (And Sydney Hobart) as somewhat akin, to racing ferraris down a 4WD only track across the simson desert to Ayers rock...

Foolhardy in the extreme..and plain *******..

Why?

You know - no one ever paid the Aussie taxpayer back - for our navy rescuing that english idiot 'Bullimore' from his keel less dismasted yacht in the antarctic..

I heard on the grape vine - the navy broke the back of the rescue vessel, due to the severity of the sea state and the need to get there fast (vessel operated beyond it's designers stated sea state capability), not to mention the risk to our sailors lives and the actual operating costs of the vessel...

That one rescue could well have cost over $100M Aussie....for ONE wealthy eccentric english idiot who should have been left to feed the penguins! IMHO

Something about our international search & rescue obligations!

If they are wealthy enough to get emselves that far south, in a boat made for river racing - well - i don't see we should be paying their taxi fare home frankly.

To my mind the Volvo 70 Ocean race & Syd / Hobart folks are of the same ilk! (and correspondingly should be treated as such)!

Course... likely not everyone will agree with me!

Cheers!

 

i'm only halfway agreeing, am surprised to hear