Are we making any real design improvements??

While I think that this discussion has run aground, or at least gotten becalmed after a brief thunderstorm, I do want to say that I hope my previous comments and crititques were not seen as being out of line here.

From my point of view, I think that the conceptual goal of this discussion is worthwhile. I applaud Wardi for raising the point and putting in his hard work in this exploration. The goal of all of my comments are to try to help provide input that will lead to an intellectually honest discussion of the topic. They were meant to plug loop holes in the process and not to really critisize any one individual personally. I think some of the comments above have been out of line. In these internet discussions, I believe that it is never appropriate to attack an individual, but that an exchange of honest critiques of the ideas being put forth helps us all learn and grow.

Respectfully,
Jeff

 

True, and laudable. I also feel that not enough "feeling" can be expressed on a keyboard, and there is a sense of escalation in some threads. If you say something borderline nasty, even if unintentional, it can be answered with something on the same lines, and pretty soon insults are flying all over the place. Not good - either for the forum or the individuals.
Wardi, let's not kill this one - yet. The original intent was to find out if modern hulls have less resistance than older ones - i.e. have we made any progress in reducing drag for a specific type of hull-form? Let's go back and re-visit that.
Why not start with a development class - non-planing if that's easier. Say 6-metres. Has the modern 6 metre become faster than the old ones? If so, why? If not, why not?
If you can factor out the materials "thang", that would be good - just focus on hullforms.
Steve

 

I agree 100% - let's get this thing up and running again! It's much too interesting to let it die away because of one individual!

Unfortunately, I used some not-so-nice words about the guest in an earlier mail. I hereby excuse, but I was p..... off by his statements. BTW: I've been called a ***** myselft once in another thread. Maybe I am - I don't know...

Best regards,
Søren

 

Heehee... You're not alone, Soren. Some newsgroups seem to feel it's a rite of passage.

Steve

 

Forgot to add - it's WHO calls you a ***** that is important. A man should always be judged by his enemies

Steve

 

It looks like Wardi deleted his response before I got a chance to read it. Its unfortunate because I thought is was an interesting comparison. One was the older style narrow beam, heavy, deriving most of its stability from ballast and I believe this is the kind of hull shape he is trying to defend. The other very light, reletively wide beam and the beam carried very far aft leading to lots of form stability. I see from pieces of his reponse in the next post that he suggests adding 1500 lbs to a Melges. Obviously that would completely defeat the design of the boat and make extreamly slow. My question would be, would removing 1500 lbs from the Etchells make it much faster. Unfortunatly that brings us back to the same problem of floating on the designed waterline but from iudging from the hull shape I don't believe the Etchells would ever be able to plane or surf even if it weighed as little as the Melges.
I hope that wardi will come back and defend his position again. I really think I can convince him I am right, given enough time.

 

I am mentioning the bleeding obvious here: no sailing boat is a hull alone - everything works in synergy together. It would not be hard to draw a set of lines for a minimum resistance hull, it would be long and skinny. That is just hydrodynamics. I think this is what Wardi is getting at; factor in form stability, resistance goes up, but so does speed.

In the old acc yachts you see - despite lots of art, science and technology, very small increases in speed are gained, if you factor out rig, keel and rudder efficiencies.

The canoebodies of these yachts, I would think were very similar; even going way back. When you get differences between yachts of a fraction of a knot, then I think you are right up against the physical limitations to minimizing resitance for a given hull configuration.

If it is a question of overall efficiency, I am sure there are many boats that have brought all the elements together is a beautifull way. Both old and modern. For a conventional yacht of medium displacement - you are close with an old 12 metre design.

I am not sure wheather this is what the issue is here.

 

i think this is not a discussion of heavy boats vs light boats as some of us are implying. I think it was more about how well we design boats for a given load. We all know that light is fast and we dont need to bother talking about that. The question is more about if a boat of similar length rig and mass and everything else were built today, how well would the old vs the new go? In truth there is no absolute data really applicable since the trend toward the lighter boats has begun. That's why the study wardy was doing was important.

 

I totally agree with A-stevo.
The problem of comparing new vs old is that iw we "redraw" an old design and in theory "build" it lighter, it would not, have been drawn the same way as it was originally.
Wardy's comparisions are indeed very interesting, at least as general data to start from, and see if the Taylor resistance really is appliciable, by comparing several boats that we have more data from and try to compare them more closely.

But that is no small task, and neither was Wardis original work a small task or insignificant in any way. But this would perhaps best be worked on at a naval education somewhere as a thesis as this is hard work without any financial benefits in the short term.

This IS very interesting and validating Wardy's ideas or proving with data that his ideas are not quite accurate would be very beneficial for us all.

Unfortunately as a part time student, I don't even have enought time to study, so it's out of the question for me, but I hope that someone, somewhere want's to pick up the torch and run with it.

ErikG

 

I'm probably dis-remembering again , but... I had been assuming that we started talking about whether we were now able to design out resistance from a given hullform. In other words, if you took an old hull, and redrew essentially the same boat, all coefficients the same, same LOA, LWL, beam, BWLm draft, etc, can we now make it faster? i.e. have we developed the ability to draw section shapes that are lower drag than in previous generations.
As dionysis says, if you take advantage of modern materials and hullforms, of course you can maj=ke a faster boat. But can you "cheat" the Taylor series by drawing better sections (that being all that can really be changed) ?

As i say, I may be disremembering the genesis of this discussion.

Steve "or maybe not..."

 

Wow! I was away for a few days and this thread really evolved. I think that after the initial shock and name-calling, there is finally going to be some worthwhile discussion.

Yeah, there probably have been some improvements over the last 30 years. If we believe that then we should be able to list them. We should be able to quote patent numbers and developers' names too. There should be the Smith transom and the Jones bow and the Korean half-something-or-other.

Let me start:
I believe that bow shapes have evolved. But I don't know if the new shapes are just ways to get more waterline length or if they are more efficient?

CBTF is the subject of multiple threads in this forum. I believe that this technology is a bonafide DEVELOPMENT.

Nobody has mentioned hull coatings. Are teflon and poly-urethane paints more efficient than gelcoats?

Do winged keels improve efficiency or are they just trying to get as much mass to the bottom of the boat without increasing draft?

I previously mentioned the "bubbler" technology that has not caught on.

I am intrigued by the airplane float shape of the Parlier catamaran hull. We are waiting to see how it performs (Parlier had to retire from the Transat).

Is there a sailboat equivalency of the stepped hulls of speed boats?

On our cottage lake, there is a Scandinavian-built power boat that has a hull just like a sailboat. But, it has ridges or grooves that run down under the hull at the quarter. This looks like an attempt to provide efficient low speed operation but also to allow quick planing.

That's enough for now. What do the rest of you think?

 

I think we should try to differentiate between pure design developments and engineering developments. (I said "try"!)

The sharper bows are design developments, the CBTF is an engineering development (or at least a combination of design and engineering). The shapes of modern light-weight sailboats are design developments made possible by the use of lighter materials, and that is engineering development.

Best regards,
Søren

 

I agree with Søren. I feel that the specific change from med displ to light weight is an engineering development. The hull design changes that have followed creating light weight planing boats are a design development.

Well I know you did say try!

BTW, Søren, is the CDE 850 in production anywhere? I read about it on your webpage ages ago, but I could never find any pic of completed boats...
I could live with owning a CDE 850 until I've built my own first design

 

I like the direction that this discussion seems to be going. Although the individual improvements are hard to quantify, they are comparatively easy to identify. I think that the change in bow shape is a good example. In the early 1980's I attended a presentation of a paper that looked at the effects of altering bow shapes. In that study, the sections aft of the midship station were kept fixed and only bow sections altered. The general shape of the bow sections were maintained but the waterline was stretched between the typical 'destroyer' bow of the era and essentially a plumb bow.

As Super piper queried, the increased waterline length showed a small reduction in drag in flat water as the boat approached the normative hullspeed allowing a higher ratio of speed to the square root of waterline length. In other words a small increase in overall efficiency. This increase over the expected linear coeficient in the hullspeed formula was attributed to a decrease in bow wave production associated with the finer bow.

The paper looked at other factors as well. As you may remember, light weight boats at the beginning of the 1980's had a tendancy to pound brutally in chop and to be greatly slowed by the impact with each wave. It was this phenomina that gave light boats the reputations for being slow in a chop. In this study one of the dramatic results of lengthing the bow waterline was the reduction in energy required to get through waves and a dramatic reduction in wave induced pitching. In other words this allowed a lighter weight boat to pass through waves more easily, and faster, and with a more comfortable motion that would also produce a reduction in the diturbance of the flow over the sails and underbody foils further adding to performance in waves.

He also noted that with heeling, the elongated bow waterline models tended to have less of a trim change tendancy to go 'bow down' with heeling.

By the late 1980's the early IMS typeform boats had also moved the longitudinal center of buoyancy (LCB) aft in the boat. This did two things, it allowed a further fining of the bow and provided greater buoyancy aft which allows the boat to begin to climb onto its own waves with a reduction in required energy. In other words the hull form had shifted to a semi-planning hullform. It should be noted that without this movement of the LCB aft, the prismatic coeficient would have dropped below an acceptable range in other words to a speed robbing number.

With the more sophisticated modeling permitted by computers careful hull form modeling allowed a minimization of the negatives that previously had been associated with moving the LCB aft.

All of that combined allowed IMS type form hulls to routinely have a hullspeed approaching 1.5 times the Sq.Rt. of the waterline vs the earlier 1.25 and 1.34 coeficients that are routinely quoted.

Lastly I want to touch on the various powerboat derived ideas being floated. Sailboats generally have so little power compared to their weight that the kinds of ideas (step baffles for example) that work well on a power boat, rarely work on sailboats other than very stripped down special purpose performance sailboats.

Respectfully,
Jeff

 

Jeff:

It is your description of the bow modifications and the shift aft of LCB that we needed to hear about. You have successfully listed and quantified these advances.

So, what else?

Is it fair to just discuss hull advances? One of my favourite topics is wing masts and rotating masts. Do less rig drag and less heel also have an impact on hull efficiency?

With regards to transoms, whatever happened to double-enders? Whatever happened to reverse-angle transoms? Are truncated/open transoms more efficient or just in style?