Are we making any real design improvements??

[Wardi]

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[Wardi]

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[astevo]

wardy.
i think much of this discussion is steming from people not understanding the purpose of you analysis. As you explained to me, the taylor data sets up a reference for an arbitary hull shape. At low froude numbers he measures test and calculated for all sorts of disp/length, and power/length ratios. this can be used as a reference point for all boats because of the general nature of this data.

I think that all of the points criticising this analysis are largley irrelevent when refer to you data or taylors data. What we have seen in this data is that increases in efficiency do not stem from the things people have been sugesting. An increase in performance due to lighter weight may not correspond to an increase in efficiency in terms of taylors data.
Such absolute performance increases are not really considered prior to this simply becuse we are in the habit of analysing performance on the basis of length alone. The bloke in the marina wants a faster 30 footer than the other bloke and he dosent are if it is lighter, heavier or shaped like a giant boot.


the point im tryng to make is that this sort of thing does not try to predict how fast a boat goes or how a boat should be designed. it is simply a reference point which can be used for all boats independent of their length or weight or what ever else you might like to measure. this was somethig that took your explanations whilst looking at the taylors data in order to fully understand.

I think that clearing this point up will help the discussion to move forward into where the real arguements will begin. that being why we see some of these trends.

and if you still dissagree on the validity of the series just have a look at the results wardy has already shown. Aside from the anecdotal evidence which we critics (myself included) claim makes the results invalid we have seen no good theories as to why the analysis is invalid. things like planing or not and lead here or there just dont matter at all in the analysis. we have to distinguish the difference b/w the analysis and the results. if we can agree on the validity of the method we can then go on to discuss the results.

so maybee we should just use the results and go from there. because with the line of logic in the last couple of pages we are going nowhere.

lets get on with the interesting stuff.
andrew stevenson

[Wardi]

Andrew,
I should like to say that your response is extremely well put and goes right to the essence of my proposal and analysis so far, I agree entirely!.

[Jeff H]

I would have to agree with you that we do not seem to be getting anywhere in this discussion but at some level I disagree with your conclusions for a number of reasons that various people have articulated which critisize the data in as follows:

-The Taylor regressions are based on PHRF ratings. For any given boat the PHRF rating is a single number that is based on its percieved performance at a single windspeed. In most U.S. regions the wind speed used is a comparatively moderate wind speed (8 to 10 knots) while really big differences in speed in newer designs occurs at the higher and lower wind speed range. (Boats like the Melges 24 really accell in very light air and in high winds where their ability to plane really comes into play.)

-Weights, waterline lengths, and sail area are being taken from the PHRF or IMS certificates and so do not reflect the actual weight, waterline length, and sail areas in sailing condition.

-That in any kind of objective measure that I can think of (speed per pound of real displacement, just plain drag, or drag to stability, drag to drive, stability to sail area, speed to length, whatever) these pre- internal ballast IMS type form boats greatly out perform older designs to a large degree.

It is on those criteria that the results come into question.
Jeff

Wardi

Again I want to make clear that I'm not criticizing the way you are comparing boat, I am just looking at the way you are comparing them and pointing out a few things that I notice. As you have said, your comparison is very much like a ratings rule. As I pointed out in my previous post we can design a boat to look very good by your measurment just as designers have designed boats around other rating rules. What is interesting is to look at a two boats that are both designed for the same purpose, lets say racing. One that would rate very poorly under your system and one that would rate very well. I mentioned the Melges 24 in my previous post because I knew it would rate very poorly. The Melges is at the very far end of the sail area/displacement spectrum and as I pointed out in my previous post, a very efficient design under your ratings would be at the other end of the sail area to displacement spectrum. Unfortunatly there isn't many very heavy under canvased racing boats since these are counter productive to speed. One racing boat that rates very well under your system that already exists is the Etchells 22 and I have sailed on one of these so I know a little bit about them. I don't have the specs in front of me but the two boats are very different. If the crew on both boats were not allowed to use crew weight to decrease heel, the differences in efficiency would be even larger. Sitting on the windward rail of the etchells had no noticable effect. The narrow beam and the heavy keel made crew weight on the rail ineffective. Its just the opposite on the Melges. Sitting on the rail makes a huge difference. The Etchells seems to go about the same speed up wind as down wind. The Melges is much faster down wind.
Obviously the Melges is a much faster boat around the course but it may not be as fast on all points of sail. Now lets look at making the Melges more efficient by your measurement system. The first thing we could do is reduce the sail area. This would make the boat slower but would it make is so much slower that the efficiency doesn't change? From looking at your date you can see a few examples of the same boat with different sail area and how it effects the PHRF and efficiency, it would make the boat slower but it would also make it more efficient. So making the Melges more efficient by your system would also make it slower which brings me back to an observation that I made in a previous post. If sail area is treated in a linear fashion as you have, adding sail area will make it faster but less efficient by your measurement. There is diminishing returns with anything that makes the boat faster. If that were not true, I could hang 2000sq feet of sail area on my 22 foot S2 and compete with the open 60's.

[Wardi]

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Originally Posted by Wardi

No this is not at all what I have found!. Certainly the very lightest displacement boats do not seem perform so well, but so too, very heavy boats and also underpowered boats do not perform well either. In fact there seems to be an optimum, sail area, not related so much to displacement, but much more closely aligned to stability. So it is definitely not true that if you keep decreasing sail area the boat would appear more efficient. There is in fact an optimum sail area to stability ratio...as might be logically expected since there is no point having extra sail area if you cannot extract the power from it. This observations is in fact one of the very useful outcomes of this study!.


...or conversely the Melges is much slower upwind....which is just the point. I think you are viewing the results with a bias towards speed/length and top downwind speed, not speed around the course!

The Etchell vs Melges is a rather good example. It would seem that the basic difference is that the Melges is around half the dsiplacement of an Etchell and they have very similar length and sail area. Obviously the Melges should be much faster. According to PHRF the difference is only 0.3 kts in 12 kts of wind, in spite of the Melges being half the weight, using moveable ballast with crew sitting on the gunwhale and planing downwind!.

Since these boats actually have very similar Length and Sail Area, perhaps we should look at this another way. Why not make a real life comparison. Simply double the weight of the Melges so that both boats then have the same D, L and SA. Race the two boats and see which is faster, you will then have a proper comparison of which is the more efficient design. An easy way to do this is put an extra 5 people or water ballast weighing 1500lbs on the centreline of a Melges and then race an Etchell.

In real terms the Etchells is not the same length as the Melges. The Melges is a 24 footer while the Etchells is a 30 footer. The 22 referred to in Etchells is the static waterline length. The Etchells sailing length is much more than a Melges.

Etchells also use live ballast very effectively, hence the class rule for max crew weight. Prior to this rule the crew weights for competitive crews were getting out of hand.

Your idea to double the weight of the Melges is rather silly. No boat is going to sail anywhere near the designed lines if the weight is doubled. Your race would be meaningless.

Fact is you seem to have constructed a meaningless case study based on linear measurements that manipulates the data to prove your point of view. You are welcome to it. In spite of your opinion keelers of similar length and displacement continue to go better than their predecessors on all points of sail.

Boats are still bound by physical restraints like wave trains and that may be what's got up your nose. You'll have to take that one up with whatever god you worship, certainly not with the naval architects.

[ErikG]

I do have to agree with our anonymous guest, but I try not to sound like an ass about it!

Doubling the weight makes it a totally meaningless comparision.
It was not designed to be that heavy and would therefore have ahorrible wet surface!
That is why the differences between design paticulars have to be compared on boats that are not as far apart as the meslges and the etchells.
If we compare the melges to a Thompsson 770. The Thompson is one foot longer and 250 kg heavier and they dont look very similar, but comparing these two boats ae more interesting, and also trying to figure out why the differences are what they are.

It IS interesting to try to figure out a general effectiveness between designs, bu personall I doubt that the basic measurments are enough...

[SailDesign]

I do have to agree with our anonymous guest, but I try not to sound like an ass about it!

Put me on the list, too. Wardi, I think you are trying to do something interesting here, but may have developed a little tunnel vision.

Steve

[Wardi]

Gentlemen, and others....
It is clear that there is nothing further to be gained in this discussion with those currently actively participating.

I therefore conclude this discussion, especially in light of recent, completely unwarranted scathing comments by those who write anonymously and offer nothing more than anecdotal commentary.

To those of you who have offered your own thoughts, positive contributions and constructive criticism, I should like to thank you for your input and wish you well in your endeavours to design better boats.

[sorenfdk]

To the anonymous guest: Of course you have a right to your own opinion, but if that is the way you prefer to share it with others, then please go somewhere else. That is no way to treat someone, who like Wardi has put a lot of work into something that should be of interest to us all! I'll try to be polite, so I won't use words like idiot, jerk or *****!

To Wardi: Please come back! I'm not sure whether you'll succeed in your endeavours (I'm not even sure that what you're trying to do is possible at all!), but as long as we all learn a little bit, then it's worth every effort.

Best regards,
Søren

[redcoopers]

Seriously,

This is just a boat design forum... Myself, I may be skeptical of some calculations, but I am still very interested in the results. There shouldn't be the opportunity to belittle someone's hard work here.

There's no reason to have an attitude on this web page (remember guest, we only use this forum for recreation, not to gain political influence). Does anyone know if we can have a moderator cut out abusive posts when they appear?

-Jon

[ErikG]

redcoopers wrote:

Does anyone know if we can have a moderator cut out abusive posts when they appear?

Sure Jeff can do anything :-)

Stuff like this makes me think that forcing posters to register is a good thing.
It's not as cool being an ass if people can find you...

[SailDesign]

It's not as cool being an ass if people can find you...

It's not cool being an ass at all, whether you are "you" or a guest.

That being said - Wardi, please don't take my post as a personal slight. I think you are trying to do something useful, but I'm not sure if it can be done at all. How do you differentiate between advances in hull design (the original point of all this, IIRC) with advances in rigs/materials/techniques? Well, I can't answer that question, but if it can be answered, this is the place and these are the people to help you figure it out.
Steve "not in the diplomatic service for a reason )