S&S Swan Figures of Merit
I am interested to learn about the Sparkman and Stephens design philosophy that played out in the late 70s and 80s as it was applied to the Nautor Swans. Also (and more specifically), how my model 431 fits in this background.

This site offers lots of quantitative information about the various models. Using the data from here and from other sites on the web, I have summarized the basic Figures of Merit for the S&S Swans (see attached table). I have included the number built (NBuilt) just for interest.

I will take this information, calculate some basic performance and stability metrics and then perform some multivariate analyses which show how the various models compare to each other. It should be enlightening and I hope spark some lively debate here. I ask first that the group give some feedback about the initial Figures of Merit table. Please check your model. Have I summarized the information correctly?

Getting the original information correct is important. I seek your assistance.

Thank you,

Kendall

I am interested to learn about the Sparkman and Stephens design philosophy that played out in the late 70s and 80s as it was applied to the Nautor Swans. Also (and more specifically), how my model 431 fits in this background. This site offers lots of quantitative information about the various models. Using the data from here and from other sites on the web, I have summarized the basic Figures of Merit for the S&S Swans (see attached table). I have included the number built (NBuilt) just for interest. I will take this information, calculate some basic performance and stability metrics and then perform some multivariate analyses which show how the various models compare to each other. It should be enlightening and I hope spark some lively debate here. I ask first that the group give some feedback about the initial Figures of Merit table. Please check your model. Have I summarized the information correctly? Getting the original information correct is important. I seek your assistance. Thank you, Kendall

Hello Kendall,

Answering your inquiry, I would say that the data for the 47 is correct. Perhaps you want to include the data for the 47 centerboard version. Furthermore, it would be nice to have the figures in both feet and inches but also in metric. Please find hereunder the details for the Swan 47.

LOA 14.47 m (47.80') - LWL 11.05 m (36.24') - Beam 4.19 m (13.76') - Draft 2.40 m (7.8') - Displacement 14700 kg (32400 lbs) - Ballast 7000 kg ( 15500 lbs) - I 18.90 m (62.0') - J 6.04 m (19.8') - P 16.98 m (55.7') - E 4.88 m (16.0') - Fore triangle 57.0 m2 (613.8 sq.ft) - Mainsail 41.4 m2 (445.6 sq.ft) - 150% genoa 85.5 m2 (920.7 sq.ft) - Spinnaker 205 m2 (2210 sq.ft) - Mast top above water I + 1.45 m (4.8') - Antifouled area ( is this the same as wet area?) 47 m2 (59´06 sq.ft)

Center board version: Displacement 15500 kg (341000 lbs) - Ballast 7800 kg (17200 lbs) - Draft 1.8/2.9 m ( 5.9'/9.5') -

I am looking forward to your factor analysis. A well done such an analysis can be a very powerful comparative tool.

Cheers

Philippe (47/050 Farouche)

Dear Kendall,

As far as I know, Swan 38's were built using three different sizes of rig. I think the most common is the standard tall rig. At least one (Infant, hull n: 014) was equipped with the special standard tall rig.

Special standard tall rig
I  16,335 m / 53,59 ft
J  4,815 m / 15,80 ft
P  14,560 m / 47,77 ft
E  3,900 m / 12,80 ft

Standard tall rig
I  15,54 m / 51,0 ft
J  4,82 m / 15,8 ft
P  13,79 m / 45,25 ft
E  3,81 m / 12,5 ft

Standard rig
I  14,78 m / 48,50 ft
J  4,82 m / 15,81 ft
P  13,03 m / 42,75 ft
E  3,66 m / 12,00 ft

Looking forward to your results!

Jyrki

Thank you for your feedback Philippe and Jyrki.

I have included your inputs into the Figure of Merits table (attached). As I understand them, the summary metric equations for stability and performance that I have learned about may not be sufficiently complex to capture the essence to the centerboard details. But there is no reason we cannot try anyhow.

I will work to provide you some of the detail of the performance and stability metrics that I know (which may be derived using the information from the Figure of Merit table) soon.

Thank you again,

Kendall

Kendall,
regarding the 411, please notice that the draft and ballast were increased after hull #0019: 7.5" 9700 lb originally, and 8.0" 10800 lb later.
If you do not want to make two different computations, you may use the last figures. Most 411´s (except mine, I think...) were modified.
All other figures regarding the 411 are the same appearing in this site and, as far as I know, are the right ones.

Daniel, 411/004

Daniel - it will be interesting to me to see the effect of the 411 changes you mentioned. So, I added another line in the table for the draft modified 411 model. Please help me out though, was this done without changing the total displacement?

Thank you and Happy New Year!

Kendall

I have run across the following seven metrics that can be calculated from the parameters in the Figure of Merit (FoM) table we have put together so far. I have loosely grouped them into Performance and Stability categories. Stability is really a bit complicated I gather and deriving something meaningful might require more variables than we have in the FoM tables. It seems that Beam at waterline would be helpful but I think it might take hull drawings to accurately get this information for each boat.

I will forward the associated equations for these next but for now their details can be found at http://www.tedbrewer.com/yachtdesign.html or http://www.johnsboatstuff.com/Articles/estimati.htm.

Do you have other suggestions along these lines?



Performance Metrics

SPEED/LENGTH RATIO
DISPLACEMENT/LENGTH RATIO
SAIL AREA/DISPLACEMENT RATIO
COMFORT RATIO
LENGTH TO BEAM RATIO


Stability Metrics

BALLAST RATIO
CAPSIZE SCREENING FORMULA

Kendall

Suggest you add Sail Area/Wetted Area ratio, and a stability criterion, for example the Dellenbaugh Angle. For this you need righting moment information from rating certificates (available from US Sailing). In case you do not have such information I can dig it out.

Other numbers which may be of interest are weight per immersion and moment to change trim

It should be noted in connection with these calculations that waterline length, displacement, wetted area, and stability are not exactly the same for individual boats of the same model, if possible use average numbers.

Kind regards

Lars

The 41 also had different sized masts (a "short" and "tall" rig).  I think the draft also may have changed a little along the way.

Lars and CBinRI,

Thank you for your suggestions. I again went through the technical data listed on our site here and found several other models with short and tall configurations (see table below).

CB - Can you offer specifics on the draft change for the different configurations of the 41?

Lars has suggested also adding some other metrics. Some of them require additional variables than we presently have in the Figure of Merit table. I am working with him offline to see if the additional variables can be obtained.

I now realize it will be difficult to include the ketch versions in our analysis here. This effort should be thought of as a research of the various sloops during the S&S Swan era.

This is progressing nicely. I appreciate everyone's thoughts.

Kendall



Metrics tentatively planned for the analysis.

Performance Metrics

SPEED/LENGTH RATIO
DISPLACEMENT/LENGTH RATIO
SAIL AREA/DISPLACEMENT RATIO
SAIL AREA/WETTED AREA RATIO
COMFORT RATIO
LENGTH TO BEAM RATIO


Stability Metrics

BALLAST RATIO
CAPSIZE SCREENING FORMULA
DELLENBAUGH ANGLE
WEIGHT TO IMMERSION
MOMENT TO CHANGE TRIM

Hello Kendall,

I am looking forward to the progress and results of your efforts. I think that your project is brilliant.

Thanks a lot

Cheers

Philippe (47/50 Farouche)

Philippe,

Thank you for your kind comment, but as you know, its much about in the interpretation, with the multivariate techniques. That is why I thought this path might be interesting. Quite advantageously, we have the full membership to help with the interpretation.

As often, the task is in collecting the pertinent, meaningful data set to analyze. And to be sure, I am not close to being an expert on these yacht design metrics. It is vital for others to chime in.

The artisan spirit in me says this approach is folly, to order/organize our beautiful boats.. they are all close to perfect as we already know. The analytical spirit in me says, try it. The analysis might reveal a process the designers went through that only they know about. This process is in the soul of our boats. We have a right to search for it.

Anyway, I appreciate the input of everyone.

Regards,

Kendall

For reasons of merging some new parameters from available IMS certificates (which use metric measurements), Lars has suggested we carry along both Imperial and metric Figure of Merit tables. The first version of the new tables are below.

Lars also informed me about the difference between AntiFouled Area and Wetted Area. We need Wetted Area for calculating some of the metrics. They will need to be developed also.

Thank you Lars.

Kendall

Reformatted for easier reading. Sorry for wasting some space.

As I noticed few inconsistencies in the figures regarding the 411, I checked the original water lines drawing and found the true numbers. I extracted the enclosed legend given in imperial units.
Kendall please amend the numbers starting from the true ones given in imperial units and fractions. Regarding the keel modification it appears as a new handwritten value beside the draft (from 6´-6" to 6´-10").
The ballast weight is written in another place (also extracted and enclosed) but, unfortunately, it is hard to be read; the new value appears to be 11,300lb. As far as I remember the ballast change was plus 350kg equivalent to about 770lb; in this case the original ballast should be 10,530lb but the pre-modification number appears more like a 10,200.
Whoever is able to solve the puzzle, is welcome.
I will contact Matteo for possible corrections of the data regarding the 411 in this site.
Regards
Daniel, 411/004.

Daniele

You make a very important observation in this connection, the numbers on the lines drawings are not the same as the numbers presented on this website. The difference is that the lines drawings show the design office numbers, and the website the actual as built numbers verified by the builder, or more precisely an average for several yachts, as extracted from rating certificates or weighing.

It is common that the design and as built numbers differ, and a decision should be made at this stage regarding which alternative to use for the calculations.

Best regards

Lars

For reasons of merging some new parameters from available IMS certificates (which use metric measurements), Lars has suggested we carry along both Imperial and metric Figure of Merit tables. The first version of the new tables are below.

Lars also informed me about the difference between AntiFouled Area and Wetted Area. We need Wetted Area for calculating some of the metrics. They will need to be developed also.

Thank you Lars.

Kendall

Kendal, thanks for your work on this table which is very interesting. I am always a bit suspicious about designer's displacement numbers. When I bought Black Tie my Swan 47 CB I had her IRC weighed on a single point crane with an RORC load cell and measurer. Almost everything had to be off the boat and the tanks emptied and the IRC number recorded was 17,770kg which is considerably more than the design numbers. I am not sure how this would apply to the other boats in the Swan range. I would be interested in the professor's perspective on this as I suspect that Nautor tended to overbuild their boats.

Regards, Gavin

Dear Gavin

All,

I have worked to include all the various model versions (yawl, ketch, centerboards, different displacements) into the Figures of Merit tables (Imperial and Metric, see attached).

The numbers included in these tables are little more than a reformatting of the information found under the "Swans by S&S" tab of our website. This reformatting makes calculations of performance and stability metrics very convenient. I have made some initial calculations and they are under review before I post them. I have also included the S&S design numbers to offer us an understanding of chronology from S&S's perspective.

Recent discussions here suggest that the numbers in the tables on the site (which I have reformatted and attached) represent S&S design details for the various models and not what are measured for certification. Several members have demonstrated that here are appreciable differences between what they observe during the IMS certification process (or other) and the details found in the tables.

I have the suspicion that Nautor builds boats as they have been specified by the designers up until the point that the new owner asks for this or that to be added or taken away. This adding or taking away continues for the full life of the boats. This process theoretically effects the total displacement, performance and stability of the boat (no matter how carefully the loading changes are spatially distributed).

It would be good to understand this variability but it can only be done by members supplying the data from their boats as they are (or recently were). If you have recent IMS certificates please consider sending them to Lars or myself so that we can summarize them statistically (and get the resulting summary descriptive statistics (sample size, mean , standard deviation, min, max) on the website). Only the summary statistics will be distributed on the website or anywhere else.

In the mean time, I am proceeding with the multivariate analysis of some performance and stability metrics derived from the attached tables. We can determine if those results are meaningful together.

I look forward to it,

Thank you,

Kendall

I expect that the study proposed by Kendall may become quite interesting but, following his initial invitation, I have a comment.

In comparing objects like boats which differ in shape and size it is of paramount importance to use non-dimensional indicators. This means, in particular, that they will be independent of the system of measurement and unaffected by whatever scaling. Just to mention a well known example: something like the Reynolds number or any of the many non-dimensional fluid dynamics indicators.
Some of the ratioes cited in the web sites of John Holtrop and Ted Brewer are non-dimensional but some are not or are made non-dimensional in an odd way.
There are infinite ways af combining physical quantities in a non-dimensional expression, only one the simplest, but for example, whichever power of length will never be able to non-dimensionalize a mass.
Whenever a mass and a length enter an expression, a meaningful density constant should also appear (maybe the water density). Same for time: if it appears in an expression together with a length, it should be accompanied by another meaningful physical constant that contains time (acceleration of gravity, for example). Sometimes water viscosity [mass/(length*time)] may be proper too.
This method has other side advantages, namely to get rid of hardly justified ad-hoc numbers appearing in many "empirical" formulas.

Daniel, 411/004

Daniel,

I understand and agree with your last comments on the desirability of using non-dimensional summary metrics. This more physics based approach would be optimal. The thing is, for the vast majority of the models, we presently only have access to the data in the Figure of Merit tables. These data include only the most basic hull dimensions, total displacement, ballast portion of total displacement, and sail dimensions.

What I propose for now is to use the data we have.. and calculate any and all performance and stability metrics we wish to derive from this basic data. If you have some metric you would like included, please send them via the forum. To be clear, I find the available set of parameters to be quite limiting.

We will try also to normalize results prior to using them in any analysis by subtracting the group mean and dividing by the variance. This technique allows disparate measures equal scale influence. It sounds harsh but it works.

Its often good to stop and think about the goal of the analysis we propose here. I suggest if we calculate the same design criteria S&S used when they evolved the Swans on their design tables, we will be able "to learn about the Sparkman and Stephens design philosophy that played out in the late 70s and 80s as it was applied to the Nautor Swans".

That is my first goal here..

But we may want to go further.. and to do so, we will need more Swan model dimension details. No one believes that the basic Figure of Merit data for each Swan model can capture the essence and character that make the models unique. But Lars suggests that the data measured, derived and included on the IMS certificates will get us a lot closer to capturing those essences. As many of you are familiar with, the IMS measurements are fed into detailed physics based computer models to determine the performance and stability responses of the boat.

This is why we have asked those interested in this process to provide a recent IMS certificate if they have one available. If data for all Swan models can be obtained, the multivariate analysis can be repeated and a new level of understanding may be revealed.

I have in mind including histograms for each performance / stability metric we derive. Parallel plots to demonstrate the full complexity (including chronological nature) of the data. Cluster analysis to give a global perspective of how the full set of Swan models partitions itself into subgroups. Finally principal component analysis to attempt to capture and understand the essence of the total data set by significantly reducing its dimensionality.

Thank you Daniel,

Kendall