Are we making any real design improvements??

Hello Jeff & Superpiper,
Firstly I agree with Jeff about the benefits of tactical advantage, and that certainly is an issue when one boat has a small advantage over another.

What I am referring to here is not anything to do with VPP. As I see it, VPP is a tool which may assist to refine a design. What I am creating is a simple basic reference point of how fast a boat of that size should be able to go and then compare with how it actually goes. This reference point has nothing to do with the individual attributes of the shape of the boat. It should be up to the designer to come up with the best shape possible.

Yes, I intend to make what I have found available for your scrutiny and would really appreciate your feedback. It should be nicely summarised within a couple of days.

 

Looking into the numbers, we see the Beneteau has a little more waterline, a little more keel depth, and about 2000lbs (11%) less displacement. Interestingly, the weight is mostly from the ballast keel. The rigs are also very different. The Beneteau has a much shorter J and longer boom than the Tartan. I can't really speak about the underbody and ballast, but certainly the Tartan rig was designed to suit the rating rules of the times. If the Beneteau is faster because it was designed to a better rule, or to no rule at all, does the difference count as "real design improvements", or just rule improvements. I'm not quite sure the boats are equivalent in carrying capacity or blue water capacity, but that is out of my sphere anyway.

There has been a lot of progress in keel shapes, and in rig development.

Another comment: the observed speed difference will be different on various points of sail. The "4 miles behind after 40 miles" is a reasonable interpretation of the difference in rating. However, boats (except the very light ones) tend to sail at closer to the same speed off the wind, with speed differences exaggerated upwind. Reaching along on a cruise, they might arrive nearly together, while on a upwind day, the Tartan might be more than the 4 miles behind.

 

Hello Jeff,
I have data on all except the Farr 36. I will make some comparisons shortly based on this data and my analysis.

I have found that even the Farr 40 ODR is rated at "9", so I doubt the "0" figure for the Farr 36, could you please check this one and reconfirm if it is correct. If you also have Disp, Length, Sail Area, draft and beam and age for the Farr 36 I could include it in my comparison.

One thing I note is that you are generally comparing performances based on Length alone. Surely displacement and sail area also affect performance. This is what I have taken into account...more to follow.

kind regards, Ian

 

A couple quick replies because I need to get out of here to cruising, but to answer the replies,

SeaDrive: I purposely chose the Tartan 41 because it really was one of the first of the IOR I boats and as such was not terribly optimized to beat a rule. In its day, these were considered outrageously fast boats so much so that when I was racing on one in the mid-1970's the conversation on board was about how none of us could imagine that boats could get any faster than that generation of boats. I think that you are mistaken about the fact that the big gains are up and down wind. I think that the big gains are on all points of sail and infact the Beneteau 40.7's real gains are when reaching lighter winds or in moderate to higher winds. Argueably there is a narrow wind range somewhere around 10 knots where the 40.7's advantage would be smaller than its rating, but as the wind falls or drops the 40.7 really would leg out.

Using my boat, a Farr 11.6 (because I know it quiet well) which is somewhat antiquated compared to the 40.7 but a 9 year newer design than the Tartan 41 and which also has the same waterline length. Reaching in winds over 15 knots it is unsual to sustain speeds near and sometimes over 9 knots. The highest speed that we saw in the Tartan 41 (surfing in very steep 7 to 8 foot waves in high winds) was just below 9 knots.

Wardi: 0 is the correct rating for the Farr 36. This is a none rule derived 36 foot one design that was designed in 2002. They are faster on a boat for boat basis than the Farr 40 which has adequate accomodations to qualify for an IMS certificate. I chose the Farr 36 and J-35 because both represented the best thinking of their times ignoring all of the rules of their eras.

Jeff

 

just saw on tv an old planked ventilating flat bottomed surfing vikingship race against a modern mono hull that -only barely- won.
dont hate me for interfering and mentioning it ;-)

 

OK, sound like the Farr 36 is pretty qick for its length. Are these the correct details of displacement, sail area etc for me to include in my study?

Dimensions
LOA 11.00m 36.1 ft
LWL 10.00m 32.8 ft
Beam 3.582m 11.72 ft
Draft - keel down 2.6m 8.5 ft
Draft - Keel up 1.83m 6.0 ft (in water)
Displacement 3,059 kg 6,744 lbs (empty)
Ballast 1,396 kg 3,078 lbs
Fin 105 kg 230 lbs
Bulb 1,300 kg 2,866 lbs
RMC 106 kg/m 764 lbs/ft
LPS 137°
Stability Index 130°

Rig Dimensions
IM 14.26m 46.78 ft
J 4.02m 13.19 ft
P 15.22m 49.93 ft
E 5.68m 18.64 ft
ISP 16.71m 54.82 ft
TPS 6.42m 21.06 ft
Mast Height WL 17.9 m 58.73 ft
Mainsail Area 56.2 sq m 604.85 sq ft
Jib Area 32.9 sq m 354 sq ft
Spinnaker Area 163.9 sq m 1,763.7 sq ft

 

Observations

Observations

1) The following observations are based on PHRF data for some 3600 boats.
Age data exists for 1000 of these boats, designed over the past 80 years.

a) Speed based on Speed/Length ratio has been steadily increasing over the years.
http://boatdesign.net/forums/attachment.php?attachmentid=1374&stc=1

b) This has primarily resulted from boats getting lighter for their length.
http://boatdesign.net/forums/attachment.php?attachmentid=1375&stc=1

c) As boats get lighter, they can go even faster for their length. The fastest boat will generally be the longest with lowest displacement for its length.
http://boatdesign.net/forums/attachment.php?attachmentid=1376&stc=1



Links:

Speed Potential
http://boatdesign.net/forums/showpost.php?p=22338&postcount=68

Performance Improvement
http://boatdesign.net/forums/showpost.php?p=22338&postcount=69

 

Speed Potential

Speed Potential
The proposed "Speed Potential" is a measure of efficiency, calculated on the following basis:

The force produced by the sail area is balanced by the resistance of the hull. For a given sail area we can calculate the force and hence resistance of the hull. With reference to Taylors data we can find the potential speed of a boat based on its D/L ratio.

In order to make this calculation easy, I developed a formula using basic curve fitting techniques to match Taylors original data. This formula is used in a simple spreadsheet from which the analysis in this study was conducted.

The calculated "Speed Potential" has proven quite reliable in predicting potential performance and in fact reflects quite closely the IMS rating speeds for all D/L ratios. Here is a comparison for the entire Sydney Hobart race fleet. The error bars represent +/- 2% of the value. This is used to confirm the validity of this tool as a standard basis for performance comparison.

http://boatdesign.net/forums/attachment.php?attachmentid=1377&stc=1

Links
Observations
http://boatdesign.net/forums/showpost.php?p=22338&postcount=67

Performance Improvement
http://boatdesign.net/forums/showpost.php?p=22338&postcount=69

 

Performance Improvement

Performance Improvement

The Performance Improvement is the % difference between how fast a boat should be able to go based on its displacement, length and sail area and how fast it actually goes, in this case determined from PHRF base rating. This can be taken as an indicator of the efficiency of the design. Those boats which exceed their Speed Potential by the biggest margin may be considered the most efficient.

a) The best performers do not necessarily have the lowest D/L ratio
http://boatdesign.net/forums/attachment.php?attachmentid=1378&stc=1

Despite this, the D/L ratio has been reducing over the years.
http://boatdesign.net/forums/attachment.php?attachmentid=1375&stc=1

b) In general the Performance of boats increased until about 30 years ago and since then there has been a small decline in efficiency. The efficiency of the best performers has not improved significantly during the years.
http://boatdesign.net/forums/attachment.php?attachmentid=1379&stc=1

Your thoughts and comments appreciated!


Links
Observations
http://boatdesign.net/forums/showpost.php?p=22338&postcount=67

Speed Potential
http://boatdesign.net/forums/showpost.php?p=22338&postcount=68

 

Jeff,
I have analysed the efficiency of each design you have mentioned, based on the displacement, length and sail area. here is a short summary of the results:
http://boatdesign.net/forums/attachment.php?attachmentid=1382&stc=1

I would appreciate if you could confirm the parameters I have used are correct. From this evaluation it would appear that the J35 is the most efficent design and surprisingly the Farr 36, which is obviously fastest for its length by a long way, is in fact the least efficient.!

There are several basic reasons for this, but it would appear the Farr 36 has insufficient stability to match its sail area and therefore does not sail as fast as it should.

The Farr 36 is around 30% of the weight of the Ericson 41, with around 230 square feet extra sail area, so it is an entirely different configuration and you should expect it to go very much faster!.

 

Hi Wardi

Hi Wardi.

Interesting stuff here. I’m familiar with the general description (approx age etc) of many of the US PHRF fleet, d’yawanna drop them to me and I’ll see if I can sort any missing details out for you?

Secondly, when (a long while ago) I went over to your place and we discussed dinghy design (for my rather large project I’m still working on) you were wondering whether anyone had a similar efficiency measurement for dinghies. I found two; one that US Yachting mag used for their one of a kinds, and a modified version of same used in Victoria. Shall I drag one out for you?

Thirdly, I don’t know that the Farr 36 is (according to gossip) actually sailing to that rating, but the Thompson 35 (which is actually 37) is sailing to something similar if you have those dimensions.

I can see if I can dig out the numbers for John Spencer’s 1960s lightweights (28’, 33’, 40’ and 73’ boats with half an eye on the rule, 35’, 45’ and 62’ go-fast boats), which could form an interesting addition to the plot. You’ll find a well-uprated Van De Stadt Black Soo in the San Francisco PHRF listings which will also give you an illustration of old ULDB speeds – she’s called “Starbuck”. Other Black Soos (in Victoria and observed performance in NSW) would be about 180 PHRF.

Finally, it’s interesting that the J/35 comes up so well. I spoke to the designer about the boat a few years back. It’s definitely the J/36 modified (as Jeff mentioned, g’day Jeff) with less interior, a bit off the stern, and a masthead rig. I can’t recall whether the foils were changed. Rod Johnstone said the main problems with the 36 were the cost and (to a lesser extent) weight of the interior and the fact that they couldn’t get a light enough fractional spar in those day. He says it would be a lovely boat with a modern carbon spar.

I just found in interesting, as it underlined (once again) how technology and social factors impact on “efficiency”.

Something that’s interesting about “progress”. It’s often said that classes that don’t progress die – yet the oldest International dinghy class of all, the 1912 International 12 (a little cat-rigged clinker lugsail yacht tender) is still bloody popular in Italy and doing OK in Holland and Japan. The class association for the 1935 O-Jolle, built for the 1936 Olympics and similar to an older heavier Finn, claim more active boats than the Finn, Moth, Canoe, all of the singlehanded skiffs put together – and like the International 12, the new boat market is healthy.

Hey, while talking boats – do you have any info (out of interest) to confirm the almost simultaneous dual creation of wide alloy Moth wings from Chris Edward (former UK, now BYRA) in 1971, and a kiwi whose name escapes me but who turned up for the ’70(?) worlds in Black Rock? Chris doesn’t recall the Kiwi wings and I don’t think many northern guys did that regatta, so it seems that both arrived at the same area by independent routes – not for the first time (flares and 18’ skiff wings were also appearing independently).

By the way, having raced some of the great boats of the ‘60s (the 12 metre Weatherly, the 38’ Sunstone which has taken her class in Fastnets 4 times (in the ‘80s and ‘90s) and been top of the year 4 times in the UK (under IOR, IMS and IRC) AND won her class in the Hobart – I can only say that there has been huge advances and I can’t see how boats are now going slower – or is it just slower for their ratios and dimensions? Do your measurements allow for the fact that boats built recently normally have 105% overlap instead of 150% genoas that were almost universal in earlier times? The J/105 data provides a clue to the importance of overlaps, the genoa boats are much faster IIRC. Finally, moderate-speed boats like J/105s are slower (but easier and more fun0 with assys.

PPS d'want me to try to find my IRC/Portsmouth/IMS/NZ PHRf conversion ratios?

 

g’day Mates,

Wardi, I want to commend you on your analysis. As I read it everything made sense until I came to your final conclusions that older boats were somehow faster. I did not want to respond until I had a chance to think about what you have written and I think that your conclusions may result from the way you set up the study.

More to the point, I think that CT249 touched on some very good points that explain your study's seemingly contrary to real life conclusion. As suggested in CT's post, it is somewhat difficult to really compare older and newer boats on a D/L basis or SA/D basis. To beat the earlier rules, older boats were often designed to have a very short static waterline that increased pretty dramatically as the boat heeled. While that does not result in the speed of a boat that has a static water equal to the rule beater's heeled waterline, it would skew the numbers a little if speed is compared to the a D/L using the static waterline length of the rule beater.

Similarly, your SA/D probably uses the total SA that is typical based on 100% fore triangle area. Again the trend has been towards smaller overlaps on jibs. 170-180% genoas were quite common in the 1960's and were needed for light air performance. Modern boats often eschew the use of larger overlapping genoas getting by on 105-110% jibs, a wonderfully rig proportion when combined with a bendy fractional rig, but also one that looks huge if the comparison between an older boat's and a newer boat's SA/D uses the 100% foretriangle. If instead the comparason used the actual sail area upon which the PHRF rating is based, then I think your conclusions would fall in line with actual experience.

Respectfully,
Jeff

 

Hello Jeff,
Yes I understand the apparent confusing conclusion.

It is not saying that older boats are faster...for their length. In fact quite the opposite, as the newer boats are definitely faster for their length, but only because that are very much lighter....as would be expected.

What it is saying, is that the newer boats are not performing significantly better for their overall proportions, ie: Displacement, Length and Sail area than the old boats, ie they are not any more efficient.

One might wonder how this could be, but it seems related to the fact that the newer boats have relatively less stability and more sail area, and so they are not getting the best out of the boat. The reason for this may become apparent when reading the IMS thread which seems to confirm exactly this trend!

I am using PHRF base data including sail area data for all boats.

 

I think you are in danger of circular reasoning. If boats are faster because they are lighter, perhaps the design improvment is that we know how to build a lighter boat. As I remember, when Lapworth drew the 'light displacement" Cal 40, etc. it was an open question whether a lighter boat could be competitive.

About a half-lifetime ago, there was an article in Yachting by Pierre de Saix about tanktesting a model of Americal. He drew the conclusion that with almost a century of additional experience, it would be hard to draw a hull if America's D/L ratio that had less resistance.

 

I am not quite sure about the circular reasoning..., but you are absolutely correct that we can now build lighter boats and therefore make them faster for their length.

But we have known all along that this would be the case. This is simply a change in configuration of the boat. Equally we could simply increase the sail area or length and make it go faster also!.

What the results are telling us, is that for the decrease in weight, the boats should in fact be going a lot faster than they actually do. ie: They should be more efficient than they are!.

This may in fact yet prove to be correct, however with modern materials you might expect that that he could achieve greater stability and go even faster for the same D/L ratio.