Are we making any real design improvements??

Discussion in 'Sailboats' started by Wardi, May 3, 2004.

  1. SuperPiper
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    SuperPiper Men With Little Boats . .

    Wardi:

    Wow, great presentation!

    Even using "Best Fit" algorithms, some of the lines/curves through the scatter of points are somewhat subjective (?). The one conclusion that is undisputed is the fact that boats are tending to get lighter. And, I would have thought that more of the boat weight may be making its way to the keel bulbs that are getting popular. So, I thought that modern boats must be getting MORE stable. However, you are suggesting the opposite.

    A few thoughts:
    If a skipper was to take his 70s PHRF racer, gut the interior, install a carbon rig and a bulb keel, would he expect a speed increase? Would the 70's hull shape (designed for X knots) still be efficient at the new speed (X+1 knots)? Is it possible that it has taken decades (or centuries) to optimize the wooden/glass boat hull shape but have not yet optimized the new lighter/faster hull shape?

    Wardi, I need to examine and think more about all of your data. Great work!
     
  2. Wardi
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    Wardi Senior Member

    Yes I would agree, and I am quite sure it is possible to much better than with the standard Excel functions. However I have made several other comparisons which all support the basic trends indicated. The basic fact remains though, that the lighter displacement boats, in general are no more efficient than the older designs.

    Actually I originally thought that this was the case also, but can confirm from discussions with some top designers and builders, that only part of the ballast is in the bulb, the rest is in the hull! This is confirmed in the IMS discussion in this forum. Notwithstanding this, some boats do have lots of lead in the bulb and are still not that efficient.

    This is a vexed question. Certainly to lower the C.G. with a bulb keel and carbon mast would make a big improvement, although I am not yet convinced that this hybrid design would necessarily give the best possible end result for efficiency. Certainly in Jeffs judgement based on Speed/Length, it would not go anywhere near the speed of the latest designs, but that is only because they are so much lighter. Personally I think you are correct in saying the that we have "not yet optimized the new lighter/faster hull shape".

    For the designers right now it is really too easy, just go lighter, with more sail and of course it goes faster, not too much genius in that formula for success. It is the materials and construction techniques which are actually giving the speed improvement. When it comes to rating boats, the role of the designer is to beat the rule, not necessarily make a faster boat. It will not be until there is an incentive to have efficient boats that we will see real "design" advances to optimize the performance for light displacement boats.
     
  3. Wardi
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    Wardi Senior Member

    G'day CT249,
    The J35 comes up OK in the comparison for Jeff, but is by no means the most efficient design.

    Yes it would be ideal if you have data available, also on dinghies.
    Perhaps what would help most is to know what basic type of boat each one is, as I am unfamiliar with many US designs. I had in mind to put together a list of the top 10% most efficent designs and categorise them as Pure racing, Racing, Cruising, crew ballasted etc so that we can see which is the best design in each category. This would be most useful, as it does not seem fair to compare stripped out day sailors with cruising boats carrying engines, fuel water etc.

    all the best
     
  4. Jeff H
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    Jeff H Junior Member

    With all due respect, I very strongly disagree with your statement about IMS typeform boats being less stable than earlier typeforms and in particular the implication that you are drawing from this statemement:
    "only part of the ballast is in the bulb, the rest is in the hull! ........ Notwithstanding this, some boats do have lots of lead in the bulb and are still not that efficient."

    I have two main issues with your statement;

    First of all the trend towards inside ballast in IMS style boats is extremely new. I would guess that this has been happening for something like a year now, but not much longer than that. And,

    Second, having sailed a lot on these IMS typeform boats, as well as earlier CCA, RORC, and IOR race boats, these (pre- internal ballast) IMS typeform boats offer an enormous amount of stability in comparison to their drag. The very recent anecdotal change in design approach on IMS typeform boats, should not lead you to believe that the type in general is less stable as these internal ballast boats are still very rare in the IMS fleet.

    Beyond that one of the strengths of the pre-internal ballast IMS typeform boats is their ability to carry the same sail plan through a wider range of windspeeds and to get by, and still remain at speed with a physically smaller sail plan in really high winds and big seas.

    When I have looked at the numbers, the really big advance in these earlier IMS boats, (besides the more efficient hull shapes at least as reported in towing tank and in actual sailing conditions) has been the fact that they generally carry a larger percentage of their weight in ballast than earlier race boats (with the exception of a brief period under CCA when centerboard boats were popular) and carry that ballast much lower in the boat both by carrying deeper drafts and carrying the weight in a bulb. While there may be a new (and deplorable) trend in IMS boats to move weight out of the keel, even as recently a 2 years ago, grand prix level IMS boats were being built with cast iron or composite keel foils so that more weight could be placed in their bulbs. The slighter lighter weight of the typical IMS boat of a couple years ago meant that they had a higher center of buoyancy which when combined with their historically low centers of gravity resulted in amazingly stable boats for their length.

    I still think that there is something really wrong with your data if you think that older IMS type boats are less efficient that previous design periods. It just is not being born out in tank testing or in every day experience. One of the simpliest anecdotal measures of efficiency that I experience with a fair regularity is the amount that these boats will forereach. Older designs would typically forereach something like 2 1/2 times their boat length. When ever I of the adjustments that I need to make is that the newer boats forereach jump back and forth between an older design and newer IMS type boat one more like 4 or more times thier lengths. Until I got used to that I was constantly overshooting. Even boatspeed under power is much greater in these IMS typeforms using the same 3gm30 Yanmars that are all over the fleets, so I really can't see any indication of less efficiency.

    I also want to point out that displacement numbers are very hard to compare as methods of measurement have changed over time. In CCA days boats were measured 'in their normal equipage and state' which meant all sails aboard, all gear aboard, partial or completely full tanks and lockers. Under IOR, boats were measured with a prescribed loading, with 'gear stored in normal position'. That means sails and sailing gear on board, tanks were typically half full, etc. IMS boats are measured dead empty. What that means is that the displacements are much closer together than your numbers would indicate. In the case of my boat, the IMS certificate (and PHRF certificate for that matter) shows a tad over 11,000 pounds displacement. From actual measurement in an IOR measurement state of loading, my boat weighs closer to 14,000 lbs.



    In the end, however you measure it (displacement to speed, or length to speed) the pre-internal ballast IMS typeforms are wildly faster than ealier designs (as shown in their phrf ratings) and get by on physically smaller sail plans. To me that sounds like they are much more efficient so I am unclear how you have set up your model so that it somehow reflects the opposite.

    Respectfully,
    Jeff
     
  5. deseely

    deseely Guest

    Wardi
     
  6. des

    des Guest

    Wardi

    This is some interseting information but I have a few questions. How did something like the J24 do in your comparison? My guess would be that it did fairly well, not because it is particularly efficient but because it has been raced so much that the people sailing them very efficiently. I also question if your measurment of efficiency accurately depicts the diminishing returns of increasing the sail area. Directly relating sail area to speed through the resistance of the hull completely ignores the losses created by the increase in hull drag and loss of sail efficiency due to the increase in heeling forces associated with the increase in sail area. Sorry for the blank post, I seem to hit the wrong key while typing.
     
  7. Wardi
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    Wardi Senior Member

    The J24 along with many pure racing boats such as Soling, Etchells 22, Dragon, 6m etc has done reasonably well. One reason for this is that they do not carry engines, fuel, water, provisions etc. and therefore should perform well. In fact it would be rather useful to categorise the boats as racing, cruising etc but I have no way to do this at present.

    I have included a sample of these boats below. PI is the efficiency measure of actual performance vs speed potential. The higher the %value, the more efficient the design.
    http://boatdesign.net/forums/attachment.php?attachmentid=1389&stc=1
    It is interesting that the J24 does not perform as well as some of the others. This is confirmed by my own observations that a Dragon will easily beat a J24 upwind in a breeze. The Hobie 25 goes well because of the trapeze, not necessarily because of other design improvements.

    While I would agree that some data may be considered potentially innacurate because they are "one off" designs etc, I would think that the PHRF rating for the other comparable classes, ie: Etchells, Dragons, IOD etc would also have been determined based on competitive fleets also. Therefore this comparison should be valid.

    With regard to the efficiency calculation, the driving force from the sail is taken to be directly proportional to the sail area. Based on this force, I simply read off Taylors test data to see what speed the boat should have. There are in fact no "theoretical" calculations involved at all!

    As I see it, it is completely up to the designer to balance the tradeoffs of sail area vs heeled resistance, efficiency losses etc in order to come up with the best possible design for those proportions of D,L & SA. The efficiency measure simply represents the outcome of this ie: is it an efficent design or not.
     

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  8. Wardi
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    Wardi Senior Member

    Hello Jeff,
    I agree with what you say about displacement measurement. That is why I have used all data from one source, ie: PHRF and assume that the displacement information is equally determined for each boat to overcome this potential error.

    I have spoken to boat builders, who as long as 15 years ago were marvelling at the concept of using titanium fittings inside the boat at the base of the mast to take rig loads, with pigs of lead strapped down next to them!. It seems that internal ballast for correction to get boats to float on their lines has been used for many years.

    With respect, I am not trying to pull the wool over your eyes or use special tricks with my analysis. I do not even use any theoretical calculations of hull resistance to determine speed. I am simply referring to well established practical test results of Taylor.

    I suspect that much of your evidence of increased "Speed" for newer boats is actually based on the speed/length of the boat and does not take into account the effects of displacement or sail area. As I have said before, speed/length has definitely increased, supporting your anecdotal observations, it is just a matter of "at what price"!

    One of the reasons it is difficult to accept these results may be that such a simple and basic comparison does not seem to have been done before!
     
  9. redcoopers
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    redcoopers Member

    Wardi,

    I'm curious about Taylor's data. The systematic Taylor series which I know of is for ships, not yachts. Furthermore, isn't this data apropriate for only upright resistance - not heeled?

    Also, how do you estimate Cp, LCB, and LCF? I know that Taylor used Cp as an parameter, but I was under the impression that his family of hull forms did not vary by LCB or LCF. The Delft testing has shown that wave-making resistance can change significantly by differences in LCF and LCF.

    Just curious about your velocity prediction,
    Jon
     
  10. Jeff H
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    Jeff H Junior Member

    Briefly,

    "I agree with what you say about displacement measurement. That is why I have used all data from one source, ie: PHRF and assume that the displacement information is equally determined for each boat to overcome this potential error."
    The displacements used in PHRF are provided by the owners. There is no measurement involved. The displacements numbers generally reflect the period in which the boat was constructed and the method of calculating displacement that was in vogue at the time that the boat was designed. So earlier boats would show higher displacements that reflect a displacement that includes 'their normal equipage and state', vs newer boats which are measured and advertised stripped of everything. In other words the actual displacements of older designs are much closer to those of newer designs than their PHRF slips would suggest.

    "I have spoken to boat builders, who as long as 15 years ago were marvelling at the concept of using titanium fittings inside the boat at the base of the mast to take rig loads, with pigs of lead strapped down next to them!. It seems that internal ballast for correction to get boats to float on their lines has been used for many years."

    I don't know what boat builders you have been talking to but trim ballast hasn't been used in production performance sailboats since the IOR era, at least not here in the States. While all kinds of stunts were pulled in the bad old day of the IOR, better computer modeling and quality control has pretty much eliminated it in newer boats (with the exception perhaps of the lastest European aberation of the IMS)


    "I suspect that much of your evidence of increased "Speed" for newer boats is actually based on the speed/length of the boat and does not take into account the effects of displacement or sail area. As I have said before, speed/length has definitely increased, supporting your anecdotal observations, it is just a matter of "at what price"!

    Again if you compare the performance of pre-internal ballast IMS type forms to earlier type forms on a speed to displacement basis, the IMS type forms do extremely well as they have a very high stability to displacment, and a very low wetted surface and residual drag. This becomes especially true when you compare these boats using their actual sailing displacements.

    Using Taylor in this manner is a misapplication that creates a circular logic that cannot be reconciled with real life behaivor. You are correcting out of the equation the factors that lead to better performance such as higher stability and more efficient hull forms, weight distribution, foils, and rigs, then of course more efficient vessels will look slower, but when you actually get out on the water your results bare no resemblence to reality.

    Respectfully,
    Jeff
    Respectfully,
    Jeff
     
  11. Wardi
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    Wardi Senior Member

    Jon,
    Yes, you are quite correct, Taylors work is based on ships models, not yachts and it is upright data. This in fact makes it a very good basis as a reference, because it is not biased to one type of yacht hullform.

    I think I need to make it quite clear that I am not actually trying to predict the speed of any individual boat.

    I am leaving it entirely up to the designer to find the best possible solution for distibution of displacement, LCB, LCF etc. Also to find the best possible balance of sail area to stability, surface area, lowest heeled resistance etc to come up with the most efficient overall design.
     
  12. Wardi
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    Wardi Senior Member


    Jeff, You may well be right about comparisons with various versions of IMS and IOR. I do not have any way currently to split the data on this basis, but woul dbe happy to do so. Perhaps I caould ask for your assistance with some of specific designs. I will compile a list.

    On the basic method I have employed....., with respect, I think you have the wrong end of the stick entirely!! I am not trying to predict the speed of any individual boat. I am actually leaving it entirely up to the designer to find the best possible solution for those factors that lead to better performance such as higher stability and more efficient hull forms, weight distribution, foils, and rigs etc, in order to come up with the most efficient overall design.

    I do not take any of these things into account at all and I do not calculate anything related to these items. So I do not understand how I can be mysteriously discounting their effects. The only thing being discounted is length, weight and sail area, so that boats are compared on a fair and equal basis.

    In practice it is the rating rules such as IMS and PHRF which do actively discount these improvements in the interests of fairness between racing crews and this is the reason I began this study in the firstplace!!
     
  13. CHRIS 249

    CHRIS 249 Guest

    Wardie;

    Do you want to post the list of designs so some us can have a shot at classifying them? We should also work out a similar classification system – something like

    Full keel cruiser.

    Fin keel cruiser.

    CCA/RORC long keel type.

    Late CCA fin and skeg boats and similar (these late ‘60s/early ‘70s US boats had much bigger rigs than the IOR types IIRC).

    ’68-’74 IOR/RORC/CCA boats (Swan 38, Ranger 37, East Coast 31, Scampi 30, Contessa 32).

    ’75-’80 IOR racers. (Farr 1104, Petersons, etc)
    ’75-’80 IOR cruiser-racers. (Farr Dickerson 37,

    IOR racers post ‘80.
    IOR cruiser-racers post ’80.

    MORC/JOG Aust. Racers (J/24, Capri 25, S2 7.9, Capo 30)

    Early IMS cruiser-racers; J/35, Lightwave 395, J/44, IMX 38,

    “Club cruiser-racers” ie non IOR cruiser-racers from the very late ‘70s but mainly ‘80s on – Farr 11.6, Northshore 38, Farr 1020, J/36. It’s a murky line between this bunch and the early IMS boats. Also some that should be here are quicker – Young 88s and 11s etc.

    Early ULDBs – a varied bunch, everything from Dash 34s, Ross 780s, Express 27s, Olson 40s, “Ragtime”, SC 70s and other maxi sleds

    Old IMS Racers (ie Mumm 36, High 5 type Farr 40, maybe ILC boats - I think some called these “Phase III IMS” boats although the ILC boats are too new for this label really.)

    Current IMS racers

    Modern sportsboats/One Designs/PHRF racers/IRM boats/IRC lightweight racers – Mumm 30, ID 35, Farr 40 OD, Kerr 11.6, Thompsons.

    Metre boat (square metre, Universal rule or International Rule would have to go together I assume).

    Inshore racer (lightweight fin and skeg) – Soling, Etchells, Flying 15, Tempest.

    It's all pretty rubbery.....some boats are easy but many around the esdges are hard.

    I suppose one thing which could be interesting is to locate a couple of very popular boats with firmly-tested ratings from each category and see how they relate.

    One thing about boats now being “inefficient”. Efficiency for racing isn’t a straight line, is it? I mean, it’s an S curve of input (whether dollars, sailing ability or sail area) versus performance, and therefore the last little “X” % is going to take more of everything. That doesn’t mean it’s not vital or significant that the improvement is made.

    I mean, my old Effineffable scow cost about $25. It would go around the course at (judging from yardsticks etc) 90%+ of the speed of Thorpie, at about 2% of the cost. Does that mean it’s more efficient?

    If I cut a Moth sail down to 50% of the area, I'd always finish last, but maybe by 25% on time. Does that mean it's more or less efficient?

    If you have to hang on an extra 10% of rag, but it means you go .00025% faster and win instead of losing, is that less efficient? OK, it may cost yoou $100k more, but if you win a worlds with a $2.1 mill campaign is that more or less efficient than finishing 2nd out of 100 boats with a $1.5mill campaign? It is definitely not, to some. Sail area etc is similar, isn't it?

    All activities hit the law of diminishing returns, do they not?? Particular those with a speed limit like displacement sailing. So a straight-line meaasurement may not be right.

    Finally, your measurements use LWL which is a bit unfair since it’s easy to get a big boat with a short LWL. Because old boats were designed to have a short measured waterline for rating purposes (end girths) which are no longer counted, that biases the system. Boats now have a longer LWL compared to older boats, even when nothing else changes, ‘cause no rule rates LWL any more and no-one uses end girths so there’s no incentive to shorten waterline artificially. I think the Dragon was a 20 sq m skerry cruiser and that rule used girths so it’s got a short WL on a long hull. The J/24 was a MORC boat and they used something like the average of 60%WL and 40% LOA to assess rated length. The rule didn’t put such a limit on LWL, it did limit LOA (unlike the skeerry cruiser rule IIRC) so the J/24 has a longer waterline despite being a shorter boat.

    Finally, that old dinghy One of a Kind rule-

    Rating = L + 1.3 Sail Area
    2

    Where L = LOA + .7 LWL
    2

    Measured WL was obtained with fully-rigged boat carrying 168 lb for each crew, at normal C of G.

    This was based on an old North American yacht racing union rule as modified for Aussie winds. One thing I’ve noticed is that it seems to give slower boats a really tough time. I’ve heard of Int 14s and Tasars winning major races, most seemed to go to 505s, FDs etc, and I don’t think ANY boat under 13’ ever did well in results I’ve seen.

    It’s a great project, I hope this is constructive input.
     
  14. Wardi
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    Wardi Senior Member

    Hello Chris,
    Many issues covered here!
    Most outside the scope of my efforts i'm afraid... but at the end of the day its about enjoyment, not money...and I do not think there is an efficiency measure for that!! :)

    I will put together that spreadsheet and let you guys classify the boats. I suspect that may make it much clearer, as it may distinguish designs of different eras and perhaps point to what general changes in efficiency have taken place.
     

  15. Chris 249

    Chris 249 Guest

     
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