Dinghy Design: Open 60 influence?

Discussion in 'Sailboats' started by Doug Lord, Jan 22, 2011.

  1. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Congratulations are in order for Mapfre-second place in the Barcelona World racing and also using lifting foils but a less refined version of straight board angled opposite to the "traditional" way Open 60 boards were angled. These boards are angled 9 degrees top outboard and allow a small amount of vertical lift to be generated.
    Because of the fixed angle ,for a given angle of heel, the straight boards don't have the adjustability of the curved foils where just a small retraction can change the lift profile of the board-allowing more or less vertical lift for virtually the same amount of lateral resistance.
    I think curved lifting foils-probably asymmetric- will be the dominant type of lifting foil used on monohulls for "foil assist" from dinghies on up as time goes by.


    Pix-Rough sketch illustrating straight angled board with a curved lifting foil:
    (click on image)
     

    Attached Files:

  2. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Dinghy Design: Open 60 influence?-SUMMARY

    Prior to post 66 the discussion mainly centered on reverse curved foils-a concept probably without merit but how I reached that conclusion is a learning experience worth a read.
    This is a summary of the most important posts from the time I first conceived of the twin curved lifting foil dinghy, the T2, thru to the first mention of using a single curved lifting foil on a dinghy:
    1- Post 66-original Tantra and Tantra II with twin curved lifting foils,
    2- Post 93- comparison to Nacra F20 foil curvature,
    3- Post 100- Why does a curved lifting foil reduce RM on a multihull but not on the T2?
    4- Post 106 & 111-more on T2 design theory and curved lifting foils,
    5- Post 113-Racing tunnel hulled scow with curved lifting foil,
    6- Post 116-Dinghy application of a single curved lifting foil,
    7- Post 120-Righting dinghy with single curved lifting foil,
    8- Posts 121 & 127- more on single curved lifting foil and on design theory.
    ===============
    Picture Summary, L to R:
    1) Sail Plan of T2, 2) Plan view of T2, 3) Approximate midship section of T2 with one foil deployed ,one retracted. Shows the center of lift of the foil substantially to leeward of the hull, 4) Illustration of the change in vertical lift with retraction of the foil, 5) Close approximation of straight angled foil to curved lifting foil. The straight angled foil always has the same proportion of vertical lift and lateral resistance while the curved foil allows vertical lift to be mostly eliminated and/or "tuned" for the conditions, 6) & 7) Single curved lifting foil deployed on one side. The foil slides in a continuous ,partially open athwartship trunk that allows the crew to grab the foil and slide it to the other side during a tack/gybe. Possible method of tying this movement to the movement of a sliding seat is being looked at. For all rough sketches click on image for best detail:
     

    Attached Files:

  3. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Dinghy Design-Curved Lifting Foils

    Be sure to check out this thread : http://www.boatdesign.net/forums/hy...-monohulls-multihulls-37508-2.html#post458035
    And also, the new "Sailracing" magazine (available for free)-April issue has a great article on the impact of curved lifting foils in the A Class cats-and will no doubt do an article on the application of curved lifting foils to monohull dinghy design in the coming years(!).

    Subscribe here: http://www.sailracingmagazine.com/back_issues.html
     
  4. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    Dinghy Design: Curved Lifting Foils

    Mike Drumond of Oracle racing has come up with a new cat-the AC 18. From the perspective of this thread there is some design news: look at the foils below. Straight section combined with a curved section.
    I still have to figure out how the trunk works but it seems it might have potential in dinghy design.

    click on image for better detail:
     

    Attached Files:

  5. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    T-foils for foil assist

    ======================
    I missed these comments earlier and want to make it clear that T-foil rudders used for "foil assist" can lift the boat reducing displacement. In International 14's and other boats they can also be used for "energy recovery" creating a net forward force derived from their proximity to the surface-they have to be relatively close to the surface for this to be beneficial.
    On the design concepts I've posted here "energy recovery" is not part of the design because I want the rudder foil fully retractable. But like the I-14 and other boats(see the papers below) the rudder foil is designed along with the curved main foil to reduce displacement and therefore wetted surface by lifting the boat. On my designs the RM is increased to allow greater sail carrying power to make up for the foil drag in light air-at speeds above 6-7 knots, the lift drag ratio of the foils + boat combination is better than without the foils and steadily improves from there.
    In the Bieker paper ,on page 38, the upwind configuration shows that lift from buoyancy is 496lb.(2206n) and the boat weight is 586lb(2606n). The difference, in vertical lift, is made up by 90lb.(400n) lift on the rudder t-foil.
    In other words, vertical lift from a rudder t-foil is a FACT exploited on a number of boats from my Tantra II concept(developed in this thread) to the I-14, Moth and other boats(National 12, some Cherubs, R Class foilers) etc. Further, on boats like Moths the foils begin to lift when the boat begins to move-the foils support a great deal of the weight before the boat actually lifts off. On my concept boats using curved main foils+ t-foils on the rudder the boat is not designed to fully fly only to significantly reduce the weight supported by the hull and therefore reduce drag.


    ----
    Note: the full Bieker paper is too large to be uploaded here but I have posted page 38(I-14 good.doc) that illustrates the lift from the t-foil. I'll be glad to send the entire paper to anyone who e-mails me. It will be easier to view page 38 on the full document....
     

    Attached Files:

  6. CT 249
    Joined: Dec 2004
    Posts: 1,692
    Likes: 77, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    Doug is right. Rudder foils used in 14s do reduce displacement at many speeds and improve handling at many speeds - that hasn't been in issue for years.

    However, as some top 14ers have pointed out, the speed and handling increase created in this way is not as great as the speed increase that could be created for less cash and complexity by simply making boats longer. Of course, from one point of view that's irrelevant because creating a boat that's faster within the rules is a major point of development classes, but from the other point of view you could say that it's significant that the foiler classes remain small or tiny and growth (if any) is very small and slow.
     
  7. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ======================
    That's an interesting comment and just doesn't appear to be correct, as best I can tell: the lift/drag ratio of a well designed foil is much greater than the hull. Not only that, adding length w/o adding SA is just adding drag.
    From another point of view, you could say that to the extent "that the foiler classes remain tiny and growth (if any) is very small and slow" it is because the foils have been applied to high performance difficult to sail boats like the Moth and I-14. While these applications have proven beyond a shadow of a doubt that "foil assist"(I-14) and full flying foils(Moth) work around a course , they have done nothing to illustrate that foils can be applied to boats that are much easier to sail than either of these.
    Some people think it is a characteristic of a "foiler" to have to walk it out to deep water , that it is a characteristic of a foiler that it is unstable off the foils, that "crashes" are a characteristic of foilers and that foilers have to be built of the most expensive material-all of which is nonsense.
    The Tantra II and boats using the same concept can be high performance and easy to sail with retractable and tunable curved lifting foils and retractable t-foils(if used). There is much "design opportunity" in creating foil equipped boats-monohulls and multihulls- that are specifically designed to be easy to handle,very comfortable, beach sailable and user friendly in every respect. That's part of the the great potential of dual or single curved lifting foils used with or w/o T-foils in monohulls and both used in small multihulls where they will unlock unheard of performance in small trimarans*. Foils are already working in small catamarans to increase speed and reduce the incidence of pitchpole.
    The surface has barely been scratched in the application of lifting hydrofoils to small boats(or larger for that matter).

    * http://www.boatdesign.net/forums/multihulls/mpx-11-very-small-high-power-trimaran-33686-15.html
    http://www.boatdesign.net/forums/mu...elf-righting-trimaran-test-model-36058-5.html
     
  8. CT 249
    Joined: Dec 2004
    Posts: 1,692
    Likes: 77, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    Adding length without adding SA is certainly not just adding drag. Ask any one of the major dinghy or skiff designers and they will say that adding length (without increasing SA) allows major speed improvements. That's why top dinghy designers say things like this;

    "Length is not quite everything. Say ninety-nine percent”.

    Length is "very (important); especially upwind and in waves - maybe not much when being blown down wind like a leaf behind a large asymmetric. Wavemaking still comes into it even for faster classes”.

    “We’ve done out a whole bunch of research where we’ve worked out what is the ideal length for a two man boat, and it’s around 17’6”( ). The ideal length for a three man boat is around 21’ ( ). And as time and technology progresses, that length will get longer not shorter. Things get lighter and stiffer, and as you’re able to build things at a lighter weight without greater mass, then the ideal length will get longer not shorter.”

    If you take the same boat and give it extra length, you basically;

    1) increase hull speed, therefore allowing the boat to move to the speed where it can start planing more easily. This avoid the issue of boats like Cherubs where it is said ""The Cherubs are at a disadvantage sailing against other boats in light winds at hull speed, since they are so short" or 14s where it is said "“The biggest limitation to the speed of a 14 upwind stems from the fact that it is a short boat with a sailing displacement to length ratio similar to that of performance keelboat”
    2) fine up the entry, which is of considerable importance when going upwind at speed;
    3) reduce the rocker;
    4) dramatically reduce the DLR; as Paul Bieker says "the concept of the hull changes drastically with displacement/length ratio";
    5) make for a boat that handles waves much better

    Ask the guys who design 14s, 12s, Moths and Cherubs and they will routinely say that the fact that one of the major restrictions of such boats is that they are very short. The Int 14 actually has a higher DLR than a 420 or 470; a 12 Foot Skiff or R Class has a DLR is similar to that of a Snipe or Mumm 30.

    These are the reasons that people like a former world I-14 champ said that it would be easier and cheaper to increase the speed of I-14s by giving them longer hulls without foils, rather than adding foils. Of course, they recognised the issues, but their point was the question of class development was more complex than simply saying faster boats = better boats.

    Of course, short boats have their own very special appeal - for example, they are light and very quick downwind in a breeze. In no way am I criticising them.

    The point is that adding length may be a more economical and lower-maintenance way to increase speed and handling than adding foils. There are more definitions of efficiency than the simple one of speed to length ratio. Ratios like speed to cost, speed to maintenance and speed to complexity are arguably at least as important.
     
  9. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ====================
    Sorry, I don't buy it. Adding length w/o sail area increases wetted surface, weight and drag.
    And your habit of quoting nameless people with no references to links discredits those quotes, in my opinion. You'll notice that most of the time when I quote somebody I name them and provide a link to their comments.
    --
    Further, adding length (without adding SA) will in NO WAY be better than adding properly designed hydrofoils which can result in speed increases of 8-12% for foil assist and 20%+ for full flying hydrofoils.
    A 14' WL dinghy has a nominal "hull speed" of 5 knots. Increasing the length 2'
    (14%) gives a nominal hull speed of 5.36 knots-an increase of 7%.
    If the boat is scaled up with the same proportions the increase of weight is 1.5 times! If just length is increased, the projected weight increase would be about 14-15% coupled with a similar increase in wetted surface-all this on the same power. No way that will favorably compare with adding a properly designed foil or foils to a boat suitable for them.
    ----
    Another very important consideration regarding this thread: the concepts discussed in this thread refer to boats that will be designed specifically to use "foil assist" and the design will maximise the benefit in ways not yet done by anyone that I know of-mainly by designing the boat from scratch to use foils and lifting a much larger percentage of the sailing weight. The type of foil assist on the concept boats in this thread is quite different than the "add-on" examples of foil assist seen in the I-14, National 12, Cherub and others.
    The International 14 has about 90 lb of lift upwind from the rudder hydrofoil which is about 15.4% of total sailing weight( see the Bieker paper or page 38 above). The Tantra II will lift closer to 70% of the boats weight using a design that incorporates foils from scratch. In addition, the curved lifting foils on the Tantra II move the center of lift of the boat ouboard significantly allowing an increase in righting moment as compared to a "normal" hull of this length.
    See summary and rough illustrations above, in post 137.
     
  10. CT 249
    Joined: Dec 2004
    Posts: 1,692
    Likes: 77, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    I can't provide links because those quotes (or almost all of them) came from personal correspondence or interviews.

    1- Was Peter Mander (world 18 Foot Skiff champ designer) in his autobiography.
    2- was Phil Morrison
    3- was Julian Bethwaite
    4- was Andy Paterson
    5- was Paul Bieker; see http://docs.google.com/viewer?a=v&q=cache:muLM-dhtOHYJ:usa.international14.org/index2.php?option%3Dcom_content%26do_pdf%3D1%26id%3D13+"INternational+14

    Adding length does add speed, which is why;

    1) an 11' Europe is the speed of a 14' Radial, despite having much less weight (about 12kg) and about 40% more sail area;

    2) a 12' Byte CII is slower than a Radial, despite being newer, having less weight and a carbon mast carrying a much larger fully-battened flextip sail;

    3) a 12 Foot Skiff, 14 Foot Skiff and 16 Foot Skiff are all close to the same speed despite the fact that the weight and sail areas favour the two shorter boats, with the 12 the lightest and carrying the biggest rig.

    If adding length doesn't add speed, why aren't all development classes built to minimum length?

    Here you will see MadEngineer's Michlet run showing a 16 foot "Moth" to normally be faster than shorter versions.

    EDIT - Link doesn't work but I couldn't be bothered...
     
  11. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ====================
    I honestly believe that sometimes you must forget what you said earlier. I clearly showed in my last post that adding length does increase speed-just not as much as adding foils can.

    But your original contention was: " However, as some top 14ers have pointed out, the speed and handling increase created in this way[adding foils-dl] is not as great as the speed increase that could be created for less cash and complexity by simply making boats longer.
    I showed above that the speed increase is substantially greater using foils on the short boat rather than lengthening it. I didn't mention it earlier but the increase in length w/o increasing SA would result in a cost increase of 14-15% which saves nothing over the incorporation of a "foil assist" rudder. I didn't even address the absurdity of lengthening the boat without a commensurate increase in SA from the standpoint of comparative performance.



    You "couldn't be bothered" ,huh?! Works for me.........
     
  12. CT 249
    Joined: Dec 2004
    Posts: 1,692
    Likes: 77, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    I honiestly think you forget what you wrote earlier - your post 142 said "adding length w/o adding SA is just adding drag." Then your post 146 said " I clearly showed in my last post that adding length does increase speed."

    I did not say that you would increase the entire boat. I spoke of lengthening the boat, as can be done simply by moving the stations an inch or so apart and leaving everything else the same. That way you increase the hull weight by considerably less than 8lb in a 12 Foot (extended to 14 foot) boat. But crew weight and everything else stays the same, so you get less rocker or less transom immersion; a finer entry if you want it; better motion through waves; etc.

    Re "I didn't even address the absurdity of lengthening the boat without a commensurate increase in SA from the standpoint of comparative performance."

    But that depends on what you are measuring performance on. Measuring a boat by its speed for its length is only one option. You can also measure a boat by its speed for handling; speed for cost; speed for simplicity or other ways.

    Here's the earlier link -http://www.boatdesign.net/forums/attachments/sailboats/718d1062839169-sailing-dinghy-design-eaxmple-resistance.jpg

    http://www.boatdesign.net/forums/sailboats/sailing-dinghy-design-1437-11.html#post10920

    I was up with insomnia last night and when I lost it I was about to crash out again.

    PS - please be consistent. Either stop making false claims that I predicted that the Moths would die, or stop demanding that I provide links to all my quotes. If you are prepared to cast slurs with no proof, you cannot demand that others provide proof.
     
  13. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ================
    1) Adding length w/o adding SA is just adding drag but I probably should have made it more clear. One of the measures of drag/resistance in comparitive ratios is SA/ ws(sail area to wetted surface).
    If the boat starts out with 35 sq.ft. of wetted surface and 150 sq.ft. of SA, I estimate that the increase in wetted surface from adding 2'(conservatively) is 15% or 5.25 sq.ft raising wetted surface to 40.25 sq.ft. Therefore, the SA/ws ratio before extension is 4.29/1 and after is 3.73/1. Clearly, though "hull speed" in displacement mode rises slightly maximum speed will be affected by the increased proportion of drag as will acceleration.
    ---
    2) My best memory is that in the days of the original Moth forum you were very anti-foils (and both Rohan Veal and John Ilett backed that up). I think I remember you saying that foils would likely kill the Moth Class. However, I can't access the old forum to prove that . But the memory stays.
    I didn't mention a single thing about your past prognostications in the Moth Class in this thread- I don't know why you brought it up........

    ============================
    I think I clearly showed earlier that the idea of adding length to a boat(w/o an increase in SA) instead of adding foils(foil assist or full flying) for the purposes of increasing speed is off base. As it is from a cost basis, or any other basis that I can think of.
    But this is not the subject of this thread-which is: the possible application of curved lifting foils to dinghy design.
     
  14. CT 249
    Joined: Dec 2004
    Posts: 1,692
    Likes: 77, Points: 48, Legacy Rep: 467
    Location: Sydney Australia

    CT 249 Senior Member

    I brought it up because of a desire to establish some type of consistency. If you are going to criticise people for not providing full citations, then you should not make allegations that are equally without evidence, such as your allegation that I predicted that foilers would kill the Moth class.

    BTW there are more forms of drag than wetted surface area, which is exactly why just about every development class in the world is built to maximum LOA. But enough of this...
     

  15. Doug Lord
    Joined: May 2009
    Posts: 16,470
    Likes: 286, Points: 93, Legacy Rep: 1362
    Location: Melbourne, Florida

    Doug Lord Flight Ready

    ====================
    I haven't made such an allegation in this thread or any other thread in the last few years ,as best I can remember(ever since my only way to prove it besides the direct commentary of Rohan and John was taken down): you brought it up here. Again, I did not bring it up, I don't intend to bring it up and it is largely irrelevant to the discussion in this thread.
    You can look at any thread I participate in: I almost always provide references/citations-that is extremely well documented and very consistent.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.