Converting from IRC to IMS

Discussion in 'Boat Design' started by Duken, Mar 1, 2005.

  1. Duken
    Joined: Feb 2004
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    Location: Berlin, Germany

    Duken New Member

    Hi !

    We currently think about buying a Prima 38 which is an excellent boat under IRC and in general termns such as buílding quality etc.

    The only problem is that we want to sail it in germany under IMS.

    So the question is very simple: What is the easiest way to make a Prima "on the paper (the IMS certificate) appr. 15 seconds slower without ruining its performance on the water ?

    Some key figures might help

    Displacement light 6,1to
    Ballast 2.7to (700kg steel fin, 2to lead bulb)
    Hull length 11,6m
    LWL 10,5m
    Beam max 3,81m
    Beam wl 2,78m
    Main 48,5 sqm
    Code1 37,9 sqm
    Draft 2,46m
    I= 15,39m
    J= 4,67m
    RM @ 1degree = 155kgm

    More might be found on the homepage of the producer www.seaquestyachts.com.

    So far we think about removing some 300kg off the bulb (and remodel the shape with balsa,gelcoat), put some 200kg in the bilge in the bow section and maybe recut the main with less roach.

    We want to bring the IMS GPH to appr. 600 (Bene 40.7 is 603 and IMX 40 is 590). Last years GPH for the prima was 581 but I do not have the IMS certificate yet so I do not know what it will be in 2005 without modifications.


    What do you think ? Any ideas ?


    Jan
    c/o sailormade Yachting
    www.sailormade.com
    Berlin/Germany
    P.S. Please do not start complaining on IMS. We have that already going at at Sailing Anarchy...
     
  2. water addict
    Joined: Jun 2004
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    Location: maryland

    water addict Naval Architect

    Have you tried sailing it as is? Do you think it's not competitive in IMS in its current state?
     
  3. Duken
    Joined: Feb 2004
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    Duken New Member

    Righting Moment is killer for IMS

    We sailed the boat last monady and loved it. The issue to convert it comes from the fact that a few basic figures are "wrong"

    ballast ration 44%
    Righting Moment 155kgm


    We saw from the results of last years RolexMiddleSeaRace that a Prima 38 comes with a rating 580. This is appr. 20sec faster than Bene 40.7. This might work in a breeze downwind but even upwind it struggles.

    So we need to modify it on the paper, not on the water....
     
  4. ErikG
    Joined: Feb 2002
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    ErikG Senior Member

    Well I havent don much IMS optimizing, but if you remove weight from the bulb and put it in the bilge it won't only change on paper, it will change in IRL as well.

    Why on earth do you wnat to race in IMS? No IRC races?
    Balsa keels make me wanna puke... [​IMG]
     
  5. Duken
    Joined: Feb 2004
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    Duken New Member

    IMS is the current rule

    Show me any IRC regata in Germany/Denmark/Sweden/Netherlands !

    We have to live with IMS, it does not matter if we like it or not (I personally do not like it but who cares about my opinion).

    Are you a Naval Architect ? I guess so, right ?

    So the question is again what makes the boat slower on IMS paper not on water ? Atleast not as bad as on paper. I could live with 5-7 seconds slower if I gain 15 sec on the paper.

    There has to be something !

    Cheers
     
  6. quicksail
    Joined: Jul 2001
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    Location: canada

    quicksail Junior Member

    First I would work on the ballast ratio and righting moment issues as these both are considered heavily in IMS. My suggestion is looking at removing the bulb and getting a new set of foils for the boat. You should be able to get high aspect and more efficient fins that will help increase performance as well as reducing some wetted surface. I am no expert but this would be my first step. Then I would look at the sails and develop some new sails that will help out the rating. You should consider the weather in your region as well because you don't want to reduce sail area to get the rating boost if it is a light wind venue and the extra horse power is needed. Finally I would look at the placement of internal ballast. Because this boat has such a fat *** end I would look closely at fore and aft placement of the weight. Again, I would look at the weather in the area to help determine this. If the wind is light I would place the weight farther forward to get the *** out of the water (remember wetted surface kills speed). If the weather is on the heavier side I would place the weight more aft as this will help the rating under IMS a little.

    These are just some suggestions as to how I would deal with this problem. If you are serious about the conversion I would make sure that you can undo them because IMS won't last much longer. It's only a matter of time before IRC will come to you guys. That's why I suggest a new set of fins instead of altering the old ones. Also, I would sit down a do some number crunching to determine the best solution for internal ballast and righting moment adjustments. A well designed spreadsheet should help out. Finally, as you guys have experience with IMS use common sense in your alterations. I would not go to crazy as you might end up with some freakstien of a boat which is dog slow. The original boat is fast so just work with that and improve. Wetted surface area is a good place to start as it effects speed greatly.

    Cheers and all the best with your project.
     
  7. ErikG
    Joined: Feb 2002
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    Location: Stockholm, Sweden

    ErikG Senior Member

    Me an NA? Nope am not, I just have loads of opinions and can't keep them to myself :)

    We don't have IRC here either but some people are trying to change that.
     
  8. terhohalme
    Joined: Jun 2003
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    Location: Kotka, Finland

    terhohalme BEng Boat Technology

    Your boat seems to be very good (too good mayby) at light wind. For IMS I would reduce the sail area enough to achieve the right GPH rating. Just ask the IMS inspector to calculate a new trial certifigate by using the 110% jib instead of a big genua. The boat will still be fast in the fleet.

    I had an "overrigged" IMS boat. I had to race against much bigger boats and with too short waterline I really had no changes. Still my boat was fast in very light condition. The races just wasn't all the time at light wind. See how old heavy boats rates quite well.
     
  9. Plaanaa
    Joined: Aug 2005
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    Plaanaa Junior Member

    Sorry for taking up an old topic, but ErikG, someone is trying to bring IRC to Sweden? That´s veeery interesting, cause we are fighting the same battle here in Finland. We are trying to create a working sportsboatclass, and IRC would propably be the best for sportsboats.
    Any idea who is trying to work the IRC to Sweden??
     
  10. ErikG
    Joined: Feb 2002
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    Location: Stockholm, Sweden

    ErikG Senior Member

    Hey Planaa

    Unfortunately no one serious enough and I'm not the man for it.
    My hopes are that the Swedish Sailing Federation will look at events around the world and say "hey they are all moving on from IMS to IRC out there, maybe we should encourage that to". The head of SSF is Stefan Rahm also tactician onboard Victory Challenge and might be approachable about it. I'll pop him an email after the Malmö events and ask for his thoughts. I wouldn't hold my breath for an answer though.

    Here in sweden we all sail the damned LYS system. Works ok'ish at times but as it cant handle planing yachts as they have vastly different speedpotental at variuos wind stenghts the get handicapped to hell. So as a result there are almost no sportboats apart from som melges and a few odd boats.
    Well the major reason for there to be so few sportboats might be 'cause Swedes are such conservative ********...

    As there are so few sportboats and LYS does work halfway decent for displacment yachts the number of people interested in getting a changes seems to be few and far between.
     
  11. Plaanaa
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    Plaanaa Junior Member

    The same old story....seems all Scandinavian countries have similar problems...
     

  12. water addict
    Joined: Jun 2004
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    water addict Naval Architect

    Prima 38 vs Beneteau 40.7

    Have you tried competing with the 40.7 as is? Is The Prima just hopelessly non-competitive in its current state?
    I made a table of basic specs of the 2 boats. They are VERY close, the only significant difference being displacement. Before cutting up the boat, I would compete, and find out its strengths and weaknesses relative to the competition first. Otherwise you are guessing. If you know for example that the B40.7 always wins in light air upwind, but you are faster in heavy air on a reach, with respect to the rating, at least that gives you an inkling of which direction to go. If you don't get a real world benchmark first, then you are relying totally on theoretical performance prediction. For two boats that are so similar in specifications, the computer models could be off one way or the other with respect to the real world, and you would not have a clue- you could make a very expensive mistake.

    p38 b 40.7
    loa, ft 38.22 39.25
    lwl, ft 32.94 34.83
    b, ft 12.50 12.25
    t, ft 7.55 7.75
    SA, sq.ft. 899 892
    ballast, lb 5796 5592
    disp, lb 12004 15211
     
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