Join Date: Feb 2000
Location: Annapolis, Md
Thanked 195 Times in 159 Posts
Rep Power: 10
Factors influencing boat balance
I think there are a lot of factors that lead to an improvement in balance as a boat heels, but it is a "which came first the chicken or the egg thing" with the IOR rule.
In the late 1970''s, in the wake of the Fastnet disaster there was a lot of light shined on the subject of seaworthiness and motion comfort. Piles or research took place and teh yachting community became quite aware that the trends in then ''modern'' race boats were getting quite unhealthy and that these trends were also affecting the design of normal cruising boats as well (For example high production boats like the Catalina 38, Hunter 34 and 40 of that era, and of course the Beneteau line was full of IOR influenced designs.)
At the same time, there was a whole range of racer/cruiser type boats being introduced that were not designed to any rule. (Boats like the J-36/35, Express 37, or Farr 11.6) These boats proved to be much faster than similar sized IOR boats of that era. People really began to question the validity of the IOR rule.
At the same time, improvements in computers allowed a lot of progress on VPP (velocity prediction program) based rating rules and in the early 1980''s the IMS (a VPP based rule actually called the MHS at that point) was just coming into being. Since the IMS did not use measurement points in the same way that early rules used measurement points, there was no gain in distorting hulls and rigs to beat a rule. In the absense of a rule that over or under rates any characteristic, a simply faster boat will still have some advantage because its speed can be used to place the boat more stratically on the race course.
Designers also began to look for unrated advantages. So for example, a boat that was in balance when upright and also could heel without developing as much weather helm would be faster than one that had its rudder dragging through the water. A boat that rolled or pitched through smaller angles, dampened roll and pitch quickly, and without a jerky motion would maintain attached flows longer and so be faster and make less leeway. The rule could not rate that advantage so huge efforts were made to improve these coincidentally important seakeeping charactisteritics.
Computers also allowed testing with full sized boats being instrumented for roll, pitch and heave characteristics. Computers allowed more detailed analysis of sailing hull form at various heel and trim angles. Computers even allowed more precise recording of the data generated in testing. Out of all of that came better race boats and that filtered down into better cruising boats as well.
Beyond all of that, there was a movement away from high form stability dependent boats. I believe that high form stability boats were rejected both for thier less comfortable motion but also because of the greater awareness of ultimate stability.
Also in my opinion, it is hard to say whether IOR died out because the non-IOR boats got so much better or whether the IOR died out and that allowed its successors to be better boats. I had the chance to talk to Geoff Stagg with Farr''s office after the first year that Goucho was on the race course and winning a large percent of the races she entered. I had written an opinion supporting the direction that Goucho represented that was published in Sailing World. In talking with Geoff, one thing that has always stuck with me was his repeating throughout the conversation how comfortable and easy these new boats were to sail especially when compared to other grand prix level boats. Of course they have only gotten better since Goucho.
The other aspect of this is the Open Class boats. I personally really do not like the direction that they have gone with thier extreme beam, but with computer modeling they too can be made to balance out quite neutrally.
I need to get out of here and go cruising.