Design effect from IOR rules

Racing blue water sailboats and most production cruisers designed before the Fastnet disaster had very narrow transoms, maximum beam aft of center and almost extreme stem angles. Many of them had the transom at the same angle as the stem, or nearly so with none of the overhang of earlier rules. After that Fastnet things changed quite radically, quite quickly to wide transoms and nearly vertical stems with max beam even farther aft.
What was it about the IOR rules of the time that the designers were skirting to bring about such a shape, or was it believed at the time that this was the fastest way to go?
I saw a section of the rules one time and read the same paragraph several times before I realised that I had absolutely no idea what I had just read.

Thanks for any light shed on this...

Feetup.

 

Read C.A. Marchaj's (pronounced "MAR-ki) book, "Seaworthiness--The Forgotten Factor". It goes into lengthy detail as to what was wrong with the IOR rule leading up to the Fastnet disaster.

Eric

 

In the IOR, sailing length was measured from a point at the bow to a point at the stern (as usual). I think (it's a long time ago) the side to side width of these "Girth Stations" was related to the maximum beam. To avoid a penalty, the hull had to be a certain width at these girth stations.

If you had narrow ends, the point where the girth stations where placed would be further from the tip of the bow and the transom, which reduced the distance between the girth stations. That then reduced your measured length and dropped the rating. There were other checks and balances, ie you could take a penalty on the girth stations as was often done at the stern.

For a long while (until about 1979) there was no actual physical measurement of the boat behind the AGS (aft girth station) and designers like Farr, Jones and the French found that you could just extend the transom right out so that it created sailing length. This didn't really work with heavier narrow-sterned boats because the prismatic was so low. It's not much use having 2m of narrow boat waving around astern if it is too skinny to do anything except provide wsa.

I think the aft girth station also had to be at the aft end of the deck. Designers found therefore that they had to rake the transom forward when they brought the AGS forward to reduce rated length.

The IOR also measured the rise of the buttocks. A steep rise reduced the rating. If designers chose this route it wasn't worth generally thought worthwhile to have a long counter as the water wasn't going to flow well around steep buttocks and then along a long counter.

Things were changing quickly at the time of the Fastnet. In the smaller classes and in Australia and New Zealand, probably most of the new boats were wide-stern fractionals. Ron Holland had started making a wider stern "conventional" boat with Imp in 1977 and Peterson had followed with Dida in 1978. Most of the Admiral's Cup fleet, for example, were moving to the wider stern by the time of the '79 Fastnet. The shift was part of a movement towards more downwind speed. Perhaps, as always, technology played a role because better downwind sails may have been making boatspeed higher in general and therefore made it worthwhile to take a penalty for higher speed potential.

I started ocean racing as a kid at the same time as the Fastnet and I really don't think the change in design and the Fastnet were greatly related. Only one of the Admiral's Cup fleet suffered a roll. None of those killed in the Fastnet sailed a masthead rig leading-edge IOR boat. Boats of a general type very similar to the boat that lost the most lives (the fairly heavy Carter 3/4 tonner Ariadne) have been sailing in ocean racers in numbers ever since. They are now regarded as solid and safe. Berrimella sailed two-handed around the world under the three great capes, and got rolled and dismasted yesterday on the way back from the Sydney-Hobart. One could surmise that a boat that has done about 10 Hobarts (winning class in one of the nasty ones) and sailed 2-up around the world is fairly safe, yet stuff happens. One could also assume that designs that have sailed singlehanded around the world via the southern ocean are fairly safe, yet three of them (Cole 43, Farr 40 IOR, S&S 34) rolled with problems in the '98 Hobart. Only one was an IOR boat. Sometimes life happens. As the Fastnet report pointed out, there weren't enough old-style boats in the race to know how they would have survived. Plenty of the Contessa 32s spent time with their sticks in the water.

Generally, around a course, the IOR boats of this time were not too slow. Most early lightweights tended to be skinny without much accomodation, and poor in light winds or upwind, so the IOR boats didn't look all that slow. Then beamier and better non-rule lightweights came in, and IOR boats started to seem off the pace.

 

CT 249;
Thank you! That was a very lucid reply, you have made sense of something that never made sense.
More power to ya mate!!

Feetup

 

CT 249, good post, as always. How do you get time to write all that?

People have tried to find defects in the Bible for centuries so of course they do the same with Seaworthiness - The Forgotten Facor but it a very very good book. Buy it, it's worth every penny.

Mikey