# Open 60 & 50 (IOMCA) rule should be changed

Discussion in 'Stability' started by Stephen Ditmore, Dec 25, 2006.

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### Stephen DitmoreSenior Member

Open 60 & 50 (IMOCA) rule should be changed

Don't get me wrong.... I'm a fan of IMOCA Open 60 and 50 class racing, the people who race these boats, the designers who design them, and the nation (France) that has embraced and supported this sport. But I see a problem with the rule; a quirk that (like quirks in the IOR rule) will drive designers to design even more freakishly wide boats. Designers coming into the game, such as Kouyoumjian, are realizing that there may be no optimum beam within the envelope of parameters represented by the current IMOCA fleet.

In many ways these boats are akin to giant dinghies, with movable ballast taking the place of crew weight shift as the major source of stability, and therefore sail carrying capability, at the fastest angles of heel. The amount of movable ballast is limited by rule D2 (attached).

To keep the math simple, compare two 60 footers, one with a 13 foot (4m)beam, another with a 26 foot (8m) beam. The waterline beams also in a 2:1 ratio, the displacements same, and the center of gravity near the upright center of buoyancy in both cases. GM will be roughly equal to BM = KLB^3 / displacement, so the wider boat will have 8 times the initial stability, and will therefore be allowed to generate 8 times the amount of righting moment from movable ballast (perhaps using 4 times the amount of ballast on twice the transverse lever).

There's a better way to limit movable ballast. Base allowed HM(movable) on most unfavorable RM(90) [not RM(10)]. This will take beam out of the equation and put the emphasis on vertical center of gravity, where it should be. Since there are tests that require the boat to be tipped on its side already, RM(90) would be an easy thing to measure, as would HM(movable), using a crane with load cell.

Make this change, and the financial horsepower of sponsored racing and the mental and computational horsepower of IMOCA development class designers can be harnessed to produce seaworthy boats converging, over time, toward a meaningful optimum (as open class boats should). Fail to make it, and these boats will increasingly become freaks created by a quirk in the rule under which they race.

I'd be especially interested in reactions from French and other European participants in these forums. Do you agree with me? Is there discussion of this quirk, and whether it should be fixed?

I would note that this does not apply to Class40, since Class40 does not allow canting keels and limits water ballast by weight alone, independent of beam. Also because Class40 has a sail area limit.

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### BOATMIKDeeply flawed human being

Won't wetted surface become a consideration at some point?

Or the lack of fine-ness in the hull lines?

We are unlikely to see a 1:1 beam ratio so perhaps they are all moving to an optimum somewhat lower than that?

Just some initial thoughts

Best Wishes

Michael Storer

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### Stephen DitmoreSenior Member

You're right....and the other rules in the D (stability) section are helpful. So perhaps I have exaggerated the problem a little. But a development class that calls itself "open" should seek to minimize the degree to which the rule drives design, allowing designers to develop the right boats, not the boats that most exploit the rule's idiosyncrasies.

With that in mind, it would be a better rule if HM(movable) were based on RM(90), not RM(10).

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### SuperPiperMen With Little Boats . .

Stephen:

Without a detailed study of your recommendation, here is one consideration. The Open classes should be the development field for the mainstream sailors. Would the weekend cruiser eventually benefit from a disproportionately wide boat? Or, would she more likely benefit from technology based on your RM(90) rule?

And as discussed in the "Notable Open & Development Class Racers" thread, could a quirky rule help grow or kill the IMOCA class?

Stephen, I suspect that you are right in your suggestion.

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### Stephen DitmoreSenior Member

I think the answer is yes. Even if a multiplier were incorporated to make most or all of the current fleet legal under the new rule, establishing a healthy relationship between movable ballast and RM(90) would result in future boats being healthier, more balanced designs.

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### MikeJohnsSenior Member

Stephen

Yes I agree the 20 degree rule will definatley drive a very beamy trend
and quickly considering this I can see no problems with the RM90 suggestion, might see some intersting shapes developing in the hull sides to get the best out of the 90 degree hauldown test

Boatmik
They will move to an optimum tradeoff between WSA and ballast ratio SA and wave piercing capability, but optimum under the rule.

Superpiper
you say "The Open classes should be the development field for the mainstream sailors" Is this mainstream racers? It is definately the development field for large ocean racers but the first consideration is to produce the fastest boat under the rule that can endure a few seasons. Other characterisitics that make them successfull are subject to scaling effects while the ocean isn't. I'm not aware of many beneficial spinoffs to the cruising world from this sort of development.

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### VegaSenior Member

QUOTE=MikeJohns;119621]Stephen

Yes I agree the 20 degree rule will definatley drive a very beamy trend
and quickly considering this I can see no problems with the RM90 suggestion, might see some intersting shapes developing in the hull sides to get the best out of the 90 degree hauldown test

Boatmik
They will move to an optimum tradeoff between WSA and ballast ratio SA and wave piercing capability, but optimum under the rule.

Superpiper
you say "The Open classes should be the development field for the mainstream sailors" Is this mainstream racers? It is definately the development field for large ocean racers but the first consideration is to produce the fastest boat under the rule that can endure a few seasons. Other characterisitics that make them successfull are subject to scaling effects while the ocean isn't. I'm not aware of many beneficial spinoffs to the cruising world from this sort of development.[/QUOTE]

What rule? These are Open boats. The only rules are a max length, some restrictions on the size of horizontal spars, max draft, max water ballast and max angle canting keel limited by a max heeling angle and many rules related with the safety and seaworthiness of the boat. All the rest (if I am not forgetting something) is Open.

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### VegaSenior Member

Sthephen, I am not sure of sure of your intention. For me this is not an esthetical issue, but a functional issue. What are intended in an Open class are faster sailboats, without compromising safety. As BoatMik have pointed out, you only take advantage from hull form stability (larger and larger transom boats) till the point drag is superior to the wins allowed by a superior RM moment and the capacity to have more sail area.

The rule you want to change makes sense to me and it seems a smart way of limiting two things and at the same time, allowing almost any balance between them: The max angle of the canting keel and the max water ballast. Why do you want to take out of the equation form stability?

I don’t think that would lead to better boats, but to boats more limited to an arbitrary rule that would lead to narrow and less fast boats without any really advantage, except perhaps an esthetical one. That would limit Design parameters.

If you make all boats comply with very strict and severe safety and seaworthiness requirements, as it is done already, the interest of an open class is to explore the max possibilities of different hull shapes regarding speed and seaworthiness. And I mean hull shapes that are not limited by any rule with the main exceptions of draft and length.

But I agree with you on one point. These hulls are mainly designed to go downwind, even if as Juan K. had pointed out, the capacities of these boats to go against the wind are much underestimated.

I am not interested in less fast or less seaworthy sailboats or a change by esthetical motives or other subjective ones like comfort on a sea motion, but I would be very interested if in the IMOCA circuit were introduced a fair amount of races predominantly against the wind.

That probably would permit that less large transom boats could be an option in the Design of the boats... Or maybe not and the actual shape could prove to be a better shape for an overall ocean use. Anyway that would be instructive.

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### RHoughRetro Dude

What is the basis for the 20deg rule? It seems completely rational to me.

Take a boat of "normal" proportions ... an early 70's IOR boat?

When the ballast(crew) is moved from one side to the other how much does lateral trim change? More or less than 20%?

I only have accurate data for my boat, the USSailing VPP calls for a crew weight of 1225 pounds. The righting arm @ 30 deg is about 1.0 foot. When I do the math, moving 1225 pound of crew from one side to the other (beam is about 10ft) I get a greater trim change than 20 deg.

I'm not familiar enough with the IOR rule to know what prevented the boats from getting as beamy as the current open class boats.

I don't see a problem, the last time I looked, the Mini's require the boats to be self righting with a 50KG weight at the masthead with the masthead in the water and the ballast at any extreme. Beam is penalized by increasing the angle from which the boat must recover. I see no point to limiting it to 90deg.

A similar rule would work on the big boats. Set a test weight at the masthead, haul the masthead into the water and see if the boat comes up (with the ballast in the least favourable position).

I would like to see Open Rules that create shapes and technology that would transfer to production boats. One limitation for a good cruising boat in many areas is draft. 2m is too much in some places, 3m is very limiting. A rule that created shoal draft ability and boats than can be sailed with small crews should be supported.

A 2m draft limit and the recover from masthead in the water test, might just solve any "problems" that the open classes are fostering.

As far as the boats being optimized for downwind sailing, that makes perfect sense also. Who in their right mind plans cruises that are predominately upwind? The ability to go to weather is a requirement for a safe boat, however 45-50 deg off the true wind in F5-6 is all you need to get off a lee shore. I'll wager that the current group of Open boats can do that. The very last thing a good cruising boat needs is a hull and rig optimised for going upwind or for racing windward-leeward courses.

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### VegaSenior Member

Rough, about that 20º rule, is more than you say. The inclination of the boat is not only due to the water ballast, but also to the effect of the keel canted to the same side. If you have a bigger angle than 20º you can do two things: Diminish the water ballast or diminish the possible max angle of the canting keel. You are free to use any combination you want providing that the boat does not heel more than 20º.

About safety, these are probably the more seaworthy and safest of all Ocean racing boats. Look at the safety requirements of these boats (I will post a link to the rules) they are huge, much bigger than for the minis.
Take a look at some of them:

“SELF-RIGHTING
During the measurement process, the skipper must physically demonstrate that the boat, once casized, is capable of self righting without outside help.
This test is mandatory for the issue of the first Measurement certificate.”

STABILITY CURVE AREA RATIO
The positive area under the stability curve shall be at least 5 times greater than the negative area.

UNSINKABILITY
B.7.1: Essential rule: In the event of all compartments being completely flooded, the boat shall remain unsinkable.
B.7.2: Unsinkable volume:
The boat shall possess a total volume for unsinkability, expressed in m3 not less than 130% of the boat displacement in m3:
B.7.3: Longitudinal distribution of buoyancy volumes:
These fixed volumes shall be approximately distributed proportionally among each watertight compartment.

Any required watertight bulkhead shall be strongly built to take a full head of water pressure without allowing any leakage into the adjacent compartment.
They shall:
- divide the boat in several volumes from stem to stern
- be transverse at least 5 in number and create 6 watertight compartments with an access for a person
- be not more than 5 metres apart
- be watertight. The passage of various cables, pipes or ducts shall not compromise the watertight characteristic of the compartments.
The first forward watertight bulkhead shall be located within 15% of overall boat length and abaft the forward end of the waterline.
b) Crash box:
A watertight box, filled with closed cell foam, capable of being destroyed in a frontal collision without endangering the integrity of the boat shall be fitted at the bow.

B.5.5: WATERTIGHT ACCESS HATCHES:
The boat shall be accessible from stem to stern by way of watertight hatches. These hatches shall permit complete access to the boat, from stem to stern and inversely, with any of the compartments flooded and without any of the other compartments becoming so.
These hatches shall have their closure mechanism permanently fitted.
B.5.6: ESCAPE HATCHES

The boat shall have two exits. One exit shall be located forward of the foremost mast (except where structural features prevent its installation). The second one shall be located astern, allowing access to, and exit from, the boat, whatever its position in the water.

COMPANIONWAY HATCH
A companionway hatch shall be fitted with a strong securing arrangement which shall be operable by one person from the exterior and the interior including when the yacht is inverted.

http://www.imoca.org/sitedata/pdfs/YB-2006-UK_V1.pdf

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### RHoughRetro Dude

Paulo,

I agree, the requirements for stability, water tight bulkheads, and unsinkability make the open racers much safer than many (most) of the "traditional" designs.

I think that the rule is probably just fine, although it produces boats that look to be unsafe when viewed by some designers. The simple addition of a draft limit to a figure that would make the boats practical for production (like the cruising Pogo 40) might see real progress towards safer/faster cruising boats.

Of course, we then end up with true shoal draft boats that are fast for their length, beachable, and that require no ballast at all ...

Randy

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### VegaSenior Member

Randy, these boats have a limit on draft: 4.5m. It is a lot for a cruising boat, but normal for a racing boat of this size. The Class 40 has a 3m limit.

Making a cruising boat from an Open 60 is not practical (these boats are really pure race machines) but there are some cruising boats inspired by these boats (hull, water ballast and deep bulb), with a smaller draft. Go to the site of the Groupe Finot and look at his cruising boats. Finot groupe is the most successful designer of Open 60s.

You can go also go the thread that I am running about cruising boats and costs and have a look at the last sailing boat I have posted, the Cigale 14. There are Cigales with 14, 16 and 18m. It is a Finot Design, and it costs no more than many other 14m boats, with the advantage of being an aluminum boat.

Paulo

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### BOATMIKDeeply flawed human being

Hi All,

This is a good discussion.

I'd like to make an additional point.

I think there is a value in having rules that promote extreme boats.

Of course you have to limit things to keep the boats of around the same type for racing.

But to my mind there is nothing more beautiful than a boat that is pushed to some sort of rational extreme.

1/ A K1 racing kayak (before or after the rule change)
2/ An Australian NS14
3/ An international Moth of virtually any of the generations
4/ An 18ft skiff
5/ An OC1 or OC2 racing outrigger canoe
6/ A speed record intending windsurfer
7/ Any of the speed record setting sailboats (my favourite of all time was Mayfly - so far ahead of it's time - simple, light and very fast).
8/ Sonderboats
9/ 30 square metre yachts

In the case of each there are relatively few rules and few rule changes. And each has resulted in boats that are not only beautiful but have been groundbreaking because they have not been too heavily restricted.

It would take me pages to write about the innovations that each has spawned.

I think the Open 60 etc have provided a lot of interesting developments (even if most of the work was done in MiniTransats (which I should have added to my list above!).

Compare it to a rule that is framed to create boring boats like the America's cup class rule - and you get a gabfest about the best area for development being the keel to hull fairing as P Oosaanen pointed out. Be too restrictive and the boats end up being both expensive and all the same with few innovations possible. An example of a poor rule.

The boats above, excepting the ACC rule boats, are or were highly innovative so the rules, in the frame of the definition I am struggling with here, are "good".

My feeling is allow the rule to be extreme and let the water and air be the judge.

Restrict only where there is a really good reason to do so. And if the boats seem capable for the purpose then consider loosening the rule a bit.

Michael Storer

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### BOATMIKDeeply flawed human being

Hi Again,

Can I give an example from history.

I have a book - "the History of British Ocean Racing".

I was shocked to discover - prior to WW2 the boats just were not sailed upwind once the wind got over 20 knots - they just couldn't do it. They would drop anchors or heave-to.

So when you see pics of Old English Cutters and their supposed "performance" remember this!

The boats that changed this were boats that the establishment considered "unsuitable" for going to sea.

Blondie Hasler and his crew of commandos in a 30 square metre ("Tre Sang"?)

And a number of Knud Reimer designed boats promoted a Adelard-Coles (he wrote the standard text "heavy weather sailing").

They were the ones who went to sea in "inshore boats" and showed the "blue water boats" that it was not only possible to take them offshore but that they would go to windward in very bad conditions indeed.

Modern Ocean Racing was born - at least in that part of the world - I suspect the Danes, Swedes, Germans, Dutch and Norwegians had been going upwind in rough upwind racing conditions for decades.

I don't think it was all that much different in the USA - major races were still being won by Schooners in a mix of conditions!

So if the RORC (Royal Ocean Racing Club) had acted to restrict the new flock of boats from entering their first offshore races - we would probably still be anchoring as soon as the wind blew up any.

So in general I'm against restriction except in terms or restricting expense of boats - and to push my hobby horse - this is the one area that would bear the best fruit in terms of participation rates in the sport - but it is the one that has been a complete failure in management by almost every conventional racing class in the world.

Best Regards
Michael Storer

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### RHoughRetro Dude

I have to disagree about the ACC boats. The AC is all about interesting match racing, not interesting boats. To insure good match racing, the boats must be very close in performance. Any rule that is designed to produce close, tactical racing must produce type formed boats. While the "match" between Stars&Stripes cat and NZ's monster mono was a race between interesting boats, the match racing was not very good.

The AC is an unique venue. The best racing would be between One-Design boats. However, racing One-Designs has smaller appeal. In North America, NASCAR is an example of a set of rules that produces good, close racing, but boring vehicles. There was (still may be) a series called the International Race Of Champions (IROC). All the cars were provided by the organizers and drivers were rotated each race. The winner of one race got the slowest car in the next race, etc. The format should have produced lots of interest but it did not. Even though NASCAR racers and F1 racers are more like One-Designs than people will admit, fans like to be able to cheer for a brand and or a driver. In the AC, fans can support boats or sailors. The "what if" is one of the things that keeps interest high. "What if" NZ hadn't lost her rig ... "What if" the wind/waves had been stronger/lighter/bigger/smaller? ... "What if" DC had been driving ...

If the boats that race for the AC were one designs, interest would wane. If the boats had large differences in performance the quality of racing would be poor and interest would wane. One of the things that keeps the AC interesting is the obscene amount of money that has to be spent to compete. The intrigue of spying and having to second guess what will work during the match add to the status of the AC.

The rate at which data can be processed type forms boats much faster than even 10-20 years ago. Trying to find a reliable 2-3 boat length speed improvement in a 2 hour race is quite a challenge. In the very limited context of creating good match racing, I think both the 12 Metre Rule and the ACC Rule have done a good job.

Randy

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