# IOR Ton Rule

Discussion in 'Sailboats' started by SuperPiper, May 7, 2008.

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### SuperPiperMen With Little Boats . .

Does anyone have a link or a .pdf of the IOR Ton Rule? In particular, I am interested in the Mini-Ton specifications.

This was the subject of a previous thread. I tried to post to it but it has expired (more than 436 days since the last reply).

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### jozSenior Member

SuperPiper

is this what you mean?

* In 1970 a new rule combined from CCA and RORC (IOR)

Rating = [0.13(L x S) + 0.25L + 0.2S + DC + FC ] x EPF x CGF
√ B x D

Note: Sqaure root B x D should be under (L x S)

S = Square root of the sail area
B x D = Estimates the boats weight through the cross sectional area of the hull amidships
EPF = gives compensation for the engine.
CGF = taxes stability

there is a MK III and MK IIIa rule to this as well.

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### SuperPiperMen With Little Boats . .

Good Start

Joz, that is fantastic. Do you have more where this came from?

Some more detail may be required:

L = Length at the WaterLine?
B = Beam at the sheerline? Or at the waterline?
D = Draft of the canoe body
Units = feet

How do I find the correction factors?
- DC
- FC
- EPF
- CGF

I once saw a document that defined the geometry and volume of the cabin space for the various Ton sizes.

4. ### Paul BPrevious Member

Your best bet will be to contact the ORC and ask for a copy. I doubt they have it as an electronic file. I tossed my paper copy of the IOR Rule years ago.

http://www.orc.org/

By the way, L, B, and D were all calculated values, not simple measurements. The IOR rule ran something like 75 pages. I believe the accomodations requirements for the Ton Classes was in a separate pamphlet called the Special Regulations.

5. ### Paul BPrevious Member

Found this in the IMS regs (http://www.orc.org/rules/IMS Regulations 2007.pdf). It tells you something about the dimensions of the interior and the required equipment for the ton classes:

Extract from 1994 Rules for the World Championships of the Level Rating Classes (“Green Book”)
13. YACHT CHARACTERISTICS
13.1 Interior Dimensions
The interior dimensions of the level rating classes are required to meet certain criteria. The
dimensions are defined below and the dimensional values of each class are given in the table in
13.2.
a) For yachts with an Age or Series Date (whichever is the earlier) of 1/1986 or later:
i) An area of cabin sole shall be defined as having the following characteristics:
It shall have a flat surface free of obstructions, which shall be continuous except that it
may be divided once in any transverse station by an engine, engine box, keelson, shaft
tunnel or centerboard trunk. For yachts with an Age or Series Date (whichever is the
earlier) of 1/1990 or later - where, in any section, there exists qualifying headroom
which is divided once by an obstruction as permitted above, the vertical height of the
underside of the deck above a fair horizontal projection of the adjacent cabin sole
through the obstruction shall not be less than the minimum qualifying headroom (H) for
the class.
The area occupied by the obstruction, however, shall not be included in the calculation
o f qualifying area for a) ii) below.
Throughout this area of cabin sole, headroom (H) as defined in b) below shall be greater
or equal to the minimum qualifying headroom (MH) found from the table in 13.2.
In any transverse station there shall be a minimum continuous width of at least half
MW.
ii) To meet the interior dimensions requirement:
The area of cabin sole defined above shall have an area greater than or equal to the
m inimum area (MA) found from the table in 13.2.
It shall have a continuous length fore and aft greater than or equal to the minimum fore
and aft length (MLC) found from the table in 13.2.
In at least one transverse station there shall be a width greater than or equal to the
minimum width (MW) found from the table in 13.2. This may be divided once - see i)
above.
b) Headroom. Headroom (H) is defined as the vertical height from the cabin sole to the
underside of the deck. (Deck beams and deck stringers may be excluded from the
measurement). To qualify as headroom for the purposes of a) above, there must be no
obstruction in the vertical from the deck to the cabin sole, for example, companionway
steps or platform.
22 IMS REGULATIONS
NOTE: For yachts of Age or Series Date (whichever is the earlier) of 1/91 or later, the qualifying
headroom (H) must be found abaft the after face of the main mast.
NOTE: For yachts with an Age or Series Date (whichever is the earlier) of 12/1985 or earlier:
a) The cabin sole is defined as surface free of obstruction designed to be suitable for the crew
to stand upon. This cabins sole shall have an area (A) over which there is the required
headroom (H) as defined in b) below. If any obstruction, e.g. an engine or engine box,
shaft tunnel, keelson, floor frame or cockpit sole, within the qualifying area of the cabin
sole reduces the required headroom, area of such obstruction will not count towards area
(A) and the extra area must be found elsewhere.
b) Headroom. Headroom (H) is defined as the vertical height from the cabin sole to the
underside of the deck. (Deck beams and deck stringers may be excluded from the
measurement). To qualify as headroom for the purposes of a) above, there must be no
obstruction in the vertical from the deck to the cabin sole.
c) The length of the cabin sole (LC) shall be defined as a continuous length fore and aft over
which it is possible to lay a cord on the level of the cabin sole having the required
d) The width (W) shall be the maximum width having the required headroom (H) measured
across the cabin sole in any transverse section or the sum of two widths measured across
the cabin sole at any transverse section but separated by an obstruction having less than the
13.2 Minimum Qualifying Dimensions
Area A Length LC Width W Headroom H
m2 ft2 m ft m ft m ft
One and Two Ton 1.5 16.140 1.8 5’11” 0.45 1’5¾” 1.83 6’0”
Three-quarter Ton 1.3 13.988 1.8 5’11” 0.40 1’3¾” 1.75 5’9”
Half Ton 0.5 5.380 1.2 3’11¼” 0.35 1’1¾” 1.70 5’7”
Quarter Ton 0.4 4.304 1.2 3’11¼” 0.35 1’1¾” 1.30 4’3”
Mini Ton 0.4 4.304 1.2 3’11¼” 0.35 1’1¾” 1.24 4’1¼”
For Mini-Tonners, sitting area shall total a minimum of 0..5 sq. metres (5.38 sq. ft.) with a
minimum height of 0.75 metres (2’5”) above the seat.
13.3 Fresh Water Capacity Minimum capacities shall be:
Two Ton 150 litres
One Ton 150 litres
Three- Quarter Ton 75 litres
Half Ton 50 litres
Quarter Ton 35 litres
Mini Ton 20 litres
13.4 Bunks Permanent bunks with mattresses shall be not less than:
Two Ton 8
One Ton 6
Three-Quarter Ton 4
Half Ton 3
Quarter Ton 2
Mini Ton 2
23
IMS REGULATIONS
The above bunks and mattresses shall be of minimum thickness of 50mm and where the
mattresses are built into the bunk the same thickness shall be maintained. The bunks and
mattresses shall be of not less than the following dimensions:
1.9 metres long, 0.55 metres wide at one end, 0.35 metres wide at the other end.
13.5 Chart Table
All yachts shall be provided with a flat area suitable for chart work.
13.6 All yachts shall be fitted with a securely installed or gimballed stove, which shall comply with
the following:
Mini Tonners and Quarter Tonners - a minimum of 1 burner
Half Tonners and above - a minimum of 2 burners
13.7 Inboard engine installation shall meet standards accepted in the country of registry and shall be
such that the engine, when running, can be securely covered, and that the exhaust and fuel
supply systems are securely installed and adequately protected from the effects of heavy
weather. (Also ORC Special Regulation 3.23).
13.8 Maximum Beam - Mini Tonners
For all Mini Tonners there shall be a maximum beam limit of 2.5 metres (8’2”).

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### SuperPiperMen With Little Boats . .

Paul, thanks for the effort. This is fantastic information.

As a start, I will confirm whether my boat meets the accommodation requirements.

Maybe someone will post the rest of the rule.

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### jozSenior Member

Super Piper

I got this information from a book that I am reading at the moment which is called The Small Offshore Yacht, by Tim Thornton, to which this is a combined rule which as made up from RORC and CCA rules in 1970 to which they called it IOR and there was no more information about that in the book. My best bet would be to find out from other members or contact the Cruising Club of America if its still in existance, or you could try the RORC in England.

I hope that helps.

8. ### Paul BPrevious Member

I doubt you will find the rule anywhere on the 'net. It has been out of use for about 20 years now. The ORC is your best bet, or if any yacht designers are in your neck of the woods they will probably have an old copy in their files (if they were doing race boats before the late 80s).

What sort of boat are you trying to check up on? Post the type and perhaps photos and some of us might know if it was a mini or not.

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### gggGuest...

No, there were all sorts of complicated calculations based on other numbers they were derived from. L, as I recall, was length between girths, so not at the end of the boat but at a calculated thickness some way in... It was all very complicated...

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### 101Junior Member

As long as there are some IOR folks about, perhaps you can answer a question about the IOR and current design. Why the high aspect skinny main? Was it just the style of the times or was there something in the rule that drove this sail plan.

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### Charly SetterJunior Member

Not as complicated as modern formulas, you could in the end design a competitive boat using a piece of paper, a pen , ruler and a pocket calculator.

I did this twice designing a 1/4- and a 1/2-ton (red cedar, west system).

And the best of all: The formula was a pack of paper. No need to buy a expensive VPP/LPP from ORC. (And 2 or three more to "cheat" the offical software )

We never again had so many new design, many of them "homebrewed", in Germany then in 1975-1985, at least in the small classes (Mini- to 1/2-tonner).

Seen from a "hobby-designer"-view sailing is absolutely boring today

The basic principles of IOR based on several geometrical measurement on the hull.
- 4 girth station defined by fractions of LOA,
- a station in the middel between the girth stations (MD)
- a forward station between MD in the front girth
and some simple (experimental) formulas, that tried to determine the influence of hullcharacteristics.

In the end boats with the same rating where quite competitive, but there was a great problem when boats with large differences in rating sailed against one another.... But that has not changed.

One of the strongest arguments against IOR was a continuos changing formula (trying to close "holes") and the resulting costs of ownership. But I think this is even worse today.

The ugly stern designs are a result of one of these "holes", but also the chined hules with vertical sides in later designs, following a rule change after the 79 fastnet race imposing penalties on boats with large deck width and low displacement.

In the end we had to cut app. 8-10m² sailarea of my 1/2-tonner as the low displacement penalty caught us during buildtime in winter 1982. The hull was more or less finished at this time and the displacement is very low (1.9t compared to 2.4-3t of the competition).

The extremly small mainsail also were a result of some formula preferences but later changed to 7/8-rigs with large rigs when people recognised that rigs with large mainsails are no handicap upwind but faster downwind and reaching.

We made this development with our 1/4-ton. In 1976 the recommendation from our sailmaker was a extremely small mainsail and a large foresail. Two years later in 1978 all new designs were 7/8-rigged and we changed our rig in 79 gaining strongly over all in boat performance (sail area unchanged). May be this was also a result of improved rigging and sail materials (the first mylar-sails appeared in 1980). I very well remember the latter 1-ton World Champion Bremen scrapping 4 rigs in two days due to manufacturing errors of the rigger. This was one of the first flexible 7/8-rigged designs.

In the end IOR was not worse then IMS/ORC taking all caveats in account. Today (under IMS/IOR) we are competing with an extremely low displacement 1/2-tonner against boats of the old 3/4-ton size (LOA 9,3m vs. 11-12m) and have to compensate them. This can´t be fair.

And cost of ownership is far higher

cu

Mathias

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12. Joined: Jan 2003
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### SuperPiperMen With Little Boats . .

That is the most concise summary of the IOR rule I have ever read. Thanks Mathias.

From your diagram, is a narrow transom and some tumblehome a typical signature of an IOR boat?

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### Charly SetterJunior Member

The drawing is a page from the IOR Mk3 (german translation) and propable shows the lines of a typical boat in the early years of IOR (1970).

It´s only used to show the different measuring points.

small transoms are typical, as long as there are no "hollows" in the stem. a steep stem is determined slow (leading to a short calculated waterline length)....

Later designs with hollows in the stemarea found a "hole" in the ruling originaly planned for measurement of designs with transom girth larger than the girth defined for the aft girth station. These designs "simulated" a nearly vertical stem and therefore a extremely short calculated waterline length.

Have a look at the X95 (X-Yachts, Jeppesen). This is a typical design.

Good sites are: http://www.halftonclass-europe.net/index.php
http://www.quartertonclass.org/index.php?option=com_frontpage&Itemid=1

Surprisingly there are strong fleets in europe, mainly UK, France but also Scandinavia. In Germany IOR-classes are dead mainly as a result of politics in the germany sailing association (DSV= Deutscher Segler Verband).

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### 101Junior Member

Thanks, It is interesting as I began on IOR boats in the 70's with skinny mains and pinched ends. Then later IOR fractional boats with greatly improved handling characteristics. Now as I look at a cruisers and seeing the old IOR boats out there I begin to wonder . . . were those really all that bad?

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### Charly SetterJunior Member

No, not at all:

I made a interesting comparison of my (build date 1982) old 1/2-tonner with the modern GP33-class:

Boat / 1/2-ton / GP33
Length / 9,30m / 9,99m
max. Beam / 3,35m / 3,00m
max. Draft / 1,78m / 2,20m
Displacement / 1800kg / 2150kg
Keel weight / 1000kg / 950kg
Crew weight 600kg 560kg

If you look at these parameters the differences are not that large. But if You look at Sail area....

Main / 27m² (21 @ IOR-rating) / 40m²
Jib / 18m² / 26m²
Spinnaker / 46m² / 136 m²

there is a huge difference.

I´m wondering how these modern designs handle this huge sailloads at conditions above 4Bft. The Leadbulb and the higher Draft will help, but I doubt that these designs will be save at stronger conditions (6-9 Bft, even in the Baltic Sea). Conditions we had to withstand several times in races but also shorthanded (2 People) on longer trips.

I´m really thinking about modifying my boat. Just to see what happens if it gets a bulb and more stability.

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