The return of IOR

12 metre

Super Anarchist
3,939
735
English Bay
To the OP, if you think that stern run was IOR, try again.

View attachment 533938
Ah yes. Liz of Lymington a David Thomas 3/4 Ton. I think besides rapidly closing the aft girth stations he was attempting to get a much deeper than normal rudder - in hopefully cleaner flow off the "bustle" than you would get in a normal extended bustle.

Kind of a handsome boat with relatively low freeboard for an IOR boat of the day. And of course the chines which he incorporated into quite a few of his designs.

Liz plan.jpg
 

fastyacht

Super Anarchist
12,928
2,596
Its been a long time but I remember the chines making a difference due to the chain girth being minimized and this affected your rating favorably.
 

spennig

Member
116
73
New Forest
Chain girth?
That's part of the International Rule (i.e. metre boats). No mention of it in IOR.
There is mention in the IOR.

307. Girth Measurement, The girths required will be chain girths ...

The other benefit of chine was the non-application of radius of curvature rules, e.g. post 1980:
3.2.6 Radius of Curvature
...
3.2.6.2.C.3 Corrections shall not be applied when the sharp radius falls on a chine.
 

12 metre

Super Anarchist
3,939
735
English Bay
There is mention in the IOR.

307. Girth Measurement, The girths required will be chain girths ...

The other benefit of chine was the non-application of radius of curvature rules, e.g. post 1980:
3.2.6 Radius of Curvature
...
3.2.6.2.C.3 Corrections shall not be applied when the sharp radius falls on a chine.
I stand corrected
 

spennig

Member
116
73
New Forest
Is there a copy of the IOR online anywhere? I have looked but not found.
Soon. I recently found my 1988 Red book (or rather Mrs S did when tidying the so called "office", i.e her dumping ground for all sorts of junk).
"Hey do you still want this scruffy old book?" -- "Yes, my assumed long lost IOR book!"

It's going to be OCR'ed into something searchable / internally referenced etc. Probably `asciidoc` so people can generate convenient outputs (pdf, odt, docx, html etc.). Then it will be added to the Github IORCalc repository.
 

kotick

Member
66
9
Catalonia
If you are into IOR, I can look up for my copy of the Green Book for level classes and post it somewhere. My Red Book is in a pitiful state and can not be shown here.
 

Squalamax

Super Anarchist
2,561
87
Ah yes. Liz of Lymington a David Thomas 3/4 Ton. I think besides rapidly closing the aft girth stations he was attempting to get a much deeper than normal rudder - in hopefully cleaner flow off the "bustle" than you would get in a normal extended bustle.

Kind of a handsome boat with relatively low freeboard for an IOR boat of the day. And of course the chines which he incorporated into quite a few of his designs.

View attachment 534052
Put the engine forward of the mast instead of lead ingots! Makes sense in a tortured sort of way.
 

12 metre

Super Anarchist
3,939
735
English Bay
Put the engine forward of the mast instead of lead ingots! Makes sense in a tortured sort of way.
The lead ingots would typically be a last minute thing to measure in at a Ton level as in Ganbare below, which is a bit of an unusual example - or a quick and dirty (and cheap) way to add sail area or some other tradeoff if performance was lacking in a certain area.

At the design stage, the best way would be to move the keel forward a few inches which would have a lesser impact on pitching moment than moving the engine forward - assuming balance is maintained, but I think there was some benefit to moving the engine forward with regards to the EPF (Engine Propeller Factor) as well but I can't recall how or if that was even the case since I lost my IOR book over 30 years ago - so this is all from memory.

Ganbare_lead.jpg
 
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My Glass Yachts NZ built Farr 1104 has the engine right behind the mast, doesn’t seem typical of the production builds. It is great for engine access but needs a lot of weight aft to keep the rudder in the water in some breeze. Probably great with 6 guys in the cockpit……. less good with 2-3.

There is also noticeable turbulence in the helm feel while motoring but that may have more to do with the rudder then prop placement.

2B58453D-A6B4-439D-908D-43531E878BF3.jpeg
 

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