COLUMBIA 1958 Scale 1:20

One drawing replaces often useless words !!! ClaudioD

Added Frames drawings in scale 1:1 .
Can be directly printed to A4 format.


Should be a light wind rocket on shallow waters, where weed could be a problem.

You are right, the basic idea was to get a “Weeds Free” model.
Just because IMO is the most elegant hull with VIM and GLEAM
Since the Sail Area is not frozen, this model with 30mm deeper kell should be good also with moderate winds !

Columbia scale drawing explained :
Scale 1: 20 - General rule
Linear dimensions divided by 20
Surface dimensions divided by 20x20 = 400
Volume dimensions divided by 20x20x20 = 8000

Loa 21.24mt divided by 20 = 1.062mt or 1062 mm
LWL 13.97mt divided by 20 = 0.6985mt rounded to 700mm
Beam 3.60mt divided by 20 = 0.180mt or 180mm increased to 185mm to help volume increase without disturbing the design lines.
Draft 2.70mt divided by 20 = 0.135mt or 135mm increased to 168mm
DSPL 26.2T = 26200kg divided by 8000 = 3.275kg increased to 3.590kg or 3590g
Bulb at model level equal to min. 60% of DSPL = 2154g
Therefore : DSPL of 3590g - Bulb of 2154 = 1436g - this is the weight amount available for the full construction ready to sail.
Sail Area 1846sqFt x 924*= 1705704cm² divided by 400 = 4265cm² fixed at 4200cm² max.- * 1 sqft = 30.4cmx30.4cm = 924cm²

Why the DSPL was increased ?

In order to increase the righting moment of the model, I decided to modify the keel shape as depicted in the above picture without disturbing the immersed hull shape. The keel was made deeper by 30mm.
This modification increased the overall keel volume and bulb weight.
To note that the 60% was my choice since I do not know what was the Columbia ballast real weight. 60% is a normal ballast average weight for this type of models, by comparison one of my 10Rater go up to 75% .
For strong winds it may be necessary to increase the Keel dept in order to add more lead.
This model has little more LWL length then an RG65 that uses 2250cm² of Sail Area and with a DSPL of around 1.1Kg.
Here we have a DSPL of 3.6kg with 4000cm² of Sail Area thus much less cm²/kg, but shorter righting arm !


Two Sail Plans :

The difference consist with the Jib Surface size and percentages.

In this example the SA surface is around 4140cm²

The mast step position will be moved accondigly to the CE .

In this design, the CE is positioned at about +9% of LWL from the CLR.

Multiple mast step socket shall be considered.


Claudio, thanks for the drawings and the explanations!

I like your modified hull, looks better! :slight_smile:

With the increased lateral area, there is less leeward tendency while accelerating.
And you got more rudder area, these ladies need some more guidance thru a dance … oops … tack and gybe :wink: !
(I use a second arm winch to support the helm by the sails)

In a couple of weeks I’ll sail against this fine Lady at Fuehlingen

Last spring she got the blue ribbon, last autum mine was first ship home :slight_smile:

As both are not far away from your’s, so perhaps some numbers:

Regina (Gracia from Graupner):
LOA: 92 cm
LWL: 74 cm
BEAM (WL): 21 cm
BEAM (deck): 20.5 cm
Draft: 13,5 cm
Displ: 4.4 kg
Sail area: 4020 cm² (3400 cm² with a smaller rig)

The white boat above, Weatherly (a modified Hegi Mistral with the rudder attached to the keel and the stern shortened by an inch):
the correct numbers I’ll take at the next regatta, but I believe she is close to 5 kg with a slightly longer LWL.

We use a handicap system with the variables LWL, sail area and displacement.
Both boats come with a factor 0.76 which is close to the limit of 0.75

So with less beam, less DISPL and wetted surface the COLUMBIA should be best between 1 and 2 Bft!

At our regattas you’ll see often reefed rigs with low camber (up to 7% draft)
and we often had a debate why scaled sailboats are more tender than their originals.
(IMHO it’s because of the range of the wind strenght between lulls and puffs (not scaled down) and the viscosity of water (not scaled down either))

So I would use your rig at the left side with the shorter main boom and the longer jib boom.
A wetted jib clew is ok, a wetted main clew is no fun! :wink:

So keep your good work comming!


Hi Wolfgang,
I note that you are an expert with this kind of models.
Also the real 12 and JClass type boats are tender, this was reported by Earl Boebert at the time when I was comparing 12Meter and JClass . These boats have a lot of sail areacompared with the limited draft and probably ballast.
The last AC monohull in 2007, out of 24tons, 20 tons were sitting in the bulb 4 mt below the hull bottom with a ratio of 0.83. Difficult to apply similar ratio with scaled models.
Righting arm is also rather low when compared with a IOM or RG65.

The first Columbia plan at #1, was already a modified one.

Have you ever tried a large jib ?
A large jib should help to reduce ‘nose down’ tendency if any.

With mine I will try to use a jib trimmer.
I’m interested with the “handicap” system, any formula ?

Good Luck for next races

I went searching on the Net and finally found a paper where it is reported that 12Meter have a ballast ratio of 68/72%, thus more then expected and assumed for the Columbia model. This will limit the weight available for the construction !
As an example the EC12 model have a ballast ratio of 75% about.
Assume a total displacement of 3690g and applying a ratio of 68% (2441g), the available weight for the construction will be 1249g
With 65% ballast ratio the available weight will be 108g more !

Hi Claudio, thanks, but I’m still learning and am happy that I hit upon this forum :slight_smile:

Regarding handicap system we use the scoring, you will find in NAVIGA’s Rulebook NS 2013 (13.3.3 - scoring, Site 35)

(I’m happy to use the calculator: )

‘The scoring formula is designed such that the racing value 1 (Rlog) is replaced by Graupner’s sailboat “Rubin”; the smallest achievable racing value, however, is 0.75. A boat with this racing value compared with a Rubin could be 25% slower for the same time limit.’

I modified the jib with a forestay up to the mast top because of the weather helm.
And yes nose diving is an issue on a running when the bow points into the back of a wave. :frowning:

I used a jib trimmer to counteract the lee helm in lulls and weather helm in puffs.
Now I have a jib arm winch and a main arm winch (and three programmable mixer) :wink:


Thanks a lot


It’s been ages since I last checked this site but it’s certainly fantastic to see your drawings for ‘Columbia’, she looks amazing.
Another set of your drawings I’ll be downloading for a future build…



Hi Row ,
nice to see you back.
It may be my next construction in the scale 1:17 instead of 1:20, specifically drawn for my Canadian friends, but the lab is not ready yet.