Another RG Hits the Water

At the Vintage National Regatta in mid-September, I lobbied Al Suydam hard about building an RG65. Al is a former US1M champ and teaches model yacht building at the WoodenBoat School. So he goes home and whips up this Palo de Aqua. Impressed with how it sails, now it gets its fancy paint job.



Earl - took another look at the photo (enlarged) and “Man” is his mast well forward of the leading keel edge. Any idea what that dimension is? I tried scaling by using other parts/known sizes and it just seems — well ---- like a “lot”.


Not offhand, but it looks consistent with the plans (which are on the CD).



Hi Dick and Earl,
me too, I was surprised with my first CD65 Tuning where the lead was much different from the one I was generally using for my M class.
After all, the answer was coming from the water side, until some months ago, it happen to consult an Italian book, actually not in commerce, written by S. Crepaz. I was very interested on this figure that I have elaborated in order to include the RC models common ratios Bwl/ Lwl.
I let you to take a look and make any comments including my interpretation on the basic diagram curves.

As already explained, in another tread, the short and wide boats have also a short “radius” and once tilted thay requires more Lead to compensate.

This annexed diagramme bring the “proof”.

Oviously, as many others parameters adjustments on sailing models, are resulting from osservations and the solutions applied to de big ones , is not proven to be good for the small ones.
Nevertheless is worth trying this diagramm and eventually adapt it to the personal experiences, as a matter of fact, will be nice if the readers could tell and mark on the diagramme the lead they use specifying the hull sizes at water level.

I have made a separate diagramme dedicated to the Sail models


This is the elaborate diagramme based on the previous drawing.
I assume that others may either confirm my assumptions either contest. I will be glad to receive comments on the subject that, I believe, concern everybody.

My CLR are all obtained with the carton and pendulum, the Bulb is not included, some consider 1/2 surface for the Rudder, some others do not consider the Rudder surface at all !! All magic numbers !


usually I use something around 10 mm distance from mast to the leading edeg for the keel, which is approximately 15% having a width/length ratio of around .24. For swing riggs which are using significantly smaller jibs the right place is approx. 20mm more towards the bow.

Hi Haegar,

something I do not understand : 10mm is equal to 1.5% of an RG65 of 650mm and not 15%.

If the ratio is 0.24, then the Lead : CLR - CE , should be, in accordance with the above diagramme, 10.1% of LWL = 65.6mm + the distance CE - Mast.
All togheter, the mast step, may fall around 73mm from CLR

Please correct me if I’m wrong ?


Seems this is an interesting topic. I keep getting confused, as much of my past “life” has been with multihulls (catamarans) with very long length to very narrow hull width ratios. It was my feeling/thought that the relationship between our boards and our mast (fore/aft) was more or less a fixed distance, but the actual location on the hull was not of prime concern. To explain what I mean - is that the lead between board leading edge and mast location remains the same - but can be shifted further astern to push the ballast (skipper/crew) further aft - and in a sense “adding” more bow length forward of the mast. When I looked at Al’s photo - the keel location appears further back that what I would consider “normal” for an RG-65, but the mast is well forward - and close towhat I would guess the other design locations are.

What I think I will try during Christmas holidays - is to print the photo of Al’ss boat on transparency material, and print other photos that I have or can locate - all to the same scale size and try an overlay. This would quickly identify designs that are “different” from the norm - whatever that might be. I am trying NOT to dilute the discussion between wide boats (monohull RG-65) and narrow hulls, (multihull RG-65) since the multihull has very littel change to underwater (waterline) shape as compared to a monohull when heeled over. Both get narrower when heeled and longer (evident with older designs with long overhangs that pick up waterline when heeled to one side) but I am guessing the relationship of change is much less for the multihull.

Claudio - in your chart, I suspect that it is relative only to a monohull, as when it heels, it begins to add weather helm to a degree. This is practical knowledeg as when sialing a dinghy, allowing it to heel over also allows it to point higher in my experience (to a point). With the amount of difference between Al’s keel and mast locations - my first impression would be that it would be very much a “lee helm” boat. It is fascinating that the physics of sialing can be so inclusive - and at the same time be so different and unique.

I need to do some measurements of my own - althought as Achim notes - I have confirmed the more forward location of a swing rig compared to a conventional mast/rig. My own boat under construction was considered for a swing rig, but only for the reason of appearance, I elected to stay with a conventional rig and not have two mast hole locations. Will save that for a later build.

Sorry for the blah, blah, blah (above) - just trying to relate to overall design and locations of CLR among both mono and multi hulls.


Hi Dick,
first, in my proven ignorance on multi hull, I heard that the 'LEAD" on this type of boat is most of the times “Negative”, in other words the CE is behind the CLR.

In view of the published diagramme I went checking my past models and adding them. The actual dots does represent the Lead % used. The ones below the average, were in fact resulting weater helming and the one far above the average line, were tested for too short time to be confirmed.
For the future constructions I will stick to the diagramme, ready to change the curve if necessary , hoping the help of some others to create a valid starting base bank for our tunings.


A complicating factor may be the severely unbalanced hull form (very narrow bow, very wide stern) which would require extra lead to compensate. The issue of hull balance was discussed here in a long thread called “hull design.” The attached paper covers the basics.



Very interesting Earl, but this document seams to me being referred to old design concepts not used anymore.

Obiviously all it is empirical, because nobody knows really what happen, since too many variables are playing different roles ! This is reconized in all conclusions of this type of papers and books.

I still believe that a Data Bank may be of great help to many modelers.

The modern hulls with narrow a long fin do obbey to another standard of tuning.

If you compare 2007 America Cup hulls and 2008 Open 60, they are totally different design concepts, the first may use Prismatic Coefficients above 0.60 while the seconds are below 0.57 just to mention one parameter.

Hope to get some help in collecting valid Data.

Thanks for the Symposium paper .


Well, my ABQ65 design has a BWL/LWL ratio of 0.18, and a conventional sailplan with a 30% jib. It tracks perfectly with the mast about 1 cm ahead of the LE of the fin. This has the added advantage that it puts the mast aft of the LCF which appears to reduce the tendency to dive on the run.

The hull is based on the student design in the paper.

Admiral Turner’s explanation of why his method yields balanced hulls is highly suspect, but the empirical evidence is overwhelming that its application yields the desired result. Nobody really knows why.

Also, while a balanced hull is a pleasure to sail, there is no evidence that the property, in and of itself, correlates in any way with speed. It is also worth noting that the America’s Cup boats are designed for windward/leeward work while the around the world ocean racers are optimized for long reaching legs.



I tottally concurs with. Stiil I found difficult to mix reals boat solutions and RC models. The need for balanced hull, is a well knone design concept to the old guy like me.
I raced several years with a very tecnical boat as the Dragon, where a little weater helm is a must, just to fill on the rudder stick a low pressure to avoid loosing speed. This low pressure was in the order of 3-4 degrees.
Actually our models cannot use this filings and the RC is just blind. In the past we where used to control the balance checking the in-out wedge between 0° and 30° and keeping the CB closed around 0.5%. The good balanced hull was generally the winner, today all that is lost unfortunately. Thanks to the Vintage amateurs, too keep alive the “savoir faire” in designing the Hull.

Just to let understanding of what we talk about when referring to the “Lead”


Sorry for mistyping - the dot was missing …
of course, 10mm are 1.5%

I just recognized, that we are discussing different things. The thread started with the distance between keel and mast (which I was referring to). You are talking about the distance between CE and CLR which is much larger, of course.

Sorry for the misunderstanding

Don’t worry Joachim,
the point is that the leading edge of the fin is not a good reference point since varying from model to model.
Please see this drawing, specially made for you, and observe the variations between the 2 models.
The only difference is that on the model B , the Fin is recessed by 14mm.
In spite of that the distance from the LE of the Fin and the back face of the Mast, passed from 10mm to 20mm !
The mast itself moved backward by 5mm.
All that to demostrate that the Fin position may change and affecting all the rest. The two boats may behawe equally well.


I think I understand what you mean. I think, I should try to recalculate my own experiences.

What you figured out as difference between the two models is lying just within the different mast positions I usually plan for my boats. I usually have three possible mast positions 5, 10 and 15 mm in front of the leading edge of the keel. Up to now in all cases the middle position was fine for sailing in moderate to fresh winds. For light wind I could use the most afterward position.
So far you confirm my rough estimations - thanks!

Joachim, I’m happy for you , but this is ok for the actual hull you have. Slight change on the Fin position or hull form (BWM/LWL) the Mast position will change too. So far, you reconize that the important thing is to identifies first the CLR, all the rest come out almost automatically.

I’m wondering if that sail plan has the CE well back from the mast. The main has that large roach and the jib is smallish(maybe). If I squint I could imagine the CE being maybe halfway between the mast and the LE of the fin. It must be something like that or I don’t think that boat would go upwind at all(exaggeration)

RIG-1 for IOM not for RG65 , sorry

My RG’s all have their bow tangent with waterline, the sails CoV is set 12% L forward of the CoD of the appendices (rudder + keel fin only).
My first RG had a “5.5M” bow (well over WL) and needed a CoD much forward of that…