This is my last design.
By having observed the AMYA boat’s list I found a gap between 41" an 45" of overall lenght.
This model is 43" long with 900 square inches of Sail Area.
I’m told that a Modern design yet with a touch of Classic could appeal some modelers.
I suggest a wooden deck laminated with glass fiber.
This model is supposed to be very fast and stable with the 475mm of draft.
Hull draf is rather low in order to reduce wave drag.
The water plan is somewhat symmetric.
The canopy is suppose to rotate around the mast to hide access to fin bolt and battery compartment. Magnetic chips will be used to keep the canopy in place.
Another version is under preparation with an higher Prismatic Coeficient, beig the actual one, more adapted to medium/low windy conditions.

This model will be the first in row for the construction.

I will be pleased to receive comments and suggestions !


Hey Claudio - Don’t you think that there are enough model yacht classes already? More will just dissipate the attention span and limited energy available in the community. Its hard enough to build interest and to support those classes that are already established. Please, focus on designing the better mousetrap for an existing class.

Niel you miss something, this section is called “New Classes” and not “Old Classes” and therefore thinking that was the right place to insert my design !

Claudio -
to respond to your question - and that of a few others… any size yacht can sail in the AMYA “Open Class” if the skipper is a registered AMYA member. Unfortunately, the “Open Class” does not sponsor or hold any regional or national regattas as a separate “open” class. If the event isn’t “open” and held by an AMYA club, the owner is out of luck.

To become a recognized class - or Class Owners Association - a minimum of 20 AMYA member boats must be registered, a constitution and rules developed with any Bylaws, and the application submitted to the AMYA Executive Secretary. If the class is different enough from other classes, then the AMYA Board may adopt/certify that class as a new AMYA class. Each year the recognized classes are “supposed” to hold a national championship, and again - those classes need to find an AMYA club willing to sponsor and hold the event. If membership of AMYA member boats drops below the 20 boat minimum, then the executive board of the AMYA can have the class removed/decretified as a recognized AMYA class status.

Unlike many other countries, some feel the AMYA has too many classes of same or similar size and type and there is always talk of dropping classes that are minimal in membership numbers, those that may not hold a championship each year and some that are “regional” in nature. Not sure if that will happen or not - but a good example are the number of 1 meter long boat classes - IOM, ODOM, Seawind, US 1 Meter just to name a few.

Let me know if this sparks other questions. As Niel points out, there are only a fixed number of persons interested in sailing, so any new class takes potential new members from the other classes. That is why some marginal classes may come and go.


Hey Claudio,

I agree with you, perfect place for new ideas…I like your design…Kinda similar to a AC hull shape with some slight modifications. I like the idea of the “old meets new” thought pattern. I have seen some real full scale boats that have utilized this idea and are beautiful. They have classic looks with modern technology.

Always good to try new thins!


Hi all,
I completely agree with Dick Lemke post. Now the question is is it necessary? was it required by a number of minimum 20 modellers? if not it is not required.

Tank you Dick,
I’m familiar with bylaws of AMYA and in the past, already discussed these matters around the AC120 with Bill Young that wrote also an article on the Model magazine. Unfortunately no one as exposed yet concrete interest for this model 120cm long.

I agree with you Dick on many aspects, but I’m also of the opinion that many boats design around 1 meter are getting old fashioned or presenting poor performances.
Life change and tastes to and probably new models could answer to new expectations.

I’m also of the opinion, I may be wrong, but the majority of the models built are not used for racing but just for fun and for the double pleasure of the construction and sailing a product selfmade. Since I’m not fanatic about races, often my designs are adressed to these persons that are the silent majority.

How long all these old fashion models will survive ? Many of them are just toys !

Hi Brian,
What is going on underwater is very often already seen somewhere ! Small variations may respond better for the intended use.

Being an ex owner of a real beautiful vintage Dragon all made with maogany, I’m particular sensitive to the wooden beauty.

The 43-900 it may recall some modern and successful real boats when observed laterally with a very sloopy stern and sharp bow, instead when seen from above, the water plan shall recall very fast racing models like some Marblehead or 10Rater.

It could become in future something like the already designed AC33, very fast and powerfull model but probably too big.

The idea to use wood stripping for the deck, like the real one, could be the final touch of elegance. An elegant boat is always nice to see like the Jclass that I adore but too big to !

43" or 110cm, pretend to be a modern looking boat, is just falling in between a 1 meter class and a Marblehead class. Not too big and not too small , just to be seen when rounding a buoy 100mt far away.

Personally I’m very proud of my M, but the design and rules are already 74 years old like me !
The IOM was born 23 years ago and the beautiful 10R class was developed 124 years ago !

I wonder how long a model boat class shall survive the modern technological progress evolution.

The named models were developped when the composites did not existed or just started with polyesters and not many could deal with.

Thinking about performances, the 43-900 is, on papers, I beliewe is more performing then many others existing models, of course all that need to be proven once on the water !


Hi All
It’s a very pretty boat. That alone justifies its existance.

Claudio, really. What a load of ****

The classes you list as “old” have survived as long as they have because they have adapted to and taken advantage of changes in technology and design trends. The original Marblehead bears almost no resemblance to a Scalpel but the latter, being a state-of-the-art M, has its roots in that design and the Class rules that evolved over time to embrace progress as well as maintain some level of uniformity.

These “old” classes are also responsible for a lot of the winch technology that r/c sailors (be they racers or not) blithely use today. As a boy I learned to sail models under vane control. The early experiments with radio were confined to rudder control only. My first sail winch was made locally and weighed as much as a brick. We would rig the sheeting system with wire loops so if one of the limit switches failed the winch wouldn’t pull the mast and rigging through the deck. Things evolve, the Whirlwind winch to the RMG to micro-servos in Footies to the incorporation of cell phone technology for transmission. These were all driven by the desire for a competitive edge. I don’t see why in reference to the existing development classes you “… wonder how long a model boat class shall survive the modern technological progress evolution.” News to you, the existing development classes drive “the modern technological progress evolution.”

Any jamoke with a computer can download a free ship drafting program, noodle around with it a bit, and draw up some lines. It is also really easy to do this and declare that it is a new design that fits in a gap between existing classes, TA-DA! No competition there. So Claudio, that M you are quite proud of, how is it doing in competition? Any wins other than local races?

My point is the same as before. What purpose does this 43-900 class serve other than to divert energy from similar existing classes? Why further thin out the few folks out there who are interested in or participate in our rather esoteric sport by adding another non-distinct clone boat? No gap filling boat has cropped up before because such an addition is superfluous.

Anyone can propose a new class, but the questions to ask yourself first is how does this idea advance model yachting, what is unique about the idea, will it attract other people to further the idea, and do you have enough energy and commitment and years left to promote it? Or is it just a expression of self-aggrandizement?

Nice looking boat! I’m not as fond of the sloped back transom, but if it sails like most of your designs, it should be a winner! Why the knee in the fin?


you are right, except that with your point of view nothing will change for decades except batteries since the servos are now ok .I remember my first model using a self made Braine gear it 1948 some years before the Vane !
Unfortunately there is only one place to be champion ! the others are whatching like me, designers are not necessarily to be a winning skipper !
Ferrari is plenty of design engineers but the racing champion is only one and not every year!!!

Hi Mike,
the rear knee is a feature used often on M class in order to compensate potential loss of surface when the boat is heeling too much
Let says that over 30°, and as a foction of the beam and water depression along the hull, the upper part of the fin, close to the hull bottom, may exit above the water level and therefore creating undesired turbulences and loosing some efficiency. This phenomenon is more visible with larger hull.
My Studio2 in the picture may show that the fin is almost getting above water and this is not good for the speed !!

Hey Claudio,

Keep it up! I for one appreciate all the work that you have done and posted for free on the net…Its alwasy important to take new paths and run with crazy ideas…we can’t be stuck in a world of “old”.


Tank you Brian for the understandig appreciation.
Very often modelers complains because it is difficults to find new plans and, if possible, free. I try myself, as I can in my little, to offer what I can do !
Here below a small sketch as complement of what already told before and representing two areas of concern when dimensioning the main bulkhead.
Some images of existing models and real boat highlighting the areas that a designer shall consider among the other thing !!
Alfa Romeo one of my preferred racing yacht with and without canopy.

Hi Claudio
I’ve noticed that your designs usually have U shaped rather than circular sections. Would you please explain why you seem to prefer this shape? Is there an advantage or is it just appearance?

Hi Don,
Some, not all, have a “U” shape. The recents one use just something in between.
The first reason is dictated by the will to reduce the hull draft when running that in my opinion is more beneficial compared of the small increase of wet surface. Deep draft is the major contributor to create a deep wave and as such to increase the hull drag. Further I noticed that this type of profile render the boat rather smooth during change of direction with almost no speed reduction so far the turn is not very sharp. Second, when the boat is heeled, the “U” shape become a “V” shape that help to keep a better close hauled .
Some will tell you that this shape may help to obtain a planning effect, myself I’m not sure of or at least I never seen such effect so far.

All above become almost a must when the ratio LWL/displacement oblige to search for volume as the model is getting smaller and the various construction weights are predominants.
Larger boat do not have similar problem since the volumes availables are confortables for the construction. In this case a compromise may help to profit of certain advantages as low draft.


PS : Just a sketch to show the shape variation

This is the last issue of the 43-900.
Main changes :

LOA of 111cm and PC of 0.586

This boat should be more adapted to stronger winds !


This late figure correspond to this model.

Claudio - It is still box sections, might as well be hard chine boat. Easier to build that way to get pretty much the same boat.

If this is not a “racing class” then why restrict the sail area? Is someone going to measure a pleasure/cruising boat? Will there be rules so someone besides yourself could design one? Or is this just your baby and a promotional tool?

I still don’t see the point of this. If you just want to tool around on the lake there are plenty of old M Class or IOM boats that are no longer competitive but are still good performers that can be bought at a reasonable price. If you want to put a silly deck house on one to make it look like a big boat, or populate it with miniature deck hands that is fine too. There are plenty of store bought or mail order boats that have the big boat look, Kyosho and others have made a business of it. If you want a building challenge then build a schooner (as in the latest MY mag.) or other classic yacht. But this sort of neither here nor there boat is going to be a disappointment when you take it down to your club and find out that it doesn’t sail nearly as well as the refined racing boats, even the old ones.

Niel -

I didn’t see anywhere that Claudio was suggesting a sail area restriction (I may have missed it, however) - so when I look at his drawings proposed, it seems he is presenting a sail area that might be “recommended” given hull displacement, keel depth and bulb weights. Folks are asking for (free) building plans, and while it might not be a class, he “is” providing something for a specific size that might be of interest to some readers. As I recall, it happened in the FOOTY Class and look where that has taken off.

On a personal note, I would rather see someone build their own boat regardless of the size instead of purchasing a “plastic” one from a set of knock-off/splashed plans that seem to be selling nowadays from Pacific rim manufacturers. At least it is someting you built - not something that you merely glued together. There are a lot of folks that enjoy the build process - and plans aren’t that expensive given final boat value - but free is always nice. Add in the huge number who don’t want to race (Hey AMYA - note this fact) and you can see what is driving the sale of the plastic boats. I do admit th ere is a lack of builders (in general) and this site seems to have a strangle hold on some of the “custom” builders for want of a descriptive word.

For the variety of sizes provided, it seems that the AC120 at least has some sort of following and we see the results of that class as it continues to grow. While this particlar size is new and falling between other sizes, take a look at the size boats Victor Products has provided - surely not much difference between a 24 inch boat, and a 32 inch boat - plus all their other offerings - and some are attracted to what they can market.

If we want to talk classes and types - I am the first to lament the lack of a significant presence of multihulls - but I’ve beaten that one into the ground a long time ago. In closing, let’s stay a bit more positive of efforts to provide building plans/sketches for any size/clss of boats. If they build one of these, maybe the next build might be an M, an A or a J boat.

Who is saying that is not a fast boat ?

The canopy not only is there for a look but serve also to get wide access to the interior.
The mast is plugged into a tube like a balestron rig. The canopy is keept in place by few magnets and can be lifted and rotated around the mast tube.
The underwater forms are the one of a racing boat very stiff when observing the Ratio of 66.6%. The SA is only an average since I assume that can go up to 6000cm² and probably more in light wind conditions. Once built I will be more precise.
If this boat will beat an IOM will be sufficient for me !!!
Hi Dick I appreciate your understanding !