AZUR a New Class M - Marblehead

Apparently in Europe the Class M appear to show some interest again after several years. It is my opinion that one of the reasons that created the loss of interest was due to the increasing costs… etc.
Now I decided to design the AZUR-1 that I will present here :

Mast “rules” and construction …

At first, appear to be similar to the 43-900. A close loock shows that the only semblance is limited to the wooden deck and sloped transom.
In this design I have favoured the reduction of wet area.


I am going to the opposite direction. My M class length boat is proportioned close to a VOR70.
The idea is to be able to plane in all directions. I think I have succeeded expecially in running reach, over 4.2 knots( hull speed 2.6knots)
I really had fun with this project


Me too Gerald,

This is the new version of the AZUR, being the AZUR-5.
In this design I enhanced the “close hauledl” course by developping a narrow hull and deeper Fin while reducing the overall weight by using a 3000g Bulb.
I suppose that by reducing wet area of the hull, I could transfer that area to the Fin for better effinciency.
Being the Sail Area the same, I also assume that a fast boat in “close hauled” will gain sufficient margin to deal with the Run and Reach. The Bulkhead surface is rather low therefore producing less drag.


Here another Plan adapted to internal waters with a lower Prismatic Coeficient


Last version of the Class M - AZUR serie including shadows in scale 1:1 ready for print

PS :
The scale 1:1 plan is ready .
It will be cut out from polystirene blocs.

Tanks to the jpparisy remark, I modified the Sail Area from 7200m² into 0.7200m² or 7200cm²

A sail plan of 7200 m² is perhaps a little too largest ? (See AZUR-8.pdf) :devil3:

Very nice work, Claudio.

As I understand, do you’ll use the same construction technics as the Fuxia65 and Trap65?

7200 cm² is just the same as the specified 0.5161m² for the type A set…

Why ?

Simple, the 5161 cm² is only referred to the surface of the fore and main triangles.
The additional surfaces coming out from the formula calculations, provide, for a Type A rig, a surface very close or even slightly above 7200cm²

It is very common to call for 0,5161m² because it is in the Rules, but the reality is another story !

Yes I will use for the prototype the same construction with polystirene panels. The orange are better then the blue ones

Here below a bad copy from a book of mine - the yellows marked surfaces are the one corresponding to 0.5161m²


The pleasant job is just started !!

This time I will use extruded polystyrene foam . I personnally prefer the yellow/orange because appears more consistent for manual sanding. The blue one is breaching more easily.
I’m not sure for, but I think that the blue one is called Styrofoam from Dow-Chemical and the yellow/orange is the Polyfoam from Knauf Insulation


The importat part consist in the preparation of the foam blocs
Tracing line limits need to be accurate in terms of position and lines orthogonality. Most of the final results will depend upon.
Next delicate operarion will be represented by the cutting following the marked traces , noting that the two bloc cutting should be rather the same !!! and really I’m not sure yet .
Two blocs are used since the cutting height of my band saw is limited to 12cm while the model is 14cm on the highest point. The actual foam blocs are 8 cm thick.


Cutting set-up and sequence.
Important detail, the working table shall presents a ‘Slippery Surface’ for better sliding control .

Next step will be dedicated to the shadows printing.


Gosh !

I got some problems ! I discovered that the panels thickness is not constant all along the lenght and this cause some adjustments problems once cut and separated and reassembled again. Very funny for an ex Product Assurance Manager in Aerospace industry !!!
The basic idea was to put two panels one above the other and cut each section and glue the prints that will serve as guide during sanding.

Now it is necessary to re-cut all blocs rectifying the thickness to 80mm when possible and still use the separation line of the two panels as such to be 30mm above the LWL of the shadows.

This is a WARNING for those would like to use this economic method to produce an Hull. Please check before the panel’s dimensioning and straightness because some may be also not plane but curved !

Checking again !!!

The reworking is completed and each single shadow bloc is bonded with 5’ epoxy


An important remark !
The paper shadows template will be aligned and glued with epoxy on each bloc .
To avoid sanding problem later is better to spread the epoxy resin inside the area leaving an edge of about 5 mm free.
This is due to the fact that once the resin is cured and all blocs assembled, the surface onto wich starting sanding will be only polystyrene without interference with hard polymerised epoxy.
Meeting on the sanding surface the hard epoxy and soft polystyrene will render the work almost impossible to reach a good finish, this is why the epoxyed surface is limited as in the drawing below before final assembly on the bloc.


the polystyrene blocs assembly work is almost complete , still 3 glueing to make.
The gross excess has been removed simply with the cutter visible in the image.

Claudio and others considering -

from my experience with this method, you only need glue between foam sections to keep alignment. Glue can be any glue, waterproof or not. I use either Elmers “White” glue, or Titebond Carpenters Glue - which ever is handy and use a big dab in center - not out to edges to allow easy sanding as Claudio has suggested. One of the guys who has built a 48 inch/1.2 meter multihull using this method used a dowel to keep all sections in line until they were shaped and glassed. Just a thought. Remember, all of this is covered/protected by epoxy/glass - and if you intend to “melt the foam” out of the glass hull covering, you want something that will disolve with acetone, gasoline or any other liquid that will cause foam to melt. Epoxy will prevent foam melt.

Hi ,
to glue the various blocs I used 5’ epoxy.
Some progress with the cutters.
The antipatic thing is that all the residues are stiking every where due to electrostaticity !


Here after a couple of hours of accurate sanding from 60 up to 180 grade.
Remain to mark the deck line and removing some material from the bottom to facilitate the dropping of the tissue.
The polystyrene work started 5 day ago, certainly an M class hull is much more time demanding then an RG65.
The surface status is good for glass/epoxy lamination.

Cutout the foam excess above deck line and replaced by smaller supports to separate the mockup from the base plan in order to facilitate the lamination. (tissue drop)
Marking completed for deck line, water line, fin slot position and rudder strut position.
These marks will be visibles under the glass/epoxy lamination.

Next preparing tissues layers : 1 x 105g/m² and 1 x 80g/m²


Lamination completed !

Attention !!! the amount of epoxy resin required is about 75% instead of the usual 50/50 %.
This is due to the unexpected polystyrene absorbtion !


Polymerisation process completed.
Small indents of picture 27 are absorbed and not visibles anymore, instead few finge’sr compressions and others small indents need repair with polyester filler. see pics .
Soft sanding completed pics 38 , just before paint undercoat.
The following step will consist of undercoat white paint.

It is the intention to avoid the use of wax and cover the hull with packing tape.