This is the new drawing made following the “reverse engineering” technique. Dimensions, form, and shadows are copied from the foam hull cutting.
Calculations are in accordance with above new drawing.
…
ClaudioD
Preparing the dual molding jig.
The ‘mask’ is printed and bonded on the plywood plate.
First operation is the ‘mask’ cut out and adjustment and second is to fix the mask on the supporting jig.
The Mask form is obtained by telephoto as to reduce, but eliminate, the parallax errors. The picture obtained is scaled to the real dimensions previously measured on the master.
The observable imprecisions will be corrected with carton cuts.
ClaudioD
Nice distribution of areas, Claudio.
Thanks mudhenck27.
The jig is ready for waxing !
I need to order the molding gelcoat
ClaudioD
Claudio, I am curious about the reversed prow. Have you found some advantage in doing this? I have noticed that one of the other Italian boats has this feature, but that boat has the objective of maximizing length by fitting tail-down in the box, which does not appear to be your objective.
Hi Walt H,
this is my first Footy design, never built one before therefore I cannot tell if it is a good idea or not, just funny fashion style !
According to some INTERNET readings about “reversed/piercing bow” I’ m curious to see the outcome if I’m able to make one !
ClaudioD
PS : just pushed a little further !
…
may be like a ‘toilet soap’
About Swing Rig on a Footy.
Because the overall CE is moving back due to the Jib swing compared to similar situation offered by the Classic Rig, it is necessary to compensate the centering/tuning, with the shift of the the mast step toward the Bow.
How much this shift is quantified, is matter of testing.
Since my experience in RCmodels is coming from the Marblehead/Class M, I remember that on that class the difference from Classic Rig to Swing Rig was about 55/60mm. Assuming, by analogy, where the M was 1280mm long and the D-Footy is 324mm long, I would assume that proportionally the D-Footy will requires : 32.4/128 x 60 = 15.18mm of shift for compensation with respect to the Classic Rig.
This of course is the “rule of thumb” that need to be verified on the water.
With the example of Sail Plan where the CE is at 35mm from the back side of the mast, I should add the additional 15mm .
According to my method* of centering the mast step shall be at 35+15 = 50mm from the fin front edge.
- the CE on my models is passing from a vertical line adjacent to the fin front edge +/-5mm. Others may have different methods.
Important point to note is the ratio of the jib surface of 25% of the total SA. Larger Jib percentages will produce negative effects.
CD
Claudio, since the fin chord is likely to be a different % of LOA for different boats, would it be more consistent to measure the CE from the LCB, rather than from the leading edge of the fin?
Bill
Hi,
Yes of course !
My projects do have the Fin max chord thickness aligned with the LCB already and this is why the Fin front edge is my actual reference.
ClaudioD
7 wax coats added, this is the last picture of today !
Gelcoat ordered, should arrive soon !
ClaudioD
…
Gel-coat arrived yesterday.
This morning started the mold lamination (1/2 mold)
The pictures shows the thick gel-coat layer and the glass tissue patches ready.
ClaudioD
Lamination completed with glass fiber tissue and epoxy :
3 x 100g/m²
2 x 162g/m²
3 x 280g/m²
ClaudioD
Claudio,
Good progress!
Just out of interest, what’s the red tape you’ve used to cover the mask part of the jig? Also, was it necessary to seal the mask to the plug so that when the gelcoat was applied it couldn’t ‘run’ between the two components?
Regards,
Row
Additional: Is there any reason you’ve used woven cloth rather than a powder bound chopped strand mat for mold production?
HI Row,
How is going your back ? Hope is getting better every day !
Yes the red ribbon is a PVC material that often used on real boats to mask the water line when painted on the hull.
The tape is sufficiently elastic that allow to follow rather well the hull contour. As you says, it is done to avoid gel-coat passing trough.
This tape do not adhere to the epoxy resin although covered with wax.
The model dimensions are too small to make use of chopped strands, I preferred to use light twill tissue to match the sharp corners.
Tomorrow I hope will not present problems with the separation since no treatment made on bare wood except wax.
Cheers
ClaudioD
The first 1/2 is made.
The separation operation will be done after the second half molding.
Now will start the second wax application
ClaudioD
One possible method to join the 2 half laminated hull.
May be possible that the balsa stripes are not necessary and relying only on the charge resin on the edges.
Another sketch in preparation - done with the meniscus method
ClaudioD
The second half mold lamination is started with the gel coat application !
Standby for 45 minutes before glass/epoxy lamination.
ClaudioD
Hi Claudio, which method of joining the two halfs are you going to use ?
I was thinking about application on larger hull size, it will be quite balancing act (and messy) applying epoxy to both edges and then lining the two halfs together while bolting the moulds together.
Just an idea that may already be used (I’ve not seen)
As you need hatch to install servo’s etc, would life not be little easier if you cut hatches out the female mould then could use 3rd possibilty laying wet FBG strip over the joints while two laminated halfs are inside the mould, further could introduce something like rubber ballon that can then expand inside the the mould to have even joint pressure while it cures ?
Cheers Alan
Lamination of 2nd half mold completed !
Standby until tomorrow (24h)
ClaudioD
Hi Alan,
honestly I do not have decided yet since, as you says, it will be the test-bench also for the 1.2.3. rounded hull, the one you have seen in my lab, and abandoned because too heavy.
It may be that I will initially fix/bond a small fiber strip/edge all around the profile of one of the two half and then joining/bonding the two parts with the mold as a guide. This argument was already treated in the 123 tread.
Cheers
ClaudioD
Hi Alan, your idea is completely according to the normal working in making this kind of molded shape.
The “closed” shape released inside a hull is a common technique utilized to make glider fuselages.
This technique is described on www.baronerosso.it about the construction and “duplication” of mine Urca footy at this link
http://www.baronerosso.it/forum/navimodellismo-vela/228245-come-copiare-uno-scafo-5.html#post2945912
http://www.baronerosso.it/forum/navimodellismo-vela/228245-come-copiare-uno-scafo-5.html#post2958571
Here a quick translation
This technique is described in detail in the manual Schaller “Epoxy resins, why and how” that is given together with a purchase “minimum” of material that I recommend to anyone who wants to get to mess with resins, this:
http://www.schaller-compositi.it/ecomm/site.php?mode=DET&idp=1197
On one side of mold, skins are trimmed flush with the edge, the other is left overflowing 5-10 mm.
As an alternative to overflowing tissue is trimmed on both mold halves and applies a strip of fabric that overflow on union; the 2 methods are similar and have advantages and disadvantages, more or less marked depending on the dexterity and shapes of the mold
In areas with narrow or small radii takes a bit 'of thickened epoxy flush with the edge of the fabric to replace that hardly follow fine folds and small radii as those of the bow.
Now lamination is completed: it rest to brush fresh resin (it is better to prepare a few grams of fresh resin) across the seam.
At this point the two mold halves are approached onto the plugs and separated with shims, goes inside the rim of tissue that comes out from the mold and then closes them.
All that remains is the final step: argue the edge of fabric “excess” on the fabric laminate in the mold adjacent through the openings with spatulas and rollers and then expect that … chemistry do the rest.
After at least a couple of days the mold is opened and the finished coving the hull that will present more or less small imperfections on the junction area as a function of the precision of the molds and of our ability to refute the fabric of union and the precision of the side trimmed.
A ballon inflated inside the mould could help in obtaining a good “closure” of the hull with less imperfection on the joint line.
Of course is necessary any opening on the mould to go inside with spatulas/rolling in order to push the fabric for union against the other side of mould… but any opening on the hull are anyway necessary to work inside and place RC system… so is sufficient to project everything before making the mould of the hull like you see on my Urca footy mould.
bye