Hi Symont, the laser is only 2 Euro item from local hardware store, it’s quick, easy and accurate. I’m using 4 mm ply for the frames and they do move when putting stringers on, especailly when they are only snug fitted onto the building board as I do, this is the only reason to recheck alignment.
After laminating I cut a second set of frames (female) that I use them for cradle of the hull to lay in while fitting out and I use same building board for the mould and the cradle frames, hence I just pop-off the mould from the building board and drop in the cradle …it’s that simple !
Just to boost your confidence in achieving target weights etc. When I laminated the hull for Enterprise my final target weight was 575g. Having made the most horrific and fundamental cock up, I ended up having to use quite a lot of fairing compound followed by an arm aching amount of sanding. Anyway, the finished weight was 618g - about 7 % overweight - which for a first attempt I felt was more than acceptable. If you’re careful & take your time I see no reason why you shouldn’t achieve a basic hull ‘shell’ weight that’s reasonably close to Claudio’s weight budget. Don’t know if you’ve laminated before, but if not then cut a few scraps of glass cloth and practice - get a feel for what is required so that it looks right, any of the build logs from the seasoned builders here will give you plenty of pointers along with Youtube & google!!
Ah the cast iron Jib trick I believe the picture your talking about is without sponsors logo’s, suggesting the boat is no longer a racing machine & possibly in private hands, hence engine was fitted for obvoius reasons.
Claudio I’m thinking about the wet surface area in regard to appendages, when looking at full size boats from AC 32 first thing that strikes me is their low aspect (short) and narrow keel fins with very long & thin rudders.
In comparison to NZL-20 plan it is the opposite with very wide & long keel fin and with shorter wider rudder ?
My question is how narrow can we make fins on RC model to reduce wet surface area ?
The best way to learn easy is to cut a piece of glass tissue , let say of 100g/m², 30cm x 30cm and weight it on precision balance. Prepare the quantityt of epoxy resin of the same weight of the tissue, based on the rule 50/50.
Lay down the tissue on a window glass or plastic film and start brushing the resin on the tissue just the quantity to get the impregnation and transpency without execeding with the resin. If the job is well done, at the end all the tissue should appear regularly impregnated and no resin left in the pot.
Heavier glass tissue like 260g/m² absorb more resin +5%.
Carbon tissue absorb +5% more resin
Kevlar/Aramid absorb +10% more resin
The AC120 hull will be laminated " wet on wet" with 3 layers of glass tissue of 100g/m² or 4 layers of 80g/m². Finer the tissue lesser microholes later, higher rigidity because of multiple sandwich layers within reasonable weight.
Much better 3 layers of 100g/m² then 1 layer of 300g/m²
Twill tissue is more adapted to curved hull forms like the J-Class, while a normal tissue is very good for form like the AC120, Class M, RG65, IOM, etc
Hi Alan,
First of all the efficiency of the fin and rudder increase with the aspect ratio , therefore a long rudder is more efficient of a shorter one with the same surface, similarly for the fin.
Two remarks , slim rudder for models are fragiles, better to use an elliptic form. The fin shall be strong and wide enough to sustain and reduce torsional effects induced by the bulb oscillations triggered by the changes of direction.
My copied rules of thumb suggest the following :
Appendage Fin & Rudder = 5.5% to 6.0% of Sail Area ; and < 5% if medium/strong wind
ie. 7800 x 5.5% or 6.0% = 429cm² or 468cm²
Again this surface is split as 3/4 for the Fin and 1/4 for the Rudder as : 429/4 = 107cm² for the Rudder and the reamaining, 107x3 = 321cm² for the Fin
With larger or smaller Sail surfaces , the appendages will be over or under sized unless are changed according to méteo conditions expected.
The best choice is the one that produce, comparatively with others boats, less drift in close hauled and less drag and speed loss when running
The form and shape of the bulb is part of this game.
Ok then looking at you bulb comparison post # 37 showing how to save 10% of the wetted surface, I would clearly go for the bulb at length of 239 mm.
I have only one blank bulb that fits width of 53 mm but it is asymmetrical with height of 43 mm, which I like as it lowers the C.G (better righting moment)
I can shape the tail of this blank bulb to beaver tail (red out-line) to maintain shorter 239 mm length to redistribute the weight for the asymmetric shape.
I note the maximum foil thickness of symmetric bulb is @ 39% of the chord length, the furthest forward I could have maximum foil thickness on asymmetric is @ 45% of cord length.
Would I still be able to maintain 10% less wetted area ?
Slow progress !!!
By checking here and there the regularity and roundness , I found few places where the strip did not adhere fully to the shadow edge. Probably due to overcutting and sanding. A small piece of paper fill the gap !
ClaudioD
My balsa had not arrived as promised & I was raring to start so I tried a long shot by planking a whole sheet of 3mm balsa below LWL where there are no tight curves, little stream to help shape it to frames perfectly and it worked ! saved a few strip planking hours & some sanding
Laid the sheet from bow to frame #9, thereafter the curves are too tight same as below the LWL hence I will use 3x5 mm balsa planks when they arrive !
I see a new sport on the horizon - speed planking!!
And of course lateral thinking - congratulations
Regards,
Row
Edit:
I was looking at your Black Magic build log again the other day and wanted to ask about the carbon foam sandwich you were using for internal framing etc. Is it a sheet that you buy ready made or do you laminate it yourself? If you do, what sort of layup schedule do you use? Cheers, Row
Although the cost is fairly astronomical, would it produce a stronger & lighter hull - I’m thinking along the lines of 4 x 90 gsm giving an overall 360 gsm instead of the 400 gsm ? Row
Hi Row, I’m working from my netbook on train heading home from Northern Germany, so hope internet gets this message through.
Q1. Carbon foam sandwich, is self made using 3 mm stiff high density foam with 1 layer of 200 CF each side (off-cuts from hull cloth) covered with peel ply and presses between A4 Perspex sheet for flat surface & easy release. Peel ply adds textured finish to CF for improved epoxy bonding.
Q2. Hull cloth weights…hmm NZL 32 was roughly 500 grams under-weight and I consider that is too light and that much free ballast is ridiculous, I would rather build NZL 20 so that she has just the right amount of ballast (110-120 gm) so I’m trying to work-out where to add weight in the construction and hull is good starting point hence I will probably use 2 layers of 240 gsm CF this time.
I have attached my rough calculations of weight budget using previous build as reference, still need to work out where to add extra weight. Using Graupner regatta winch will add another 50 gms and maybe put the rest in the deck or around the keel box…unsure yet.
You sound like your building this hull too, is that right ?
Claudio you have done much neater lay-up of planks from frame #9 to stern by using apex of frame curves as starting point, than I did … I have fanning angled overlap of planks on the stern frame, which I kicked myself for doing as I only did it to avoid having to make planks over 100 cm…:rolleyes:bugger !
Hi Alan,
your observation is correct !
I first fixed a strip joining the stern with the apex of frame 0 by triyng to let the strip taking is own curve direction. I this way I split the planking surface in to separate areas, lateral and bottom.
The image show better the idea. Sorry for the artificial light !
In your budget I noticed that you included the rudder in the “3000g” of the Rules. Is not what it is required, the 3000g refers only to the FIN + BULB only.
Personnally, as written several times, multiple layers of tissue help to obtain a rigid body by the self sandwich effect. 4 layers of 90g offer better strenght then 2 layers of 250g and not only, because the 90g tissue is more compact and the multiple layers assembly help a lot to reduce leakage and “craters” formation.
Ciao
ClaudioD
No, not building at the moment, really struggling to get any quality workshop time at the moment & really want to get Enterprise finished before I move on. NZl-20 is certainly on the cards for the future though, mind you so is the CD-43 - sometimes wish Claudio would stop designing for a while so that I can play catch-up !!
Many thanks for the info on the carbon foam sandwich - I’d like to use something similar when I get round to fitting out. Like the look of your weight budget - how does 249g compare to other AC120 internal ballasts? Perhaps a bit of the spare could be used for additional lamination around the hull where the fin box is and then dispense with the diagonal shroud load rods and go for a pair of ring frames at either end of fin box? Perhaps not really necessary from a structural viewpoint but it would make it bomb-proof…
Thanks Claudio …that was Friday brain drain error, chart now changed & added another 40 grams
Row the chances of catching up with Claudio designs is nil my friend I try and not look at his new design postings but it never works and always end up having a peek and now have whole draw in my filing cabinent dedicated to CD plans !:lol:
I’ve have never asked others about their internal ballasts so I don’t know sorry, I think some run over regulation weight looking at the active LWL for various reasons.
NZL 32 Keel/Mast box with diagonal load rods is not showing any signs of weakness so far, but with NZL 20 I will be using foiled CF mast that has more lateral flex & needs higher shroud loads to keep mast in column, so your idea is a good idea worthy of more thought, thanks.
I believe the picture your talking about is without sponsors logo’s, suggesting the boat is no longer a racing machine & possibly in private hands, hence engine was fitted for obvoius reasons.
I try and not look at his new design postings