Thankyou Claudio and Dick, very interesting subject, your posts assist me in my own mast configuration decisions greatly. Dick, I would be very interested in any analysis you could dig up.
By the way Claudio…I applaud you for your innovative ideas presented in this thread, It is the most educational yacht building/ design thread I have seen in years…and you word your lessons so the novice can easily understand. Thankyou again.
Gary
I appreciate Gary, it is my pleasure !
Claudio
Gary, the ‘pro’ for wingmast use (and solid wingsails for that matter is simply efficiency - for a given area a well designed wingmast rig will generate more lift. As Dick has said, the mast alone (without a sail) can be sufficient to drive the boat.
However, this last point is also a potential con on full-size boats where you can’t simply remove the mast and pack it in the boot of the car at the end of the day - at a mooring a wingmast will still generate lift and that can be destructive, which is why you tend to only see small chord masts (i.e. the mast is only a few percent of the total rig chord) Other cons are that wingmasts are more difficult to build and weight (aloft) can be an issue.
I disagree with Claudio on oval sections being more efficient than round for a fixed mast. If I were using a fixed mast I would go for a round section but allow the sail to rotate about it by using a pocket luff of rings, not a luff cord or sliders.
For what its worth, I’m slowly working on a wingmast (and wingsail) for my cat and I think I have it sorted well enough to take it to the next stage and actually build one. The chord of the wingmast will be ‘significant’ and I think I’ve worked out how to build in some twist as you go up the mast. My main concerns are around the weight/strength compromise.
Ray
That’s a very interesting teaser Claudio :tapedshut I started making my own sails quite some time ago, just to learn about sails shaping to get enough knowledge & experience with the idea of making a wing mast & sail for my 1 metre, I was inspired by what I saw these guys doing.
http://www.harborwingtech.com/faq.htm
K1
Ray,
you may be right, I reconize that it is a very interesting argument, but Out of Topic.
The title of this tread is : " ETNZ IACC120 Dual build…
I would suggest, to all interested, to consult the tread “Building a Wingmast Rig” you have already initiated under General Discussion > How to ?
Thanks
Claudio
Claudio, agreed, I don’t want to divert attention from these builds.
The previous thread you mention was seeking info, I’ll start another thread when I’m ready to go.
Ray
Perfect Ray, I will follow you because I’m also interested
Cheers
Claudio
Hi All,
Just another interesting source of informations :
http://www.modelyacht.org/my/mysample.html
Can be downloaded
Cheers
Claudio
Hi All,
Fin box composite version is a success :bouncy: for construction used 1mm high grade aircraft wooden sheet and laminating 150 gsm FBG using Perspex lamination method for high gloss finish to inside of the box to allow for easy slide in of the fin & waterproofing. Weight at this stage is 27 grams. Further requires outer layer of FBG and I will put an 1 mm alloy plate on top of the fin box so that is more durable for the fin bolt sliding in & out of the box.
Yesterday I made up a sub section of the hull off the mould and mounted it in the cradle to make sure I get this fin/mast support assembly right.
Claudio, I’m now planning construction of the entire fin/mast assembly and come to the point of chain plate positioning for the shrouds, I’m thinking of having two shrouds (upper & lower) and have marked the “0” position for the mast luff edge being 652 mm from the stern as per the plans.
I have always had shrouds on my boats directly abeam of the mast (no forward spreaders up the mast) and for AC 120 thinking the chain plates are about 30 mm apart. Looking at the transverse beam & the “0” mast position line I’m unable to put chain plate aft of the line unless I widen the widen the beam at the sheer line by another 20 mm, is this ok ?
Further, we need to allow for the thickness of the deck when making the assembly, are we going to be using 4 layers of FBG again or do you recommend laminating FBG to sheet wood?
Cheers K1
K1
I put again this drawing that include all the important dimensions :
…
This stand for a Sail Plan of 74dm². Note the CE distance from Mast Luff side.
Because of the Mast Rake of 1.5° , the Mast Step is 75mm ahead of the CE vertical.
If the boat will show too much Weather Helm , than a Lead of 10% or even 12% could be used.
From 8% to 12% there are about 4cm, this means the mast could be displaced in the range of 4cm.
Actually the distance to the mast luff is 692mm and 1012mm for the jib assuming the minimum lead of 8%.
Again !!
Different Sail Plan = different Mast/Jib step position .
The 652mm refers to a CE at 34mm from the mast.
The shroud “plates” shall consider the need of multi holes adjiustment to cope with the mast position. Personally, the shrouds are at the same transverse position of the mast step
I hope not to adds confusion by adding this Sail Plan of 78dm² - here the CE was at 34mm from the mast as in the original plan, but the mast rake is at 0°.
…
Cheers
Claudio
Opps :splat: … was reading the hull plan without the sail plan, thank you
DONE ! Under “Technology” section
Very Good Dick !!!
probably I will partecipate, but I’m afraid when discussions start with deep theories that become difficult for me to translate them into pratical applications adapted to our models !!!
Thanks any how .
Cheers
Claudio
Caludio -
one very popular (and International) monohull class is the International 10 Rater.
They are one of the few (maybe only) large monohull classes to use the rotating mast concept, and I would guess that if they are here in the U.S. and in the U.K. - they must also be sailed by a few in your country.
Boats are close to the same size as a Marblehead, so it may be worth looking into when you have time.
Regards, Dick
Hi All,
For me this stage of constructing the fin box mast support assembly was the most critical so far and as mentioned earlier had made up a sub section of the hull off the mould and mounted it in the cradle for measuring & fitting.
Laminated two sheets 3 mm ply together using 50 gsm FBG and cut out the mast support blanks. Then made up transverse beam using 3 mm aircraft ply and measured out mast step position for both 78 & 74 dm2 sail plans and marked “0 positions” on the beam along with chain plate positions, just to ensure nothing was going to conflict later.
Allowed “estimated” 2 mm thick deck and adjusted beam same distance below the sheer line. Then aligned and glued fin box and mast support to the transverse beam. Once cured cut and glued in the 5 mm CF tube supports diagonally from base of mast support to the transverse beam.
Target weight for the entire assembly was 275 grams and it weighed in at 78 grams !
Claudio are my weight allocations correct? Thinking I may have mis-calculated somewhere as my numbers say I’m 225-257 under total target weight so far !?
Next up is deck making, Claudio on your AC 33 build you made the deck out of balsa sheets of 1.5mm doubled with glass cloth of 50g/m² on both sides. However I recall a comment from you later saying the deck was too heavy !?
Can you please clarify for me the deck material specifications ?
Cheers K1
Hi Alan,
first : congratulations for your meticulous method of work.
The weight allocation for the supports was probably too high, but I do not see yet the FBG or CF reinforcements laminations as the rudder support.
My deck with balsa and FBG was too heavy. Next time I will make a wood mockup onto which I will laminate the deck cockpit.
In principle the laminated monobloc (2 layers of 100g/m²) deck should not be more than 120g , therefore your allocation is rather generous. The deck can be composed of two parts, the front one being a simple flat lamination .
Cheers
Claudio
Thanks Claudio 
Forgot to mention that I have not added the servo tray on the fin bloc yet, have been looking at getting new drum winch servo’s, the Graupner Regatta looks like the best option 
In regard to the hull laminations I have been looking around for CF and was planning to put them in when we bond the deck to the hull. On your AC 33 you have 3 hull support laminations 1) rudder 2) fin bloc and 3) in the area where you have jib rack, should I allow for all three albeit I don’t have jib rack below deck as you had on AC 33 ?
Thinking about the deck, I would like to make it out of one piece rather than two. Remember I would also like to have the bevel on the foredeck sheerline, I can include it on the deck or cut the deck and hull later and glue in a FBG strip, what do you think is easiest ?
Then cockpit deck plan looks straight forward until it comes to the transom where the flat cockpit deck then takes the shape of the curved transom. Looking at Alessandro’s old & new ETNZ I see he has moulded the deck cockpit on his new boat, looks cleaner but means making a mould. I’m uncertain which way to go, what are your thoughts ?
Cheers K1
Alan,
What has done Alessandro is very good (foto blue). He has made a unique body for the deck.
You should include the bevel by making the Master. This is long, but pay off.
If the jib is using a beam across the deck, then you may limit the laminations to the sides only.
Cheers
Claudio
Hi All,
Today made couple of stern deck pieces off the mould from FBG, next cut the struts off the mould down to deck level so I could use the mould to draw out-line for deck template (3 mm ply)
Plan is to use clear 2 mm Perspex over the deck template and glue-in the foredeck bevel and the cockpit deck using Perspex as well, then I can make complete deck in one piece (upside down) and have hopefully have perfectly smooth finish from the Perspex when complete (no sanding :p) only thing I need to work-out is how to get smooth transition from the square cockpit deck to the curved stern deck 
tomorrows challenge :rolleyes:
Hey Goose whats happening on your side of the pond mate … ?
Cheers K1
Hi K1
tomorrow I will try to draw the cockpit’s shadows as such to make a mould. Something like that : …
I let you knows
Ciao
Claudio