Hi Claudio … all instructions taken on board, saved few days of fine tuning prep … THANKYOU !!!
Hi Claudio, I’ve been thinking about where I went wrong with LWL and researched back through our posts and found the following:
Alan Post # 499 My question is: As a starting point, what correct position of the bulb C.G in relation to the hull C.B ? currently have guessed bulb C.G to be 15 mm behind hull C.B line … or is there a formula or something else I can use as a reference point ?
Claudio Post # 500 This is the only criteria I know, the bulb, among others, shall be fixed in order to keep the fully equipped boat in horizontal position on the still water, along the water line.
Once obtained the horizontality, is a good practice to slide the bulb a couple of mm backward in order to lower the stern. This asset will become normal again once the wind will start blowing into the sails.
You can guess what I did not do ? … (:headache:dumbkopf) With a new (lighter) keel fin in the pipe-line for tuning refinements I will follow your instructions of sliding the bulb back after finding C.G …this time !
Do you think moving bulb back to 20 mm behinf C.B line will be enough ?
Cheers Alan
Gidday Jim,
Just re-read your post
How on earth did you get fin down to 110 grams ? your C.G must be a world record !!! waiting for your measurements
Cheers Alan
Hi Alan,
What said in previous post are still valid.
10-15 mm is rather common distance betwen bulb CG and Hull CB.
Not all the boat are identical , therefore some variation are normal.
Rarely I have seen 20mm, but here again most dipend on the overall construction and mass distribution.
Until you have not definetively decided for the rigging , is probably wise not change much at bulb level but rather with ballast masses inside the hull.
ie: 100g at the stern may correspond to 2mm move backward of the bulb.
This of course depends on the ‘tuning’ .
Cheers
Claudio
Hi Alan,
What said in previous posts are still valid.
10-15 mm is rather common distance between bulb CG and Hull CB.
Not all the boats are identical , therefore some variation are normal.
Rarely I have seen 20mm, but here again most depend on the overall construction and mass distribution.
Until you have not definetively decided for the rigging , is probably wise not make additional changes at bulb level but rather with ballast masses inside the hull.
ie: 100g at the stern may correspond to 2mm move backward of the bulb.
This of course depends on the ‘tuning’ .
Cheers
Claudio
How on earth did you get fin down to 110 grams ? your C.G must be a world record !!! waiting for your measurements
Cheers Alan[/QUOTE]
Sorry for the delay, I havn’t been near the yacht lately. I will let U know!
One way to get a heavier bulb:
As this is my profession I am always looking at different rules and thinking outside the box to gain an advantage.
So, the keel does not go all the way up to the deck, instead I placed it only 50mm into the hull.
shorter the fin length = lighter fin= more weight in bulb. That simple.
Yes there is a bit of thinking and extra weight gone into the structure in the hull to maintain the stiffness, but my prototype boat is 200g light anyway so I am not worried.
So, why when the rules say the max fin & bulb weight is 3000g, do you want "dead"weight in the fin department. Shave it off the top and into the bulb it goes!
I hope that helps & I Hope that I havn’t infringed any rules!
Cheers,
Jim
Hi Jim, great solution, reading the rules there does not appear to be any infringement …well done !
Cheers Alan.
P.S Good luck in the TP 52 med series
…2980??? Super light weight boats and components??? Gentlemen, do you want to came here and gain the IACC 120 CUP???
WOW the challenge becomes really interesting!!! But Shosholoza RSA-09 glued with epoxy the cup to the deck…it is not so easy to detach it!!!
Cheers
Matthias
The life is short: sail hard!
IACC120 Alinghi Challenge Roma
SUI-100 & SUI-91
www.iacc120cup.altervista.org
Hi,
so far the appendages can be removed as per Rules § C. 5.1. no problems !
Cheers
Claudio
Hi,
For sure the fin is removable! As per the rules.
The 50mm fin box height is because the hull is immersed about 45mm in that zone - this means fin bolt through hole is then safely above the LWL… You could go less if you want… Just as long as there is a watertight feature somewhere!
Glad that it has not caused any rule issues!
I had a crazy thought about “ballasting” the rudder to max weight by making the rudder tip in lead too - maybe just a tad too far?..
Cheers,
Jim
“Gentlemen, do you want to came here and gain the IACC 120 CUP???
WOW the challenge becomes really interesting!!! But Shosholoza RSA-09 glued with epoxy the cup to the deck…it is not so easy to detach it!!!”
Ouch … !! so what you are saying Matthias is that a free boat comes with the CUP too !!! :p:lol::lol:
Jim, as I have already the fin boxes in all my hulls I don’t think I will try putting shorter ones in (too much surgery) … for now I will lighten fins by drilling the section within the fin box and transfer the savings into the bulb.
“I had a crazy thought about “ballasting” the rudder to max weight by making the rudder tip in lead too - maybe just a tad too far?..” Your in a top AC team and your saying it is tad too far, you are ringing our bells surely buddy 
as you say earlier part of your job is to think outside the box to gain an advantage, why should IACC 120 be any different ?
Your crazy thought just got incorporated in my hull to get some more weight toward the stern for sailing on the water-line in heavier airs, I have 40 gramms going into a spare rudder now … btw, if you don’t have the rules they’re attached here …keep them crazy thoughts coming :glasses:
Cheers Alan
Hi Alan,
“hollowing out the fin” is quite common, the leading edge on some full-sized AC yachts can be hollow to save weight in the fin…
Ericsson 3+4 had the same idea until the Measurer decided that this didn’t constitute a “solid” fin, even though the main body of the fin was machined out of a solid billet of high tensile steel.
Having a hollow steel fairing welded on the leading edge was deemed illegal and cost E3 points as remanufacturing a new fin takes 3-4 weeks and they couldn’t make one in time for the start of the VOR.
Be sure to fill any holes in the fin with light foam so that Rule E 3.3 (part 3) is satisfied and you will be fine. I believe this point does cover the fin in its entirety… Maybe try cutting the fin head in toward the top instead by removing the top ‘corners’. Then the fin is not hollow, and no re - filling is required.
Cheers, Jim
Assuming the fin nominal weight of 150g , the gain obtained with a shorter fin could be about 17.3g, (see drawing above), therefore the fin new weight will be 132.7 g
To reach 110g , it is still necessary to gain 22.7g (57%) that shall come from the fin construction overall. An hollow fin is one solution !
Therefore in my opinion a shorter fin is contributing only to about 43% of the total gain to reach 110g.
Now, under the conditions that the bulb can be 2890g instead of 2850g, ( 150g - 110g) it contribute to an increased ‘righting moment’ of about 1.4% and this is non bad at all !
A hoolow fin :
Uploaded with ImageShack.us
Cheers
Claudio
Hi Claudio,
I am suprised to see a blend of ply and carbon in the hollow fin suggestion.
In my opinion it would be better to lay up a flat sheet of carbon uni’s all running one way and a single layer of woven on top to act as a binder. If this is done with vacuum on a piece of waxed glass or a perspex sheet, the pulled finish is very, very nice. This is then cut in two and becomes the foils outside skins. There is no need for the ply at all.
I was wondering if there would be benefits of either allowing the fin to flood, and increasing its mass for gusty conditions or maintaining the void as a hollow and thus increasing the displacement for lighter conditions…?
Cheers,
Jim
Hi Jim,
you are right, I din’t tought about using a pre-prepared laminate. I will try, unfotunately I do not have vacuum at home and the vacuum cleaner is not powerfull enough.
The fin, in my opinion, shall be better keept as additional displacement as I do all the times, I do not see really much benefit to let water entering the hollow volume compared to the added displacement.
Thaks for the suggestion, I’m pretty sure that Matthias and Alan will be interested too of course.
Cheers
Claudio
Yes I agree the flat sheet of carbon laid up would be better than the ply, definitely add stability to the entire fin. Conventional fin construction as we all know is fairly simple, however, hanging 2,890 gram bulb on end of 110 gram hollow fin, which only has 4 mm CF rod within the fin, begins to stretch the limits of my imagination for this type of fin construction … any ideas on how to attach the bulb to the fin securely?
Jim you just reach the limits of my technical knowledge regarding considering the pro’s & cons of flooding a hollow fin, however, the rules (thanks Matthias for the update issue 1.3 by the way) states:
E.3. Keel & Rudder. E.3.3 CONSTRUCTION The construction is unrestricted except for :
(a) The Keel and Rudder shall be removable from the Hull.
(b) The Keel and Rudder shall not :
(1) be connected or linked together,
(2) be articulated
(3) have openings through which water could flow when in use
Hence point 3 would most likely prohibit this interesting point? …but I’m interested to hear the benefits of either allowing the fin to flood, increasing its mass for gusty conditions or maintaining the void as a hollow and increasing the displacement for lighter conditions…?
Cheers Alan
Hi Alan, a little late but congratulations on finishing your build so nicely, been following it since day one and was very impressed how quickly it all came togeter in the last month.
Cheers
Gary
Hi Alan,
Finally got to have a sail yesterday lunchtime, and before I did, I measured the C of G.
205 mm from the bottom of the hull…
Just started on my Ultralight edition Hull and components, but it will be a while before any bits get stuck together as I am pretty busy at the moment!
Cheers, Jim
Gidday Gary, thanks mate …have been watching your impressive multi hull construction …absolutely perfect !!!
Holly Smoke 205 mm !!! 
Matthias at 200 mm and he’s me at 180 mm …lot of work to do to catch-up that 25 mm :lol: well done Jim.
No much time myself this weekend only managed minor surgery on a spare rudder increasing from 33 grams to 75 grams max by placing lead into the rudder tip & doing a weight watches exercise on # 2 hull …managed to lose another 35 grams there, hopefully my big win will come from getting my hands on carbon masts, but more importantly getting some stick time for fine tuning.
Cheers K1