Ahoy mates,
Again, and always, I will say that the mathematics is sound, and generally accepted enginering principles are used, but the lack of original design data creates a "theoretical" close approximation and only after using common sense should they be tested. In either event, I will state unequivocally, that this is strictly for educational purposes and I do not suggest or endorse use of any findings I may publish in this forum and to do so constitutes a sole risk for which I will not take any responsibility should it kill, maim, injure or inconvenience you or anyone else in any manner or form whatsoever. In fact, I will not even be responsible to apologize if you find that reading of this thread is a waste of your time. Now that we got that disclaimer sounded off and out of the way, lets go to work.
Feel welcome to request clarity on any information if demed necessary and I will do my best to provide it. I wil try to provide the information timely but be patient if it takes a little time since some of these calculations are tedious.
First, does anyone know what the midsection coefficient, prismatic coefficient and water plane coefficient might be for the 36? I can do magical things with this information. I have used approximations to generate the following findings. I may include some corrections from prior posts as well.
I: 44'
J: 15.5'
P: 38'
E: 13.9'
For some wild reason, these figures don't seem to add up visually. It seems like J should be longer as well as P should be taller when looking at the design.
Fore triangle CE: It is at a height of 18.8', for an area of 239ft^2
Mainsail CE: It is at a height of 21.2', for an area of 236ft^2
Combined CE: It is at a height of 20.13'.
Air draft: 47'
I will be able to provide more accurate figures once I find the CE on the sails by way of physically measuring them, but this is extremely close if not dead on.
The bridge deck clearance The height is 2.04'.
The LWL Area has now been more closely calculated to 89.87ft^2 - this is a correction.
BMT: Traverse stability is 72.75'
BML: Longitudinal Stability is 70.81'
WS: The wetted surface of the hulls is 186.4ft^2. Based on the B/T ratio, the wetted surface is actually considered high even though it is by every measure quite low. With a B/T ratio of 2 as opposed to 1.1 for this design, the 2 would have simulated a wetted area more closely resembling a parabola or in simpler terms, a wineglass/cylinder yielding the least wetted area.
For example, as an oversimplification and only to clarify it in my own mind, if we were to keep the waterline beam dimensions the same width to maintain the 15. 1 LWL/B ratio, then the beam at the waterline of 2' would mean that a B/T ratio of 2 would cause the draft to be designed to 1' deep. If we wanted to keep the draft 2' instead, then the beam would have to be 4' wide, thereby reducing the LWL/B ratio to 8.5. This makes her an outright dog and kills the designed wave making reduction incorporated into the hulls.
Design Category: All calculations thus far appear to reflect that she has been designed to category B as defined by the European Union. Her design wind speed is 32 knots. The following results are derived and the definition for category B is:
"OFFSHORE Category B", designed for offshore voyages where conditions up to, and including, Force 8 winds and significant wave heights up to, and including, 4 meters may be experienced"
Link where more info can be found.
http://www.ibinews.com/ibinews/ebb/tech_6.html
Actually I'm struck at the fact that the mathematics has her designed so closely to category A. I think that minor modifications (which we may get into later, wayyy later,) will make her category A capable. All this time, the design has been viewed as a coastal cruiser when deep down inside she has it in heroto head offshore. Granted she may not be offshore ready because it takes more than stability and capability to define that, but as a category B, she has a better chance of limping back to port than a coastal cruiser if caught in a blow. This finding is quite amazing.
Heeling Moment of sails: The 39890 ft#'s, is the moment used for rig design
Righting Moment of Design: 32,479 ft#'s
Max Heel Angle: The result is 0.0983 rad or if converted, 5.6 degrees and 7 degrees. It should be obvious that it will not be difficult to get the windward hull unstuck. The heel angle of 5.6 degrees is based on "lightly loaded and race ready" and the 7 degrees is based on full displacement. Still, it would behoove a skipper to always question the deceptive calm experienced from sailing at small angles of inclination since the hull will fly with just 7 degrees of heel.
Entrance angle: The bow entrance angle is 8.4 degrees, this could be way off and I would need to measure it to know for certain. I have seen the 36 in action and the bows did not appear to penetrate wet so I suspect that the angle is too shallow and would probably be a lot closer to 11 degrees.
Height of 1 Hull: The height is 4.3' but this will also be measured and made final.
Foot print weight: She has 6.76# ft^2 and this wil be used to estimate the cost to build a new Mac 36 today. For this study, it can be said that she is extremely light per ft^2 compared to other catamarans.
Hull Volume: 491ft^3 and it is the entire hull perimeter without any internal accommodation included. This is considered in my mind quite cramped. To put this in perspective, as a measure of a cube, you must be prepared to exist in a cube that is 7.87ft^3. It can be done because there is enough room for 2 people to lay comfortably and stretch out to take the crook out of your back, but now take away 40 cubic feet of flotation and another 5 cubic feet of accommodation and restrict the width and height and it's a whole other picture.
Hull Beam to Length: This calculates to 9.2%
Hull Height to Length: This calculates to 12%
Windage: This calculates to 6.4% and it is excellent! Catamarans are not known for their pointing ability, but with a deep board and this kind of windage, she should be inside of 10 degrees to mono hull pointing angles, although she may then also suffer mono hull speeds for pointing so high.
Draft to Height: This calculates to 47%
LWL/Water plane Area: This calculates to 39.5%
LCB: This calculates to 56.3% aft
VCB/Draft: This calculates to 47.5%
LCF: This calculates to 57.1% aft
CLA: This calculates to 47.5% aft
Deck Clearance : This calculates to 6% of LWL. This is actually the bare minimum vertical distance that should be taken for offshore work because the slamming on the bridge deck would be intolerable and may cause structural concerns, but, it is genius when there is no bridge deck and only netting exists and all the windage can be eliminated.
Leed: This is 7.6% of the LWL for a distance of 2.6'. This also is a common percentage. Does any owner know if there is a lot of weather helm on the design when operating at a V/L speed greater than 2.44? If the helm is balanced, then I would suspect that the figure should be smaller, but I will know for certain when I get exact measurements.
Length/Draft: This calculates to 17 and it is good.
SLR: The speed to length ratio is 1.9 and provides a true representation of expected V/L speeds averaged over a 24 period. It turns out from GPS readings and other Bar room tall tales of incredible speeds, that the design does in fact exceed 2 and 3 times LWL^0.5, but, according to the calculations, the design is fixed at 1.9 times LWL^0.5. It may be conservative and there are other accepted methods for calculations, but for now, lets try to keep the grand tall tale of the huge fish that got away at the bar.
Okay. I'll calculate some more when I get a chance. The search engines are completely devoid of information and it apears that it will all be left to me.
So which head chief can make one of these ---->
for the 36 so I can have one since I apear to be the only one?
Thanks for reading.
Maybe I should try to establish some specifics for performance and stability mathematicaly? That may answer some questions like the ever important wind and sea operating envelope? I suppose I can take some measurements and calculate some ratios etc? Would there be any interest for this information by forum members or is the effort not worthwhile.
Shoot, it may be that the design may have been "designed" by the time we are done with her.
just go sailing, learn as you go and stay out of the nasty weather. 
