Perhaps Beebe got it wrong

I have read all the above posts with great interest. Remember I am not a sailor and Black Magic is a fantasy boat. That said BM will be designed with crossing the Atlantic as goal number 1. Goal number 2 is to win the Fastnet race on time on time handicap.
Researching yacht racing I have come to certain conclusions, namely racers break things. What makes racing dangerous is racers break things because when lesser men reef their sails racers do not reef until it is really unavoidable and sometimes they get it wrong. This oversimplification ignores the fact that heavy weather is dangerous all by itself, made worse by inexperience.
I discovered "Grimalkin" capsized in the 1979 disaster, thought it would be a poor sea boat and was surprised to discover that in my opinion it is really quite a good boat. At 30ft LOA it seems a bit small for the Fastnet race. there could be size restrictions in place now. Again In my opinion no one entered in the race was too inexperienced. My logic is really inexperienced sailors know themselves to be so and would not enter. I have nearly finished my calculations BM will have a 22mm planked hull externally sheathed in FRP at about 23000lbs plus with ballast 46% this is about a ton more than I had hoped for. The extra weight is due in part to 150 imp gallon fuel load when seems to be 80 is more usual.

 

in almost any form of racing, be it sailboats, race cars, motorcycles, etc, you have to push both the limits of the equipment and your skill, right at the edge of crash or mechanical failure, or you will not likely win.

when watching down hill ski racers, you will see often they are on the ragged edge of control, so the winners usually have a history of either crashing, or winning.

Even is sailboat club racing you are more likely to break something or pitch pole in a cruising yacht during a club race than taking a cruise. if you want to win you will be getting the best performance out of all aspects of the boat and crew, pushing the limits if the wind blows hard. It is a very different kind of day in a boat when on a cruse, or in a race, even in the same boat and on the same day.

 

Most racing boats SUCK as cruisers , too nervous for an autopilot , hard to get a self steering working well and weight is a dirty word and few cruisers will empty their toothpaste tube to just a day or two worth.

A Ferrari stinks dragging 40 sheets of plywood home , and a station wagon stinks at attempting to go 175mpg or run thru turns at near 1 G.

Decide what you want , there are no station wagons that win at Le Mans,,,

Today a really fine 90/90 can be created.

100% sail boat , but looses 10% for the engine , prop drag, fuel tanks ,spares and tool box weight.

100% displacement power cruiser, but looses 10% dragging extra keel weight and draft , and all that mast and rig thru the air.

 

Black Magic

Ok I understand i can't have everything but I have tried. My own opinion is BM would be a decent cruiser But would not have a snowballs chance in hell of winning a race without a handicap. Here are the results of my calculations. I,m sure a real Naval Architect might find I have made mistakes.
LOA = 42ft, LWL = 38ft, B =12.33ft, BWL =11ft. T = 6ft(fin keel) Tc =1.23ft
Displacement 1/2 fuel/water = 23784lbs ballast ratio 46% Power 35hp Beta diesel. Fuel 150imp/Gall
Sail area 1050ft sqft (cutter rig)
SAD = 20.27
Capsize risk factor = 1.72
Comfort ratio
Water plane area = 272 sqft
ItWP = 1883
BM = 5.1
Vcb = -.46
GM = 4.9
SSV = 27.5
AVS = 123 Deg
Roll time 2.2secs
Stability Index = 0.58
I have not worked out the Dellenbaugh angle I would have used JIPE numbers to guess the healing arm but a guess is still a guess. I think AVS and SI are a better measure of stability.
I have chosen epoxy/wood/frp construction with the backyard builder in mind. I am now looking at the same boat in aluminium and I think it would turn out lighter, certainly if the design requirement were cruising not racing.

 

Perhaps nothing to do with this thread but the latest (Jan-feb2014) issue of PassageMaker Magazine just showed up in my email. In it I find a picture of Beebe's boat Passagemaker under sail in the Rio Dolce in 20 knots of wind. They claim 5 knots reaching with big genoa and main. "Passagemaker enjoys sailing provided you don't want her to point." They (current owners) mention the short (36') wooden mainmast has been replaced with a 50' aluminum pole to carry the big genoa.

 

24k# for a 42' boat? that's a slug. My 49' full keel ketch rigged (telephone poled) center cockpit with permanent FG dodger weighed 26k# And that thing had a Ford Lehman in the basement.

the Fastnet is raced by Mini 6.50s (6.5m long) and many do quite well. The reason the 79 fastnet was a disaster had more to do with bad boat designs than anything else. the way the handicap rule had been written that was in use at the time (IOR) created boats that were very tender, relatively slow and unstable downwind with coach roofs that were overly light (to improve on stability).http://phillippahuttonsquire.com/french-mini-fastnet-on-491/

 

Beebe's Passagemaker is very relevant as it was not the first across the Atlantic he and his boat proved it wasn't a one off publicity stunt. My first design goal was to design a similar boat, the sailing rig was always the weak link on Beebe's boat. The Sail/motor type (Black Magic) was born in my mind when I decided the best way across the Atlantic was in a Tad Roberts designed passagemaker in wood or aluminium. I think Michael Kasten makes the prettiest boats and I think I share some of his design philosophies like a preference for single chine hulls. Passagemaker built in Singapore has teak planking. Displacement for BM was based on Douglas fir and plywood of fir because I think its strong cheap and plentiful. It seems many strip plank hulls are planked in Cedar (white ?) this would effect both weight and strength. Can someone say how it compares with fir.

 

to Baltic Bandit

Thank you for the reply, I was afraid my spec wasn't good enough to provoke comment. SLUG!!, If I had a heart it would be broken. I don't think a boat with an SAD of around 20 should not be called slug, FATTY would be more appropriate. Black Magic is about a ton heavier than I wanted it. If Par is right and scantlings were reduced by only 5% BM would easily lose that ton especially if I dropped the added FRP of 100g/M per sq ft added internally for strength and to completely encapsulate the wood. Heating/cooking/sleeping and fuel arrangement were generous.Perhaps I have come up with a Jack of all trades master of none. I think I will start again, be more spartan with the living arrangements and use Cold molded wood rather than Plank on frame and see what I get.
mik

 

Why not fir.

Well there is good reason why white or red cedar are used in place of fir. amongst them are
differences in wet/dry shrinkage rates (lower for cedar)
differences in compressive, longitudinal and tortional strength (see Bram Dally's work on this with West Systems http://www.westsystem.com/ss/assets/Uploads/Ew21longterm.pdf

the key isn't to "go Spartan on living arrangements" but rather I think that the key is to start with building a shape and a structure that is resiliant, strong, stiff and light.

Stiffness matters because a stiff boat converts propulsive energy into actual movement much more efficiently than a soft boat. so that means lower loads, better fuel efficiency, better sea-keeping etc etc. Lightness does this as well.

I would suggest that modern materials are not necessarily to be avoided. Mixing modern and old as appropriate can yield great benefits. For example I know of a gorgeous Wylie 52 that was built with cold molding on the interior and exterior skins but with a foam core. The result was an incredibly stiff, light and well insulated hull

But fundamentally the issue is that the kind of hull shape that works well for power is different than what works well for sail. The reason being that a boat built for sail is built around what the immersed shape looks like an that immersed shape is designed for an off-axis stability point. Whereas power is set up for on axis stability. And you kinda have to pick

 

Back to the drawing board

Strange as it may seem Black Magic has not been drawn for the simple reason I am not much good at it. However, The displacement of ~24000lbs was more of a calculated/estimated weight budget. I must make a drawing however rough, this will allow me to more accurately estimate frame, plank and bulkhead weights. For ease of construction as well as drawing BM will now be a single chine hull LOA 42ft B~12 Tc~4.5 with full keel+ brewers bite. A further fin keel would require few alterations. Construction plank on frame. FRP sheath inside and out. The pilot house will be ply or plank on frame if I can make it light enough.

 

One factor (displacement) does not make or break a design. Design is a balancing act, weight must be balanced against structure, budget, sail area, wetted surface, beam, interior volume, etc.....

Cruising boats are heavy, every one out there doing it is over design weight. This is because the designer/builder did not foresee all the crap the owner and his wife consider essential equipment.

One man's slug is another man's race horse....

 

A good way to start any design is to look at comparables...here's one

http://www.hallberg-rassy.com/yachts/aft-cockpit-boats/412/

 

HRs are not known for heir performance

 

Off to London for christmas

I made a big error in the weight estimate for Black Magic. Easy to do considering the number of formulas I'm dealing with. Gone to London thanks to all of you for the help you have provided me.
Merry Christmas Mik