Fast cruise biplane catamaran concept

[Lorenzo Carrara]

Hello to everybody.
I'm an italian student of nautical/naval design at University of Genova.
I would like to show you a project we (me and two fellows) are developing for a course exam.

It's quite uncommon, so every suggestion will be thankful.

Here it is:
we intend to realize a boat for cruising, and charter-oriented. But fast when needed (running from incoming storms, getting to and from distant places in less time), and with an eye on enviromental impact.

LOA 23,2mt
BOA 13,7mt
Draft_hull 0,72-0,80mt
DISPL 25-30 tonn

TYPE: bi-rig fast cruising wide catamaran
HULL: round-bottom, wave-piercing bows, inboard flare (this have to be modified to a 45° degrees starting from dwl, as seen here http://www.windspeed.com.au/yachts/s...oard_flair.htm)
Retractable appendages for beaching.

CONSTRUCTION: aluminium (thick plate with few web stringers for the bottom, thin plate with web structure for the rest)

RIG: biplane rig widely spaced for less interference (12mt between masts) with soft wing sails, like Omer wing sails http://www.omerwingsail.com/ or Tim Dunn's ones.
Luff 22mt, base 7mt, approx 260m^2 total sail area.
Big (50cm diameter) unstayed masts buried deep in bilge (approx. 2.5mt between low and top bearings).
Winches for halyard & sheet (electrically assisted) in cockpits.
Camber & vang hydraulic with controls from both cockpits.

ELECTRIC ENERGY: photovoltaic panels on top of coachroof (~90m^2), two wind turbine (into sterns or near helmsman position), two watergen towable generator. Enough battery in a separate bilge to store daily production. Our goal is to use only that energy to supply every on-board systems, and to have a few amount to use for electrical engines.

ENGINES: two diesel (or maybe methane) 85cv engine with built-in 7kw alternator convertible to 10kw (peak) electric engine. We can use it electrically with battery store (6-7kn for about 8 hours every day) Or, when needed, thermically with fuel (up to 12-13kn).
We are interested in bio-methane fuel for it's low-carbon footprint: it can be obtained from livestock wastetaters & urban waste, reducing widely the CO2 emitted.

ACCOMODATIONS: 6 double cabins + 2 sailor's cabins. 8-place dinette plus two separate tables that can be joined to the main dinette to get 12-14 places.
External areas with foldable tables and addictional chairs: 6+6 covered places in aft well and 4+4 covered places in fore well.


Maybe there's something I forgot to write, so ask me whatever you need.

Thanks in advice
Lorenzo

[Kanibal]

I`m new here, and i don`t have experience with boats, but i think this catamaran will suffer to much wind impact, and be slowed down a bit.

[Lorenzo Carrara]

Originally Posted by Kanibal

I`m new here, and i don`t have experience with boats, but i think this catamaran will suffer to much wind impact, and be slowed down a bit.

You're right. Our vertical fore-coachroof entrance adds a bit windage: we have to do some calculations to get the exact amount of speed reduction, but I think I'll not be much. And the rig is very powerful indeed.
The alternative is a inclined fore-coachroof profile: it'll be more complex to build (it has large sliding doors) and it eat useful space.

[Petros]

two things come to mind, the rudder looks a bit small to my eye. And why the twin sails? One large sail will be more efficient, and possibly less rigging and equipment. I know the concept of twin sails, but I do not think they have resulted in faster boats in practice.

Drag reduction is an important concept often overlooked in yacht design, and the faster the speed of the boat, the more drag becomes a factor in overall performance.

nice looking cat, good luck with the project.

[Lorenzo Carrara]

Originally Posted by Petros

why the twin sails? One large sail will be more efficient, and possibly less rigging and equipment. I know the concept of twin sails, but I do not think they have resulted in faster boats in practice.

Maybe I am wrong, but should be quite difficult to put an unstayed mast (required for the soft wingsail 360° rotating sails) in the centre of the cat (although ideal config. for a tri).
We dunnot intend to achieve better performance with the biplane rig, but only to improve sail management (lower CE, slighter masts, simply to reef, less traction on sheets).

[michael pierzga]

Cats have huge deck space.. Great for charterboats. I dont know much about wing masts ans sails. It appears to be huge windage for an anchored or alongside vessel. How do you control them ? How do you keep the vessel from sailing off the anchor ?. How do you manuver in tight harbors ?

[Lorenzo Carrara]

Originally Posted by michael pierzga

How do you keep the vessel from sailing off the anchor ?.

You are talking about the high windage?

Originally Posted by michael pierzga

How do you manuver in tight harbors ?

Worse than 22m x 8m cat, obviously, but better than 32m x 13m cat, i suppose

[michael pierzga]

...my instict says high windage. Perhaps in your design you take precationary steps. Powerful bow thruster for harbor work and perhaps an anchoring " dagger board" or cetreboard ,very far forward, so that the windage, lateral resistance keeps the boat into the wind. Ive see Frers do this with jumbo sloop rigged monohulls to keep them from tacking off thier anchor .Look at the underwater profile of the Frers yacht "SILL" I believe she has it

[ThomD]

I assume we are now going to enter a phase when every new design has a recurved bow on it. Just as plumb bows eventually drove out bow overhang, we now are going to take it further with recurved bows. In a non-class, non-weight sensitive environment (relative to six double berths), I don't really see the benefit. One is giving up boat, rather than gaining it and will loose buoyancy at the bow, pumping more water all over the decks etc... I don't know that this change has been thought through.

I have zero faith on rigs plunked down in Cad with no real details on how it is all going to work. The cat itself is a wonderful base for a centrally located rig, with lots of safe space to work around it, and stay it, and control it. I don't see any detail as to how this rig will be controlled, reefed, etc... It lookd precariously located near the wet stuff, I don't really think it has been thought through. The idea is to make it easier to control, because the size of the rigs will be smaller, but first off they are only smaller if efficient, and aren't blanketing each other at low operating speeds that are typical. To me, that rig only works if crazy amounts of carbon, and possibly sail handling power equipment are brought to bear, and for that you could easily control a larger centrally located rig. It is the design trap were one advantage is achieved at the expense of about 10 problems created.