Corsica 15 R A New Design for Solo Sailing

Discussion in 'Multihulls' started by Chris Ostlind, Jul 15, 2010.

  1. Chris Ostlind

    Chris Ostlind Previous Member

    OK, guys... time to stir it up a bit on these pages.

    Here's a new boat just developed for fast solo sailing. The Corsica 15 R is a light, demountable design for performance day sailing that has been created for homebuilders.

    Here are the specs for the boat.

    Corsica 15 R Specifcations

    LOA 14’ 11” (4.54 m)
    BOA 13’ (3.96 m)
    Displacement 650 lbs. (294.8 kg.)
    Sail Area (upwind) 174 sq. ft. (16.17 sq. m)
    Main 132 sq. ft.
    Jib 42 sq. ft.
    Spin 142 sq. ft. (13.19 sq. m)
    Mast Length 25’ (7.62 m)
    Draft (board up) 1’ (.3 m)
    Draft (board down) 42” (1.07 m)

    This boat is designed for a stitch and glue build in marine plywood with epoxy/glass skins. The Corsica 15 R is a demountable design with aka beams hard fastened to the amas. The inboard ends of the akas are four-sided conical shapes that allow quick setup with no binding issues. The akas are pinned in place and the tramps remain mounted to the ama/aka assembly.

    This boat is not equipped with any sort of trick lifting foil arrangement in order to keep costs, weight and build simplicity near the top of the design criteria. There is a simple, diagonal daggerboard which slides through a trunk in front of the mast step. The rudder head can be a unit from just about any beach cat that has a flip-up feature, or the builder can go with a more deluxe setup from Dotan. A longer rudder blade is suggested for control throughout the sailing range.

    The sealed mast is a cut down stick from a Hobie 16 that includes the addition of a spreader system from a Hobie 18. The mast can be raised in the traditional beach cat style, manual lift method. OR, the skipper can also rig a set of sheaves on the top of the raised dagger board so that it can be used in a gin pole effect in combination with a simple hand winch on the trailer.

    The skipper sits in the main hull in a semi-reclined position, much like the driver of a Formula 1 car. The main deck of the cockpit is slanted aft for self-draining through the open transom. All controls are led to the cockpit and the rudder is controlled with foot pedals. For those who wish to put the hammer down, the skipper can exit the cockpit and sail the Corsica from the tramps with a tiller extension and an easy re-routing of the sheets.

    The jib and spinny are furler launched. The jib is of the self-tacking variety and the spin is flown from a removable prodder that originates as a carbon windsurf mast. First preference for the main would be a fresh, fully battened, square top sail, but a recut main from an H16 in great shape will also work. It is suggested that the recut, or new sail also include reefing points for sail area control while on the water.

    The Corsica 15 R is a straight-forward, solo beach trimaran with efficiently shaped hulls and a distinct performance identity in a quickly assembled package at the launch ramp. It is easily buildable in a home garage from well-known materials and has provisions for the use of used kit in good shape to keep costs under control. The boat will be simple to maintain to maximize available hours on the water and it can be towed by a compact car on any used beach cat trailer with minor modifications. The trailered width of the demounted package is road legal in any country on the planet.

    Attached Files:

  2. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    Does the boat weigh 650lbs? If not what does the all up ready to sail boat weigh minus crew?
    -What is the L/B of the main hull at the waterline?
    -Is the boat designed to fly the main hull?
    - What is the L/B of the ama at its designed maximum immersion?
    -What is the SA/WS ratio at its most optimum?

    By "developed" what do you mean? Have you built, sailed and tested this boat?
  3. TimothyM
    Joined: Jul 2010
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    Location: Maine

    TimothyM Junior Member

    That looks like a fun boat to sail. I know some ice boaters that would feel right at home in that cockpit.
    Love the renderings too.
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  4. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    I think it's a hot looking boat as well. It's just a shame that it doesn't appear that it could fly the main hull. And that information available from other designers like Kurt Hughes and the Kitchens(Weta) is not available here. It would be such a great service to the public for the details of designs like this to be available to the public-to help them understand the unique design requirements of a trimaran.
    I believe that as trimarans become more popular due to many factors that people will want to know more of the detail and what it could mean to them.See here for the details on the Weta tri and on Kurt Hughes 12 footer:
    If you go to Kurts site you can find a lines plan posted for his 12 and 16 footers from which many of the details above can be calculated. If you have any questions about the Weta an e-mail to Chris Kitchen or Roger Kitchen results in a detailed reply. Thats the way it should be ,in my opinion.
  5. jwboatdesigns
    Joined: Apr 2010
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    jwboatdesigns John Welsford

    Chris, nice work. Are plans complete and available? $?
    Just looking at her, it would be fun to fly the main hull, whats the volume to displacement ratio of the akas?

    John Welsford

  6. Chris Ostlind

    Chris Ostlind Previous Member

    Hi John,

    Thaks for the kind words.

    Plans are not complete yet. The boat is very close to finalized, but still just a bit of a work in progress. When she is completed, I suspect that plans will go for something like $250.

    Amas are sized at 172% of displacement.

    Attached Files:

  7. Doug Lord
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    Doug Lord Flight Ready

    RM vs HM


    It sure would be-if the boat was designed for it. I'd ask for a little more detail.
    At the displacement mentioned in the first post-650lb- and the beam of 13'-the righting arm is close to 6'. That makes the Righting Moment 6 X 650 or At an estimated CE-CLR ,for a cut down Hobie main, of 11' that makes the Heeling Moment:
    1-in 1lb per sq.ft pressure==11 X 174= 1914ft. lb,
    2-in 1.8lb per sq.ft pressure= 11 X [174X 1.8]= 3445
    To put this in perspective, the max wind pressure an F 18 cat can sail in with two crew on trapezes, without depowering, is 1.8lb per sq. ft. pressure. And in that pressure(a lot of wind) this boat still won't fly a hull.
    Of course, my figure for CE to CLR is an estimate, but thats why more detail would be so helpful.
    The more design detail presented the better. If presented well it can help answer questions like this while at the same time enlightening the reader as to the design choices made.
    One thing I checked, based on the drawings in the last post, was the angle of heel of the whole boat with the main hull just above the water. The figure I measured was 26 degrees-which seems high to me.
    I think this is a good looking boat and I'd like to know more about the details...
  8. jwboatdesigns
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    jwboatdesigns John Welsford

    I'm aware that the aka volumes are only part of the equation when it comes to flying the main hull, so really my comment about that was not appropriate to this design. Your comment about the sail area and heel angles are right, and I suspect that Chris has designed in a very high safety margin that will suit relaxed sailing or novices, the heel angle with the aka depressed enough to carry the boats entire weight being high enough to spill a lot of the wind and depower the rig before the main hull lifts, it would take a lot to capsize her.


    1 person likes this.
  9. Chris Ostlind

    Chris Ostlind Previous Member

    Astutely observed, John.

    Looking critically at the semi-reclined sailing position of the skipper is at the heart of the whole design approach. Go ahead, run some numbers. Very soon, it becomes clear that having a very quick, small trimaran, that offers a wide latitude of wind speeds before being pressed into an unsafe condition, is an optimal setup.

    I never really cared if this boat could fly its main hull while sailing. It's quite enough that the skipper gets to light it up, raise the main hull sufficiently that wetted surface drag is seriously reduced and never really place the boat in a tenuous condition, where it is prone to problematic pitch-poling and capsizing.

    Let's get real after all.... this is a 15 foot boat for recreational sailors who are looking for good speed and a really exciting time on the water. Is it really necessary to build everything so that it is balls to the wall 24/7 in order to get a really great and really satisfying boat for one's needs?

    I say it isn't and I really like the boat as a crisp, play boat of the multihull variety. Easy to build, easy to maintain, no fiddly nonsense, such as banana foils, to hamper the process and a whole lot less to worry about while sailing.

    To me, this is the kind of boat that has been needed as a commercial product for a very long time. It reaches into the recreational market much more effectively than does a foiling craft that will cost significantly more to produce and maintain, it can be built from easily obtained materials that will save enormous amounts of money for the builder and best of all... it can be trailered by any small economy car anywhere in the world.

    What's not to like?
  10. jwboatdesigns
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    jwboatdesigns John Welsford

    How about a tandem cockpit, sailing around the bay with your lady reclining in your lap, flickering past the monohulled slowcoaches like a swallow chasing mayflies would be pretty close to paradise?
    yes I know, no sooner do you design something then some jerk suggests that you change it in some way. Happens to me all the time and these days I generally just say "tough, wait for the next design"

  11. Chris Ostlind

    Chris Ostlind Previous Member

    Since you mentioned it, John... about a year and a half ago, I did a boat near to the size of the Corsica 15, that cleanly matches your suggestion with a minor adjustment to the seating style.

    The Solo 16 Sport trimaran and offers capacity for two adults for day sailing with the skipper sitting right behind his crew down low in the cockpit. The rig is nabbed directly from a wayward Hobie 14, or equivalent, and the boat should enjoy lively sailing just a notch below what is being delivered by the Corsica 15R and its much more powerful rig and half the load.

    To Solo 16's are under construction right now, with plans for one of them to enter the Watertribe Challenge next March.

    Attached Files:

  12. Chris Ostlind

    Chris Ostlind Previous Member

    One of the fascinating parts of the design process for the Corsica 15R is that while I was running the numbers for the boat with the existing, 174 sq. ft. sail package. I also ran calcs for simply installing a stock, Hobie 16 rig with it's 216 sq. ft. sail area (main and jib).

    This is a sail area gain of 42 sq. ft. from an easily obtained complete rig that can be had just about anywhere in the world.

    Potential for this boat?... interesting, to say the least. So, who is ready to push the boundaries of a well-known, conventional rig relationship on a small, sit-inside trimaran that can be launched off the beach?

    I am entertaining offers for the first build of this boat, with free plans and email support during the construction and testing phase. Send me a PM, or email, directly to, if you are interested.
  13. Gary Baigent
    Joined: Jul 2005
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    Gary Baigent Senior Member

    Neat design Chris, plus it has a kind of nasty, edgy and attractive appearance from front and rear views.
    Doug, why do all small boats have to fly the main hull? This design will be fast enough for the clientele it is aimed for. And if you really wanted flight (but why bother on this moderate sports bike) those amas could easily take surface piercers. But then beef up this and beef up that, more complexity ... forget it.
  14. Doug Lord
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    Doug Lord Flight Ready

    Gary, NO current small trimarans under twenty feet, that I am aware of, are designed to fly the main hull!
    There seem to be more and more of the same old same old-no serious innovation. If this boat was to use the 16 rig it might fly the main hull (in over 1.5lb per sq.ft pressure!) but no way is it "designed" for it. Further, the immersion of the lee hull would be very great and very high wetted surface drag at an incredible heeling angle of 26 degrees!
    With that much sail area and the crew in a fixed position there is virtually no pitch resistance in this design. Same holds even if the crew could move to the limit of the crossbeams. Designing a trimaran that will fly the main hull is not as simple as tacking on more sail area.....
    This is a good looking boat but trying to pack on the power would probably be a mistake in terms of pitch resistance as the boat is designed.
    There is a question that ,if answered, would add to the understanding of the pitch characteristics of this boat:
    Where is the heeled longitudinal CB of the ama as compared to the static, level longitudinal CB of the main hull? In other words does the CB of the boat move forward relative to the CG as the boat heels? That would create "natural" designed in pitch resistance(if it matched the pitching moment).

    Why doesn't the designer build it and test it-especially with a full 16 rig?!

  15. Chris Ostlind

    Chris Ostlind Previous Member

    Thanks for the kudos, Gary. I have had a lot of fun all throughout the conceptualizing process, the roughing-in of those ideas, the inclusion of some features and elimination of others... the whole thing. Perhaps the most fun was the task of creating a boat that could be built easily by everyday folks in their own garages while using materials that are well-understood by even casual boat enthusiasts.

    Yes, I know... some would have us believe that it's necessary to over-do each and every boat and design until they are crying from their own complexity. What is never recognized in that process is that the more one adds complexity, the further one drifts away from the mainstream until there are virtually no remaining sailors with an active interest.

    Personally, I think that this is a typical American take on how stuff is supposed to work. We seem to expect that each and every example of the next thing down the line needs to be some wowee-zowee quantum leap of technology and if the product does not contain that element then it's a failure.

    I happen to believe otherwise. It is my opinion, and boat design history backs me up on this, that design evolution is a slow-burn fuse of a game that is marked by incremental movement in thought, as well as function. The proponents of flash see that, of course, as positively glacial as an exploratory avenue. They expect nuclear bomb explosions each and every time that a new boat is introduced and find themselves deeply depressed when their fringe expectations are not met. It's even more frustrating for the folks who continuously scheme for this type of grenade design style when they have no physical outlet for their passionate dreams.

    Truth is, most big changes in boat design development have not been of the large, splashy variety without concurrent major changes in materials science that supports the new design directions. By far and away, the evidence suggests that the process is actually one of a deliberate, piece at a time, massaging of materials, aesthetic design cues and function; brought together in fresh combinations.

    Do I think that the Corsica 15R is a new, nearly exploded bomb about to go off in the boating community, setting the place on fire and securing my name among the rock stars of the design environment? The answer is not at all. It is an interesting niche craft with but few predecessors at this size. It does bring a new boating potential to an area where homebuilders have not had much access prior to the Corsica being introduced.

    What I am looking for is another, incremental piece of the puzzle that has been created as thoughtfully as possible for my intended market... the homebuilders of this planet. Rather than flash, I'm much more interested in seeing these boats being built, big smiles on the faces of those skippers as they zip past in their new, sporty machine and the reports from same as they tell of a boat that has been a ton of fun, got them out of the house on a Saturday and was pain free to maintain over years of powerful service.

    That's what smells like victory to me.
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