8 Meter Day Sailer

Discussion in 'Multihulls' started by landbound, Sep 20, 2010.

  1. landbound
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    landbound Junior Member

    I am no Sailor – as a child – so long ago I won't tell you when, I sailed dingies and beach cats.

    I'm semi retired in Bali, Indonesia and thought I might try the water again. I surfed the internet and thought a TomCat 6.2 might do the job. Sadly Indonesia has high import duties and landing a foreign boat into Indonesia virtually doubles the price. I approached a young naval architect in Bali with a view to building something comparable in Indonesia. He told me what I had in mind and where I wanted to sail was unsafe in such a small boat and that 8 meters was a safer size.

    I told the architect what I wanted, safety first, shade second and the simplest sail plan possible. An unstayed Uni rig would be my ideal. In short a giant Hobie Bravo with shade. I did not really want anything in the hulls at all but my significant other is not too keen on answering the call of nature in the ocean , So I changed my wish list to an enclosed head in one hull and a closet in the other. Things do get pinched in Bali so locking things in the hulls is not such a bad idea. I did not want a galley, I have no interest in sleeping in a a narrow coffin. Electrics are not important- happy to use a torch. I would carry on board a waeco cooler and might bring a BBQ. I explained that my choice of a cat was dictated by deck space not speed and that bobbing along at 6 knots was fine with me.

    My desire for a simple sail plan was not simply dictated by being a crap sailor but also because after observing all the cats in Lembongan Bay over two weekends not one raised a sail. My suspicion is that the effort of raising the sails for a short trip back to the mainland left the owners cold and the temptation to turn on the motors was too strong. I know that I can be lazy too, so a single sail with a single control (a la Hobie Bravo) I might just be more likely to raise it than turn a key.

    The young Naval architect came back with some plans for a lovely boat but not all what I wanted, his boat would be fast, sail well and look good. It had no shade, two bunks in the hulls and the sort of sail plan that delivers performance main/jib/genoa. The architect told me what I wanted was impossible and crazy. You could not have a bimini with 2 meters clearance (I am 1.95). An unstayed rig / wishbone boom or other can not work on a cat and ultimately what I wanted could only be done on a much bigger cat. And what I wanted would be bloody ugly and sail like a pig.

    Ugliness and slow speed do not frighten me but unsafe does. I again surfed the internet and looked at 8 meter offerings. The smallest boat I could find with a 2m Bimini was the Maine Cat 30 (9 meters). The only unstayed mast I could find was on a Radical Bay 8000 and it was a bi-plane.

    My question to you sea dogs and design gurus is – Am I right in drawing to the conclusion that the architect is right. The sort of boat I want – see JPG attached – can not be done at 8 meters and below 1000kgs weight. Similarly the simple rig on a Hobie Bravo does not scale to achieve say 25m2 of sail area.

    Interestingly I read a review of the Moxie 37 which said the trend was towards day boats which in fact was what most cats were used for by private owners. The Moxie is beautiful to look at – I am not qualified to talk about value or performance but I wonder does a boat have to be 37 feet long to provide the same amenity – if you have no need for bunks for five people and a galley.

    Re inventing the wheel is not a good idea particularly when I have not the skill to do it. I have scoured the web and there seems to be many 8 meter cats that cram in accommodation and others that are purely for sailors like the Radical Bay 8000 – Is there anything already designed as a day sailor that gives plenty of standing room under shade.

    PS What I have looked at Radical Bay 8000, Maine Cat 30, Aventura 28, of these the Aventura 28 comes closest but I simply don't want all the stuff in the hulls and would like more shade.
     

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  2. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

  3. DarthCluin
    Joined: Mar 2009
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    DarthCluin Senior Member

    James Wharram is building a new 27 footer (8.2 m.) called the Amatasi. It has removable cuddy cabins. Construction plans will not available untill after the prototype is finished, however study plans are available now.
    The links are here:
    http://wharram.eu//live//article.php?story=20100715135624601
    http://wharram.com/sales/index.php?main_page=product_info&cPath=3_8&products_id=26
    Get your sea legs back with Slider. If you decide you need a larger boat, perhaps the Amatasi plans will be done by then.
     
  4. catsketcher
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    catsketcher Senior Member

    Unstayed aint simple

    I will look out for contradictions from Rob Denney but I don't get why anyone would want unstayed on a cat. It isn't simple - the engineering and the construction is very hard.

    The Hobie is a bad place to start from in an engineering sense. Loads go up by the cube as you increase length so there are things you can have on a small boat that can't be easily done on a big one. Unstayed cat masts are one example.

    Of course it could be done - you will just have to throw lots and lots of time and money at it. Therefore it is not simple.

    If all you want is a daysailer with cover then go a two stage bimini. The front stage would be low over the seated area and then a two metre high section where you walk. A bimini is pretty low windage as long as you don't start covering it in.

    My advice - go two or three stays a side on a simple tube.

    The closest thing to what you want in my reckoning is the Constant camber cat designed by Jim Brown John Marples. These guys have really been around and know what works.

    http://www.duckflatwoodenboats.com/mainpages/gallery?KID=56

    cheers

    Phil
     
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  5. landbound
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    landbound Junior Member

    Thank you catsketcher

    Dear Catsketcher

    Thank you for taking the time to reply.

    I am not an architect or an engineer, for my sins I wasted time at University studying Maths so the cubic expansion in relation to both loads and mass is not completely alien to me.

    This is why one of my queries is the scalabilty of a Hobie Bravo/Windsurfer Rigs. From personal and professional experience I know well that the expansion of components in any manufacturing process and in subsequent operations leads not to a cubic expansion but an exponential increase in f***ups! I am therefore not surprised when on the beach in front of the hotel I see unstayed masts. What I don't know and don't understand is where this approach stops being vailid. Is it really engineering complexity or rather that the mass manufacture of Aluminium tube of varying wall thicknesses and diameters is so prevalent and competitive that the manual process of constructing a tapering carbon tube is cost prohibitive.

    I note in the exchange between two knowledgeable advocates of unstayed masts that they were looking as a rule of thumb for a 7% deflection and that to calculate the deflection a double integration was required - the calculation is really not that complex. What may be very difficult is the manufacturing process to achieve that deflection - I simply don't know.

    I am in essence just puzzled that you can't have "a tube to pop in a hole" instead of a complex load distribution system via stays with equally complex system of ropes as opposed to the system on a Hobie Bravo. Clearly my puzzlement is founded in ignorance but I am curious if there is a rule of thumb where weight/height/weight make such a mast "too hard" or "too expensive".

    A Hobie bravo weighs 90Kgs, a wind surfer weighs less, clearly an unstayed mast "works" at these low weights. Is there an infelction point, say in Kgs or meters LOA or Mast Height, where even a carbon tube becomes impractical.

    I know what a good engineer wil say ............"It depends on righting movement etc etc, with the greatest respect to engineers this is probably why people like Dyson who are not engineers sometimes design revolutionary products. Almost the entire training of a good engineer is towards optimizing known art both in terms of effiency in outcome and use of materials. A good designer working towards a market as opposed towards efficiency might say. If I can use a plain tube (no taper) with non optimal deflection but strong enough not to break then it may sail like a pig but cost so much less, be so much easier to handle that the sort of idiot that can manage a Hobie Bravo (Me!) might be able to sail it.

    This brings me back to my query is there point where an unstayed single mast (lets forget bi-planes for this email) becomes too hard. Perhaps real sailors are so enthusiastic about performance that no one is interested in the kind of simplicity that appeals to me because performance losses would be so huge without a complex custom engineering study and labour intensive manufacturing to produce for example the required degree of flex. On the other hand it may be that materials advances in carbon fibre allow a simplistic, "it won't break" approach up to say 5 meters in height but not therafter. I don't know the answers to these questions and net surfing has not helped me.

    Again thanks for your reply, this is an extarordinarily interesting forum with some very knowledgeable and enthusiastic posters.

    Best

    Guy
     
  6. catsketcher
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    catsketcher Senior Member

    Cats have no bury

    There have been a few unstayed mast cats. They usually used the aerorig idea. They needed big cabins to provide enough meat in the middle of the crossbeam.

    Dick Newick did one of the first ones in the late 80s and the boat didn't work well. An aerorig cat I saw had a whole extra rig made for it. It was the only secondhand large cat I ever saw that came with two whole rigs.

    I think you are going about the whole thing the wrong way. Instead of saying "I want easy to sail so it has to be unstayed" you would be better off saying "I want the easiest rig to sail on a 30ft cat."

    Boats are slow and so we have to be careful not to let our fascination with planes cloud our judgement. Wires are great - you can hold onto them, you can put jibs up on them, they allow the rig to be lighter and much less stressed. If you want a cat and the prime reason for it is to go unstayed then fine but it will cost you more and you will do a heap of experimenting to get it right.

    As most cat designers are builders with no formal qualifications and there is no money in research (except for the super racers) you won't find any free data on unstayed rigs. (The only cat I ever was worried about structurally was designed by a young qualified engineer who had never built a cat) You could pay Eric Sponberg and he will be able to design you a mast. But it will cost.

    My vote - wishbone boom 3 or two stay a side rig. Easy to make and sail.
     
  7. landbound
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    landbound Junior Member

    Reply to Cat Sketcher

    Thanks for your comments, I suspect you are correct and that the superficial appeal of unstayed masts may well be founded in my ignorance as much as it is a wish to have "just one rope to pull on" as per a Hobie Bravo.

    I also note you implicitly indicate that perhaps the lack of unstayed implementation is influenced by cat research economics. Unsurprising this is, as it equates to asking Kodak circa 1980 to develop digital photography.

    I am grateful to those like who reply for, I am not foolish enough to think that those who have sailed a great deal are either merely traditionalists or wrong. It is very silly to dismiss something that works for what appears a better idea without being very cautious.

    I am sure you will understand that I remain hopeful that someone might offer a suggestion on how it might be done, even if the reply is constrained by size/displacement after which all the complexities you allude to make it uneconomic.
     
  8. cavalier mk2
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    cavalier mk2 Senior Member

    As an alternative a tacking outrigger/cat could have an unstayed rig in one hull. Phil Bolger designed an offset rigged cat but I can't remember if it was stayed. The other way is a unstayed mast in each hull for the biplane rig but then it is simpler to have a single stayed mast. The Wharram tacking crab claws are a neat rig with minimal staying.
     
  9. landbound
    Joined: Mar 2007
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    landbound Junior Member

    Reply to Richard Woods

    Thank you for directing me to your site - I found the information very helpful. I do take exception to the implications of looking for a designer with your experience. Frankly no young designer/architect is ever going to get a job until you "pop of the perch". As a father I would hope the same job experience criteria are not demanded when my son goes job hunting or it will be the ranks of the unemployed until he can fill "Dead men's shoes" !

    I was particularly interested in your criticism of forward helms - I note the importance that you attach to keeping warm and dry and further note that your cruises take you to Canada and Russia - places not known for their balmy air !

    For my part I never intend moving south of Timor or North of Singapore and never out of sight of land. Would your comments still apply ? Further yesterday I just had another sun spot cut out with advice to keep out of the sun - the anglo irish genes don't help in the tropics and shade become a must while a cuddy can be swapped for a cheap hotel.

    It remains I like what you do and were I in colder climes what you offer would be most appealing.

    Guy
     
  10. cavalier mk2
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    cavalier mk2 Senior Member

    To get the bury without a deck cabin you would need to go deep with a center pod. Sharply Vd to near the surface it shouldn't pound too much and could be shaped to handle other chores like foils, rudder, engine etc... a footwell could also lower the bimini height. Rayaldrige has threads on similar center structures.
     
  11. Eric Sponberg
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    Eric Sponberg Senior Member

    Landbound,

    First, thanks to Catsketcher for the pitch. Second, you may want to read the article on the state of the art of free-standing rigs on my website which will likely answer most of your questions:

    http://www.sponbergyachtdesign.com/StateoftheArt.htm

    Third, specific answers:

    Is it really engineering complexity or rather that the mass manufacture of Aluminium tube of varying wall thicknesses and diameters is so prevalent and competitive that the manual process of constructing a tapering carbon tube is cost prohibitive.

    Tapered aluminum tubes of varying wall thickness, which might be ideal for a lot of free-standing masts, in fact are not easily found. Wall thickness is usually constant. Often the strength might not be sufficient. Each tube still has to be engineered to the boat at hand--a tube mast for one 10 Meter Loa heavyweight boat would not be appropriate for another 10 Meter lightweight boat. Desired deflections might also vary from boat to boat, so it is really difficult to make standard tapered tube designs to support production runs. This leaves us, actually, with the choice of using carbon fiber and molding it to our needs.

    I note in the exchange between two knowledgeable advocates of unstayed masts that they were looking as a rule of thumb for a 7% deflection and that to calculate the deflection a double integration was required - the calculation is really not that complex. What may be very difficult is the manufacturing process to achieve that deflection - I simply don't know.

    We who design free-standing masts all have slightly different criteria for determining the appropriate amount of deflection. It is important that we do consider deflection, as a mast that bends too much will cause the sail to invert (curve in the opposite direction) or be too stiff and not bend enough to gusts. The engineering is not that hard for an engineer who knows what he is doing (that double integration), but it is the determination and writing out of the laminate schedule, to a process that the builder can build, that is more difficult. Now you are matching the engineering numbers to the building process. If you are going to build the mast yourself, then you need LOTS of detail about how to lay up the mast. The strength and deflection of the mast depend on the size of the mast section at any given height, and how that mast section tapers along its length. What falls out of those calculations is the wall thickness all along the mast. That information has to be converted to a laminate schedule, made up of unidirectional carbon fiber and off-axis carbon fiber, which might be 0/90 carbon cloth, +/-45 (double bias) carbon cloth, or UDR oriented in the off-axis directions as necessary. That mix of fiber orientations is absolutely critical to the life and behavior of the mast. It depends, too, on what types of carbon fiber fabrics are available at the time and in the location in the world where the mast is built--that determines, in part, how the laminate schedule is drawn out. Also, are you going to use a wet-layup technique, or are you going to use pre-pregs? Are you going to lay up over a male mandrel, male molds, female molds, etc.? How are you going to put the parts together? All that affects how the laminate schedule is created so the the builders can understand the process and build the mast. A production mast builder will have all his own preferred materials, techniques and processes, and so the laminate schedule will reflect that. They may very well draw out their own laminate schedule rather than rely on an outside designer's.

    As for taper, I like to use entasis taper, which actually creates fatter sections up high than a normal straight taper. This affects strength, deflection, and ultimately the laminate schedule.

    I am in essence just puzzled that you can't have "a tube to pop in a hole" instead of a complex load distribution system via stays with equally complex system of ropes as opposed to the system on a Hobie Bravo. Clearly my puzzlement is founded in ignorance but I am curious if there is a rule of thumb where weight/height/weight make such a mast "too hard" or "too expensive".

    No, there is no rule of thumb. Each mast must be designed to the boat at hand. The boat's righting moment is the primary load determinant to engineering the mast. On a multihull, if one were to design to the boat's righting moment, which on a multihull is HUGE--the point at which the windward hull just comes out of the water (not an uncommon experience on a lightweight daysailing multihull)--then the mast would be VERY HEAVY and VERY EXPENSIVE, two things that are totally anathema to multihull sailors. So you have to make an arbitrary decision--what load are you going to design to? And after you build the mast, you have to make sure that you don't exceed the safe limit of that load. This is done solely to reduce weight and cost. A stayed rig on a multihull can be relatively light by comparison, and even they are designed, usually, to some arbitrary limit below the boats maximum righting moment. This is the attraction of keeping a stayed rig on a multihull--low weight and low cost. I should also point out that if you have a single free-standing mast on a catamaran, it has to be mounted on the crossbeam, and so the crossbeam has to have sufficient structure and depth to grab hold of the mast. This can difficult to do, depending on the boat design. It is far easier to go with a bi-plane rig where the masts are stepped in the hulls which are normally deep enough to hold the masts anyway--it simplies construction. The criteria of what design load do you use still applies. But overall, the masts are less tall than a single mast.

    Is there an infelction point, say in Kgs or meters LOA or Mast Height, where even a carbon tube becomes impractical.

    Theoretically, no, there is no limit engineering wise. The only limit, really, is the size of your checkbook. How much money do you want to spend to build the mast? This is true with anything regarding boats, or anything in the world for that matter.

    If I can use a plain tube (no taper) with non optimal deflection but strong enough not to break then it may sail like a pig but cost so much less, be so much easier to handle that the sort of idiot that can manage a Hobie Bravo (Me!) might be able to sail it.

    Strength and deflection are not mutually exclusive parameters. You can have both. If you choose not to have both, then it is because you are compromising on cost, weight, and performance. You get what you pay for.

    This brings me back to my query is there point where an unstayed single mast (lets forget bi-planes for this email) becomes too hard. Perhaps real sailors are so enthusiastic about performance that no one is interested in the kind of simplicity that appeals to me because performance losses would be so huge without a complex custom engineering study and labour intensive manufacturing to produce for example the required degree of flex. On the other hand it may be that materials advances in carbon fibre allow a simplistic, "it won't break" approach up to say 5 meters in height but not therafter. I don't know the answers to these questions and net surfing has not helped me.

    A lot of people appreciate the simplicity you are after. Try to find a good used Freedom cat ketch, or similar boats like a Herreshoff, Spar Hawk or a Tanton Offshore--they are very difficult to find because people like them so much, they are so simple to sail, that they hang onto them for years and years. The vast majority of the free-standing masts are made of carbon fiber, which has now been with us for many decades. As stated above, there is no limit really as to the size that you can build. And personally, I believe that a good free-standing masted boat has every bit as good performance as a stayed rig boat overall. The performance can be much better if the mast is a rotating wingmast. Strength and deflection go hand in hand and one typically designs to both criteria. The latest free-standing wingmast that I have done is the largest I have ever worked on, for the GT80 Sloop being built in The Netherlands. The design followed all the principles discussed here, and the builders will be the boat builders themselves, so the process is designed to match their capabilities and the materials that they will have available.

    I hope that helps.

    Eric
     
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  12. rayaldridge
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    rayaldridge Senior Member

    Not to be overly critical of your young naval architect, but why must the boat be 8 meters again? I don't think there's any magic number that divides seaworthy boats from unseaworthy boats, but if you're just daysailing, why not a smaller cat? A Tiki 21 has sailed around the world, and just competed very well in the Jester challenge.

    When I was first thinking about Slider, I considered a freestanding mast, mainly because I was interested in archaic rigs and whether they could be successfully adapted to multihulls. Of those, the lug is my favorite, but needs an unstayed rig to keep some of its advantages. I eventually went with a sprit-sloop rig, stayed, and it turned out well.

    Here's a piece about the decision process I went through:

    http://slidercat.com/blog/wordpress/?p=52

    Shade is definitely helpful in hot climates. I went with individual biminis over each hull:

    [​IMG]

    These don't have much windage. They could be built as dodgers to provide protection from bad weather.
     
  13. Angélique
    Joined: Feb 2009
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    Angélique aka Angel (only by name)

    Wharram Amatasi 8 Meter Day Sailer . . .

    The new Wharram Amatasi, 8 Meter (27 ft), Day Sailer . . . . .

    [​IMG]

    http://wharram.eu//live//article.php?story=20100715135624601

    Its also in Classic Boat Magazine, july 2010, design contest article:

    http://ipcmarine-gb.zinio.com/reader.jsp?issue=416129087&o=int&prev=si

    Go with the cursor to the bottom and use the page selector to select page 54 for the beginning of the article. From page 54 to 59 (the contest) can be enlarged by clicking on the page. There are also tools at the top if you go there with the cursor.

    Good Luck!

    Angel
     
  14. outside the box

    outside the box Previous Member


  15. outside the box

    outside the box Previous Member

    Excellent post Eric always appreciate reading your post's thank you.
     
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