Cross Indian ocean in 4 meters dinghy sailboat

Discussion in 'Boat Design' started by Nauticals, Mar 4, 2018.

  1. kerosene
    Joined: Jul 2006
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    kerosene Senior Member

    I will unsuscribe.

    ”Designing” an ocean crossing sailboat with zero hours of either (even self) studying yacht design principles or actual sailing is arrogance and ignorance combined.

    Nature of boats is really easy to read book. Skene’s yacht design book is also a good book.

    You are making your own life harder by ignoring solutions others have figured out and wasting your time in building an inferior boat.

    In an earlier post it was pointed out that volume in ends results in less comfort. You shrugged it off by stating that ut is an adventure.

    Re-read those passages again and change comfort to survivability.
     
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  2. Nauticals
    Joined: Mar 2018
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    Nauticals Junior Member

    @kerosene no comment, should i repeat that im not a boat designer or that i would had take a related course if i wanted to read a hundred books or this how i like to waste my time.. if you have something practical to suggest do so, otherwise you too wasting your time. I make it clear from the beginning what im looking for and im very thankful to all those that gave me links and practical info for related topics as it contribute a lot.
     
  3. Manfred.pech
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    Manfred.pech Senior Member

  4. chinaseapirate

    chinaseapirate Previous Member

    This guy,

    was a good friend of the man (notorious in Ferndale, Wa - at least the building inspectors) I was helping to complete the never ending construction of his house. I almost got to meet Alexander Doba- maybe I still will. The reason I mention this is because I don't believe his kayaks had extremely good luck crossing the Atlantic 3 times. It was its length and very low DLR that allowed him to cross so easily( and want to do it again!!). He and his friends built them, wise choice. If its just a money issue (the length of your boat) remember, (or learn for the first time - anyone out there in audience) an 8 meter kayak is a cheaper/easier/stronger build than a 4-5 meter "fatter" monohull. I would most certainly put some outriggers on it. Or even better a single longer one and turn it into a proa. Maybe I'm assuming too much, but since you seem specific in making a passage to Mauritius, i figure the destination is your main goal and not setting any record for "shortest boat" to cross such and such. If this is true, don't set your limit on what you think is manageable to build by length, figure it by weight, then design it 11:1 (Length to Beam at waterline-anything close). You will arrive quicker, sleep easier, and have taken a far less risk. If you plan on stopping or even are forced to land somewhere other than the final destination...bring an anchor - plan to land at 8-9 AM. The 2 -4 meter trade wind swells may seem like child's play out at sea but whole different story near shore - which is rarely the real shore anyways. Seriusly your more likely to be stranded on a deserted island or be eaaten by sharks near a coral head or just plain drown than having to experience capsize or sinking at sea. And if no one has mentioned it yet - you will get hypothermia even in 85 degree water eventually. I'll give you anything more specific you ask about design or experience at sea...I'm immune from scary ships pictures,hypothetical structural failures and seamonsters- just post a specific question- I'm also liability proof. If you know who the name associated with 1988 stars and stripes Olympic Catamaran design was, you should also note he was not an architect but a builder FIRST and LAST- he got veto power.
     
  5. David Cooper
    Joined: Jan 2015
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    David Cooper Senior Member

    What use are the tiny outriggers? If they're going to have hydrofoils on them, that might make sense, though only if the boat can go fast enough to generate useful force from them. If they're just little floats, all they'll do is add drag while the keel does most of the work of keeping the boat upright, while if you make them bigger, they make the keel redundant and may prevent recovery from capsize. It's a really awkward combination which doesn't yet make sense.

    And why not read just one book on yacht design? It will save you money and time, as well as stopping you wasting a lot of good wood and other resources on something that may be truly woeful. It's fine to reject what you've learned afterwards if you find that you still have good reasons for going against more conventional designs, but you don't yet understand what you're rejecting.
     
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  6. Nauticals
    Joined: Mar 2018
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    Nauticals Junior Member

    @David Cooper regarding the outriggers i was thinking that they re looking useless in that state. i want to keep the hull small. This sections are only draft, yet building a smaller hull (3.4m) just to test few things.

    About books, indeed i agree with kerosene. What i was pointing out it was not about books itself but just the negativity of kerosene. He probably know far more than i know, or might not. But indeed forum communities are not about only to say read this and done because this will made any forum useless, because we could just have only a directory with description of books instead. Forums are for us to talk direct into a topic (i think) and share so we can make better.
     
  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I disagree that reference to books are not good. It is impossible to post the whole text of a book in each post. You have to do your homework and read these references.
     
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  8. chinaseapirate

    chinaseapirate Previous Member

    Just looked at the drawings Nauticals. It seems to me that you are designing to you own knowledge of what is bulletproof, simple, and strong and that your sure that you can build to spec. Myself, I see only three glaring errors (I'm assuming you ran out of paper and your rudder is not to scale...if not then four), and a fourth not shown in the drawing- its implied though - see bonus suggestion) .Overall it looks stout, for your intended purpose , and easy design to follow from a single 3 x 5 index card. Frames are great, joinery good, and although it doesn't have sweet lines could still go downwind 6kts+ and hypothetically make windward progress. Ok with statement? everybody?? Good then.
    #1 (and I realize your drawings are not complete) I dont kow what your making the skeg out of(shape ( shaped 3" marine ply?, 1/2" titanium? or what?) but, If strong enough it will rip your hull apart as shown. Best suggestion I can think of offhand is ordinary 3/16 steel, two pieces, bolted to either side of you boat into 2 of the frames shown. Actually more like four because you would need to double each, and also double the plywood over that meter of the boat, sides, deck, bottom. Bring them together into a V and attach the 100kg bulb. The weight and depth look more than adequate for a 950 kg skinny yacht. Which brings me to
    #2 Is this a cargo ship or something or did you just look at a typical displacement of a production 20 ft keelboat for the figure of 950kg? I can't add up more than 600kg empty, 3/4 ply ,keel,bulb,rig, and I can easily see it with less keel, 1/2" ply rigging ,anchor, desalinator, trolling motor, battery,at 500kg or less.
    #3 those outriggers are beyond useless as is. Under sail any ways the will just drag, bad enough to interfere drastically with control of the boat in fact if completely submerged, As shown in the drawing appox halfway submerged at rest they will provide 70 kg of buoyancy five feet from resting center of buoyancy. By the time your crossbeams dig in they will provide 140 kg about 2 1/2 feet from center of buoyancy which is about a third of the effective righting moment of your keel/bulb. They will however become the main drag component of your boat, slowing it down,and pivot you sail full face against the wind if your hull isn't already laying down flat. All is not lost however. If you remount them with a 90 degree twist (flat side down), attach them at either end to crossbeams (add 1), which can slide port to starboard and vice versa, you can still utilize them at rest or mild weather, centered, as "flopper stoppers" , and underway slide the beams to weather, using the weather one as a "hiking " ramp. Overall they will give you more room and stability just don't plan for them anything but to kiss the water from side to side one at a time. Use a leash when you go "hiking", and draw some bulkier crossbeams...

    Bonus suggestion- Right at the point where your design shows the "sides" bending together to form the bow... discontinue the curved bottom panel of your hull. Reshape the side panels to where the stem starts about 40 mm above where it is shown, your waterline is off 15-20cm (I'm positive) . Then follow the side panels with your flat floor panel, completing the sloped triangular shaped box. From there - splurge and buy 2 meters squared of fiberglass and a gallon of polyurethane expandable foam. With boat upside down, bond to the floor a few laminated stringers (fit them in under the discontinued round bottom or better don't even have it built yet) meeting at the stem. Plane these to your ideal shape. Do the same to the last meter of your stern also (may need two gallons of foam total). fill the spaces solid with foam a bit higher then all the stringers. shape it when dry and glass the bow/tern bottoms. Probably better to do the whole hull first with the flat bottom floor the you can put laminated stringers the full length. The problem is that the drawing is impossible to form at the bow and stern as shown without cutting up the plywood in many more places than you show. There is compound curvature there. And you cant match the tubular midsection with 3 or 5 chines or carry it through in one piece with any amount of steam bending or 1/32" plywood lamination. You can with foam and glass.

    Last note- There is no practicing with epoxy, except application and waste. The bond is either 100% good or 100% no good.
     
  9. Nauticals
    Joined: Mar 2018
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    Nauticals Junior Member

    I have questions regarding beam-weight and mast size and weight.

    I can calculate how much sail the boat needs, but im not sure what's the mast size and weight should be. Im reading that as less the beam is, the less sail could be put up. And im very confused about that.

    My boat gonna be 6.5 meters and will weight full loaded around 2000 kg. I believe that i would need probably around 20-25 sqm sail area. However how the mast size and weight will affect the boat? How long mast should i have regarding my beam and weight? and in general how i can calculate that for different beams and weights?
     
  10. JSL
    Joined: Nov 2012
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    JSL Senior Member

    There are lots of good books that will help you learn aspects boat design to address sail area, mast height etc.
    or
    hire a naval architect / yacht designer to help you out.
    or
    review existing designs that might meet your needs.
     
  11. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    There is no cook book recipe that can answer your questions in a reliable manner.
    The height of your mast...or the waterline width are not directly codependent. How the weight is distributed with respect to the center of buoyancy and a bunch of other factors enter into the selection of the various design parameters.

    If you are determined to design your own boat then you have to do some serious study whether you like it or not. Failing to do so puts you on a suicide mission if you mean to traverse the Indian Ocean.
     
  12. Nauticals
    Joined: Mar 2018
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    Nauticals Junior Member

    @messabout im doing a serious study for some time now and i have consider most of the parameters. Here i am, to the mast height relatively to the boat's beam and weight. As you mention i haven't find something reliable for this matter and that's why i came with this question for anyone if knows to put me to that direction so to know what im looking for. Im designing my own boat, i have already came with a plan, scale model etc. yet this is a missing piece before i proceed with my design. Im really looking into sails at the moment because im gonna do all by myself.

    @JSL thank you for your suggestions. If i wouldn't design the boat myself, i wouldn't ask this question but rather i will hire someone to do so. Im reviewing existing designs but it is important for me, not just to copy it but to understand it also. If you have a specific book and chapter related to this matter please suggest. Or any relevant information.

    I believe this matter is related to the weight distribution of the boat and the weight and height of the mast as well the hull in sides in that area. However another thing but very related to that, is what happens with a sail on it, and what does the over sail could do. It is important to know how it works, but i believe the vast majority of naval architects and designers don't know too far more from a cad simulation. Even the stability points require a lot of practical testing if not using a cad simulation. However this what i assume only. How more on mast with the sail. If somebody knows can contribute with information.
     
  13. David Cooper
    Joined: Jan 2015
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    David Cooper Senior Member

    If you were building a dinghy, the beam of the boat would put a limitation on how far the crew can sit out to balance the boat, but if you have a heavy keel doing that job instead, the boat's beam is less significant, although it still makes some difference because the more the boat tips over, the further away the keel is from the average part of the hull that's below the water's surface, so that leverage is greater with a wider hull. If you're using outriggers, they multiply the leverage effect many times and completely remove the need for the heavy keel.

    This all relates to how much power you can usefully generate from the sails before the boat tips over too far (or flip over if it's a multihull), but in light winds you can gain from having a taller mast and greater sail area, while in strong winds you can always reef. What matters most is that you have enough sail for the weight of boat, and the ability to reef easily. The strength of the mast will depend on how much power you want the boat to be able to take from the sails, and since you aren't racing, you can simply copy the sail area and mast strength from a similar size and weight of cruising yacht (though erring on the side of a bit of extra strength because of the extreme conditions you might be placing yourself into).

    I wouldn't worry about calculating it - just look at similar boats and match them. If you don't put enough sail on it, you'll be horribly slow, whereas if you have more than necessary, you can simply reef sooner (and it won't be too much sail whenever the wind's light). Given that your boat will likely be heavily over-engineered and considerably overweight, it may need more sail than boats made by professional designers, but fortunately it should be able to handle more too, so you should probably go for more sail area than similar sized boats rather than less.
     
  14. JSL
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    JSL Senior Member

    some more:
    a: Skene's Elements of Yacht Design is a good book.
    b: Wide boats are more stable (form stability) but they may not self right if you capsize: they can be stable when inverted.
    c: Keep an eye on your weight vs waterline length. A high displacement length ratio will perform like an iceberg.
     

  15. Nauticals
    Joined: Mar 2018
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    Nauticals Junior Member

    @David Cooper you have been very helpful, i really appreciate all the information you have given, also other people too. you are very right in many of your guesses, including heavy over engineered. If you could know please can you give me any idea regarding, mast weight and sail and the required ballast it gonna need? Also regarding the keel, how much heavy should be related to the total weight of the boat?

    @JSL thank you for your notes, i will check this book
     
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