Learning boatdesign. Can u have a look at "my" boat?

Discussion in 'Boat Design' started by sailingdaniel, Aug 6, 2011.

  1. sailingdaniel
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    sailingdaniel Junior Member

    Added a maybe better pic...


    Change the lower wl so they are now right.

    I still wondering if u think i have got the different ratios right..

    I read that for different "speeds" / SLR, Fn the LCB should be in different places.. Also the transom is submerge the LCB should move 6 % aft. (in principles of yacht design) I have a slightly submerge transom and the LCb at 4 % .. The Fn i have "optimised for is 0.4 and than the LCB shold be at ca 3.5 % if the transom is not submerged.. ??

    I bean reading and searching info on the net of the Curve of area, In some places i find that it should have a shape of some fancy name i dont remember now.. I also googled for pictures. I find many line drawings but few whit the curve of area.. This seam to be a "top secret" thing . I would think its one of the most important thing to understand a hull... I should look "good" comes up in many places.. Does anyone has some thoughts on that.. ??? In the pdf i added u can see that curve at different angels of heal as well..

    If someone knows a place on the net where u can find many examples of line drawings i will be interested to know..

    Iv got some good input so far.. im hoping for more..

    If someone has something more to add ill be glad. anything at all..
     

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  2. BATAAN
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    BATAAN Senior Member

    Nice job and looks like a fast racing boat but scary (to me) in a bad gale when short handed, and that skinny bow looks like a poor place for enough anchors, proper fairleads, a windlass and chain. Remember, cruising means anchoring in bad places sometimes, not just sailing ever onward towards the horizon, and a 52' boat with roller furlers presents a lot of windage and needs big anchors, heavy rodes and a way to stow and handle them and recover chain from deep water. I wonder why you are trying to design such a highly developed racing type as a quite expensive cruiser with your limited knowledge of the factors involved.
    Even building a large sailing model (1/12 scale) out of styrofoam faired with sheetrock mud and then glassing, then hollowing it out, adding a deck and rig it will tell you a lot about how it sails and steers and trims with scale weights. A week's work and $300 will give a tangible thing you can hold in your hands and look at from all angles and sail across a pond and see if you can get it to balance. This is not finished, painted or otherwise for display, so can be rough in places that don't matter. Few seem to take this approach today, but Nat Herreshoff always designed from a 1/2 model, then took the lines off of it.
     
  3. sailingdaniel
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    sailingdaniel Junior Member

    Thanks again bataan for your reply..

    I think your advice to build a small model is one of the best advice for me. I am not very good at computers, but i like to think that i have a good understanding of physics in the "real" world if u know what i mean. So your model advice i think can work well for me one day..

    The 27/10-2008 i was in a very windy anchor place in Madeira, I was stuck there fore a week. That is when i made my first sketch. That looked very traditional. From then i started to read and learn.. And along the way my "dream" boat change a lot.. A friend gave me a book of Dashew and his Sundeer boats. I was sure his ide was as bad as it gets and his ide was soooo wrong.. But some where along the line i had to change my mind. when i was reading in "principles of yacht design" it was clear to me that his ide made sens.. So i had to admit to everyone i had change my "religion" :) . But im not a "fundametalist" in any way. I see the beauty and reason for all kinds of boats.. That is the only "why" i can give at this time... Boat design seam to be a lot like religion to me anyway ....

    The reason I want a boat that can go fast is the same reason some people say they want heavy boats.. That is when its blowing u dont have to reef so soon. That is for a heavy boat that can take the extra force. But i think also for a light fast boat that is a little bit under rigged. That can speed up and that way absorbe the wind . (downwind that is) , but that is just my ide...
    Also some where far back in my mind is the ide of going nonstop around the world single handed like Robin Knox Jonson and CO....

    Anchor: The forward 3.5 m i want to have as space for anchor, chain , fenders , (empty) jerrycans , sails , ropes , dingy , outboard , collision area ,etc . so there will be room for chain 3.5 m from the bow down low where it belongs..

    Im now in Mauritius ,maybe when i get back to Skandinavia I have change my mind again. Love is blind they say... :) If not i hope i at least have learned much more..
     
  4. BATAAN
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    BATAAN Senior Member

    Dashew's SUNDEER series were very logical and expensive modern motor sailors, fast and technical, long and lean, and have crossed all oceans quickly and comfortably. I notice they finally ditched sail completely and took the logical step of making it all motor though.
    And about if a 'heavy boat you don't have to reef so soon' you are saying the typical grossly under-rigged double-ender intended for the North Sea in winter, then yes, your statement is true. You don't have to reef because the rig is too small. A heavy boat needs, and can carry, larger working sails.
    My own very very heavy cargo design necessitates the first reef in about 8 knots of wind, when I strike the mizzen sail, so she is not under rigged like some vessels you may be thinking of and averages 125 miles per day at sea on a 34' waterline and has done 140 once on the trip to California from Canada. See the SHIPBUILDING thread under Wooden boat construction on this forum. Heavy does not have to be slow.
    On a vessel with a long skinny bow, the place for the windlass and chain is far aft, close to the mast, at the after end of your 3.5 m reserved space. The 2-40kg anchors, their housing troughs and strong roller, plus the roller furlers, pulpit etc is all the weight you want out there when you are trying to get to windward in a bad sea and light air. All is not joyous sledding downwind, and weight in the ends quickly degrades performance of a skinny-ended boat by adding greatly to the pitching moment. If you work hard to get a high performance cruiser, don't turn it into a slug. The ends should have no more than an oilskin hat in them ideally. Bristol Channel pilots in the age of sail were fanatical on this issue and their vessels and area of operations are well known. Even fat ended BERTIE became much more docile in tacking when I moved tanks and anchors and chain aft somewhat.
    This is another example of what works for performance and racing does not always work for cruising and voyaging, which is basically cargo carrying. Chain, anchors, water, food, extra sails, more food, dinghy (and it better be a darn good one), kayak, life raft if you carry one, books, musical instruments and a hundred other things. All the heavy stuff, tanks, chain, mast, ballast should be as close to the center as possible for performance, yet for comfort it's best if the weight is spread out. Racers just don't make good cruisers, but if what you want to do is spend months at sea on long passages and not cruise, your idea seems like one way to look at it.
    Remember, if you go cruising you will go aground eventually, so if your vessel has a long skinny fin with a heavy weight hanging from a canoe-form hull, the floors and stringers in the bottom must be much stronger than necessary for pure sailing loads, therefore heavier.
    Bob Griffiths' long slim AWAHNEE visited Antarctica and circumnavigated in 60 degrees South among other notable passages and she is an efficient sea-going machine built very cheaply out of ferro-cement on an Australian beach from parts of a wreck. No high tech nothing, just good design and seamanship here.
     

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  5. sailingdaniel
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    sailingdaniel Junior Member

    Baatan . I have looked at the sailing video, the sushi looks almost as god as the mainsail. :)

    Your added pic looks like a nice boat. I dont know much about cement but im a little skeptic to that material.. But the boat is a beauty ..

    Dashew has turned to the dark side i know. :) but his boats still sails. Some say they are no good to windward. If u are ok whit a deeper keel i think that would help..

    I agree whit weight up in the bow is no good. It makes a huge different on my small 33 fot boat whit 25 fot wl.. mowing the anchor chain and windless to the mast was one of the first modifications i did.. And when sailing to windward i sometimes move as much can from the ends and strap it down on the saloon floor..

    On my drawing u can see that there is a cabintop ( is that the name ) aft of the mast and the freeboard is high as well. Therefor i can have a higher floor from 7m to 11m from the bow. That gives space for ca 1100 liter of fuel/water on each side under the floor, sofa , gally. It also give space for bigger/higher floors to take the load from the keel. That will also be the best place for beers , cans and other heavy "bulk" stores.. And a big battery bank.. This way i can also look forward from inside and see the head sail and maybe a big ship when I cook , etc.. also the limit of positive stability get higher and the boat gets drier whit high freeboards.. The are downside to this as well i know, but its a compromise that seams ok for me..

    The boat i try to draw might be 16m long, that does not mean i have compare it to other 16m long boats.. I might compare it to other boats the same weight instead. Ore other boat whit the same size rigg and sails. Ore whit the same livingspace.. Length seam to be the biggest "thing" in racing, it also matters for what u pay in a marina.. I dont race ore go in marinas. And as the hull is just a part of the total cost of a boat and that scaling a boat in length seams to me to give less loads than weight , beam and stabilety it makes sens to me as it also seam to the most easy way to increase speed..

    But dont get me wrong , I dont try to convince U ore anyone else. As i said before, I like all kinds of boats and there is good reason for most of them.. I just explain how I think..
     
  6. groper
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    groper Senior Member

    daniel, much of our discussion on DLR/slenderness is difficult to apply to a sailing monohull as you have alot of other issues to deal with like stability, heeling, sail power, acceptable keel draft and counterbalance mass etc and you really need to figure out an accurate weight of this boat before going any further... do you know for certain that your displacement will be in the ballpark based on your indended construction methods and desired accommodations and equipment?

    From the weight, you will be able to optimize it more accurately for the likely speeds it will do in moderate breezes that are comfortable for cruising... You see, it seems you have designed a high speed yacht hull form that will require a large rig to complement it whilst also being built light for it to go fast... makes for thrilling sailing but unfortunately its also quite a handfull if you get caught by surprise in strong winds whilst making passages and your attention is elsewhere below... and forget going fast if you plan on carrying all the "passage making" mod cons on board to weigh it down... therefore you really need to question your priorities otherwise you will end up with a yacht that is neither fast OR comfortable...
     
  7. Bijit Sarkar
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    Bijit Sarkar Naval Architect

    I am sure you mean an L/B ratio of 5 and not B/L. That would be landing a plane sideways on a runway. :)
    Anyway, I would advise a larger L/B ratio. bulkers and barges would be in the rage of 5 to 6 . For your boat, I would advise an L/B ratio of 7 or nearabouts.
    However, such a long slender boat will give you better forward propulsion but a bit difficult to manoeuver. Let your rudder to projected underwater profile area of the boat be around 3% for good manoeuvering - but it would also mean higher rudder torque.

    I am sure you will do a great job . Take PAR's advice - I have always found him speaking a lot of sense.
    Rgds
     
  8. sailingdaniel
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    sailingdaniel Junior Member

    Thanks both groper and Bijit..

    Yes Bijit i mean L/B :) . your suggestion of a L/B of 7 sounds a bit high for me on a "small" boat like this.. And your 3 % rudder , that would be 3 to 3.5 m2 , i think that would be more than needed..

    Groper, thanks again for giving advice.. I cant say that i know its possible to build a hull like this for that given weight.. I have been looking at different boats on the net.To compair ballast, disp , draft, build material , SA, etc .And the weight is a guestimate from my side.. But i cant win a argument here to prove that..
    I asked about foam cores an epoxy a while ago. So now I am trying to understand that, but there i have a long long way to go before i can calculate for strengt/weight. Im hoping to get some books later this year.. So for now this is just a guess.. But whit a deep draft bulb keel i think its a not to bad "guess".



    But i thought i could get some input on the boat/lines/numbers i have shown, as i first asked. Maybe i should have started whit : IF this boat is possible to build...

    A this is an open forum anyone can ask what ever but no one has to reply.. I try not to ask to "stuped" questions. And im very happy for all answers iv got so far..

    Lot of answers are about storms, school and general sailing experiance.. the last 9 years i have lived all but maybe 50 days on a boat. working the coast of norway , sailed over 3 big oceans singelhanded and more.. So i have some ide of what i want.. Not saying i know a lot , but i know a little about floating things anyway..


    So are u saying that 120m2 SA is to little for this hull. Will it do really bad in light winds?

    My questions about the different ratios/lines still stands..

    Thanks everyone ..
    Daniel
     
  9. BATAAN
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    BATAAN Senior Member

    Daniel, I wasn't recommending ferrocement for your boat, just pointing out that AWAHNEE was built of it and was successful despite a heavy and awkward hull material.
     
  10. sailingdaniel
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    sailingdaniel Junior Member

    Hi Bataan .. I understand what u mean. If i sounded negative ore anything i didnt mean it.. There is for sure a lot of comfort in a heavy boat. I have meet a few cruisers who sail ferrocement boats and they all do just as well as the rest..

    by the way , looked at your picture in your profile,, nice pic ... :)
     
  11. BATAAN
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    BATAAN Senior Member

    Scurvy dogs and dogette at work.
     

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  12. jak3b
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    jak3b Junior Member

    The shades somehow "fit" lol.
     
  13. BATAAN
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    BATAAN Senior Member

    One of the 2nd Assistant Director's jobs is to make sure all shades disappear when cameras roll.
     
  14. PAR
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    PAR Yacht Designer/Builder

    Guessing about weight, guessing about trim, guessing about volume distribution, hull form refinements, appendages, ratios, what could go wrong here . . .

    There's not short cut, you need the education and discussing each design element and assumingly, the structural elements when you get to that stage, in an online forum seems about as long a way around the block as you could take.
     

  15. BATAAN
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    BATAAN Senior Member

    What PAR is trying to say I think is this is far too technical and sophisticated type to be designed by "eyeball", but needs more than your present design education can give it. This forum isn't design college, but a support group, and you need to start at the beginning when you are presently trying to start at the end. You have a finished product in mind, without the process of developing that product. I can draw a flying saucer. I can't make one fly.
     
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