Did a dream got shattered?

Discussion in 'Boat Design' started by BertKu, May 16, 2010.

  1. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Although I made as many calculations as possible and it shows that the waterline has dropped, or otherwise said, the boat is lighter in the water. It is a pity that I haven't been able to come up with solutions to make the boat more stable. I could put more lead in both keels, which gives it a better center of gravety. I also could put more Sealed Lead Acid Batteries in the bottom of the hull. It would give me more energy. Absolute a pity. It had the right lenght, I could stand up in the cabin , it had all the detailed drawings for all the extra's I needed. It would not be the fastest and lightest boat on the water, but it gave me a solid , seaworthy boat. Detachable rudder, twin keel for the motors with rudder or reversal system build in. ( I cannot reverse the electrical motors due to the way the shaft is mounted to the pulley) The possibility to mount a small storm jib. If no positive suggestions will come forward from this forum, I will have to see what I can still do.

    Refer to the attachement Hartley4.jpg

    But it looks like I have to rely on the modified Fisherman, Firsherman.jpg.
    I have to crawl like an old man into the cabin, smaller boat than I like to have and one has two holes for the two single beds area, instead of one secluded nice spaced double bed like the Hartley above. No mast, not storm jib, no twin keels for stability. But it is light and that's all.

    For me to calculate the various calculations I need to do, nobody was willing to give a reply to : How can I calculate the wind forces by the various strong and weaker winds. i.e. what would be the force on a 1 square foot, or square meter 2 meter from a point in kgm or Newton or whatever.

    Bert
     

    Attached Files:

  2. CatBuilder

    CatBuilder Previous Member

    Am I understanding correctly that your problem is that this boat is not heavy enough?? She is riding too high on the water?

    Seems if I am reading this correctly, there are plenty of ways to overcome this problem. Most people have the opposite problem.
     
  3. hoytedow
    Joined: Sep 2009
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    Location: The Land of Lost Content

    hoytedow Fly on the Wall - Miss ddt yet?

    Always could take on more water, provisions, etc.
     
  4. tugboat

    tugboat Previous Member

    is your problem that your not sitting at the waterline? couldnt you just add ballast? cement works good- steel etc...most boats need to be ballasted. dont worry you will solve it...good luck
     
  5. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thank you catbuilder.

    The problem is that I bought a plan for a 28 feet sailing boat and thought that I could modify the plans and reduce it by 13%

    However everybody stated that the boat would be unstable and I did my calculations and yes, it is indeed true what they say. Yes I could put some more Sealed lead acid batteries in the bottom of the hull and yes, I could start loading some more lead in the two keels. But I like the apealing view I made of the reduced sailing boat and yes, it is in my view more suitable on the open sea. However yes, it also means that the propulsion power I have avialable is limited. The Fisherman is certainly a better choice from that point of view. But I don't like the way two people have to sleep through two holes and also it is actually just too small.

    I thought it was a brilliant idea to reduce a plan by 13%, but like Tom and Easy and many other have said, it has become too unstable. My hope is, that after I have put the drawings I made on the boat.net, maybe somebody could come up with some ideas, we haven't thought about.
    Bert
     

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  6. hoytedow
    Joined: Sep 2009
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    Location: The Land of Lost Content

    hoytedow Fly on the Wall - Miss ddt yet?

    Whatever you finally end up with I hope it carries you to a safer environment than the one you are in.
     
  7. CatBuilder

    CatBuilder Previous Member

    This might be crazy, but now that you have figured out that the boat will be unstable if shortened by 13%, why don't you build it the same way the plans tell you to - at 100%?
     
  8. apex1

    apex1 Guest

    I would not call that crazy. It is one of the very few sensible comments i have found by so far on Bertie´s plans.

    But it is not possible to drag those people away from their preconception, no matter how many experts comment on it.

    The real crux is, they waste their own lifetime and drag others into the same hole.

    Wasting the time in the boatshed, instead of bothering internet communities, people like him would have already accomplished half a boat to a proven design.:(
     
  9. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Catbuilder. Thanks for contributing to this somehow heated argument. There are good reasons why I cannot build it at 100%. The main reason , one cannot trail that size of the boat in this country. However by reducing the plans by 13% alll around, it would be able. But like everybody says, it reduces the stability. HOWEVER THERE ARE NO PLANS FOR AN ELECTRIC SEAGOING VESSEL !!! Thus I have to feel my way around. Take a knock when somebody runs me down. but stand up and find my way untill 100% of all the questions I have created for myself have been answered.

    Secondly, Apex1 Gruss Gott, I have done the calculations and you are right,
    it reduces the stability. But let me now ask you the question, you seem to know quite a bit about it. Let me repeat myself, there are no plans for a seagoing electric driven vessels, the size, the build, the shape, the comfort, the way I like it. Except to modify an exsisting plan. And I like the Hartley plans.

    COULD THE INSTABILITY BE COMPENSATED BY:
    a) making the 2 keels slightly deeper . Be carefull what your answer is, I will calculate the result.
    b) The orginal design has both keels straight down. Could the stability be improved by having them instead of straight down, at 90 degrees against the hull. With other words, the lower ends are pointing outwards. In that case I have to forget the rudders build into the keel, but I have to use the mechanical reversal method.

    Unfortunately, I will not dive into a shed and start making something , which is not what should be a succes plan, in which I have the confidence that it will work. Apex1, you have to do better than the remarks made.
     
  10. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    In the opening statement #1, I asked a question. If you such a bright German boy, why not have the decency to show me that you have knowledge. Please answer my question placed in the opening statement.

    "For me to calculate the various calculations I need to do, nobody was willing to give a reply to : How can I calculate the wind forces by the various strong and weaker winds. i.e. what would be the force on a 1 square foot, or square meter 2 meter from a point, in kgm or Newton or whatever."
    Bert
     
  11. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    I like to apologize to the readers. I have gone through most of the threads placed by APEX1, very few had some positive help, thus I cannot expect to get some sensible answer from him. I will ignore him in the future.

    May I ask the audience, are there tables, or thumb rule formula's to calculate the windforces on an object??
    Bert
     
  12. daiquiri
    Joined: May 2004
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    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Bert, you can use this simple online tool for the estimation of sail drive and heel forces: http://www.wb-sails.fi/news/SailPowerCalc/SailPowerCalc.htm

    But let me say that I have read this discussion (and the previous one, about Flareline 18) with some degree of curiosity, because it appears that you don't fully understand some important physics governing the boat design.
    You have recently discovered some elements of scaling thanks to mr. Lathorpe. And at some point you even wrote that you didn't know what a transom was before discovering it through this forum. Please correct me if I am wrong on that.

    Yet, you want to add frames, shrink/expand boat dimensions, modify the superstructure, modify the propulsion plant etc. of a design(s) you have purchased from that NA from New Zealand.

    This creates a conflict in what you would like and what you can do, imho. You would not like to spend big money for this boat, but you are seriously at risk of having to pay that money twice: the first time for a boat made upon plans modified by you according to advices taken here and there on internet forums, and a second time for a boat purposely and correctly designed for you by a person who knows his job (a Boat Designer).

    You say that there are no designs available for the boat of your dreams? Then why don't you make a detailed list of your requirements (a Statement of Requirements - S.O.R.) and hire an experienced person to design that boat the way you want it to be? You can also place that list here. I am sure there are many people here who would be willing to do it for you, but it has to be done following a logical path which starts from the SOR. The cost will probably not be so high as you might believe and will surely be less than the cost of two boats (or of one bad boat with a zero re-sale value...).

    Sorry for not giving you the so desired numbers which will allow you to build the boat... :)
    Cheers!
     
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  13. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Thank you so much, I will certainly use that information.

    I am learning fast , but indeed need still quite some learning to do.

    And I am greatfull for that information.

    You are correct, I only knew in my own language all the names, not the English one's

    Totally correct , I bought 3 plans from them

    Totally correct, but this very boat designer has to learn basically the same as I have to do, due to the fact that very few designers have acquainted themselves with electrics. Their knowledge on hulls, cabins etc. are superb. That is their advantage. But for the rest, they are on an equal footing. There is no fuel tank, the motors are small and light and not 300Kg. Suddenly the designer has to learn about 16 to 32 batteries in serial or parrallel and their consequenses, 100 - 200 Ampere routing of cables with their electromagnetic fields etc. etc. Yes there are a few in England and probably in the USA who has that knowledge for river boats.

    That is correct. Have you ever seen a boat like the one in thread No 1 , the one with the short mast for an emergency sail and electric driven? A boat with 2 electric motors? One with a detachable rudder for emergencies? Actual, it is not a bad design, just that according to some, I have the stability wrong.
    For that reason I ask this audience, is there a way to correct this instability.

    If the answer is NO, not in your life. I will give up. But I am not willing to design a complete boat myself . I could be fiddling around with some boatdesign software, but I am not willing to do that, as I do not have the experience for that. We all know the rule, garbage in is gargage out. Although I have a reasonable knowledge of computers and electronics.

    Yes I could do that. I have to think about it, how I could express myself in such a way, that I get out of it, what I would like to have. I may also do a correspondence course at the university, all what I lack is the understanding of the hull, it appears.

    I do appreciate your help given, at least you express yourself in a gentleman's manner. I love the area you live in, beautifull.

    Just a naughty note. Preparing for a holiday is half of the fun. This is the same for making a boat.

    Bert
     
  14. erik818
    Joined: Feb 2007
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    Location: Sweden

    erik818 Senior Member

    Bert,

    Here's the equation for calculating e.g. the wind resistance for a boat. The math for calcualting resulting force from the wind flow at a sail or a foil is different.

    Cd is reasonably constant for subsonic objects and depends on the shape. I use 0.3 because Rick Willoughby did, and it's similar to what I'm used to for projectiles with a blunt entrance. You can probably reduce Cd with better aerodynanic shape, but I don't think you'll ever get below 0.1.

    Erik


    F = 1/2 * air density * velocity² * Area * Cd

    Air density = 1.225 kg/m³
    Cd = 0.3 approximately, depends on shape
    Area = Cross section area, m²
    Velocity = relative wind speed, m/s
    F = force, N
     

  15. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member


    Thank you Erik,
    I love it. I thoroughly enjoy it, when somebody comes up with solutions. Thank you very much.
    Bert
     
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