Love to have a small sail on the boat

Discussion in 'Boat Design' started by BertKu, Aug 1, 2015.

  1. Petros
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    Petros Senior Member

    yes, exactly. On a smaller rig it can be much simpler than they show on larger rigs, where they want lots of adjustments. I have built them for small boats with just a halyard and one sheet. multiple sheets (or "sheetlets") allow for fine tuning of the twist. but for just day sailing I have not found making it more complex is not necessary nor desirable.

    You might read up on it some on this thread: http://www.boatdesign.net/forums/sailboats/junk-rig-modern-hulls-39567-8.html

    But the focus on those is for larger cruising hulls. I have used a very simple one on 8' to 14' long dingys and have been impressed with how simple and easy it is to use, and remarkably efficient. When sailing with other similar sized boats down wind, I would beat out the other boats even though my junk rig was much smaller than the more conventional sailing rigs on the other boats.

    You reef it quickly by lowering the halyard and than tying the lower two, or three, battens (or "boomlets") together. it is very fast and clean.

    attached is picture of very simple modified junk (I altered the shape to make it more elliptical to improve efficiency) made from a $6. 7' x9' plastic tarp, it has one sheet. shape is adjusted with tension on the halyard, or adjusted by changing the size of the loops that go around each batten and the mast.

    Also attached is a document about how one forum member sets up his junk rig, which is a good primer for you to consider.
     

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  2. Manie B
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    Manie B Senior Member

  3. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Thanks Manie, both, the solution of Petras and that from you will solve my problem. I may have to consider a smaller sail. I don't need to sail at 20 knots, I leave that over to the youngsters. Truly appreciated. I discovered a flaw in my motor circuit. I designed and placed a large 68.000 uF / 100 Volt electrolytic capacitor in the motor housing as buffer for the PWM currents. It worked beautiful, until I forgot to place the potentio-meter in the middle point, whereby the capacitor get soft started from either 24 or 36 Volt. I had it switched to 24 Volt and the capacitor's inrush current melted the contacts and blew all fuses. Basically it is a short circuit when the capacitor starts up. You have to wait until I have modified the circuit and boat before I can shoot a movie of the performance of the boat. Sorry for that. Bert
     
  4. BertKu
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    BertKu Senior Member

    Thank you so much for the solution. You and Manie have made my day. Thanks. Bert
     
  5. BertKu
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    BertKu Senior Member

    Hi Manie,
    I should be finished next week and then when the weather is good, I will make a video.
    Lucky I think I have been able to come up with a solution to solve my blowing of fuses and melting relay contacts. It happened never before as I was always careful. This time I had the potentio-meter turned towards 24 Volt direct and that meant the electrolytic capacitor got straight away placed parallel to the 24 Volt 144 Ampere/hour batteries. Needless to say a few hundred or thousand Ampere rush in current All what I am now trying is a BC327-40, 3 diodes and an extra reed relay. As soon the potentio-meter is NOT basically in the middle, the transistor base is short circuit, thus the relay contacts which connects the motor controller and capacitor to the battery does not pull in until the MOSFET switch has opened up and start charging the electrolytic capacitor. Should I now have the potentio-meter in either 24 or 36 Volt position, the relay does not come in, until I have turned the potentio-meter. Because the DC to DC transformers switch the MOSfets slowly on, the rush in current should be lower and therefore it will not melt the contacts, nor blow my fuses. Refer “explosion” proof switches thread.

    ElectricKayak, Should you read this thread, I don’t think you have to be worried about the problems you mentioned on lose screws and magnets. I am using the 130KV, Maximum 6 Kw , 90 Ampere/72 Volt 12mm shaft Turnigy motors and only if the motor is running at full capacity the screws and magnets could come off, but not at 12 and 24 Volt like my and your application.

    Bert
     

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    Last edited: Aug 12, 2015
  6. Petros
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    Petros Senior Member

    There is no "correct" sail size for any given sized hull. There are conventions and traditional sizing rules based on what people find useful, but for what you are doing you only need to make it big enough as you feel comfortable with in terms of handling and control of the rig.

    A large sailing rig will allow you to make better head way in light wind, with the trade off being more rigging and sail to mess with (and reefing sooner).

    But a small sail would serve you just as well, less cost, lower loads on the rig, and much less rigging to stow when not using it. A smaller sail means you will not move along as fast in any given wind, and in really light wind you would have to use your motor move often.

    On small sailing dingies it is a much harder trade off to make since too light a wind means you can loose steerage and have to resort to oars to get back to the dock with too small a sail. Not really as important in issue in your boat because you have the motor when there is not enough wind to move you along.

    So keep it small and simple, get used to using it, and than you can decide later if you want to make a larger sail once you have some experiance with it. If you make a simple tarp or Tyvek sail to try out, you would not have much invested in it, and than you can always make a larger one later if you feel you can use a larger sail.

    I have made a number of simple tarp or tyvek sails, using duck tape for the seams and reinforcements (only takes about an hour or two and $20 worth of stuff to make it). Typically they work well enough for just local playing around on a lake or near shore in Puget Sound, that I never bother to make a "permanent" sail out of more expensive materials. Proper sail cloth would allow for more compact storage and perhaps they would be more durable, but that has not been an issue for the size of boats I have built.
     
  7. BertKu
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    BertKu Senior Member

    Thank you Petros, that was great valuable information. My thought was, I have solar power to let the boat run at low speed with maybe 200 - 300 watt from the panels. A little help with a small sail would be covering all possibilities I have, I have a small sail then, I have battery power, I have solar power and if it really matters I have oars!!. When I was young I was often sailing 25 m2 with just using the main sail or just the head-sail. Easy handling, sometimes cumbersome, but fun. By the way I found a very nice website which gives all kind of terms in our own languages and have the translation for it in French, Italian, Dutch , German etc. Very helpful sometimes.

    http://www.sail-the-net.com/translate/sails-and-rigging-terms-translated.html

    Thank you very much Petros. Bert
     
  8. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    Hi Manie,
    My apology Manie, but I have to disappoint you. I found out the real problem. I will only be able to shoot a video in a few weeks time. I was already wondering why the Ampere meter was jittering when I was all the times testing the boat out. Lucky I have not yet been on the sea, until all little problems are solved. I have started a thread in “boatdesign.net/forums/onboard-electronics-controls/” for some advice.
    Bert
     

  9. BertKu
    Joined: May 2009
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    BertKu Senior Member

    Hi Manie, at last I resolved the blowing of the fuses and melting of the contacts with a different design. My problem was as follow. In the design of thread 20, when the +24 Volt was at the 2 outer points of the potentio-meter, it worked. However as soon I shifted the potentio-meter it blew the fuse and melted the contact again. I have now placed a darlington, which together with the diode will sufficient drop, to disconnect the + 36 or + 24 Volt.
    The weather is clearing and next week i will make a plan to have the boat on the water. Bert
     

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