what to do with this? (a small, nimble paddling boat)

Discussion in 'Boat Design' started by breschau, Nov 30, 2010.

  1. breschau
    Joined: Nov 2010
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    breschau Junior Member

    I am trying to design a small, nimble paddling boat for myself. It will be used in the mediterranean sea as a play boat/travel boat. Cockpit is closed to calculate ssd graph only, it will be open with a spray skirt.

    Render and hydrostatics data from freeship, wave forms and resistance graph from michlet. Ssd and dsd graphs and stability data from freeship. I am not sure about the value "Z of wind area COG", hydrostatics screen has a value "Z of wind area COG abowe DWL" do I add draft height to it or use it as is ?

    http://www.4shared.com/photo/9yzA88Hi/sharkey1.html
    http://www.4shared.com/photo/0BcVelNQ/sharkey2.html
    http://www.4shared.com/photo/ey00KNOY/sharkey3.html
    http://www.4shared.com/photo/XSUbjY7B/sharkey4.html
    http://www.4shared.com/photo/4jjdRiCe/sharkey5.html
    http://www.4shared.com/photo/eqVcNbCt/sharkey6.html
    http://www.4shared.com/photo/Fl2OaKL5/sharkey-ssd.html
    http://www.4shared.com/document/iHUigInB/sharkey-cc.html
    http://www.4shared.com/document/_InM25ex/sharkey-hs.html

    Any comments are wellcome. I am not trained in boat design so be blunt and clear.

    Edit: Mistyping
     
  2. ancient kayaker
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    It's a bit difficult to judge properly with the low resolution pictures and without dimensions. You can post .fbm FreeShip files using the Go Advanced posting feature which has a Manage Attachment tool; these would be easier to interpret.

    Estimating from the cockpit, it looks to be about 20'/6m long, which will not aid agility, but has considerable rocker which will add to agility but detract from speed. This is fairly typical of commercial rotomolded sea kayaks, I suspect because it looks fast but makes for a stable boat, to keep lawyers obsessed with lawsuits (especially in the USA) happy. The width looks to be about 25"/0.3m, a little wide for a sea kayak. I cannot identify the waterlines in the image I am getting but the bow seems blunt and there seems to be a transom; these will likely create drag. I am also concerned whether there is enough foot space under the foredeck and the (presumed) small cockpit may make entry and exit more difficult than necessary unless assitance is available.

    Most hydrostatic values are measured from the waterline; the only one I am aware of that needs to have the draft added is the metacentric height, usually identified as KM. This shows initial, or primary stability; a moderately stable kayak might have a value of about 1.2'/0.36m. You can have too little - more of a problem to an inexperienced paddler - or too much - which will make the hull rock excessively when a wave or boat wake passes underneath from off the beam.

    What material and construction method are you planning to use? That will have some impact on the design. As a general rule, unless you are particularly interested in designing boats and wish to learn by experience and experiment, it is better plan to buy plans for an established boat: there are many excellent designs avilable through the internet. I learned whatever I now know by building canoes to my own designs - canoes cost less to build than kayaks - the first 3 or 4 were not very useful.
     
  3. breschau
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    breschau Junior Member

    You are right the grid doesnt appear very clear on the pics. I have attached the fbm file this time.
    Cockpit is only place holder. The boat is actually 15feet long and 23inches wide. Without the upward sweeping tips of traditional designs, I thought I should add some bouyancy to the ends to keep it balanced. I can change it if its no help with brooching/diving.
    I also attached the stability curve for easier access. Didnt know I could attach pictures. It says maximum heeling angle is 70 degrees. Does that mean I can lean down into the sea ? I must be missing something.
     

    Attached Files:

  4. breschau
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    breschau Junior Member

    Sorry missed the last part of your answer. I am researching possibilities but leanning on some form of FRP build. Thus the form is not optimised for paneling. I am not looking for a single boat to use and discard. I wish to acquire the skill to make it so that I can make my own whevever I want one.
     
  5. breschau
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    breschau Junior Member

    I am going to accept the shame of bumping my own thread and ask a couple of more direct questions.
    The model shows a coordinate for COG of the boat. In such a small boat main weight will be myself, I have to find the real COG. Can I just put the weight vectors on xyz coordinate and calculate the combination vector? If I find the correct COG, do I need it right over BLC, will it effect stability if there is some offset on x axis?
     
  6. cthippo
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    Location: Bellingham WA

    cthippo Senior Member

    Looks like a nice design, nice lines on it.

    What is your design weight capacity?

    @ ancient kayaker...

    25" may be broad beamed for you, but for some of us (who are a little broad beamed ourselves) it's a minimum! :p

    There is no way I could get into a boat with a cockpit ring of less than 22" i.d.

    My current boat has a 30" beam and I wouldn't want to go too much smaller. It's amazing how being 6'1" and 270 lbs makes you too big for 80% of the kayaking gear out there!
     
  7. breschau
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    breschau Junior Member

    Ahh a visitor on my thread, welcome I was afraid I'd end up with a monologue.

    Its abit slimmer than 25. If you wish you can see the details in the attached .fbm file on the previous posts. I am planing 105kg minimum weight at 12cm and 120kg maximum weight at 13cm. Me being 80kg, boat being between 15-20kg (hopefully) , clothing safety gear paddles etc should come around 105. I am reserving the extra 15kg for vine,sausages and pickles.

    Thank you for the comment on the shape but do you see any problems other than the cockpit size, anything I should work on?
     
  8. cthippo
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    cthippo Senior Member

    Great, another boat I don't fit into :p

    I generally use 300 lbs (136 kilos) as a planning weight, so I guess I'm screwed. Just remember it has to fit you, and it's nice to have room to move your legs once you get in the boat. I have problems with my legs going to sleep due to compression of my sciatic nerve, so I need a lot of legroom so I can keep changing position. Also, remember to reinforce the cockpit ring as it will be taking a lot of weight when you're getting into and out of the boat. Unless you hit something (which i do a lot) this is the area of the boat which will be exposed to the most stress.

    Will you be dividing the boat into watertight compartments? Have you thought about how you'll do the hatches yet?

    Looks like an awesome project, can't wait to see how it turns out.
     
  9. breschau
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    breschau Junior Member

    Whit the current hull form it is not hard to change displacement although I wont advise going into that untill its done building and testing. I dont expect there will be a problem with lengthwise fitting. Being short has its merits, but I will check the hull section corresponding to my feet as you have suggested.
    I am planning for 2'' biax tape ribs as reinforcement inside the hull sections, matching the stations. Cockpit rim will be anchored to them.
    Hatches wont be easy to make and even harder to ensure waterthightness. If that can be ensured at all. I may reconsider after evaluating the pain in the *** magnitude of packing without hatches.
    Since a hatchless setup rules out cargo sections. The only place to put bulkheads are the aft and stern tips, for flotation aid. On one hand that will create deadspace that cannot accessed or seen. On the other hand glassed in foam is desirable over flimsy flotation bags for durability. I am still trying to find a solution.
     
  10. cthippo
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    cthippo Senior Member

    You don't have to re-invent the wheel when it comes to hatched. Lots of places sell drop in hatch assemblies. You just cut a hole, apply some glue, and drop the whole thing in. The seal is part of the pre-made assembly and so the only place it may leak is where you seal it to the hull.

    A cheap way to do buoyancy bags is to take giant zip-loc bags and fill them with styrofoam packing peanuts then tape the bags closed. It's way cheaper than the commercial ones and lighter too. Keep in mind you have to carry the finished article and those grams start to add up after a while!
     
  11. breschau
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    breschau Junior Member

    I have seen reviews about leaking hatches on some mass production boats. Even on a plus four grand designer issue. Having said that, if you know a reliable brand for spare hatch assemblies I will keep it in mind for possible retrofitting later.

    The tip for the flotation bags sounds good. My alternatives for glassed in foam and flotation bags were alot more expensive or complicated. A thumbs up for duct tape and garbage bag inventions.
     

  12. breschau
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    breschau Junior Member

    With a twist of fate I stumbled upon Eric Sponberg's tutorial threads. Which in turn itched me to open michlet and check resistance graphs of a series of models with diffrent Cp and hullforms. Seemingly similar hull forms showed rather drastic diffrences on the resistance curves :?:. Model shelved for further study.

    My thanks and best regards to the forum community.
     
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