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Discussion in 'Boat Design' started by Guest625101138, Jul 14, 2008.

  1. Charlie Marlow
    Joined: Aug 2014
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    Location: SoCal USA

    Charlie Marlow Junior Member

    My two main interests are boats and motorcycles. Swimming in the pool, I had an idea to join the two. I want to build a type of water bicycle that I can pedal around the pool, but I want the whole thing underwater. I want to float with just my head out of the water. I plan to make the basic craft out of PVC pipe, with foam noodles as flotation, with a forward rudder activated by handlebars, and a pedal crank turning a twisted chain driving a propeller I will make myself out of PVC and sheet metal. I need to know how far apart the two sprocket axis must be to work best. I plan on a 1:3 direct drive (one turn of the pedal crank will equal 3 turns of a prop I estimate will be about 12" diameter and of eyeball pitch. I want to keep purchases parts to a minimum, besides drive. I'd like to use a plastic chain and sprocket since the whole thing will be underwater and exposed. (A google search of twisted chain drives lead me to this site)
     
  2. Rocky Mtn Russ
    Joined: Aug 2014
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    Location: Colorado

    Rocky Mtn Russ Junior Member

    Thanks for doing some analysis and comment Coach Dave. I’ve just returned from a 10 day kayak fishing trip on Lake of the Woods, Ontario with 4 other guys. This trip included small outboard motors mounted on the kayaks for the first time. The kayaks used were all Hobie’s. After much further discussion, the guys have decided they’d rather be in their own peddle kayaks than to ride in my proposed 5 person boat. So I’m scaling down the boat accordingly.
    My goal now is to design/build a smaller boat suited to carry just me, and a lot of camping gear. I’d like a drier ride than the Hobie offers, so I’m thinking of 10 inches of freeboard (more outrigger canoe than kayak). This will still be a stabilized monohull of probably 18.5 feet in length, with a waterline beam of 20 inches. Total displacement goal would be 500 lbs including the AMAs, which I think would be in the water for stability. The AMAs would need to be short, maybe 4 feet long with a displacement of only 25 lbs each. Short AMAs positioned toward the stern will make fishing and paddling (as a back-up to peddling) much easier. Total waterline beam including the AMAs would be about 42 inches. A designed draft of 6 inches. Continuous cruising speed of 5 mph is needed so I can easily keep up with the other boats. Based on my 17.5 foot wooden sea kayak, I think this new boat will weigh about 80 lbs with the drive system.

    Again, I would appreciate suggestions, comments, and analysis. I'm wondering how much energy is required for 5 mph? Also wondering if a shallow draft with a wider beam is more or less efficient than a deeper draft with a narrower beam. Thanks.

    Russ
     
  3. blisspacket
    Joined: Jun 2005
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    Location: st augustine

    blisspacket Junior Member

    greetings RMR, in response to your last, "how much energy" to push 5 mph. Yes, featherweight and carcassweight gas outboards in the 2-3 hp range would do just fine. There's a passel of energy in a shot of gasoline. I'd favor the watercooled over the aircooled gas outboards, leaving Honda out of the picture.

    If you truly want to measure the energy to determine "how much", you're looking at electric, where wattmeters tell you very specifically how many HP you're using. And the downside there is there are no batteries that give you an accurate visual of how much more run time you have. The techies will give you hopefully accurate estimates.

    Torqeedo electric outboards are the top of the line, with excellent engineering and efficiency. Test one, try it out, if you're interested in that route.
     
  4. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Somewhere within this giant list is an analysis that shape is not as important as having great length for speed/efficiency for the same displacement. Sculling boat shapes might be a good model.

    PC

     
  5. Coach Dave
    Joined: Jun 2011
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    Location: Malabar, FL

    Coach Dave Junior Member

    Charlie,

    If you google search on SpinFin you'll see 14 3/4" between the sprocket axes which is for a 1/4" pitch chain. With a bicycle chain (1/2" pitch) you'd have to double that, i.e., ~30" between the sprocket axes. I don't know how tightly you can twist a plastic chain before it would cause issues - something you can experiment with. The twisted chain should be a Mobius strip for longevity. You will have a lot of underwater drag so high speed should not be one of your design goals! :)

    Dave
     
  6. Charlie Marlow
    Joined: Aug 2014
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    Location: SoCal USA

    Charlie Marlow Junior Member

    Coach Dave-
    Thanks, but the design has changed. I stopped by a bike shop, looked at chains and sprockets and decided I didn't want that much under water. I'm thinking some kind of right angle drive, using a readily available drill drive, or something I may jimmy up with socket universals.
     
  7. upchurchmr
    Joined: Feb 2011
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    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    Go back thru this thread.
    That is what most of it is about.
     
  8. Skyak
    Joined: Jul 2012
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    Location: United States

    Skyak Senior Member

    Russ,
    5 mph is a pretty good clip for a single touring. 500 lbs is quite heavy for the kind of boats that average that speed. Leg drives can be more effective than the double paddle that is my reference so I don't think the target is completely unreasonable but the plan for short outriggers displacing anything continuously blows the whole plan in my estimation. The speed/length ratio of your main hull is around one -fine cruising, but your outriggers are at 2 =wavemakers.

    The thought I can't escape is that 500 lbs would have to include some very dense stuff to fit in a 20 inch wide hull and if you packed that dense stuff correctly (low) you should have no need for draggy outriggers. I think smartly designed paddle floats on a double paddle would be better to deploy only when fishing.

    The other thing I can't grasp is 10 inch freeboard and 6 inch draft going fast continually. That sounds like too much area for wind and waves to hit. I think you need a lower closed deck if you intend to keep up with your friends on windy days.

    I know it may sound disingenious to point you toward a conventional kayak shape but over thousands of years of life or death use they reached some pretty good conclusions.

    About narrow & deep vs wide and shallow you are clearly in the narrow and deep at 20 inch WLB. For your speed length ratio around one wave resistance is reasonable so you are looking to minimize wetted surface area with a semicircular section. If you need an inch or two of beam to fit your stuff or provide stability increasing the canoe beam is much better than short outriggers. The added beam will also make your boat stable enough to use when it is not loaded.

    The drag of your hypothetical boat? 7 to 10 lbs if you do it right? It's hard to say and easy to screw up. I suggest you get kayak foundry to design the hull and calculate the properties, then post a pic on this forum. They will catch any mistakes and the software should have no problem predicting properties.
     
  9. Coach Dave
    Joined: Jun 2011
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    Location: Malabar, FL

    Coach Dave Junior Member

    Russ,

    Sounds like you had a good trip in Ontario.

    I ran Godzilla with 18.5', 500#, let it optimize draft and beam. It came back with 56 watts required (74 input watts at 75% efficiency) for 5 MPH with 7.9" draft and 16.3" beam. Then I constrained the draft to a maximum of 6". That increased the power required to 59 watts (79 watts at 75% efficiency) for 6" draft and 19.3" beam. This analysis is just for the monohull. The 42" beam overall for the stabilizers may not be sufficient. 6 or 8' would be less likely to tip. The stabliizers should be just barely skimming the water surface to minimize their drag. You could reduce the freeboard with fore and aft cargo holds or a spray skirt so you aren't fighting the wind so much.

    Dave
     
  10. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    And that is for dead flat calm, so add 20-30% seaway margin for real conditions. 74-79 watts is ~ 1/10 Hp sustained, which is approaching serious amateur cyclist ability.
     
  11. magny7
    Joined: Jan 2010
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    Location: Surabaya

    magny7 Junior Member

    Have you consider not propeller but fin based mirage drive pedal boat. From their promotion video it looks that it performs better. Granted it is promotional video, but if you want to try why not experiment a little..
     
  12. TomCat58
    Joined: Dec 2013
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    Location: Washington State

    TomCat58 Junior Member

    100 percent solar

    Ah Yes a subject dear to my heart. Gas and oil free boats. I have been playing with this idea and have built a few and I think I pretty good boat this time.

    Please give me feed back ![​IMG]

    https://sites.google.com/site/serenitysolarcanoe/

    TomCat
     
  13. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Tom:
    Like your web site. Your design provides for stability, shade, and solar power, good for extended use. Your battery backup is a good idea.

    Troll motors have the advantage of being cheap and an easy set up, but waste a lot of energy. Changing to a model air plane prop helps efficiency on the TM, but then you still have the drag from the block cross section of the motor under water.

    I think extended use is rare for most boats, read somewhere that the average is well under 10X per year and for short trips mostly during major holidays.

    Hope this helps.

    PC



     
  14. magny7
    Joined: Jan 2010
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    Location: Surabaya

    magny7 Junior Member

    That is awesome panorama and the experience is stunning i presume. But if its me, I'll ditch the kayak body and go slender with trimaran. You'll might have more deck space with comparatively less drag/more speed.
     

  15. TomCat58
    Joined: Dec 2013
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    Location: Washington State

    TomCat58 Junior Member

    solar canoe design

    portacruise: Thank you

    Yes any drag effects the performance so I design the pontoons to barely touch the water on just the rear sections while cruising. As the need increases the pontoons use more of there surface to stabilize.

    The trolling motor is very affordable and yes not so efficient but with a limited budget its working ok. I did however buy one of the newer Minn Kota's that claim to go 5x longer then some of their other cheaper models. It has a computer control board using a pulse system. The other factor is the trolling motor is almost water proof. Everything on this canoe has or will get wet sooner or later. The trolling motor has come off once while the boat was tied up on a sandy shore. I got it out of the 2 feet of water and dried it the best I could and it works just like new :)

    Thank you for your comments I am on a constant learning curve to improve my canoe. The next improvement I think I will make is to replace the two 29 series deep cycle batteries with Lithium Lifepo4 electric car type batteries.

    That improvement from my research promises to greatly improve speed and extend how long the batteries last.

    TomCat
     
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