Pedal Powered Boats

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

  1. Guest625101138

    Guest625101138 Previous Member

    The blade is more effective if it is not fed air. The difference between an aerating blade and non-aerating is about 3 times when in a full turn. So to get the same turning force a blade that can get air will need to be about 3 times bigger in area. It works out around 3W v 10W at my normal design speed and turning requirement.

    A shaft that goes through the hull or located in a faired tube with the blade underwater will not get air. If you want a tilt up rudder then have a short hull extension that takes the shaft. They do this on sailing cats to get an efficient rudder but also achieving collision protection. A single rudder on one hull is all that is needed. Having to provide structure for a central mounted rudder is just added weight. You will never "fly" a hull. It also has to have a deep blade to avoid getting air.

    I use so called dipping rudders. There are two rudders with preset angle of attack. When I want to turn I lower the appropriate rudder. This saves the 3W most of the time. It also makes the boat easily beachable because the rudders are normally out of the water. It does not quite have the feel as a single rudder but 3W is almost 3% of my usual operating power so worth the minor irritation. The more I use them the better they feel.

    Rick
     
  2. Guest625101138

    Guest625101138 Previous Member

    Greg K got his new ocean boat wet today. Here is the first impression with some photos:
    http://www.adventuresofgreg.com/HPB/HPBmain.html

    He has also put together an album of the design and build:
    http://picasaweb.google.com/adventuresofgreg/ExpeditionBoatBuilding#
    It shows the evolution of the cabin and accommodation.

    The main purpose of this early test was to check stability with the design keel and set up of the drive leg. Everything worked well. He was very pleased with the result. Performance was a tad under design but there are a few things to get right yet so I expect it will come in very close.

    I am looking forward to the outcome of his shakedown cruise in October.

    Rick
     
  3. I57
    Joined: Feb 2008
    Posts: 172
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    Location: Melbourne, Australia

    I57 Senior Member

    Tilt up rudders

    Read your post about rudders that are not fed air are more efficient. You made the comment _ "A shaft that goes through the hull or located in a faired tube with the blade underwater will not get air. If you want a tilt up rudder then have a short hull extension that takes the shaft." Not sure exactly what you mean by a short hull extension? Have included a pic of my swing up rudder.

    Ian
     

    Attached Files:

  4. Guest625101138

    Guest625101138 Previous Member

    Ian
    The hull extension would not turn in what I am describing. Rather it would flip backwards and upward to allow the rudder to skip an object or ride up on the beach.

    The rudder shaft would preferably exit the extension under water so it has no direct path to feed air down the leading edge in a turn.

    In a turn, the lift side of the blade will drag air down because it has negative pressure. This dramatically reduces the effectiveness of the blade for turning. It means you are dragging a much larger blade area through the water all the time to produce the required tuning force for the little time the rudder actually does its job.

    Rick
     
  5. I57
    Joined: Feb 2008
    Posts: 172
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    Location: Melbourne, Australia

    I57 Senior Member

    Rudder

    Rick

    Thanks for the feedback, however I won't use it for this boat, maybe the next one. With a swing up rudder is it worth making one that is narrow at the top and tapers out underwater to reduce the amount of air being sucked down or would the gain be negligible.
    Have put in 50mm dia outrigger poles and revamped the seat after its collapse, boat a bit heavier but a lot stronger.
    Greg K's boat looks great, see how he goes on the ocean.

    Ian
     

    Attached Files:

  6. Guest625101138

    Guest625101138 Previous Member

    Ian
    Could make it worse. It is really getting into detail that you will get advantage from as you try to eek out every bit of speed for effort.

    Your boat is getting to the point where you have sorted most aspects and would now benefit from a rebuild with lowest weight in mind. The seat looks much firmer with loads better resolved. It is very reclined compared to what you started with.

    Have you tested it yet? I am going to the lake on Saturday. I hope to pedal in the morning and get my son down to photograph the turbi-prop boat in the afternoon. It will al depend on weather of course.

    My new prop has proven very good for the weed but there is not much around anyhow. I have been doing full length of the lake without any weed. All the long stringy stuff has died off with the cold weather.

    Rick
     
  7. I57
    Joined: Feb 2008
    Posts: 172
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    Location: Melbourne, Australia

    I57 Senior Member

    Boat test

    Rick

    Had the boat out breifly at Carrum on Sunday and will try to get to the lake on Saturday. Am still refining the boat, so when I get it right I can think about a lighter boat.

    Ian
     
  8. Frappacino
    Joined: Aug 2009
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    Location: aus

    Frappacino New Member

    hey Ian, is your boat a kayak with rick's flexible shaft drive fitted? or something similar ?

    if so, i wont mind taking a look to see how you did it and what the performance is - if u are taking it out this wkend u mindif i come take a look see?
     
  9. I57
    Joined: Feb 2008
    Posts: 172
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    Location: Melbourne, Australia

    I57 Senior Member

    Proa

    Frappacino

    My boat is a proa, this is the best setup for the gearbox I have. It is fitted to a spring steel shaft turning a 450mm dia prop. The boat is a main hull 5m long and a 4m outrigger, I sit half over the edge of the boat. Hope to be at Lysterfield lake on Saturday so yell out if you see me.

    Ian
     

    Attached Files:

  10. Guest625101138

    Guest625101138 Previous Member

    Greg just posted a video of the first trials on his ocean boat:
    http://www.youtube.com/watch?v=OXSZLt_6eFg

    The speed does not look very impressive but the final seconds beside the sailing dinghies shows relative speed.

    Rick
     
  11. portacruise
    Joined: Jun 2009
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    Location: USA

    portacruise Senior Member

    Rick, will Greg be using a version your folding prop in his ocean trek?

    Porta

     
  12. Guest625101138

    Guest625101138 Previous Member

    No. The current aluminium prop is for the trials. He will get a stainless one made for the long trip. He intends to carry a complete spare drive leg and I have suggested he consider different pitch props. One would be for easy going and the other for hard going.

    It is quite easy to remove the drive leg and the well is about 100mm higher than the water level. Hence this can be done at anytime. It also gives the ability to inspect the leg and keel for fouling. These should prevent any fouling of the rudder. Getting to the rudder without getting wet will be a challenge.

    It is still early days but I was expecting him to get above 8kph with the current set up at his 150W. The fact that the boat is not painted and the keel not properly faired could detract a little.

    We looked at some of the speeds of other boats that have crossed oceans. I reviewed the hull for the two guys who crossed the Tasman in the kayak. They could hold 5 to 6kph both paddling at sustainable effort in dead calm. If the wind was above 25kts on the nose they went backwards. On the trip they averaged 1.3kph; often went backwards.

    The aim with Greg's boat is to have low windage. He should be able to make way in wind to about 100kph. This gives the ability to claw off lee shores, which has proven to be a major concern for rowers.

    Rick
     
  13. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Within looks impressive, Rick. The low windage for a relatively large looking boat for the available power is exciting: It suggests that a derivative pedal cruiser might be feasible: a smaller version of your solar electric hull? The only attempt at this I have seen is L' Escargot, and I'm sure it must have struggled with windage. Would there be weight issues with a 'cruiser' version of Within though, if built from cheaper materials - ply or glass fibre?
    I was also interested in what you said about two different props for easy and hard going - could you enlarge a little on the advantages of this over just reducing cadence for easy going?
     
  14. Guest625101138

    Guest625101138 Previous Member

    TT
    The attached will give you an idea of the advantage of different pitch props.

    I did 20km in tough conditions this morning - Ian did not show up. The Melbourne doppler radar shows speeds above 90kph. I was a little protected and probably experienced 70kph gusts and average around 30 to 40 kph. The wind blows almost straight down the lake.

    From the attached graph it is easy to see when I am going upwind or downwind. I stay at low speed in the first part of the upwind leg, holding around 5kph, to avoid getting drenched. Once the waves drop I pick up to my comfortable force on the cranks. Although I am trying to hold heart rate at 150bpm I become force constrained around 8kph in these conditions; less in the gusts. If I worked at 150bpm my legs would tire very quickly. On the downwind leg I get a nice balance between the required force and heart rate.

    Heart rate correlates well with power. So it can be taken as the power level I am working at. Like any engine there is an optimum rpm. I like to work around 70 to 75rpm. At this level my power output is around 130W. I am aiming to work harder this year to lift that.

    Greg likes to work at 80 to 85rpm to put out 150W. This is my design point for him. If he gets heavy weather on the nose he can still work at 150W without getting leg soreness if the he uses a lower pitch prop. If you look at peleton riders they hold a cadence around 90rpm.

    There is a significant benefit from an overall average if you can work at constant power. My average today was only 8.12kph but I covered one leg at almost 11kph and the other around 8kph. The average was affected by slowing to avoid ploughing through waves but there was quite a lot to be gained if I was not leg force constrained.

    In conditions like today Greg could probably hold the same average as I maintained because his windage is substantially lower. I worked out he should be able to make way in 100kph winds.

    You can do a simple test at a gym to find your ideal cadence and power level. The recumbent machines will have a power mode where you can set the torque at different values and look at the power you are producing. For long duration cruising I suggest people do one hour around their aerobic limit and then find the cadence and power they are most comfortable with. This is the design point I use for their prop to suit them.

    You could make a more economic version of Greg's boat in glass. Remember it is designed to carry provisions, navigation and redundant equipment to last 100days. For shorter day trips or overnight you could put that into a less expensive but heavier layup.

    I already think I could do better than the current boat design but I did not get the idea until Greg had committed to detailing the current boat and he felt a full redesign would have eaten up a lot of time. He was happy with the performance projections of the current boat and the video gives an idea of their satisfaction with the outcome. I must admit I am a little jealous. It would make a competent coastal cruiser I expect. However it is quite expensive for its intended purpose. I think considerably lower cost than an ocean rowing boat but still not much bang for buck.

    I have spent a few nights sailing at less than 4kts when racing and still got where I was going so the speed should be acceptable. It will outperform any other single person rowing boat or kayak that is ocean capable for long distances.

    Rick W
     

    Attached Files:


  15. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Many thanks for your detailed reply, Rick. I am slowly getting my head round the relationship between aerobic fitness (heart/lung) and anaerobic (muscle) fitness. think I need to read up on the biology of aerobic respiration: I am trying to remember how the ADP/ATP(??) cycle works. obviously heart rate dictates the rate of Movement of blood, and will be closely related to the transfer Of oxygen to the blood at the lung surface, and the amount of oxygen available at the muscles to release energy. heart rate and rate of breathing are normally related closely, but we can conciously override our natural rate and breathe faster or slower for a period. aerobic fitness limits our maintainable heart rate and available power. The muscle pain which limits our ability to do 'hard' work (cycling up a steep hill) is caused by the build up of lactic acid in the muscle and relates to the anaerobic fitness of the muscle - the efficiency of extraction of energy by the ADP/ATP process.
    if you know a good 'primer' web resource for this, I'd be grateful!
    thanks Rick.
     
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