Sternwheeler Power Requirements

Discussion in 'Propulsion' started by BigMuddy, Jan 17, 2022.

  1. BigMuddy
    Joined: Jan 2022
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    Location: Missouri

    BigMuddy Junior Member

    I'm in the planning stages for a shallow draft sternwheel boat for use on the Missouri river.

    Yes, I know props are more efficient. This boat is for shallow water, so I'm not going to be using an outboard or anything with a prop.

    I know there has been similar threads, but I wasn't able to find any particularly useful information.

    The boat will have two paddle wheels at the stern with separate motors to allow for the wheels to turn in opposite directions to make steering easier. Each motor will spin each wheel at a maximum RPM of 63 with a cruise RPM of 44.

    That may sound slow but these wheels will be 8 feet in diameter, so going by the surface speed at the outer circumference, 63 rpm would translate to something like 18mph surface speed at 100% efficiency.

    Obviously we don't live in a perfect world, so let's say the paddlewheels have 65% efficiency. That's probably a pessimistic estimate, but let's go with that. That would still translate to 13.3 MPH at full wheel speed.

    Each wheel will be 8 feet in diameter and 3 feet wide. The "paddles" will be 11.25 inch wide boards because the boat will likely never draw more than 11 inches of water.

    The boat itself will never weigh more than 23,000 pounds total. It will probably have about 16,000 lbs total weight most of the time.

    Edit:
    There are two different hull designs that I'm considering. Each will be a simple barge with raked ends. The first is 55.5 x 8 feet. Narrow, but easy to transport and probably easier to push through the water. It would have cat walks added after it's at the launch site. Overall width would be 10 feet with the catwalks.

    The second design would be basically the same, but 55.5 x 10 feet, also with catwalks, so it would have an overall width of 12 feet.

    The

    Each motor will generate 800 foot pounds of torque at each wheel with a combined torque for both motors of 1600 ft lbs.

    With these numbers, does anyone here know if that will be an adequate amount of torque to reliably drive the paddle wheels and propel a boat that weighs about 20,000 lbs?

    Any suggestions would be very helpful, if you don't think it will work, tell me why and please include real world examples or real world experience. Or math that I can understand, I'm not an engineer so I don't know calculus.

    Thanks
     
    Last edited: Jan 17, 2022
  2. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum BM.

    I don't know anything about paddlewheels - although I think you might be surprised by how efficient they can be when designed properly.
    I would be a tad concerned though about your barge dimensions of 55' x 8' - that is rather narrow.
    What are you going to be using the barge for?
    And what sort of superstructure will be added above the deck level?
    What is the hull overall depth? You note that the maximum draft will probably be no more than 11".
    You will need to consider the stability aspect as well - do you have any sketches that you can post of your proposed design?
    Edit - in view of how you have just joined, it is probable that you won't be allowed to post any attachments until you have made a few other posts first.
     
  3. BigMuddy
    Joined: Jan 2022
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    Location: Missouri

    BigMuddy Junior Member

    Thanks for the warm welcome.

    I spent about two hours playing around with a CAD program to get an idea of how this design would look. This isn't a "final draft" or even close to being the final design. Basically, it's not very detailed yet or fully thought out. And again, I'm not an engineer.

    These pictures were taken with my phone to show a friend, so quality isn't as good as it could be.

    The pictures show the 8 foot beam version. The hull depth is 2 feet. The superstructure will consist of a simple cabin with just enough head room for taller people (7 feet interior head room). The overall height would be something like 9.5 feet at the roof of the main cabin. This isn't counting the pilot house. The top of the pilot house would be about 16.5 feet.

    The hull will have bulkheads, and it will be completely sealed with the exception of several access hatches that will probably be located inside the cabin.

    IMG_20220116_184642866~2.jpg IMG_20220116_184601104_HDR~3.jpg maxresdefault (13).jpg 557b89907e60f.image.jpg

    I'm designing this boat for cruising around on the river with a few friends and maybe going on an excursion to other river towns every now and then. I want a boat but with almost all the comforts of being at home, like a big RV but on the water.

    The 8 foot beam version might be too narrow, or might not have enough freeboard. Before you judge too harshly, I'd point you to a sternwheeler on the Missouri river called the JOSEPH M LABARGE. I included pictures of it so you can see exactly what I'm talking about. It's been around since the 1930s I think and hasn't sank yet despite the extremely low freeboard.
     
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  4. gonzo
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    gonzo Senior Member

    Your first step is to calculate the resistance of the hull at the target speed. All the rest of the calculations will be derived from that.
     
  5. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Thanks for this - the Joseph M LaBarge does look very neat.
    Does the length of 55' re your design include the paddlewheel?

    I did some googling re Joseph M LaBarge, and found these links -

    Columbia couple offers sternwheeler rides on the Missouri River https://www.columbiamissourian.com/news/local/columbia-couple-offers-sternwheeler-rides-on-the-missouri-river/article_0ba3e7ea-5483-5a4f-a4d4-8488922e53b0.html



    They mention that this paddle wheeler is about 80' long (I presume including the paddlewheel and aft deck behind it - but excluding the bow gangway?) and I am estimating from your photos that she might be about 16 - 18' wide?
    She will have much better stability than your proposal - especially as the overall height of the two vessels will be similar.
     
  6. BigMuddy
    Joined: Jan 2022
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    Location: Missouri

    BigMuddy Junior Member

    I have no idea how to begin doing this. I found a calculator that allows you to find the bollard pull force required for towing a barge, I'm not sure if this would be applicable. I don't see why not considering that my design is just a glorified barge.

    https://www.mermaid-consultants.com/bollard-pull-for-barge-with-cargo.html

    I'm going to experiment more with this calculator later today. The numbers I got for the 8 foot wide hull were about 1000 lbs resistance at 10 knots. I need to make the hull wider, probably at least 12 feet wide so the numbers will go up significantly.
     
    Last edited: Jan 18, 2022
  7. BigMuddy
    Joined: Jan 2022
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    Location: Missouri

    BigMuddy Junior Member

    I really like their boat, in a way they kind of inspired me. They bought it for $50,000 if I remember correctly, but they had to replace the hull shortly after purchasing it. I think it was some odd amalgamation of wood and steel, a wood hull underneath steel plates.
    From what I remember they just had a new steel hull built to replace the old one.

    The 55 foot length of my design does not include the paddlewheel. Including the paddlewheel it would be 64 feet LOA.

    Later today I'm going to modify the existing version in CAD. I think 12 feet would be a good width, probably a lot more stable than the previous version.

    The paddle wheels will have to be wider too, I'm thinking 5 feet wide per wheel.

    The cabin is probably good at 8 feet wide, but I might increase the width to 10 feet depending on how it looks with the wider hull.
     
  8. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Please do increase the beam to as much as you can - even 12' is still rather narrow for a boat this size, especially one with a 'top deck' wheelhouse as well.

    And with a hull depth of 'only' approx 2' over a length of 55', you are going to have to consider the longitudinal strength of the vessel carefully, even on a quiet river.
    What material are you planning to use for hull construction?
    I am thinking that you are going to have to ensure that the superstructure is tied in properly to the hull, such that it contributes to the hull girder's resistance to longitudinal bending. This will also help to prevent the hull racking or twisting.

    Re propulsion, are you planning on using gasoline or diesel engines to drive the paddle wheels - or even electric motors?
     
  9. gonzo
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    gonzo Senior Member

    Bollard pull is only useful for tugs to start moving a ship. It will not give you any useful values. You need to have the dimensions, shape, weight and target speed to start a basic resistance calculation. That is up to you to determine.
     
  10. BigMuddy
    Joined: Jan 2022
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    Location: Missouri

    BigMuddy Junior Member

    For the hull material I'm convinced aluminum is the way to go, but steel is a viable option too. I'm hoping that supply chains can get back to normal in the next year or so and take some pressure off the markets. I can afford to pay the highly inflated prices for building materials but I'd prefer not to if I don't have to.

    The drive system I had in mind would use hydraulic motors driven by a diesel powered hydraulic pump, but I was also looking at hybrid options. If I went with a hybrid drive system it would be diesel electric.

    Either drive system would likely have to incorporate reduction gearing, and the final drive would be roller chains going to the paddle wheel shafts.
     
  11. gonzo
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    gonzo Senior Member

    Hydraulic systems don't necessarily need reduction gearing. You size the pump and motor to generate whatever RPM you need. The downside of hydraulics is that any leak will be a major violation. If you do use hydraulics, the installation must prevent any accidental leaks. Any combination system will increase losses. Is there a reason for it? A diesel engine coupled to the shafts should work fine. If you are using a chain drive, reduction through sprocket size will be adequate. In fresh water, steel is a good competitor to aluminum. Corrosion is less of an issue, so the plating can be thinner. Diesel electric on an aluminum boat has to be properly engineered and installed, or the electrolytic corrosion will destroy the boat in short time. This is not as much of an issue with steel. To reiterate, until you calculate the hull resistance, the rest has to wait. That value will drive all the other calculations.
     
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  12. BigMuddy
    Joined: Jan 2022
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    Location: Missouri

    BigMuddy Junior Member

    I haven't had a chance to do too much work with the CAD design, I got the "new" version started but I still need to change a few things and add a lot of details. I'm having to deal with some bureaucratic BS, and as usual that takes forever.

    I can give you specific numbers, they will probably be very close or "good enough". Thankfully hull volume is easy to calculate with a simple barge hull.

    With a 55.5' long 12' wide hull, it will displace 25,846 lbs when it is submerged 8 inches. I would really try to keep it at or below that weight, I think that's a good number to shoot for.

    Cruise speed would ideally be 9 or 10 knots. According to displacement hull speed calculations, the "hull speed" would be 9.63 knots. I'm not sure if that applies to barge hulls.

    I wouldn't be opposed to using a diesel or gas engine (or maybe two, one engine per wheel) with a transmission or gear reduction. If it's simple and more efficient, by all means.
     
  13. gonzo
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    gonzo Senior Member

    The displacement is the sum of every weight included in the boat. That would be the hull, deck, machinery, electrical system, propulsion systems, water, fuel, crew, food, etc. That weight will determine what volume of water it will displace, and therefore the draft. It is a tedious but simple process to do. Simply calculate or find the weight of every part and accessory and add them up.
     
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  14. Blueknarr
    Joined: Aug 2017
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    Blueknarr Senior Member

    Big muddy

    Welcome to the design spiral.

    Do as gonzo say. What will your design really way?

    Is design realistic?
    Modify plans as needed.
    Rerun the numbers.

    Repeat Repeat Repeat Repeat
     

  15. alan craig
    Joined: Jul 2012
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    alan craig Senior Member

    You've already defined your power in the first post: 800 ft.lbs x 66rpm/5252=9.6hp for each paddle wheel.
    Apart from that a complete manual transmission from a car or truck might be a really handy fit for two paddle wheels;
    Manual trans gives forward /reverse/neutral and a range of gearing, one of which can be locked when you find which is most suitable.
    Retain the brakes on the axle and use them to stop one paddle to assist maneuvering.
    As Gonzo said, chain final drive for easy adjustment of final transmission ratio.
     
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