High torque engines

Discussion in 'Boat Design' started by Boston, Apr 27, 2009.

  1. rasorinc
    Joined: Nov 2007
    Posts: 1,853
    Likes: 71, Points: 48, Legacy Rep: 896
    Location: OREGON

    rasorinc Senior Member

    Perhaps, consider re-designing the bottom of the hull to a deep V. 3/12 up
     
  2. Boston

    Boston Previous Member

    Frosty
    the pellet stoves claim huge efficiencies
    Im not even comfortable quoting them until I get some references

    the steam is condensed and reused without cooling it to far past the condensation point

    and the engine runs way better if cooled and its not in any of the calculations

    Ras
    I been kicking round the idea of a tunnel in which the prop could spin
    its a design consideration ive seen before but would need to research if it becomes evident Im stuck with a prop that offers to little efficiency
    Rick suggested originally a one meter prop that was 69% efficient at the rpm of 740 wich also means I could forgo a transmission

    Im just working out a few new ways to do some relatively old stuff so if I get a few things wrong in the process or if it seems Im redesigning the wheel
    its just the beer talking and Ill see reason in the morning
    har har har

    cheers
    B
     
  3. Ad Hoc
    Joined: Oct 2008
    Posts: 7,773
    Likes: 1,678, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Boston

    If you think you'll get 69% efficiency on a prop on that boat, you're doing more than redesigning the wheel...
     
  4. Guest625101138

    Guest625101138 Previous Member

    The 22" prop is heavily loaded so benefits significantly from a well designed shroud. The attached shows the potential gain. There would be slightly increased drag with the shrouding but this would be a good solution.

    Rick W
     

    Attached Files:

  5. Boston

    Boston Previous Member

    way to go Rick
    I knew you would come up with something
    ok
    a 22" prop with a shroud is able to run at 84% efficiency
    thats in the range I wanted

    ok so one thing about these abbreviations
    velocity of rotation in newtons
    let me go look that up and see if its anything like RPM
    which I need to know so I can calculate HP / torque and know my engine is compatible
    ok RPM it is


    11669 newtons ended up being 112 hp which is well within the range of this engine at this gear ratio
    1600 rpm from 740 rpm equals a ratio of roughly 2.2
    so were getting somewhere
    matter of fact its so well within the design limit I could throw a few more gear into this system and create an azipod kind of scenario
    Ild be eliminating the ruder but adding two geared connections and a swiveling nacelle could be advantageous but that is yet to be determined
    also there are structural considerations that may make the system impractical

    hp = T ( rpm ) / 5252
     
  6. Guest625101138

    Guest625101138 Previous Member

    Speed of rotation is commonly given in rpm.

    Force or thrust is given in Newtons (N).

    Torque is given in Newton metres (Nm).

    Power is torque by rotational velocity. For consistent units the rotational velocity needs to be in radians per second. rps = rpm/60 * 2 * pi. Torque in Nm times rotational speed in rps gives power in Watts.

    Simple really. You do not need to worry about the amount of power a horse can produce or how many British Thermal bits are in the fuel pellets. Get the pellet energy stated in Joules so they are readily translated to watts. A watt is one joule of energy produced in one second.

    Rick W
     
  7. Boston

    Boston Previous Member

    its metric Rick
    I went to school when the dinosaurs roamed the earth
    and around here that means quarts and ft/lbs and 1/32 inch
    this metric thing is killing me

    5 meters a second is 11.18 miles an hour acceptable spead at roughly 1/2 the engines peak capacity assuming the rpm is 1600

    velocity of rotation as measured over one minute in N certainly has a rpm look to it but I got that its in radians a radian not being one complete revolution
    nice touch
    there are 6.28 radians pr each 360 degrees
    thus 1600 / 6.28 = 254.7 which cannot posibly be right

    define velocity of rotation in newtons
    and how it related to rpm please

    the calculator you used does not relate rpm

    1 btu = 1055 J
    good wood pellets contain 17,000,000 btu per ton at a cost of $175 to $225 each, works out to about half the cost per btu of diesel but its bulkier and weighs more

    41 Kilowatt Hours = 147600000 Joules
    pellets get 17 000 000 Btu per ton = 17 935 950 300 Joules per ton so 1 ton of pellets will drive the hull at hull speed for 121.5 hrs

    thing is its not the fuel Im concerned about
    nor the conversion factor to steam
    its the power available from the engine at some reasonable percentage of its max capacity
    without the prop rpm I cannot calculate that
     
  8. Guest625101138

    Guest625101138 Previous Member

    To get decent results from the prop shroud it needs to be designed to suit the operating conditions. It is not just a tube surrounding the prop.

    It needs to take into account the increase in velocity through the prop. Hence the inlet is larger diameter than the outlet and the outer surface needs to be designed to offer low drag.

    There are not many specialist suppliers in the field.

    There has been a couple of recent threads on the topic.

    Rick W
     
  9. Boston

    Boston Previous Member

    I read them but didnt participate cause my knowledge is limited in that area
    I can make one or have one made once a determination is made as to the best configuration

    I need to consider my gearing so I can calculate the hp needed to turn the prop
    that boat had two 210 hp engines that produced about 500+ ft/lbs at peak efficiency each
    they ran at about 1800 rpm to hit that although the gear ratio is unknown and ate 4.6 gallons an hour each
    ends up being 137 kw/h each and 724 Nm also at 1800 rpm each
    this was substantially more power than the boat originally had, but thats what they put in the rebuild to get it up to 10 knots cruising and 14 max
    so the engine Im thinking of is slightly weaker
    but Im willing to pull few tricks to get it up to speed if they work and are not to much torture
    the key element that makes me think this engine will work is that when I compensate with gearing for the high torque and low engine speed I get
    900 rpm at 150 hp and 900 ft/lb or 300hp at 1800 rpm and 450 ft/lbs which is about what the diesels are except for the torque
    torque = kick in the pants or the amount of time it takes you to get up to speed
    Im ok with that
    I think

    I might have done that wrong hp = T ( rpm ) /5252

    900 x 1800 /5252 = 308.45 hp so ya I think I did the gearing right

    if its not working out with the numbers and the prop size there are other solutions ( although I think I got it pretty close for a efficient set up )
    I could go with two smaller steam engines 125 hp each for a slightly lower range but two large screws shrouded and spinning slower
    the two smaller engines combined weight is about 500 lbs for the castings where as the one large engine weighs 700 lbs so I would actually be getting a higher power to weight ration
    this is one reason I wanted to get things figured out for a single large engine
    I like the simplicity of fewer moving parts but there might just not be enough go to a single larger engine

    so now we get into two screws instead of one and thats another mystery
    besides two smaller props spinning faster are less efficient eh
    so it sounds like I want to stick with the largest props I can fit under the boat spinning slowly in shrouds
    now were getting crazy
     
  10. Guest625101138

    Guest625101138 Previous Member

    The attached curve will give you an idea of how wasteful it is to push this hull over 9kts.

    A shrouded 22" prop only requires 41kW to do 9kts. This is 20% of what is required to do 14kts with a shrouded prop. That extra 5kts means you need to shovel pellets 5 times faster.

    Rick W
     

    Attached Files:

  11. Boston

    Boston Previous Member

    dam
    9 knots it is
    thats funny
    you want the lines for it

    that brings it back into the relm of a single engine again

    and no shoveling for me
    some guy a few hundred years ago came up with electricity

    those guys didnt even remotely need those two huge diesels given that your numbers are bound to be at least in the ball park
    and it also means I could move down to a single 50 to 125 hp steam engine using 1/2 the lb/hr of steam and a single boiler system

    the 125 hp engine turns at 1500+ rpm eats 1200 lbs of steam pr hour at max and should have 125= T ( 1500 )/5252
    125/T= 1500/5252 or
    125/t = .28560548
    125/.28560548 = T
    = 437.67 ft/lb at max output for a 125 hp engine at 1500 rpm

    1 hp = .7457 Kilowatts
    41 Kw / .7457Kw per hp = 55 hp
    that's bloody incredible Rick
    course there is an energy loss in there somewhere but still
    thats not much to get this thing moving

    so the efficiency was 84% so
    100/84= 1.19 x 55hp = 65.5 call it 70 hp to cruise at about hull speed of 9,3 to 9.8 knots

    thing is Ive got tons of torque at a 1:1 ratio and the larger prop shrouded say 14" advance and 22" diameter going ? rpm provided for a lot of efficiency
    velocity of rotation in newtons 1600 1/min = ? rpm
    that would have taken me a month to figure out Rick
    points to you for being a good sport
    B

    maybe not
    thing wont let me points you
    said something about another beer before I can give any more reputation to people
    imagine that


    1 btu = 1055 J
    good wood pellets contain 17,000,000 btu per ton at a cost of $175 to $225 each
    works out to about half the cost per btu of diesel but its bulkier and weighs more

    41 Kilowatt Hours = 147600000 Joules
    pellets get 17 000 000 Btu per ton = 17 935 950 300 Joules per ton
    so 1 ton of pellets will drive the hull at hull speed for 121.5 hrs
    I think thats bound to be wrong
    hmmmm
    how about 121.5 x .84% efficiency = 102 hours or 938
    still seems like to much
    boiler efficiencies in the 90% range are not uncommon
    my pellet stove claims an ash remaining of 1% which means there was a near impossible conversion to the gaseous state
    to be safe Ill say a 80% boiler and burner efficiency rate combined
    102 hours x .8 = 81.6 hours or 751 miles per ton of fuel

    at the same speed and revs the diesels would be at there lower limits and burning 1.3 gallons an hour each or 2.6 gallons an hour for both
    over 81 hours thats 210 gallons at $3 a gallon or $630
    the pellets per ton to go the same distance cost about $175 - $225
    although the diesels would most likely be pushing a smaller diameter prop of less efficiency and at a higher rate of consumption per hour to speed along
    why, is my next question
    instead of bombing around the bay like some fool in rut
    how about slurping down a martini and wondering if the girls going to remember she is naked before that sail boat slides past and and there kids start screaming for grand dad to come see
     
  12. Boston

    Boston Previous Member

    answer is
    for the small steam engine
    22" prop with a 14"pitch spinning at about ? rpm


    next trick is to go back and figure out the metric puzzle and how it relates to prop rpm

    rps = rpm/60 (2)(3.1416)
    ok now I see it
    somehow I blew right over that when I originally read it
    thanks

    whats the 2 in there Rick is that what brings me up to the number of radians in 360 degrees
    kinda looks like it

    1600 = rpm/60 * 6.2832
    1600/6.2832 = rpm/60
    254.6 = rpm/60
    254.6 *60 = rpm
    15,279 = rpm

    hmmmm and that's got to be wrong
    let me guess
    rps isnt 1600

    rps = radians per sec
    velocity of rotation in newtons 1/min then does not equal rps
    and once again the metric system nomenclature has kicked my ***

    no worries
    I want to take advantage of a steam engines ability to run forwards or backwards and run this thing without a transmission so I need to have the rpm's at the naturally occurring rpm range for the hp to drive the hull at typical cruising speed
    thus I need to know what the rpm of the prop is
    but Ive pretty much got this thing down except for that
    my engine rpm at 70 hp is 625 on the big engine
    for the large steam engine about 625 rpm so I would need to either recalculate the pitch or gear up the shaft speed
    for the smaller engine about 1200 rpm at 94 hp and 900 lbs of steam pr hr is going to be my max cruising power sustainable

    Im going to cheat and plug in the known parameters into my best prop calculator
    we came up with a 22' prop and a 14" pitch shrouded at 83+% efficiency

    calculated for the smaller steam engine spinning at 900 rpm and 70 hp the second set of numbers in { } is for the smaller engine at max potential
    engine torque = 408 ft/lb { 438 }
    shaft hp at prop = 68 ( no gear box ) { 121 }
    prop rpm = 900 { 1500 }
    prop torque = 396 ft/lb { 425 }
    displacement = 25 tons
    wl =57'
    speed in knots = 9
    speed length ratio = 1.192
    shaft hp available = 68 { 121 }
    pounds pr shaft hp available = 736 { 412 }
    hp required at prop = 70
    lb pr shaft hp required = 716
    80% of max prop shaft rpm =720 { 1200 }
    theoretical required prop pitch = 15.2 { 9.12 }
    1) estimates slip of un-shrouded prop = 40.01%
    2) estimated slip of shrouded prop = 17%
    1) required un-shrouded prop pitch at 9 knots = 21" at 25" diameter rpm = 720 { 15" at 22" diameter rpm = 1200}
    2) required shrouded prop pitch at 9 knots = 18" at 22" diameter rpm = 720 { 12" at 22" diameter rpm = 1200 }

    way to go Rick your determination of a 22' prop with a 14" pitch is in the ball park ( rpm of ~ 1000 )
    I knew you would be perfect for this conversation
    cheers
    B
     
  13. pistnbroke
    Joined: Jan 2009
    Posts: 1,405
    Likes: 34, Points: 48, Legacy Rep: 404
    Location: Noosa.Australia where god kissed the earth.

    pistnbroke I try

    I am with frosty I think you are going about this back to front ..If I read this right you have a boat with twin prop shafts with propellers and you you want to rip this out re build the holes and then make another for a single shaft.....crazy .too expensive ..why not stick with the two shafts?? did I read you run this thing with only one engine going .......sounds like 1 steamer and a gearbox / two steamers /one steam and one exist diesel..........too much theory and not enough practical professer commented the students
     
  14. Guest625101138

    Guest625101138 Previous Member

    Running at 1000rpm at 9kts requires 22 x 18 prop per attached.

    Rick W
     

    Attached Files:


  15. Boston

    Boston Previous Member

    thanks Rick
    I figure the calculator I posted was in American Imperial so although I can relate to it better that way. you would probably stick to your own.
    thing has a ton of information it gave me though
    thanks again for the help

    Mr Piston
    the boat is still on paper and Im trying to work out some details so that as I bring the design along I will have as few surprises as possible. Im altering the original engines lay out and fuel source and so my take on it is to work everything out before I start cutting up timber rather than after. Its kinda a hobby of mine to work out a few details and then build rather than build a little, tear stuff apart and build a little more, then maybe rip more stuff apart and so on. I got this funny notion that my way ends up faster and better. Work it out ahead of time, build it once.
    its got a ring to it

    Ive been a general contractor for a long time and once upon a time played with a lot of math so my take on any project is I should be able to stand on the ground looking at the prints and calculate the length, cut and pitch of any rafter hip or peak on the roof pretty much using only a^2 + b^2 = c^2
    ( even jack and ******* rafters are no problem when calculated so )
    and then yell at someone how to cut something.
    should end up perfect unless some fool didn't follow the dimensions on the prints

    every bodies got there own way of doing stuff
    and this is just mine
    cheers
    B

    without looking it up
    can anyone tell me the substitute value for 12 if your calculating for a hip or valley rafter on say a 6/12 pitch
    ( even the carpenters in the squad have most likely have been using speed squares so long they wont get this one )
     
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