Carbon Fiber Hull over Shaped Urithane Foam

Discussion in 'Materials' started by Pablo4077, Nov 27, 2004.

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Whitch hull design for EV aplication on a Catamaran

  1. Planing

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  2. Tunnel Hull

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  3. Displacement

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  4. Semi-Planing

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  1. Pablo4077
    Joined: Nov 2004
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    Pablo4077 Junior Member

    I am working on an all electric catamaran 18' length 6'8" max width boat design for fun/hobby.
    one of my objectives is to create the ligtest hull posible for inland waters. This serves several porpusos -
    1. energy consumtion reduced
    2. minnimises displacement for narow/long hulls
    3. Easey transport out of water

    I have been reserching this on my days off(hahahaha) and have come to the conclusion that carbon fiber w/ S-glass over 2-lb. density urethane foam would be the quickest easyest and lightest way to build the two hulls. I havent giten to the deck yet but that will be simple as this will be a 2-3 person boat for crussing/fishing on wisconson lakes. I desided on 2lb urithane as this could save the boat from some sinking disasters, but i am woried that it might not add much strength. my crusing speed I hope to acheave is 15 mph and hopefully max at over 25mph.

    Any sugetions or flaws in my thinking? I would appretiat any kind advice on this subject as I'm new to this and I know that know matter how much planning and reserch one man dose, input from experianced people can save your *** in the long run.

    As for cost, I'm not woried about it.
     
  2. Eric Sponberg
    Joined: Dec 2001
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    Eric Sponberg Senior Member

    Pablo,

    Polyurethane foam is the poorest foam you can use, because it has such low strength and stiffness, and it breaks easily. And two pound density does not have near the strength you need. If you want to use foam core, you should be considering PVC foam like Divinycell or Airex, or an SAN foam such as Core-Cell. To my mind, Core-Cell would be the best, in about at least 5-6 pound density.

    I saw your other post on the electric drive idea. Have you contacted the Electric Vehicle Association? They have all the necessary equipment for rigging out an electric drive on a boat. You can contact them at EVAmerica@aol.com.

    Eric
     
  3. Pablo4077
    Joined: Nov 2004
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    Pablo4077 Junior Member

    Thanx for the reply

    I really like the idea of Core-Cell. I think I will make a male plug mold of the Urathane at 2lb then a layer of s-glass 0.96" / core-cell 0.250" /s-glass 0.032
    carbon 0.032"/ Kevlar 0.010"

    I still need the urathane for my mold and am going to hand carve the profile witch i am verry good at, just this size is quite new to me.

    The electric motor system is of my own design with 2 Advanced DC 19 hp motors controled buy a micrologix 1500 plc with 2 pwm outputs. the battery bank is the only thing i'm woried about as weight distribution will be part of the hull design.

    so every one knows, I am a horible speller and if you have a problom with it I'm sorry but my math skills and creativity more than make up for it.

    Thanks for the reply Eric. This opend up some new posibilitys for me.
     
  4. Eric Sponberg
    Joined: Dec 2001
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    Location: St. Augustine, FL, USA

    Eric Sponberg Senior Member

    Pablo,

    Your laminate does not seem right. You have only one layer of S-glass on the inside, but three layers of S-glass, a layer of carbon, and a layer of Kevlar on the outside. This makes for a very unbalanced laminate. To be really good, the inside and outside laminates should be mirror images of each other so that they both work the same for strength and stiffness. Also, Kevlar should never be on the very outside of the outside skin. Light Kevlar should only be used next to the core, to protect the hull from puncture damage, but also to be protected itself by the other outside layers against damage to itself. Kevlar is very difficult to repair for small cuts and minor abrasions, which it will experience on the very outside layer.

    S-glass these days is relatively hard to come by. I would say that if you have some, it is OK to use, but you may find it is hard to buy, and therefore, you may want to go with all carbon instead.

    Regards,

    Eric
     
  5. Pablo4077
    Joined: Nov 2004
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    Pablo4077 Junior Member

    That makes cents on th mirror image thing but as for the kevlar, the reason i added it at all was for its abrasion resistant qualitys. I probly won't add it at all if it can't hold up to midsize lake conditions.

    I do have some s-glass in the shop but only like 1.5 liner yds. left over from my buddys playstation box moulding he made for his car. All carbon would be realy cool but i still would like to mix the s-glass and carbon for the better modulas.
     
  6. Eric Sponberg
    Joined: Dec 2001
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    Eric Sponberg Senior Member

    Realize that mixing S-glass and carbon makes for more modulus than the S-glass, and less modulus for the carbon. The final result will between the two. That may or may not be a good thing. Going all carbon would give you the stiffest laminate.

    Eric
     
  7. Pablo4077
    Joined: Nov 2004
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    Pablo4077 Junior Member

    Thank you for your input Eric, this is helping me with several design parameters as I'm working through this.

    I do want the hull to have a slightly less stiffness then an all carbon hull as I will be loading and unloading this of a trailer all the time. The Idea behind using the carbon was to thin the hull and make it lighter while adding strength and stiffness. Keeping some glass adds thickness for less money and some flex to the hull. The exact modulas is not known to me yet as I need to calculate the weight of the boat and the over all strength to support itself on a trailer. I want it just strong enough on trailer with some flex for the trailer and light and stiff enough for the 20-25 mph on the water. As the Kevlar was ruled out as this would be hard to repair, this type of design will be easier to think about.

    I still need to calculate total displacement without load and with full load.
    Total width of the hulls to achieve the 2' max depth in water fully loaded.(there should be a name for this dimension from water line to deepest part of hull)
    The angle of the bow(top view)
    Whether I want a displacement or planning hull, or somewhere in between. I am thinking that displacement for energy conservation is the key here. But must obtain a max speed of 26-30 mph with a total hull length of 18' Max. I know that the hull speed calculation is not the same for a catamaran but there is fineness (not spelled right) of hull calculation that is more applicable. I saw this on a kayak web site some where. Still unsure of this one though. Probable waterline length around 16-17' would only give me a 5.6 knot hull speed. (Not very fast.) but a catamaran should give me < [hull speed] max speed. By how much I have yet to determine.

    So there are a lot of variables to figure yet but I'm sure it will be a combination of composites. The mirror from one side of the core to the other has helped simplify this for me and the decision on Cell-Core 6lb. has helped. Also I am going to use epoxy for total strength. I may add some carbon fiber ribs on the inside for structural reasons but where how much and to what extent is still left up to the hull shape.

    Will adding some planning hull shape or planning pads, Hydrofoils, plaining foils give enough lift to help attain top speed at a reasonable cost of conservation of energy? I really don’t think so as the cat is designed to be very slender on displacement hulls. The lighter the faster is what it comes down to, so maybe all carbon isn’t such a bad route. But will the hull have enough flex to undertake road conditions on a trailer with a minimum hull thickness? The trailer could be made to support more surface area of the cat but how would getting the boat on the3 trailer be affected.

    There are a lot of things for me to think about yet before I get the foam and rollers out, but this is the part of it I like. Solve as many problems as you can and then live with or modify what you have done as little as possible later.
     
  8. wet feet
    Joined: Nov 2004
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    wet feet Senior Member

    Two things about Kevlar to be aware of;first it goes really fuzzy when abraded.Second it loses strength rapidly when exposed to UV light.Both factors make it a good idea not to use it too near the outer surface of a laminate.
    Your target speed seems very high compared to the electric boats I have seen.Do you have some special technology available?
     
  9. Pablo4077
    Joined: Nov 2004
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    Pablo4077 Junior Member

    It is not new technology, its old technology called horsepower and Energy.
    The problem with electric motor systems is not lack of power (actually an electric motor is in all ways more powerful and more efficient. The real problem with Electrical Vehicles is the energy storage system vs. weight/space.
    A good example is that some guy in California(I will give links Later, when I find them) made his own sports car totally EV that can outrun a Dodge Viper in the quarter mile buy more than a second, but the viper can stop fill up his tank and keep going. With batteries being as expensive as gas over there lifetime in miles, it is purely a performance vs. efficiency thing. I plan on using 2 19 HP 96VDC motors with a max of 50 HP peak.
    This means I need 8 batteries in series for 96VDC just to run the motors. And then there is how long I can run the motor before the batteries are drained to 10 VDC which is the lowest you should ever run them down to. This equates to the amp/hr rating, witch is not an exact science. Each battery will probably weigh 30-80 lb. each x 8 = 240-480 lbs. for just one bank. Each bank will give me ## Amp/hrs which will dictate how long I can drive the boat around and at what speeds. Then there are the Capacitors for quick discharging of current (the current is also equal to the torque the motor is giving), these add weight to the boat but give little to no noticeable IR Drop because they are as close to the motor as possible and have very little internal resistance. Similar to the Caps you put on your power amp for faster and bigger bass response. I am going to use a PLC with 2 PWM outputs to 2 SSR's and program my own logic in to control the motors ramp to speed rate and current locking and stuff like that. This will give me a way to maximize the power in the batteries so as little goes to waste as possible.
    The reason I'm going with electric motors ultimately is the simplicity and configuration options I have with the drives and or controls there are out there. This may seam like a silly idea to most but it interests me a lot. Simply put a gas motor will give you the long hours on the lake at a reasonable cost, but they are loud, polluters, and low in performance vs. an electric motor.

    Call me silly but I see ppl driving down the road with TVs and DVDs in there steering wheel just because they think it’s cool. Now I'm ranting, (hehehe) long day.

    There are race boats out there that are all electric and there are pleasure boats too. But there are very few that can do both. This is one of the reasons I decided on a catamaran. They are far superior in energy usage as displacement hulls go, and far superior in speed as racing is concerned (is there a middle ground?). I plan on making a displacement hull style Catamaran at 18' with 2 20 hp electric motors (this means that I have 2 50 HP peak and a liner tourqe curve). Dose this sound like I could go 25 MPH?
    I hope but I don't really know as I am learning about this as I go and am using these numbers as starting points.
    http://www.electricboats.co.uk/intro.html -this is a great starting point for anyone interested in electrical motors for boats and what it takes to size every thing properly
    http://www.electric-boat-associatio...k/technical.htm - this is another great place to start.
    The problems with the web sites listed above are they are about duration not performance. There is a huge tradeoff between the two unfortunately.
    http://www.wurts.net/ElectrifiedMotorSports/elecms2.htm - This is high performance EV but you wouldn't drive it to work hehehe.

    Now when it all comes down to it in a boat, the key factors are hull design, Weight, HP, and money.

    And so everry one knows I used spell check so you could read this and not wan't to kill me. :D
     
  10. Pablo4077
    Joined: Nov 2004
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    Pablo4077 Junior Member

    This is based off the:
    Electric-Boat Drag and Power Calculator

    Length of Hull 4.877 m (only used for calculation of Re)
    Wetted Area of Hull 4.98 m2
    Speed 10.28 m/s
    ditto 37.008 km/h
    ditto 19.96 Kts
    Reynold's Number 50,135,560
    Coefficient of Drag 0.0028
    Drag 743 N
    Propulsive Power 7,640 W 10.24189124
    Eta Propeller 80 %
    Eta Gearing 100 %
    Eta Motor 80 %
    Eta Motor Controller 98 %
    Battery Voltage 120 V
    Current 100 A
    Cable Length 3 m (to motor and back)
    Cable Cross-Area 5 mm2
    Cable Resistance 0.01032 Ohm (Copper)
    Cable Voltage Drop 1.04 V
    Cable Power Loss 104 W
    Eta Cable 99.2 %
    Electrical Power (Motor) 11938 W 16.00295506
    Electrical Power (Battery) 12281 W

    Granted this is not ideal or even near it and I'm not sure how this will apply to a cat. These are fuigurs of:
    1 motor at 150 lb, 598 lb batteries, 500 lb load, 300 lb hull and 0.5x deck for a total displacement of 186 gallons. I am going to base my hull design on these numbers. If anyone has any suggestions please poke holes now, not when it’s built, hehehe.
     
  11. Guest625101138

    Guest625101138 Previous Member

    You need to learn about flat panel boat construction. For the sort of boat you are considering it is the best method. Making a solid plug and covering it with carbon fibre is not a good solution unless you remove the plug. You then need quite a few layers of carbon to get the stiffness. It will be very expensive.

    You should also consider a trimaran configuration with unloaded stabilisers.

    Is your length a firm constraint? I expect you would get a more efficient boat with a trimaran configuration but I would need to check it.

    Depends on how serious you are. If it is just a mental exercise then keep doing what you are doing.

    Rick W
     
  12. robherc
    Joined: Dec 2008
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    robherc Designer/Hobbyist

    FYI: I think the term you're looking for here is "draft." The "draft" is the measurement of how deep the lowest point of the hull/keel when the boat is floating level in calm water. Otherwise, maybe you meant the "design water line" which is actually very similar (difference is that draft is a real-world measurement, while DWL is what you're WANTING the draft to be).
     
  13. Guest625101138

    Guest625101138 Previous Member

    I checked the power calculation you had against the best possible 5m long hull and your figure under estimates by a good margin.

    I then checked the calculator. You need to read the note beside the calculator:
    "EBA member Theo Schmidt has provided two spreadsheets to quickly determine the "best case" drag and power for a craft of any size with a smooth surface, no disturbances like immersed transoms, and traveling at a speed where the wave-making is negligible. All that is needed as input is the wetted surface area, the speed, and the approximate length. The spreadsheet also allows setting the medium to "air" and thus gives the drag and power of an equivalent optimal airship hull, e.g. an optimal fairing for reducing wind resistance."

    You cannot make a hull that is 5m long and run it at 10m/s without it making substantial waves. This is the reason your result is wrong.

    Also you cannot just add the wetted surface for both hulls. You need to do the power calculation for each hull and then add them. The wetted surface for the best hulls is 3.4sq.m. So your total is low anyhow. The calculator is only about 10% low once you do the hulls separately. This is still not strictly correct because the two hulls interact but the interaction is not great.

    What you want to do can be done but you need to rethink some aspects.

    Rick W
     
  14. Manie B
    Joined: Sep 2006
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    Manie B Senior Member

    Rick you obviously did not notice that this thread DIED in 2004 = sorry pal but you are talking to the trees :D
     

  15. Guest625101138

    Guest625101138 Previous Member

    Now Manie that is funny because it popped up in the Unread List - I did not check the dates. I wonder if he built the boat and got terribly disappointed.

    Rick W
     
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