Help Explaining Why Excess Speed Breaks our Boats

Discussion in 'Boat Design' started by Marty Gingras, Mar 18, 2007.

  1. Marty Gingras
    Joined: Mar 2007
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    Location: California

    Marty Gingras New Member

    Hello all,

    I need your help.

    I have a background in mechanics (years ago I owned and operated a repair shop and boatyard) but am now a managing biologist.

    I recently began managing a fisheries research and monitoring program that is boat-intensive.

    Our field operation is in bad shape for many reasons, including crazy workload, lack of proper prior supervision, and lack of education.

    The current crisis is that we have many broken boats, including a bunch of otherwise good high-quality aluminum boats with damage (broken welds, cracks through the bottom plate) that is clearly attributable use beyond design and/or construction specifications.

    We work in a windy area with lots of 2-4ft wind waves and some of these boat can do 40 kts. Some of our boat operators beat the hell out of the boats.

    I have instituted a 20 kt speed limit until I can fully understand the issues, and am getting feedback that the speed limit hurts the program because the program is built on speed. The usual assertion is that the operators have lots of experience and are the best judges of appropriate speed. This just ain't so!

    Thus, I need to do two things: Understand the issues and explain the issues.

    I hope you can help me explain the issues.

    Can you give me some equations that explain how shock loads increase with speed or something similar that describes the adverse effects of speed?

    I'd also love to learn about policies used by other organizations to address this issue.

    Can you help?

    Thanks much.

    Marty Gingras
    Supervising Biologist (Fisheries)
    California Department of Fish and Game
    Bay Delta Region
    4001 North Wilson Way
    Stockton, California 95205

    Phone (209) 948-3702
  2. johnnyv
    Joined: Mar 2007
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    Location: New Zealand

    johnnyv Junior Member

    Well it's fairly simple really.
    The faster you go the harder you hit the water.
    The harder you hit the water the stronger your hull needs to be for any given hull type.

    As for equations the kenetic energy one works half mass x velocity squared.
    Double the speed and you have four times the energy.
  3. buckknekkid
    Joined: Oct 2005
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    buckknekkid Senior Member

    Ask any offshore racer

    After spending a lot of time throttling an Offshore race boat ,my only analogy is that its like having a car accident every 10 seconds for 60 minutes. thats why they break.
  4. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member

    You might find more direct, documented numbers and graphs looking at crash car test results. I would think they would parallel what happens to boats. It's got to be an exponential kind of thing, like double the speed quadruples the forces or something.

    The policy I always ran into was if you didn't do what the boss wanted, you got fired. Abusing equipment was not what the boss wanted. Sam
  5. ted655
    Joined: May 2003
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    Location: Butte La Rose, LA.

    ted655 Senior Member

    Are they ALL breaking? All the same way, in the same places? All , in spite of who is operating them? All the same boat? Doing rthe same job?They say Lindberg could fly farther on the same fuel others had to land, & on overhauls, his engines always had less wear. Some truck drivers in a fleet of identical trucks NEVER have a problem.
    It's obvious to blame speed and that may be a big factor, but I would gather complere & minute details on each boat, all the conditions I could think of. Time, length of operation, water conditions, operator, load & placement, etc. I would track at least 25-30 data inputs on each boat Then I would plot/ chart it on something like Powerpoint.
    Welds may be suspect @ construction time OR the welding plan may be wrong for a particular joint. The material may be beyond it's ability. The structural size or spacing may be wrong. What & where is breaking? Are there splits, cracks or wjoint failures? Operators may be keeping the boats at a harmful harmonic level. Are other owners experiencing any problems? It will be a job to gather and match all the data, BUT I bet the answer is there.
    Find as many "sames" of all the boats & as many differences and plot them all. See where they cross or paralell and the reason your boats break will read like a cheap novel
  6. Raggi_Thor
    Joined: Jan 2004
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    Location: Trondheim, NORWAY

    Raggi_Thor Nav.arch/Designer/Builder

    Dynamic pressure = some constants x speed ^ 2
    If you double the speed you have four times as high pressure.
  7. tom28571
    Joined: Dec 2001
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    Location: Oriental, NC

    tom28571 Senior Member

    The energy equations above are correct but the actual forces are likely to be much greater. At high speed the boats will be leaping off waves and slamming down into the next one. Great fun for macho jockies if you don't own the boat. This is unpredictable in a specific case and you either need specially constructed boats (deep V hulls built for offshore work) or more discipline on the operators. The latter is the most reasonable path.
  8. Racemore
    Joined: Mar 2007
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    Location: Jacksonville Fl.

    Racemore New Member

    What he said.I think you should be able to find a better boat that can last better than the ones you have.If you have to have aluminium you need a RIB like the Coast Guard is using.

    Jack who???:D
  9. Loveofsea
    Joined: Jan 2007
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    Location: Southern California

    Loveofsea New Member

    Repower with smaller engines. Don't allow the hull to go fast enough to self-destruct.....

    prop the new engines for longevity~
  10. Guillermo
    Joined: Mar 2005
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    Location: Pontevedra, Spain

    Guillermo Ingeniero Naval

    What is the deadrise of those boats? Are they designed (and so scantled) for offshore or inland operation? Could you provide us with more info on them? Maybe also some photos?
  11. Poida
    Joined: Apr 2006
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    Location: Australia

    Poida Senior Member

    G'day Marty, all the reasons you quote there are probably all the reasons why the last bloke quit the job

    I run a maintenance department and Tom hit hit the nail on the head, if they don't own it they don't respect it. In our case we keep fixing it. Keeps me in a job anyway.

    Loveofsea's suggestion could run into a safety hazard. As you are working in a windy area, you have to make sure the engine power is enough to bring you back to shore in a heavy wind. Unfortunately that means you have extra speed without the wind and even more when you are travelling with it.

    You didn't say what size the boats are. Can you get any new ones made of steel.

    There are lots of cluey people on this forum and I would suggest you provide photos sizes etc. and you could probably get some good advice pertaining to correct engine size, optimum speed etc.

    Could also be that the boats were built under the quotation system ie the manufacturer with the lowest quote won the job.

    How old are they, can you get back to the manufacturer and get him to fix them and advise you wont be buying his boats next time if he doesn't.

    Best of luck
  12. water addict
    Joined: Jun 2004
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    Location: maryland

    water addict Naval Architect

    Aluminum is very poor material in fatigue. If the boats are old, and have been run hard, and have cracks, most likely they are shot.
    If you have the budget, sounds like you'd be better with some frp boats.
    If you need to stick with the old boats, you will have to baby them.

    Loads are only half the equation. The structural adequacy is the other. Sounds like you need stronger boats if you have experienced operators telling you that they aren't over-reaching the boats' speed capacity and they are coming back cracked. FRP is usually far superior in fatigue than aluminum if designed and built well.
  13. SailDesign
    Joined: Jan 2003
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    Location: Jamestown, RI, USA

    SailDesign Old Phart! Stay upwind..

    Talk to the manufacturer of the boats - ultimately it is he who is responsible if the boats canot hold together at the design speed.
    You say "they can do 40knots", but is that what they were _designed_ to do? Are the engines on them bigger than mfr's specs?
    Talk to the guy, make him responsible for his product.
  14. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Determine from the manufacturer whether they approve of 40 knot operation. I doubt that they will agree to that kind of abuse. Why do you need to go so fast ?? Are the operators running drugs are or they collecting samples ? How old are the main offenders ? (that'll give you some clues) I'm guessing that you are using fairly small boats with outboards. It is easy to be irresponsible with small boats and big power.

    SamSAm has a sure fire solution. Without a seconds hesitation, **** can the guys who abuse the equipment. I have operated a manufacturing facility for many years. I learned the expensive way to put a screeching stop to equipment abuse as well as dangerous or stupid behavior. Dont dismiss the possibility that you may be held responsible for some one getting hurt or drowned, even though the accident was their own fault. Tort cases are really popular these days. Do what you have to do.

  15. longliner45
    Joined: Dec 2005
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    longliner45 Senior Member

    dont be so fast to shitcan anyone ,,,find the root problem and go from there ,,you have time and money invested in the guys,,thier knowledge is worth something ,,,,,maybe its as simple as fatige on old boats ,,,or payload ,,a miriad of guesses,,, they may have good reasons to go fast ,,to get away from weather ,,or to deliver valuabe cargo ,,they are probably just trying to do the best they can ,,,,,youll be alright,longliner
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