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Boat weight?

Discussion in 'Catalina 310' started by marchem, Oct 9, 2017. Add this thread to a FAQ

  1. Apex

    Apex

    Joined Jun 19, 2013
    603 posts, 40 likes
    Oday 28
    US Muskegon
    LOL love it Jim. I can't help but jump in. Love physics and math riddles (sometimes)
    Just to keep it rolling. My boat floats higher in the fresh water river, but sinks a bit when I hit the Gulf.
    Quiz: What is the Displacement weight in the river?
    ***SAME Volume of the water displaced changes because of specific gravity change, Weight of the water displaced is still the same (ignoring diesel spent, and beers pissed overboard)***

    Quiz: When I stand on my electronic bathroom scale and then lean over about 20° angle, did I lose weight?
    This one is really tricky.;)
    ***what are you leaning ON to get to 20degrees Jim? That is where your weight was distributed to instead of the scale cells***

    Quiz: If a truck full of sand pulls up on a public scale and it reads 43,100 lbs, a small pick up pulls up and 2 guys
    get out and shovels 4 more shovels of sand on the big truck. New reading 43,000 lbs.
    Did the truck steal some sand?
    ***Good puzzle, I imagine the truck is not fully on the scale, and they shoveled sand outside of the off-scale axle. Changing weight distribution, removing weight from the on-scale axle.****
    Go for it!
     


    JamesG161 likes this.
  2. LakeShark

    LakeShark

    Joined Sep 15, 2016
    196 posts, 38 likes
    Catalina 22
    US Minnesota Minnesota
    You guys stink! I am a sucker for riddles and puzzles! @Apex beat me to most of them though. However I have a different view on the truck one. One guy got out of the loaded truck (driver) and the other out of the PU (also driver). The 4 shovels added to the truck on the scale did increase the weight but the driver never got back in! Therefore the truck weighs less on the scale.

    Now to go far beyond. If we figure each man shovels 25 lbs with each scoop they would add 100 lbs to the truck. Since the truck now weighs 43,000lbs this means the driver weighs 200 lbs and going down the road the truck will weigh 43,200 lbs!
     


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  3. JamesG161

    JamesG161

    Joined Feb 14, 2014
    1,800 posts, 247 likes
    Hunter 430
    US Waveland, MS
    This thread had 3 science themes. The Quiz was to see if most of it was read.
    1) Boat Weights [Buoyancy/Gravity]
    2) Angle of Lift [Vectors/Force]
    3) Believable results [Precision]

    Quiz was meant not to "overthink" the questions.
    Hint: Think simpler.
    @LakeShark just the sand only;)
    @Apex My body was fully on the scale, touching nothing but the scale.

    Jim...

    PS: These were similar to some questions posed by my Science Professors.
     


  4. JamesG161

    JamesG161

    Joined Feb 14, 2014
    1,800 posts, 247 likes
    Hunter 430
    US Waveland, MS
    @LakeShark your posts contain the correct Quiz answers.:)

    I did leave out the E=mC2, mass theme, though.:laugh:

    Hit: Big Truck is fully on the electronic scale and paying for the Sand. All people are drinking Coffee with the scale tender, inside the office.
    Jim...
     


  5. LakeShark

    LakeShark

    Joined Sep 15, 2016
    196 posts, 38 likes
    Catalina 22
    US Minnesota Minnesota
    Wow it must be fall as we are well down the rabbit hole on this one. The OP question was answered 7 posts in and here we are 38 posts later and now we're talking about weight and dump trucks. Boy the world better look out when the temps turn cold and sailors are not out on the water!:hijack:

    How did I ever even get here? I only have a 22 foot boat currently and use a pickup with a trailer to pull it out of the water! Ohhhh my the work of idle hands and time!:laugh:
     


  6. 2 OLD PIRATES

    2 OLD PIRATES

    Joined May 2, 2012
    160 posts, 1 likes
    Catalina 310
    Ca Ontario Toronto
    Fin Keel
    Hull length 31’ 1”
    Waterline length 26’ 6”
    Beam (width) 11’ 6”
    Draft 5’ 8”
    Light displacement 10701 lbs

    Ballast weight 4400 lbs

    Ballast type Lead
    Wing Keel
    Hull length 31’ 1”
    Waterline length 26’ 6”
    Beam (width) 11’ 6”
    Draft 4’
    Light displacement 10300 lbs

    Ballast weight 3999 lbs

    Ballast type Lead
     


  7. Jackdaw

    Jackdaw

    Joined Nov 8, 2010
    7,160 posts, 1,122 likes
    Beneteau First 36.7 & 260
    US Minneapolis MN & Bayfield WI
    That's gotta be backwards..... wing/shoal keels almost always weigh more than the fin; this is done to keep the CG the same with less draft. While its possible for that to be right I've never seen it done before.
     


  8. JamesG161

    JamesG161

    Joined Feb 14, 2014
    1,800 posts, 247 likes
    Hunter 430
    US Waveland, MS
    Ans: The same as the Displacement weight on Dry Land. It is Boat's Architect best estimate of his design Displacement weight.

    ______________
    Ans: No! At least while I was on the scale, I didn't lose weight. [Also the strain cell in the Bathroom scale gave the same readout. No matter the angle;)]

    _____________

    Ans: No! Truck scales, like the boat lift weights, are very imprecise. Usually only top 3 digits are good. For the sand case of 43,xxx lbs , the xxx is unknown. So the truck weight is 43,000 ±500 lbs. If the Pick Up truck guys had loaded the truck with exactly 100 lbs of feathers, the truck weight would be 43,000 ±500 lbs.:)

    Jim...
     


  9. marchem

    marchem

    Joined Nov 16, 2012
    425 posts, 14 likes
    Catalina 310, 2000, #31
    US Santa Cruz, CA Santa Cruz
    Jim, if your boat sinks a bit in the Gulf, then the density of the water there must be less (as long as the actual boat weight stays the same :)). I would expect the Gulf to be more salty, which would increase it's density. Only if the salinity stayed the same and the Gulf was warmer would the density change as you described.

    Still a good question.
     


  10. marchem

    marchem

    Joined Nov 16, 2012
    425 posts, 14 likes
    Catalina 310, 2000, #31
    US Santa Cruz, CA Santa Cruz
    Jim, I agree that the weight doesn't change, and the strain cell on the bathroom scale gives the same reading no matter the angle-until you fall over. But in a travel lift, with slings that hang down at an angle, the strain cells will read higher than the actual weight of the boat. Even a 7 degree angle will cause the force to increase by 1%; maybe close to the resolution of the measurement (see question #3), but it's still a real increase.
     


  11. Meriachee

    Meriachee

    Joined Aug 1, 2011
    1,845 posts, 297 likes
    Catalina 270
    CA Edmonton, Ab Wabamun - on the orange ball
    Get a picture of that 45 degree strap before and after the boat falls off. Then there’s the basis for an acceleration discussion followed by an ashphalt deflection calculation. :)
     


  12. Ralph Johnstone

    Ralph Johnstone

    Joined Jan 4, 2006
    2,374 posts, 219 likes
    Hunter H-310
    CA West Vancouver, B.C.
    Couldn't be simpler .............................. :snooty:

    dropped boat.jpg

    I rest my case .
     


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  13. marchem

    marchem

    Joined Nov 16, 2012
    425 posts, 14 likes
    Catalina 310, 2000, #31
    US Santa Cruz, CA Santa Cruz
    Actually, at 45 degrees the load factor is about 70 %. Still needs to be considered. Luckily for us the lift is rated for much heavier boats than us.
     



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