Conference unifix::sailing

re .0:

>>> The most credible one was to hoist up a 2 ton boat and see what happens.  
    
Finding someone to volunteer their boat for such an experiment might be 
difficult. That aside, there is the question of safety and liability. 
Overhead lifting is rather risky, and you should have a very large 
safety factor. If you're going to experiment, I'd suggest trying to lift 
a 4 ton concrete block. This would still only provide a proven two to one 
safety margin. A professional consulting engineer specializing in cranes 
would be a good idea and would be cheaper than a lawsuit.

    re .1
    
    That WAS the opinion of a professional consulting engineer.  The whole
    point of the question is to avoid destructive testing.  Knowing the
    ultimate capacity of the crane isn't too helpful if it can't be used
    again.
    
    - gene

re .2:

When I hired a surveryor to assess the seaworthiness of my boat before 
going to Bermuda, I expected a better answer than "sail to Bermuda and 
see what happens". That's about the answer your crane surveyor gave. 
Refuse to pay his bill and hire someone else.

Gene,

the answers you've gotten so far seem truly worthless.  I'd hold on to my
money.

I would not want to do the test of the 4 ton cement block and assume from
it that it's safe to lift 2 tons.  Even though the crane may be capable of
lifting 2 tons (or 10 tons for that matter) it does not mean it should.  Most
mechanical structures will age and fail much more quickly if you exceed some
magic number (which is determined by the overall design, and materials used).  
What this means is that maybe you can move the 4 ton concrete block a couple 
of times, and some 2 ton boats a few score times, but while the crane 
would've lasted almost indefinitely at 1.5 tons, it could be caused
to die early if you push the limit.

Now, a mechanical engineer should be able to look at your crane, examine it,
model it, research the materials and ages and past history of it and come up
with some idea of what the "never exceed" limit is.  This and experienced
Mech. E. could do in about 30-40 hrs of work.  If you figure that you can
probably get somebody pretty darned good for $300/hr, you'd be looking at
~$10,000.  This would still be just a guess (but a good one), unless the
engineer actually takes it one step further and runs some VERY expensive tests 
to measure fatigue and possible invisible cracks in various structural parts.  
I know I would not want to do any of it without hefty malpractice insurance.  

MIT has a tremendous Mech. E. department, and you might be able to get
a bargain on a young professor, who would have most of the work done by
a graduate student.  I can give you some names if you like.

How about the crane manufacturer though?  They may be in the best position 
to help you out.  They are bound to have the crane already modeled, have 
expert engineers familiar with it on hand.  They must be able to tell you 
what (if anything) you need to do to extend the capacity of your crane.

F.

    
    	The computations are not all that bad, most any intoductory text on
    applied mechanics will have this type of example.  This will allow you
    to compute the bending loads at the attachement point of the beam, and
    where the pole pivots.  The real problem is knowing the real strength
    of these critical components, and the attachement to the slab.  I doubt
    that without spending a fair amount of money you will get anybody
    to certify its capacity.  The liability risk in the U.S. with a lawyer
    on every corner is too great.
    
    	Gene, do you know anybody at one of the ACTs some of these systems
    have strucutral modeling codes on them.  Building a model and running
    it would only take an afternoon.  You would need to supply specifics,
    on the materials in the column, the beam, and the attachement points. 
    I used to do ship hull structural modeling in a past life but it would
    take me quite a while to do this stuff now.
    
    	Actually on another note my sailing plans may be changed, forcing
    me to look at sailing out of Marblehead.  What is the cost at the
    sailing center, where is it located (in general terms, I can find the
    Eastern YC, and Boston in a pinch), and do they have any space.  Almost
    forgot the big one what about parking.
    
    Forrest

    I know lots of guys who would love to volunteer their boats for the
    test.  Especially if you could hacksaw halfway through the cables
    before hand!  
    
    Dave

    re .6 
    
    and dave standing behind them to scream they are light if they pass! ;>)
    
    
    john
    
    

RE: .4,

>>>  How about the crane manufacturer though?  They may be in the best position 
>>>  to help you out.  They are bound to have the crane already modeled, have 
>>>  expert engineers familiar with it on hand.  They must be able to tell you 
>>>  what (if anything) you need to do to extend the capacity of your crane.

That's the best (and cheapest) idea of the bunch.  If they built it for 
1.5 tons, you certainly won't get any certification for 2.0, but there's a 
*chance* that material/construction costs jump in different steps than 
lifting motors do.  Maybe the structure was designed for up to some larger 
capacity than 1.5 tons, and the rating is determined by the motor they 
installed.  A long shot, but worth finding out.

BTW, the original builder should be able to provide precise data on
section sizes, steel type, anchor design and fabrication, etc.  You'll 
need all that at the least in order to even contemplate doing the 
calculations with any basis for accuracy at all.  Perhaps if you can 
provide all the data, an engineer might do calculations for a lower cost 
than doing everything.  But I agree with whoever said that getting
anything you could hang a legal hat on is going to cost more than a few
volunteers' time. 

I remember watching a pier derrick going up in Vinalhaven many years ago.  
The local boys all came down, and the result was a consensus (reached in 
Downeast style with plenty of thoughtful pauses and no raised voices)-- 
undoubtedly somewhat overbuilt, but every dollar spent went into on-island 
materials. 

J.

Re. .5

Hmmm, the most you can get out of simple calculations is going to be an
idea of what the static loadings are on different load bearing members of
the structure.  This is really insufficient for a device that must withstand
repeated (hundreds of times) loading and unloading.  Additionally, it's one
thing to know what a material's strength is when it's new, quite another when
it's been subjected to oxydation, fatigue, abuse etc.  The simple calculation
will be interesting--if it rules the upgrade completely out than that's all
for that idea--but not conclusive if it doesn't rule it out. 

On the other hand it's not unlikely that the original manufacturer may
have an idea of what to do to upgrade the capacity.

F.

I'm NOT a mechanical engineer, so don't take my word for it, but:

If I remember my high school physics correctly, the 2 ton weight will exert as
much leverage on the sleeve at 75% lateral excursion, as the 1.5 ton weight will
exert at 100% excursion, so the sleeve (and I beam) should be safe to 75%
excursion. Similarly, the 2 ton weight will exert as much leverage on the
mounting bolts at (slightly more than) 75% excursion, as the 1.5 ton weight will
exert at 100% excursion, so the mounting bolts should be safe to 75% excursion.

If it were my crane, I'd feel free to use it for 2-ton loads, within the
inner 75% of its reach.

Again, I'm NOT a mechanical engineer.

--RS

>If it were my crane, I'd feel free to use it for 2-ton loads, within the
>inner 75% of its reach.


This seems to make sense to me but then....
Anyway, an earlier reply that mentioned a less expensive professor at MIT
was also on the right track but maybe talk it a bit further.

I know that most schools are always looking for real-time projects, we
used to get some work done here at DEC by college students involved
in Comp. Science or Elec. Eng. programs. I personally have done some stuff
with WPI several years ago.

Anyway, I'd suggest proposing this to several Engineering oriented
schools in the area such as WPI, Northeastern, Oh ya, maybe even MIT.
Students would do the work under supervision and the expense would be
minimal. I remember expenses being something like cost of materials
and travel.

Just a thought, Ray.

>If it were my crane, I'd feel free to use it for 2-ton loads, within the
>inner 75% of its reach.

Your assumption if I'm not mistaken, is that the limiting factor is the 
bending moment at the base.  This may or may not be true, but I would
not risk it with MY crane.

F.

I am surprised that any organization would knowing plan to use 
equipment beyond the manufacturer's published rating. The 
litigious attitude prevalent in today's society almost insures 
trouble. My recommendation is get equipment rated for the job.

Joe

That last reply had a typo-- "insures" should have read 
"assures." 

    
    	How possible would it be to buy and install a bigger setup? Seems
    that several yards are out of business, or headed that way.
    
    	Now, if you could scrounge a barge, there's LOTS of idle stuff down
    the river from me, in the Fore River Shipyard   >8*{   !
    
    	Good luck!
    	Scott.

    After some phone calls I located the engineer who designed the crane. 
    As it turns out, he'd already done some calculations on what would be
    needed to do the upgrade.  Apparently the question had been asked at
    the time of the original installation. 
    
    There are two choices.  The cheap one is to reduce the horizontal
    travel on the boom by 1 foot.  The more expensive one is to weld add'l
    gussets at the base of the crane to keep it from toppling over while
    retaining the full horizontal travel.  With an increment in price of
    about $600, that's an expensive extra foot of travel.  But, we are
    trying to reduce the window around low tide during which we cannot
    launch, so we'll probably go with the expensive option.
    
    The engineering turned out to be the easy part.  Getting the town
    engineer to OK the plan is proving to be sticky.  He's "concerned"
    about the depth of the concrete footing supporting the crane.  The
    designer, who was there at the pouring, says it's adequate.  But there
    are interests other than technical ones at stake here.  The town owns
    the land under the crane and the "Emperor" of Marblehead leases it from
    the town during the winter as an overflow storage area for his boatyard
    business.  The Emperor thus defrays the town's cost of owning the land
    which it purchased at market value ($$$) from the original owner.
    
    The Emperor feels the presence of a "cheap" crane in town will
    jeopardize his hauling and launching revenues.  As a close personal
    associate of the town engineer, there has been some informal
    influencing going on to de-expedite the upgrading of our crane.  As far
    as I know, I have been the Emperor's only patron.  The other boats use
    another small crane in town or bum off their yacht club friends.  So he
    stands to lose the $180 I pay each season for my round trip launch and
    haul.  However, since he also owns a major chandlery in town, and since
    8 new E22's have joined the fleet and will use the crane, and since
    E22s break fittings at an egregious rate, the Emperor should recover
    his loss with add'l equipment sales after the first heavy air weekend.
    
    Now I just have to convince him of the wisdom of this logic.
    
    - gene