[C320-list] Leak in bilge

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Well, I'm a structural engineer.  After reading this post, I was confused too.  Here are some clarifying remarks by an SE.

1.) If you draw a free body diagram, you will see that the keel bolts do in fact hold up the keel.  The connection between the keel bolt nut and the top of the keel will in fact stretch these large SS bolts as it compresses the hull in this area.

2.) I would agree with this statement, but adding one important item that these bolts do in fact support the keel.

3.) True that a threaded bolt and threaded nut transfer rotary gorge into vertical movement along the axis of the bolt to hold two surfaces together.  It is not clear to me what the rest f the statement is getting at, especially the remark about Archimedes who ave us th principal of buoyancy.

4.) A torque wrench is typically calibrated to take into account the friction between the nut and the threads in the, so called, "machine.". The torque in the wrench is calibrated to relate to the axial load (or pretension) in the bolt.

5.). I'm not sure if this is correct.  Preload is not related to material strength.  Machine design tables would provide this information.  Preloaded is determined by stiffness properties of the bolt (Hookes Law) in proportion to the elongation of the bolt due to the tightening of the bolt with the nut.

6.) True is the numbers for bolt capacities and keel weight is correct.  However, not likely due to stress concentrations on a hull with only one bolt attached when it was designed for six bolts and also prying stresses due to the eccentricities between one bolt supporting the keel (I.e. The CG og the keel is eccentric from the on bolt).

7.) Again, based on my remarks above, preloaded has nothing to do with supporting he keel, other that to reduce the strength available of the bolt to support the keel.

My recommendation based on my engineering knowledge.  Tighten your keel only when it is supported in the mud or in the yard.  Clean the threads and nut assembly per the previous recommendation.  Tighten to the specs and in the proper sequence recommended by Catalina.

You know what they say...

Architects know a little about everything,
Engineers know a lot about nothing,
And Contractors know everything about everything!

David Swanson
S/V Emily Ann
2007 C320 MK II, No. 1107
Mukilteo, WA

David B. Swanson, P.E., S.E.
Principal, LEED AP
Director, Structural Engineering

Reid Middleton, Inc.
(425) 741-3800 office
(425) 741-5011 direct
(425) 508-7971 mobile

www.reidmiddleton.com


On Jan 19, 2011, at 10:28 PM, "Bruce Heyman" <bruceheyman at cox.net> wrote:

> I'm not a mechanical engineer but this problem intrigues me.  I believe it
> does not really matter if you tighten the keel boats in the water or on the
> hard. As my brain at this point can only remember that in some point in the
> distant past I took physics I hope I'm not totally botching the concepts.
> In no particular order:
> 
> 1) The keel bolts do hold the weight of the keel, but more importantly they
> compress the area between the keel and the bilge putting the keel trunk in
> compression.  
> 2) The high torque requirement, 235 foot pounds, is to perform item one
> above and does so by stretching the stainless steel bolt.  Hard to believe
> that a 1" SS bolt stretches but it does and I believe this would be called
> preload. 
> 3) The bolt and nut is a machine that provides significant mechanical
> advantage.  Basically the threads form an incline plane making it much
> easier to turn the nut compared to the lateral forces generated along the
> axis of the bolt.  Thank you Archimedes (wonder if he was a boater?). 
> 4) The torque measurement is not only a measure of the work done in the
> machine (threads) but also the friction on the nut face and the surface of
> the threads.  That is why it is important to take the nut off, clean both
> surfaces and make sure they are dry and free of contaminants.
> 5) If the breaking strength of a 1" - 8 threads per inch bolt is 60,000 lbs
> the clamping or preload would be 14,992 lbs when torqued to 249 ft LBs.
> 6) As our keels only weigh 4400 lb's this means that one bolt when properly
> adjusted would be able to hold the weight of more than three keels.
> 7) As we have multiple keel bolts, all torqued to 235# the preload more than
> swamps out the relatively trivial weight of a single keel.  I don't remember
> how many keel bolts we have but if we have 6 then the total preload is a
> staggering 90,000 lbs.  This is 20 times the weight of our keels.
> 
> Maybe I'm all wet (pun intended) but I believe you are free to torque your
> keels in the water.  Furthermore it is safe to remove one nut at a time and
> clean it up before you reinstall it and torque it to 235 ft lbs.
> 
> Bruce
> Somerset #671 SoCal
> 
> -----Original Message-----
> From: c320-list-bounces at lists.catalina320.com
> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of Allan S Field
> Sent: Sunday, January 16, 2011 11:04 AM
> To: C320-List at Catalina320.com
> Subject: Re: [C320-list] Leak in bilge
> 
> Bruce - you are correct in that the Association has the torque wrench and
> sockets to tighten the keel bolts. However, the boat must be out of the
> water with at least 70% of it's weight supported by the keel. Think about it
> - if the boat is in the water and the weight of the keel with a gravity
> assist is pulling the keel down, what torque wrench and what sailor have the
> strength to pull that puppy up?! In fact, the bolts first get loosened
> before torquing. And yes, loose bolts do weep and need to be torqued after
> the first year then never again, at least according to Gerry Douglas. -
> Allan
> 
> Allan S. Field
> Sent from my iPad
> 
> On Jan 16, 2011, at 1:27 PM, "Bruce Heyman"<bruceheyman at cox.net> wrote:
> 
>> Can be tightened in the water.  The Association has the equipment you need
> to do this job.  I thought the manual said to tighten them after the first
> year and then you were done forever.
>> Bruce
>> Somerset 671 SoCal
>> 
>> Bruce Heyman
>> (949) 289-8400
>> BruceHeyman at cox.net
>> 
>> -----Original message-----
>> From: Kurt Budelmann <krbmd77 at charter.net>
>> To: "Catalina320.org" <C320-List at Catalina320.com>
>> Sent: Sun, Jan 16, 2011 18:02:06 GMT+00:00
>> Subject: [C320-list] Leak in bilge
>> 
>> Hey, I am having a slow leak in the bilge right by the bilge pump.  No
> collections of water fore or aft of this location.  Can water leak down from
> top of mast?  Can water leak from the keel bolts?  Also there is a floor
> joist crossing at that location but I can find no evidence of leaks from
> ports.  I don't think keel bolts were ever re- tightened and the boat has
> never been out of the water since original launch.  Can the bolts be
> tightened in the water or does the boat have to be on the hard?
>> 
>> Kurt R Budelmann
>> 
>