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T.R. Bauer
Joined: 17 Nov 2007
Posts: 1733
City/Region: Wasilla
State or Province: AK
C-Dory Year: 1993
C-Dory Model: 22 Cruiser
Vessel Name: C-Whisperer
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 Posted: Thu May 15, 2014 12:35 am Post subject: |
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| The weakest link in your system is its maximum rating no matter which one of the suckers you put in. |
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Sunbeam
Joined: 23 Feb 2012
Posts: 3990
City/Region: Out 'n' About
State or Province: Other
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Photos: Sunbeam
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| Posted: Thu May 15, 2014 1:39 am Post subject: |
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| T.R. Bauer wrote: | | The weakest link in your system is its maximum rating no matter which one of the suckers you put in. |
I'm not sure I understand what you are saying. I do get that ground tackle is a system, and that a system is generally no stronger than its weakest link. But I'm not sure that's what you mean (?)
If that is what you mean though, then the reason I posed the question is that I wasn't sure that the forces on a bow eye would be "equivalent" to, say, the shackle, which is otherwise my weakest link by quite a bit (because I have 1/4" high test chain, but it is not possible to get high test shackles to fit it). So in other words, say the shackle is rated at 1500# working load and 2000# breaking load (I'm making those figures up for the sake of discussion, although I have the real ones elsewhere for reference). Then does that mean the bow eye need only be rated that high to be "equivalent"? OR are the forces on the bow eye different so that in order to be "not weaker" it needs a higher WLL/BLL? In my lay-person's mind, it just seems like forces on the fixed bow eye might be greater than forces on the "fluidly placed" shackle (that is between the chain and the rope, and generallly gets a relatively straight-line pull). And what about trailering? These questions are why I posted. |
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BrentB
Joined: 15 Jul 2006
Posts: 4419
City/Region: Greenwood
State or Province: IN
Photos: BrentB
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| Posted: Thu May 15, 2014 10:10 am Post subject: |
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Having a better part is ok but proper installation is important too.. It seems to me that one limitation is the hull thickness in area. Is it re inforced with fiberglass mat or just buildup of extra epoxy ? With a strong pull, the eye could pull out like a tooth.
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Brent Barrett |
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thataway
Joined: 02 Nov 2003
Posts: 20821
City/Region: Pensacola
State or Province: FL
C-Dory Year: 2007
C-Dory Model: 25 Cruiser
Vessel Name: thataway
Photos: Thataway
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| Posted: Thu May 15, 2014 10:30 am Post subject: |
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This is the type of rig which is used for towing 25 foot boats at up to 25 knots across open water and the Gulf Stream. In these boats, the hull interior is re-enforced with layup of several layers epoxy/cloth, such as 1708 /then mating SS plates on the inside of the hull. The strength is probably limited by the shear load of the 5/16" Bolts--The shear strength of each of these bolts is at least 3,500 lbs. (total over 40,000 lbs) The weldment would be more than a 1/2" SS U bolt. The load is spread out over a substantially greater area.
So if the U bolt, and its specs is not enough--you can always go to this more substantial fitting.
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Bob Austin
Thataway
Thataway (Ex Seaweed) 2007 25 C Dory May 2018 to Oct. 2021
Thisaway 2006 22' CDory November 2011 to May 2018
Caracal 18 140 Suzuki 2007 to present
Thataway TomCat 255 150 Suzukis June 2006 thru August 2011
C Pelican; 1992, 22 Cruiser, 2002 thru 2006
Frequent Sea; 2003 C D 25, 2007 thru 2009
KA6PKB
Home port: Pensacola FL |
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BrentB
Joined: 15 Jul 2006
Posts: 4419
City/Region: Greenwood
State or Province: IN
Photos: BrentB
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| Posted: Thu May 15, 2014 10:41 am Post subject: |
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cool
thanks
Do we need twins?  |
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Sunbeam
Joined: 23 Feb 2012
Posts: 3990
City/Region: Out 'n' About
State or Province: Other
C-Dory Year: 2002
C-Dory Model: 22 Cruiser
Photos: Sunbeam
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| Posted: Thu May 15, 2014 1:33 pm Post subject: |
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| BrentB wrote: | | Having a better part is ok but proper installation is important too.. It seems to me that one limitation is the hull thickness in area. Is it re inforced with fiberglass mat or just buildup of extra epoxy ? With a strong pull, the eye could pull out like a tooth. |
I will definitely be reinforcing the bow in this area. In fact, this is one (more) reason for a new bow eye - longer legs to be able to go through some backing. Not sure exactly how I'm going to do it yet, but there are numerous ways that can work well, and I will figure that out once I'm "in there."
At one time I was involved in a project to install a bow towing/anchor eye on a largish power boat (ironic, given this thread  ). It was interesting following the loads along (because as you say, it's no good anchoring a strong piece to a weak substructure) and visualizing how to make it happen. A naval architect/engineer was involved, but we also had to figure out how this could work in the real world (installation access and procedure, etc.). In the end it turned out to be a combination of a tang (picture a chainplate, only parallel to the long axis of the boat), which carried most of the load to a reinforced bulkhead, and a plate much like shown above only larger (for looks, to have something to bed, and to carry some of the load to the skin).
Of course our small boats have smaller forces, but still everything has to "match up."
Back to the backing: I'll have to see how it looks once I'm in there again, but I'll probably do some combination of a few layers of biaxial cloth in the area, plus a fitted/epoxied backing block. Included will be making a flat/parallel surface on the after side for the washers/nuts to land on. |
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BrentB
Joined: 15 Jul 2006
Posts: 4419
City/Region: Greenwood
State or Province: IN
Photos: BrentB
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| Posted: Thu May 15, 2014 11:19 pm Post subject: |
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thanks
very informative |
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