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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 01-04-2012
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Mast Wire Race Access

I´m in the process of rewiring my mast and wondering how to improve access to the race. Right now, the VHF, running/steaming/spreader lights, radar cables, etc. all go through a separate hole in the fron of the mast just below deck level. If I turned this into one larger hole tofacilitate wiring and to reduce chafe caused by the 90 deg. bends would I compromise the integrity of the mast?

All these wires enter just below deck level where it acts as a pivot point. it is a Hood mast and about 1/4¨thick there. I will try to get some photos of thhe area for better explanation. Till then any advice is welcome. T

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Old 01-04-2012
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Photos take away the guess work!
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Old 01-04-2012
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I also have a Hood mast of similar size (a bit smaller I guess). Interesting that my mast wires come out just a few inches above the end of the mast under the cabin sole level. This keeps them out of the way at least, if not easily accessible. I wonder if it was a choice by the boat manufacturer to do it one way or another?

As for your question, I would imagine it depends on how large a hole you are thinking about. All my wires come out of one hole that it about 1.5" in diameter. Gives no accessibility to the inside of the mast at all. I am taking my mast down in a couple of months to replace all of the wiring and to add extra attachments to the conduit since a couple of the pop rivets have come loose. I will have to consider the hole question, but I don't imagine I will change it. BTW, the Hood masts are great, heavily-built pieces of kit - I imagine could take a lot of abuse with hole drilling.
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can I safely combine all holes into one without compromising the mast????
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Old 01-04-2012
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I would say YES! Make a narrow oval using the top and bottom holes for it's ends. Or two larger holes, one covering the two bottom and the three top holes.
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Last edited by DelmarRey; 01-04-2012 at 06:02 PM.
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Old 01-04-2012
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I would think that the smaller holes have less effect on the mast than a bigger single. Do the wires run thru a grommet of some kind ?(chafe and hard bends)??
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Old 01-04-2012
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I would talk to a spar specialist. The many small holes you have reduce stress concentrations much better than one or two large holes. If you make one or two large holes you may start to get cracks raidating out from the hole. Think of stress like flowing water in a stream. The water can flow around many small obstructions easier than flowing around one or tow large obstructions. This is what leads to stress concentrations and then cracking.

BTW, once the wires go into the mast, are they just loose or do they run into a conduit? Mine are loose and I need to do somthing about this- don't like them ratteling around in the mast.
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Old 01-04-2012
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The strength of round holes are amazingly strong. As long as the holes have a smooth radius w/polished off edges it should be fine. Cracks start in sharp corners and existing cracks. Fallen Arches: The Surprising Strength of Eggshells


.
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Mast Wire Race Access-matlsci_img053.jpg  
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Last edited by DelmarRey; 01-04-2012 at 06:49 PM.
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Old 01-04-2012
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Quote:
Originally Posted by DelmarRey View Post
The strength of round holes are amazingly strong. As long as the holes have a smooth radius w/polished off edges it should be fine. Cracks start in sharp corners and existing cracks. Fallen Arches: The Surprising Strength of Eggshells


.
Cracks can occur even on smooth surfaces:
Fracture mechanics - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Fatigue_(material)
Among other things (like fatigue) it comes down to how much stress is on the part. Even with smooth radius and polished edges if a part is over stressed or over fatigued, it will fail.

Last edited by casey1999; 01-04-2012 at 07:26 PM.
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Hell, I've got 6 halyard exit holes in my mast, grouped together. Just one of which is probably as big as this wire mess. I wouldn't have second thoughts of doing the hole(s) especially where it's located and supported by the deck.

When an axial load is applied to a piece of material with a uniform cross-section, the normal stress will be uniformly distributed over the cross-section. However, if a hole is drilled in the material, the stress distribution will no longer be uniform. Since the material that has been removed from the hole is no longer available to carry any load, the load must be redistributed over the remaining material. It is not redistributed evenly over the entire remaining cross-sectional area but instead will be redistributed in an uneven pattern that is highest at the edges of the hole as shown in the image. This phenomenon is known as stress concentration.
As long as there is enough mass (mast) around the hole the weight can be transferred around. If there is a flaw in the hole, then stresses get transferred differently. You want a nice smooth transition, either round or oval.

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