Join the C34 Association Today!
[C34 Home] [C34Tech Notes] [C34 Tech Wiki] [Join!]
Please login or register.
Advanced search  

News:

Pages: [1]   Go Down

Author Topic: New Radar bracket - will it compromise the strength of the mast?  (Read 2397 times)

0 Members and 1 Guest are viewing this topic.

KeelsonGraham

  • Forum - Seaman
  • **
  • Karma: 0
  • Posts: 44
    • View Profile

Hi all,

Iím upgrading my radar from an 18Ē Furuno to an 18Ē Raymarine Quantum. My fitting guy has a spare Raymarine mast mount and proposes taking the old Furuno one off and attaching the Raymarine one.

Iím concerned that another entire set of holes in about the same place on the mast is going to make it look like a gruyere cheese and compromise the structural strength of the mast.

Am I worrying unnecessarily?

Graham
Logged
2006 Catalina 34 Mk II. Hull No:1752

Ron Hill

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 61
  • Posts: 7755
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #1 on: August 19, 2021, 02:58:06 PM »

Grahm : How far out are the holes between the two different brackets??  Also how big are these hole??

A thought

Logged
Ron, Apache #788

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 35
  • Posts: 4229
  • "Positive Impact" 1984 C-30 mk-I #3573 trbsfk M-25
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #2 on: August 19, 2021, 11:54:35 PM »

Any how many fasteners in each bracket? The spacing of each bracket?

Consider this -- unless holes are WAY TOO CRAZY in size, or number, or spacing -- replacing a hole with a tightened fastener pretty much replaces the compression strength of the metal that is lost due to the hole.  Not 100%, but it's not like you have drilled a ton of holes and let it as swiss cheese. 
Doing that doesn't do anything if the section is in tension, but bolting on a bracket would increase the tension strength of the area.

Some details please?
Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

Bill Shreeves

  • Forum - Petty Officer 1st Class
  • *****
  • Karma: 4
  • Posts: 303
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #3 on: August 26, 2021, 07:39:24 PM »

just a thought, without the benefit of your spacing or sizes your dealing with, what about attaching the new bracket to adapter plate(s) then attach the plate(s) to the old mount points?
Logged
The only thing that always works on an old boat is the owner...

Bill Shreeves
s/v "Begnnings" 1987 Shoal Draft #333
M25XPB, Worton Creek, MD

waughoo

  • Forum - Petty Officer 1st Class
  • *****
  • Karma: 5
  • Posts: 486
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #4 on: August 26, 2021, 08:18:26 PM »

^----- This -----^

If you can stand the visual appearance of an adapter plate on your existing radar mast mount, it will solve any issues of too many holes in the mast.
Logged
Alex - Seattle, WA
91 mk1.5 #1120
Std rig w/wing keel
Belafonte

KeelsonGraham

  • Forum - Seaman
  • **
  • Karma: 0
  • Posts: 44
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #5 on: August 28, 2021, 03:29:25 AM »

The existing mount has 8 rivets attaching it. The new mount has 12. I think that making a bespoke adapter plate out of 1/4Ē aluminium would be a better solution. Iím not at all bothered by appearances but I really am wary of a total of 20 holes all drilled in the same area of the mast. Even if the 8 old holes are re-rivetted to fill them, it just doesnít feel like the right thing to do.
Logged
2006 Catalina 34 Mk II. Hull No:1752

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 35
  • Posts: 4229
  • "Positive Impact" 1984 C-30 mk-I #3573 trbsfk M-25
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #6 on: August 28, 2021, 11:03:32 AM »

The existing mount has 8 rivets attaching it. The new mount has 12. I think that making a bespoke adapter plate out of 1/4Ē aluminium would be a better solution. Iím not at all bothered by appearances but I really am wary of a total of 20 holes all drilled in the same area of the mast. Even if the 8 old holes are re-rivetted to fill them, it just doesnít feel like the right thing to do.

It appears youíve already decided and looking more for confirm, but without a picture or some template of the two or something of solid info (hole size and spacing), and where itís mounted, thereís not much solid structural recommendation can do.   If I had some solid info I could determine that, but alas!
Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

KeelsonGraham

  • Forum - Seaman
  • **
  • Karma: 0
  • Posts: 44
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #7 on: September 06, 2021, 04:58:22 AM »

Just to close this thread out. I spoke to our local very reputable mast and rigging experts. Their view was that itís generally not a good idea to drill more holes in the same place in the mast. It can be done, provided that the old holes are filled with rivets. But their recommendation is to machine up an adapter plate to fit to the existing support.
Logged
2006 Catalina 34 Mk II. Hull No:1752

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 35
  • Posts: 4229
  • "Positive Impact" 1984 C-30 mk-I #3573 trbsfk M-25
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #8 on: September 06, 2021, 10:51:42 AM »


Their view was that itís generally not a good idea to drill more holes in the same place in the mast.


Are they making the adapter bracket?

No doubt an adapter is the most conservative way and satisfies your peace of mind, but that wasnít the original question.  Thereís the most conservative and thereís perfectly acceptable and safe.  Facts and specifics are king when assessing any mod. ďit depends.Ē

Would the riggers say that drilling one more hole when you have only one hole, is unacceptable?  Are two more unacceptable when you have two?  Whereís their red line.

Ponder these:
- No doubt, if asked to install radar in the first place, they would absolutely refuse because ďgenerallyĒ itís better not to drill ANY holes in a mast or any spar. 
- Itís ďgenerallyĒ better to not add more weight aloft, but they recommend adding additional weight (an adapter)?
- No doubt, they would refuse to install spreader lights or a flag halyard block because itís ďgenerallyĒ better to leave structural members w/o additional hole. 
- Itís ďgenerallyĒ better to have floor joists intact with no holes, but if the engineers didnít already figure out where itís safe to drill them, and how large we wouldnít have electricity and plumbed water in our houses.

Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain

KeelsonGraham

  • Forum - Seaman
  • **
  • Karma: 0
  • Posts: 44
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #9 on: September 08, 2021, 06:16:42 AM »

Hi KW,

I consulted in person with AllSpars who are probably the most respected riggers in the UK. They didnít say you mustnít drill more holes in the mast. In fact they said that they have done this for many customers - always re-riveting the old holes. However, on balance they thought it better to machine up an aluminium adapter, anodise it and fit that instead.

They did offer to discuss it with the mast manufacturer but I generally feel happier with the adapter plate approach.

Iím more familiar with aircraft structures, where drilling large numbers of weight-saving holes in key structural members is the norm. But, unlike aircraft, these are small radius holes which must to some extent concentrate stresses. If we can avoid this why would we not?
« Last Edit: September 08, 2021, 06:21:18 AM by KeelsonGraham »
Logged
2006 Catalina 34 Mk II. Hull No:1752

KWKloeber

  • Forum - Master Chief Petty Officer of the Navy
  • ********
  • Karma: 35
  • Posts: 4229
  • "Positive Impact" 1984 C-30 mk-I #3573 trbsfk M-25
    • View Profile
Re: New Radar bracket - will it compromise the strength of the mast?
« Reply #10 on: September 08, 2021, 11:18:04 AM »


If we can avoid this why would we not?


Keelson, I agree; Why it it can be avoided?   

Oh, you meant, "Why drill holes," I thought you meant "Why add cost and additional weight aloft" if it can be avoided?  LOL

We all have to do what we feel comfortable with.  I overkill many things that are unnecssary; it's just the engineer in me -- but so is knowing when I overkill because I want to and when it's because it's marginal.

I understand that the cost of worth the peace of mind, but it's just coincidental? that they're also the ones who get the income for an adapter.

As to size, a truss (which is what an aircraft structure is) is made with as large holes as can be accommodated for reasons of economy -- it's infinitely more expensive and more manufacturing issues to anything with many small holes that one large hole.

Cheers,  post a pic of the install if you can.
Logged
Twenty years from now you'll be more disappointed by the things you didn't do, than by the ones you did.
So throw off the bowlines.  Sail away from the safe harbor.  Catch the tradewinds in your sails.
Explore.  Dream.  Discover.   -Mark Twain
Pages: [1]   Go Up