[C320-list] Moving Main Sheet position on boom

[Utility Email]

Brad,

Hopefully, this helps.  

I'd just flip it and drill one new hole if that it all you need to clear your dodger or whatever else you are trying to clear.  Drilling one new hole is better than two.  Also, one new hole with a flipped fitting will provide better edge margin (distance) between all of the drilled holes compared to drilling a pair of new holes.  Better edge margin means less weakening in the aluminum near the holes and less stress concentrations that can lead to fatigue cracking with high cycles of load.  

Considering that the holes for this fitting are on the underside of the boom (at the neutral axis for side loaded bending from the main), strength reduction of the boom from this new fitting placement seems like it would be minimal.

Don't forget to smooth sharp edges of the newly drilled hole and also use a some type of dielectric compound (Lanacote or Tuffgel) between the new stainless steel bolt and the aluminum mast to help present galvanic corrosion.

Have fun with this work.

Dave

Dave Swanson
S/V Emily Ann
2007 C320 MK II, No. 1107
Mukilteo, Washington

On Apr 1, 2012, at 8:14 AM, "Brad Kuether" <bkuether at comcast.net> wrote:

> We have bridged this topic before, but now I am actually going to pull the trigger on this....
> 
> I want to move the rear most main sheet attachment on the boom forward.  I have two options and want to hear any recommendations for or against them.
> 
> Option 1 - "Flip" the attachment point, so I only have to drill one new hole.  Essentially moving it forward the entire length of the attachment.
> 
> Option 2 - Move it forward by half the length, drilling two new holes, which will surround the forward hole and cover it up when I am done.
> 
> I don't have an engineering degree.  Is option 2 "dangerous" because now I have 4 holes in the boom fairly close together?
> 
> Thoughts?
> 
> Thanks so much in advance!!!!
> 
> -Brad, Mary, Monica, and Jarod
> "Independence"
> 2004 Catalina 320 Hull 1006
> Middle River, MD