Rope vang pulled itself out of the mast

[zachduckworth]

Hi all,
I have a 30 sailboat with a boomkicker and a rope vang. A few months back the vang yanked it’s two-bolt base on the mast free. I then attached it to the base of the boom kicker with a prussik loop make of dynema line. Yesterday it pulled the base of the boomkicker out of the mast. By “pulled out” I mean it stripped the bolts out. I am wondering why it is doing this, and what I’m doing wrong. Any advice appreciated.

[JPA Cate]

Any sign of bubbling on the mast around where the fittings popped off? If so, what probably happened is that the dissimilar metals corrosion spread and all holding them in was aluminum oxide; the threads disappeared.

If you go to repair the situation, you need to put something like inner tube rubber or a very thin bit of cutting plastic (like people chop veggies on) between the s/s and the aluminum. Also, the threads of the bolts or screws should have some form of anti-corrosion stuff on them (Duralac is one), and when you screw them in, it will transfer to both sides. You will probably need to tap in larger diameter holes.

Also, you might want to sister the aluminum for a little strength, and more thread depth...

Ann

[zachduckworth]

There is definitely corrosion, no tefgel used. I’ve been meaning to add some to all the SS fittings.
Bigger holes will def be needed. The force that pulled the vang out before actually bent the steel plate that it attached to slightly. I need to get that vang back on. Even with this I’m glad I don’t have a backstay…

[Bowdrie]

Yeah, because of the angularity, the fittings on both boom and mast can be under very severe loading at times.
If deck stepped, is there some way to take the vang to some fitting or arrangement that fastens to the step?

[wholybee]

Boom vangs have a very large load, and IMHO 2 bolts isn't enough. Even 4 would be minimal in my opinion. 6 or 8 is better. On a small 30 footer maybe 4 bolts are fine. But not 2.

That said, it seems common that people will just use a standard padeye, and then they get torn out like that.

[zachduckworth]

Can anyone recommend a part to reinforce the base of my mast so this doesn't happen again?

[Brioche]

If you are deck stepped then you can get a "mast plate" which is a flat plate under the mast with turned up sides with holes to attach blocks or shackles. Garhauer and others sell them. You could have one made pretty cheaply to fit your mast, also.