Cracked Forestay Chainplate


Ellen Cahill
 

We recently cross the Atlantic in Saol Nua, a 1986 Mango. Just before sitting down to breakfast to mark our halfway point we spotted a very significant break in our forestay chainplate. With 1200nm to go I was extremely anxious but also very grateful we spotted it before the mast came down. We decided to furl in the Genoa for the remainder of the journey and using two spare bottle screws secured the forestay to the two bow cleats. We also attached the inner forestay.  We checked the condition of the plate every 2 hours for the remainder of the journey. 

On the mango the chainplate is an upsidedown 'Y'. One half had severed completely and a crack had initiated in the other. I inspected the rigging before we departed but I suspect evidence of a crack may have been on the inside of the plate. We had 20knots on the aft quarter and fairly calm seas so it pointed to an issue existing prior to our departure.

Thankfully we made it will the rig intact and have since replaced the chainplate. I climb the mast and carefully check the rig before any passage over 24hours but now, with the boat that bit older I'll be keeping an eye on the chainplates! 

Any else ever seen this happen?

Ellen Cahill,
SV Saol Nua
Mango #45


Karen Smith
 

Ellen,

This kind of failure is not unusual with stainless steel, and can be seen on many stainless parts in saltwater service, especially those under cyclical loads just like your headstay chainplate.

We had this happen with one of our jib cars, and if I zoom in close on your photo, I am pretty sure the same scenario presents itself.  https://fetchinketch.net/2019/07/26/failure-analysis/

The other place I have seen this happen on our boat is in the shackles on the boom outhaul cars. The usual assumption is they break because of overloading, when they actually have been greatly weakened by nearly invisible crevice corrosion before the failure.

The shape of this piece and its location on your boat means that it is very hard to actually give it a really effective visual inspection, even if it was removed from the boat and in hand.

The best way to prevent it is to be sure than any welding is first class, by somebody who really knows stainless steel, and it is fully electropolished afterwards so there are no pits or cracks for corrosion to get started.  Then careful inspection on a regular basis with a magnifier looking for incipient cracks.

Bill Kinney
SM160, Harmonie
Charleston, SC, USA


Mark McGovern
 

For what it's worth, it looks like Amel changed the forestay chainplate design for the Super Maramu.  Our forestay chainplate is one solid piece of stainless steel:



--
Mark McGovern
SM #440 Cara
Deale, MD USA


Matt Salatino
 

It’s likely that the “Y” had to be welded.
It’s very difficult to maintain the metallurgy of stainless, the proper mix of chromium, nickel, etc, through the welding process. Putting that welded chainplate on the bow, constantly washed by salt water, is asking for trouble. No wonder they changed the design. Good move.

~~~⛵️~~~Matt Salatino A50 #27

On Feb 1, 2021, at 5:21 PM, Mark McGovern <mfmcgovern@...> wrote:

For what it's worth, it looks like Amel changed the forestay chainplate design for the Super Maramu.  Our forestay chainplate is one solid piece of stainless steel:

<IMG_20201213_170323993.jpg>

--
Mark McGovern
SM #440 Cara
Deale, MD USA


Ellen Cahill
 

Thank you very much for the detailed explanation. The fracture was not in fact on a weld but rather on a bend. Even if it was bent under proper heat tratments I suspect that it still caused stress concentrators to occur in this area. The fracture surface looks very similar indeed to yours Bill, mostly dull and grainy with signs of slow crack propagation. 

So careful inspection and regular washing seems to be the best preventative solution before replacing parts.