I spent a few hours on MB installing a overflow bottle for the coolant and greasing the sheet winches. A good day except I lost my glasses overboard in 6 metres. It had to happen eventually.
As I was rowing out I saw a new boat. Looks like a harbour boat, nothing onboard to suggest it is a passage maker. Sturdy things these vessels.
What is the consensus on the cause?

Quadrant Marine has the solution according to their website..

A badly rigged preventer possibly

Perhaps hoisting the topping lift, rather than the halyard?

The length of the boom from the mast to the break looks about the same as the distance to the side stays.

So I would say it's most likely from an uncontrolled gybe.

Not a great advert for Quadrant Marine!

Hard to tell from one picture.

It could well have just broken under vang load (ie not up to task). it looks like it probably snapped upwards from the way the alloy has beer canned horizontally at the bottom, maybe it hit a stay as Gravy said, then in its weakened state, snapped.

There's plenty of ways it might have happened though.

due to shaking a reefed main out with the topping lift and vang, still attached.
it snapped at the vang attachment point.

i learned the hard way.

must of been cranked pretty tight!

Looks like the boom was either made from two pieces, or repaired, with a a stiffener added below the joint. If the vang is strut type, then sheet load could have broken it.

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nosecabin said..

due to shaking a reefed main out with the topping lift and vang, still attached.
it snapped at the vang attachment point.

i learned the hard way.

Thats a bummer, looks repairable though.
A nice sporty looking carbon fiber splint would be just the shot

Its a pretty flimsy looking boom to start with, and look where the mainsheet attaches.
the aft half of the boom is unsupported, so it could have snapped trying to get leach tension with the rather powerful looking vang.

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stray said..
Its a pretty flimsy looking boom to start with, and look where the mainsheet attaches.
the aft half of the boom is unsupported, so it could have snapped trying to get leach tension with the rather powerful looking vang.

Yes, that mainsheet attachment system is strange, and your theory is logical. However the bulge at the bottom of the fracture point should have made it strong in tension. The clean break also points to a botched weld repair. This boat is a 2003 US production design so you would expect it to be well sorted.

I bought a new boom for my Martzcraft 35 2 years ago, it's nearly double the diameter of that one. Sailmalker estimated size to suit sails. So does look very light weight to me.

Is it really called "Upyers"? What a tacky name -a bit like calling a boat "F%#k You".

If someone is going to sail around on a boat that is abusing everyone else then it's hard to feel sympathy when they break something.

Proventer or stay the kink in the boom suggests a horazontal load.

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Chris 249 said..
Is it really called "Upyers"? What a tacky name -a bit like calling a boat "F%#k You".

If someone is going to sail around on a boat that is abusing everyone else then it's hard to feel sympathy when they break something.

His last boat must have been a power boat, they stick with the off names

Well, a gybe could do it, it does look a bit flimsy.
Pot calling kettle....