42: Lagoon 42 loses mast

[tuskie]

Originally Posted by Lagoon42

En français car je ne connais pas le mot anglais je parlerais de "mise en résonance"

My poor french translation is "resonance / vibration due to useage". C'est tout?

[Lagoon42]

Cela peut-être une cause en plus

[Pete7]

Folks, the forum language is English.

Regards

Peter

Moderator

[Moontide]

Re-tensioning the shrouds is always easier when sailing instead of at the dock. Just sail hard on the wind or close reach and tack slack out of leeward shrouds. Tack and repeat the process. Less load on the turnbuckle threads and worker. Much easier than trying to do while at the dock.

Bill

[belizesailor]

Originally Posted by Moontide

Re-tensioning the shrouds is always easier when sailing instead of at the dock. Just sail hard on the wind or close reach and tack slack out of leeward shrouds. Tack and repeat the process. Less load on the turnbuckle threads and worker. Much easier than trying to do while at the dock.

Bill

Most pro riggers do a static (at dock) tune and then a dynamic (under sail) tune.

[jugga]

Originally Posted by Lagoon42

It is a reply comment by à sailor in a other forum:

No one injured... Great news !
However, I've noticed the rigging is getting loose with sea condition over 2/3 meters high due to high excessive shaking of the rigging under load on the new models 39, 42, 52s I have been sailing recently. (shroud and stays must be monitor from close after each day).

Interesting ... all 3 these models (39, 42 and 52) have a mast that is positioned more aft than other Lagoon models

[tuskie]

Originally Posted by Lagoon42

Cela peut-être une cause en plus

"This may be a cause in addition"

Sorry Pete, thanks for doing your job. I won't keep up the crap translations, but many are very keen to know the reason for Lagoon42's dismasting.

So, it looks like the rig wasn't tensioned as part of the commissioning process. It seems that turnbuckles may not have been locked as vibration or "resonance" may have made the rig more loose "in addition".

[Factor]

Given the amount of lagoons launched and the relative rarity of issues like this - it certainly doesnt sound like a design or build issue rather a reminder to keep an eye on rig tune, on any boat

[arsenelupiga]

avoiding resonance / shaking seem to be best way by reef or slow down.

resonance can bring down bridges, buildings so it is extremely powerful force that no material can withstand forever.

learned something new here : new criteria when to reef.

[PaulinOz]

Originally Posted by Factor

Given the amount of lagoons launched and the relative rarity of issues like this - it certainly doesnt sound like a design or build issue rather a reminder to keep an eye on rig tune, on any boat

Well said, I believe that is twice in a year I have agreed with you, but I may just be getting old and forgetful.

[CatNewBee]

The 42 is a new construction, they moved the mast aft and the compression pole is located at the entrance of the salon.

It could be, that the deck at this point is dynamically not that stiff / rigid than the construction of the good old lagoons, the deck and the roof are not very strongly interconnected because of the large opening between cockpit and salon. The structure on the old design was stiffer, having the glass front as enforcement for the structure / support for the mast and the compression pole. The aft position can cause dynamic deformations between top and lower deck being interconnected only by the compression pole and 2.5 meter side-wise by the salon walls. Also the main sheet traveler at the aft of the upper deck adds some dynamic load and is transferred through the poles to the structure of the hulls. If the rig is not under tension and the mast base is not high enough, it could lead to this incident.

I am curious, if other new lagoons have the same issue, they all have this "new" design, where the mast was moved aft and is standing alone on the compression post in the mid of the salon/cockpit on the weakest point of the deck structure with long levers in all directions.

[arsenelupiga]

I think there is destructive force of structure resonance possible. Like bridge that collapsed due to wind only in US. Resonance produces extreme short term loads that can cause structural damage.

I doubt rigger tensioning rig can adjust properly to avoid resonance issues with single test sail.

Owner should really adjust rig tension if noticing resonance. Alternative is that boat works itself out to let it go in some place so that resonance disappears by itself (if lucky without damage) . Noticing resonance during sail is critical issue to get rid of it asap, before damage occurs.

Wonder how many masts was lost due to resonance. Would imagine monohull going windward can produce some serious resonance as well - mast/keel shaking.

there is more to the boat/rig than I thought up until recently.

[donradcliffe]

Originally Posted by Factor

Given the amount of lagoons launched and the relative rarity of issues like this - it certainly doesnt sound like a design or build issue rather a reminder to keep an eye on rig tune, on any boat

Given that the L42 is a different design than most previous Lagoons, the jury is still out. The problem could be (1) poor rig tension, (2) a mast step lower than previous versions, (3), the new configuration with the mast and shrouds further aft and a free standing compression post, or (4) a combination of all three.

If I was a L42 owner, I'd immediately check rig tension, and work on a redesigned mast step which captures more of the mast.

The owner says the mast jumped out of the step, but I'm mystified as to how it could disappear into the ocean without putting large divots in the fiberglass around the step. It appears that there are turning blocks on deck for the halyards and mainsheet, which would not only put hundreds of pounds of downforce on the base, but would also limit how far the base could travel if it did jump the step.

Comparing the L42 to the L400, I note that the shrouds are attached much further back on the hulls. If the structure of the boat starts to twist in larger seas I can see that the L42 would be more prone to having the shrouds go slack than the L400, and perhaps create the observed 'resonances'.

[CatNewBee]

The longer the lever, the lower the resonance frequency and the higher the amplitude of the waves.

[Catapault]

Originally Posted by SV DestinyAscen

Video makes it clear owner has a habit of flying the parasailor only without the main - someone can correct me but I recall certain cat manufacturers precisely recommending against such practices because of a lack of backstays. I'd bet a drink the mainsail was down, mainsheet and topping lift loose.

Rig might have just been a little loose without being retensioned after expected stretch - voila rig gets lifted forward and comes down.

Prob a good thing the mast isn't pinned - pins won't save the rig from coming down and will definitely breach the hull and give you problems in rough seas.

I would imagine, when flying a kite with no main up, you keep tension on rig by Tightening up on Topping Lift + Main sheet, effectively acting as a backstay ?