Preventer trouble

[Quoddy]

I have questions about how the preventer acts. It’s being used on a broad reach.
1 What happens when you broach?
2 What happens if you get by the lee in a gust? Can you simply steer out of it, back to your original course?
3 What happens if you can’t and you broach by the lee?

 

[sailingdog]

In most of those cases, a preventer will cause your boat to get knocked down and keep it pinned down until it is released, since the sail can't cross over properly. This is the reason I highly recommend using a boombrake rather than a preventer. With a boombrake, the sail and boom will move over, but will do so at a slow enough speed to not be really a danger.

 

[Don12364]

Years ago I sailed under a skipper who owned a 34' yacht. He always used a preventer when running but was also very aware that yachts have been lost when pinned down by the mainsail and then flooded.
He used to buy metal turning blocks from Woolworths. These were made for garden clothes lines and were Mazak alloy. Mazak is a weak zinc aluminium alloy and old Frank had load tested them to make sure they would break when subjected to the loads which would pin the yacht down. He bought them in batches and tested one or two and filed groves to make sure they broke at the required load.
How cool is that.

BTW:- In his day job he was the chief surveyor for the British Admiralty.

And you can't steer out of a broach if your rudder is in the air!

 

[zeehag]

i like to use a line to tie boom over when i am not using sail---keeps the noise and needless movement to a minimum..lol....i donot use a true preventer, as it were---line is easily cut with riggers knife and keeps things out of the way and from breaking instead of flopping and banging.

i consider a yacht a boat which can and does have a place to land and store a helicopter....lol--34 ft doesnt quite make it! even my formosa 41 isnt a yacht!! is a sailboat or a ketch......

 

[rardiH36]

I really haven't used it as such considering the relative short distances on any course within the confines of San Francisco Bay, but I configured my boom vang to detach from the mast base bail to move to the toe rail for the purpose of a preventer. I don't have a stopper knot at the bitter end of the boom vang line, so releasing the boom vang clutch (mounted on the cabin top within reach from the cockpit) would free the boom/sail. Someday I'll probably venture out for longer trips and will be tempted to use the boom vang as a preventer. Is this a workable solution .... or am I eventually asking for trouble?

 

[sailingdog]

I'm not a big fan of using predicted failure for safety gear. If you were aboard his boat and in line with that preventer line and got hit by the block when the line let go, you'd likely be dead or headed for the hospital. Hoping something will break at the right moment in time is rather foolish and stupid IMHO.

Years ago I sailed under a skipper who owned a 34' yacht. He always used a preventer when running but was also very aware that yachts have been lost when pinned down by the mainsail and then flooded.
He used to buy metal turning blocks from Woolworths. These were made for garden clothes lines and were Mazak alloy. Mazak is a weak zinc aluminium alloy and old Frank had load tested them to make sure they would break when subjected to the loads which would pin the yacht down. He bought them in batches and tested one or two and filed groves to make sure they broke at the required load.
How cool is that.

BTW:- In his day job he was the chief surveyor for the British Admiralty.

And you can't steer out of a broach if your rudder is in the air!

 

[SamLust]

Hey sailing Dog. Don't ever go into a building. The fire sprinkler system is based on controlled breakage. Wouldn't want to rely on that, would we.? Oh, also, don't have a boiler of any sort in your house. The safety valve on that works on similar ideas also. Wouldn't want to leave anything like safety to a silly spring. How about your inflatable life jacket? Wouldn't want to rely on that pesky trigger mechanism, would we. "Honey, where's my Mae West?"

I would point out that what has been discribed here is an absolute end-game safety release. Not a system that is expected to provide release every time things get a little hairy. Any preventer can be released as required. If it can't, it's a noose.

 

[sailingdog]

I am perfectly aware that the sprinkler system is designed around a component that is designed to melt at a specific temperature, and that the salt tablet in the PFD is designed to dissolve when submersed...but these are not controlled breakage IMHO.

Relying on a block to break under load is asking for trouble due the the amount of kinetic energy the line can store up while the block reaches that point. Also, there are quite a few more variables in whether the block will break that make it far less predictable than the metal valve closure on a fire sprinkler or the salt tablet in a PFD inflation mechanism. Just a few would include depth of the cuts he adds, the quality of the alloy, whether the part was defective or not, how much corrosion the part had undergone, whether the load is applied gradually or suddenly, etc... That puts anyone in the vicinity of the block in danger.

If you've never seen a loaded line snap—you have no clue what you're talking about. Yes, it's an end-game safety release... but there are better alternatives to doing something that dangerous. Having a block that can shoot across the boat deck at high speeds unpredictably when it is completely avoidable is stupid.

Hey sailing Dog. Don't ever go into a building. The fire sprinkler system is based on controlled breakage. Wouldn't want to rely on that, would we.? Oh, also, don't have a boiler of any sort in your house. The safety valve on that works on similar ideas also. Wouldn't want to leave anything like safety to a silly spring. How about your inflatable life jacket? Wouldn't want to rely on that pesky trigger mechanism, would we. "Honey, where's my Mae West?"

I would point out that what has been discribed here is an absolute end-game safety release. Not a system that is expected to provide release every time things get a little hairy. Any preventer can be released as required. If it can't, it's a noose.

 

[peptobysmol]

i like to use a line to tie boom over when i am not using sail---keeps the noise and needless movement to a minimum..lol....i donot use a true preventer, as it were---line is easily cut with riggers knife and keeps things out of the way and from breaking instead of flopping and banging.

i consider a yacht a boat which can and does have a place to land and store a helicopter....lol--34 ft doesnt quite make it! even my formosa 41 isnt a yacht!! is a sailboat or a ketch......

And while SD is at it. I'll take issue with the use of the term "yacht" I have friends who know nothing about sailing but call my "boat" a yacht. Of course, in Oklahoma if its bigger than a jon boat it might qualify as a yacht. Imho, you can call it what you want. I prefer to call it a sailboat however. Calling it a yacht does seem a little high falutin to me. Sooo... I guess I agree with you but not in principle?

 

[woodster]

Calling it a yacht does seem a little high falutin to me. Sooo... I guess I agree with you but not in principle?

so do you know where the word high falutin comes from......its a term used by the old river boat passenegrs back in the days of wood fired boilers.....seems the smoke stacks were stright and the ash would come out and hit all the passangers and burn them ....then they figured out that by cutting fluts in the stacks that the embers would fly out and away from the upper decks and not burn the passengers on the upper decks....whitch by the way.....was also the first class part of a river boat back in thoses days ...so when the second class passengers were on board they called the upper deck the place where the high falutin passengers were.....

regards

woody

 

[Rick D]

Preventer

I use a preventer on longer races and downwind cruises. It is a Garhauer vang rig with lots of 5/16 line which reaches back to the cockpit for a quick cam release. I also use a rubber dock line snubber at the foot of the tackle (between the bottom shackle and the bottom block) so that there is give before any shock loading. Has worked well for me.

PS: having been on two boats which exploded a block, I am aware that it can be a missile. Not sure if I'd have the same concern in this case, but it sure is something to consider. BTW, in both cases, they were uncontrolled (and unplanned) jibes. Also a good reminder that inexperienced or AADD helmsmen can be dangerous downwind.

 

[shemandr]

In a jibe a friend was hit in the head by the GPS mushroom antenna which was picked up by the mainsheet and flung at him at the helm. He immediately collapsed at the wheel. A happy ending - he was not seriously hurt. He did have a big knot on his noggin', he was in extreme pain for for a few minutes and everyone on the boat was immediately launched into a frightful emergency mode. I wouldn't use a block as a weak link.
The last boat I was on that rigged a preventer bent the boom. It wasn't a gentle curve. I would never say never but I don't like them.

 

[Joe]

You don't necessarily need a block and tackle rig for a preventer. You're just trying to stabilize the boom, not cinch it down, and being able to release it quickly is vital. Any way........IMHO the safest and most convenient boom preventer system is to run a line(nylon would be preferred) forward from the boom end to a turning block on the foredeck then back to a cockpit cleat. (Actually, two lines, one for each side.) You could use the fitting for the spinnaker pole's foreguy to attach the block, for instance, attach singles to the toe rail.

When you jibe, simply uncleat the preventer on one side and adjust the other when the boom is in it's new position, all without leaving the safety of the cockpit. You can leave both lines attached all the time, or disconnect from the boom when not in use if you like.

Here's an example of a long line knotted in the middle and clipped to a simple rope bridle. Each end runs forward to a turning block then back to cockpit. No blocks on the boom, no going forward to disengage; simple, safe and effective.

 

[Don12364]

If you were aboard his boat and in line with that preventer line and got hit by the block when the line let go, you'd likely be dead or headed for the hospital. Hoping something will break at the right moment in time is rather foolish and stupid IMHO.

Before your remarks could be considered valid you really ought to know the size and location of the block and the way in which it was deliberately weakened to ensure failure under the loads he tested it under. Then again the way it was rigged and what would happen when it failed is relevant too.
Clearly the boom snapping over was a serious health hazard, but rather that than loosing the yacht.

Also please understand your opinion is being weighed against the Chief Surveyor for the British Navy, albeit of some 40 years ago.

The block was about 1" long in total and, as previously stated made of an aluminium alloy with a sheave diameter of little more than 1/2".
From memory the preventer line came from the bow, through the weakened block at the boom end, along the boom, through a second conventional block on deck at the foot of the mast and thence back to the cockpit. Should the block fail the sheave would have been thrown forward.

And then again, cotton or hemp ropes did not contain the same strain energy that today's synthetics do. We realised that it was better to have the block fail than to have the preventer break and face its unknown whiplash effect.
And Frank was a Scotsman and didn't want to pay for a new length of rope when a shilling Woolworths block would do!

One notes in passing that it is quite normal for engineers to design links which are designed to break and shear pins are used universally and even in outboard motor transmissions. Quill shafts are routinely specified in aircraft gas turbine engines with necks specifically designed to fail at a predetermined torque should an accessory seize.
They have even been used on catamaran rigs to cause the rig to fall down and save lives rather than have the vessel turn upside down.
Unfortunately my friend's 30' cruising cat was not so equipped and his wife drowned when it capsized in the Solent. The mainsheet jammed on the winch and the cat capsized before anyone could get to it with a knife. A version of old Frank's weakened block on the mainsheet or shearpins on the shrouds could have saved her.
I was racing the yacht with the preventer at the time, also in the Solent.

 

[Mac Daddy]

Nice setup Joe. May have steal that idea.

 

[Quoddy]

Brake and Preventer

Thanks for the ideas. I think I will lead the preventer lines back to the cockpit and run them through a boom brake on the boom. This way when they are released the boom swings freely. When they are set the brake becomes the weak link that will allow the boom to move slowly under high pressure.