Preventers

[Sea Change]

The worst shock load of all would be a slack or stretchy preventer allowing the boom to swing so far that the preventer itself slammed against the shrouds.

 

[Dockhead]

The worst shock load of all would be a slack or stretchy preventer allowing the boom to swing so far that the preventer itself slammed against the shrouds.

That's exactly what John says in his article, and I think you and he are right.

 

[Roberto]

If you are attaching your preventer to the place where the main sheet attaches, then, even if it's a bit forward, presumably the boom is engineered to take the loads there.

i guess what i don't know is whether you have drawn the whole boom in your figure, or whether you have drawn just to where the main sheet attaches. I know you have said the boat has a short boom, but is it end-boom sheeting?

modern boats often have end-boom sheeting, and the boom is not really designed to take a bending moment forward.

But there is also another potential problem; the loads on the preventer itself

the further forward one attaches the preventer, the greater the potential loads.., irrespective of where the main sheet attaches.

so the next question is: is your preventer and all its attachments strong enough to take the load generated by that geometry? Your main sheet might be 4:1, or 8:1, is built with strong fittings, and is designed to handle the load..., whereas the preventer is probably a single line..., what are the fittings?

as shown above, the further out on the boom you can get the preventer attached, the lower the loads on that system, and the difference can be dramatic.

The boat had several version and the sheet arrangement came in various types: end of boom tackle, two/third boom tackle (two multi sheaves blocks or various single sheave blocks spaced apart - which I have), even single sheet German, the boom can basically resist everything; the mainsail is relatively small by modern standards.
This is the boom strap I made for the preventer (should probably be enough to lift the boat ), all the other components are roughly sized accordingly.


I also replaced all the mainsheet block attachment padeyes formerly located along the lower side of the boom with straps, when sailing downwind the blocks are free to turn around the boom so it removes a lot of the torque on the gooseneck; with all this talk of extraordinary loads, these attachments (for preventer, sheet blocks, etc) on the underside of the boom are a punch in the eye in engineering terms

 

[Snowgoose-1]

The boat had several version and the sheet arrangement came in various types: end of boom tackle, two/third boom tackle (two multi sheaves blocks or various single sheave blocks spaced apart - which I have), even single sheet German, the boom can basically resist everything; the mainsail is relatively small by modern standards.
This is the boom strap I made for the preventer (should probably be enough to lift the boat ), all the other components are roughly sized accordingly.

View attachment 192580
I also replaced all the mainsheet block attachment padeyes formerly located along the lower side of the boom with straps, when sailing downwind the blocks are free to turn around the boom so it removes a lot of the torque on the gooseneck; with all this talk of extraordinary loads, these attachments (for preventer, sheet blocks, etc) on the underside of the boom are a punch in the eye in engineering terms
View attachment 192588

View attachment 192589

Interesting thread.
I'm currently looking to install a permently rigged boom brake.

 

[Laser310]

I think there is a strong argument to be made for larger cruising boats to have mid-boom sheeting to a hard dodger, or companionway arch.

on even a 45ft boat, that mainsheet can kill someone, and by 50 or 55 it's a real danger.

i'm mostly a racing sailor, but even I think that for a cruising boat, the loss of performance is minor compared with the safety gain.

The other thing I see a lot now- even on supposedly "good" cruising boats like X-Yachts and now Arcona, is putting the primary and mainsheet winches on a pod right in front of the hem, at the aft end of the cockpit bench - it looks great.., the buttons are right at hand...

I did a lot of sailing on an XP-55 that has this setup.

but this is right where the mainsheet lies, and it's actually sometimes difficult to even operate the winches on the leeward side with the mainsheet there. And you definitely want to be operating the winches on the old leeward side in a gybe on these boats because the mainsheet is going to come right across the winches on the other side in the gybe.., and what if it ends up not being as controlled as it should have been?

Anyone near those winches in an accidental gybe is facing serious injury on a 55ft boat.

Maybe there is no place in the cockpit of a 55ft boat that is 100% safe, but putting all the winches in an obviously unsafe place is a really poor design choice.

 

[Laser310]

I don't have a good photo from the XP-55 I have been sailing on, without a lot of the crew, so I found a pic online that kind of shows what I am talking about above.

This is an XP-55, and it looks like the new Arcona 50 might have a similar setup.

the mainsheet is not rigged, but it attaches to the deck at the little thing in front of the cover for the emergency tiller.

note how when running, the main sheet is going to lie across the leeward winches and the bank of clutches, making this a very dangerous place to hang out. If you are on the windward winches trying to do something- the most comfortable side to be on, and the side without the mainsheet in the way - you are in the death zone for an accidental gybe...

 

[Fr J Hackett]

Garcia 52 Exploration, Boreals are similar.

 

[Dockhead]

I don't have a good photo from the XP-55 I have been sailing on, without a lot of the crew, so I found a pic online that kind of shows what I am talking about above.

This is an XP-55, and it looks like the new Arcona 50 might have a similar setup.

the mainsheet is not rigged, but it attaches to the deck at the little thing in front of the cover for the emergency tiller.

note how when running, the main sheet is going to lie across the leeward winches and the bank of clutches, making this a very dangerous place to hang out. If you are on the windward winches trying to do something- the most comfortable side to be on, and the side without the mainsheet in the way - you are in the death zone for an accidental gybe...

That's a strong argument for a centre cockpit with boom-end sheeting, taken to a traveler aft of the cockpit.

 

[Laser310]

That's a strong argument for a centre cockpit with boom-end sheeting, taken to a traveler aft of the cockpit.

i am personally not a huge fan of the centre cockpit until the boast get large - i've sailed on a few Oysters.

the cockpit is too high for me

the centre cockpit was okay on the Oyster 625, but below that length it just feels wrong.

The Swan 54, which I have sailed on quite a bit, has an aft cockpit but with companionway sheeting for the mainsail. I think it's an excellent cruising boat; if you can afford it...

some of those 54's also have the ability to sheet to a traveler, if racing - you can switch back and forth.

but the companionway sheeting is much safer for cruising on a boat that size.

 

[Laser310]

A stock photo of the Swan 54 - but it happens to be the one I have sailed on

The sheet is actually well forward of the cockpit - you definitely loose a few degrees of point, but it is a safe setup

 

[Metalicmike]

Not sure I understand that statement - the injuries and fatalities generally occur AS the boom crosses the cockpit, not “after” as you suggest. Hence why most of us keep the preventer tight and rigged to the bow to prevent the boom sweeping the cockpit.

And separately you said that stopping the boom slatting is not necessary for you as “then you hoist the spinnaker and sheet in the mainsheet”, which again I struggle to understand.
Unless sailingna fast multihull or planning / foiling race boat, most cruisers tend to go best quite deep downwind, and don’t bring the apparent wind forward of the beam like very fast racers with asymmetrics. Therefore not clear why you would sheet in the mainsheet when setting a spinnaker?

Just preference, sailing single handed is about keeping things simple.

 

[Fr J Hackett]

Just preference, sailing single handed is about keeping things simple.

Yes it's about keeping things safe, under control and as simple as possible to cope with the aforementioned. Simple is not always the best option and often leads to unfortunate consequences typically being responsible for many industrial "accidents"

 

[Metalicmike]

I gave up motorcycling when I moved to Tenerife and often think about buying another. I know my limitations and how to keep myself safe, if I was at all reckless I would still be driving a motorcycle and sailing.

 

[Dockhead]

A stock photo of the Swan 54 - but it happens to be the one I have sailed on

The sheet is actually well forward of the cockpit - you definitely loose a few degrees of point, but it is a safe setup

That's a German mainsheet. I had that on a previous boat. The most polite thing I can say about it, is that it sucks!

A really powerful hydraulic vang will mitigate that suckiness somewhat, but only mitigate.

We had a normal rope vang, so the suckiness of that arrangement was unmitigated. Never again.

 

[Dockhead]

I gave up motorcycling when I moved to Tenerife and often think about buying another. I know my limitations and how to keep myself safe, if I was at all reckless I would still be driving a motorcycle and sailing.

SafeER, not safe. I miss bikes, but they are unreasonably dangerous. I have enough scars, and will not go back to them, however much I would love to.