Returning Rigging Tension Forces To The Mast

[ducked]

About 7 mins in. I can't remember hearing about (or thinking of) that trick, but it seems to make sense (to me, but I no expert).. There will still be an inward compression force on the hull, and some upward tension, but that might be preferable to all upward tension

OF course a bit of an obstruction, even more so if one ran individual shroud returns to the mast base, but a Folkboat doesn't offer wide-open spaces anyway.

Probably not any actual use to me since the Trident is coachroof stepped without a compression strut, but still quite an interesting idea.

 

[William_H]

I think you need to consider a slice through view of your hull with cabin on top, mast pressing down and shrouds resisting mast sideways force.
Your boat must have stout cabin top or cross member under the mast supported by struts at the sides. The compression loads from a mast are very big. If you are concerned fit a steel rule or similar so you can measure actual compression collapse between the floor and cabin roof. When under sail pressure.
Yes the loads of the shrouds via chain plate need to be transmitted down to the keel or ballast to complete the load path. There is some force trying to pull chain plates together towards mast but generally the cabin and hull ring are easily capable of resisting this force. So basically don't worry.
My little boat 21ft was subject to a pull down test to confirm self righting (for racing rules compliance) The boat was tied fore and aft to jetties and then the mast was pulled via a halyard down until the mast was horizontal. A load cell was used to measure force needed to hold mast down. (around 30kg) Now thinking about it we have the ballasted keel and ballast (200kg) sticking out sideways. Being held up out of the water by the leverage of mast to compression post pulling on shroud. A mathematician could calculate forces. In reality no concern. Yours should be the same. ol'will

 

[ducked]

I think you need to consider a slice through view of your hull with cabin on top, mast pressing down and shrouds resisting mast sideways force.
Your boat must have stout cabin top or cross member under the mast supported by struts at the sides. The compression loads from a mast are very big. If you are concerned fit a steel rule or similar so you can measure actual compression collapse between the floor and cabin roof. When under sail pressure.
Yes the loads of the shrouds via chain plate need to be transmitted down to the keel or ballast to complete the load path. There is some force trying to pull chain plates together towards mast but generally the cabin and hull ring are easily capable of resisting this force. So basically don't worry.
My little boat 21ft was subject to a pull down test to confirm self righting (for racing rules compliance) The boat was tied fore and aft to jetties and then the mast was pulled via a halyard down until the mast was horizontal. A load cell was used to measure force needed to hold mast down. (around 30kg) Now thinking about it we have the ballasted keel and ballast (200kg) sticking out sideways. Being held up out of the water by the leverage of mast to compression post pulling on shroud. A mathematician could calculate forces. In reality no concern. Yours should be the same. ol'will

I'm not worried, at least not yet, since it'll be quite a while before my mast is standing up to anything other than its own windage, and if I get my finger out it wont be standing up at all over the winter.

I'll do your collapsing check when/if the time comes, though. How much movement would be expected?

I just thought this triangulation (?) of the rigging tension to the base of the mast was (a) logical, captain, and (b) novel. (at least it was to me. If its commonplace in salty circles, well, I dont really move in them currently.)

 

[justanothersailboat]

The force all has to join up to the keel however it's done. He's passing some of the force through that internal extension of the standing rig rather than through the hull or hull frame. I don't think this is very common, I have not seen it before. I think it's more normal for designers to put in enough bulkhead (or frame) size to make a strong ring of hull in line with the mast, meaning there's no need for anything else.

On that boat, where there is no bulkhead near the mast, it just might be worth it to stop the shroud tension from trying to deform the hull, if the hull is slightly underengineered there. If you have a boat with a bulkhead across there I would have guessed it would be pointless. Or even a sufficiently heavy rib forming a strong ring. On the other hand those wires are going to be inconvenient every time he tries to slide along the seat to the bow.

I can't remember the type of boat you have but isn't it quite different in design/construction from that Folkboat? My inclination with all these structural things is only to change it if there's clear evidence the original design isn't working out...

 

[dunedin]

To.my mind the arrangement in the original video is a terrible bodge to try to address some msjor weaknesses rhat must be in the hull and/or deck. And the thin wire looks like a major trip / cut hazards.

Many boats do this properly. We have large s/s tie rods down from the chain plates in the deck, that connect into a major sub structure that holds the mast foot. Immensely strong but neat and tidy.
We also have thinner rods from the mast up to under the halyard turning blocks, to take the halyard tension out of the deck structure.
Proper engineering.

 

[thinwater]

Nearly all beach cats use a similar approach, with what they call a dolphin strike under the mast. Obviously, you need a strong transverse compression member. My Stiletto 27 mast sat dirrectly on the dolphin striker, with zero weight on the beam.

Not sayin' it's a good idea on a mono.

 

[oldbloke]

The use of space frames and wires to support the rig and manage the rig tension was quite common in dinghies and racers in the 80s and 90s. With the coming of carbon and epoxy and boats designed for same you can build in all the stiffness you need in more elegant and unobtrusive ways

 

[ducked]

The force all has to join up to the keel however it's done. He's passing some of the force through that internal extension of the standing rig rather than through the hull or hull frame. I don't think this is very common, I have not seen it before. I think it's more normal for designers to put in enough bulkhead (or frame) size to make a strong ring of hull in line with the mast, meaning there's no need for anything else.

On that boat, where there is no bulkhead near the mast, it just might be worth it to stop the shroud tension from trying to deform the hull, if the hull is slightly underengineered there. If you have a boat with a bulkhead across there I would have guessed it would be pointless. Or even a sufficiently heavy rib forming a strong ring. On the other hand those wires are going to be inconvenient every time he tries to slide along the seat to the bow.

I can't remember the type of boat you have but isn't it quite different in design/construction from that Folkboat? My inclination with all these structural things is only to change it if there's clear evidence the original design isn't working out...

As per my original post (TLDR?) probably not appropiate (nor, hopefully, required) for the Trident since its a deck-stepped mast with no compression post, so the loads couldnt be transferred to the mast base in this way.

I suppose they could be transferred more directly to the keel, but I'm not considering doing that.

 

[ducked]

Nearly all beach cats use a similar approach, with what they call a dolphin strike under the mast. Obviously, you need a strong transverse compression member. My Stiletto 27 mast sat dirrectly on the dolphin striker, with zero weight on the beam.

Not sayin' it's a good idea on a mono.

Hadn't thought of that but it does seem to be pretty closely comparable.

I suppose it would be even more directly comparable if the mast extended below the deck level and replaced the striker, though that'd be a bit inconvenient. You could lash it at deck level, or I suppose it wouldn't really have to be located there at all

 

[justanothersailboat]

As per my original post (TLDR?) probably not appropiate (nor, hopefully, required) for the Trident since its a deck-stepped mast with no compression post, so the loads couldnt be transferred to the mast base in this way.

I suppose they could be transferred more directly to the keel, but I'm not considering doing that.

For some reason I totally missed that last sentence and I'm not sure how, sorry.

I think in the Trident your mast is over a bulkhead which effectively has the load path of those wires inside it and many more besides - isn't it? A good design that works in huge numbers of boats of many sizes.

Other people's folkboats don't seem to have wires like the one in the video so presumably have enough strength in the hull and deck beam... I wonder what's wrong with that one.

 

[William_H]

Just looked at the video and saw the wire joining chain plates together. Now this might seem logical if you are considering the hull under extreme tension of shrouds pulling mast down equally. As in setting static tension.However real loads are on just one shroud /chain plate at a time. So no force trying to spread the hull/chain plates rather a force trying to press chain plate /hull in towards middle. Here we rely in the structure of hull to hold gunwhales out against the load. I think OP will find no tension on his stay across the inside of the hull when pressed on one tack. Indeed it may go slacker. In other words remove it. ol'will

 

[ducked]

Just looked at the video and saw the wire joining chain plates together. Now this might seem logical if you are considering the hull under extreme tension of shrouds pulling mast down equally. As in setting static tension.However real loads are on just one shroud /chain plate at a time. So no force trying to spread the hull/chain plates rather a force trying to press chain plate /hull in towards middle. Here we rely in the structure of hull to hold gunwhales out against the load. I think OP will find no tension on his stay across the inside of the hull when pressed on one tack. Indeed it may go slacker. In other words remove it. ol'will

I'm the OP
I have no stay across the inside of my hull
So I can't comment on its actual behaviour.

For that I have to go by what the bloke that saved the Folkboat in the video says.

It sounds like he's not sure whats going on, but I suppose that additional rigging might be giving him some additional diagnostic information.

Is there any reason to believe its doing actual harm?

 

[William_H]

I'm the OP
I have no stay across the inside of my hull
So I can't comment on its actual behaviour.

For that I have to go by what the bloke that saved the Folkboat in the video says.

It sounds like he's not sure whats going on, but I suppose that additional rigging might be giving him some additional diagnostic information.

Is there any reason to believe its doing actual harm?

My apologies Ducked. No reason to think it would do any harm unless he falls over it. ol'will