Canting rigs, wingmasts, and capsize prevention
I’ve been thinking a bit about the mast and rerighting of the boat in case of knockdown/capsize for ‘Firstborne’. While I will have a lee pod and as such consider a capsize to be pretty unlikely, I do think it remains a possibility, and it is something which I’m ardently considering in the design process. Some time ago in one of the threads on the forum here (I think it was either on the pushme-pullyu or autoflight thread) we talked about Cheers and Dick Newick’s other atlantic proas having masts which were inclined a couple of degrees, to give the boats a chance to reright on their own in case of a capsize. Dave stated that the boats had done precisely that on several occasions. First off, can someone verify or debunk those claims? From the photos I can find online it doesn’t really look like the masts on Cheers are inclined one way or another, but if it’s only a couple of degrees it’d be hard to spot on a photo, so I’d be very thankful if someone could verify the claim—‘Project Cheers’ anyone?
Essentially my thinking at the moment is the following: if my 8m mast were inclined to leeward about 10°, then the masthead would hit the water at 90° of heel (at which point the boat should still have a small amount of positive stability due to the pod and heavy gear in the bottom of the vaka). If I had a wingmast with a comparatively large section, say a chord of 60cm (2 feet), then the mast would have a fair bit of volume in it, and it’s got a long lever in any case. Ideally the mast would stop the boat from going turtle, even without sails up, and give it moment on its side to just allow it to reright itself when the next wave comes by. If such a wingmast proves inpractically heavy, or if it doesn’t have enough volume, one could include a self inflating masthead float [1], to greatly increase the amount of buoyancy at the masthead once it hits the water.
Since I was planning on deck-stepping the mast on a ball-joint anyway, I could just make all the rigging into running rigging, and design the mast to cant +/-10° in the windward leeward direction. That way I could have the mast vertical when skimming or flying the ama, thus avoiding unnecessary performance losses on the rig. 😉 On the other hand, when the weather is about to detiorate, then in addition to reefing the main, getting the jib down, and a storm jib up, you could also cant the rig 10° to leeward to ‘harden’ the boat against capsizing.
Is this idea workable? What factors influence how much volume you’d need in the water at the masthead to prevent going turtle? How much volume do you need? Do you need an inflatable masthead float? Should the ama automatically dump its water ballast in a knockdown, to avoid it working against the mast, should you go over 90° heel? [2] And how much does a big wingmast like that weigh anyway? What kind of scantlings are we talking about here? Are they prohibitively heavy when built out of say plywood and fiberglass or kevlar? [3]
What do you all think?
Cheers,
Marco
Footnotes:
[1] The masthead float would be packed in the top of the mast somehow, with a salt-pellet trigger like the ones on the self-inflating lifejackets—protected from the rain obviously. If the whole thing is mounted on a halyard which runs up on the outside of the mast next to the mainsail track, and runs down inside the mast, then it would be possible to get the mechanism down after a successful rerighting, and then deflate, repack, reload, and rehoist the device for the next potential capsize, without having to go up the mast, or leave a big inflated thing flapping in the wind at the top of the mast.
[2] A simple hatch on the top side of ballast water tank in the ama, held down by an elastic cord would achieve that trick. When upside-down / sideways the water would literally come pouring out of the tank, and if the hatch is above the ama’s inverted waterline then that would work even if the boat has gone turtle, which would make rerighting much easier.
[3] Carbon fiber is intransparent to most radio waves, a plywood + fiberglass or kevlar mast would allow placing the VHF antenna and active radar reflector inside the mast, which I think would be great to help protect them from damage in a capsize. While kevlar is expensive, we’re probably only talking about a couple hundred euros extra for enough of the stuff to build the mast, so that’s tolerable if the weight of fiberglass proves to be too much.
Marco,
You should read John Pizzey’s 3 articles about all things proa, but especially the bits on canting rigs where he was not so much interested in the self righting issue as much as canting the rig in advance, so that it spilled wind sufficiently early so that you never got to a capsize situation.
I can’t seem to find them on the new format Proafile, so here is a link to the old Proafile location:
http://proafile.com/magazine/article/the-proas-of-john-pizzey
Rob
Thanks for the tip! I read them all last night, that was was some pretty interesting reading! 😊
On Pizzey’s boat, in particular ‘Flight’ the mast is stepped on the leeward side of the vaka. That means when the boat is knocked down, the entire mast and all the sails are lying on the water surface doing their best to arrest any further heeling motion. With plenty of RM left due to the leeward inclined rig, the boat will self right easily.
That’s a very cool concept, but what about if the maststep is not on the leeward side, but on the windward side, and you do have a leeward pod? That’s what I had in mind. I’ll have to have a look in the CAD model what the waterline would be at 90° heel, but given that there is over 1m distance from the leeward edge of the pod to the maststep at the windward edge of the vaka, the maststep will definitely be a good bit above the water, meaning that unlike Pizzey’s solution, not the entire mast and sailplan will hit the water at once when knocked down. Instead, the masthead would dip in first, and at progressively higher angles of heel, progressively more of the mast would come into contact with the water. The sailplan, which is most likely heavily reefed at that point, will come into play very late.
With this sort of a setup you’d be relying much more on pure volume at the masthead, as opposed to the entire rig lying on the sea surface. It could be that it’s not enough though…
Cheers,
Marco
P.S. - Structurally, I want the maststep to be near one of the sides of the boat, as that makes it much easier to brace the maststep from below without making the cabin useless. The reason I picked the windward side, was to make the staying base on the leeward side a bit wider, so the forestays help hold the mast up in the event of a backwinding. The windward offset should also help with the balance of the boat a little bit.
With this sort of a setup you’d be relying much more on pure volume at the masthead, as opposed to the entire rig lying on the sea surface. It could be that it’s not enough though…
You won’t get full full rig buoyancy at 90 degrees, a la Pizzey, but as I said, the rig helps to dump power early, so you are less likely to ever get to the scenario you are contemplating. Slackening off or canting the rig seems to be standard practice for righting a multihull anyhow. So a system where you can control cant helps to prevent a capsize in the first place and then is step 1 to recover from a capsize even without any special devices.
Try this link also:
http://www.f-boat.com/pages/background/capsizearticle.html
I doubt that you could ever get sufficient rig buoyancy via wing masts or masthead flotation devices without paying too great a performance price the rest of the time in terms of windage and weight aloft. Hobie 16 cats tried floats on top of masts for a while, but you don’t see them any more, so I suppose that says something.
P.S. - Structurally, I want the maststep to be near one of the sides of the boat, as that makes it much easier to brace the maststep from below without making the cabin useless. The reason I picked the windward side, was to make the staying base on the leeward side a bit wider, so the forestays help hold the mast up in the event of a backwinding. The windward offset should also help with the balance of the boat a little bit.
Totally logical….Jzerro, Pacific Bee, Madness and Jester 2 all do as well, for the same reasons….Maybe you can’t have it all, but it is worth a try….....
Rob
Thanks for posting yet another helpful resource Rob!
While I wouldn’t want a permanent saucer on the top of my mast, having some numbers for the volume certainly helps. The Farrier masthead float idea on the other hand is right up my alley; just what I had in mind. 😊 Using a trigger based on heel angle rather than water contact seems like a very good idea since you get much earlier deployment of the masthead float, and potentially avoid problems with false-positive activation due to rain etc. Placing the CO2 bottle at the bottom of the mast seems like a fairly good idea in principle, but the thing the Farrier system is really missing in my opinion, is what you do AFTER you’ve been knocked down, saved by the float, and then rerighted your boat? How do you get the masthead float repacked?
Thus far the only idea I’ve had is running a halyard in through the top-plate of the mast, so you can pull the packed float right into a little compartment in the top of the mast. That doesn’t work with having a CO2 bottle at the base of the mast, and it has so problems of getting it in there properly, and getting it down, etc.
I kind of doubt you could find a material which is stretchy enough to avoid having to pack anything at all though… Like a big balloon, with some long rubberbands over it, just inflate when you need it, and then deflate it again and it’s effectively “repacked” itself. That would be great, but I’m skeptical that it’s feasible.
Or maybe something like a spinnaker-trumpet in the top of the mast would do the trick, then you’d need some way to get the whole thing out of the trumpet in a real hurry though so it can be inflated quickly… If that’s feasible, then you could have the CO2 bottle at the base of the mast and have as many kockdown/reright cycles out of the system as you wanted, in very rapid succession if needed…
Anyone got another potential solution here? Or an idea on how to make one of the above practical? I’m open to any and all suggestions here, no matter how unconventional or weird they may be! 😊
Cheers,
Marco
Check this idea at my Website: http://www.multihull.de/proa/proakent.htm
It’s in German, but pics says all.
Cheers
Othmar
Letting the rig cant to leeward on a spring / bungee in a gust is really clever, you get the cant automatically then. You would probably have to play with the tensions on stays and shrouds a bit more often when you want to account for smaller changes in wind strength though. I really like it though because it protects you at all times, and not just when you consciously thought about leaning the rig over in advance, to protect yourself from a capsize. This way you can just sail, and if you get blown over, the rig will cant by itself and protect you.
It’s a really cool idea, especially for a smaller boat. If I do decide to build a small temporary proa using Firstborne’s ama this autumn, then I’ll definitely give that a go! 😊
I still need some way to get the masthead float deployed and restowed though if I want to use the system on the big boat… Personally I quite like the idea of having a small ‘spinnaker-trumpet’ in the top of the mast to haul the deflated float in. The question is just how to get it out of the trumpet in a hurry when you need the system to deploy. Pulling it out on a halyard risks getting everything tangled and clogged up inside the mast…
Another option would be to blow it out of there like a potato cannon, using CO2, and then inflate. Basically I’m thinking you just keep the float inside the top of the mast in a special tube, permanently partially inflated, to say 1.5atm, just use a pressure regulator to do that. When you are about to capsize, you have some system that opens a high pressure CO2 valve and the masthead ‘cannon’ fires, pushing the floatation bag out of the tube/trumpet. Once it’s out of the cannon, the flotation bag suddenly has the space to inflate further, which the pressure regulator then takes care of all by itself. To repack, you depressurize the bag, pull it back into the trumpet compeltely, reopen the regulator, and then rearm the ‘cannon’ and you’re ready again. As a plus, if the bag or the low pressure part of the system ever develops a leak, you’ll know because the low pressure system will depressurize itself after some time.
It’s not any more complex than the parachute recovery systems I’m used to back from when I worked with moderately sized amateur rockets, but it is a bit on the complex side for a yacht, and it would have to be pressurized and ready to deploy for a period of weeks and not hours, which raises the bar on how impervious to weather and how airtight the system needs to be by quite a lot. So I dunno, and you’d have to be darn sure the thing doesn’t get stuck in the mast, but fires cleanly every time… Developing and testing it would certainly be good fun though. :D
Anyone have a simpler idea? Preferably something that doesn’t require moving parts? 😊
Marco
And here’s a possible solution, no cannons required… 😊
Explanation: Just picture taking a piece of plastic tubing, and putting the lip of the balloon over the end of it. You can inflate the balloon, or when you let the air out, if you had a rubber band which was attached inside the tube and on the inside of the balloon, the rubber band would pull the balloon into the tube (the lip of the balloon would still be on the tube obviously). Add a gently spring-loaded normally-closed lid, to cover the thing the keep the rainwater out of the balloon when it’s inside-out in the tube, and you’ve got what I’m proposing to do with a floatation bag and my mast.
What do you guys think?
Cheers,
Marco
Hey Othmar,
the more I think about the idea you posted concerning the mast which cants to leeward in a gust, the more I like it . There is one big problem though: what about the forestays? If the mast is offset to windward a bit, then the moment the mast cants to leeward a little, your forestay tension is at zero, and then your mast is potentially flapping around.
One solution might be to not mount the mast on a ball joint, but on a hinge so it can really only cant to windward or leeward and have the forestays on the axis of rotation. I was thinking of putting the mast on a hinge instead of a ball joint anyway, since then I can use the mechanism to help step the mast on my own as well. I really want a mast which is offset to windward though, so what can you do about the forestays? With the forestays at the bows, slightly to leeward of the mast, you’d have the slacking probelm, and if you are then hit by a gust on a close reach for instance, the mast cants, the forestays slack, and then the driving force component of the sail has to be held up by the amst and the hinge alone, without any real stays to help it withstand the loads.
Do you have any solution for this problem Othmar?
Cheers,
Marco
The really great things about it are the wonderful safety benefits, and there is even a performance gain in there too because in gusty weather, you can keep more sail up than you could without the system, making for a potentially higher average speed. Without the system you’d have to reef so that at whatever the max windspeed in the gusts is, your boat doesn’t go over on you / you have whatever you consider an adequate margin of safety for the given conditions in the gusts. With the system, you can leave a bit more sail area up, and the rig will just dump the extra power by canting during the gusts, while during the lulls, you have access to the full sail area, or more than what you would have up, if you had been forced to reef more deeply.
Maybe the forestay problem can be solved by moving the attachment points for the elastic shrouds, closer to the vaka, on the iakos somewhere, so they alone can provide the longitudinal support for the rig? Or maybe run a bridle from the ama to the vaka bows, and attach the shrouds to the middle of that bridle, so that the ama is supported too, despite the shrouds going to midway across the iakos for instance?
Marco
Hey Othmar,
the more I think about the idea you posted concerning the mast which cants to leeward in a gust, the more I like it . There is one big problem though: what about the forestays? If the mast is offset to windward a bit, then the moment the mast cants to leeward a little, your forestay tension is at zero, and then your mast is potentially flapping around.
Do you have any solution for this problem Othmar?
Cheers,
Marco
There are two cases of operation:
Slup rig.
You can arrange the fixed-points of the fixed stays in one line with the mast base. In this geometrical constellation it’s no problem to hold the tension of the stays if the mast cants to leeward. The rig is struted by the telescopic pole to leeward and windward.
Crab claw rig.
Same configuration as above, but the stays are running stays. To hold the mast in position after shunt a stopping mechanism is need, eg. a stopping line for the running stays (see sketch).
Othmar
Where the bermuda / sloop rig is concerned I agree with you, but what if you can’t do that? What if the base of the mast is offset to windward, and the bows don’t lie on the same axis as the mast?
Easy answer - in this case it’s not possible, because during mast bowing to leeward all angles to the stays are changing.
But why must be the mast offset to windward? The static will done by the strut, and there is no other need for a windward position.
It’s true that you could design the strut to take the loads when backwinded, which would eleminate the need for the forestays to be set to leeward of the mast a bit. The other major reason I want to have the mast set to windward though, is so that the maststep is above the side panels of the hull, and not stepped in the middle of the deck. It’s much easier to get the required stiffness at the sheer, than it would be on deck. Furthermore you lose the option to have a single central hatch, and the ability to have a Cheers-style interior steering station, at least for a small boat. Offsetting the mast to windward slightly may also help with the balance of the boat, and it widens the slot between the mainsail and the jib, which might be good for upwind performance (less likely to backwind the main).
Another thing just came to mind as well concerning the setup: the chainplates for the stays have to be at the same height from the waterline as the joint on the maststep as well, for the tension in the stays to truely remain the same despite canting of the mast. It has to be one and the same axis of rotation, in 3D space. I was always thinking about it in 2D from a top-down view before. My foredeck is a good 25-30cm below the height of the deck at midships though, and if you add the extra height of the maststep (the height from the deck to the acutal axis around which the mast rotates), then there will be another couple of centimeters of difference as well. The bows, or at least the mountpoint for the stays, of the boat would thus have to be the same height as, or slightly higher than, the midship deck. That’s not really practical for a boat with a cabin, I have more than enough freeboard at the bows already anyway (~75cm if I recall correctly).
To reiterate, the problem is as the mast cants over to leeward to depower, you need some way to keep tension on the forestays, even if the maststep and its axis of rotation are to windward and higher up than the attachments points for the forestays—if you don’t do anything, the forestays will slacken completely. There’s no such thing as a free lunch, but the question is: is there a clever trick with which you can solve all these problems for a stayed rig?
Cheers,
Marco
P.S. - The fallback solution for me would be to say I don’t allow dynamic canting of the rig, you can just set the stays and shrouds so the mast takes on a particular static cant angle and that’s that, but then you lose the ability to use the dynamic canting for depowering of the rig during the gusts. In very gusty conditions (say V_gust - v_lull = 40% of average windspeed) the dynamic canting of the rig to automatically depower during the gusts (instead of having to reef deeply), could allow you to carry something like twice as much sail area as you could without the system (heeling moment is proportional to the SQUARE of the windspeed after all) . During the gusts, the performance of a reefed main and the dynamically canted rig would be the same, but during the lulls, the dynamically canting rig would be upright with its full sail area, and have an significant performance advantage over the deeply reefed sailplan. So how can we make this work…? 😊
One rather complex way of doing it, would be to attach the forestays to a pneumatic or hydraulic piston which pulls on the stays. If the pressure in the piston is too low, you let more air / hydraulic fluid into the piston *[1], and if the pressure is too high (during a lull, the elastic shrouds are trying to pull the rig upright again), you dump pressure from the piston *[2].
In gusty weather that does require a continuous source of compressed air / hydraulic pressure though, which is an inconvinient requirement to say the least, and having moving parts which are responsible for keeping your rig upright, is perhaps not the best thing either. Imagine a valve fails, and you more or less suddenly don’t have any forestay tension anymore…
Marco
*[1] use an off-the shelf pressure regulator attached to your gas source for that
*[2] use an off-the-shelf pressure release valve