Self righting multihull?

[Paul Scott]

Nice to have you back again, Paul. After your February posts I came up with a few ideas you might want to consider, especially since I see you are open to a bi-mast arrangement. Tilt those sealed freestanding carbon masts outward 10 degrees or so and install the mast bases as close as possible to the outer side of the hulls. Once you get up to 45 degrees or so in a knockdown the outer sheer and mast should be starting to create floatation and righting moment in addition to a gradual loading of the mast eliminating the shock load, with or without a topmast float. The entire mast is being used for flotation and righting, not just the mast top. The 10 degree or so mast tilt should go a long way to preventing the cat from turtling and allowing the mass of the cat (not past vertical) to bring it back down upright. The mast base tube should be elongated crosswise at deck level to allow the masts to pivot upright at the dock. Mast tilt can be controlled manually with a 10 degree male/female radius wedge placed either inside or outside the mast. Perhaps the lower center of sail area using bi-masts may make it possible to get by with 8' beam, on boat lengths in the mid 20s, without ballast.

A sporty early evening heading North to Port Townsend at the North End of Admiralty Inlet a month ago got me thinking about multihull capsizing- wind way outside of the Westerly forecast went suddenly (like in 5 minutes) from ~10k to clocking gusts in the 40’s heated up by Marrowstone Island, with the outgoing tide, and Kelp where it usually isn’t. We didn’t heel over much more than 30 degrees (40’ Mono, 8.5 draft keel- think ~ early Class 40 but a bit narrower). Sea state was lumpier and thrashing more than Mr Brown’s video. The few times I couldn’t steer the valleys, we were literally thrown sideways in to them. It was a lot like Sailing Lasers in between the Lake Washington floating bridges during a 35K winter storm. Which I admit was big fun, but a bigger boat, um, amplifies things. Brought to mind sailing the small Sol Cat in a sudden 25K southerly off Kirkland in a 2’ chop, and if I hadn’t had the trapeze, I would have gone over. Anyway, back to Admiralty Inlet, I was thinking whether a boat without a keel would stay upright? Russell I don’t think describes the motion of the G32 in the chop as he righted, which would be interesting. (He does imply drifting, I think, and IIRR, both tanks were full). Judging by violently capsizing a Laser in insane conditions, sometimes I got thrown so violently that the tip of the mast would spear a downwind wave, and was forced downward by wave circulation- how would a multihull with a sealed mast or a mast with a small dirigible at the top handle that, especially during extreme acceleration? (Doing moguls on a Windsurfer doesn’t count because you can bail in mid air…)

Anyway some thoughts while procrastinating mowing the weeds.

 

[Russell Brown]

Were my experiences with self-righting any help?
We sail is pretty wild conditions here sometimes. These videos's don't show when it gets really wild, but give some idea.

 

[Paul Scott]

Were my experiences with self-righting any help?
We sail is pretty wild conditions here sometimes. These videos's don't show when it gets really wild, but give some idea.

Russell- Point Wilson can be so lovely….. Steve Rander once described Rage jumping off a wave and landing going downwind at ~20 knots like a garbage truck hitting a house- care to coin a metaphor about the top video? (the waves look pretty well formed and regular- the waiting is the hardest part?) The thing that struck me on our sail was how random the waves were in the tidal rip against the wind, which made anticipating them interesting- how much does that complicate multihull sailing in gnarly conditions? The G 32 seems to take the big stuff well- you had the tanks filled in both videos? Started mainsheet?

 

[myszek]

Long time ago I played with the idea of a self-righting tri without any ballast, with low-buoyancy amas and buoyant A-frame masts. She resembled Tanzanian Ngalawa:

7m long, 800kg displacement, 25sq.m. sail. With very short heeling arm, she can theoretically sail without reefing up to 20m/s wind speed. With buoyant masts, she maintains positive stability slightly above 90deg of heel.
But I am not sure, whether it makes any sense...

regards

krzys

 

[seandepagnier]

Were my experiences with self-righting any help?
We sail is pretty wild conditions here sometimes. These videos's don't show when it gets really wild, but give some idea.

Those are indeed rough conditions.. I have experienced in Indonesia 6-8 knot currents (straits between Indian and pacific ocean) with 25 knot contrary wind, but also 3 meter contrary swell. I have sailed in storms where I could see tunnels of air through the breakers where the top 3ft spilled over shattering solar panels the waves being well higher than the mast. This was on a 27ft monohull but I am concerned about my current boat (kraken 33) in similar conditions.

I think mostly a trimaran would be "ok" in theory anyway (the one I currently have maybe could break apart) if I sailed slowly, but that is the real issue of righting the boat: the ability to sail faster. I have had gusts of wind double my boat speed in a few seconds, and completely bury the leeward ama, getting the boat up near 15 knots. If I already was going 15 knots before the gust, what would happen?

Today I was sailing 10-12 knots into province town, but I have 2nd reef and half the headsail. I am afraid to push the boat harder. Also afraid to push the boat in rough seas. Probably my lack of experience, but if the boat could right itself I would learn exactly how fast the boat could be sailed and if I flip every few days that could be considered normal.

So the real question is, and no one answered yet: Is it possible to capsize most pacific proas? It seems like they are still susceptible to somehow breaking the rig and ending up flipped over although perhaps more difficult to do?

 

[seandepagnier]

Another thought is to have a small submersible with high torque propeller and drive system that can pull the boat using a rope. This ends up being a more efficient propulsion system anyway and gives better maneuvering because the propeller can stay deeper below waves.

In the event of capsize, the tow rope attached to the front of the boat, the UAV could swim under and pull with sufficient force to right the vessel and be trained to automatically do this like a turtle flipping itself over.

 

[Robert Biegler]

Another thought is to have a small submersible with high torque propeller and drive system that can pull the boat using a rope. This ends up being a more efficient propulsion system anyway and gives better maneuvering because the propeller can stay deeper below waves.

Provided that the added efficiency is not offset by the drag of the rope. And reversing would take a longer time, because the submersible has to travel twice the length of the tow rope before it can start to pull back.

In the event of capsize, the tow rope attached to the front of the boat, the UAV could swim under and pull with sufficient force to right the vessel and be trained to automatically do this like a turtle flipping itself over.

That reminds me: a multihull that can flood a hull would still have some stability from the volume of structural material, and perhaps some air bubbles. That residual stability might be overcome if there is a thruster near the flooded hull, mounted so that it is underwater when capsized (perhaps under the trampoline), and let it push the flooded hull underwater and then around. I suppose that should also work for the idea of flooding the bows of a catamaran. The thruster could have a propeller with quite low pitch and large diameter, because speed hardly matters, only high thrust.

Another option is to swing the amas of a trimaran back, like the Danish Dragonfly designs, but pitch the rotation axes forward a little so that the amas rise up when they swing back. Incline the rotation axes a bit more on one side, to let that ama rise up more. When upside down, that will both raise the centre hull out of the water, reducing damage from water sloshing around inside, and heel the boat, ideally enough that it falls on its side. Then unfolding the amas, if there is enough power to do so, should complete righting the boat. I have no idea how to keep a stayed rig where it belongs through that process, so unless someone comes up with a bright idea for that, this scheme would be suitable only for an unstayed rig.

 

[Russell Brown]

So the real question is, and no one answered yet: Is it possible to capsize most pacific proas? It seems like they are still susceptible to somehow breaking the rig and ending up flipped over although perhaps more difficult to do?

Most definitely you can capsize a Pacific proa. I've never done it, but of course it could happen.

 

[Paul Scott]

Hails of derisive laughter, I presume, but what about this? Gets rid of the lee bulge- kind of an ultra skinny freestanding mast proa sports boat? Think of the rudders as ~ CBFT

 

[ALL AT SEA]

Hails of derisive laughter, I presume, but what about this? Gets rid of the lee bulge- kind of an ultra skinny freestanding mast proa sports boat? Think of the rudders as ~ CBFT View attachment 190587

I've drawn similar sketches, and the proa seems the best candidate for a self righting multi, especially with a buoyant mast. Rather than a permanent weight in a fixed keel, I keep coming back to the idea of an ama that pivots down when the boat to create leverage to get the boat back on its feet. A three part beam with the centre part fixed to the main hull, the two outer parts hinged. Some sort of block and tackle from the end of the fixed centre beam to the lowered ama would be winched in to bring the ama (possibly with water ballast) back into position, bringing the main hull and mast up with it.

Sorry about the rough 'night shift' sketch, it should be rotated 90 degrees counter clockwise. The squiggly line is water.

 

[ALL AT SEA]

Also - I remember reading in a Multihull magazine about a Len Surtees trimaran that was launched upside-down, was self righting, and may have done a circumnavigation - I think her keel was concrete. Only reference I can find on the internet is another thread in this site from 2012- "Wide hulled trimaran" -

I'm still thinking about wide-bodied trimaran hulls. I found this trimaran design by Len Surtees, with a length of 38' and the main hull waterline width looks to be maybe 6'. Payload 4000lbs. Much closer to what I'm looking for than anything else. Would just need to make it demountable.

Does anyone know what its sailing characteristics are? Apparently Osprey was purchased by Tristan Jones, renamed Outward Leg, and sailed across the Atlantic and through various rivers in Europe. Has anyone read Jones' books concerning this voyage?

surteesmultihulls.com - This website is for sale! - surteesmultihulls Resources and Information. http://www.surteesmultihulls.com/11m-re-rightable-trimaran

As shown in the photo below, Surtees initially launched Osprey upside-down, then self-righted it, just to prove that it could be done.

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[myszek]

Most definitely you can capsize a Pacific proa. I've never done it, but of course it could happen.

I did. A 7m Janusz Ostrowski's Pjoa with traditional crab claw rig.
It was only a 90deg knockdown, the sail in the water stopped the rotation. We wasn't able to right the boat until released the halyard. Then the sail remained in the water and the boat raised.
Later Janusz made some experiments and finally turned the turtle on Pjoa; it was impossible to right her up from that position.
Jacek Sterna, another proa fan from Poland, made thick, buoyant yards in his proa to prevent overturns. As far as I know, he never capsized so far.

regards

krzys

 

[Paul Scott]

Also - I remember reading in a Multihull magazine about a Len Surtees trimaran that was launched upside-down, was self righting, and may have done a circumnavigation - I think her keel was concrete. Only reference I can find on the internet is another thread in this site from 2012- "Wide hulled trimaran" -

I'm still thinking about wide-bodied trimaran hulls. I found this trimaran design by Len Surtees, with a length of 38' and the main hull waterline width looks to be maybe 6'. Payload 4000lbs. Much closer to what I'm looking for than anything else. Would just need to make it demountable.

Does anyone know what its sailing characteristics are? Apparently Osprey was purchased by Tristan Jones, renamed Outward Leg, and sailed across the Atlantic and through various rivers in Europe. Has anyone read Jones' books concerning this voyage?

surteesmultihulls.com - This website is for sale! - surteesmultihulls Resources and Information. http://www.surteesmultihulls.com/11m-re-rightable-trimaran

As shown in the photo below, Surtees initially launched Osprey upside-down, then self-righted it, just to prove that it could be done.

• 
  osprey-first-launching-1980-300x202.jpg
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  16.5 KB
• 
  len-and-semi-displacement-hull-300x208.jpg
  File size:
  14.2 KB
• 
  11m specifications.jpg
  File size:
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It’s a shame that Surtees’ stuff is vanishing from the web- he really took L F Herreschoff’s baton and ran with it.

 

[peterbike]

I've drawn similar sketches, and the proa seems the best candidate for a self righting multi, especially with a buoyant mast. Rather than a permanent weight in a fixed keel, I keep coming back to the idea of an ama that pivots down when the boat to create leverage to get the boat back on its feet. A three part beam with the centre part fixed to the main hull, the two outer parts hinged. Some sort of block and tackle from the end of the fixed centre beam to the lowered ama would be winched in to bring the ama (possibly with water ballast) back into position, bringing the main hull and mast up with it.

Sorry about the rough 'night shift' sketch, it should be rotated 90 degrees counter clockwise. The squiggly line is water.

ALL AT SEA ; I think this is a brilliant idea. afaik, nobody else has proposed this ?
The idea could be expanded upon with 2/3 beams - so not limited to racing proa's ;
but could be applied to open bridge deck cats as well. (unless someone can come up with a reason why not ?....)

 

[peterbike]

Related to above ; I really should have said,
Weight to windward proa's rather than bridgedeck cats.
Maybe someone clever can come up with a concept for open bridgedeck cats as well ?