Another stability question

[Manateeman]

I’m not a cat person, but I love boats. Chris White and I sailed out of the same small harbor on Buzzards Bay. He’s a good designer. I learned my fluid mechanics in an MIT research company and I’m impressed with what Chris designs. So the question is simple. What about his foil masts.
If you link to a commercial autopilot like my Simrad which has a sail by wind function, would the cat behave better in a super gust?
Not a downdraft. I’ve been in one bad one. Yikes.
Aircraft deal with the issue of unwanted forces all the time. Aren’t foil masts the solution short of some complex system.
Can foil masts reduce the gust threat.
Mark, still a mono manatee

[chrisr]

Originally Posted by Chotu

Ok, ok. It varies. You're right. I was thinking of a limited situation.


I wonder how much only using the windward dagger board can help in a gust capsize situation when close hauled.

a powered-up cat, with centerboards should never have the leeward c/b down in marginal or gusty conditions. it is too easy for the boat to 'trip' over the leeward board.

minikeels on the other hand allow the boat to 'slid' sideways in the gusts...similar to the way a mono will heel over to de-power

btw, a trick which can save you in an 'ultimate' situation is to use a deliberately undersized link somewhere in the system (eg headsail sheet). ideally such will 'blow' before things get catastrophic !

cheers,

[thinwater]

Originally Posted by chrisr

a powered-up cat, with centerboards should never have the leeward c/b down in marginal or gusty conditions. it is too easy for the boat to 'trip' over the leeward board.

minikeels on the other hand allow the boat to 'slid' sideways in the gusts...similar to the way a mono will heel over to de-power

btw, a trick which can save you in an 'ultimate' situation is to use a deliberately undersized link somewhere in the system (eg headsail sheet). ideally such will 'blow' before things get catastrophic !

cheers,

No, No, No.


There is no reason to have a cat with daggerboards and not use the leeward board. It is the one that does the work. Sailing with the windward board is 70s wisdom that is far, far out of date. A most, you would likely pull both up 50%. Also remember that the boards are virtually impossible to move in heavy weather (too much side load).



I have a boat with fixed keels (mini-keels?). It does not slide sideways, it points well and will fly a hull when pressed. In fact, it should be obvious that as the boat is pressed deeper the lee hull is pressed deeper and the mini keel becomes more efficient. If it can slide side ways it is a hopeless design that cannot sail to windward.


The weak link theory has also been debunked. Anything that would fail at the correct moment will fail from fatigue within hours and will NOT allow the boat to pull hard, for example off a lee shore, when needed.


Yes, I've sailed also sorts of multis, board and keel, for 40 years. The solution is to pay attention and to reef early when it is gusty. Watch the clouds and learn them. Watch the water in the distance. Learn local weather patterns. Gusts never come from nothing.

[Alistair242]

A square top main can spill a bit of extra air in that case and most cats will be considering a reef or already have one in 15kts AWS and would be thinking about the second close hauled with 15 kts TWS.

[jdmuys]

Originally Posted by chrisr

btw, a trick which can save you in an 'ultimate' situation is to use a deliberately undersized link somewhere in the system (eg headsail sheet). ideally such will 'blow' before things get catastrophic !

cheers,

No need for that. You can now install an automatic sheet release clutch, coupled to a heeling sensor. Gerald Bibot shows the system in his Marsaudon TS5 in this video:

https://www.youtube.com/watch?v=aZCGiRAC1s8

Starting at 5:05. It’s in French, but the video is (relatively) explicit.

Note that the Marsaudon TS5 is a light and fast cruiser, not a racer. Nonetheless, it’s fast enough for some people, such as Gérald Bibot, to adapt it for racing, in this video for the Route du Rhum in 2018.

[Lemsteraak]

Much of stability has to do with buoyancy and acceleration. With catamarans we would always worry about pitchpoling rather than capsizing. When you are surfing down the face of a big wave, you hope the bows don't "pearl", dig in. This is based on my experienced sailing "B" class cats in the ocean but you can scale it to larger cats. That is why you need to keep them light, and overweight multihull isn't considered as safe.

When the wind hits your sail, you certainly get pressed by it but some of the force is shifted to acceleration. In the case of small dinghies, they have an added safety feature, they can go up on a plane. If you watch a serious racing dinghy like a 505 in heavy wind, you think they are out of control. When they are up on a plane they develop a huge amount of stability because they are riding on top of the water and they accelerate in a gust ... well until they hit a wave and pitchpole because they run out of buoyancy to lift the nose.

I was teaching a friend how to set a spinnaker on his old Daysailer. We got hit by a huge micro burst with the spinnaker set. I just knew on this old boat that we were in for a death roll, but she just lifted up on a plane and we were in for the ride of our life. The force turned to acceleration and because we could get up on a plane, our buoyancy was huge. I am now a big believer in this type of dinghy because if you get into rough winds, you can get up on a plane and you will be fine with the added buoyancy and reduced drag.

So, back to the original question, a monohull hit with a big gust and windshift will heel and spill most of it off, with a little bit of acceleration. A multihull being lighter should see a lot of acceleration. This is why when you are in knock down conditions on a monohull, you point up and spill the wind. On a light multi-hull, you do the opposite, if you lift a hull, you want to turn downwind and accelerate out.

[chrisr]

Originally Posted by thinwater

No, No, No.


There is no reason to have a cat with daggerboards and not use the leeward board. It is the one that does the work. Sailing with the windward board is 70s wisdom that is far, far out of date. A most, you would likely pull both up 50%. Also remember that the boards are virtually impossible to move in heavy weather (too much side load).



I have a boat with fixed keels (mini-keels?). It does not slide sideways, it points well and will fly a hull when pressed. In fact, it should be obvious that as the boat is pressed deeper the lee hull is pressed deeper and the mini keel becomes more efficient. If it can slide side ways it is a hopeless design that cannot sail to windward.


The weak link theory has also been debunked. Anything that would fail at the correct moment will fail from fatigue within hours and will NOT allow the boat to pull hard, for example off a lee shore, when needed.


Yes, I've sailed also sorts of multis, board and keel, for 40 years. The solution is to pay attention and to reef early when it is gusty. Watch the clouds and learn them. Watch the water in the distance. Learn local weather patterns. Gusts never come from nothing.

you are welcome to your opinion...but i will stick to mine thanks

cheers,

[RaymondR]

Originally Posted by Chotu

It's all about dumping the mainsheet if caught with too much sail up.

This is a concern of mine as well.

Does anyone know of a reasonable "fuse" or "circuit breaker" for this purpose?

One might be far from the helm and sheet controls when a sudden gust hits, traveling on autopilot. In this case a more automatic system, based on the heeling angle of the boat might be best. Something that releases on a certain number of degrees of heel or certain tension on the sheet.

Pondered on this a number of times.

You could put an air cylinder in the boom with a wire back through a turning block to which the main sheet is attached. A pressure regulator in the air supply is set to the pressure required to hold the cylinder retracted but in a gust the increase in main sheet load would extend the cylinder allowing the main sail to dump air. When the gust passed the cylinder would retract resetting the main sheet and sail to pre gust setting.

Since it would not be required to operate at high pressures the entire gadget could be incorporated into the boom as part of it's structure.

[Tsalta]

Hi,

Thanks for all the responses.

Ok, say the scenario is Wife #1 is on watch and I’m having a kip. We are heading to windward in a steady 15kts. No expectation of anything gusting greater than 20 kts. What sail plan should we have deployed?

Should I plan contingency for 20kt, 30kt, 40kt ...... gusts and sail around under staysail forever?

For the people cruising around as a couple, how do you run the boat during passages for safety first with regards to sail plan to windward?

(Am I right to expect sailing downhill under headsail only is relatively risk free regarding wind changes?)

Cheers

[Octopus]

Firstly, a modern cruising cat provides so many safety benefits over a mono that the remote possibility of inversion doesn't even enter the equation. Secondly, any cruising cat that your boss will be happy sailing will only invert in conditions that the boss would never let you contemplate encountering (think mid-Atlantic in February).

Sailing by numbers is sensible on a cat (despite what others say on this thread), because there is so little feel for the true weather conditions, but also because on a modern cruising cat you tend not to 'sail' in an active sense, as you are too busy enjoying a normal life (I have a video showing our six children sat round our saloon table obliviously playing cards, after my wife and I had just returned from the cockpit after reefing in F8/9 winds).

There is a chance of being caught out by a wind shift, but modern cruising cats have huge stability, because of their high displacement, wide beam and conservative sail area, so it is likely to be a non event. I think here of a time when we inadvertently sailed into a wind acceleration zone, just South of La Palma, shortly after setting out across the Atlantic. The wind speed went from 10 knots to 50 knots in a matter of moments under full sail. It was a little alarming for us, but the boat was absolutely fine.

[Dpackie]

Originally Posted by jdmuys

No need for that. You can now install an automatic sheet release clutch, coupled to a heeling sensor. Gerald Bibot shows the system in his Marsaudon TS5 in this video:

Starting at 5:05. It’s in French, but the video is (relatively) explicit.

Note that the Marsaudon TS5 is a light and fast cruiser, not a racer. Nonetheless, it’s fast enough for some people, such as Gérald Bibot, to adapt it for racing, in this video for the Route du Rhum in 2018.

This seem obvious to me. Integrated systems. Falling off to accelerate away from sudden gusts when overpowered seems a lot like stepping on the gas as a railroad grade crossing gate starts to drop. You'll probably make it easy, but if not, the results are catastrophic. Broaching makes a mess down below, but clean up is easy.

I want to add, the depth on knowledge on these forums is mind blowing. Thanks so much to everyone, it's super fun to have the resources to learn for free. I've dabbled in a lot of hobbies, such open source learning is not often found.

[Cheechako]

Originally Posted by Tsalta

Hi,

First post. Pls be gentle.

I’ve only ever sailed mono’s but the only way I’ll ever get the boss on board a boat long term is on a cat. Space, comfort and all that non essential stuff.

Anyway, last week helming on a Farr 40ft in a nice steady 15kts close hauled heading for the top mark, we encountered a nice 30 degree wind shift and gust up to 25-30 kts.

My question is regarding how do cats handle this? What if you have the AP on and are inside making a cup of tea and don’t see the bullet?

From what I have read, cats are reef by the numbers so potentially there could be too much sail up. Am I going to end up inverted?

Cheers

You'll hardly know that's happening in most cruising cats. Which in some ways is a danger. But I've encountered that type of thing up to 40 knots of wind and full sails up after entering a channel coming out from behind an island etc.. The anemometer let me know it was blowing that hard. The hulls didn't lift noticeably at all. Eventually I got a reef in before we saw much accompanying sea action further into the channel.

[smj]

Originally Posted by Dpackie

This seem obvious to me. Integrated systems. Falling off to accelerate away from sudden gusts when overpowered seems a lot like stepping on the gas as a railroad grade crossing gate starts to drop. You'll probably make it easy, but if not, the results are catastrophic. Broaching makes a mess down below, but clean up is easy.

I want to add, the depth on knowledge on these forums is mind blowing. Thanks so much to everyone, it's super fun to have the resources to learn for free. I've dabbled in a lot of hobbies, such open source learning is not often found.

You don’t fall of to accelerate you fall of to reduce the apparent wind, or in other words to de power.

[Dpackie]

Originally Posted by smj

You don’t fall of to accelerate you fall of to reduce the apparent wind, or in other words to de power.

Reducing the apparent wind only happens with an increase in boat speed. That much I am certain of. Do big cats plane up when not surfing a wave?

[smj]

Originally Posted by Dpackie

Reducing the apparent wind only happens with an increase in boat speed. That much I am certain of. Do big cats plane up when not surfing a wave?

Not altogether correct. Think of it this way, if your motoring at 10 kts directly into a 10kt wind your apparent wind will be 20kts. If your motoring at 10 kts going directly downwind in a 10kt wind your apparent wind will be 0.
That’s a 20kt difference in wind strength just determined by the direction your boat is traveling.