Catamarans in 50kt winds

[beiland]

Originally Posted by Dockhead

Sure, and my sails are carbon laminate, and almost all my running rigging is Dyneema. I'm using low friction rings and spliced Dyneema strops instead of blocks, and I use twings instead of jib cars.

But these are all technologies which have been well developed and used successfully in real life, at least on racing boats.

It appears as though you have considerable experiences with some of these more modern rigging materials. I have a few questions for you if you don't mind, as I am not abreast of all the advancements in the past few years....been working on my new marriage and retirement

[beiland]

I was looking for something else that this fellowed wrote,...and ran across this..

sail aerodynamics - Page 11 - Boat Design Forums

Take a look at Polhamus' leading edge suction analogy, expecially figure 2. Although the paper is concerned with planforms that have more sweep than a typical jib, the flow picture at a jib's leading edge is quite similar.

A sharp leading edge basically has no forward facing area except for the slope of the sail's camber. The low pressure peak at the leading edge gets pointed more to leeward than would be the case for a more rouded leading edge. Here's a physical way of looking at it. The air has to turn through a certain angle in order to follow the lee surface of the jib aft of the leading edge. If the air does most of the turning curving around the leading edge, that orients the suction more forward. But if the air flows past a sharp leading edge and does its turning around a vortex or leading edge separation bubble, then the low pressure of the turning is oriented at right angles to the sail's surface instead. This is still pointed forward relative to the boat, but you'd rather have it pulling forward and to windward instead of forward and to leeward.

This is the basic idea behind Polhamus' analogy. There has to be a low enough pressure over a large enough area to turn the air and produce a given amount of lift. You get the same lift in either case, but the sharp leading edge has a drag component that the rounded leading edge with attached flow doesn't.

The ideal shape would be thin everywhere except near the leading edge, like this Liebeck section:

As a practical matter, jibs with head foils have proven to be every bit as competitive as jibs with wire luffs or hanks. They are an example of a jib with a thick leading edge.

my response...
You're right Tom, that 'very thin foil' leading edge can be a real problem in the practical world as well. In gusty, shifty conditions it would be real difficult to maintain an ideal flow over the headsails, particularly at this leading edge. Originally I had thought the big round furling foils of Profurl units were less efficient than the oval or foil shaped sections of some other manufacturers. But as I explored the situation further I became more inclined to utilize a round-shaped furler foil on my twin-headsailed rig. This round shaped foil rotates more evenly, and could be made more robust. And it would act to cut down some of the 'sensativity' associated with a very thin leading edge. Some 'bluntness' at this leading edge actually transmits an advanced signal to the incoming flow.

[12BCruzn]

I've skipped over the last 292 responses so forgive me if this was already mentioned but as far as safety at sea, I recall Chris White concluding in The Cruising MultiHull that the biggest danger one faces at sea isn't capsize, large waves and high winds but man over board, for which he found catamarans to be the safer option, most likely due to lack of heeling.


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[mikereed100]

Originally Posted by 12BCruzn

I've skipped over the last 292 responses so forgive me if this was already mentioned but as far as safety at sea, I recall Chris White concluding in The Cruising MultiHull that the biggest danger one faces at sea isn't capsize, large waves and high winds but man over board, for which he found catamarans to be the safer option, most likely due to lack of heeling.

It has been mentioned before, but bears repeating. The greatest danger to sailors is not capsize, sinking, pirates or alien abduction; it is falling overboard, and in this regard cats are undoubtedly safer, particularly in the conditions that the OP (remember the OP?) is concerned about. All boats have become safer with the advent of roller furling and cockpit reefing but cats tend to be gentler on their crew since the motion is not so exaggerated. I've been tossed around my cat but never to the extent that I have on my monos, which in turn makes injury less likely. "No bruising cruising" as they say. Another consideration is that, for a lot of people, the quick motion of a cat is less likely to cause seasickness, which in turn allows crew to function better when the sea is up.

[donradcliffe]

Quick motion = higher acceleration.

Bruises are more a function of interior design--Ikea interiors = more bruises
Open interiors = more bruises

Somewhere back in this thread there was a mention of a woman who went round the world with her family on a cat--she fell overboard.

[tomfl]

Originally Posted by Dockhead

Sure, and my sails are carbon laminate, and almost all my running rigging is Dyneema. I'm using low friction rings and spliced Dyneema strops instead of blocks, and I use twings instead of jib cars.

But these are all technologies which have been well developed and used successfully in real life, at least on racing boats.

Not trying to dis the advantages of all these examples of what the cool kids are using because they offer advantages. In fact I would point out that while only marginally related to things like flipping and damage related to it lipo batteries are lighter, smaller, easier to maintain and less likely to hole the hull if they break free in a capsize and bash in the hull of a sailor.

Of course the down side of lipos and many of the other thing mentioned is cost. I am in the process of switching to soft shackles in some places on my boat in great part based on price. I would love to switch to dyneema in case of the running and standing rigging but can't justify the cost based on having existing working and running rigging. For a builder selling a new boat the advantage of a lower price may well be greater than superior function offered by dyneema rigging.

Bottom line for a lot of folks is that the new stuff, even if it is better, does not offer the best bang for the buck. And even if it does it may not be widely accepted as doing so to the boat buying public. One reason I have a Seawind 1000 with hull extensions is at my price point it offered the best bang for the buck. There are plenty of boats I view as "better" like some of the Chris Whites, Outremer, Gunboats, and several other. Sad to say all the boats I rate as better than the Seawind are several hundred thousands of dollars more than the Seawind.

Even if I found an Outremer close to the price point of a Seawind 1000 there is still the problem that I already have a Seawind I would have to sell to take advantage of the Outremer deal. The same problem exists for many of the smaller upgrades.

Kinda like "if it ain't broke don't fix it".

[mikereed100]

Originally Posted by donradcliffe

Quick motion = higher acceleration.

Bruises are more a function of interior design--Ikea interiors = more bruises
Open interiors = more bruises

Somewhere back in this thread there was a mention of a woman who went round the world with her family on a cat--she fell overboard.

Didn't say it was impossible to fall off a cat, just requires more effort and application than most people are willing to dedicate. By contrast, falling off a mono is so easy that even a lazy SOB like myself can manage it.

[UpOnStands]

have a look at a video of any mono in winds above 20 knots and non-flat conditions. people in the aft cockpit have very little usable floor space due to the heel and deck motion can be severe.

[StuM]

Originally Posted by donradcliffe

Quick motion = higher acceleration.

No quick motion = more frequent but shorter duration accelerations.

Bruises are more a function of interior design--Ikea interiors = more bruises
Open interiors = more bruises

Bruises are more a function of how long the acceleration lasts and consequently how far you are thrown and your terminal velocity.

Somewhere back in this thread there was a mention of a woman who went round the world with her family on a cat--she fell overboard.

One instance doesn't make a trend

[12BCruzn]

Natalie Wood fell (?) off of a monohull. At anchor, no less. Alcohol could have been a contributing factor of course and there's never a shortage of THAT stuff around. Especially at anchor.

A delivery captain once told me he knew of 5 men who had been lost at sea while urinating off of the ama of trimarans (not all at the same time, btw). . . I started using a bucket after that. . .

[Redreuben]

Is it true they find most bodies lost at sea with their fly undone ?


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[KJThomas]

Originally Posted by Mr B

The Straightsman, Is that the same one that sank in the Yarra in Melbourne with its doors open early,

Originally Posted by 12BCruzn

Natalie Wood fell (?) off of a monohull. At anchor, no less. Alcohol could have been a contributing factor of course and there's never a shortage of THAT stuff around. Especially at anchor.

A delivery captain once told me he knew of 5 men who had been lost at sea while urinating off of the ama of trimarans (not all at the same time, btw). . . I started using a bucket after that. . .

It was a standing joke when I was instructing for Coastguard.
"90% of all males rescued on the water have their flies open".
In other words. "Use the bloody bucket".

Another hazard was spotted while on a sail training ship.
It was standard practice on this ship to get everyone up for calisthenics and a swim at 6.30 when at anchor.
We had all 26 young ladies on board, lined up doing star jumps when a bleary eyed middle aged male climbed out of the cabin of an of an adjacent yacht and started to pee over the stern.
Have you ever seen anyone blush from head to tail.
Especially with two dozen girls wolf whistling and cheering as he retreated inside.

[El Pinguino]

Originally Posted by mikereed100

.......Another consideration is that, for a lot of people, the quick motion of a cat is less likely to cause seasickness, which in turn allows crew to function better when the sea is up.

You never made the trip from Harwich to the Hook and back on one of the 50 knot Stena cats........

Nor made the crossing of Bass Strait on a Seacat...aka 'Vomit Comet'.

Strange they don't run cats across Bass Strait anymore... something to do with not being allowed to operate in seas greater than 4 metres.....

[tp12]

Originally Posted by El Pinguino

You never made the trip from Harwich to the Hook and back on one of the 50 knot Stena cats........

I can't remember the vessel we were on but I have done that trip; when I was racing at Assen. We didn't have any problems.

Originally Posted by El Pinguino

Nor made the crossing of Bass Strait on a Seacat...aka 'Vomit Comet'.

Strange they don't run cats across Bass Strait anymore... something to do with not being allowed to operate in seas greater than 4 metres.....

I've only flown across the Bass Strait but I'd suggest your 4m limitation would be for a specific design of Cat as a Cat could be designed and built for that purpose, just as a mono could.

[hoppy]

Originally Posted by El Pinguino

Y

Nor made the crossing of Bass Strait on a Seacat...aka 'Vomit Comet'.



Strange they don't run cats across Bass Strait anymore... something to do with not being allowed to operate in seas greater than 4 metres.....

I was wondering what happened to it. I did the trip 18 years ago.

Lately I've been seeing one of those cats around the Aegean.

Even with the Meltemi blowing hard I don't think they will have 4m seas to worry about.

I guess as a wave piercing design, sea height is going to be an issue.



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