Mono vs multihull

[SVNeko]

He only stands back there when he wants to. I'm sure it sails by joystick otherwise.

[ArtM]

Originally Posted by smj

My god that's about the most unseaworthy helm I've ever seen. Is this supposed to be progress?

If you don't like that helm, theres another one right on the other side.

[Southern Star]

I had been avoiding this thread like the plague for fear that it would devolve into an irrational expression of personal bias, but find that it has actually stayed pretty civil. In any event, there were a couple of points that I wanted to address:

Early on Boatman 61 suggests that the cats that flipped were old ones like Catalacs, Iroquois etc., due to the narrow beam. Talbot refers to the warranty that Tom Lack had against raising a hull on his Catalacs and isolates the Iroqouis as it was 'designed by a dinghy sailor'.

Let me start by providing some information about the designer of the Iroquios - J.R. (Rod) Macalpine - Downie. He was not merely a 'dinghy sailor' but rather, was quite possibly the pre-eminent designer of racing and performance cats of his time. Rod's 'Thai Mark 4' won all six races of the 1962 European One of a Kind Regatta. He followed that with 'Lady Helmsman', which won the first IYRU International Catamaran Challenge in 1963; indeed, as I recall his designs went on to win that presitgious cup for seven consecutive years. He was an incredible pioneer in the design of performance cats and his Lady Helmsman included the world's first rotating wing mast. His 'Crossbow' catamarans won 5 consecutive 'Player's Fastest Sailboat' trophies with a top official speed of 41 knots, albeit one was unofficially clocked at at 60 knots in 1984. He and his partner Reginald White also teamed up to produce two hugely successful offshore racing catamarans for Robin Knox-Johnston, including the 70 foot British Oxygen.

The Iroquois was perhaps the first performance cruising cat and its emphasis was decidedly on the performance end of the spectrum: it had relatively light displacement, a fine entry and modified u-sections aft, a relatively high SA/D ratio, boards rather than LAR keels, a relatively high bridgedeck for a 30 foot cat (which in turn raised the Cg and the Ce of the sailplan), and a trampoline forward rather than the solid foredecks in vogue on cruising cats in the 60's.

The resulting boat was very fast indeed - I believe that one may have actually won the Round Britain race in the late 60's. Unfortunately, it was early days for production catamarans and many thought that they could be sailed as hard as self-righting monohulls, or the non-performance oriented Prouts and Catalacs of the same era. Really it is no different than some of the 'modern' performance cats such as Chris White's Atlantic series: while they carry a LOA/BOA ratio of in excess of 50%, their huge SA/D ratio means that they need to be reefed early. A couple of years ago one capsized, in significant part because her crew were flying too much sail for the conditions.

The attack on narrow beam is also a bit simplistic. Yes, the ratio of beam to length is an important factor in reducing capsize. However, there are many others:
1. LWL - just as with a monohull, a cat with a longer waterline will be more roll resistant that a shorter one, all things being equal. It is worth noting that many of the early cats that capsized were much shorter than the typical cruising cat of today.
2. Displacement - just as with a monohull, transverse stability increases with displacement. Again, many of these early cats were not only short (typically, 28 to 34 feet overall), but also had much less displacement than most current cruising cats.
3. A solid foredeck, as was used in most early Prouts and Catalacs, also increases the risk of pitchpoling as it allows seas to break on the deck, with the potential of burying a bow. Furthermore, if a hull is lifted it allows a greater underbody area for winds to catch and continue the roll over into a complete capsize.

In spite of these disadvantages, incredibly few early Prouts and Catalacs capsized or pitchpolled. This is in spite of the fact that they were produced in relatively large numbers (I believe that the Prout brothers alone produced around 1000 cruising cats) and over the decades, many have completed (and continue to complete) successful ocean crossings, etc. Why did neither the Prouts nor Tom Lack ever have to pay out on their warranties against capsize? There are a number of factors that led these boats, in spite of their relatively narrow beams , short LWL's, low displacement and solid foredecks to remain capsize resistant:

1. Cg (center of gravity). A lower Cg increases resistance to capsize and most of the early Prouts and Catalacs had much lower Cg's (due in part to lower bridgedeck clearance) than the current crop of catamarans. It should be kept in mind that beamier cats need increased bridgedeck clearance as tunnel width is a huge factor in slamming: eg., a 12 foot tunnel will allow 50% more water to enter the tunnel and come into contact with the bridgedeck than a boat with an 8 foot tunnel. Furthermore, a narrower tunnel allows a greater 'slick' effect, or shading by the windward bow for entry of seas into the tunnel. Finally, just as a relatively narrow Jeep or off-road vehicle can 'straddle' boulders or surface irregulaties better than a wider one, so too can a narrower tunnel allow a cat a better chance of 'straddling' surface irregularites in the sea.

In the result, a cat with a 50% wider tunnel needs at lest a 50% higher bridgedeck clearance (and many naval architects suggest that as beam exceeds 50%, the actual ratio and not just height increases). Accordingly, the Cg of the vessel also rises up and this reduces transverse stability.

2. Ce (center of effort) of the sailplan: Again, making use of the 'lever principle', a higher Ce for the sailplan increases the risk of capsize. As the bridgedeck gets higher, so too does the sailplan. This problem is compounded in many current cats by the use of flying bridges (eg, the Lagoon 44 and 45) which place the boom itself extremely high off the water. So too, the flat-top mains that are currently in vogue also operate so as to raise the Ce of the sailplan and reduce transverse stability. Compare this with the relatively low rigs on many of the early British Cats (the Iroqouois excepted); consider the 'Prout rig' - a cutter rig that was oriented more fore/aft, rather than up and down and one can immediately see that the Ce of the sailplans was much lower than virtually any current cat.

3. Windage - The greater the windage, the greater the risk of wind or wave assisted capsize. Consider the high, slab sides of the design of most current cats against the earlier Birtish cats (in part in order to gain headroom, as well as because the bridgedecks must be higher) - again, wind and waves from abeam have a greater area (and less aero/hydo dynamic shape) to operate on. This also increases the risk of capsize.

Consider the following: what is more likely to sway side-to side in a cross-wind, or to roll over in a sharp turn, a sports car wih a low center of gravity and an aerodynamic shape, or a bus? Even though the bus is much wider, its higher center of gravity and greater windage due to slab-sidedness and height, all reduce transverse stability. Of course, in a catamaran we must also add the much higher Ce for the sailplan of the new catamarans.

Simply put, to suggest that only older, narrower cats can capsize is incorrect. Furthermore, one must always remember that beam is only one of the factors that relates to lateral stability, or resistance to capsize.

Brad

[ArtM]

Wow great post. I haven't finished reading it yet, but want to thank you for adding some solid factual information to the topic (of course, I'm assuming its true - as is all information posted on the Interwebs)

[Wylieh]

Wow I agree, thanks for the facts, had to read it a couple times but it makes a lot of sence. By the way if u need a hand with that construction let me know depending on timeframe I may be in the area trying to sail, and I wish I new how to sail like I build. Cheers!

[tomfl]

Originally Posted by Southern Star

SNIP
2. Ce (center of effort) of the sailplan: Again, making use of the 'lever principle', a higher Ce for the sailplan increases the risk of capsize. As the bridgedeck gets higher, so too does the sailplan. This problem is compounded in many current cats by the use of flying bridges (eg, the Lagoon 44 and 45) which place the boom itself extremely high off the water. So too, the flat-top mains that are currently in vogue also operate so as to raise the Ce of the sailplan and reduce transverse stability.
SNIP
Brad

I snipped out a lot of what you posted because I agree with it.

But your comment about flat top mains seems to be somewhat of an over simplification. If you follow some of the threads about square tops here and at SA you can find lots of comments along the line of a square top being an automatic first reef because as once the wind pipes up the top of the main opens up and spills the wind naturally.

I have a Seawind with a square top and while I do not pretend to know how to get the most out of it I will say that after even a little experience sailing the boat it is clear the square top can be a real after burner if it is trimmed right, specifically by moving the traveler.

While I have never experienced this I would also posit that a square top would start spilling wind at a lower wind speed than a pin head and give one a clue it is time to put in a real reef. On the other hand a pin head would allow one to proceed with no reef at higher wind speeds. This could become an issue if the wind continued to increase.

As I said I do not pretend to completely understand how to sail a square top, and the number of threads about square tops would lead me to conclude that I am not the only one in this boat. But I would say I am a big square top fan after only limited experience using one.

Bottom line for me is any sail design, no matter where the CE is located can be over powered and it is the responsibility of the skipper to see this does not happen.

[mcarling]

Originally Posted by Wylieh

Thanks Capngeo, I was not aware of that, my wife likes the stable platform of the cat and my kids (3) like the space, but I prefer the grace and speed of a mono. But the roll and sink may have swayed me to go with a cat. Also they have far less draft right?

You like the slow speed of a mono? Ok, to each his own. Yes, multihulls have far less draft than monohulls.

The chances of a catamaran or trimaran capsizing are at most as a high as the chances of a monohull sinking and probably lower. I would rather be at sea with a capsized boat than a sunk boat.

[boatman61]

Hi Brad... was not de-crying the designs in any way... even my tongue in cheek Wharram comment was there to pull legs.. they have/can capsize if I can sail one on a single hull... really gets you hoping your lashings are tight...
Just saying that's how the legends started back then amongst the old salts.. and every pitchpole/capsize is more confirmation in their eyes... to be passed on as 'The Word'..
If I was in that camp no way would I have stepped on a Cat, let alone taken a 40yr old Catalac to Pendik in Turkey from the UK.

But a great Post none the less..

[stevensuf]

Last year - November the 6th to be precise, we were knocked down by a freak mini waterspout squall off the coast of Morocco.

We released the geno sheet (we had less than half the genoa out and no main) and righted the boat,last i saw the wind gauge was 65kn, the wind went from 7kn to 65kn in less than 2 mins and backed over 200 degrees, we suffered very minor damage. The tip of the mast went under water and the wind vane was knocked sideways.

On the same day a french flagged Fountaine Pajot Belize 43 was capsized also off the coast of Morocco, most likely by a similar freak squall all 5 hands on board were lost.

If you go digging, you will find most cats are capsized by freak winds, I never thought it would happen to us, how freak these freak winds are is anyones guess, but i think they are far more common than most people think they are.

If you google loss of s/v anna an atlantic 57 cat, the exact same thing happened to them.

I believe if you sail a cat anywhere there are squalls you must reef very early or go in irons.

I for one , am very glad that day i was on a mono or i would have been another statistic.

[Sabbatical II]

After 15 years of cat experience we are heading north soon in our mono. This model is self righting, won't sink and contrary to what I learned on this thread, she is not at her best wind up her bum. Genuine free offer!

[Wylieh]

Originally Posted by Sabbatical II

After 15 years of cat experience we are heading north soon in our mono. This is a genuine free offer!

Thanks for the offer but I'm allergic to kitty cats.

[Mr B]

My 14 foot cat, Paper Tiger, If I didnt get turfed into the air while sailing it, from submerged bow digging in and pitch poling, there was no wind, I had a float on the top of the mast, (two litre milk container,) it stopped it from going totally upside down, And it was hammering before it flipped. Just a pure fun machine and fast,

The Gemini, Pitch poling, No way I could pitch pole it,
Everything up, Screaming wind, Doing some thing absolutely stupid, Maybe, But I think I would really have to push it, to get it flipping over the bows,

I did nearly roll it over sideways, I had both centre boards down, and the boat turned beam on, (Auto pilot dropped out,)
That was fun, NOT, I was about half way up the side of a wave, Beam on and the Lee centre board dug in, I would say the boat was about 70 degrees, Good thing, I was in the cock pit at the time and just swung the boat down the wave, Saving me,

The Lee side board must be up in bad weather, The windward side down fully, Keeps you on track, and easier on the Auto pilot,

The Gemini is the safest boat I have ever sailed or motored, And I have motored a few,
Sailing is not my Forte, I have always been a motor boat man, In Mono's.

The Gemini is well within your financial bracket, Thats why I bought one,

[nimblemotors]

Now that is a monohull that looks appealing to me.
Or wait, this isn't the "junk all over the cockpit" thread, oh well, facts remain.

Originally Posted by s/v Jedi

[somedayy]

Originally Posted by stevensuf

Last year - November the 6th to be precise, we were knocked down by a freak mini waterspout squall off the coast of Morocco.

We released the geno sheet (we had less than half the genoa out and no main) and righted the boat,last i saw the wind gauge was 65kn, the wind went from 7kn to 65kn in less than 2 mins and backed over 200 degrees, we suffered very minor damage. The tip of the mast went under water and the wind vane was knocked sideways.

On the same day a french flagged Fountaine Pajot Belize 43 was capsized also off the coast of Morocco, most likely by a similar freak squall all 5 hands on board were lost.

If you go digging, you will find most cats are capsized by freak winds, I never thought it would happen to us, how freak these freak winds are is anyones guess, but i think they are far more common than most people think they are.

If you google loss of s/v anna an atlantic 57 cat, the exact same thing happened to them.

I believe if you sail a cat anywhere there are squalls you must reef very early or go in irons.

I for one , am very glad that day i was on a mono or i would have been another statistic.

The same thing happened to me in the Gulf of Mexico, but I was on a 200' steel boat. It was perfectly calm (or close to) and about 5 of us guys were on the back deck securing for the night.(I was a commercial diver) when all the stuff we had hanging at the front of the boat started blowing all over the place. Someone yelled "Hurricane" and we all dove for shelter and something to hold on to. I looked up in time to see a small water spout going down the side of the boat. I hate to think of what would have happened if I was on a small sailboat.