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Old 25-09-2009, 21:42   #1
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Speed Statistics of Mono vs Twin Hull Cruisers

Hi,

I've read with great interest the mono vs twin hull thread. The issue of whether cruising cats are indeed faster than cruising monos seems to be contended with no statistics or facts being presented so far.

To shed some light, I pulled the results from the ARC 2008 (from their website) and entered it into Excel and plotted the actual hours used vs length of hull.
The data are not adjusted for use of engine, which averaged 11% of the time. I have just guessed the length of the boats from their names - perhaps it's slightly off in some cases.

Looking at the graph, it seems that cruising cats are slightly quicker than cruising monos, at least on this particular voyage. Are the data representative for long-distance cruising in general? At least the boats should be loaded down with cruising gear, killing the argument that "cats are only faster without load, as soon as you load them down with full cruising gear they slow down to mono speed".

What do you think? Any comments?

(I've included the full dataset if anyone wants to play with it)

Cheers
VikingCat
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Old 26-09-2009, 03:17   #2
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The normal way to assess vessel performance is to calculate it's 'hull speed factor' - that is what multiplier of square root of waterline it sails.

Doing that to this dataset the result is that both multi's and monos acheived exactly the same - averaged 1.27 times sq rt of waterline. To do that calcualtion I made some some average assumptions about waterline length because monos tend to have longer overhangs than multis.

So, I would have said the conclusion from this data is the two designs sailed pretty much the same speed (liven their length), within the data quality we have.

A second conclusion would be that these boats in the ARC are pushed harder (about 20% harder), normally with more crew, than typical cruising boats. When we have looked at average speed factors for typical hunsband and wife crews doing non-arc passages we typically find they sail at around 80% of 'hull speed' (or a speed factor of about 1.1).
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Old 26-09-2009, 03:33   #3
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Greetings and welcome aboard the CF, VikingCat.

Interesting study.

I wonder what happens when you compare two equal “value” (cost, rather than length) boats?
When selecting a new (to me) boat, I’m more likely to be constrained by some minimum size, and some maximum cost, rather than by a maximum length.
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Old 26-09-2009, 04:38   #4
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Nice work
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Old 26-09-2009, 04:51   #5
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Having done the ARC myself in 2002 and being loosely associated with the organising company for nearly 10 years I can say that Evan's suggestion that ARC boats are pushed harder is correct. I worked on averaging 6.5 knots over the course and achieved that (actually we averaged 7.1 but sailed 200 miles more than the rhumb line) In cruising mode my wife and I work on 5 knots as we sail very conservatvely when just the two of us are aboard.

Going back to the ARC though... Yes, most boats are pushed harder. But, there are a large number of fast, cruising monohulls amongst the fleet... Swans, Oysters and the fast versions of volume production boats. The catamarans are mainly out and out cruising catamarans and even condomarans so there performance is perhaps more impressive.

Incidentally, ARC2008 was the slowest for many years due to lighter than normal winds.
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Old 26-09-2009, 05:48   #6
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The comfort or liveablity of each was not included. I don't care too much how long a crossing takes when it is liveable. Of course it was not in the question, so one day a thread on that subject could be started.
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Old 26-09-2009, 07:47   #7
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Quote:
Originally Posted by GordMay View Post

I wonder what happens when you compare two equal “value” (cost, rather than length) boats?
.
Damn you, Gordy! I was just about to say that!

A 40 foot new Cat is worth a hell of a lot more than a new 40 foot mono.

A Lagoon 44 is DOUBLE the cost ofa new Beneteau 54

(Both are made by the same company)


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Old 26-09-2009, 07:59   #8
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A 40 foot new Cat is worth a hell of a lot more than a new 40 foot mono.
Sure is.

But Of course the comparison is a little strange - MY 35 foot cat has more space than a 40 foot mono. Indeed for what I paid for my cat (new) I could have bought a new 40 foot dodgy french mono or a new 40 foot yank mono - roughly - with the same options etc. Give or take $10K
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Old 26-09-2009, 08:01   #9
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It cost about the same to make a Malibu as it does a Corvette. Because it is desirable to own, and not as many made. The Vette cost is many times the Malibu. Supply, and demand comes into play........i2f
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Old 26-09-2009, 08:34   #10
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Greetings and welcome aboard the CF, VikingCat.

Interesting study.

I wonder what happens when you compare two equal “value” (cost, rather than length) boats?
LOL, come on Gordo .. that's cheating
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Old 26-09-2009, 08:56   #11
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I've owned both a 26 foot monohull and 26 foot trimaran pocket cruisers. With out a doubt, the tri was faster in flat conditions. However, this was reversed once there were any seas due to under deck slamming.

If you can reach hull speed, I think the hull speed formula is helpful: Max hull speed equals the K value for that hull(s) times the square root of the water line length. An average K value for a monohull might be something like 1.4 where as for a multi it's likely to be over 2. Of course, adding weight to a norrower hull will submerge more of it, thus usually decreasing the K value more for a multi-hull than monohull.
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Old 26-09-2009, 16:34   #12
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Well, I would chose a cat for the easy route anyway - think COMFORT.

Then, ARC is a downwind ride and downwind crossings tend to have too little wind rather than too much - this is true at least for the Atlantic crossing (Canary to West Indies) and the Pacific one (Panama to Aus).

The potential max speed of the design does not really matter - what matters is how easy it is for a specific design to achieve good speeds in light downwind situations. And nothing beats a cat in light conditions downwind. One could only argue that a Class 40 (or an Open 40) is just as fast. Yes, it is. But do not try to live in one.

I asked dozens of cruisers over 6 years and 3 oceans on how much time their passages took them and the cats always came on top, length per length.

BTW If you want to banish me to Jan Mayen for my glorifying of cats, then PLS send me there in a MONO ! ;-)))

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Old 26-09-2009, 17:28   #13
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Quoting GordMay
"I wonder what happens when you compare two equal “value” (cost, rather than length) boats?"
Assessing value as more than just the cost?
Crewing with two while accommodating six. Changing sails single handed. NOT being laid flat or rolled over. Not sleeping in the cellar. Dry clothes. Not replacing crockery.
These things add up.
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Old 26-09-2009, 18:27   #14
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I'm just thinking that perhaps there needs to be some sort of qualitative formula such as Speed x Comfort X Reliability X Safety X Quality/ Cost = X. Whichever X number comes out higher is the better boat.
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Old 26-09-2009, 19:13   #15
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Quote:
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... Speed x Comfort X Reliability X Safety X Quality/ Cost = X. Whichever X number comes out higher is the better boat.
I would love to see the day when boats stop being seen as vessels traveling through the rarefied space of relative factors and start (once more) being taken for what they are - sailing vessels. And this 'sailing' thing is probably the first factor we should put into any (serious or only half so) equation.

So - whatever the god of moderation suggested, PLUS "divided by the body of water that is to be sailed in the craft".

Deal?

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