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Old 30-09-2009, 20:45   #31
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Seems to me in looking at the graph, that a 40 foot multi is about as fast as a 50 foot mono. That's about right - a typical 40 foot cat will be as "big" as a typical 50 foot mono.

Let's keep the mono vs. multi discussion out of this - it really IS religion. And we got ours on a Belize charter...
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Old 30-09-2009, 22:33   #32
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We are a 64' mono and do about the same speed as a 47' cat with wind under 20-22 kts (talking about cruising designs, no race monsters). A 42' cat is always slower and a 50' cat is always faster so that 47' looks reliable. We are a fast mono and I have absolutely no problems with cats of my size being faster, why would I? So I find it hard to believe that mono-cruisers that are slower than me have a problem with that fact, it seems a bit foolish to me to argue about it.
For us, the fun starts at 25+ knots when we come up and plane, while the cat doesn't have sufficient underwater flat surface area for planing.

But, with smaller boats, the weight factor for a cat becomes harder to deal with because the smaller cat has less weight carrying ability while most cruisers want to bring the same amount of "stuff" regardless of boat length. The smaller mono isn't hit as hard with a weight penalty and that changes things. This is why I think a cat for full time live aboard cruisers should be 40' and up. All the 30-38' cats with liveaboard cruisers we meet are bogged down by the weight they carry and they are happy to admit that and have no problem with it. Why would they, they choose to trade some speed for having more of their "stuff" aboard.

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Old 30-09-2009, 22:43   #33
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I think I have too much time on my hands. I examined the statistical relationship between hull length and actual hours. Here's what I found based on the data provided. There are only 12 multihulls, which is statistically too small a sample to draw firm conclusions. There are 142 monohulls, so my conclusions are much more robust. There seems to be a relationship between hours and length. It appears much stronger for monohulls than multihulls. Here is a plot of the expected hours predicted as a function of length:



There is an inverse relationship between hours and length for monohulls. Length explains about 28% of the variability in time for monohulls, but only about 4% for multihulls. Again, the multihull sample is too small to trust these numbers.

Overall, this makes sense. Hull form, sail plan and skipper all factor into the vessel's speed. The multihulls are skewed because 1/4 of the boats are Lagoon 420's, which are quite slow. What I found particularly telling is that length only accounted for about 28% of the variability in time for monohulls. The hull speed formula based on LWL means less than I thought!

Brett
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Old 30-09-2009, 23:39   #34
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Brett,

If you have any time left for this, you should plot the average of the actual samples. I think it will be close to the plotted prediction.

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Old 01-10-2009, 01:37   #35
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. I examined the statistical relationship between hull length and actual hours.
Brett

Great work Brett!!!!!!!!!

I didn't read he earlier posts re hull speed of cats because I don't belive they conform to hull speed as we know it.

Also there are very few racing monohulls being cruised, but there are a large number of cat owners whose boats are kept very light and of a more strong racing pedegree.

So few 38 foot monohuls would beat a 50 foot montohull. However there are a lot of 38 foot multihulls that would easily beat 50 foot cats. Take a lagoon 44 for example which is definitly a cruising bot against a light racing cat going downwind.

A light cat would plane in 15 kts up the bum where a 44 would not.

With monos there would be none or very few that would plane.

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Old 01-10-2009, 14:06   #36
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Sorry this interesting thread got hijacked by mono/multi again. But there is some interesting stuff in here.
1. The slenderness of a cat hull, when greater than 8 or 10? generates such a small bow wave that the stern doesn't squat so the boat doesn't run uphill.
2. Wetted area is inevitably greater on a multi so light wind peformance depends on huge extra sails, but they fly easier of two bows? I've not tried yet.
3. Cruising cats are not fitted out to drive well into wind, the genoa travellers are often too far apart, the keel arrangements are not designed to work well as boat speed falls off a bit so they slip and generate drag if water speed isn't kept up.
3b. Racing cats with daggerboards are not the same animal and maybe this accounts for the big spread seen on the graph above.
3c. Cats often have lifting or free-sailing prop arrangements, more so than mono's?
4. Cruising Cats are designed, built and fitted to do fairly well in moderate conditions. Most mono's are built with more of a mind toward racing, even within their own class/type. Not many ocean kindly mono's enter races.
5. Modern mono's with broad sterns (most unladylike) plane more readily at the cost of pitching more aggressively, that's something we cats have to learn to live with.
6. A cat, when over pressed, pitch poles, a mono falls sideways and pops back up (usually).
Load Carrying? My 4.5t cat will carry well over a ton when cruising. Enough surely!
They are different animals, race horses don't pull carts.
I grant that mono's are much more fun until it's time to get cooking.
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Old 01-10-2009, 14:57   #37
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Great work Brett!!!!!!!!!


A light cat would plane in 15 kts up the bum where a 44 would not.

With monos there would be none or very few that would plane.

Mark
I used to think that, but I've since found out it's incorrect. The Edmond Bruce study found that boats with slender enough hulls can greatly exceed hull speed without planing.

I posted the "Banque Populaire" video to demonstrate that - the boat was nearly quadrupling hull speed but wasn't planing.

On this site: Allura Marine | Welcome there's a short video of a power cat going at around 3 times it's theoretical hull speed, but very clearly not planing.

In general cruising cats don't plane, even though many of them can do much better than theoretical hull speed.
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Old 01-10-2009, 15:10   #38
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Great work Brett!!!!!!!!!

I didn't read he earlier posts re hull speed of cats because I don't belive they conform to hull speed as we know it.

Also there are very few racing monohulls being cruised, but there are a large number of cat owners whose boats are kept very light and of a more strong racing pedegree.

I disagree. I've seen quite a few ex-racing monohulls turned into cruising boats. I think most ex-racing mono's eventually end up being used as cruising boats.

Multihulls designed for racing aren't anywhere near as suitable to be used for cruising. Most have no bridgedeck, and extremely narrow hulls.

The multi's in the ARC would almost certainly be cruising boats, although some may be performance oriented cruisiers.
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Old 01-10-2009, 15:21   #39
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I disagree. I've seen quite a few ex-racing monohulls turned into cruising boats. .
Really? I've seen very few less than 10% of monohulls, prolly betwwen 5% and 10%. Must be the different areas we sail in. Look at cruiser-cruisers not lolipop boys in Chesapeake bay. Here, where I am there is 1 ex-racing boat out of 65. (and only 4 cats)

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greatly exceed hull speed without planing.

.
I wasn't using a planing as a technical word. I mean go faster than hull speed.
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Old 01-10-2009, 15:29   #40
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Really? I've seen very few less than 10% of monohulls, prolly betwwen 5% and 10%. Must be the different areas we sail in. Look at cruiser-cruisers not lolipop boys in Chesapeake bay. Here, where I am there is 1 ex-racing boat out of 65. (and only 4 cats)

But how many mono's are actually built as racers vs how many built as cruisers? Possibly somewhere between 5% and 10%. So it's likely a high proportion of racing mono's end their lives being cruised.

IMO purpose built racing cats are far less likely to end up being cruised. And any that are would need a lot of modification.
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Old 01-10-2009, 15:30   #41
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I agree with "cruisingcat". I've never seen a planing cat. It's their hull speed that is so much higher while many use the "general" formula for calculating hull speed with that 1.34 or so multiplication factor. However, that factor differs with the design of the hull.

Also, when someone (Mark I think?) writes "light cat" I am assuming we're talking about a racer? Even those don't plane afaik. And mono's don't plane? Every modern mono racer planes!

Eleven: your point #5 is correct. We pitch more than a 64' non-planing mono design. It's acceptable because our waterline length (also 64') reduces it again.

But load carrying: what's a ton, not much! I can carry 1,000 US gallons water+diesel which is 3.5 tons right there! If you have a 300 liter water tank and a 200 liter diesel tank, you're halfway that ton already. Two crew and that's another 150 kilo's, leaving 350 kilo's for "stuff". Next is the dinghy + outboard and you haven't got much left for bottles of rum or clothes! ;-)

I also think Prout is one of few cats that lift a central prop out of the water. This whole setup is what makes the Prout so hard to turn under power, even with the rotating "tail" and why most cats have 2 engines and 2 always submerged props.

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Old 01-10-2009, 21:43   #42
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"racing" catamarans

I can't really think of any catamaran manufacturer that produces a catamaran for racing in sizes above 30 ft. The faster boats, Outremer, Gunboat, Catana, Shuttleworth, Chris White all have what you would need for cruising, enclosed heads, designated well appointed galleys, seperate cabins for sleeping, but granted some have more spartan finishes. So pretty much all of the bigger catamarans are made for cruising. Versus say a purebread racing monohull such as a Farr 40 which down below is basically a hollow shell.
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Old 02-10-2009, 00:23   #43
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Trying to have a discussion anything to do with cats on this forums is like banging ones head against a wall.
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Old 02-10-2009, 00:44   #44
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Not wishing to fuel any mono v multi argument as I like all boats, but we did the ARC in 2007.
Three handed, loaded down in cruising division. There were at least 15 cats in the entry list, at least same length as us if not longer.
Not one of them arrived even close to our time.
IMHO the general rule that monos go uphill and downhill a little quicker, multis reach a lot quicker, is still a valid statement.
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Old 02-10-2009, 04:03   #45
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I agree with Swagman, insomuch as most of the cats we see are the standard production cats from the big companies like Lagoon, FP, R&C etc. These boats are nearly always way too heavy and under rigged for safety reasons. Many if not most end up in the charter business, and all the builders know that just a single flip/pitchpole will cost them business.

FP stopped the production of their probably best performing boat, the Maldives after one or 2 pitchpoled, not because there wasn't a market for them.

I have a FP Tobago 35, and monos of comparable length would go faster than us on anything but a reach in decent winds (>10-12 knots).
After adding about 25% area to the mainsail, and a taller rotating wing mast, I can now keep up with the good monos from around 8-10 knots TWS on all points of sail. (With comparable sails set) I can now point just as high, but have probably 10 degrees more leeway when hard on the wind.

Above 16-18 knots TWS we are faster from around 45 degrees relative.

The heavier cats will do between 50% and 50% plus 10% of TWS in winds up to a bit over 20 knots if they also use a spinnaker of some sort.

The goos monos will get up to 15% above theoretical hull speed off the wind. Something like an X-yacht for example.

Depending on wind speed and direction on a long distance cruise, I would think that cats and mono would be around the same speed, if sailed by the same crew.
The comfort factor will always have the cat ahead of the mono.

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