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24-08-2008, 00:53
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#1
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Registered User
Join Date: Aug 2008
Posts: 7
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Bridgedeck clearance Leopard
Hi guys, I have been told that the Leopards lack the bridgedeck clearance for comfortable passagemaking and are designed for coastal use. This seems t make sense considering where they are most seen but I was wondering if I could have your opinions / experiences please?
I am considering a 470 for a world cruise.
What is the bridedeck clearance? I am told 7% of the LWL is the minimum and that it should be no less than 70cm.
Also, what is the difference between the clearance at the bow and the stern as the Leopard slopes...?
Thank you!
AM
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24-08-2008, 02:59
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#2
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Marine Service Provider
Join Date: Dec 2006
Location: Brisbane Australia
Boat: Multihulls - cats and Tris
Posts: 4,859
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It is interesting to note that the more recent Leopard 40 designed by morelli and melvin has a much higher bridge deck clearance (around 850-900mm) than other Leopards. A guide to whether a cat has sufficient bridge deck clearance is whether the manufacturer lists it, if they don't then it hasn't.
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24-08-2008, 22:45
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#3
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Registered User
Join Date: Sep 2006
Location: Out of the Office
Posts: 909
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A guide to whether a cat has sufficient bridge deck clearance is whether the manufacturer lists it, if they don't then it hasn't.[/quote]
Love it !!!
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24-08-2008, 22:52
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#4
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cruiser
Join Date: May 2007
Location: Everett, Washington
Posts: 765
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Hear him! Hear him!
Quote:
Originally Posted by DtM
A guide to whether a cat has sufficient bridge deck clearance is whether the manufacturer lists it, if they don't then it hasn't.
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Love it !!! [/quote]
So true, and so true of every statistic, I might add. The so called Fastcat 435, when on its marks according to published figures on Multihull Maven, has the rather high displacement length ratio of 153.5 - a figure you won't find on the Fastcat website! The Outremer 65, to give some perspective, has a D/L ratio fully loaded of 86.5. Smaller D/L = lighter for its size. The Lagoon 67 has a lightship D/L of 82, so if you add, say 12,000 pounds of paylaod, it has a D/L, loaded, of 107. So, the performance of the Fastcat reported by Gludy is no surprise.
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25-08-2008, 03:29
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#5
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cruiser
Join Date: May 2008
Location: Brecon, Wales
Boat: St Francis 50 on order
Posts: 269
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Quote:
So, the performance of the Fastcat reported by Gludy is no surprise.
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Was to me!!
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25-08-2008, 08:42
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#6
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cruiser
Join Date: May 2007
Location: Everett, Washington
Posts: 765
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Quote:
Originally Posted by Gludy
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Hi, Gludy - With a fully loaded D/L of 118, the St. Francis is actually quite a bit lighter than the Fastcat 425 is at 153.5, lighter relative to its size, that is. This is why I do these calculations, because without them, you don't really know what is light or heavy in proportion. Since you and the Admiral wanted a lot of comforts aboard, the only way to get speed is to go up in size, which of course, you did. The lower D/L ratio quantifies this, and predicted faster sailing loaded. You also got a 5 foot longer waterline, and of course, when sailing at speed, the key determinant is the square root of the waterline.
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25-08-2008, 09:16
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#7
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Registered User
Join Date: May 2004
Location: Ontario
Boat: PDQ32
Posts: 265
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Quote ----the key determinant is the square root of the waterline.----
I don't know that the hull speed formula means much with slender hulls - my PDQ32 regularily sails in double digits - sailed 11.4 yesterday in about 17 knots of wind.
Unfortunately with the trend to squeeze in more accomodations the wide hulls do tend to calc out more like a mono.
__________________
henryv
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25-08-2008, 09:17
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#8
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Registered User
Join Date: Oct 2006
Location: Tortola
Posts: 756
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A couple of points: All Leopards are delivered from SA on their own bottoms - this is hardly "coastal"!
Personally, having sailed and delivered yachts for many years now, I find that centi-metric differences in bridge-deck clearance dont make a great deal of odds: if its rough and you are going to windward, you are going to slam anyway. Having said that, there are some slightly more sea-kindly shapes in the under body which dissipate (for want of a better word) the slamming.
Lastly - Big Cat - I always understood that the Square root of water-line length ration to give theoretical hull speed (note; theoretical, not actual!) is not true of catamarans and that they dont have a theoretical - they just go faster with more wind. Tony
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25-08-2008, 09:24
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#9
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Registered User
Join Date: Jun 2006
Posts: 674
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Hull speed is relevent for displacement vessels. Both Catamarans and Monohulls are displacement vessels - to an extent. Once the vessel reaches hull speed, the only way it can go faster is to rise up out of the water - surf. Catamarans do this with relative ease compared to monohulls due to weight.
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25-08-2008, 09:59
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#11
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cruiser
Join Date: May 2007
Location: Everett, Washington
Posts: 765
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Sailing catamarans don't surf
Quote:
Originally Posted by jzk
Hull speed is relevent for displacement vessels. Both Catamarans and Monohulls are displacement vessels - to an extent. Once the vessel reaches hull speed, the only way it can go faster is to rise up out of the water - surf. Catamarans do this with relative ease compared to monohulls due to weight.
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Sailing catamarans do not surf, except for the rare few equipped with hydrofoils. They are displacement vessels. Surfing is like skipping a stone across the water, you are using dynamic lift caused by speed to raise the vessel partly above the surface of the water. Sailing catamarans are fast because they are narrow, and as you might expect, it is easier to push something narrow through the water than it is something wider.
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25-08-2008, 10:09
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#12
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Registered User
Join Date: Aug 2008
Posts: 7
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Thats all good but does anyone out there have first hand experience of the Leopard 470 or know what the clearance is? I cant find the info anywhere!!
Thanks again!
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25-08-2008, 10:49
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#13
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Registered User
Join Date: Jan 2008
Location: Fort Lauderdale, FL
Posts: 310
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BigCat,
If cats don't surf, what do you call the increase in boatspeed speed that follows the cresting of a following sea under your transom?
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25-08-2008, 11:03
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#14
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cruiser
Join Date: May 2008
Location: Brecon, Wales
Boat: St Francis 50 on order
Posts: 269
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Big Cat
Thanks for explaining why the St Francis is so much faster than you know what - the mystery for me is cleared up.I can now see why a light slow cat with a short sharp sea and well over 20 knots of wind and all its sails up needs engine power to even tack! There was not enough speed built up to overcome the braking effect of the sea.
I have only one mystery left to solve .... why each thread turns into the same subject even when i do not raise it!!
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25-08-2008, 11:12
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#15
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cruiser
Join Date: May 2007
Location: Everett, Washington
Posts: 765
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"Surfing" is not surfing
Quote:
Originally Posted by Abaco
BigCat,
If cats don't surf, what do you call the increase in boatspeed speed that follows the cresting of a following sea under your transom?
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Abaco, are you serious, or are you quibbling for sport? It's called surfing, but the phenomenon is not to be confused with planing, which a fast planing power boat does. I have surfed down 25' waves on a 12,000 pound 35' monohull, but I wouldn't say that it was a planing boat. It takes a huge amount of power to make a boat plane. Vessels under sail just can't summon that much power unless they are very, very light, much lighter than any cruising catamaran. See:
http://www.2hulls.com/archive/Gen%20...erplaning.html
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