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Old 17-03-2008, 12:20   #61
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Alan, your "K Factor" would be 3.55, I think. The above is a typo.
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Old 17-03-2008, 12:23   #62
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These links give specifics about PCs for specific multihulls. In the Woods' article, it gives his target, which is .63 for catamarans.

boats.com - Boat Review/Test: Perry Design Review: Contour 44
boats.com - Boat Review/Test: Perry Design Review: Contour 30 MkII
http://www.multihull.com.au/www/pdf/pdfs/vega.pdf
hull shapes
BoatCraft Pacific - Boat Plans and Kits
True Wind 32 Catamaran by True Wind Catamarans
NAUTICALweb - Marchi Virgola 33</TITLE> <!--#set var=
Proa File | Cheap, Capable Cruisers III
Lynx 40
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Old 17-03-2008, 12:49   #63
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"Thanks. 0.65 sounds very high! Bringing the max. waterline width forward brings the hull speed down and adds resistance according to some of the latest thinking as far as I understand." Alan, the PC is the relationship of section areas to the midsection area, and you don't necessarily have to change your waterline to get a higher PC. The center of the area of the waterline on the design shown on my site is 7.4% aft of the center of the waterline, and the widest point of the waterline (more accurately, the center of the widest part of the waterline, as the waterline is parallel for almost 4' at that point,) is farther than .66% aft of station 0.
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Old 17-03-2008, 12:55   #64
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I have posted my thought about the Radical Bay steering problems at New Bi-Rig Performance Cruiser
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Old 17-03-2008, 14:14   #65
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I would describe the Gunboat 62 as having moderate rocker, and no immersion at the bow. See Sailing Magazine : Perry on Design
for a profile drawing. It was designed by: Morrelli & Melvin Inc. They are built by: Multihull Catamaran Sailing Yachts, Luxury Catamarans - Gunboat
Tribe, I think the first of these, can be seen under sail at: UnCut Video - Now Playing "The Fabulous GunBoat 62 Sailboat" More can be read at: Sailing World - The Gunboat 62, Comfort at Speed . So, who volunteers to e-mail Morrelli and Melvin to let them know that they have no clue what they are doing when it comes to catamaran design? Volunteers? Anybody?
The Gunboat 66 has a draught of 2 feet. That doesn't allow for much rocker, even with zero immersion at the bow.
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Old 17-03-2008, 14:27   #66
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How much is lots? How high is the sky?

"The Gunboat 66 has a draught of 2 feet. That doesn't allow for much rocker, even with zero immersion at the bow." How big is big is not the kind of question that lends itself to analysis. This just takes us back to questions of hull form and displacement. It definitely has rocker, and I have described it accurately, I think, as "moderate," in the sense that a few older boats have more (think Chris White designs,) and some very light boats (think Harryproas," have less. I take it you don't want to either eat your words or put down M & M. This would make equivocating your best option--
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Old 17-03-2008, 14:42   #67
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Looking at a profile photo of "Outahia," an Oram 44, I see some rocker. The bow looks maybe 9" deep, and the hull depth looks maybe 18" deep. All the photos of Outahia show the transoms slightly immersed. The transom bottoms look like they are about 18" above the lowest point of the hull. This is why I like to tuck the transoms up, and give them some "v," - I don't trust owners not to overload the boat.
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Old 17-03-2008, 15:09   #68
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Oram, rocker, and displacement

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Looking at a profile photo of "Outahia," an Oram 44, I see some rocker. The bow looks maybe 9" deep, and the hull depth looks maybe 18" deep. All the photos of Outahia show the transoms slightly immersed. The transom bottoms look like they are about 18" above the lowest point of the hull. This is why I like to tuck the transoms up, and give them some "v," - I don't trust owners not to overload the boat.
***** ***** ***** ***** ***** ***** *****
The irony of this is that the design shown on my website, therefore, has less rocker than the Oram 44, if we define the Oram 44 by its average rocker--averaged between 9" forward and 18" aft = 13.5" My design, fully loaded, has 14" of rocker on a 50% longer boat. At a designed displacement of 11464 lbs, no wonder the transom is immersed. Sorry, no toothbrush and toothpaste allowed-they aren't in the schedule of permitted weights. He has assumed a DL of 60. That requires some pretty darn rigorous discipline when putting your stuff on board. A further irony is that the best way to adapt this design to carrying more weight is to keep everything the same, except for increasing its rocker. That is easily done, if the design was made in a computer.
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Old 17-03-2008, 15:12   #69
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I've been on Outahia. The bottoms of the transoms are just at water level. She is heavily loaded - the owners live aboard full time, and have done since she was launched.

If 2 feet over 66 feet is "moderate" then OK, the Gunboat has moderate rocker. Does that make your day for you?
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Old 17-03-2008, 15:19   #70
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***** ***** ***** ***** ***** ***** *****
The irony of this is that the design shown on my website, therefore, has less rocker than the Oram 44, if we define the Oram 44 by its average rocker--averaged between 9" forward and 18" aft = 13.5" My design, fully loaded, has 14" of rocker on a 50% longer boat. At a designed displacement of 11464 lbs, no wonder the transom is immersed. Sorry, no toothbrush and toothpaste allowed-they aren't in the schedule of permitted weights. He has assumed a DL of 60. That requires some pretty darn rigorous discipline when putting your stuff on board. A further irony is that the best way to adapt this design to carrying more weight is to keep everything the same, except for increasing its rocker. That is easily done, if the design was made in a computer.
Yes, I'm sure you know more about Outahia's load carrying ability than her owners do. You've seen some photo's after all. I happen to know the owners and the builder, as well as the designer, but, you've seen some pictures.

Outahia regularly cruises the Kimberly region. You have to be pretty much self sufficient there. They have stayed there for 4 months at a time. When I was aboard they had provisions which they said would "probably last them a year if it had to".

They also carry a quite heavy dinghy, with a decent sized outboard.

But hey, you've seen photos.
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Old 17-03-2008, 15:21   #71
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Red face Go ahead, make my day!

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I've been on Outahia. The bottoms of the transoms are just at water level. She is heavily loaded - the owners live aboard full time, and have done since she was launched. If 2 feet over 66 feet is "moderate" then OK, the Gunboat has moderate rocker. Does that make your day for you?
--Maybe not my whole day.
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Old 17-03-2008, 15:29   #72
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The initial poster brought to mind the John Hitch design "X-IT" which is cruising somewhere - 50 something LOA and a beam WL any lady would be pleased with, NO rocker and head on looks like a "manta ray" lifted above the water... Impressive performance from a very quiet sailor.... some pictures exist on boatdesign.net if a search of X-IT or John Hitch or Hitchhiker rig - my idea of a cruising yacht if you are not (NOT) a hoarder as weight KILLS multihull performance... Googling Michelet-Godzilla will find a site to download that software - it works with Freeship-plus and on win 2000 or lower... both are free to download...

Bob Oram's designs are efficient and use a milti-chine build for below waterline, Bob Oram Design

The only "flat bottomed" cat I know of is "Fallado" & she is for sale at Multimarket - Fallado

Kanga Bartels uses a hull form that is efficient in his displacement powercats, as does Robin Chamberlins recent efforts... "slightly fatter" fersions of the same concept are used by maincats (I think it is) in USA... There are many other designers producing the "slender hulls" concept for cruising sail as well... BE WARNED, in multihulls weight kills the optimum performance the designer has invested lots of effort and research to achieve...
Do you buy a beaut high performance vehicle and put ALL your personal effects in it? - including the ballast left over from your previous mono build project?
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Old 17-03-2008, 15:29   #73
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So, bigcat, what you are really saying is that your design has very little rocker too. It's just that up till now you didn't know about it. Maybe your computer knows what it is doing after all.
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Old 17-03-2008, 15:31   #74
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Gullibile little me!

"I happen to know the owners and the builder, as well as the designer, but, you've seen some pictures." --Sorry, I guess the photos that Oram posted on his website were doctored to make the gullibile believe that the boat was overloaded when it really wasn't. I guess you can take your toothbrush and toothpaste after all, then. I guess that also means that a DL of 60 is really high, after all, as well. Bob Oram Design
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Old 17-03-2008, 15:55   #75
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"I happen to know the owners and the builder, as well as the designer, but, you've seen some pictures." --Sorry, I guess the photos that Oram posted on his website were doctored to make the gullibile believe that the boat was overloaded when it really wasn't. I guess you can take your toothbrush and toothpaste after all, then. I guess that also means that a DL of 60 is really high, after all, as well. Bob Oram Design
And you're basing all of this on some photo's? Wow you really are an expert.

Outahia carries enough gear for her owners to live aboard full time, and to cruise remote areas for extended periods. She has also been through 3 cyclones, been struck by lightning, and run onto a reef. She isn't overloaded. The owners, the builder and the designer don't think so anyway.

I guess they haven't seen the photo's.

Then again, maybe you're just full of ****.
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