Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors
  #106  
Old 01-21-2017, 07:02 PM
Emerson White Emerson White is offline
Junior Member
 
Join Date: Aug 2012
Rep: 61 Posts: 94
Location: Nordland, WA, USA
It is a measure, it's not the only measure. Ballast percentage is a measure of weight distribution but there is a huge difference between the COG of a boat with 10 tons of lead in a bulb on the end of a long fin keel and a boat with 10 tons of concrete in the belly below the floorboards.

You can move volume out fore and aft without changing the Cp, but there is a limit to how much you can do that before you start to make the hull really bizarre.
Reply With Quote
  #107  
Old 01-21-2017, 11:38 PM
bscatam bscatam is offline
Junior Member
 
Join Date: Mar 2016
Rep: 16 Posts: 65
Location: Black Sea
For cruising cats Cp = 0,57-0,60 is good. As to weight \structure. I think its OK. At least on my spreadsheet of materials and and equipment weight.
Reply With Quote
  #108  
Old 01-21-2017, 11:41 PM
Emerson White Emerson White is offline
Junior Member
 
Join Date: Aug 2012
Rep: 61 Posts: 94
Location: Nordland, WA, USA
Quote:
Originally Posted by bscatam View Post
For cruising cats Cp = 0,57-0,60 is good. As to weight \structure. I think its OK. At least on my spreadsheet of materials and and equipment weight.
My understanding (which may be flawed) was that cruising cats could get away with a lower Cp because the additional displacement for length made them less tender. If you are designing a lightweight cruising cat this might be something to consider.
Reply With Quote
  #109  
Old 01-22-2017, 12:55 AM
valery gaulin valery gaulin is offline
Junior Member
 
Join Date: Jan 2017
Rep: 7 Posts: 98
Location: Montréal
I am with UpOnStands with explanation. Exactly what i have understood while reading about prismatic coefficient.
Reply With Quote
  #110  
Old 01-22-2017, 02:23 AM
TeddyDiver's Avatar
TeddyDiver TeddyDiver is offline
Gollywobbler
 
Join Date: Dec 2007
Rep: 1650 Posts: 2,506
Location: Finland/Norway
Quote:
Originally Posted by UpOnStands View Post
true, the prismatic coefficient is a very "rough" measure of volume distribution. The maximum immersion cross-sectional area can be placed at the designers pleasure. The general assumption is that its placed close to the center of hull length - but got to give the designers something to play around with
Water-plane coefficient is a better measure what comes to hull form vs pitching IMHO.
Reply With Quote
  #111  
Old 01-22-2017, 02:39 AM
DennisRB's Avatar
DennisRB DennisRB is offline
Senior Member
 
Join Date: Sep 2004
Rep: 228 Posts: 1,232
Location: Brisbane
Quote:
Originally Posted by TeddyDiver View Post
Water-plane coefficient is a better measure what comes to hull form vs pitching IMHO.
Yes well imagine the bows of 2 different but similar hulls with the same Cp. One gains its Cp by having a narrow waterline and deep forefoot, the other hull has wider waterline at the bow (higher water plane coefficient) but shallow forefoot. Both hulls displace the same at the bow, but one gains the displacement by being wide, one by being deep. The narrow one will cut through waves better and likely have a smaller bow wave. But its smaller waterplane will mean its resistance to hobby horsing will be worse. But then again being able to slice through waves will mean less moment to initiate hobbyhorsing to begin with?
Reply With Quote
  #112  
Old 01-22-2017, 02:46 AM
DennisRB's Avatar
DennisRB DennisRB is offline
Senior Member
 
Join Date: Sep 2004
Rep: 228 Posts: 1,232
Location: Brisbane
Quote:
Originally Posted by bscatam View Post
Explaining design futures.
1. Aft helms. General idea is for family cruising cat design with possibility of 2 up to 4 guests on board. So I make deck and cabin space integrated to accommodate 8-10 person. In case of main bulkhead helm it is not possible.
2. Cabin roof slope. Attaching drawing. The aft part of B deck is doubled and raised with 125 mm for cables to achieve wire link between starboard and port steering wheels. I will publish my solution soon.
3. This is a cruising cat so 90% of time is on autopilot.
After seeing the cross section I believe a flat or much flatter roof will be better and doable for the sake of steering cables. Surely such a high windage an FP looking cabin top seems a questionable design compromise just so your planned steering mech works. IMO the steering system needs to be looked at if a huge sloping roof is the concession that needs to be made to accommodate it.

A large flat cabin top will be a nice lounging area with cushions sometimes. I certainly hung out on the flat cabin top of my last cat to enjoy the 360 view with a beer in a beautiful anchorage.
Reply With Quote
  #113  
Old 01-23-2017, 09:04 AM
bscatam bscatam is offline
Junior Member
 
Join Date: Mar 2016
Rep: 16 Posts: 65
Location: Black Sea
Layout.

Layout.
Attached Thumbnails
40 ft cruising cat design. First steps.-taru-j2.jpg  40 ft cruising cat design. First steps.-taru-j3.jpg  
Reply With Quote
  #114  
Old 02-10-2017, 07:27 AM
bscatam bscatam is offline
Junior Member
 
Join Date: Mar 2016
Rep: 16 Posts: 65
Location: Black Sea
Steering

Double steering station setup. Conduit and open wire Combination. Rudder synchronisation with aluminium rod.
Attached Thumbnails
40 ft cruising cat design. First steps.-dss4.jpg  40 ft cruising cat design. First steps.-dss3.jpg  40 ft cruising cat design. First steps.-dss2.jpg  

Reply With Quote
  #115  
Old 02-11-2017, 02:53 AM
UpOnStands UpOnStands is online now
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 290
Location: Sydney
just saw this on the new TAG 50
twin aft helms but the helmsman sits side on - certainly cannot complain about sight lines up the hull sides. Not sure I like the immediate step down to get to the winches.
edit: its likely that the passerelle and swim ladder flip completely over to fill in the gaps while sailing.
Port side passerelle and starboard side swim ladder
They say the rudders are liftable - trying to find more detail.
(originally posted in wrong thread)
Attached Thumbnails
40 ft cruising cat design. First steps.-tag50_catamaran_tag_yachts_sailing_south_africa.jpeg  
Reply With Quote
  #116  
Old 02-23-2017, 04:43 AM
bscatam bscatam is offline
Junior Member
 
Join Date: Mar 2016
Rep: 16 Posts: 65
Location: Black Sea
Steering assembly

Steering assembly left station.
Attached Thumbnails
40 ft cruising cat design. First steps.-sta.jpg  
Reply With Quote


  #117  
Old 04-15-2017, 02:37 AM
bscatam bscatam is offline
Junior Member
 
Join Date: Mar 2016
Rep: 16 Posts: 65
Location: Black Sea
Final design

Final design renderings.
Attached Thumbnails
40 ft cruising cat design. First steps.-nl2.jpg  40 ft cruising cat design. First steps.-np1.jpg  
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Crowther design 226A (42 foot cruising cat) DennisRB Multihulls 14 04-03-2017
02:51 AM 
Help with design first steps? voodoo92 Boat Design 12 05-27-2014
02:21 AM 
22m cruising cat design concept Becaris Multihulls 114 09-07-2009
09:34 AM 
What are the steps to getting a patent on a design? AlaskaFisherman Boat Design 13 07-23-2005
05:02 PM 
Summary of Power & Propeller Design Steps JohnHeart Boat Design 8 07-08-2003
04:01 PM 

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.

All times are GMT -5. The time now is 09:05 AM.


Powered by: vBulletin Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2017 Boat Design Net