Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors
  #106  
Old 02-26-2017, 10:14 AM
pogo's Avatar
pogo pogo is offline
ingenious dilletante
 
Join Date: Mar 2010
Rep: 73 Posts: 332
Location: Germany Northsea
Quote:
Originally Posted by UpOnStands View Post
you do know that that at a practical level all yacht bows have some radius, can be several cm. The reasons are strength and impact resistance. A knife-edge of fiberglass is extremely weak and very expensive to build.
We sail and walk around marinas and we have touched many stems. Have you?
This is not a criticism, its an acknowledgement that our terminologies may be clashing.
Here is a good example of a modern full bow. The radius is generous at the top of the stem to make fabrication simple and provide more deck space for mounting stays etc. The large radius stem is more draggy on wave impact but the designer feels that the top of the stem hitting water is an extreme event and if that happens the increase in drag will not be the main concern of the sailor. As the stem approaches the water, the radius drops rapidly as water contact becomes more frequent so the extra drag becomes a more important factor determining average boat speed. Designers would sacrifice their mothers to get an extra knot of speed.
I don't agree w. you.
The first frames are above WL always V-shaped. Together with the " modern" vertikal stem ( for a longer WL) this results in a bigger radius at deck level.
Simple 3d geometrie.
Please compare with older yachts with forward raked stem, whole stem has one radius.
http://www.google.de/search?sclient=....0.Kk0OC9cUA7k

Why do mono - and multihulls with vertical stems , x - bows , inverse bows have no bigger radius at deck level ?
Tumblehome hulls , at least the first frames !

http://www.google.de/search?sclient=....0.Kk0OC9cUA7k

See also the latest " Hugo Boss" and wave-piercers.


What do we learn ?
There is a trend towards sharp stems.
Together with the set back masts the seemingly more little volumed sharp bowsections they have a long enough leverage arm to compensate negative trim-angles ( bow bourying ). " Seemingly" , ' cause the volume is hidden in the length.
Those bowsections don' t loose as much speed as a conventional v- shaped bow section when buried.
The v- shaped bow sections answers to a negative trim- angle with progressive increase of volume , of static lift --for the cost of speed - thus more torque for pitchpoling---a brake.
These bows can be seen as " non- sharp bows " .
When waterline comes to deck level , the now negative angled deck ( (flat deck ! ) generates negative lift. one can imagine what happens --see Hobie 16. Brutal pitchpoling.

The other world, the very long tumblehome bow sections , very sharp, nearly wave pearcers. The most drastic boats are " Sodebo" and her sistership "IDEC" , irens design.
Even Under negative trim-angle these boats are going " thru".

.....and IDEC spoke to the ocean:
" Me, I am the sharp , hot knife, you are the butter ."

There is a famous vid of Sodebo nearly pitchpoling after her start to single handed rw record attempt.
Can somebody post it please ?


Note that these radical racer solutions are not for cruising boats . They are impractical , you have a much longer and very narrow bow without a deck.

But, the trend for bows is : be sharp and long.




pogo



P.S
"Sharp" .
I 've an old Joe Jackson LP , 1979 british New Wave --- "Look sharp" . I gonna hear it now.
__________________
Immer handflach Wasser unter`m Schwertschlitz !
Reply With Quote


  #107  
Old 02-26-2017, 04:01 PM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 290
Location: Sydney
Quote:
Originally Posted by pogo View Post
#1 The first frames are above WL always V-shaped. Together with the " modern" vertikal stem ( for a longer WL) this results in a bigger radius at deck level.

#2 Why do mono - and multihulls with vertical stems , x - bows , inverse bows have no bigger radius at deck level ?
Tumblehome hulls , at least the first frames !

#3 There is a trend towards sharp stems.
#4 Together with the set back masts the seemingly more little volumed sharp bowsections they have a long enough leverage arm to compensate negative trim-angles --- etc etc


#5 Note that these radical racer solutions are not for cruising boats . They are impractical , you have a much longer and very narrow bow without a deck.

#6 But, the trend for bows is : be sharp and long.
sorry but you failed to read the thread carefully. OP wanted to know why stems were not deliberately designed to prevent separation/drag, i.e. why aren't they rounded rather than sharp.
Your #1 is contradicted by your #2. Simply, if the designer wants a traditional style bow he uses V frames otherwise not. OP has extensive sailing experience so the rest 3/4/5/6 are true but not answering the OP's question.
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
Rigging a pointy skiff for sail hospadar Sailboats 2 04-13-2011
07:52 PM 
Is there validity to the notion that a pointy stern, a canoe stern, is safer at sea saltydog123 Sailboats 27 04-01-2009
03:20 AM 
Pointy or square stern? hector.r.g Sailboats 8 07-09-2008
06:35 PM 
reverse bows tshino Multihulls 3 04-20-2008
08:20 AM 
Reverese bows SC1 Boat Design 26 06-01-2006
08:36 AM 

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 01:44 PM.


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