Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors
  #136  
Old 01-29-2017, 01:44 PM
pogo's Avatar
pogo pogo is offline
ingenious dilletante
 
Join Date: Mar 2010
Rep: 73 Posts: 332
Location: Germany Northsea
Quote:
Originally Posted by Doug Lord View Post
Thanks, Pogo. I was wondering if it had been tried as a bridgedeck board on a cat. It's been used on many monohulls.
It has been tried with success, but
The centerboard of " shambala" is not gybing, it' s an articulating centerboard ( up to 10 degrees) , see link in post 128.

pogo
__________________
Immer handflach Wasser unter`m Schwertschlitz !
Reply With Quote
  #137  
Old 01-29-2017, 04:48 PM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 283
Location: Sydney
Shambala may not have the traditional gybing dagger board but the basic intent is the same I believe -- alter the submerged thrust line to make better speed to windward.
Reply With Quote
  #138  
Old 01-29-2017, 05:35 PM
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
Shambala may not have the traditional gybing dagger board but the basic intent is the same I believe -- alter the submerged thrust line to make better speed to windward.

Yepp, u got it.......nearly.
Shambala's centerboard additionally can be tilted forward for sailing upwind under genoa or stormjib only.

pogo
__________________
Immer handflach Wasser unter`m Schwertschlitz !
Reply With Quote
  #139  
Old 01-29-2017, 07:43 PM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 283
Location: Sydney
As you said in your first mention - complicated.
Reply With Quote
  #140  
Old 01-29-2017, 10:00 PM
brian eiland's Avatar
brian eiland brian eiland is offline
Senior Member
 
Join Date: Jun 2002
Rep: 1903 Posts: 4,654
Location: St Augustine Fl, Thailand
...just happened across this reference to a rather old vessel that appears to make use of some centerboards on the centerline of the vessel....


Quote:
Originally Posted by brian eiland View Post
Does that 'double hull boat' here appear to have boards on the center line ?



Last edited by brian eiland : 01-30-2017 at 06:15 AM. Reason: should have included the previous page of text from that old article
Reply With Quote
  #141  
Old 01-29-2017, 10:13 PM
brian eiland's Avatar
brian eiland brian eiland is offline
Senior Member
 
Join Date: Jun 2002
Rep: 1903 Posts: 4,654
Location: St Augustine Fl, Thailand
Quote:
Originally Posted by pogo View Post
It does, see Dufour T7 , prototype third place Minitransat 1979.

http://www.maritime-identity.com/het-midzwaard/


pogo
Can this be translated also?
I'm having trouble understanding how the pivot shaft can be operating in two plains of action??
Reply With Quote
  #142  
Old 01-29-2017, 11:08 PM
brian eiland's Avatar
brian eiland brian eiland is offline
Senior Member
 
Join Date: Jun 2002
Rep: 1903 Posts: 4,654
Location: St Augustine Fl, Thailand
Retractable Centerboard

If I were to go back to the conventional idea of a centerboard trunk in each hull. I might give this idea some consideration as it lessens the drag of those slots in the bottoms of the hulls.


What about adapting something like this arrangement to that flat plate nacelle structure of mine...just brainstorming

Nah, ...its worth more effort to make the centerline bridgedeck option work.
Reply With Quote
  #143  
Old 01-30-2017, 12:14 AM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 283
Location: Sydney
how's this? the brown stuff is not the water level
the red sealing strip is hinged to the back edge of the board and is wider than the slot opening
Attached Thumbnails
Bridgedeck centreboard why don't they work???-screen-shot-2017-01-30-3.02.55-pm.jpg  Bridgedeck centreboard why don't they work???-screen-shot-2017-01-30-3.03.11-pm.jpg  Bridgedeck centreboard why don't they work???-screen-shot-2017-01-30-3.04.20-pm.jpg  

Bridgedeck centreboard why don't they work???-screen-shot-2017-01-30-3.05.27-pm.jpg  Bridgedeck centreboard why don't they work???-screen-shot-2017-01-30-3.06.54-pm.jpg  
Reply With Quote
  #144  
Old 01-30-2017, 06:19 AM
brian eiland's Avatar
brian eiland brian eiland is offline
Senior Member
 
Join Date: Jun 2002
Rep: 1903 Posts: 4,654
Location: St Augustine Fl, Thailand
Quote:
Originally Posted by UpOnStands View Post
how's this? the brown stuff is not the water level
the red sealing strip is hinged to the back edge of the board and is wider than the slot opening
Is that meant to be a hull mounted CB?

And if the 'closing strip' is "wider than the slot opening", how does it ever get up into the slot with the board in its up position?
Reply With Quote
  #145  
Old 01-30-2017, 06:47 AM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 283
Location: Sydney
the closing strip works only when the board is down.
basically when the board is up its front face projects slightly below the bottom of the hull which provides sealing of about 70%. Fore and aft of the board there are matching skegs, not an LAR but more of a beaching strip.
But boards are not on my list and most definitely not centerboards in the hulls.
Reply With Quote
  #146  
Old 01-30-2017, 09:34 AM
Angélique's Avatar
Angélique Angélique is offline
aka Angel (only by name)
 
Join Date: Feb 2009
Rep: 1632 Posts: 1,382
Location: Belgium
-
Quote:
Originally Posted by brian eiland View Post
Retractable Centerboard
If I were to go back to the conventional idea of a centerboard trunk in each hull. I might give this idea some consideration as it lessens the drag of those slots in the bottoms of the hulls.
What about adapting something like this arrangement to that flat plate nacelle structure of mine...just brainstorming

Nah, ...its worth more effort to make the centerline bridgedeck option work.
From post #4 of the thread Very Old Catamaran Plan C 1895:

Quote:
Originally Posted by Angélique View Post

Some more info of the year 1900 and older: _ A Manual of Yacht and Boat Sailing
See also Page 457 (457) (of 667 pages total) in the above linked book of the year 1900....

Quote:
__________________
Angélique
Reply With Quote
  #147  
Old 01-30-2017, 04:20 PM
Mulkari Mulkari is offline
Junior Member
 
Join Date: Jan 2012
Rep: 10 Posts: 24
Location: Latvia
Quote:
Originally Posted by Tom.151 View Post
Brilliant boat! Truly an inspiration of simplification.

Would love to see more pics of the boat - especially out of the water hull shapes, and the rudder arrangements, and more of the centerboard ..



?? Are the 90 degs and the 80 degs accidentally reversed here ??

Anyway, thanks for posting so we could see a bit of a tease of the centerboard details.

Excellent!
Cheers,
I will try to post more details when I get to my other computer. The whole system is very simple centerboard is made from wood with fiberglass glued over. It is mounted between two stainless steel plates with reinforcment ribs. Whole assembly is bolted to mast beam. Hinge on which board pivots also holds side stays keeping board vertical against side loads and also helps resist bending loads coming from mast.

Hull shape is conventional with V shaped front section, semicircular middle and aft. Rudders are kick up attached to transom like on most beachcats.

By 80 and 90 degree angles I meant angle between tacks shown on GPS track basically if you are tacking while sailing upwind good boat should make 90 degree angle when beating upwind. 45 degree on starboard tack and 45 degree on port tack.

Quote:
Would you mind sharing details/sketches of your centerboard?

Is the catamaran design yours or someone else's? (Wood's Skua?) I'm curious what the hull is made of? The other catamaran that you have a video of (https://vimeo.com/104815976) appears to have a very thick hull, maybe of foam? Finally, on the outboard ends of the pole that connects the two tillers there appears to be two horizontal rods, one at each end. (From 0:30 to 0:45) I'm scratching my head trying to figure out what they are for?
Reply With Quote
I will try to post some sketch. Design is custom made by me with help from another Latvian multihull builder. Hulls are foam sandwich construction.

The green cat in another video is my first boat built 11 years ago. Hulls are carved from insulation foam then cowered with fiberglass that's why they are so thick.

The horizontal rods attached to pipe connecting tillers are extensions to make steering easier when sitting on the side seats.

Quote:
Thanks for your posting.

I do have a question however. In the video it appears as though there is a forward and aft 'stay' to the blade that attaches below the waterline. Is that so, and if so how does it kick-up??
The red line is to pull the board down and hold it in position. It is stretchy enough so it usually don't break if the board hits bottom. The white line going aft is for raising the board and also prevents the board from pivoting forward.

Quote:
Of course a surface piercing board will work----but it will be very inefficient .
See the turbulent wake it makes in the video, at the 40 second mark,
Also, as has already been mentioned, the bending stresses on the board and the extra weight of the structure to hold it, must be addressed. The lesson of "Occams razor and the Gordian knot" comes to mind.
It is good enough for cruising and only easy way how to make board that kicks up on impact. I sail a lot in Estonian islands where water over large areas is only 2 - 4 meters deep with large boulders hiding just below the surface. If you go off the marked channels sooner or later you will hit something. I gladly trade half a knot or so of speed for a board that don't break in half or rupture a hull in serious impact.

The support structure to hold the board weighs around 8 - 10 kg. I doubt the slots and all the reinforcments to mount daggerboards into hulls would be much lighter.
Reply With Quote
  #148  
Old 01-30-2017, 05:40 PM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 283
Location: Sydney
Very nicely engineered, particularly attaching the side stays to the board pivot pin.
resolves a lot of the stresses.
Did you design the rigging arrangement to make the centerboard match the mast?
Most catamarans have the daggerboards forward of the mast but the key point on your arrangement is the centerboard can mount on and stiffen the mast beam.
Reply With Quote
  #149  
Old 01-30-2017, 08:04 PM
UpOnStands UpOnStands is offline
Senior Member
 
Join Date: Nov 2015
Rep: 16 Posts: 283
Location: Sydney
For general comment.
To minimize intrusion of the centerboard into the bridge deck, how negative would it be to trail the board as shown here?
The board (orange) is in the up position -- no support structure shown.
Getting a little more interested in the idea -- but.
Attached Thumbnails
Bridgedeck centreboard why don't they work???-screen-shot-2017-01-31-11.00.46-am.jpg  
Reply With Quote


  #150  
Old 01-30-2017, 09:22 PM
brian eiland's Avatar
brian eiland brian eiland is offline
Senior Member
 
Join Date: Jun 2002
Rep: 1903 Posts: 4,654
Location: St Augustine Fl, Thailand
Quote:
Originally Posted by UpOnStands View Post
the closing strip works only when the board is down.
basically when the board is up its front face projects slightly below the bottom of the hull which provides sealing of about 70%. Fore and aft of the board there are matching skegs, not an LAR but more of a beaching strip.
But boards are not on my list and most definitely not centerboards in the hulls.
There may be a misunderstand here, and if so excuse me.

I think you said the 'closing strip' is on the back side of the board,...and I believe this is the side of the board that has to come up fully into the CB trunk/slot. If it is wider than the slot/trunk, then how does it get up there?

There have been MANY slot closure ideas experimented with in past years. Most were not to successful due to their vulnerability to damage.

And cleaning the slot/trunk and the CB itself during out of the water maintenance is just another reason I chose to mount my central board(s) in such a manner that they are always retracted from the water doing non-sailing times (thus stay clean, and very productive).

And the maintenance on the control lines is easily accessible. (unlike hull mounted CB's)

And they kick-up (automatically if so desired) when striking an object or the bottom, unlike daggers.
__________________
RunningTideYachts.com
Distinctive Expedition Yachts
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
Bridgedeck Clearance nickvonw Multihulls 11 07-30-2011
10:32 AM 
Best shape for bridgedeck? Alex.A Multihulls 8 03-31-2010
05:52 AM 
FJ centreboard susho Fiberglass and Composite Boat Building 0 10-04-2007
12:00 PM 
Centreboard optimisation abindoff Boat Design 11 03-26-2006
09:15 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 02:17 AM.


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