Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 04-07-2013, 21:30   #76
cruiser

Join Date: Sep 2011
Posts: 267
Re: Rocna Repositioned

Jonathan wrote;
My pontifications tend to be on the basis of a regular seabed type with an even composition that will increase in density with depth. Certainly as the anchor dives the increased density of the seabed will decrease the ability of an anchor to dive (and this, with the increased resistance of the chain will contribute to how deep it goes before bottoming out). Any resistance to diving, thick shank, thick fluke etc will discourage deeper diving (which is why we have thin shanks compared to those beefy shanks of the original CQRs and Danforths).

What the chain does is lift the end of the shank (toward the top of the seabed) allowing the fluke to become horizontal. Without this upward force from the chain as it angles further from the horizontal the anchor would just go down and down as the load is increased (until load and seabed resistance are in balance

Jonathan you are absolutely spot on with your analyses, many times we dig to check anchors entry angle, once the chain is equalizing the drag resistance of an anchor, the anchor will adopt more of a horizontal position with less diving angle, if you go from chain to cable the anchor will dig deeper (less Rhode surface competing against the anchors diving angle) before levelling out.


Oh and Noelex, your hat design was no less than what I would have expected to suit you.


Regards Rex.
congo is offline   Reply With Quote
Old 05-07-2013, 00:22   #77
Registered User

Join Date: Aug 2012
Boat: none
Posts: 87
Re: Rocna Repositioned

Have to agree with the roll bar theory,i tend to think it was a good marketing gimmick to differenciate a new anchor design.
I originally had a 60lb delta as a primary and a 60 lb Manson Supreme as a secondary as the delta had worked well on a previous boat,but I found it slowly dragged it self in very soft mud,but when I tried the Manson in the same ground it stuck like glue, so I sold the delta and bought a 80lb Manson as my new primary.
Only problem was the hoop prevented it from lodging properly in my anchor rollers under the catwalk,so I cut off the hoop, AND guess what it didn't make a damn difference,it has never not set even in a change of tide,i even dived on it while some one dropped it on the bottom and it always fell on its side and dug in straight away because of the weight at the tip,having the bar would have made no difference to its performance whatso ever. BAN THE BAR>
cruiz9 is offline   Reply With Quote
Old 05-07-2013, 06:45   #78
Registered User
 
endoftheroad's Avatar

Join Date: Dec 2008
Location: Key West
Boat: Westsail 32 and Herreshoff 28
Posts: 1,161
Thorcat,
So what then is your take on the Boss?
endoftheroad is offline   Reply With Quote
Old 05-07-2013, 07:36   #79
Registered User
 
Delfin's Avatar

Join Date: Aug 2010
Location: Anacortes, WA
Boat: 55' Romsdal
Posts: 2,103
Re: Rocna Repositioned

Quote:
Originally Posted by thorcat View Post
Have to agree with the roll bar theory,i tend to think it was a good marketing gimmick to differenciate a new anchor design.
I originally had a 60lb delta as a primary and a 60 lb Manson Supreme as a secondary as the delta had worked well on a previous boat,but I found it slowly dragged it self in very soft mud,but when I tried the Manson in the same ground it stuck like glue, so I sold the delta and bought a 80lb Manson as my new primary.
Only problem was the hoop prevented it from lodging properly in my anchor rollers under the catwalk,so I cut off the hoop, AND guess what it didn't make a damn difference,it has never not set even in a change of tide,i even dived on it while some one dropped it on the bottom and it always fell on its side and dug in straight away because of the weight at the tip,having the bar would have made no difference to its performance whatso ever. BAN THE BAR>
That is interesting. I believe you, but Scout's honor, it works as well without the hoop?

Comments, others?
__________________
https://delfin.talkspot.com
I can picture in my head a world without war, a world without hate. And I can picture us attacking that world, because they'd never expect it. - Jack Handey
Delfin is offline   Reply With Quote
Old 05-07-2013, 08:11   #80
Registered User

Join Date: Aug 2012
Boat: none
Posts: 87
Re: Rocna Repositioned

Quote:
Originally Posted by endoftheroad View Post
Thorcat,
So what then is your take on the Boss?
Wasn't aware of the Boss anchor until I just googled it,but I guess it just proves the point, the Bar isn't required.
cruiz9 is offline   Reply With Quote
Old 05-07-2013, 08:32   #81
Registered User
 
Delfin's Avatar

Join Date: Aug 2010
Location: Anacortes, WA
Boat: 55' Romsdal
Posts: 2,103
Re: Rocna Repositioned

Quote:
Originally Posted by thorcat View Post
Wasn't aware of the Boss anchor until I just googled it,but I guess it just proves the point, the Bar isn't required.
I always suspected that the Rocna had a roll bar because when Mr. Smith copied the Bugel, it had one. Then, Manson copied the Rocna and it had to have one too. Perhaps the roll bar is like the tail fins on a 1969 Caddie? Appearance of function for marketing purposes?
__________________
https://delfin.talkspot.com
I can picture in my head a world without war, a world without hate. And I can picture us attacking that world, because they'd never expect it. - Jack Handey
Delfin is offline   Reply With Quote
Old 05-07-2013, 16:22   #82
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Rocna Repositioned

Boss, I have not used one and the closest I've been is at a Boat Show. I suspect they are like a Bruce. The Bruce is chunky and has a pretty thick fluke with a very large leading edge with lots of surface area to that leading edge. I suspect that leading edge retards penetration along with the chain. But provided the anchor is big enough it will not 'bottom out' (with the fluke horizontal) and it would always have the fluke at an angle, providing resistance to sliding forward. Smaller ones, for the size of load, will simply bottom out and slide forward. The Boss looks to me like a modern interpretation of the Bruce, where they are using stronger steels allowing them thinner profiles (though the shank looks as if this might have gone too far) The thinner profile will allow it to continue to dive more deeply (as there is little resistance). Manson did test a 15kg to 5t holding capacity which does suggest the idea that it does dive much further than most other anchors. The danger of course is that it then becomes difficult to retrieve (say if used as a storm anchor in a genuine Storm).

If the anchor, any (but must be diving), is 'too big' it will not bottom out and will always have the fluke at an angle to forward movement, offering resistance and providing holding capacity. This, in my mind, is the reason for 'Bigger is better'. Being too big, they never bottom out and any increased load simply forces them to set further. The 'Bigger is better' will also have small chain, for the size of the anchor, and may even have downsized chain anyway - adding to the 'success' of Bigger is better' (less chain resistance).

Bruce anchor (the oil rig people) used to have a video on their website taken of a model anchor in a glass tank being set in a transparent medium. It showed the anchor diving, them bottoming out - I'm not sure if it is still there, the video I mean. Someone will say they do not sail an oil rig, nor use an oil rig anchor (unless they use a Bruce) but I think the mechanisms similar.

If you have a cat and sail somewhere with big tides you can check this all out. Set the anchor as hard as possible, then set a much smaller one, equally hard. let the tide run out - then dig the anchors out, carefully from the side, at low tide. The little one will be more horizontal then the bigger one. if you are really careful you will see the reverse catenary of the chain. You will need big tides to do this, or the hole will simply fill with water as you dig. Seem contrived? cat owners do need to do it, sometimes, as they might need to move the anchor to stop the cat drifting when the tide comes back in again.

Jonathan
JonJo is offline   Reply With Quote
Old 05-07-2013, 17:26   #83
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Rocna Repositioned

Take the roll bar away from the Rocna and you remove a huge bit of surface area resisting 'further' diving. It will thus dive further than an unmodified Rocna, it still has the upturned heel, producing some compression and resistance. If its too small it will pull almost unimpeded through the seabed when it bottoms out - but if large enough, there should be no issues.

its a question of how important is the roll bar to self righting in all situations. It has the Lyall self righting shank - and if the dimensions are right - the roll bar is simply - a gimmick and - nuisance? Obviously if in some circumstances it does not self right, or undersized - then its essential.

Jonathan
JonJo is offline   Reply With Quote
Old 05-07-2013, 23:25   #84
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Boat: Bestevaer.
Posts: 14,678
Re: Rocna Repositioned

I think Jonathan's assessment of the roll bar is accurate . The Rocna has various mechanisms to help ensure it will adopt the right attitude to set and the toe will dig in.
The roll bar is one of those mechanisms. If it is removed the other mechanisms may be sufficient for the anchor to set. I would be very doubtful that the other mechanisms are going to be sufficient in all conditions and I would discourage anyone from removing the roll bar from an expensive anchor.

I would also expect if the anchor is marginally set, in a hard substrate, that a change in the direction of pull would induce more list in the anchor and its resetting ability would be hampered.

The above is only speculation. Many tests and observations would be needed to establish the truth.

Presumably Rocna did this when developing the anchor. The roll bar adds considerable expense to the anchor and prevents it fitting on many boats (as in thorcat's case)There is strong pressure to develop anchors that are as good as the roll bar anchors but fit all boats. Its difficult to understand why a company would produce a product that limits market share and adds manufacturing expense unless necessary.

It would be interesting to hear from thorcat on the type of substrate he normally anchors in. This would help our understanding in determining what conditions the anchor will self right without the roll bar.
noelex 77 is offline   Reply With Quote
Old 05-07-2013, 23:29   #85
Marine Service Provider
 
ternmarine's Avatar

Join Date: Jun 2013
Posts: 33
Re: Rocna Repositioned

Quote:
Originally Posted by noelex 77 View Post
I think Jonathan's assessment of the roll bar is accurate . The Rocna has various mechanisms to help ensure it will adopt the right attitude to set and the toe will dig in.
The roll bar is one of those mechanisms. If it is removed the other mechanisms may be sufficient for the anchor to set. I would be very doubtful that the other mechanisms are going to be sufficient in all conditions.

I would also expect if the anchor is marginally set, in a hard substrate, that a change in the direction of pull would induce more list in the anchor and its resetting ability would be hampered.

The above is only speculation. Many test and observations would be needed to establish the truth.

Presumably Rocna did this when developing the anchor. The roll bar adds considerable expense to the anchor and prevents it fitting on many boats (as in thorcat's case)There is strong pressure to develop anchors that are as good as the roll bar anchors but fit all boats. Its difficult to understand why it would be included unless necessary.

It would be interesting to hear from thorcat on the type of substrate he normally anchors in. This would help our understanding in determining what conditions the anchor will self right without the roll bar.
ternmarine is offline   Reply With Quote
Old 05-07-2013, 23:50   #86
Registered User

Join Date: Aug 2012
Boat: none
Posts: 87
Re: Rocna Repositioned

In answer to your questions, the 60 and 80 lb Mansons have been used for the last 5 yrs on my present boat on hundreds of occaisions all over Australia, Indonesia,Malaysia ,Thailand in all bottom types and depths up to 25mtrs, rivers with strong changeable tides, it always sets strong and fast.
I tested the 60lb er on land and at the beach to see how it would react to dropping at different angles and then the same tests after the hoop was cut off and the result was the same even when a 180 degree direction change was done.
Others may have done much more thorugh testing but I was happy enough with what I did to justify removing it, and I havnt been disappointed, so I had no hesitation in doing the same cut to my 80lber.
cruiz9 is offline   Reply With Quote
Old 06-07-2013, 00:05   #87
Moderator
 
noelex 77's Avatar

Cruisers Forum Supporter

Join Date: Jul 2007
Boat: Bestevaer.
Posts: 14,678
Re: Rocna Repositioned

Thanks or the update.
I am familiar with Australia which has mainly soft to very soft sand, medium mud, and loose broken coral/rubble. There are small areas of soft mud, but I have never seen hard, or even medium hard sand in that country. (Although its a big place ) I have never cruised Indonesia,Malaysia ,Thailand did you encounter any areas with hard substrates?.
noelex 77 is offline   Reply With Quote
Old 06-07-2013, 00:43   #88
cruiser

Join Date: Feb 2011
Location: Pittwater, Sydney
Boat: Lightwave, Catamaran, 11.5m (38')
Posts: 1,000
Re: Rocna Repositioned

Thorcat - lovely yacht! If you know it, was Forza 2 the same design? What size chain are you using and what sort of winds have you experienced.

Jonathan
JonJo is offline   Reply With Quote
Old 06-07-2013, 00:52   #89
Registered User
 
DumnMad's Avatar

Join Date: Mar 2012
Location: Nelson NZ; boat in Coffs Harbour
Boat: 45ft Ketch
Posts: 1,559
Re: Rocna Repositioned

Quote:
Originally Posted by thorcat View Post
Wasn't aware of the Boss anchor until I just googled it,but I guess it just proves the point, the Bar isn't required.
Good on ya mate. A lot of BS in anchor promotion.
DumnMad is offline   Reply With Quote
Old 06-07-2013, 17:16   #90
Marine Service Provider
 
ternmarine's Avatar

Join Date: Jun 2013
Posts: 33
Re: Rocna Repositioned

Quote:
Originally Posted by JonJo View Post
Take the roll bar away from the Rocna and you remove a huge bit of surface area resisting 'further' diving. It will thus dive further than an unmodified Rocna, it still has the upturned heel, producing some compression and resistance. If its too small it will pull almost unimpeded through the seabed when it bottoms out - but if large enough, there should be no issues.

its a question of how important is the roll bar to self righting in all situations. It has the Lyall self righting shank - and if the dimensions are right - the roll bar is simply - a gimmick and - nuisance? Obviously if in some circumstances it does not self right, or undersized - then its essential.

Jonathan

Take the roll bar away and you have a Spade, protected by patent, simple really.
ternmarine is offline   Reply With Quote
Reply

Tags
rocna

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Knock Off Anchors CampDavid Anchoring & Mooring 27 24-02-2012 10:28
I Returned My Rocna and Bought a Manson evm1024 Anchoring & Mooring 23 23-08-2011 21:02

Advertise Here


All times are GMT -7. The time now is 19:23.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.