Computer model of rode behavior - SailNet Community

   Search Sailnet:

 forums  store  


Quick Menu
Forums           
Articles          
Galleries        
Boat Reviews  
Classifieds     
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Charts
Clothing
Electrical
Electronics
Engine
Hatches and Portlights
Interior And Galley
Maintenance
Marine Electronics
Navigation
Other Items
Plumbing and Pumps
Rigging
Safety
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here






Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
 Not a Member? 

Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


Reply
 
LinkBack Thread Tools
  #1  
Old 03-27-2009
pdqaltair's Avatar
Senior Member
 
Join Date: Nov 2008
Location: Deale, MD
Posts: 2,281
Thanks: 1
Thanked 36 Times in 36 Posts
Rep Power: 7
pdqaltair is on a distinguished road
Computer model of rode behavior

Rode - Dynamic Behavior

Rode - Static Behavior

Rode - Dynamic Behavior

Not my information, no one I know, but thought provoking. Though I don't agree with all of his conclusions and it is clear that the model is too simple, he makes a good case for a good mix of chain and fiber. He also put a lot of work into this.

But let's trade thoughts.
__________________
(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")

"Well, I just climb up to them."

by Joe Brown, English rock climber




To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #2  
Old 03-28-2009
AdamLein's Avatar
Senior Member
 
Join Date: Nov 2007
Location: SF Bay area
Posts: 1,862
Thanks: 1
Thanked 0 Times in 0 Posts
Rep Power: 8
AdamLein will become famous soon enough
It echoes a lot of the opinions I've read here, but with some formal reasoning to back it up.

One thing I noticed he did, though, when analyzing the dynamic load on all-chain rode vs. all-nylon rode. For the all-chain rode he assumed that the force on the rode was sufficient to lift the entire rode off the bottom, and gave the force. He made the same assumption for the nylon rode but didn't mention the exact force. This would occur for a much higher force for chain than for nylon, so the comparison isn't totally fair. If the force that lifts the all-nylon rode were applied to the all-chain rode, then presumably the catenary could absorb the extra tension due to a sudden gust, and the lack of elasticity of the chain would not be an issue.

Other than that, very rigorous treatment. I'll have to let it set in my brain and then uh, back down on the engine, metaphorically speaking.
__________________
s/v Essorant
1972 Catalina 27
Reply With Quote Quick reply to this message Share with Facebook
  #3  
Old 03-28-2009
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,282
Thanks: 5
Thanked 27 Times in 18 Posts
Rep Power: 11
billyruffn will become famous soon enough
Very interesting (not that I could understand the math)..... but last time I checked chain didn't chafe either at my bow nor on stuff on the bottom, nylon does. Chafe has a tendency to disconnect the anchor from that which is being anchored, in which case most of his curves flatline pdq.

IMHO, case closed.
Reply With Quote Quick reply to this message Share with Facebook
  #4  
Old 03-28-2009
pdqaltair's Avatar
Senior Member
 
Join Date: Nov 2008
Location: Deale, MD
Posts: 2,281
Thanks: 1
Thanked 36 Times in 36 Posts
Rep Power: 7
pdqaltair is on a distinguished road
Do you use a snubber?

Quote:
Originally Posted by billyruffn View Post
Very interesting (not that I could understand the math)..... but last time I checked chain didn't chafe either at my bow nor on stuff on the bottom, nylon does. Chafe has a tendency to disconnect the anchor from that which is being anchored, in which case most of his curves flatline pdq.

IMHO, case closed.
In which case, you are enjoying the best of both worlds... no? The snubber damps wave impacts, and the chain catenary damps the gusts. You see, he neglected all of the damping effects - for example, the model showed your boat bouncing on the chain, which it clearly does not - so what he really showed was that a rope DOES NOT damp gusts longer than the absorption period of the rope. It makes them greater by allowing the boat to slide back.

The real story is that you need JUST enough snubber to manage the waves. And that squares with your experience, I think.
__________________
(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")

"Well, I just climb up to them."

by Joe Brown, English rock climber




To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
  #5  
Old 03-29-2009
billyruffn's Avatar
Senior Member
 
Join Date: Sep 2004
Location: Massachusetts
Posts: 1,282
Thanks: 5
Thanked 27 Times in 18 Posts
Rep Power: 11
billyruffn will become famous soon enough
Do I use a snubber? You bet. And I really don't care if it parts due to chafe because the chain is wrapped around a cleat. The snuber does as you say....absorbs the initial shock of the waves and the chain then does what it's susposed to do -- keep the anchor in the mud and,... this is very important, attached to the boat.

All mathmatics aside, chain rodes are much more conducive to a good night's sleep.

Last edited by billyruffn; 03-29-2009 at 01:21 AM.
Reply With Quote Quick reply to this message Share with Facebook
  #6  
Old 03-29-2009
pdqaltair's Avatar
Senior Member
 
Join Date: Nov 2008
Location: Deale, MD
Posts: 2,281
Thanks: 1
Thanked 36 Times in 36 Posts
Rep Power: 7
pdqaltair is on a distinguished road
As I said, the best of both worlds... for a big boat.

Quote:
Originally Posted by billyruffn View Post
Do I use a snubber? You bet. And I really don't care if it parts due to chafe because the chain is wrapped around a cleat. The snuber does as you say....absorbs the initial shock of the waves and the chain then does what it's supposed to do -- keep the anchor in the mud and,... this is very important, attached to the boat.

All mathmatics aside, chain rodes are much more conducive to a good night's sleep.
However, there are smaller boats that cannot tolerate the weight, and don't generate the chafe either. A chain rode would have been absurd on my first "cruising" boat, a 1300# Stiletto catamaran. 10% of the boats mass, all in ground tackle and all in the bow. Very different - different answer.

The interesting thing about the math, after adjusting for damping, is that it suggests that a fiber rode is only really useful if light weight is a factor, and so, unknowingly, I think it supports the conventional wisdom that cruising boats are well served by chain with a longish snubber. Lighter boats? There is a cross-over point somewhere between your boat and the Stiletto; I don't profess to know where. As my current boat is ~8000#, I wish I knew. In a few years I will need a new rode.

A good nights sleep is the goal.
__________________
(when asked how he reached the starting holds on a difficult rock climbing problem that clearly favored taller climbers - he was perhaps 5'5")

"Well, I just climb up to them."

by Joe Brown, English rock climber




To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Quick reply to this message Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

 
Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On


Similar Threads
Thread Thread Starter Forum Replies Last Post
The Second Anchor Tom Wood Gear and Maintenance Articles 0 07-06-2004 09:00 PM
Onboard Computer Care Jim Sexton Seamanship Articles 0 10-07-1999 09:00 PM
Onboard Computer Care Jim Sexton Gear and Maintenance Articles 0 10-07-1999 09:00 PM
Onboard Computer Care Jim Sexton Cruising Articles 0 10-07-1999 09:00 PM


All times are GMT -4. The time now is 09:03 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.