Fin keel and heaving-to - Page 2 - 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
  #11  
Old 07-14-2010
Jeff_H's Avatar
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,595
Thanks: 5
Thanked 96 Times in 72 Posts
Rep Power: 10
Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about
I am not sure how to answer that because if a boat has a fin keel "the other parameters" usually would not be "identical" (to a boat with a long keel). But more to the point in my experience the slick left by a boat has some impact on motion comfort and less of an impact on safety in breaking waves, so that in my mind simply making a larger slick is not directly translatable into saying the boat is more safe in breaking waves.

It probably goes without saying that boats behave as a system of a whole. Keel type is but one aspect of that whole and since the term fin keel really describes a broad spectrum of keel shapes and sizes and each behave differently, I would not say that generically fin keel boats are either safer or more dangerous than longer keel boats when lying abeam to large waves.

Jeff
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies
Reply With Quote Share with Facebook
  #12  
Old 07-14-2010
cormeum's Avatar
48' wood S&S yawl
 
Join Date: Aug 2009
Posts: 421
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 6
cormeum is on a distinguished road
Well forereaching at 5 knots isn't going to leave you in your "slick" for any length of time. (to bad there isn't multiquote here). If you're not behind the slick it'll do no good.

I'd be curious as to how well fin keeled boats of various keel chord ratios behave under wave impact- intuitively, you'd think that having a small longitudinal plane would make the boat more suseptable to wave motion when heaved-to.
__________________
"Never attribute to malice that which can be adequately explained by stupidity." - Robert A.Heinlein
Reply With Quote Share with Facebook
  #13  
Old 07-14-2010
CalebD's Avatar
Tartan 27' owner
 
Join Date: Jan 2008
Location: NYC
Posts: 4,585
Thanks: 4
Thanked 90 Times in 83 Posts
Rep Power: 7
CalebD will become famous soon enough
Try heaving to. You will like it.
__________________
"The cure for anything is salt water~ sweat, tears, or the sea." ~Isak Denesen

Everybody has one:

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Reply With Quote Share with Facebook
  #14  
Old 07-15-2010
shaile's Avatar
Junior Member
 
Join Date: Dec 2009
Posts: 20
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
shaile is on a distinguished road
Quote:
Originally posted by Jeff_H
.... I would not say that generically fin keel boats are either safer or more dangerous than longer keel boats when lying abeam to large waves.
but Jeff, in another post
(What is the keel contribution in capsizing.
you said that "... when you have a deep draft keel that is short fore and aft, there is a tendency of that keel to stall as the water is moving closer to perpendicular to the keel. When the keel stalls, it generates smaller sideward resistance relative to its area .... the tendency of modern deep fin keels to stall reduces the impact of surface sheer and so reduces the tendency for surface sheer to rapidly heel the boat. As a result, even if shallower than a modern fin with bulb, a full keel or lower aspect ratio keel could actually have greater tendency towards a surface sheer induced capsize."

As I understand, while in breaking waves there are to cases in which the shape of the keel is to be considered:
1 - when you are caught unexpectedly abeam to breaking waves. In this case it is better to be with fin keel since it produces less sheer forces and hence has less tendency to capsize.
2 - when you prepare for the breaking waves by heaving-to with or without a para anchor. In this case the question is whether a fin keel (with low aspect ratio) can properly heave-to and whether it produces the same "magical" slick that protects from the breaking waves.

If the conclusion is that fin keels are positive in case 2 then one can conclude that fin keel is safer in breaking waves.
If the conclusion is that fin keels behave less positive in case 2 then the question is what to prefer, full keel which better in case 2 but worse in case 1 or fin keel which is good in case 1 and worse in case 2.

Shai.
Reply With Quote Share with Facebook
  #15  
Old 07-15-2010
Jeff_H's Avatar
Moderator
 
Join Date: Feb 2000
Location: Annapolis, Md
Posts: 6,595
Thanks: 5
Thanked 96 Times in 72 Posts
Rep Power: 10
Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about Jeff_H has a spectacular aura about
Shaile:

It's like I said in both posts, there are a whole lot of factors that determine the safety of a boat in in breaking waves. It is all about the individual boat as a whole and not any one specific trait. The generic keel type really isn't inherently close to being one of the most significant factors.

In all cases and all vessels, there are trade offs and compromises, factors and counter indicators. You need to look at the vessel as a whole. While there are clearly full keeled vessels which make great offshore cruising vessels, there are also full-keeled vessels which are dangerously under-ballasted and whose motions will wear out any crew. By the same token, the same can be said about fin keeled boats. The reality is in the specifics of the boat in question.

If you asked me, I would tell you that full keels are an anachronism. Full keels worked well in the days when the materials and methods of building boats limited the stability and sailing efficiency of the boat, and when small offshore cruising boats were closely based on working watercraft; but somewhat ignored the reality of a typical working watercraft's need to carry a whole lot of load in an inexpensively constructed vessel.

Today, our materials and methods of construction allow us to build boats which are more efficient and easier to handle, and which have tremendous stability relative to their drag. But this is not to say that all modern designs are inherently equally seaworthy or equally capable of providing a safe and comfortable offshore vessel. As I have said to you before, it is all dependent on the specifics of the boat in question.

With regards to the comment from my esteemed colleague Cormeum, I would agree that "forereaching at 5 knots isn't going to leave you in your "slick" for any length of time. (too bad there isn't multiquote here). If you're not behind the slick it'll do no good" but my own GPS observations have been that fin keel boats when hove-to make between a knot and a knot and a half of leeway and that only a small portion of that is forereaching with the slick leaving the boat at 120 to 135 degrees from dead ahead; in other words, approximately varying between 30 to 45 degrees abaft abeam. The angle is not all that different than I have experienced on my previously owned traditional full keel designs (like my folkboat or 1939 Stadel Cutter) but my sense is that the leeway speed is greater and so the slick is larger.
Jeff
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Curmudgeon at Large- and rhinestone in the rough, sailing my Farr 11.6 on the Chesapeake Bay and part-time purveyor of marine supplies
Reply With Quote Share with Facebook
Reply


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
What is the keel contribution in capsizing. shaile General Discussion (sailing related) 33 01-06-2010 05:14 PM
Catamaran heaving to questions... yellowwducky Learning to Sail 9 10-28-2009 12:01 AM


All times are GMT -4. The time now is 05:03 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.