SailNet Community - Reply to Topic

   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 > General Interest > General Discussion (sailing related) > Backing up (or not)
 Not a Member? 


Thread: Backing up (or not) Reply to Thread
Title:
  

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

Message:
Trackback:
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:
 

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.



Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below


Topic Review (Newest First)
07-20-2013 06:50 PM
Seaduction
Re: Backing up (or not)

Regarding backing, a fin keel boat turns like a ballerina pirouetting on her toes; a full keel boat turns like a ballerina pirouetting on a flat foot. (I'm just a simple person.)
07-20-2013 06:33 PM
chrisncate
Re: Backing up (or not)

I always liked to warp into the slip, but I don't know if that could work as a blanket catch all for other types of boats. I liked to pull up in the fairway parallel to the dock, cut power if it wasn't already cut, then manually work her in backwards using lines and my hands (A-30).
07-20-2013 02:56 PM
MedSailor
Re: Backing up (or not)

Quote:
Originally Posted by davidpm View Post
Someone out their must have a full/cutaway keel boat for a lot of years and has figured out the trick of at least predicting it's behavior.
Where are you?
Unless I get attacked by a Sharktopus, backing out of my slip at the beginning of the trip is usually the most stressful part of the voyage. My boat is heavy 30,000lbs, has a 6' full keel, an underpowered engine (36HP), and a prop in an apeture.



I no longer find her unpredictable in reverse at all. She is in fact, very predictable. The secret, I have found, is in accepting what she can and can not do, and estimating the forces that will be at work before untying.

I'll try and explain. My pivot point is located just forward of my wheel, where the mizzen mast is. That means that all windage forward of that will try and blow the bow off. In fact, there is so much forward windage, that my boat apparently heaves to with a FULL mizzen only, with the 150sqft sail and the forward part of the boat's windage being about equal. So, 40ft of boat, including my bowsprit (which is at the end of the lever) act like a unidirectional-wind-powered bow-thruster. I also know that my LH prop causes the boat to strongly prop walk to starboard. I also know that my rudder will not overcome much opposing wind, and will barely keep up with prop walk if there is no wind.

Knowing these things, and knowing that I can't overcome them, I have to work with them. Before I untie I look at my masthead wind indicator and feel the strength of the wind. I know the wind blowing the bow one way or the other will be the biggest actor. Once I know that, check for current, and account for prop walk. I kind of imagine all these vectors in my head and decide how I can affect them and make a plan.

Often the wind blows from my starboard side. This will blow the bow to port. The prop walk will compound the problem. If I "try" to overcome this in reverse with the rudder, I'll be making an insurance claim. I HAVE to accept the limitations of my craft and not pretend that if I just twist harder on the wheel she'll go.

So, I do something else, like shorten up the starboard bow line, release all others, and release it last so I start backing up crooked, and straighten out as I go. Or I use a burst of forward with starboard rudder to straighten out, then resume backing.

Basically, I know the forces that will act in opposition or unison to affect my steering, and I know and accept that the rudder is a small, not a large player in the overall plan. I imagine the vectors, make a plan, untie my lines and see if I was right.

I hope my long-winded ramble made some sense and helped somewhat....

MedSailor
07-20-2013 01:26 AM
Daveinet
Re: Backing up (or not)

Quote:
Originally Posted by SunnnyD View Post
Great thread; just to chime in, I have a 22' with a little 6hp outboard hung on the transom off-center with the transom-hung rudder. When I am backing out of my slip, I have found that if I keep the tiller straight and steer with the motor (with a little help turning the boat as we hand walk it out of the slip to the end of the finger pier, I get enough steerage to get her turned in the right direction. My motor won't do much to slow the boat when I am docking, so I rarely try to use it in that capacity, but I have found that unless I want to really bring her around fast, steering with both the tiller and the motor is not needed.


My only question is this: I have a swing keel that I can crank up, and I am wondering if it makes the boat easier or harder to steer in reverse if it is up vs. down. I suppose I can try it out but it ain't broke at the moment, so why try to fix it?


Any thoughts?
I have an idea for you. This is what I did to my previous boat. Made things much simpler. Since I can cleat my tiller, that also holds the engine straight as well. Makes life much more predictable.



OK for my next thought, everyone is going to hate me, but from my experience in driving jetskis, I think the best solution is a jet pump with a reverse bucket. The reverse bucket gives you a lot of control for docking, just keep the throttle up, and control your motion with the reverse bucket. Depending on which way the bucket goes, you can pull the bow or the stern in toward the dock. Bucket control needs to be independent of throttle control.
07-18-2013 12:01 PM
ltgoshen
Re: Backing up (or not)

I have tried to back my boat a few times and it was so slippery I gave up. I have a rh Folding prop. Not much help in rev or in Fwd for that matter. My shaft is a bit off-set as well.
Any Idea how to use the rudder against this prop configuration to get rev steerage?
Below is a shot of the offset.

Thanks for your help.



07-18-2013 04:36 AM
SunnnyD
Re: Backing up (or not)

Great thread; just to chime in, I have a 22' with a little 6hp outboard hung on the transom off-center with the transom-hung rudder. When I am backing out of my slip, I have found that if I keep the tiller straight and steer with the motor (with a little help turning the boat as we hand walk it out of the slip to the end of the finger pier, I get enough steerage to get her turned in the right direction. My motor won't do much to slow the boat when I am docking, so I rarely try to use it in that capacity, but I have found that unless I want to really bring her around fast, steering with both the tiller and the motor is not needed.


My only question is this: I have a swing keel that I can crank up, and I am wondering if it makes the boat easier or harder to steer in reverse if it is up vs. down. I suppose I can try it out but it ain't broke at the moment, so why try to fix it?


Any thoughts?
07-18-2013 03:18 AM
poopdeckpappy
Re: Backing up (or not)

Quote:
get the boat moving and then put it into neutral. ......... The idea is to go into and out of gear.
This is the only way to back a full keel boat, just enough thrust to make way then back to neutral
07-18-2013 01:48 AM
SlowButSteady
Re: Backing up (or not)

Quote:
Originally Posted by bobperry View Post
Hmmmmm,,,,,,I'll buy that. I need to ponder it a bit but it sounds good to me.
I think you may have part of the answer but I still think that the center of pressure on the keel plays a big roll. If it were static you would still have the same turning arm in reverse. I think having the control surface on the leading edge also may be the reason the C of P moves aft.
Another way to look at this is to think about what happens to the flow over the keel in the forward and reverse directions. Let's start with the boat moving forward; the flow is (or at least should be) laminar all along the keel and its attached rudder. Now, turn the rudder a bit to Port and the flow should stay pretty much laminar as long as it isn't cranked too far. There may be a few vortices being shed off of the trailing edge of the rudder, but these will only increase drag without having much of an impact on lift. So, turn the rudder to Port, lift increases on the Starboard side of the keel, the stern swings to Starboard and the bow turns to Port.

What happens when the flow is reversed (i.e., the boat is backing)? With the rudder centered the flow is again laminar. The maximum chord (the thickest part of the keel) is probably in the wrong place, but let's not worry about that for now. OK, turn the rudder to Port again and what happens to the flow? Now the edge of the rudder is the first thing the flow "sees" as it impacts the keel. Since this edge is relatively sharp (compared to the forward edge of the keel) the flow separates right at the leading edge (or what is the leading edge while backing). This causes vortices at slow speed and turbulence as the speed increases, in this case all along the Port side of the keel. This pretty much ruins any lift the keel might otherwise generate (i.e., the keel is "stalled"), and directional control is more or less nonexistent.
07-17-2013 07:32 PM
CaptainForce
Re: Backing up (or not)

I like the explanations above; however in addition to the posts above, there's a very simple added explanation once you have momentum. In forward you can compensate for prop walk with the action of the prop wash over the steering rudder. In reverse there is no prop wash over the steering rudder.
07-17-2013 05:30 PM
bobperry
Re: Backing up (or not)

Hmmmmm,,,,,,I'll buy that. I need to ponder it a bit but it sounds good to me.
I think you may have part of the answer but I still think that the center of pressure on the keel plays a big roll. If it were static you would still have the same turning arm in reverse. I think having the control surface on the leading edge also may be the reason the C of P moves aft.
This thread has more than 10 replies. Click here to review the whole thread.

 
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


All times are GMT -4. The time now is 04:32 AM.

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.