Trim tab linkage for a kick-up rudder blade - 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 > On Board > Boat Review and Purchase Forum > Sailboat Design and Construction
 Not a Member? 


Reply
 
LinkBack Thread Tools
  #1  
Old 03-25-2008
Junior Member
 
Join Date: Nov 2006
Posts: 18
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
ClubOrlov is on a distinguished road
Trim tab linkage for a kick-up rudder blade

I am hauled out in St. Augustine, and one of the things I have to replace is the rudder blade. It's a 32-foot cutter ketch with a transom-hung rudder. It has a rudder blade that kicks up if the boat hits shallow water (as does the centerboard). I want to add a wind vane (a simple horizontal-pivot arrangement with push rod linkage to trim tab) controlling a trim tab on the rudder blade. The thing that has me stumped is how to set up the trum tab control linkage so that it can cope with the rudder blade kicking up. The pivot range on the trim tab has to be 20 degrees or so each way. Has anyone seen or heard of such a thing?
Reply With Quote Share with Facebook
  #2  
Old 03-25-2008
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
Club-

It might help if you said what kind of boat it was... since someone who owns that boat may have done something similar. The problem is that the trim tab linkage has to deal with both the pivot and the shifting of the trim tab's physical location when the rudder kicks up. Do you have a photo of the rudder setup??
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Share with Facebook
  #3  
Old 03-25-2008
JohnRPollard's Avatar
Moderator
 
Join Date: Mar 2007
Location: Chesapeake
Posts: 5,680
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 10
JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough
Have you contacted the manufacturer/designer of your vane? They may already have engineered a solution.
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Pacific Seacraft Crealock 31 #62

NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT
Reply With Quote Share with Facebook
  #4  
Old 03-25-2008
Junior Member
 
Join Date: Nov 2006
Posts: 18
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
ClubOrlov is on a distinguished road
The boat is a 1989 Chris Morejohn 32. It's a sharpie hull, cold-moulded, fiberglass over plywood. 2-foot draft, does 6-8 knots out on the ocean. Chris is currently pondering the same question.
Reply With Quote Share with Facebook
  #5  
Old 03-26-2008
Senior Member
 
Join Date: May 2006
Posts: 825
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 9
chris_gee is on a distinguished road
Surely the shaft that turns the tab is vertical and attached to a horizontal plate. Is there a problem making that attachment able to turn vertically fore n aft with a pivot bolt through a bracket?
Reply With Quote Share with Facebook
  #6  
Old 03-26-2008
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
Chris-

Most kickup rudders have a serious problem with trim tabs for wind vanes. The kickup rudder has a pivot point, and the trim tab needs one as well... however, the pivot point for the trim tab has to accommodate the movement caused by how far from the rudder's pivot point the trim tab is located. So it generally has to slide as well as pivot—or otherwise accommodate the horizontal and vertical components of the rudder kicking up. Making something like this isn't easy or simple, especially if you're trying to make it so that it doesn't interfere with the windvane or rudder's functions. It also has to allow for transmitting the turning movement past the pivot mechanism without damaging the pivot mechanism or torquing the trim tab's shaft out of alignment.

Quote:
Originally Posted by chris_gee View Post
Surely the shaft that turns the tab is vertical and attached to a horizontal plate. Is there a problem making that attachment able to turn vertically fore n aft with a pivot bolt through a bracket?
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Share with Facebook
  #7  
Old 03-26-2008
JohnRPollard's Avatar
Moderator
 
Join Date: Mar 2007
Location: Chesapeake
Posts: 5,680
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 10
JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough
Quote:
Originally Posted by ClubOrlov View Post
The boat is a 1989 Chris Morejohn 32. It's a sharpie hull, cold-moulded, fiberglass over plywood. 2-foot draft, does 6-8 knots out on the ocean. Chris is currently pondering the same question.
Is Chris the designer of the vane as well? If not, I would contact the vane designer/builder.

The best solution might be to avoid a vane that uses a rudder trim tab. Otherwise it just seems like you are needlessly complicating what could be a fairly simple installation, since most vanes already have a kick-up rudder feature. Consider an outboard version of the Cape Horn:

Outboard models
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Pacific Seacraft Crealock 31 #62

NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT

Last edited by JohnRPollard; 03-26-2008 at 09:22 AM. Reason: spelling
Reply With Quote Share with Facebook
  #8  
Old 03-26-2008
sailingdog's Avatar
Telstar 28
 
Join Date: Mar 2006
Location: New England
Posts: 43,291
Thanks: 0
Thanked 9 Times in 9 Posts
Rep Power: 13
sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice sailingdog is just really nice
John-

There are a lot of different vane designs, some use trim tabs, some use auxiliary rudders, some require neither, and some use a servo pendulum blade. You're right in that if he doesn't already have the wind vane, he'd probably be better off getting one that doesn't require a trim tab—ideally, he should get one that doesn't require an auxiliary rudder or pendulum servo blade either, since either would cause problems with grounding in some situations.

However, the trim tab, servo pendulum blade and rudders are generally required for a wind vane to generate sufficient turning force to counter the helm on some boats. If his sharpie doesn't have high helm loads, he might be able to get away with a simple wind vane, that doesn't require the amplification of a trim tab, servo or aux rudder.
__________________
Sailingdog

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
.

Still—DON'T READ THAT POST AGAIN.
Reply With Quote Share with Facebook
  #9  
Old 03-26-2008
Junior Member
 
Join Date: Nov 2006
Posts: 18
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
ClubOrlov is on a distinguished road
Well, the designer of the wind vane is me - I don't have the cash to shell out for a Monitor or an Aries. Plus, I am replacing the rudder blade (core rot) so why not add a trim tab while I am at it? There are two reasons to add the trim tab: one is that I want a wind vane, for going against the wind for long periods of time without having to man the helm; two is that I have a Simrad tillerpilot, which is cheap enough for me, but too wimpy in heavy seas, so I want to link it to the trim tab instead of the rudder itself.

The pivot of the trim tab will be back of the pivot of the rudder itself. Trim tab blade will be about 20% of the area of the blade. I want a linkage that will disengage when the rudder kicks up and reengage when it goes back down. Since the swing of the trim tab is only +/- 20 degrees or so, I am think of putting a horizontal steering plate right above the pivot point of the rudder blade with a v-slot in it, and having the trim tab have an interesting-shaped protrusion at its top that sits in the v-slot of the wishbone plate when the rudder blade is all the way down. When the blade kicks up, the protrusion should gently slot itself into the bottom of the rudder body, which consists of two vertical boards that hold the rudder blade, holding the trim tab in the same plane as the rudder blade instead of flopping side to side and causing (even more) erratic steering. (Steering gets quite interesting when the blade kicks up; as in, get your heel on the tiller because your arms are too small.)

The designer is working with a later version of the same transom-hung rudder design (a better one: more balanced) so we'll probably end up with slightly different designs.
Reply With Quote Share with Facebook
  #10  
Old 03-26-2008
JohnRPollard's Avatar
Moderator
 
Join Date: Mar 2007
Location: Chesapeake
Posts: 5,680
Thanks: 0
Thanked 2 Times in 2 Posts
Rep Power: 10
JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough JohnRPollard is a jewel in the rough
If you have a proper steering vane, you won't have to worry about the strength of your tiller pilot in heavy going. Those are the conditions when the steering vane typically will work its best, and the tiller pilot won't be used.

A lot of folks have hooked up tiller pilots to steering vanes,in order to provide light air and compass course-keeping capability, with low power consumption. But I seem to recall it's most commonly done with servo-pendulum types. The tiller pilot replaces the input from the windvane, and the servo pendulum provides the power to turn the main rudder. The servo pendulum is usually kick-up style.

Personally, I would not want a permanent trim tab affixed to the main rudder if I had other options. I would want the ability to get all the steering vane components out of the water when I didn't need it.

Hartley sells plans for a DIY steering vane:

Hartley windvane self steering plans
__________________

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Pacific Seacraft Crealock 31 #62

NEVER CALLS CRUISINGDAD BACK....CAN"T TAKE THE ACCENT
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
Building a Rudder Newport 30 Armchairprotest Gear & Maintenance 5 04-07-2009 01:11 PM
Synchronized Sail Trim Carol Cronin Racing Articles 0 03-16-2002 07:00 PM
Emergency Steering John Kretschmer Seamanship Articles 0 03-08-2002 07:00 PM
Emergency Steering John Kretschmer Gear and Maintenance Articles 0 03-08-2002 07:00 PM
Emergency Steering John Kretschmer Cruising Articles 0 03-08-2002 07:00 PM


All times are GMT -4. The time now is 09:26 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.