Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 07-06-2013, 02:46   #16
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Self steering (again)

Quote:
Originally Posted by Snowpetrel View Post
These look great, what size did you get, and what price where they? The Stainless Steel or brass look good but if the hdpe ones are big enough it might also work fine (or cheap enough to replace frequently..) I need to build a vindvane for the new boat at some point. Probably an auxiliary rudder with a servo pendulum so I am looking for something like this for the vane to servo pendulum connection.

Cheers

Ben

kh25 module 2.5 15/30 teeth $74au
__________________

__________________
charliehows is offline   Reply With Quote
Old 07-06-2013, 02:47   #17
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Self steering (again)

as far as the cable thing goes - knock yerself out guys. But the cogs work better.
__________________

__________________
charliehows is offline   Reply With Quote
Old 07-06-2013, 08:51   #18
Senior Cruiser
 
Jim Cate's Avatar

Cruisers Forum Supporter

Join Date: May 2008
Location: cruising SW Pacific
Boat: Jon Sayer 1-off 46 ft fract rig sloop strip plank in W Red Cedar
Posts: 11,461
Re: Self steering (again)

Quote:
Originally Posted by Delfin View Post
My Cape George had a completely unbalanced rudder as well. I'm afraid I can't remember the exact % of my trim tab, but one thing to remember is that with a wind vane, you really are not trying to move the rudder a great deal - just enough to stay on course. As a result, you don't need huge amounts of power in the tab, and I found that even my small one generated more than enough. As a guess, I would think that 15% would be fine, and on your vessel a 4 to 5 inch tab should work fine. I would be curious to hear what size Jim Cate's was and whether he agrees.
G'Day guys,

I sold that boat and vane a decade ago, and all the drawings for the vane are on I-2 in Hobart and I'm in California for the foreseeable future... hence this is from memory (increasingly untrustworthy these days!).

Anyhow, the tab was about 20% of the rudder width, possibly a bit less. But remember, this was an auxiliary rudder, not the main rudder, and it was semi-balanced. In fact, in the end I kinda reverse-engineered the thing: built the rudder and tab, then adjusted the balance of the rudder to get the response that I wanted. Hanging a tab on an existing main rudder is a different thing entirely.

But, thinking about it a bit, with a longer keel boat that tracks well, your thoughts that small rudder deflections will be all that is required may well be correct. My boat was an old IOR one-tonner and likely a lot less stable in yaw than an H-28. Again from memory, I would see frequent 10 to 15 degree rudder movements as we sailed along off the wind. To windward almost no correction was required, so little rudder movement noted. Remember that with an aux rudder you take out any weather helm with the main rudder and then lock it in place.

Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm users. And I would sure at least give Dyneema cables a try... I think that they would be brilliant!

Cheers,

Jim
__________________
Jim and Ann s/v Insatiable II , lying Port Cygnet, Tasmania once again
Jim Cate is offline   Reply With Quote
Old 07-06-2013, 10:24   #19
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Self steering (again)

Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm users. And I would sure at least give Dyneema cables a try... I think that they would be brilliant!

Cheers,

Jim[/QUOTE]

I think when i designed a unit based on cable controls i tried to reinvent the wheel - the way i used them didnt work. If you have seen them used effectively then using them in that way will probably work too. What i concluded was that tried and tested systems based on the most commonly used 90* cogs to transfer the drive from the vane to the pendulum werent beyond my ability to fabricate and that is what worked for me in the end. I did a lot of reading at the time and the most common mention of cable systems pretty much graded them as fairly unsuitable, which is what i found in practice. The thing i feel most people dont understand about cables is that when a cable turning through more than a few degrees of directional change is put under pressure the friction effect is distributed over the entire length of the cable and housing meaning it quickly becomes very resistant. So it matters how they are used in the unit.
__________________
charliehows is offline   Reply With Quote
Old 07-06-2013, 13:10   #20
Registered User
 
Delfin's Avatar

Join Date: Aug 2010
Location: Anacortes, WA
Boat: 55' Romsdal
Posts: 1,390
Re: Self steering (again)

Quote:
Originally Posted by charliehows View Post
Lastly, I don't understand CH's antipathy towards the cable drive systems. The dire friction situations he quotes don't agree with my experience at all, nor the experience of hundreds of AutoHelm users. And I would sure at least give Dyneema cables a try... I think that they would be brilliant!

Cheers,

Jim
I think when i designed a unit based on cable controls i tried to reinvent the wheel - the way i used them didnt work. If you have seen them used effectively then using them in that way will probably work too. What i concluded was that tried and tested systems based on the most commonly used 90* cogs to transfer the drive from the vane to the pendulum werent beyond my ability to fabricate and that is what worked for me in the end. I did a lot of reading at the time and the most common mention of cable systems pretty much graded them as fairly unsuitable, which is what i found in practice. The thing i feel most people dont understand about cables is that when a cable turning through more than a few degrees of directional change is put under pressure the friction effect is distributed over the entire length of the cable and housing meaning it quickly becomes very resistant. So it matters how they are used in the unit.[/QUOTE]

Not quite sure you have the plot outline here, but I believe the OP is looking at mounting a trim tab on an outboard hung rudder, not a servo pendulum design. Driving a tab with gears might be possible, but pointless since cabeled systems work flawlessly for those who actually have them.
__________________
http://delfin.talkspot.com
When stupidity is a sufficient explanation, there is no need to appeal to another cause.
- Ulmann's Razor
Delfin is offline   Reply With Quote
Old 07-06-2013, 21:49   #21
Registered User
 
Chrisc's Avatar

Join Date: Aug 2006
Location: Whangamata. New Zealand
Boat: H28
Posts: 210
Re: Self steering (again)

To clarify, my self steering system currently under build is a trim tab mounted on a transom hung rudder. I have used 90 degree gears on servo pendulum systems that I have built in the past with (some) success. From my experience, the mechanical linkage between the air vane and the servo pendulum or trim tab is vitally important - it really needs to be entirely without play and with minimal resistance, light, strong and with not even a hint of binding through out the entire range of movement. I find all this quite difficult to produce in my antiquated workshop.
I accept that sheathed cables could also be problematic from a friction viewpoint if not laid correctly, however they hold the promise of a fluid, play-free movement from air vane to trim tab - a very desirable attribute.
Since I am a retired person with time on my hands, I am going to have a go at a cable system, mainly because it really piques my interest. Shimano make a very nice sheath for their high end bike brakes that has a teflon core inside a stainless steel spiral and the whole thing enclosed in a uv resistant plastic outer.
Wish me good success.
__________________
Chrisc is offline   Reply With Quote
Old 08-06-2013, 16:56   #22
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Self steering (again)

Chris, i found a cheap, effective way to build cables was to use black polythene narrow bore irrigation hose - costs absolutely peanuts - and heavy duty fishing line, using ironbark wood blocks bored to take the cable housing ends.
its just one of the things i tried and i mention it because of your post above. I think if its laid out in a straight run over a short distance it works extremely well and because the materials are so cheap keeping plenty of spares aboard is easy. But cables dont like turning corners, they dont like heavy loads, and they dont like pushing, so if you can avoid those things in your design they have the potential to work effectively. Good luck, and keep us posted.
__________________
charliehows is offline   Reply With Quote
Old 09-06-2013, 00:44   #23
Registered User
 
Chrisc's Avatar

Join Date: Aug 2006
Location: Whangamata. New Zealand
Boat: H28
Posts: 210
Re: Self steering (again)

Sir - you are a genius!
I know the irrigation hose you mention, in fact I think I have some. This sort of help and advice is what I love about this forum.
__________________
Chrisc is offline   Reply With Quote
Old 09-06-2013, 05:10   #24
Registered User

Join Date: Aug 2010
Location: sydney, australia
Boat: 38 roberts ketch
Posts: 1,021
Images: 3
Re: Self steering (again)

Quote:
Originally Posted by Snowpetrel
These look great, what size did you get, and what price where they? The Stainless Steel or brass look good but if the hdpe ones are big enough it might also work fine (or cheap enough to replace frequently..) I need to build a vindvane for the new boat at some point. Probably an auxiliary rudder with a servo pendulum so I am looking for something like this for the vane to servo pendulum connection.

Cheers

Ben



kh25 module 2.5 15/30 teeth $74au


I just remembered why i chose those - because the bore sizes fit standard s/s round bar so theres no need to turn any shafts down for them, you just build the relevant shafts using that size bar...the other thing i found really useful is; theres two heavy duty s/s pipes that only come in 2 foot-ish lengths that are a nice snug fit inside each other - ideal in strength of material for both pendulum shaft and aux. rudder shaft. they dont usually store that stuff with the round bar, i found it sitting at the end of some shelves...
__________________

__________________
charliehows is offline   Reply With Quote
Reply

Tags
steering

Thread Tools
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




Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 22:49.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.