Self steering - the progress part 3

[Chrisc]

Finally, it is finished, apart from bunging the whole thing on the back of the boat.
The build took longer than anticipated, mainly because of down time waiting for the rudder to dry out sufficiently so it could be reshaped and fibreglassed - a mission in itself! Overall, I am pleased with the result of the project so far but of course the final arbiter of my success or otherwise will be if the thing actually steers the boat. Originally, vane movement was transmitted to the trim tab tiller via 1.5mm spectra in small bore irrigation tube, but a lot of cycles on the test bed showed the spectra line starting to cut into the tube on the bends so have reverted to the bicycle derallieur cable and sheath idea. Cable is stainless and the sheath teflon lined and so far no wear is showing up during testing.
Next report will be a sailing one, and even if its a complete cock-up, I will submit an honest assessment.
So, hope like hell it works..

[SVTatia]

Looks great - good work so far. Now the fun begins. Good luck and keep us informed.

[Sailorman Ed]

Nice job !!! Can you explain where you got the design and also details of the bicycle cable? I think I see the ends in one picture.

[Chrisc]

The design parameters come from WINDPILOT: selfsteering under sail and Yacht Surveyor, Yacht survey, Boat survey, steel and aluminium yacht surveys. The first link has a very informative book free to download, and the second link a paper that covers all the basics of windvane steering geometry. The original idea for cable steering was pilfered from the Autohelm manual, available online from Scanmar. Windvane construction relies on a number of hard and fast rules, eg the relationship between rudder and trimtab, trimtab and vane, angles of inclination and geometry (explained in the downloads). It does not really matter how you wrap up the package so long as the basic parameters are adhered to, and your construction eliminates friction and inertia from the system as much as possible. In my case, the final design was dictated by the materials that I had available and what I was allowed to salvage from the non-ferrous scrap bin at our local engineering works.
Attached a pic of the cable attachments on my gear. Bicycle gear cables have a little ball on one end. The cables thread through the 'U' shaped bits, secured by the ball and then down thru the two tubes. Shimano make high end derallieur cables and sheaths from stainless and teflon that are friction free. Your bike shop will have them.
If you are about to embark on the construction of your own gear then be warned - it is a very addictive activity!!

[Caribsailors]

I very much like your design for the vane!. I have been working on a similar project as I need to remote mount the vane, and have steered (no pun intended) to Auto Helm and their cable system.

Your vane design has aligned with what I had envisioned and would very much appreciate if you would have any design specs/drawings you'd be willing to share?

I have been working with Cape Horn concept but thought of a ball/screw for the feedback rudder medium. But as others have said "why reinvent the wheel"

But I do Like your Vane design!

Cheers

[Chrisc]

hello Caribsailors, I am a bit ashamed to admit that I'm a 'seat of the pants' operator and the vane was a very much a make it up as you go along affair.
However, if you PM me I will send you a bunch of close up photos and will make a few drawings with the principal dimensions.

Chris

[Normanby]

Hey Chris,

I'd like to see some photos - out here in public if that's okay.
I see you have an H28, i have a Compass 28 and H28s were on my shopping list before i bought the Compass.

I've just finished the Lechter book on self-steering and have my heart set on using a trim tab on the primary rudder. Trouble is the rudder is inboard, and i can't get my head around the engineering difficulties of using a trim tab on an inboard rudder. How to get the control up to deck level from underwater?

What did you do with your H28?

I really like my transom and am loathe to clutter it up. My favourite view of my boat is from astern, i feel the same way about women...

Cheers,
Matt