Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors
Old 04-10-2017, 11:46 PM
jdory jdory is offline
Junior Member
Join Date: Aug 2015
Rep: 10 Posts: 59
Location: Nome, Alaska
Need catamaran rudder head advice

I'm rebuilding a 30' cruising cat
(30' cruising catamaran repair log)
and have 1.5" round bar rudder shafts in 316L stainless. Living in very rural Alaska no one here has a mill that can cut keyways. My old rudder heads were aluminum with keyways so I had to protect against corrosion with goop as well as have keys. To get keyways cut into these new shafts I would need to ship to Anchorage where I can get the keyways cut for $200 for two shafts, but also would take a couple hundred to ship down and back.

Design isn't specific on this point but looks like a detail shows something not much more than a small section of pipe slipped over the shaft with a through bolt. I could do that myself - got the cobalt drill bits. Also a guy in town is good at tig welding stainless if I need to beef up any straps from head to tillers. I'll include a pic or two of old jury rigged system that worked under motor (never had it rigged for sail). I could still use this head without a key and just run a bolt or roll pin through it. It would clamp tight.

So looking for advice/pics of folks' rudder heads.

Second question - If I cut keyways or drill a through bolt, should I put ackermann geometry into that keyway/hole in relation to centerline of the rudder blade or just plan on bending inward each tiller, if that works?

Here's old head and tiller attachment, and a pic of James's boat steering system I'm shooting for similar:
Attached Thumbnails
Need catamaran rudder head advice-rudderhead.jpg  Need catamaran rudder head advice-tiller_connection.jpg  Need catamaran rudder head advice-steering_system.jpg  

Reply With Quote
Old 04-11-2017, 02:53 AM
PAR's Avatar
PAR PAR is offline
Yacht Designer/Builder
Join Date: Nov 2003
Rep: 3967 Posts: 17,963
Location: Eustis, FL
What is the shaft head fitting made of, Aluminum? I sure don't like the cast in key, but if it's aluminum, it's understandable from an engineering point of view. If the shaft head fitting can clamp down pretty good, you might just consider a couple of (bigass) set screws, which I'd install in some stainless "helicoils" to insure they don't strip with adjustment and loading. This you could do yourself, assuming some good bits and reasonably careful work. In short, if that cast (aluminum) key can do the job, a couple, maybe three setscrews can too.

Yeah, you'll have to keep ackermann angles in mind when you put the steering back together. The way most do this is by "clocking" the shaft head fitting, so both sides land on the crossbar with similar angles. I wouldn't be surprised if the key and slot are clocked, which solves the problem. You can bend the tiller brackets, but I don't like this as much as you're introducing an additional "moment" to the assembly, though this isn't all that uncommon either.
Reply With Quote
Old 04-11-2017, 10:26 AM
jdory jdory is offline
Junior Member
Join Date: Aug 2015
Rep: 10 Posts: 59
Location: Nome, Alaska
Thanks Par, some good advice.

The head pictured is aluminum but I think it is just milled out of thick stock, not cast. The key is stainless and removable. Not "clocked" to ackermann.

The more I think about it the more sense to just reuse what I have. I like the idea of set screws - I assume one would divot the shaft somewhat where the set screw bears against it.
Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
Rudder head blowout! paxfish Multihulls 6 07-01-2015
07:31 PM 
Request Advice for Rudder Replacement HighFly_27 Boat Design 4 11-11-2012
12:01 PM 
Need advice on building a wooden rudder smtoole Sailboats 13 02-27-2011
07:48 PM 
Head up or head down in threatening gust? sandy daugherty Multihulls 4 09-01-2008
09:32 AM 
Advice needed:making carbon rudder stock Pjd Boat Design 9 04-30-2006
04:34 AM 

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.

All times are GMT -5. The time now is 08:29 PM.

Powered by: vBulletin Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2017 Boat Design Net