Rudder post

[KnottyBuoyz]

Do these need to be a solid shaft or is pipe ok?

Boat is a single diesel trawler, 40-50HP, 11,000 lbs.

Rudder will be NACA0012 profile, foam core composite. Inner structure will be 19.4oz per sq yd SAERMAX multiaxial carbon fiber and outer 1708 Biaxial F/G.

Heavily leaning towards bootlegging a design for an articulated rudder which might put a little more stress on the rudder post. Would a 1-1/4" 316L Sched 80 pipe work?

[SamSam]

The biggest stress point is above the blade where the shaft goes into the hull. You might put a short piece of solid shaft inside the hollow one where the max stress will be if you need/want to use a hollow shaft.

[KnottyBuoyz]

Originally Posted by SamSam

The biggest stress point is above the blade where the shaft goes into the hull. You might put a short piece of solid shaft inside the hollow one where the max stress will be if you need/want to use a hollow shaft.

Cool. I was leaning towards a solid shaft from the flange on the top of the rudder shaft up into the boat. Makes sense really.

[KnottyBuoyz]

What's the most common material for rudder posts? I'm guessing Stainless but as others have said not ideal for underwater. I'm almost contemplating a carbon fiber post within the rudder blade up to the flange which would mate to a SS flange shaft that goes up into the rudder post packing gland/bearing. Comments? Suggestions?

[KnottyBuoyz]

Anybody used carbon fiber tubes or rods for rudder posts?

http://www.graphitestore.com/itemDet...d=34&curPage=1

[Gilbert]

I would question your choice of a foil shaped rudder for a power boat.
Even with a balanced rudder blade as you show in your sketch a rudder in the wash of a propellor it will have a few degrees of a dead spot both sides of center where the rudder will not supply a turning moment to the hull unless the rudder is wider at the back than the front. If you have an autopilot, the pilot will 'hunt' in this area causing a delay in steering response. Type www.metalmarinepilot.com into your browser and you can read about some research results on this subject. If you send them information about the rudder and prop size and location they will even tell you exactly how they would recommend you make your rudder. For free.