Rudder Angle and Ackerman

[Alisske]

I thought any angle over 35 degrees makes the rudder essentially a brake.

I had a misaligned rudder on a single screw downeast. When i bought it, it would turn to port fairly welll, but hard over to starboard, it was a pig. (Was going 25 degrees port and 45 degrees starboard). It made steering unpredictable. Would steer well to starboard until hard over then went dead.

The prior owner installed a bow thruster to help. Lmao.

After i made the adjustment (the ram was places in the wrong spot in the steering arm) it steered much better in both directions etc…

At planning speeds, your not going to use full over steering amyways. Its all about lower speed steering anyways

[rslifkin]

Originally Posted by Alisske

I thought any angle over 35 degrees makes the rudder essentially a brake.

I had a misaligned rudder on a single screw downeast. When i bought it, it would turn to port fairly welll, but hard over to starboard, it was a pig. (Was going 25 degrees port and 45 degrees starboard). It made steering unpredictable. Would steer well to starboard until hard over then went dead.

I think it depends a bit on the shape of the rudder (and things like whether the rudder has a keel in front of it, or a skeg) and also how the boat moves through the water. My boat has its pivot point fairly far forward, so the stern gets moving sideways fairly quickly in a tight turn. That likely increases the maximum usable rudder angle, as the angle of water flow over the rudder is reduced once the boat starts to turn. If I could swing the rudders to the stop quickly enough that the boat wasn't noticeably turning before I hit the stop, then there might be some risk of a rudder stall from excessive angle. My rudders are also spade rudders with just the props in front of them, but because it's a twin, there's no keel or anything else to impact the waterflow over the rudders.

[Alisske]

Mine was single behind a keel. Semidisplacement round chine hull

After the adjustment, it steered better both ways and more predictably.

When i measured the actual rudder swing and saw the “lopsideded ness” to it, everything made sense.

Again, i believe a rudder i er 35 degrees becomes a brake. (Hydrodynamically)

[rslifkin]

Originally Posted by Alisske

Mine was single behind a keel. Semidisplacement round chine hull

After the adjustment, it steered better both ways and more predictably.

When i measured the actual rudder swing and saw the “lopsideded ness” to it, everything made sense.

Again, i believe a rudder i er 35 degrees becomes a brake. (Hydrodynamically)

From what I know, that 35 degree figure is pretty typical for a flat plate rudder. And any rudder is going to have a good bit of drag at higher angles. Foil shapes, etc. can have different angles before they stall or develop any bad behavior though, and whether there's prop wash across the rudder or not is a factor too. Some rudders can go beyond 35* without stalling (just some extra drag but no bad behavior or loss of steering) while others (particularly on sailboats) may stall before 35*.

The other big question becomes what the actual angle of the rudder is to the water flow once you're in the turn. The rudder may be turned 30* relative to the boat, but with the boat turning, the actual angle to the water flow can be significantly less.

Full rudder on my boat definitely slows the boat down noticeably at lower speeds, so there's certainly a lot of drag there. But no bad behavior, it just turns.

[Alisske]

Good explanation (thx)

Yeah line was basically a flat 3/8 bronze plate. I guess nothing is that simple as one hard fast rule. (Lol)

Thx and be well