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rslifkin · 03-18-2023, 02:20 PM

I've always heard the prevailing wisdom that planing hulls typically have a 70* rudder sweep (35* in either direction). And that with twin rudders you typically want some Ackerman in the steering geometry so the rudder towards the inside of a turn streers to a higher angle than the rudder on the outside of the turn.

I was doing some work on my steering today and decided to check how far my rudders actually swing. Despite my boat being a planing hull (top speed around 25 kts, fast cruise at 17-18), I have over 90 degrees of rudder swing. And oddly, it has some reverse Ackerman. The rudder to the inside of a turn gets to 45 degrees, the outside rudder gets to about 50 degrees at full travel.

This certainly explains why this boat turns so tightly, but I'm a bit confused by the reverse Ackerman. It also explains why 5 turns lock to lock doesn't feel slow.

What's the group's thoughts on such high rudder angles on a faster boat and especially the reverse Ackerman?

03-18-2023, 02:20 PM	#1
rslifkin Guru City: Rochester, NY Vessel Name: Hour Glass Vessel Model: Chris Craft 381 Catalina Join Date: Aug 2019 Posts: 6,688	Rudder Angle and Ackerman I've always heard the prevailing wisdom that planing hulls typically have a 70* rudder sweep (35* in either direction). And that with twin rudders you typically want some Ackerman in the steering geometry so the rudder towards the inside of a turn streers to a higher angle than the rudder on the outside of the turn. I was doing some work on my steering today and decided to check how far my rudders actually swing. Despite my boat being a planing hull (top speed around 25 kts, fast cruise at 17-18), I have over 90 degrees of rudder swing. And oddly, it has some reverse Ackerman. The rudder to the inside of a turn gets to 45 degrees, the outside rudder gets to about 50 degrees at full travel. This certainly explains why this boat turns so tightly, but I'm a bit confused by the reverse Ackerman. It also explains why 5 turns lock to lock doesn't feel slow. What's the group's thoughts on such high rudder angles on a faster boat and especially the reverse Ackerman?