Skeg hung rudders

[sailaway21]

I think stalling upon initial steering input is more a function of underwater hull form than rudder design. Beyond that, there's little to be gained and much to be lost, turning the rudder much past 30-35 degrees. Now that's a stall.

[sailhog]

Last summer, while sailing among a pod of dolphins, one of them hit our rudder so hard that it "whipped" the wheel out of the hands of the eight year old boy who was manning the help at the time. The boat is a 28 year old C30 and has a spade rudder... The only reason I mention this is that the collision did result from "driving over" a submerged object which, as Sway pointed out, would likely be pushed aside by the keel. Anyway, the rudder post and stock were not damaged, but definitely it got my attention...

[Plumper]

Originally Posted by sailaway21

I think stalling upon initial steering input is more a function of underwater hull form than rudder design.

Can you explain that? I am not sure what you mean.

Gaz

[sailaway21]

Without tearing into dynamically stable versus unstable hull forms, there are some that seem to need a bit more "kick" to get turning. Others respond to the smallest input. I would subscribe it to afterbody hull form, rudder size and shape, and ultimately flow over the rudder. Obviously, on a sailboat it is difficult to determine under sail versus the modeling tank. Increases in heel, speed, and leeway are all going to influence rudder balancing and any propensity to stall at a given rudder angle.

[Plumper]

Sorry, I still don't get it. Why does underwater hull form have more effect on rudder stalling than the shape of the rudder?

A boat with no rudder doesn't stall.

[Giulietta]

My rudder does stall, but clearly lets you know about it. The good news is it un-stalls rapidly too.

In fact, with my boat, if are not carefull when tacking, and because it pivots on the keel, if you are "over eager" it will stop the boat...hand brake type thing...

In reverse, you really need to center the rudder, then get speed for it to change the boat...if you don't...it just keeps going back with the rudder completely sideways.

It behaves funny, and you need to unerstand it...when you turn too much...it stalls then gets into a "sieways" position where it stops the boat..the feel is easy, and with a little experience you can feel it coming...

Its one of the things I laugh when other sailors sail my boat for the first time. a few inches wheel rotation will make you fall off your feet!!

Ask Tom and Val hehehe I got used to it..that's the way i want it anyway...

[sailaway21]

I'm referring to your post #46 and "initial stalling". If by "aggressive" there, you meant rudder angles of more than 30-35 degrees, I'd say that stalling is inevitable with any rudder unless the speed is very slow and there's prop wash over the rudder.

[Plumper]

Has that anything to do with the underwater hull form you mentioned earlier?

[Ilenart]

Originally Posted by Jeff_H

That is somewhat eroneous these days. Brewer's book was written back in the 1970's and a lot has happened since. The reality is that post hung rudders are no more prone to stalling than skeg hung rudders. The issues are vitually the same and relate to the rudder's aspect ratio, foil shape and camber depth rather than whether the rudder is post hung or skeg hung.

Jeff

Jeff,

thanks for the info. Not sure myself as I have not sailed a boat with a spade rudder. The quote actually comes from his book published in 1994. I even found the page on google books. I cannot post the link but if you google "spade rudder stall" it brings up the quote on page 40 of "Understanding Boat Design". Makes me wonder why I brought the book!

Ian

[tdw]

Originally Posted by JohnRPollard

TDW,

I still can't say for sure, but looking at the drawings my best guess is that your rudder "stock" extends straight down from the tiller head through the leading edge of your rudder. This would make it an unbalanced spade rudder, which is a favorable design for straight-line tracking, not unlike our skeg hung rudder but lacking the skeg. It lacks the "power steering" feel of the semi-balance rudder, but since your VDS 34 is fitted with a wheel you probably don't notice the extra effort necessary to turn the rudder.

Another advantage of this arrangement is that a small piece of material (either a bent piece of bronze or some kind of plastic/rubber flap arrangement) can be fitted to the bottom of the hull just slightly forward of the upper leading edge of the rudder, to prevent warps, grass, or other debris from wedging and snagging in the gap between the top of the rudder and the bottom of the hull. With a balanced rudder, the forward leading edge of the rudder pivots out to one side or the other, making that gap larger and more difficult to shield.

P.S. I like the lines of your boat and the sensible interior layout.

John,
Hadn't looked into this thread for a few days so missed your post until now. I take your point, indeed some VDS 34s have a mini skeg fitted that would work as you say. Mind you the gap twixt top of rudder and hull is very small.

Oh, and thanks for your kind words on the design. She does indeed have a nice sensible interior layout. The only things I don't like are more to do with her overall size. V-berth is a bit tight up forward and she could do with a larger head but I guess that's why we are looking to go up a size of two.

Cheers