Full or modified full keel rudder attached...why not vertical rudder?

[nematon785]

On many sailboat designs with a full or modified full keel, I notice the rudder is often swept forward at the lowest point of attachment rather than vertical. The design does not make sense to me, it looks like it would cause the tiller or wheel to be heavy and increase weather helm, some of the effect when turning hard over would push the stern down or even slow the boat rather than steer especially at hull speed. An example here is a typical alberg design cca hull, the rudder sweeps forward as depth of hull increases.

I am not a naval architect, so I am guessing there is a good reason for this racing rule perhaps, asthetics, or better yet, a positive handling quality?

The contesa 26 is another good example here. Maybe it is just a folkboat thing?

Anyone know the reason for this design feature?

[roverhi]

It's an attempt to reduce wetted surface on a full keel boat for light air performance. Yes, it's illogical but racing and rating rules have made for some pretty weird under water profiles. IIRC, a forward canted rudder is less effective than a vertical rudder though can't remember the physics of it.

[Steveschr]

It's funny, I just read about this in Hiscock's Cruising Under Sail. He writes it's done to decrease wetted surface by shortening the keel and agrees that if there's too much rake the boat will exhibit the symptoms you describe. I own a full keel boat with the rudder swept forward and it drives great

[ggray]

Hiscock really had the problem demonstrated to him.

One of his Wanderers steered so badly because of this, he had to have a major, major rudder rebuild to correct it, soon after it had been built.

There was an article in Cruising World, I think, describing this surgery.

[Don C L]

Well I have one of those CCA long keels and angled rudder, and it sails well, balanced well and it turns just ok, but it does turn. I do not know the answer to your question though and I wish I did! A quick search turned up nothing definitive and no good drawings of comparing rudder angles. My ASSUMPTION has always been that the narrower rudder would be stronger but that the angle provided a longer surface to the water flowing over the rudder to act on, but then that is just a goofy guess. As with any boat, the rudder effectiveness declines as it heels, and our CCA boats like to heel so it behooves us to be sure the boats are well balanced and rigs tuned so there is a minimum of weather helm. And you are right, the rudders act as brakes after a certain point.

[nematon785]

Hey Don!

next time I'm in Oxnard we should do lunch at the fish n chips/sushi place near vintage marina. I'd love to see your boat if you don't mind visitors. I almost got my grubby paws on a columbia 29 a while back, but somebody beat me to it.

I'm still looking for my 1st boat, I'm focused on an ericson or cal around 35 foot. hoping the summer time brings out a few more options.

[Adelie]

CAMarchaj discusses this in his book, "Seaworthiness". There was a period where keel length rather than LWL was a factor in handicapping boats for racing in the mid-1800's under the Builder's Old Measurement (BOM) and Thames Measurement (TM) rules. Hence the raking of the leading edge aft and the trailing edge forward to minimize keel length which is rated relative to waterline length with is what really is related to boat speed. Like a lot of things the design practice outlived the original reason. While raking the trailing edge forward probably does reduce wetted surface, there are plenty of other design possiblilities that would also work with the materials then available, it was just a function of them overcoming existing design customs.

Hiscock's experience with needing to redesign and rebuild the rudder for Wanderer-V was mentioned in Marchaj's book.

[Don C L]

Originally Posted by nematon785

Hey Don!

next time I'm in Oxnard we should do lunch at the fish n chips/sushi place near vintage marina. I'd love to see your boat if you don't mind visitors. I almost got my grubby paws on a columbia 29 a while back, but somebody beat me to it.

I'm still looking for my 1st boat, I'm focused on an ericson or cal around 35 foot. hoping the summer time brings out a few more options.

You bet! I'll PM you. We'll take her out!

[Valmika]

Originally Posted by Don C L

You bet! I'll PM you. We'll take her out!

Hey. I like that fish and chips place. Can I get in on that action? Or maybe you guys come down here and we get take fish and chips out on my boat

[nematon785]

Hi Valmika! sounds like loads of fun. I will undoubtedly provide entertainment for the boating community when I first splash my new (to me) boat, sailing around with 20 fenders out everywhere I go, wearing 3 life jackets at a time, snarled in my own jackline, saying inane things on the radio, getting towed etc... so some friends around the marinas would definetly be appreciated!

Speaking of rudder angle, would a spade rudder swept back rather than forward (example a cal 34) exhibit the opposite or other noticeable characteristics? such as raising the stern when hard over, slowing the boat?

I am also curious if an angled rudder shaft places unbalanced loads on the bearings in a rudder post/spade configuration.

It seems like the modern design among racing boats is a deep high aspect foil that is vertically hung, but cruising vessels even brand new still sport all sorts of rudder layouts.

Obviously these boats are all well proven, and this is an academic discussion, but it is interesting to me.

[S/V Alchemy]

Originally Posted by Adelie

CAMarchaj discusses this in his book, "Seaworthiness". There was a period where keel length rather than LWL was a factor in handicapping boats for racing in the mid-1800's under the Builder's Old Measurement (BOM) and Thames Measurement (TM) rules. Hence the raking of the leading edge aft and the trailing edge forward to minimize keel length which is rated relative to waterline length with is what really is related to boat speed. Like a lot of things the design practice outlived the original reason. While raking the trailing edge forward probably does reduce wetted surface, there are plenty of other design possiblilities that would also work with the materials then available, it was just a function of them overcoming existing design customs.

Hiscock's experience with needing to redesign and rebuild the rudder for Wanderer-V was mentioned in Marchaj's book.

Good memory! I have a lot of these old volumes in the shelves but some of the niceties have gone done the memory hole as I have to remember things like my MMSI.

[Adelie]

Originally Posted by nematon785

Hi Valmika! sounds like loads of fun. I will undoubtedly provide entertainment for the boating community when I first splash my new (to me) boat, sailing around with 20 fenders out everywhere I go, wearing 3 life jackets at a time, snarled in my own jackline, saying inane things on the radio, getting towed etc... so some friends around the marinas would definetly be appreciated!



Speaking of rudder angle, would a spade rudder swept back rather than forward (example a cal 34) exhibit the opposite or other noticeable characteristics? such as raising the stern when hard over, slowing the boat?



I am also curious if an angled rudder shaft places unbalanced loads on the bearings in a rudder post/spade configuration.



It seems like the modern design among racing boats is a deep high aspect foil that is vertically hung, but cruising vessels even brand new still sport all sorts of rudder layouts.



Obviously these boats are all well proven, and this is an academic discussion, but it is interesting to me.

High end racing boats use plumb high aspect fin and rudder because that is the most efficient. The downside is that they can collect seaweed. Some race boats have little windows in the hull at the leading edge to check for weed accumulation.

On cruising boats you don't want the windows because they are both a weak point in the hull and an added maintenance item. Instead the fin and rudder sweep back to shed weeds.

In the case of the Cal34 the rudder shaft sweeps back so it is perpendicular to the hull at that point. Thus the top of the rudder stays tight to the hull regardless of rudder angle and it doesn't suffer tip losses at the top. If the post were plumb the trailing portion of the top of the rudder could not be tight to the hull or it would bind on the hull at moderate rudder angles.

[Don C L]

Originally Posted by Valmika

Hey. I like that fish and chips place. Can I get in on that action? Or maybe you guys come down here and we get take fish and chips out on my boat

Great! Who's bringing the beer?

[picklesandjesse]

Originally Posted by ggray

Hiscock really had the problem demonstrated to him.

One of his Wanderers steered so badly because of this, he had to have a major, major rudder rebuild to correct it, soon after it had been built.

There was an article in Cruising World, I think, describing this surgery.

I remember this. They had sailed from NZ in the new boat and arrived in Coffs Harbour. Got to have a cup of tea with them. They looked so old and weak but were super organised and Susan knew where every item on the boat was. Later they sailed down to Pittwater and Hank Kaufmann at Lovett Bay boatshed redesigned and built a new rudder for them. He was a good friend of Joe Adams and designed some of the Northshore boats.

[roland stockham]

I may be completely wrong on this. My understanding is that an elliptical shape on any wing reduces turbulence and drag produced by tip vortexes. Long keel boats are designed to sit on the keel alongside so can't have this shape but some taper helps. Also if done right it can produce significant lift when going to windward heeled. This is definitely true on the Folkboat, I have occasionally seen positive numbers for leeway from them. Remember to think of the keel as a second wing flying through the water and balancing the wing flying in air rather tha a static counterbalance.