question on rudder design

[Dan McCosh]

Always wondered why older boats with the rudder attached to the keel often had a steeply raked rudder post, rather than vertical. Seems as if it would add drag.

[John B]

The period which was my special interest was just after the transition from the 'old' boats of the 1880's to the new breakthrough boats of the 1890's.
The progression being from longer keels and more vertical rudders to shorter keels with cutaway forefoots and more inboard rudders. Bringing the rudder heel foward made it raked but causes a braking drag as you turn it. But in general the drag of the hull is lessened because of less wetted surface underwater .
It can't have been too bad because those basic hull forms and that rudder style stayed with us right through until the early / mid 60's when established designs began to have vertical spade rudders fitted for better control racing , particularly running and under kite. For example ,quite a few new ' hot' S and S boats suddenly were pulled and changed halfway through a season or were changed in the off season for next as well as some top racers from the 30's and 40's here. Some boats kept a vestigal keel rudder as a trim tab.
Another attribute of a well inboard rudder was great turning, my 1907 boat was really nimble and although running in a seaway she could have been better, it wasn't a bad experience. I just think it became accepted Naval architecture as how it was done, how you minimised wetted surface, and it was accepted that way for a good 50 odd plus or minus years.

[Peerie Maa]

^ There is another reason for raking the stern post. It was easier to build a carvel planked boat with fine lines.

[John Meachen]

Wasn't there a rating rule that penalised length of keel?

[sp_clark]

CLC's Waterlust expedition canoe's prolly got this design out of 'tradition' despite being a modern approach (lapstrake plywood, epoxy) to a century-old watercraft. Makes for really fussy mounting of rudder hardware it does:

Waterlust.png

I know one builder who opted for adding a sternpost of sorts and extended skeg so as to avoid the fussiness I encountered building mine.

I may yet do something similar despite having mine finished & launched if for no other reason than to explore the differences between the two approaches.

[Peerie Maa]

CLC's Waterlust expedition canoe's prolly got this design out of 'tradition' despite being a modern approach (lapstrake plywood, epoxy) to a century-old watercraft. Makes for really fussy mounting of rudder hardware it does:

Waterlust.png

I know one builder who opted for adding a sternpost of sorts and extended skeg so as to avoid the fussiness I encountered building mine.

I may yet do something similar despite having mine finished & launched if for no other reason than to explore the differences between the two approaches.

ISSATSO?

[John B]

The period which was my special interest was just after the transition from the 'old' boats of the 1880's to the new breakthrough boats of the 1890's.
The progression being from longer keels and more vertical rudders to shorter keels with cutaway forefoots and more inboard rudders. Bringing the rudder heel foward made it raked but causes a braking drag as you turn it. But in general the drag of the hull is lessened because of less wetted surface underwater .
It can't have been too bad because those basic hull forms and that rudder style stayed with us right through until the early / mid 60's when established designs began to have vertical spade rudders fitted for better control racing , particularly running and under kite. For example ,quite a few new ' hot' S and S boats suddenly were pulled and changed halfway through a season or were changed in the off season for next as well as some top racers from the 30's and 40's here. Some boats kept a vestigal keel rudder as a trim tab.
Another attribute of a well inboard rudder was great turning, my 1907 boat was really nimble and although running in a seaway she could have been better, it wasn't a bad experience. I just think it became accepted Naval architecture as how it was done, how you minimised wetted surface, and it was accepted that way for a good 50 odd plus or minus years.

A favourite of mine and one of the S and S boats I was particularly thinking about above.
Screenshot_20221229_132606_Trade Me.jpg
Satanita is a Firebrand from 1966, you can see from her keel shape that she was launched with a keel hung rudder ( fairly lightly raked compared to earlier boats) and was retrofitted in her first season with the skeg/ rudder aft. It was a time of change, another well known S and S here was hauled in her first year, rudder shifted aft and her whole stern cut away and filled out to give her firmer quarters in order to gain sail carrying power. Ranger and Fidelis , both Reimers influenced types around 60 ft + were changed too( although Ranger later reverted to her 1938 keel hung rudder)
An interesting period. Incidentally , the reason the brand new 60 ft S and S Ta Aroa was so radically cut and changed ( including a visit here from Olin himself to work it all out) was that she couldn't beat Ranger, the 1938 60 ft Reimers influenced type which had dominated Auckland racing for 30 years.

[wizbang 13]

Is part of the reason to balance the rudder Nick?

[Peerie Maa]

Is part of the reason to balance the rudder Nick?

Not in the sence that a foil is ballanced, A ballanced rudder cannot be hung on a stren post as about 1/4 of its area is forward of the stock.

[sp_clark]

ISSATSO?

The fussiness came from working out exactly where fasteners could be placed to hold gudgeon & pintle, lacking a dimensional sternpost as on your faering Nick.

Available rudder hardware's either flat-mounted to a conventional transom or parallel-armed to fit onto a thicknessed sternpost.

Once I got my items re-shaped to match the contours of the stern, securing lower pin took some trial-and-error owing to the lack of space down low inside, between the stern panels where fasteners had to be just long enough to allow nuts to be secured but not so long as to interfere with one another coming from opposite sides.

Assembled_Rudder.jpg

I used your suggestion for positioning my hardware so that mounting rudder before launching'd be straightforward, and it is that! There's a little bit of friction on those pins when mounting the rudder, enough so that it doesn't want to float free once in the water but not so much that it affects how the tiller responds to input in use.

[Andrew2]

I have a similar rudder set up on my Oughtred Whilly Tern, though the pintles are a bit more angled like Nick's.
Odd thing is, it doesn't 'weathercock' but acts like an overbalanced rudder. So, if rowing, I have to centre it with a bungee/line system, or it goes straight over to one side or the other and makes progress very difficult.
A2

[stromborg]

Odd thing is, it doesn't 'weathercock' but acts like an overbalanced rudder. So, if rowing, I have to centre it with a bungee/line system, or it goes straight over to one side or the other and makes progress very difficult.
A2

While I don't row my Eun Mara i have the same issue with her current rudder, it flops right over if left untended and I'm convinced acts as a brake when tacking. One of my upcoming winter re-fit projects is a whole new assembly that will include a foiled rudder. Some sort of sculling oar might be in the works too, but that will be another thread.

[Peerie Maa]

There's a little bit of friction on those pins when mounting the rudder, enough so that it doesn't want to float free once in the water but not so much that it affects how the tiller responds to input in use.

That is where the Scandinavian/Shetland captive bolt on the upper pintle is of real benifit.
You drop the lower gudgeon over the lower pintle. Then lift the bolt and swing the upper gudgeon sideways into alignment, drop the bolt through the gudgeon and bobs the relative of your choice.

[JimConlin]

The weight of the tiller wants to swing off the centerline.
If the rudder is buoyant, it too wants to go off center.
Fixes might include weighting the rudder off-axis, lightening the tiller or using a different steering system.

[John B]

Some of the very big/ extreme examples with raked rudder posts like Reliance for example, exploited the tendency to float the helm off centre by having water ballasted rudders, so as to alter both trim and helm balance while sailing.
A couple of our local boats of the general type , mid 1890's through early 1900s were restored in recent years with bouyant rudder blades with the idea of adding buoyancy aft for performance reasons. They forgot about or did not know about the side effect which we're discussing here and had tillers that would hammer over to one side or another at rest, and somewhat goofy handling when sailing. They had to ballast the blades to get them back to a more intuitive feel.

(Edit: and this is why I have reservations about Mike's rudder in his current restoration in Building repair, Its going to be fascinating to see how that works out)

Another factor and similar in a way to the original question of " why are they raked" , the answer being it was the belief of Naval architects/ designers of the day and for the next 50 odd years that it was the best way to acheive a performance gain, is that yachtsmen and designers 'all' believed that a hard mouth, a heavy helm made a boat that performed best to windward. Weather helm defaults to sending the boat upwind and a beefy guy on the tiller would force the boat down to its sweet spot.
This existed right up until quite recent times when the combination of materials, foil expertise and other methods to acheive a boat that both perfomed to windward and still had a balanced helm running hard in a breeze( like canards for example, that shifts lateral plane forward for windward work and aft by removing for downhill). I've had conversations with the winner of the One Ton Cup in 1970 ish on the subject( a very famous NZ yachtsman), where it was still believed that a sailing yacht should have 5 degrees of weather helm when sailing to windward right up until say 20 years ago approx.
Now of course a top boat will have feather light helm on all points of sail due to non distorting blades both up in the air and perfect blades down into the water.
So what we would now think of as unacceptable both for comfort and performance reasons was most definitely acceptable to the experts of the days on performance grounds right through until maybe the 1970's /80s or so, or later .

[Dan McCosh]

Interesting answers. Still, it seems as if the rake introduces a force component at a relatively steep angle to the direction of travel, rather than maximizing the force that directly produces yaw--the steering force. Would the water flow at an angle of heel have something to do with it?

[stromborg]

Those big wide-bodied racing boats have gone to twin rudders, notice how they are canted out? I'm guessing counteracting the heel has something to do with why they do that.

[John Meachen]

I think that might be a mistaken guess,the force to counteract the heeling moment would be enormous.I believe the rationale is that with wider sterns,a central rudder would be lifted clear of the water to some extent.On top of that,it is logical to have the vertical axis perpendicular to the section so that the gap between the hull and rudder doesn't become much larger when the helm is moved.The downside is that a lot more hardware has to be bought and installed and sometimes this is justified by the extra volume of the wider hull.

[Canoeyawl]

I have a similar rudder set up on my Oughtred Whilly Tern, though the pintles are a bit more angled like Nick's.
Odd thing is, it doesn't 'weathercock' but acts like an overbalanced rudder. So, if rowing, I have to centre it with a bungee/line system, or it goes straight over to one side or the other and makes progress very difficult.
A2

So, when sailing if you let go of the helm, the rudder goes hard over and stays there?

[kbowen]

Interesting answers. Still, it seems as if the rake introduces a force component at a relatively steep angle to the direction of travel, rather than maximizing the force that directly produces yaw--the steering force. Would the water flow at an angle of heel have something to do with it?

I am interested in this answer. But isn't what Dan calls drag also lift, but in a different plane? If the rudder stock is raked then hauling the rudder off the centerline going to windard when the boat is heeled is indeed drag but it is also lifting the stern? And shoving the tiller to leward would be digging in the stern, is this correct? Could there have been any reason that this might have been a benefit? I have a Mackinaw boat with a raked sternpost and I have always wondered why the old timers did this. There is a deep historical legacy in small craft of the coast of France and the West coasts of the British Isles & Ireland for a raked sternpost and it is hard to imagine that most of those folks were obsessing about reducing wetted surface.

Ken

[Mike1902]

Some of the very big/ extreme examples with raked rudder posts like Reliance for example, exploited the tendency to float the helm off centre by having water ballasted rudders, so as to alter both trim and helm balance while sailing.
A couple of our local boats of the general type , mid 1890's through early 1900s were restored in recent years with bouyant rudder blades with the idea of adding buoyancy aft for performance reasons. They forgot about or did not know about the side effect which we're discussing here and had tillers that would hammer over to one side or another at rest, and somewhat goofy handling when sailing. They had to ballast the blades to get them back to a more intuitive feel.

(Edit: and this is why I have reservations about Mike's rudder in his current restoration in Building repair, Its going to be fascinating to see how that works out)

Oh ye of little faith

Been doing a bit of tank testing at the local pool.
The yellow tape is the bottom edge of the rudder head and reasonably close to the waterline when mounted on the dinghy.

IMG-8831.jpgIMG-8847 (1).jpg

First up was submerging the rudder vertically to see how deep it would go before reaching positive buoyancy, 3/4 of the rudder area below the waterline submerged.
When raked, about 2/3rds of the rudder area below the waterline was submerged, meaning it became more buoyant because the direct overhead loading was lessened.

IMG-8852.jpgIMG-8884.jpg

When inserted into the rudder head, the added weight submerged the rudder and part of the rudder head to close to where it will sit in the water when mounted on the dinghy.
In the right image above I held the top of the rudder lightly between thumb and fore finger then raked the rudder forward at the bottom as well as sideways imitating an angle of heel.
I then walked along the edge of the pool pushing the rudder. The whole unit was very stable, when turning the rudder from side to side the amount of force required was enough to indicate a firm tiller.

The unit as a whole did not want to lift sideways and I let it support itself (buoyancy) when moving forward.

The degree of accuracy may be a bit rustic but the feel is good and by that I mean that the force required by the thumb and fore finger to hold everything in line was minimal.
When applying a turning force, there was an amount of resistance that indicated a helm that would track ok.
Of course the pivoting point provided by the pin and gudgeons will be forward of where I was holding ,which should only improve the performance...I hope.

Cheers,
Mike.

[Andrew2]

So, when sailing if you let go of the helm, the rudder goes hard over and stays there?

Didn't see this for a few days.
Yes, the steering forces are very light, but if I do let go, the helm drops to leeward. Happy with that, as it has slight weather helm. The comments about floating above would make sense when not moving, but not when some flow is over the rudder. It is something I just put up with and the bungee/cord system sorts it.

[John B]

Oh ye of little faith

Been doing a bit of tank testing at the local pool.
The yellow tape is the bottom edge of the rudder head and reasonably close to the waterline when mounted on the dinghy.

IMG-8831.jpgIMG-8847 (1).jpg

First up was submerging the rudder vertically to see how deep it would go before reaching positive buoyancy, 3/4 of the rudder area below the waterline submerged.
When raked, about 2/3rds of the rudder area below the waterline was submerged, meaning it became more buoyant because the direct overhead loading was lessened.

IMG-8852.jpgIMG-8884.jpg

When inserted into the rudder head, the added weight submerged the rudder and part of the rudder head to close to where it will sit in the water when mounted on the dinghy.
In the right image above I held the top of the rudder lightly between thumb and fore finger then raked the rudder forward at the bottom as well as sideways imitating an angle of heel.
I then walked along the edge of the pool pushing the rudder. The whole unit was very stable, when turning the rudder from side to side the amount of force required was enough to indicate a firm tiller.

The unit as a whole did not want to lift sideways and I let it support itself (buoyancy) when moving forward.

The degree of accuracy may be a bit rustic but the feel is good and by that I mean that the force required by the thumb and fore finger to hold everything in line was minimal.
When applying a turning force, there was an amount of resistance that indicated a helm that would track ok.
Of course the pivoting point provided by the pin and gudgeons will be forward of where I was holding ,which should only improve the performance...I hope.

Cheers,
Mike.

Excellent, I'm very interested to see how it works out on the boat given the observations of the fails on the big boats I mentioned.
I think the best thing to do is to just bring the completed boat on up to Northland for some extensive testing/ trials.

[Mike1902]

Excellent, I'm very interested to see how it works out on the boat given the observations of the fails on the big boats I mentioned.
I think the best thing to do is to just bring the completed boat on up to Northland for some extensive testing/ trials.

I think you are right, JB.

When you take it out solo, I will take research photos from the Panga.
The capsize drills will be very informative regarding flotation and righting ability, oh and safety in general I suppose.

Can the Panga tow a dinghy doing an impression of an iceberg?

Jokes aside, the Northland waters are high on the list of places to camp cruise.

Cheers,
Mike.