Why is my boat pointing into the wind?

[GreaseWspoon]

Originally Posted by Jim Cate

People seldom complain about a rudder being too powerful. In your place I'd make it fairly deep and enjoy the added control that this brings. I won't advise a specific dimension, for I don't know squat about that boat, but remember, if for some reason a deeper rudder has undesireable effects on your boat, it will be pretty easy to hack off a few inches from the heel of the rudder and reglass it. Not so easy to ADD depth with good strength.

Jim

That’s a great point

[pdxsailordiver]

Cascade Owners Unite - SeaKnots
On Seaknots site there is a cascade owners group. I posted there asking for plans for the 27.
With some luck somebody has a set.
Tim

[Captain Bill]

Originally Posted by GreaseWspoon

Update: the rudder skeleton is complete and I still have not been able to find the original dimentions For a cascade 27 rudder. I have had no luck getting ahold of russel from cascade, if any of you have any ideas for finding this Information or any advice on what you would recommend for how deep to make this thing it would be much appreciated. Another question : the two part expanding foam I was planning to use is only 2 pound. Do I need something more dense ? The drawing is what is left of the rudder (the bottom is broken off) So I really just need to know how how deep to make it.

2lb foam is very weak. Foss Rudders says on their web site that they use 20lb foam in their rudders. I have been researching this because my Foss rudder foam has failed. According to their web site their foam is temperature sensitive and even sunlight on a rudder painted a dark color can destroy the foam. Did the literature provided by my boat manufacturer mention this? In any case 20lb pour-able foam is readily available and it's probably a better idea to use a higher density structural foam than low density flotation foam.

I should note that I have a similar weather helm issue when I have the main trimmed too tight in strong winds and I loose steering effectiveness above 10 knots. I came across a document on rudder design a few months back on the internet and found that the designers of my rudders broke a cardinal rule of rudder design and rounded the leading edge of the bottom third of the rudder for aesthetic purposes and essentially ruined the foil. My hulls are rather strangely shaped and I believe they en-train a lot of air, especially near the top of the rudder at high speeds. So the top of the rudder is less effective and the bottom of the rudder is poorly shaped so steering goes to crap. When I rebuild my rudder I will use the same foil all the way to the bottom.

[Montanan]

Originally Posted by GreaseWspoon

Also I’ll include some photos of the form I built. My plan is to fill it with foam and then hand shape it like a surfboard , then glass it. Just need to know how how long to make it, I have it set around 45 inches right now just as my guess. Is this plan crazy?

First impression, there appears to be rather little lateral armature support for your foam just the four V shaped supports and those don't seem to extend fully aft or down. The rudder supports that I have seen either have metal panels running the length of the rudder and lateral V strengthening the metal panels, or the V supports are supported fore and aft with a length of welded metal so as to tie the lateral armatures together as a unibody framing, [albeit not many as one doesn't get to see the innerworkings of rudders very often, almost only from the outside and on a boat]. Reference images attached as examples, there being many such images on the web. The bottom of your rudder will need stiffening support to handle the severe loading; realize that the end of your rudder will see extensive forces so it needs to have stout supporting, I would not trust foam to hold up under twisting loads.

As to its performance and balance with the vessel, much will depend on your choice of NACA foil shaping and indeed the length of the working surface.

It appears your box provides for greatly longer rudder than your drawing, up to about 45 inches from the 30 inches of your drawing of the broken off rudder. But making it extra long, certainly allows for future shortening by cutting off a bit and reglassing the bottom if needed. A larger rudder will shift the CLR aft which should make the vessel less prone to desire to turn up wind, ie., experience "weather helm" because of the greater aft mounted lateral resistance foil [rudder] . A larger rudder does make steering more powerful.

I have heard arguments for having the lower portion of a rudder made without metal supports such that if it comes into harsh contact with a solid object, [such as grounding, or hitting a log] that the bottom can breakaway and be sacrificial leaving the upper less likely to be bent, or at least less severely bent. Sort of like using foam for making the leading edge of the vessel's bow so as make it easy for shape but also an easily replaceable and repairable bumper surface.

[Montanan]

A reference article:

https://wavetrain.net/2012/09/21/fib...-construction/

[Captain Bill]

Here is a link to the Foss rudder web site showing the same type of internal supports that the OP is proposing.

https://www.newrudders.com/rudder-construction/

[Montanan]

Originally Posted by Captain Bill

Here is a link to the Foss rudder web site showing the same type of internal supports that the OP is proposing.

https://www.newrudders.com/rudder-construction/

An excellent reference, note their use of 20 pound expanding foam as structural fill and the use of the vertical welded bar to tie each of the lateral armature bars together to act as one unibody solid frame and not the independent lateral armature bars.

[GreaseWspoon]

Great info from all of you I really appreciate it . I ended up doing a small test pour of the 2 pound foam I already had and it seemed to be the same density of the foam in the original rudder so I decided to use it. I added small plywood blocks on both sides of each rib so there wouldn’t be any foam taking pressure in between the ribs and the laminate and I plan to do a very Thick laminate. Hopefully this can be made stout enough, thoughts? Here is a photo of how far I got in shaping today , far from perfect.

[Montanan]

There appears to be very modest camber. The foam does not exceed the thickness of the rod.

Have you chosen a NACA like foil design? If so which are you attempting to emulate and shape?

Reference to a website from which you can select foils and print out the profile for your shaping comparators. http://http://airfoiltools.com/airfo...il=naca0018-il

Keeping it simple, recommended reference: Foil FAQ

I have read that NACA 0012 to 0018 are commonly used for rudders.

Excerpts therefrom:

"The most basic NACA section profiles are "symmetrical" and are good for rudders, especially, but also leeboards, daggerboards and centerboards. These are called the "four-digit" series and are identified by the name "NACA 00XX".

Look at your board end-on (in other words, a fish-eye view from underwater). The Y dimension is measured in both directions from an imaginary centerline through your board. It gives you both thickness and curvature. Connect the dots with a flexible batten (for example, 1/2-inch PVC tubing works for large foils. On small ones try piano wire, or if you have musician friends, a bass guitar G-string).

The chord is the "width" or front-to-back dimension of your board(s). For example, on certain Bolger boats the rudder and leeboard are both 10 inches wide. That's the chord. The thickness of a NACA section depends entirely on the chord of your board.

Finally, don't cheat. You'll discover that foil sections are thicker than you imagine. That's OK, because a proper foil shape has much less drag than you think looking at it. The thicker the foil, the more lift it will give you. The drag also increases as the foils get thicker, but you can't really separate drag and lift.

The main difference between a "thin flat plate" and a NACA foil is that the foil will generate lift, i.e. power, at a higher angle versus the boat's direction. Where a plain flat rudder will tend to stall and simply slow you down somewhere around +/- 5 to 10 degrees from center, a NACA foil will be effective over maybe twice that range. Your boat's rudder will work better. Tacking will be easier. A little bit of weather helm translates into more sideways 'push' upwind.

As a leeboard, centerboard or daggerboard the difference between the plate and foil would be much less pronounced because the boat is usually moving "crabwise" through the water at a much smaller angle than you'd use at the helm when tacking. As long as it doesn't vibrate, a flat plate is probably as effective and a lot less hassle than a shaped foil section"



Notes to the Chart

(1) The values listed beneath the NACA numbers are the distances + and - to the foil surface from the centerline in % of chord.

(2) Cut values for 0012 and 0018 in half to get 0006 and 0009. Double 0015 to get 0030. Halve 0006 to get 0003.

(3) It's conventional to make the chord 5% longer than you really want, and then slice off the last 5% to form a blunt strong edge after laying out the foil profile. Example: you want a 20-inch chord rudder. Calculate profile based on 21 inches, leaving off last 5% or 1-inch when laying out.

(4) The nose of a NACA 00-- foil is always circular. Fair this in by eye as best you can using a compass or template or some sort (bottom of McDonald's coffee cup). This radius can be generated by the formula referred to above. (I'm still not talking.)

(5) The thickness of a NACA foil is always greatest at 30% of the chord from the nose.

[GreaseWspoon]

I have been trying to copy the old rudder which didn’t have any foam wider then the post. I will take a look at the link, I’m not done shaping

[GreaseWspoon]

Originally Posted by Montanan

There appears to be very modest camber. The foam does not exceed the thickness of the rod.

Have you chosen a NACA like foil design? If so which are you attempting to emulate and shape?

Reference to a website from which you can select foils and print out the profile for your shaping comparators. http://http://airfoiltools.com/airfo...il=naca0018-il

Keeping it simple, recommended reference: Foil FAQ

I have read that NACA 0012 to 0018 are commonly used for rudders.

Excerpts therefrom:

"The most basic NACA section profiles are "symmetrical" and are good for rudders, especially, but also leeboards, daggerboards and centerboards. These are called the "four-digit" series and are identified by the name "NACA 00XX".

Look at your board end-on (in other words, a fish-eye view from underwater). The Y dimension is measured in both directions from an imaginary centerline through your board. It gives you both thickness and curvature. Connect the dots with a flexible batten (for example, 1/2-inch PVC tubing works for large foils. On small ones try piano wire, or if you have musician friends, a bass guitar G-string).

The chord is the "width" or front-to-back dimension of your board(s). For example, on certain Bolger boats the rudder and leeboard are both 10 inches wide. That's the chord. The thickness of a NACA section depends entirely on the chord of your board.

Finally, don't cheat. You'll discover that foil sections are thicker than you imagine. That's OK, because a proper foil shape has much less drag than you think looking at it. The thicker the foil, the more lift it will give you. The drag also increases as the foils get thicker, but you can't really separate drag and lift.

The main difference between a "thin flat plate" and a NACA foil is that the foil will generate lift, i.e. power, at a higher angle versus the boat's direction. Where a plain flat rudder will tend to stall and simply slow you down somewhere around +/- 5 to 10 degrees from center, a NACA foil will be effective over maybe twice that range. Your boat's rudder will work better. Tacking will be easier. A little bit of weather helm translates into more sideways 'push' upwind.

As a leeboard, centerboard or daggerboard the difference between the plate and foil would be much less pronounced because the boat is usually moving "crabwise" through the water at a much smaller angle than you'd use at the helm when tacking. As long as it doesn't vibrate, a flat plate is probably as effective and a lot less hassle than a shaped foil section"



Notes to the Chart

(1) The values listed beneath the NACA numbers are the distances + and - to the foil surface from the centerline in % of chord.

(2) Cut values for 0012 and 0018 in half to get 0006 and 0009. Double 0015 to get 0030. Halve 0006 to get 0003.

(3) It's conventional to make the chord 5% longer than you really want, and then slice off the last 5% to form a blunt strong edge after laying out the foil profile. Example: you want a 20-inch chord rudder. Calculate profile based on 21 inches, leaving off last 5% or 1-inch when laying out.

(4) The nose of a NACA 00-- foil is always circular. Fair this in by eye as best you can using a compass or template or some sort (bottom of McDonald's coffee cup). This radius can be generated by the formula referred to above. (I'm still not talking.)

(5) The thickness of a NACA foil is always greatest at 30% of the chord from the nose.

The link doesn’t work. Which exact foul shape do you recommend?

[Montanan]

Originally Posted by GreaseWspoon

I have been trying to copy the old rudder which didn’t have any foam wider then the post. I will take a look at the link, I’m not done shaping

That keeps the project simple and if the rudder is what Cascade specified then it should perform similarly. Similarly, adequate, good, inadequate?

Here is a link to the airfoils website where one can obtain the shapes if you wish to go that route.

Airfoil Tools

Another good reference:
Getting the most from your Rudder


Camber adds lift, and drag, but also tends to aid in providing for a wider range of angle of attack before stalling compared to a flat rudder. Angle of attack being the amount of degrees turned off center line.

When your rudder is turned too far over it will stall and you will feel an abrupt lack of directional control and typically considerable noise [the sound of cavitation] and vibration and a lot, A LOT, of drag and slowing. Slowing is not all bad when a boat tends to be getting out of control, think of it like a brake which is what it will become, a water brake. Ditto as to rounding up into the wind when experiencing weather helm which will lead to luffing and slowing.

Additional reference, titled Sixty years of research on ship rudders: effects of design choices on rudder performance.
https://www.tandfonline.com/doi/pdf/...2.2016.1178205

Excerpt:

Flat-plate profiles are normally rectangles in two dimensions
(square head in Figure 4). They are the simplest flow-deflecting
devices to design, the easiest profiles to produce, and the cheapest rudders to buy. To reduce the form drag, flat-plate profiles
may have semicircle or triangular leading and trailing edges
with faired tips (round head in Figure 4). Thieme (1965) indicated that the flat-plate profiles may achieve high efficiency in
straight-ahead condition. Liu and Hekkenberg (2015) showed
that this high efficiency only appears at small angles of attack,
i.e. up to approximately 5°. After this, the lift coefficient stalls
and the lift-to-drag ratio collapses. Additionally, flat-plate rudders stall at a smaller angle than other profiles due to earlier and
stronger flow separation (Liu and Hekkenberg 2015). At present,
flat-plate rudders are frequently seen on small boats and antique
inland vessels but not common for modern seagoing ships.

NACA profiles are the most widely applied rudder profiles

After a decision of the profile, detail rudder design of properties should be considered. Avoiding ambiguity, the rudder properties discussed in this paper are illustrated in Figure 5. see picture below.
These properties affect the rudder hydrodynamic characteristics and determine the effectiveness and the efficiency of the
rudder. Main properties discussed in the following sections are
area, thickness, span, chord, and aspect ratios. Sweep angles,
taper ratios, and tip shape have relatively small influences on
the rudder hydrodynamic characteristics.


Keep your shape simple, and perhaps shape it to say something resembling NACA 12 to 18 ish. As presently constructed your rod is defining the thickness and the placement of that thickness and sweep angle of the rudder, so unless you change things up those are kind of your build around dimensions from which one gets to taper from which apparently is what the damaged rudder you are replacing has. The rudder should be comparable to the thickness of your semi-skeg; I can't see any benefit for it to be much thicker or thinner than the leading skeg dimension.

I would recommend to not attempt a fishtail thin aft edge, it will be too weak, you will need to blunt the end to maintain some thickness and stiffness. Stiffness generally increases by the cube of the thickness, thus don't taper in the vertical direction so as to thin the lower section below your metal lateral supports as that part will require all the strength it can obtain by your foam fill material. I'm a bit dubious as to 2 pound foam being structurally sound, albeit if you thicken up the layering of fiberglass perhaps you can get away with less rigid foam. One thing is for sure with 2 pound foam if your rudder breaks off it going to float, like a surf board.

Good luck with it.

[Jim Cate]

for the OP:

If you look back to the early days of the thread, in post 23 I posited that your sudden loss of control was due to your rudder stalling. The posts just above from Montanan (good job there, BTW) point out that simple,near flat plate rudder designs tend to stall early and suddenly. Now you are building a new rudder, and as you describe it, one that does not have a well designed foil shape at all. Does it not seem likely that the new one will suffer the same failure modes as the original if you don't make an improvement in the shape?

With the info that Montanan has already posted, such a design is within your grasp. To not take advantage of the opportunity seems foolish to me.

In your place I'd be looking at one of the fatter and more forgiving shapes. The only rudder I've personally designed and built utilized a 0018 shape. This was for an auxiliary rudder for a wind vane, where t he angle of attack was determined by the vane angle, not a human helmsman, and I hoped for it not to get into stall mode. This was successful in my application... not exactly analogous, but with some similarity to yours.

So, IMO if you really want to eliminate your original problem, you will need to make a design improvement, not a replication.

Jim

[Don C L]

I may have missed it but its a new rudder stock right? Are you going to cut a key way in it?

[Martin S]

Probably may have had similar experiences, I certainly have and was a equally puzzled as you. it took me a while to get the sails balanced and oddly I found reducing the job helped. Every boat is different and lots of good advise on sail balancing has already been given. Keep at it.