Got my new rudders today and installed them on the boat
You can see the size difference with the stock rudder on the left. These are 54" by 12" Stock is 45" by 10" The foil shape is also different, hopefully better. The tough part is adjusting the stop screws to get the right angle. I have fittings for the stop screws installed in the right location, but the leading & trailing edges of these rudders are slanted a bit aft, so I'm not sure if the trailing edge should be going straight down (perfectly perpendicular to the transom) or allowed to slant aft a bit. Any ideas would be appreciated.
Who says the Mac can't sail in the heavy stuff? All you need to do is replace the keel, rudders and sails Almost there. Just have to order those UK Tape-Drives. I thought these boat were supposed to be "affordable?"
delevi
The Rudders look great, but I wonder if the cost will justify the results. We upgraded a similar sized keelboat rudder, from a barn door rudder (Large Rectangular Style) to a High-profile class approved design. The new rudder performed better when heeled over on the wind, as the increased depth of the rudder provided better control.
Rudder Construction Two rudders are shown in the official plans, referred to herein as the "Original Rudder" and the "Spade Rudder". The new Spade Rudder is recommended.
Pictures posted to show change in this class rudder
I like the look of your new rudder, and wish it were longer for more depth when heeling. It may be materials and hardware, limit the rudders size as MacGregor engineered the original, aware of its limitations.
Keep up the great work; you are on the cutting edge for improving our Macs.
As Joel from IDA said, my boat is a floating experiment. I know the barndoor keel works, since I have virtually no leeway. I know the Mac rudders don't work in heavy air with uncontrollable roundups, so hopefully the larger barndoor rudders will do the trick. We're talking 150% increase in wetted area per rudder. The foils are also much thicker. I'll post results after some time on the water. My stock sails are badly blown out so I won't be able to get accurate results until I get my new sails, a work in progress.
As for more length... I think I'm already pushing the envelope. The limitation is the relatively small bracket attachment area, though beefier as it trails down, but still limited by the bracket size. Any longer and there would be serious risk of rudder failure under stress, not to mention the added steering loads. This is probably as good as it will get. With the increase in size and the claim of significantly improved foil shape, per Joel, I suspect the improvement will be significant. We'll see. Hope this works.
We're talking 150% increase in wetted area per rudder.
Might be 50% increase, or 150% of the original, but no way it's a 150% increase.
You want to adjust the tilt so that on a line through the verticle pivot pin, slightly more of the rudder area is behind the pin axis than in front. This will make the rudders slightly self centering while keeping the loads on the steering gear within reason. To far forward and they will be unstable; too far back and the steering loads will be too high.
Might be 50% increase, or 150% of the original, but no way it's a 150% increase.
That's what I meant Chip. 150% of original. My bad for the lack of clarity. What do you think about putting a level to the trailing edge, getting it as close to vertical as possible? I assume that would be the best alignment.
What do you think about putting a level to the trailing edge, getting it as close to vertical as possible? I assume that would be the best alignment.
Hard to say. From your photo, it looks like the area is fairly well centered on a line through the horizontal pivot pin hole, but unless you have a picture installed I can't picture the vertical pin in relation. I would suggest drawing an imaginary line through the vertical pivot pin, or hang a weight on a string from the pin, and try to center them, but with a little more wetted area aft of the line.
I would consider this only a preliminary setting to avoid breaking something; but I really think you need to be prepared to test and adjust the first time you try them out. Motor at low speed, and if the steering loads seem high, adjust them forward, and vice versa. Obviously best in a calm, uncrowded area, and if you could do it while on the water. Grab your mask and snorkel, and tie your tools to your wrist or something.
Delevi
MacGregor Powersailor and Thunderbird Sailboats have been a great part my boating experience. I like big and small, but these have become the most interesting for providing the best of boating experience in an affordable, manageable, proven designs. Just as the MacGregor Powersailor is the benchmark of trailerable Motoring/Sailing, Swiss army knife of WaterbeggosThe Thunderbird of similar size , weight and attributes provides a remarkable sailing experience in a Cruising and Performance package of one of the most successful "One Design Class" hard chine sailboats of all time.
Thunderbird sailing performance has no bad habits. Fast in light air and exceptional performers in heavy air, even as the waves build, they have become known as Dragon Killer. Thunderbirds continue to provide fits for skippers in PHRF competition. The Tbirds are so fast and their skippers so good, that the PHRF handicap has progressively decreased (gotten tougher) over the years, a rare occurrence for an aging design. Sail Magazine rated the Tbird in the top ten of All Time PHRF Performers , and now sporting a new larger spinnaker, they even compete with masthead spinnaker boats, a well sailed Thunderbird will almost always contend in its handicap division. PHRF Southern California Rates 198, and will be lower when the new large spinnaker is evaluated, maybe the high 180's. Recent transom and cockpit redesign has produced a Cruising Sport boat put on show.
Leon,
I didn't quite understand Chip's post but his comment raised another thought since our phone call. It's obviously inconvenient to try to measure plumb in water that's 60 degrees, but before mounting them, you CAN create a true horixontal line that will show above the water.
Measure that true 90 degrees from the trailing edge and mark it at rudder-top .... a Sharpie, or a masking tape or other tape material can give you an indicator above the water. Then you can use a small bubble level at that line to understand approximately how the trailing edge is angled.
Guess you're already out there working it though ... good luck.
Not sure what Frank didn't understand, but here's an explanation anyway:
The rudder steer by pivoting vertically about the the pin; I believe it's typically called a gudgeon pin.
As the rudder is travelling through the water when pointed straight ahead, no problem, no steering loads.
As the rudder is turned, just like a wing, it is presented to the flow at an angle; it genreates low pressure on the aft side; the rudder tries to move in the direction of the low pressure and creates an unbalanced force, turning the boat.
If a line through the pin bisects the wetted surface area of the rudder, so there is effectively equal area forward and aft of the pin, the forces on the rudder itself will balance about the pin. The total sideways force generated by the rudder will be taken by the pin itself, there will be no self centering action the steering will remain balanced with no additional loads on the steering gear.
Say there is an excess of area aft of the line through the pin. The loads are no longer taken by the pin alone. The unbalanced loads will attempt to straighten the rudder out, and in order to maintain the angle on the rudder, the steering gear has to take up the additional forces. This is what happens in an exagerrated sense when the rudder hold down line is loose and the rudder trails aft.
Primary results are in! In one word, FANTASTIC! I spent Friday afternoon adjusting the rudders, hoisting sails, testing, dropping sails, re-adjusting etc. I felt an immediate improvement in control when motoring out of the marina. For starters, I could turn to starboard in reverse, something I could not do well with the stock rudders due to prop drag (cant remember the exact term for this.) Motoring at low speeds with the db & rudders down, the thing was like on rails, even with a strong current.
Saturday, the Admiral & I sailed all day on San Francisco Bay, starting out at Oyster point, about 12 miles south of the SF Bay Bridge, making our way to Tiburon for a late lunch and adult beverages at Sams Anchor caf�(they have a dock.) and sailed all the back. I would say we covered approx 38 miles (both ways.) Winds were about 12-15 knts, with gusts in the 20s on the way there and picking up to 20+ in the late afternoon on the return trip. I have done this sail many times in the past in similar conditions with the stock rudders, during which I would experience a few dozen uncontrolled roundups. Saturday, I rounded up three times. Two were my fault due to an overtrimmed jib. My sails are so blown out, it is difficult to maintain good sail shape. The third was sort of my fault. I had the full main up and the jib furled in to storm jib size. If I reefed the main, I probably wouldnt round up at all. The difference with the new rudders was amazing. Every time the weather helm would start to build in a gust, I would give the wheel about a to a half turn and she kept her course. Oh, and theres a bonus! Each rudder is almost as long as the dagger board and has almost the same shape. The amount of added lift is tremendous. On route to Tiburon, I was beating upwind, trying to clear the tip of Angel Island on the same tack. With the wind blowing from the north west, it would be a real pain to tack back and forth since, I would have to go 90 degrees across the bay on one tack lots of added mileage and time. With my running back stay cranked down hard and the new rudders I was approximately 30-35 degrees off the wind. Im not kidding or exaggerating. I was pinching just a bit with the main & traveler sheeted at centerline and the jib sheeted tight, but not tight enough to backwind the main. I steered in & out of the pinch zone to keep the heel angle under control due to the extreme sheeting angle. Average speed 5.5 mph. Average heel, 20-30 degrees. It felt like I was sailing right into the wind. I was truly amazed how close I was able to point. Yes, I cleared the tip of the island and arrived to Tiburon on a single tack. I would recommend these rudders to anyone who sails in heavy air and is frustrated with uncontrolled roundups. The added pointing ability is gravy in my opinion, but darn good tasting gravy. Now is where I need some help.
I still dont have the adjustment of the angle in the down position quite right. Due to the different foil shape the downhaul line attachment on the rudder is probably not quite in the same location. I can crank it down until it fully stops. I removed the stopper screws and it stops about an inch before the stopper at the transom. The line is super tight and cleated. In this position, the blade points slightly forward (towards the bow.) While moving, however, the rudders trail slightly aft. NO matter how hard I crank them down, they will still trail. I can actually pull the uphaul line and watch them come up a few inches. This presents a problem in gusts when counteracting weather helm. The loads on the helm increase, not drastically, but enough to get me concerned about the steering system. I believe the rudders trail because the downhaul line is not set perfectly vertical, probably a bit forward of the tube leading through the boat. I would appreciate any suggestions to correct this. Thanks.
Fair Winds,
Leon
Last edited by delevi on Mon Aug 07, 2006 8:54 pm, edited 2 times in total.
Great to hear Leon. I too just got my new rudders today. Mine are the standard modified rudders. I understand Joel at Idasailor did something special for you? In any case I'm going to install mine this wednesday I hope. I'll let you know how it goes . Your results are encouraging.
Great news Leon! Not sure about your remaining issue, though it sounds unfortunately like excess drag overpowers the hold-donw rope?? Hope that's not true. But your description of the changes in controllability is exactly what I had pictured as we sailed a couple of weeks ago.
Chip, l too am unsure what exactly I didn't understand, since both your posts read clearly today. In other words, you're saying that the extending line from the gudgeon pin defines the rudder's rotational axis. There's some optimum balance point of rudder surface (area) ahead of, or trailing behind that axis.
The greater the trailing area, the greater the turning forces acting on the hull, brackets, etc. The greater the leading area, the lesser are the turning forces, also lesser are the turning efforts at the brackets and the wheel. More leading area is like adding power steering, but a diminishing advantage. It's a bit like the effects of changing caster for an auto or bicycle.
Gut tells me that 75% of the rudder surface belongs aft of the rotational axis ... but I'm sure there must be a nautical design guide somewhere);
bet Joel has that rule of thumb right at his thumb-tip!.
p.s. When I followed Sailnet's Mac-classic list, they discussed a 'standard' rudder mod to add surface area to the front of those rudders (~ 2" ??), reducing the tiller forces and holding effort, and also improving directional control. Making one's own rudder was a popular & common mod for the Classics.
Careful experimentation is required as Frank suggests. Two ways to lighten the load on the tiller or wheel: move rudder bottom end forward or add more area to leading edge. Either will work, however, there is a point where if the leading edge anywhere on the rudder is too far forward of it's pivot point on the transom hangers, the helm will get squirrelly, that is, won't hold a course, is too easy to turn off cener, but hard to get back into a straight course again, thereby loading up the whole steering system again. Been there, done that on another boat one time long ago.
I do value the improvements in our MacGregor sailboats concerning performance, stability, control, and modifications. The enhanced benefit of control, from new rudders of greater size has benefited this boat. I question the BWY comment below, but refrain from holding this value in the case of a stock boat. The BWY upgraded at the factory with a Bulb keel design, in line with Delevis weighted after market dagger board 20% of the BWY experiment. Granted the BWY experimental boat received a MacGregor Factory benefits in construction, weight savings, and reinforcement. The expressed satisfaction with factory rudder size and operation other than an adjustable drag link is unexpected. The need for more rudder as the stock Mac is heeler hard over in stiff wind, to overcome rounding up, can be related to poor sail shape (Blown out sails, as Delevi freely admits) as BWY has benefited from day one with reduced weight aloft and the best of laminate sails. We are anxiously waiting the purchase of new Sails, (Hopefully the Main and Jib with appropriate controls for the heavy Frisco winds) raising the level of performance and charting the coarse for all other Mac owners for the benefits pioneered byDelevi and others not willing to take the risk, but sharing their improvements.
BWY Todd Wrote:
So far the only change to the steering system of the boat is the addition of our adjustable rudder crossbar, this allows precise adjustment of the rudders to be sure they are exactly parallel to each other, Cheryl seems pretty happy with the steering and rudder feel, and if she thinks it's OK it must be good! Of course we also have our Custom Steering system so we can easily disconnect the engine while sailing, this is just so important for both steering feel and safety.
Mine are the standard modified rudders. I understand Joel at Idasailor did something special for you? In any case I'm going to install mine this wednesday I hope. I'll let you know how it goes . Your results are encouraging.
