Reworking a non standard rudder

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Reworking a non standard rudder

Postby Postville » Thu Oct 06, 2022 8:07 am

On the Dat Sailer II I got the rudder is not original. In comparing it to the drawing in Roger Conrads information-
Height from pivot to bottom of rudder 30", not 23"
Pivot to leading edge 8", not 6"
Leading edge to trailing edge 9.5", not 11 3/4"
Transom to pivot 10", not 9"
Pivot above bottom centerline 9", not 1"
The tiller is 5" above the transom

The boat sails well and comes about quickly. The main issue is that if you let go of the tiller , the boat goes to leeward. I am used to a boat going upwind.
What is most important to correct and where to start?
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Postville
 
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Re: Reworking a non standard rudder

Postby tomodda » Thu Oct 06, 2022 9:07 am

Where are you sitting in the boat? Suggest scooting forward.
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Re: Reworking a non standard rudder

Postby Postville » Thu Oct 06, 2022 1:49 pm

I usually sail with my wife who sits by the cuddy and handles the jib sheets, I am in the stern about half way towards the centerboard trunk.
I will try moving forward next time out.
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Re: Reworking a non standard rudder

Postby GreenLake » Thu Oct 06, 2022 3:04 pm

Lee helm: I would look to mast rake. Make sure that is set up to spec. (There's a North Sails tuning guide for the DS that gives a way to check that).

The rudder isn't the cause. Yours looks nice.
~ green ~ lake ~ ~
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Re: Reworking a non standard rudder

Postby GreenLake » Thu Oct 06, 2022 6:57 pm

Let me elaborate a bit, in case that wasn't clear from my short remark:

Not enough mast rake (base of mast too far back, or forestay too short in relation) will move the center of effort forward to where it acts in front of the center of lateral plan (that is, forward of the pivot point defined by the centerboard). As a result, the bow is driven down.

Could of course also happen if you trim your main really badly and your jib perfectly, which would interfere with the balance between the two. So, if you suspect that you're not trimming in your main all the way, you could try to change that and observe if that has an effect.

Another thing to check: is your centerboard actually vertical when in the water and while sailing? If angled back, that moves the CLP back, which has the same effect as moving the center of effort forward.
~ green ~ lake ~ ~
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Re: Reworking a non standard rudder

Postby Postville » Thu Oct 06, 2022 7:46 pm

Good point about the centerboard. I usually just let it drop and do not cleat it. I am sailing on a manmade lake that has a lot of shallow areas I am not familiar with.
I will try cleating it down next time out.
I will also check the mast rake.
Thanks for the tips.
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Re: Reworking a non standard rudder

Postby tomodda » Thu Oct 06, 2022 10:23 pm

Hi Postville:

I'll also elucidate a bit, please excuse that I'll be writing as if to a beginner sailor. Don't think you are a beginner, but this may be useful to someone else, who knows?

First of all your rudder.. if you are not holding it, then it has minimal effect on the boat's movement, as there is no force on it. So your Lee Helm problem is not your rudder. As GL wrote, it's a beautiful rudder and I wish it were allowed in the DS Racing Rules... High Aspect, deep, apparently with a NACA profile, with a sensible set of rudder cheeks and made of a beautiful wood. If you want to get fancy one day, apply a bit of what old-time bicycle racers used to call "Drillium".. Drill out some holes in the rudder cheeks to lighten them. Any weight you save at the rear, even if just a few pounds, contributes to better boat performance (see below).

Sailing is all about balance. Very specifically, we are balancing the force of the sails in the air against the force of the hull, centerboard, and rudder in the water. Even though the in-the-water surfaces are so much smaller than the in-the-air surfaces (sails), they balance out because water is so much denser than air. If you did not have the underwater portions, then the boat would just skid sideways to the leeward (think of a plate with a sail on it), if you did not have the air portion then you wouldn't move at all. Both work together. The underwater portion has a Center of Lateral Resistance (CLR) that works like a pivot point, around which the entire boat can swing. The above-water portion has a Center of Effort (COE) which is the theoretical point that sums up all the forces on the sails. Both CLR and COE are constantly moving as the hull moves in the waves and the wind shifts on the sails.

Now, generally speaking, you want the COE to be BEHIND the CLR... so if you let go of the rudder, the boat will head up into the wind (Weather Helm). As you know by now, if the boat has a tendency to bear off to the lee (Lee Helm), then you run the risk of being overpowered. You want just a bit of weather helm, the COE should be about a foot behind CLR, no more, actually maybe closer to 6 inches behind. Just enough so that the boat turns gently upwind if you let go the rudder. Too much and you're creating turbulence, bad! Ever see a catamaran throwing rooster-tails? That's weather helm... Anyway, how do we get the COE behind CLR?

First option is to make sure the CLR is properly forward of the COE. Make sure to put your Centerboard down as far as you can for the conditions (amount of water under your hull), if it's at half-depth then the CLR will be set back a bit. Then sit forward... Remember, our boats are unballasted and weigh only 550lbs, so YOUR weight has a considerable effect on trim. Your wife is where the crew ought to be, right behind the cuddy, but you should be sitting almost right next to her. All else being equal, the CLR is somewhere on the front half of the centerboard, in other words right under the front thwart. So, if you are sitting between the rear of the Centerboard and the Transom, you are moving the CLR back at least a foot, just with your weight. Sit forward! Only exception is when you are running with the wind, then you want to scooch back (quite a bit if you are under spinnaker, I sit on the transom). GreenLake has more about this all in his writeup on Basic Sailing Techniques (viewtopic.php?p=36889#p36889). Once you gain experience with the DaySailer, you'll find out that you can pretty much steer with your bodyweight, scooch forward to turn to windward, scooch back to turn to lee. For what it's worth, even if it's just a tiny bit, Drillium (lightening the rudder cheeks) will help you keep your overall weight forward.

The other way is make sure the COE is far back enough. As GL wrote, proper mast rake is key. Not the first thing I'd do (get your weight forward!), but important. However, the COE is actually very dynamic, for instance if you douse your jib the COE goes WAY back (good luck tacking). That's an extreme example, but you can see where sail trim affects the COE, trim in the main or loose the jib and COE goes back, vice versa and it goes forward (up to a point in both cases). Anything that you do to affect the mainsail's Draft also affects COE, so that would be Cunningham, Outhaul, and Vang (my favorites). And then there's mast bend. We're getting into the weeds here, things that affect the COE by mere inches, but crucial inches... :)

Walk before you run, learn to distribute your weight properly, i.e Sit Forward. As I wrote above, CLR is also dynamic, it moves as the boat goes thru waves and/or heels. Your main way of controlling it is always your weight, where and how you sit. Truth is, I mostly sail with my ass. :D Last year, I said that to my son and he made me watch the car-racing movie "Rush" (great film!), where Nikki Lauda says: "God gave me an okay mind, but a really good ass, which can feel everything in a car." Same same with our Daysailers!

Fair winds,

Tom
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Re: Reworking a non standard rudder

Postby GreenLake » Thu Oct 06, 2022 11:43 pm

Tom, very nice. I went ahead and added that link for you.

With respect to mast rake: while it may not be the easiest to fix, it is very easy to verify. You can suspend something small and heavy from the main halyard and that halyard should end up hanging a few inches behind the mast (mast raked aft). If the mast is perpendicular, or worse, angles forward when the boat floats empty then you have a real problem. Fine tuning is done by running a tape measure between mast top and transom. North Sails and other places publish a reference value (should be good unless your mast was ever shortened). Both techniques are easy and if they indicate that the mast is set up correctly, you can cross that issue off the list.

With respect to the centerboard: if that's not cleated, it would be my prime suspect. Now, in shallow waters I would encourage anyone with a CB downhaul to change the cleat to one that releases under too much tension. Otherwise you are courting CB damage, which is not fun. These cleats are typically clam cleats or V cleats with an extra release mechanism. A bit of digging online should yield a supplier, or you can use this link.

With respect to seating position: my own experience seems to indicate that heeling the boat has a more noticeable effect on steering than fore-aft balance. The latter definitely affects speed, though. But I may be influenced by the basic trim on my boat. In some conditions it is near neutral, but doesn't have lee helm. That means that the difference would be just the degree of weather helm and the feel of that is also a noticeably dependent on speed, so for me at least, one variability may mask the other. The speed effect can be measured under motor. It can be up to .5 knots for maximum weight shift (from sitting near the motor to sitting on the cuddy deck). Measured away from hull speed when motoring at about 3 knots.
~ green ~ lake ~ ~
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Re: Reworking a non standard rudder

Postby tomodda » Fri Oct 07, 2022 9:18 am

Thank you, GL!

Yes, agreed, most of your steering while underway is done by continuously controlling angle of heel. Keep 'er flat, lean in or out for subtle steering changes. Your fore/aft position just gives you a range to work in (a "groove", if you'll allow the analogy). It's all explained with a lot more depth and clarity right here:

https://sailzing.com/manage-upwind-helm-balance-for-speed-and-feel/

Sidenote, I love going to this SailZing site for all my sailing questions and musings, check it out!

Best,

Tom

P.S. This guy (watch the video):

https://sailzing.com/raise-your-board-in-heavy-air-three-reasons/

...claims to be adjusting his board dynamically while going upwind to control weather helm, even in light-to-moderate air, claiming it gives him more speed without affecting his leeway. Huh! He's sailing a Scow, not a DS, but interesting.... Always food for thought on the SailZing site, and something to try next time I'm out on the water.
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Re: Reworking a non standard rudder

Postby Postville » Fri Oct 07, 2022 9:52 am

Excellent information, thank you both so much.
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Re: Reworking a non standard rudder

Postby tomodda » Fri Oct 07, 2022 12:05 pm

You're quite welcome! If you ever want a race-legal rudder, I'll be happy to swap with you. :) All kidding aside, you've got the rudder that the Daysailer should have been designed with originally. Sailing theory was different in 1957 and now we're stuck with our slow barn-doors.....
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