Rudder rigging

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Rudder rigging

Postby tinafred » Tue Sep 06, 2016 3:21 pm

Soooo, it was a slow day and I was hot, tired, and sore, therefore I decided to work on my DS3. The rudder has been stiff to raise since I bought the boat using fair condition 5/16 in lines. I looked thru past entries under rudder rigging, lines, rope and various other subjects in the "rigging" section hoping to find out how the lines should flow without success. Any help with locating past entries focusing on this or directions on how the lines find there way from the rudder to the tiller would be appreciated. Thanks ahead of time, Fred "did I mention I have a new mast and sail" Thompson.
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Re: Rudder rigging

Postby GreenLake » Tue Sep 06, 2016 4:58 pm

Fred, I'm going to move this to the "Repairs/Improvement" section, as it's not specific to a DS3.

You are referring to uphaul and downhaul lines for your rudder. Perhaps with those terms your search will be more productive. (Try "site:forum.daysailer.org/forum" without the quotes a the start of your google search. That tends to give you better results than searching using the forum software).

I'm not sure there is any way these are rigged that is totally common across different models, model years and personal customizations of DaySailers. So, in order to give you better advice it would help to have a picture of your setup. 5/16" sounds like it's rather massive for the purpose. I think even 3 1/6 might be more than enough. The forces on these lines are not very big and you don't need to handle them constantly (those are usually the two reasons for upsizing).

If you are using up/down haul then you don't want any friction in the pivot. So, first thing would be to check/confirm that the rudder blade swings freely.

An uphaul is slack until you need it (at the dock or beach). Normally it's tied to a hole in the top rear edge of the blade. You could lead it over the rear of the rudder head and cleat it off on top of the tiller.

The downhaul is tied to a hole in the front end of the rudder. It would usually run between rudder head and transom, perhaps to a cheek block and from there it's cleated off at the side of the tiller.

The downhaul is tight while sailing. The cleat should be an auto-release V cleat; otherwise you risk damaging the rudder and transom in a grounding.

If you have no need to raise the rudder (for example if you launch in deep enough water and can mount the rudder after the boat is off the trailer) then you can dispense with an uphaul. If you sail mostly in lighter winds, you may find that cranking the pivot bolt until tight it gives you enough friction to keep your rudder down. (Except if you've ever waxed your blade...).
~ green ~ lake ~ ~
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Re: Rudder rigging

Postby tinafred » Wed Sep 07, 2016 7:55 am

Thank you, your guidance as always was most helpful Mr Greenlake.
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Re: Rudder rigging

Postby KingsTransom » Sat Sep 10, 2016 6:24 pm

Are rudder lines a user-added improvement? My `75 DS2 has none, and shows no sign of ever having any.
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Re: Rudder rigging

Postby TIM WEBB » Sat Sep 10, 2016 10:40 pm

Yes, I don't believe they were ever stock. Pics of my arrangement are in my gallery.
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(I used to be Her "staff", in the way dogs have owners and cats have staff, but alas no longer ... <pout>)
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Re: Rudder rigging

Postby tinafred » Mon Sep 12, 2016 7:57 pm

Mr Webb, what size rope do you have running along your rudder?
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Re: Rudder rigging

Postby TIM WEBB » Mon Sep 12, 2016 9:56 pm

1/8" Sta-Set, IIRC. *Might* have been 3/16" - CRS disease!
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Re: Rudder rigging

Postby GreenLake » Tue Sep 13, 2016 12:36 am

1/8" should be plenty strong for the purpose, but I doubt it was Sta-Set if at that size. Sta-Set is a double braid and I've only see it listed from 3/16" on up. If I had a piece of leftover Sta-Set (or XLS, the next grade up) at 3/16" I might use it. If I were to purchase a line specifically for this purpose, I'd go with something else.

I like FSE Robline Dinghy Control line at 1/8" because the cover makes it easy to grip, and it does hold well in cleats, but you can also knot it easily. (Given that you will need very short lengths of this, the fact that it costs a few cents per foot more shouldn't be decisive).

I use this for outhaul and reef lines on my DS, and would definitely use it for something like that. It's overkill from a strength point of view, but I like the neat appearance of it and the fact that it comes in such a small diameter, so secondary lines like downhauls, uphauls, cunninghams, outhauls and reef lines aren't so visually prominent.

There are some other alternatives. I used a different type of line for my outhaul before that, it was a single braid at 3 or 4mm, with a slightly knobbly appearance. Because of that, also very grippy and did hold knots well. If I can locate something that matches that description, I'll add it as a update to my thread on Ropes for various Lines.

If you have a local store, where you can inspect the rope before buying it, just check out anything around 1/8" (3-4mm) and try to tie a knot in it (and check whether it feels reasonably grippy). I either do it that way, or I check out boats of fellow sailors and get "rope envy" :)
~ green ~ lake ~ ~
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Re: Rudder rigging

Postby TIM WEBB » Tue Sep 13, 2016 3:38 pm

I used Sta-Set I already had (leftover extra from the jib downhaul line), so yes, it probably was 3/16" then.
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Re: Rudder rigging

Postby DigitalMechanic » Thu Sep 15, 2016 9:17 am

Here are some pictures. I have a fairlead on the top of the rudder and a horn cleat on the tiller. Used some old braid attached to bungie cord with a Heaving knot (http://www.animatedknots.com/heavingline/index.php?Categ=boating&LogoImage=LogoGrog.png&Website=www.animatedknots.com#ScrollPoint). Bungie end is attached to the bottom of lower rudder blade, the other end attached to the top of the lower rudder blade.

Once I have the boat in the water I push the lower blade down, and pull the cord tight so there is pressure on the bungie, then tie the line off on the horn cleat. If I hit something it will pop up. To reset push it back down :)
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Re: Rudder rigging

Postby GreenLake » Thu Sep 15, 2016 1:05 pm

Nice pictures. They give a good view of your design.

I like the use of the bungee cord to provide a measure of "give" in the system in the event of a grounding. (And it pulls the rudder back into position after it got deflected, e.g. due to ground contact, weeds or whatever).

In theory, one limitation of this kind of design is that the force on the rudder increases with something like the square of the speed as you sail faster (e.g. get on a plane). When you pre-stretch the bungee, you effectively set it at a certain (not very large) force. As you sail faster, the force on the rudder increases rapidly, until it matches the force on the bungee. At that point the rudder starts to deflect. Even if you pull the bungee a bit tighter, you postpone that point only by a little, because the force on the rudder rises so quickly with added speed.

That's where an auto-release cleat has an advantage - it requires much higher forces to release, more like the forces experienced only during grounding. (An auto-release cleat also stays released, so if you hit an oyster bed with your rudder, for example, unlike with a bungee you won't press the rudder down while you drag it across. In fact, for an alternate design, you might use a bungee as an uphaul instead to fully raise the rudder after the cleat releases).

With your motor you can push your boat up to hull speed (and then some) so presumably you checked the downhaul up to those speeds. So this theoretical drawback might only show itself if you got your DS on a plane.

Now one thing I don't like is the location of the forward attachment of your bungee. As it is, the flow over the top third of your rudder will be disturbed by the bungee, which adds drag and cuts down on the already not very great efficiency of the stock rudder design. I also can't see a reason why that location improves the function of the downhaul - so if I had to guess I'd assume this was chosen for symmetry? (For the uphaul, the location does increase the lever arm a bit and, being downstream of the rudder blade, it would appear to have less of an effect on the flow).

BTW, I thought the purpose of a heaving knot was to make the end of a line heavier for throwing it. There's something called a heaving line bend (https://en.wikipedia.org/wiki/Heaving_line_bend) that appears to be designed for joining ropes. That knot, or the double (triple) sheet bend, or the racking bend would seem to be appropriate for trying to connect a line to a bungee. The last of these would seem to be the most secure given the way bungee cord can be tricky to tie (see links in the Wikipedia article).
~ green ~ lake ~ ~
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Re: Rudder rigging

Postby GreenLake » Thu Sep 15, 2016 1:16 pm

PS: do you trailer with your rudder attached? I wonder because of the way your mast support allows the rudder to stay mounted. (Mine goes in place of the rudder, using the gudgeons).
~ green ~ lake ~ ~
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Re: Rudder rigging

Postby DigitalMechanic » Thu Sep 15, 2016 2:08 pm

GreenLake wrote:Nice pictures. They give a good view of your design.

I like the use of the bungee cord to provide a measure of "give" in the system in the event of a grounding. (And it pulls the rudder back into position after it got deflected, e.g. due to ground contact, weeds or whatever).

In theory, one limitation of this kind of design is that the force on the rudder increases with something like the square of the speed as you sail faster (e.g. get on a plane). When you pre-stretch the bungee, you effectively set it at a certain (not very large) force. As you sail faster, the force on the rudder increases rapidly, until it matches the force on the bungee. At that point the rudder starts to deflect. Even if you pull the bungee a bit tighter, you postpone that point only by a little, because the force on the rudder rises so quickly with added speed.

That's where an auto-release cleat has an advantage - it requires much higher forces to release, more like the forces experienced only during grounding. (An auto-release cleat also stays released, so if you hit an oyster bed with your rudder, for example, unlike with a bungee you won't press the rudder down while you drag it across. In fact, for an alternate design, you might use a bungee as an uphaul instead to fully raise the rudder after the cleat releases).

With your motor you can push your boat up to hull speed (and then some) so presumably you checked the downhaul up to those speeds. So this theoretical drawback might only show itself if you got your DS on a plane.

Now one thing I don't like is the location of the forward attachment of your bungee. As it is, the flow over the top third of your rudder will be disturbed by the bungee, which adds drag and cuts down on the already not very great efficiency of the stock rudder design. I also can't see a reason why that location improves the function of the downhaul - so if I had to guess I'd assume this was chosen for symmetry? (For the uphaul, the location does increase the lever arm a bit and, being downstream of the rudder blade, it would appear to have less of an effect on the flow).

BTW, I thought the purpose of a heaving knot was to make the end of a line heavier for throwing it. There's something called a heaving line bend (https://en.wikipedia.org/wiki/Heaving_line_bend) that appears to be designed for joining ropes. That knot, or the double (triple) sheet bend, or the racking bend would seem to be appropriate for trying to connect a line to a bungee. The last of these would seem to be the most secure given the way bungee cord can be tricky to tie (see links in the Wikipedia article).


It may not be the best setup, but it has not failed me yet... with an emphasis on "yet". I have had the boat up to speed where I believe it starts to plane. Well, I am not sure if it was a partial lift or actually on plane, as I do not have a spinnaker and from what I hear that is the only way to get on a full plane. But something was definitely different. I have not been able to do it again since. Not sure what that perfect condition is, but the boat's attitude really changed when we got it, and everything happens so fast, lol. It feels like the boat is gliding through or on the water a bit, but the bottom of the boat is a quickly pounding on the surface of the water. It becomes more difficult to keep up with trim, and the tiller fights you pretty hard as well. If I thought for a second that I had a hand to spare I would have picked up my phone and turned on the GPS, lol. That may have gave some clues. Anyway, point is whether it was planning or not, the boat was going really fast, things were kind of violent, and the rudder stayed down the whole time. Maybe that was just luck? Maybe the bungee was allowing it to give way some and constantly pulling the blade back down? I would not know because I sure wasn't trying to take my hands off the sheet and the tiller, nor my eyes off the sails and the water to try and look, lol.

As for the motor, I hate the noise it makes... I try and keep it rev'd as low as possible and still make the boat move at a decent speed. The new motor is inherently much quieter (at nearly any speed), and I can run it much lower because of the extra HP which equals even lower volume. But again the sounds still racks my nerves so I have not really tried to see how fast it can push the boat. The good news is that we are able to have a conversation with it running now. Though I have not tried it, I do image the 4hp would make it go hull speed.

I will check those knots out as well. It is fun to learn new knots :)

When I go to the ramp a mile (or maybe less) down the road, I will be lazy and leave the rudder attached. If I go anywhere else I usually detach it and throw it in the cuddy (so it does not slide around). I get nervous that too much bounce/shake/jiggle from the roads (or flaws in the roads) will tear things up. My tiller handle does not appear to be in the beast shape either. One of my anxieties is that it will spontaneously break while on the water one day (if I ever figure out how to do the partial planing thing again, lol). But for trailering the tamer has to be on, so that probably provides unnecessary trauma to the tiller on trips further than down the road, so I remove it.
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Re: Rudder rigging

Postby GreenLake » Thu Sep 15, 2016 6:25 pm

I simply rely on friction (which is even more limited than your design). But I know one symptom of the rudder coming up is that it feels like it "fights back". That's because the lever arm becomes longer and the same angle of deflection takes more effort to maintain.

Friction works well for me up to about hull speed. After work the winds usually die down a bit, so getting past hull speed is less frequent. However, if it gets close, the rudder force will exceed the friction and after I slow down I'll have to push the rudder back down. If I forget, the feel of the rudder will remind me to check.

So, I would think that you were probably seeing the effect that I was mentioning, but your bungee corrects things immediately on slow down.

If you just have a mile, you practically live at the ramp :)
~ green ~ lake ~ ~
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Re: Rudder rigging

Postby DigitalMechanic » Thu Sep 15, 2016 8:43 pm

Yep it is kind of nice being so close. The drawback of the close ramp is that I have to deal with the current and bridges. But I would rather spend that time on the water getting out (even under motor) than on the road towing a trailer. On the up side, downtown is beautiful and there is a lot of very cool scenery to enjoy on the way out past those bridges. I think you might have seen a photograph or 2 of the scenery I have to put up with ;)

On the rudder thing, are you saying that there would not be extra pressure put on the rudder in a scenario where the boat was going very fast, say trying to plane? That extra resistance I felt was from the rudder blade swinging aft from the friction of the water? If so, that is interesting. Might call for a change on the design, because I remember keeping the tiller tamed was a tiring job at that particular moment at time.... But I would do again in a heartbeat, lol
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