Nacra Rudder Rake

First, if you are using the Pivmatic cleats, if they are the ones with the plastic clam cleat, replace them with the aluminum clam cleats, and use a knobby line that has zero stretch. I found that at speed the line would slip thus increasing the weather helm. Make sure you are getting the rudder all the way down.

Moving weight forward also reduces helm, drive the bow.

Now to your question, when all else fails remove some material from the rudder where it meets the bottom of the casting so that the rudder can go further under the boat. Don?t do too much or you may end up with lee helm and then need the set screw to keep the rudder further aft.

How bad is your helm?

edited by: nacra55, Jan 06, 2010 - 11:09 PM

i would certainly try everything i could before i touch the castings.

I know little about nacras but what about adjusting your mast rake? this can help or hurt tremendously with helm issues.

have you tried lifting your windward rudder? if yes does that effect it? (if it does it could also be a tow (toe?) issue. do you have weather helm on both rudders?

can you drill the rudder (fill the old hole.. drill a new) to adjust its alignment (vs. drilling a casting)?

good luck, take pics... keep us posted

Hey Dave,
Ron and I definitely know these platforms and are very familiar with this. He is spot on.

Once you start raking the mast back, you adjust helm by removing material.
http://www.thebeachcats.com/index.php?module=pictures&g2_itemId=18434&g2_imageViewsIndex=1
I use a belt sander, works good and it very easy. Measure the rudder rake while on the trailer with the blades locked down. Scribe a pencil line with a straight edge. Remove a little at a time. The picture shows a moderate adjustment. On my latest platform (modern cut main, very agressive rake) I had to make a more aggressive cut that got into the core. If you need to go that route, cut beyond where you want to go, build it back up with epoxy filler, and then belt sand back down where you want it. The reason to do this is to seal up the rudder case. You don't want a penetration in the core. Water will eventually kill it.

This system of adjustment is easy. Do not modify the castings, and drilling the pivot holes in the blade is a total crap shoot, which gives you no room for adjustment.

I had the problem with getting the rudder down and solved it by installing new pivmatics and rigging a 2:1 pull on the rudders.

I think I had almost no mast rake this year but am getting a new flat top sail, so I might try to rake it back a bit more.

What I don't know is how much toe in/out I may have had in the rudders. Now that I will have an adjuster I will pay more attention to it. THat is the most likely culprit at this point.

I also haven't played with setting the dagger boards much, I will look at that before I start removing material.

Darn, I was hoping that I was missing something and there was a built-in (i.e. reversable) adjustment for rudder rake. Sigh, belt sander it is, if it comes to that.

oh wait,... did you try to adjust the auto-weather helm button first? Its right next to the engine compartment

Darn, I was hoping that I was missing something and there was a built-in (i.e. reversable) adjustment for rudder rake. Sigh, belt sander it is, if it comes to that.

Go back and read Ron's post. You can adjust after the fact with the screws. That's why this is the preferred way to do it.

Damn, missed that one. Might be under the ice cream machine too. 🙂

I was reading about F18s that have a set screw for adjusting the rudder rake and was hoping... Sigh, just makes we want an F18 more.

D.

Wait.. nacra's have an icream machine? damn... i want one now! 🙂

It's an aftermarket, one of the innovations on the new 20. They took the idea from the US's Nuclear Submarine fleet. 🙂

Come on... I've been on our subs...no ice cream there either...
(something to do with excessive gas's building up pressure inside the subs)....

However.. i was on a Norwegian Mine Layer and it had a bar (an innovation i later brought to my ship). 🙂

Oh yea.. i was also on a Canadian destroyer.. they also had a bar.. We (USN) drank every drop of beer on the boat... and then took the crew to our enlisted club to drink Sour Mash (Jack Daniels)... we then all got in fist fights! good times...

Hmm, Tom Clancy was wrong then... or maybe it was the Nimitz Class Carriers that have the ice cream machine - the submarines may have had slurpees.

Those Norwegians sure know how to party! Nothing else to do in Norway, except cross country ski and pillage coastal towns in the UK. 🙂

Hmm, must you must have been on an Iroquois! Biggest ships we have right now. They are reasonably modern, fast and have a crazy helicopter landing system! We finally got some decent submarines a couple of years ago, hopefully a new heavy cruiser soon.

What is it with Jack Daniels and fist fights? I can drink Rye all I want and be happy, 2 shots of Jack and I want to punch someone!

D.

haha .. this was 20 years ago that i was in norge and 22 when i we drank the canadian ship dry...

yea. i dont drink whiskey or tequila anymore ... i end up in mexico.. married.. in jail... etc

like a true sailor.. i only drink rum (and actually am back on the wagon)

my 5.2 rudder casings have a hole for a rudder rake adjuster screw, but it looks like they've never been used...

so the rudders are as far forward as possible, which seems to give just the right amount of helm feel with the tiny amount of mast rake i use

sounds like the problem is elsewhere...

Aye, probably still an Iroquois though. These days I prefer a good Scotch to anything else. I did drink a Tawny Port that was older than me (37) the other day. Damn nice drink but it should be for $50 a shot!

Likely, the problem lies in my mast rake, but it was a question I wanted answered. Obviously it wasn't a common problem with the stock setup so they didn't need an adjuster. I will have to look at my mast rake more closely, it may have been farther back than I thought. The idea of adding a set screw to the rudders is a good idea, I will consider it when I get to that.

Thanks guys!

Dave,
Don't look at it as a problem, because it is not. It's all about tuning the boat and getting it balanced, (i.e. CE & CLR), and then it gets fast. The "problem" is nowhere else. Rake the rudders forward or reduce mast rake.

You won?t see this anywhere and it goes against anything you will read, but if you have too much forward rake in your mast, it will increase the weather helm.

I had a similar problem on my 5.5 SL and kept raking the mast forward. It just kept getting worse. I asked a fellow sailor what my problem was and he said to rake it back. It worked.

Don?t worry about the set screws or reshaping the rudder. Measure your rudder toe in and adjust it so that it is almost neutral, within a 1/16 of an inch. Make sure that the rudders are going all the way down and are not slipping in the clam cleats; this could be the most likely cause. Keep your crew weight forward, don?t sit on the stern. The skipper should be at the dagger board well and the crew at the main beam. Then experiment with mast rake and find the sweet spot. While experimenting with the rake try and keep wind and crew weight a constant. As the wind and weight increase so will helm.

As Phillip said, It?s all about tuning.

I'm definitely planning on playing with the mast rake.

That is also a good point about crew weight distribution. I'm still not used to the way the Nacra can handle crew weight forward and dive the leeward hull so far under. I tend to keep the crew weight back too far I think. My old hobie 16 instincts still tell me to hang off the back of the boat or your going to pitch pole. 🙂

WOLFMAN
Here is a picture of one of my rudder castings. You can see the adjustment screw at the top right. I could back it out, & gain almost 1/4" greater rake,(lee helm) or turn it in to add weather helm. Looking at the picture, it would be very easy to shave a few mm from an appropriate spot to gain more lee helm. You are an engineer, a cursory study of the geometry of the rudder down line will quickly show how a slipping/stretchy pull down line will result in some weather helm.
I am certainly no expert, but after a week in Cuba reading my newly gained copy of Catamaran Racing, I think I understand exactly what Philip & Ron were talking about. I certainly would never drill the casting/rudder, to paraphrase MUMMP, you could really ph@#$K it up, with no way to backtrack.
I learned quite a bit from this thread. I brought my rudder assembly home, & studied it with regards to Phil Bermans books + the info in this thread. I think Mr Berman is a very accomplished Cat sailor, but his books are almost exclusively Hobie. MOST of the physics are the same, but I think other Cats different setups/hulls/rigging mean some of his ideas may not translate exactly to a NACRA.

edited by: Edchris177, Jan 09, 2010 - 10:38 PM

3 questions for Ron & Philip...or anyone with knowledge. What is the hole in top left of the rudder casting for? It is only on one casting, the other does not have this hole.
Also, MUUMP, with regards to your post above, could you enlighten a Noob as to what CE & CLR regard to... center of effort? can't think of CLR other than a rust cleaner:-D

How much free play is OK between rudder & casting? Right now I can slip 2 credit cards between casting & rudder, there is a bit of play if I wiggle the rudders sideways. Should I attempt to build the rudders up, wrap waterproof tape around the casting where they rub? What do you cosinder excessive? I have read about shims/washers, wouldn't it be better to build up the are where the free play is (the worn white line in the casting cutout in picture above). That would provide much better support for the rudder as opposed to a shim/washer on the bolt.

Picture 2 shows the Pivmatics that I have. The rudder down line that came with the boat is shown. That is as far "into" the Pivmatic as I can get it. It doesn't seem like it goes down far enough into the teeth of the jam cleat. Are these cleats worn & should be replaced, or is this line diameter to large? Can anyone sow me a picture of what a line fully engaged in the cleat looks like? Pulling this line tight (assembly is not mounted on the boat, I can't do the same job with it on the floor as I could on the boat)then pulling on the rudder to simulate water force, seems to show the line slipping/stretching...with resulting displacement of rudder towards the up position, which would result in weather helm.
RON, what line would you recommend, diameter & type, (no stretch nobby) They are pretty short lines, cost wouldn't be much.
I also realize the connection between the rudder tubes & the cross tie is not as shown in the assembly manual, a few parts from Murrays, or D Berger will cure that.
Wolfman, this is what my adjustable cross tie looks like, looks pretty simple to adjust & get rid of any rudder misalignment. Damn, I wish I had the boat at my home garage, I'm itching to tweak.

Wolf. here is a shot of the pivmatic & adjustable tiller

Is this enough "bite" or is the jam cleat worn, or line to lasrge?

edited by: Edchris177, Jan 09, 2010 - 10:51 PM

Ed,
The line in your pivmatic looks too big. Shouldn't be larger than 1/4" that looks like 5/16. That being said it dosen`t have to go too far into the cleat to jam solid. That would probably cleat just fine. Those look like the aluminum cleats so you shoudn`t have to replace them.

I would also suggest a very low stretch line for the pulls. That line looks like a regular poly, you may want to step up to something better, Sta Set works well. I just got some VPC line for mine, relatively cheap and is a vectran blend, so almost no stretch. I`ve also heard really good things about Salsa line. APSLTD.com is having a 15% off sale on all line right now, good deal I just bought $300 of high and mid tech line!

I just got a similar adjuster from D Berger and I`m expecing it to fix the helm issues. I can`t wait to see if my castings has a similar set screw!! That would make rake adjustment much easier.

Oh the return shock cord that goes through the tiller is kind of a crappy system. As the shock cord degrades the rudders don`t pop up as well. I changed mine to a dual pull line with a 2:1 purchase uphaul as seen here: http://www.rclandsailing.com/licsa/LICSA98rudderuphaulproject.htm

This REALLY helps you cinch up your rudders! I also just bought some pure elastomer cord from APS and that is supposed to have about twice the return pull of shock cord and it doesn`t degrade. I will give it a try on the pop ups this summer!

D.

Ed,
#1 Hole is for NDR.
#2 CE=Center of Effort, CLR=Center of Later Resistance
#3 You should tighten up the casting with the pivot bolt, it will flex but be careful. This will take up the slop. You should have a large plastic shim between the blade and the casting on each side. You can make one out of a milk jug or order from Murrays. One other thing, the clevis pin that the rudder hold down line goes over, . . . it should have an aluminum tube over it that acts like a roller bearing.

Your Pivmatics (cleats) are not aluminum (factory cleats never are). Look carefully and see if the teeth are worn dull or grooved. If the teeth are worn your line will always slip, creating excessive weather helm. The hold down line should be a high quality double braid or similar. Stretch isn't your problem here. The idea is to have a quality FRESH line that retains in round shape in the cleat, and resists the repeated abrasion on the same spot.

Another thing. Keep an eye on the rivets that connect the tiller arm to the casting. They can get loose and add more slop.

Replace the return bungees when they start to break down, I used 5/16" bungee and loaded it with a fair bit of tension. My opinion is that when everything in rudder system is tuned and functioning as designed, the system works perfectly.

Those are the plastic cleats. They are black. The aluminum ones are silver. The pivmatics are starting to get old and the ears, where the ring ding goes thru to hold it to the tiller and what they pivot on when they pop up, will break. They look silver instead of black. They are made from hot stick material.

http://www.murrays.com/archive/32-33.pdf See page 33 Item G and H

I liked Sta-Set X 3/16 inch but it is very hard to find. I tend to down size everything. Not bigger than .25 inch. Marlow Excel Racing 5mm may work if you can find it I think it is being discontinued at least at West Marine. APS has it. I like a stiff line.

Your line needs to be replaced. It looks slick. I would change this line out every other year if it gets much use and stays in the sun.

I do not remember the length but it is about the same a trap line 3.5 feet. Some twig balls on the end help with the pull down.

About the hole, I have never seen one there.

From the looks of the holes in your tiller arms at the connection to the tiller crossbar, you still have the bolt that is welded to a U shaped piece that connects to the tiller cross bar. This weld will break. Once it breaks on both sides, port and starboard, your tiller crossbar will rotate and will lock the steering. Sucks in a blow. Some zip ties will get you thru the day. See the tiller tie bar upgrade kit next to G and H on the link above.

I rigged my pull down line 2:1 for a while. The problem is that it takes 2x the force for the pivmatic to kick up. You can shave some off the sides of the pivmatic to change this. I went back to 1:1 for fear of ripping out my stern.

Thanks for the info. Correct, I do have the plastic pivmatics. I took a toothbrush & cleaned them up for a closer look. They do not appear to be worn, & show no grooves. I thought the old lines were 1/4", just goes to show, look once measure twice, they were in fact to big. I had to drive to Queens & back today to drop off #1 daughter at university. The good thing is there is a West Marine in Kingston, so I picked up some Sta Set 1/4" for new lines. It goes right into the cleat, just below flush. I see what MUMMP means about a solid core. The Sta Set seams to resist flattening, & jams in tightly. The pivmatics look OK, but I think I'll order at least one of the aluminum ones, & keep the old one as a spare, or at least a couple of spare parts for them.
Also thanks for the shim tip. I made a couple of shims from a plastic juice jug, & they eliminated the blade slop, without having to tighten the pivot bolts any. There is still some play due the crossbar connections, but I'm going to order the proper parts to change out the bolts it uses now, as per NACRA55 suggestion.
I'm going to go with bungee cord for uplifts. I will never trailer this boat, except pull out & put in,& that is only from the backyard to the garage in front for winter storage, so I'm not concerned with a positive hard uplock for trailering. I think merely releasing the downlock line & having them flip up will be simpler when approaching shore...my shore is pretty shallow the first 10 feet out.
I saw the Murrays catalog listed 5 1/2 ft of 5/16" bungee for the pull up. I'm thinking that is enough for BOTH sides? MUMMP, do you remember what length you used on each side to get a proper tension? No use trying to re invent the wheel if somebody has a system that works.
I'll check on the roller tubes where the line goes around, I have lots of little pieces of SS tubing to make them if they are missing.
Item last, regarding the hole.
MUMMP pardon my ignorance, but what does NDR stand for? Non destructive ...? Reminds me of the first Airbus course I did years ago on the A-320. We were handed a 23 pg book of acronyms & abbreviations, & told we better start learning them or the manual would make no sense. "The PF shall always confirm with the PNF any changes made on the MCP, & also confirm that the desired change is reflected correctly on the FMA, & the aircraft reacts as expected by crosschecks of the PFD & ND." HUH?? Where would I find them.. "Don't worry son, it'll all make sense after a few months."

edited by: Edchris177, Jan 10, 2010 - 09:19 PM

Ed,
The nacra parts list says you need 4' of line per side for the pull down. Shock cord stretches about 100% so if you have 5 feet you will likely be OK.

The reason i am in favor of more positive kickup is becuase the when you release the pull down line it has a tendancy to recleat itself after you let it go, so if the rudder doesn't pop up the whole way it gets stuck half way up. Then I end up draging the rudders in the sand when I beach. Not a big deal since the pivmatics will kick up if there is a lot of force, but still annoying.

MUMMP pardon my ignorance, but what does NDR stand for?

NDR=No Damn Reason . . .

when you release the pull down line it has a tendancy to recleat itself after you let it go, so if the rudder doesn't pop up the whole way it gets stuck half way up. Then I end up draging the rudders in the sand when I beach.

This happens to me as well. I don't have pivmatics, so I have to watch the rudders closely when coming in to shore. I've thought about doing away with the shock cord and using a second 'up' line that I can cleat, but haven't taken that jump yet. Maybe after another season.

I've thought about doing that, I find that I'm so busy pulling up dagger boards and rudders and letting out my sheets as I come in that I would really prefer an automatic pop up. So I am going to try and make it work with this elastomer cord.

If not I will just have to get a better crew who can raise the daggers faster and handle the jib. Not sure how to tell the wife that she's fired though...