Rudder Reference Unit for autohelm - what on earth is it?

[JeremyF]

I think I've been a plonker yesterday. Have I been stitched up?

My LBS treat has been planned to be a wheel autohelm for the Bavaria 34.

I called onto the MES stand and challenged them to sell be the Raymarine ST4000+ Mk2 at £600.

After a look at the trade price list he said yes. We then got talking about fitting, and he went to talk to a collegue. On his return, he said that I needed a Rudder Reference Unit at £120, because modern light boats drift all over the place without one.

So, not undertanding a word of the explanation why the unit needs to know where the rudder is pointing, , I duely forked out.

Now, there's no mention of this rudder reference unit on the Raymarine web site, and I would have thought (hoped) that there is a pretty strong correlation between where the wheel is pointing and where the rudder is pointing!

Please can I have the advice of the forum. If I've been stupid, I guess I can cancel the order

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Dawn Chorus</font color=blue>

 

[Joe_Cole]

I asked exactly the same question at the Raymarine stand at SBS yesterday!

The unit, which is briefly mentioned in their literature, is supposed to give feedback to the instrument to tell it exactly where the rudder is. My boat has a tiller and I was told that I wouldn't need the Rudder reference unit as the operating ram (or whatever it is called) had adequate feedback. I didn't ask anymore about the feedback unit, but maybe its needed when the rudder is hydraulically operated?

I'ld get onto Raymarine and ask them, you may be able to contact them on their stand today. Frankly I would "suspend" the order until it is cleared up.

I didn't by the ST4000. Can't justify £600 when I'm after new sails as well!

Regards

Joe Cole

 

[JeremyF]

Coincidence indeed. Does anyone have a number for Raymarine at the show?

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[Guest]

Hi Jeremy

I've got one on my Bav 34 - If ordering an autohelm from Opal on a new boat it is fitted as part of the order. It consists of an arm that connects to the rudder in the
space behind the aft cabins.

I presume that it provides the unit with a reference as to where the rudder is when you engage the clutch - otherwise you would have to always centre the wheel before engaging the clutch?. It might also help if the clutch slips?

It also gives you a bar display on the unit of how much rudder is being applied even when the autohelm isn't on - sometime useful to sneak a look at how much rudder the helm is applying when thinking about reefing!

Steve P

 

[JeremyF]

Light vs heavy

Hi Steve,

Well, its good to know that Opal fit them from new with this, but I'm still none the wiser why its needed. Why should a modern lighter boat need one, but a heavier displacement one not need one?

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[paultr]

ST4000 experience

Last year we replaced our faithful belt driven autohelm (wheel steering). This worked great but I wanted to do away with the hassle of connecting unit and belt and also have ability to link to plotter - control freakery from the chart table.

Initial results were very dissapointing - boat weaving either side of course. Quite easy to alter the amplitude and wavelength of this weaving using the powerful? ST4000 software - I could do everything but eliminate it! Spoke to helpful Raymarine who suggested I may need a RRU.

As our steering was quite heavy I decided to change rudder bearing first to give George II a better chance. This season he has been much better but still not as accurate as the simple belt driven George I he replaced.

I am pretty sure Raymarine have had other customers with the weaving problem (various items on CWBB/ SB et al).

PS Boat is narrow beamed, mod displ Westerly Pentland

 

[JeremyF]

Re: ST4000 experience

Thats helpful input, Paul.

Whats CWBB/ SB, incidently?

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[Guest]

Re: Light vs heavy

The raymarine manual (I think you can download it from their web site)
states that a rudder reference unit is required for hydraulic steering and recommended for optimum performance with cable steering.

I guess a light boat that is more skittish on the helm benefits from this extra feedback much more than a heavy boat where the steering is more damped.

I dont use the auto pilot much & have dont think I've used it in anything more than F3/F4 but (with the rudder reference unit fitted from standard) it has always done an excellent job of steering my 34 - much better than me!!

One useful feature is the ability to program additional data pages - so for example if your GPS is built in at the chart table you can set the autohelm unit to display SOG and COG at the helm.

Steve P

 

[JeremyF]

Re: Light vs heavy

Thanks, Steve. Its good to know that its standard fit, but given a direct correllation between wheel and rudder, I don't get it. Ive made an enquiry on the Raymarine web site.

Ive already got so much stuff back at the steering binnacle, the idea of even more data is hardly compelling!

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[paultr]

CWBB

Cruising World Bulletin Board & our own Scuttlebutt

 

[Chris_Stannard]

The answer lies in the fact that your Bavaria has wheel steering with cables. If you tighten the cables up enough to remove all backlash, they are too tight and put a strain on you rudder stock, so they are always a bit slack. To overcome this an RRU will tell the system where the rudder head is, and apply corrections accordingly, rather than trying to figure it out from the wheel which has a fair degree of play. Hence you will get a better response from the system. There is no extra gear in the cockpit, the rudder reference position appears at the bottom of the auto pilot control panel.



Chris Stannard

 

[andy_wilson]

Can afford? Best deal not at the boat show.

Try MES Ltd, Bristol, £529.95 plus P & P. 0870 1221099

Enough change for an extra row of reefing points in a new mains'l.

 

[JeremyF]

Thanks Chris. That explains why it would yaw around if one is not fitted.

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[jfkal]

Well I do not have one and the Autohelm works reasonably well. However it gests confused at times it seems wheezing back and forth as if it tries to determine where the heck center is. I bought a RRU and have yet to install it. If I where you I would not feel so bad. Yes you might have been able to do without but yet it has its assets telling the Autopilot where the b...y rudder really is. One thing it cannot determine though is whether you lost the rudder or not. You would need the Autohelm RPS, the rudder presence sensor. Sorry I was pulling your leg.

 

[JeremyF]

From the good advice (as usual) from the forum, I'm going to keep my order for this bit of kit. It just seems to be a bit of a con to make it an option, when the reality of smaller wheel-steered modern yachts are cable-operated, with some slack between wheel and rudder.

The Raymarine website has virtually nothing on it at all


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[jfkal]

Its on the website. But to save you the search I can forward the manual to you if you let me have your e-mail address )

 

[Col]

My planing boat has one for the Cetrek setup, apparently to stop weaving.
Hydraulic fast reacting ( when on the plane) steering. Must have a damping effect.

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