Nacra F20 rudder failure

[mnic]

Having just returned from an epic 500 km sailing marathon across Lake Malawi in Africa during which we suffered two rudder failures i was wondering if any anyone else has had similar failures and if they can be pin pointed to either poor sailing technique or too light a construction

Failure 1 occurred on a downwind leg with the bag up - boat speed was averaging between 18-22 knots - water was pretty flat with small chop and the odd 1/2 to 1 m swell - the windward rudder was down and without warning the aluminum casting broke close to the bottom rudder gudgeon pin

Should we be sailing with the windward rudder up ?

Is the rudder design on the f20 a little light for the forces being experienced - to my knowledge the F18 Infusion has the exact same rudder casting

our boat is about 4 years old - fatigue??

 

[Foghorn77]

The Nacra 20 had that same casting and they broke the same way all to regularly. billet instead of cast would be awesome ,but then you'd lose the transom as the weak spot and the casting is easier to fix than a gudgeon or a transom.

 

[opherdor]

You are a lucky man indeed - 4 years and only your first rudder casting to fail??

We have broken quite a few, some brand new, some a few months old. Don't think we have had many castings last several years on any of the 5 boats here.

It is unusual for the windward casting to break, not the leeward one. The normal breakage mode is for the bottom part to break, the casting then twists sideways and the top breaks, leaving it free...

The most fun is when you let go of the tiller, the broken rudder flies backwards, dragging on the good rudder, which then breaks off itself, leaving you without rudders, spinnaker up and hopefully no leeward shore close by. Happened to us a couple of years ago, and to another boat last week. We put a bungee through the pin holes on the top rudder raising mechanism so that when you capsize the rudder doesn't flip over. This is passed through the gudgeon, and doubles to keep the rudder from flying back when the casting breaks.

It is a well known problem, which Nacra has addressed with their usual FCS (f@@cked up Customer Service):

1. Tell sailors they are sailing wrong and insist they have never heard complaints

2. Quietly put out an "improved" version, neglecting to tell sailors.

3. Said improved version is no better, 4 have broken in Israel during the last year.

4. They have not had castings in stock since the beginning of the year at least, if you really really beg they tell you they have some they are keeping for new boats, so they don't ship for stock but will send them "quickly" if you break yours.

Sailing with the windward rudder up is not healthy for you or the boat, you should always keep both down on such a powerful beast.

If you are experiencing strong pressure on the rudder you may need to adjust rudder rake or mast rake, but most failures occur because of insufficient design of the beast.

And while on the subject, do check your front beam often, they tend to crack near the hull - we have had that twice (Nacra know about this as well, and have put out a shoddily strengthened beam from the FCS, which as usual they are not telling sailors about until they break)

Now, 500km on lake Malawi sounds fantastic, would love to hear more and see pictures

 

[zebaru]

I wonder if the casting are just 'luck of the draw'?

When we wadded up our F20c in the GT300, the upper ss eyes that screw into the castings got all deformed and bent, and the gudgeon pins got bent. The boat was upside down in the surf for at least a half an hour with the rudders popped and flopping about wildly with every wave. It came ashore with the top castings flipped back and the rudders hard over.

Three years later, we are still using those castings, and have had a handful of wild rides with no apparent problems.

View attachment 208300

 

[F18 Sailor]

Without x-ray inspection of the casting upon removal from the mold, you can't guarantee their isn't a void, or that the alloy was smelted properly. In higher production cast parts, >10% failure isn't uncommon. Isn't it ironic that Goodall design have changed to a solid milled casting for 2014, and the FCS casting is solid carbon?

 

[SCARECROW]

Without x-ray inspection of the casting upon removal from the mold, you can't guarantee their isn't a void, or that the alloy was smelted properly. In higher production cast parts, >10% failure isn't uncommon. Isn't it ironic that Goodall design have changed to a solid milled casting for 2014?

You've had too much cool-aide.

Goodall have changed to bent aluminium tube stocks cause they're cheap. They even say so on their own website.

 

[macca]

Might be cheap. But the Goodall ones are stiffer, stronger and nicer.

 

[drew584]

Might be cheap. But the Goodall ones are stiffer, stronger and nicer.

They are also lighter than the old cast ones

 

[juniordave nz]

Well designed carbon is the way to go. Castings can be dodgy in corrosive environments. Depending on the way the casting is done. But the grain structures can have higher concentrations of various elements along their boundaries which can cause excessive corrosion. Also any voids near or on the surface cause areas of high surface area and grain boundaries that can be attacked.

Bent or milled usually have much better grain structures and if bent alloy is annealed properly then the bends wont be more susceptible to corrosion.

 

[F18 Sailor]

Carbon isn't legal in the F18 class outside the tiller extension...that is one reason the system on the F20c is what it is. The other reason is it is a tried and true system, with thousands and thousands of ocean race miles and thousands of beach launches on it. I prefer it over the Goodall/A-Cat style system for that application. But once in a while you get a bad casting.

 

[MauganTornado]

I was rather lucky to never break a lower casting while I had my old N20. One thing to be sure to check is whether or not the casting has any vertical play on the gudgeons. If it does then the top eye bolt can slip off and torque the lower part of the casting, leading to either a casting failure or a gudgeon failure.

I always slapped a couple washers on the top of the bottom gudgeon once the rudder was on. Took up the slack and didn't let the rudder slop around on the pins.

 

[genealex]

Just had a breakage of the casting at the bottom gudgeon on the N20. Just snapped off, top was still attached, luckily the top is held by the adjuster screw so the rudder flipped side ways without doing further damage. Going to windward at a good pace in a 15-20 knot wind in relatively flat water. The break was clean, showed no abrasion or oxidation, so it apparently snapped without prior fracture.

 

[Sailabout]

I'd say the Nacra casting are very nice and all the broken ones I have seen have had zero flaws

Its justs not strong enough to do the job