Rudder lashing issues

[Thomas Nance]

Hi Wharramers

I have recently purchased a Simpson Woodwind 9.1 catamaran. The last owner/builder used a few Wharram ideas in the build. It has a tiki 30 rig, which is going very well, it also has lashed rudders. This weekend while sailing in some larger seas the rudders started moving from side to side. The lashings were creaking and the whole rudders were twisting. I have added a video of this happening on my page here. Can anyone help me? Are they too looses? Have they stretched?

I know a lot for people are switching from pintle style attachments to lashing, I don't want to go back the other way if I can get the lashings to work.

Any advice would be a big help.

Cheers

Thomas

[Don Brazier]

Hi
One big difference between your rudder design and the Wharram system is that the Wharram rudders are lashed in four places along the whole length of the rudder. This is possible because of the skeg. Without a skeg your rudder will cause a good deal of leverage on the top lashing. Thanks for the video which is a great help in understanding what is happening. Tightening the lashings may help a little, but they may also be slipping through the holes in the rudder Which is not intended.
How long has your catamaran been sailed with this set up?
Don

[Thomas Nance]

Thank you for your help. The boat was built in 2009 but due to personal reasons the owner/builder didnt sail it a lot once launched. This sailing is possibly the hardest it has had since launch. I have sailed it 2 or 3 times without the rudders moving but came to the boat this Friday and noticed the rudder was on a lean and once out sailing in waves there was more movement as shown on the video. I understand a 4th set of lashings would help as then there isn't a "middle" lashing to pivot around.

[Björn]

I suggest you change the lashings against thicker rope with much less stretch e.g. dyneema. The rudders should pivot better around the "waist" of the figure of eight. Depending on the length of the rudder I would adapt the number of lashings to the according Wharram design.

[Thomas Nance]

Yes I could do both of those things. Are you saying to use thinker line? Its probably around 6mm at the moment. There is currently not enough room to put in a 4th set of lashings in however I could move the middle lashings up to fit a 4th under it. Does anyone suggest filling the lashing holes once the lashing has been done with epoxy to glue it all together? 

[Galway Bay]

Thomas - lovely boat. And Don makes very good points. I myself do not use lashings. However they seem to work well - I do not remember anyone posting that they have had problems.

You say you first noticed this when you returned to the boat. Could it have dried out with the board down or got hung up some way to strain/loosen the lashings ?

Again not only do Wharrams have skegs but they also have a high stern post so the lashings are spread out over a much longer distance. Your arrangement may simply be too short to work. I don't think the number of lashings is the issue - you do not seem to have room for much more anyway.

Sometimes small details make all the difference in set-ups like this. Thickness of stern post / leading edge of rudders, diam. of holes/distance from edge, tight ropes, etc.  Your rudder case looks much wider than a Wharram style one. If the rudder edge is much wider than the stern post this might cause a problem.

Much of this is just me throwing ideas about but maybe it will help.

 

[Charles Eugene Marie]

Hello. in this configuration, the lever arm subjected the centerboard rudder on the articulation seems excessive to me. the high and low of it suffers a lot. In my opinion it should be passed to metal or add a spoiler and spread the joint by lacing the entire length.

Hello. dans cette configuration, le bras de levier que fait subir la centerboard du safran sur l'articulation me parait excessif . le point haut et bas de celle-ci souffre beaucoup. A mon avis il faudrait soit passé au metal, soit rajouter un aileron  et étaler l'articulation par laçage sur toute la longueur.

[Andrés]

I think the gap between the rudder and stern should be small, see how it is made in the picture of the T26 plans.

Wharram suggest filling the holes with thickened epoxy or sikaflex but I didn't do it. 

The lashings must be put really tight and the rope should be of a non stretching type (I use prestretching dacron but dyneema as suggested may work better). 

But in the Wharram's boats the load is spread along all the edge of the rudder and you can't do that in your rudder configuration so it could be a bigger problem here. You can make a little skeg and enlarge the rudder case so you can add another lashing underneath the others. If it is not very big this skeg does not increase the draft, but it is a big job and it is not sure that it will be enough.

 

[Galway Bay]

Lots of good advice here. I take it that Gael's spoiler is google translate for skeg. There is a huge difference between your photos and Andre's. A Wharram of 9.1m would have the hinges spread out over a distance of approx. 1.5 / 1.8m. You have only 0.5 / 0.6 ?  If you fill the holes and it stops the ropes slipping it will probably fix the problem but the lashing system will still be under 300% of the load envisaged by Wharrams so I think this modification is badly thought out and I would feel much safer going back to the original designer's recommendations.

[Björn]

I did not see the picture before, indeed there is no more room for a lashing, however the ropes looked fairly thin, maybe you try retentioning and better material first before you change the thickness.

Thomas Nance said:

Yes I could do both of those things. Are you saying to use thinker line? Its probably around 6mm at the moment. There is currently not enough room to put in a 4th set of lashings in however I could move the middle lashings up to fit a 4th under it. Does anyone suggest filling the lashing holes once the lashing has been done with epoxy to glue it all together? 

[Thomas Nance]

Thank you for all your help. Its great to be able to have access to so many people around the world who know exactly what I am after. Its all good advice. On the weekend I attempted to tighten one of the lashings and even with my poor attempt it did seem to help initially, however after a sail it was moving around as before. I plan to beach the boat next weekend and replace the line with a thicker non stretch line and take extra care to keep the lines tight. I will also probably epoxy the lines in their holes on the boat side. I feel a skeg would help spread the load but this is a bigger project.

The retracting rudder is a good idea but hasn't been executed very well. I have been thinking if removing the case and attaching the rudder directly to the hull. I will still have the same issue of having only a short length to attach the rudder.

Keep the ideas coming, it is much appreciated. 

[Galway Bay]

Thomas - the more time I have to think about this the more unhappy I become. In fact I feel a Rant coming on.

  This is not the only issue with the rudder hangings. This rudder is generating huge stresses on the lashings due to leverage over a short base. Also the rudder has no protection [ skeg ] against impact. How much will it take to rip a chunck out of that stern post ?  All those drilled holes over such a short distance must have weakened it ?

  "Nice to have" and "Philosophy" won't save your ass from crap engineering.  

   Hang on I am only starting my Rant now -

   Go back and check this boat everywhere this builder did mods.  That rig - are the chain plates up to spec. and bolted with  heavy bolts to full size backing plates.  Are they located where the designer put them to take the load ?  Then check everything else.  Hopefully this is the only piece of crap he has sicked on you.

  Now how was that for a "Rant" ??  Marks out of 10 anyone ??

[Thomas Nance]

7/10 i think. Cant say its really what I want to hear. Chain plates are ok. I have had a surveyor look over it with a positive outcome however it wouldn't have taken into consideration things like any mods to the original plans. So far, apart from the rudders all seems well.

Well if the rudders are a shitty design outcome, what is the solution? I don't know what the original design had.

My plan was to head up to the boat again this weekend and beach the boat to relash the rudders. If that doesnt seem ok then Im stuck. Really what I would like is a big skeg with a simple rudder (balanced or not) heavy duty, one you can rely on. However...I have a delivery skipper booked for about 3 weeks time to sail it 300nm down Tasmania so dont have the time for big projects.