Transom hung rudder options - 50 ft catamaran

Note : Tiller Steering

Time to make some decisions regarding the rudders soon and reviewing the comments still seems undecided. Perhaps a renewal of comment will drum up some ideas... I like the semi balanced transom hung idea, albeit the question remains whether to make it removable or solid permanent mount? The sooner decision is made the sooner the engineer can provide build details. Look forward to some thought. Remember this cat is setup for (TILLER) steering.

 

Gday

It is hard to work out the best approach without any drawings of the boat. If your boat is to have a low stern with steps then putting a transom mounted rudder will have some added problems - the tiller length will increase and the steps will be hard to use. If you have a high and chopped stern then the transom mounted approach would be fine. Like all things the rudder is affected by the rest of the boat. Why any one would not have steps on a cat larger than 32ft is beyond me so no transom rudders on the 50 footer.

I use transom mounted rudders on my short and high ended trailer sailer cats. I use cassette mounted rudders on my low stern with steps large cat. Going permanent with rudders on a cat is dumb. You will often go around with your boards fully up. I so this about half the time. If you hit with your rudders on the bottom or a rock you will rip them out of the stern or break the rudders. I know Lock Crowther did permanent rudders but his were short and underhung. With surface piercing rudders you will need longer blades and they will be very liable to rip out the back. Often you will be going in thin water and then just touch with the blades - if they kick up you let them and push them down again later. If they stay down you stop and get blown to the lee. Then again - How do you dry out with deep permanent rudders? If you can't dry out why have a cat?

To be truthful this sounds a little piecemeal. The rudders should be part of a holistic approach - your designer if he is any good should be able to tell you all of this and give you all of the options. I would be a little worried about the rest of the boat if he can't guide you well on this aspect.

cheers

Phil

 

Phil,
Things are very much under construction at the moment. I have the option to choose rudder setup. The transom has opening offset to side but has no swim steps and has a fairly vertical transom face.(only slightly raked). There is also seating aft for the helmsman as well as a winch station for sheets, traveller, etc. The halyards and reefs will be handled fwd at the mast station.

Similar layout as shown below except it's a bridgedeck cat and i would like to have the rudders transom hung. (a carbon shaft rudder is $$ and not removeable)

 

On a Cat your size I would be very nervous about outboard rudders. They would have to be very strongly built and probably cost just as much as an underslung rudder. Carbon fibre is not necessary. Galvanised steel tubes with their screw on end fittings are cheap as dirt and very strong.
Dennis Armstrong had outboard rudders on his Seawind 33 and had to turn back when they were badly damaged on a club sail to Lord Howe from Sydney in a Southerly buster.
John Hitch had no problems with his spade rudders on his Crowther Spindrift in the same sail.

 

That said I am not so keen on spade rudders except for their abilities to keep the
transom clear for things like steps,outboard motors and scoops etc:
They are OK when used with wheel steering but have a bad habit of stalling out
if a tiller is pulled too abruptly when going fast, especially in rough water.

 

The problem with pivotting or lifting outboard rudders is that the stock has to be no lower than the hull waterline, which puts a huge strain on the lower pintles in a large boat with long rudders. Small boats are not so highly stressed and can get away with it.
Dennis Armstrongs pivotting rudders were literally twisted off.
As Phil says----lay this one on your designer.

 

I went through options on rudders on my slab sterned small cat and couldn't go the Farrier style daggercase because of geometry. The Farrier case is very low so if you hit the rudder it stays in the much of the case as it rakes aft. With a deep case the rudder quickly swings out of the case and only a small bit is left in the case - up top where it does little.

As said before - you can't do a boat like this with permanent transom rudders and the Farrier style is out - draw it kicking up.

So go stainless shafts on the rudders. To keep the dollars down make your own glass tubes and get a friend to weld the tangs on the shaft for you. When buried in the foam and cedar no one will know the welds are rough but strong. I made my cassettes easily and can't think of my boat without them. I differ from Oldsailor - I love my underhung rudders and the cassettes are great. On two different occasions I have spotted a crab pot or fishing float too late to avoid and the boat has creamed over it. If you get the fuse right - I use flexy pipe - the next thing you see is one rudder kicked up. The great thing about cats is that you still have some control with the other rudder. So I get another fuse and push the rudder down and keep sailing. If you have no cassette or a permanent transom rudder you are in a pickle. In fact I like to raise my daggerboards as much as possible because it is far easier to go over a float or weed with kick ups than hit with the dagger - I picked up a float with a dagger once and it wasn't easy to deal with.

But then again - why go the slab stern? On a 50 footer to miss out on swim steps or an easy way to get out of the dinghy or a great place to get out of the kayak seems really incredibly silly. We like the water and if you are like us then having a good swim platform is great. I can get out from my kayak onto the bottom step and it is really useful when dried out. I put a bucket on the sand and then you clean your feet and then walk on up. You would need 10 super good reason in my books to not have steps on a modern cat. Don't do it cause Gunboat do it or something - form should follow function not dictate it. Just the other day I saw a mono putting a swim platform on his slab sterned 45 footer. He needed the utility.

cheers

Phil

 

You can make your own carbon rudder tubes, I talked to Bruce Arms after he set the round Oz record. His tubes were carbon uni wrapped around a cedar plug. As the tubes weren't perfect he added two extra thickening rings of carbon uni where the bearings would be. Then he put the thing on a lathe and turned the two thicker rings down and got them perfectly round. Very nice, strong, light and cheaper than stainless.

 

I dont get the rudder you guys are calling "Farrier style", i built one almost identical for a 25ft uldb mono i designed and built 25yrs ago but when i laid up the case around the blade i only held the trailing edge closed with a single nylon bolt as a fuse so the blade could escape out the back as the case flexed open on impact with debris, the Farrier example shown has a whole lot of metal bolts which would prevent the blade kicking back so something is sure to break if the impact is hard enough. Other than that mine was almost identical. I like this type of rudder as long as you can angle it forward so you have balance. I currently have an old Gemini cat which has this settup where the blade is angled fwd but unfortunatly the cases are welded up out of 1" ss tube and they tend to fatigue and need rewelding from time to time, they would be much better in composite imho. Malcolm Tennant used this type of rudder on the 43ft Bladerunner design as well as most of his smaller cats of course.

Steve.

 

The last example in the pics looks nice, very simple cases to build, im assuming the pivot bolt will be right near the top at the center of the radius which will hold the sides together but the tang that the tie rod bolts to looks weak to me. The problem with kickup rudders is they dont steer well in a partially kicked up position and would put a lot of strain on the case. They work on beach cats but they dont draw much water even when down so they are either down when sailing or you pull it up just as you are running it up the beach,wheras on a big cat you need steerage in shallow water when you are motoring. My son just crushed a fleet of racing monohulls with my 42yr old Pacific cat sailing almost the whole 10 mile race with the rudders kicked up as the bungees were not strong enough to overcome the water pressure, the helm was very heavy and its amazing something didnt break, he ended up 12 min ahead of the next boat, the Olson 40 he usually races on offshore. I would probably go with some version of the cassette rudder but make it strong and with a fuse.

Steve.

 

What kind of cat is that? I really like the steering setup. Any info appreciated.

 

Sig 45. Very,Very Nice boat!

 

Of course one can have a vertical retractable rudder with balance !
You simply make the upper hinge on the rudder longer, the blade will be swept forward, negative then. This configuration also avoids ventilation.
Pix here in my replies 50 and 52 ? :
http://www.boatdesign.net/forums/multihulls/planing-catamaran-30415-4.html

pogo