Lifting rudders

[gjeffery]

I have a twin keeler and when the boat dries out the hull remains stable. However, the high aspect ratio rudder extends to the depth of the keels, and is vulnerable; particularly on an uneven bottom, or when drying out on a lee beach.

This partly reduces the benefit of having a twin keeler! Has anyone any experience of sourcing a lifting rudder, as a replacement for a (partly balanced) transom hung rudder?

 

[graham]

It allways amazes me how designers design boats to dry out then leave the rudders vulnerable.

I think the balanced part of the rudder will be a problem as it must be under the hull I would think ?

The Rudder on my small lifting keel boat slides up and down on a stainless rod which is held by a top and bottom bearing onto the transom.Next time I am on the boat I will try to photograph the lifting arrangement if thats any help.

What type of boat is it?Other owners may have come up with a solution.

 

[geoffatstanpit]

Parker Lift-Keel Yachts ( www.parkeryachts.co.uk ) do swing-up type transom-hung lifting rudders for their range of boats from 21 ft to 33 ft. I know of 2 Parker 21 rudders successfully fitted to Seal 22s

Geoff

 

[William_H]

You could of course remove the rudder when moored however another 4 possibilities come to mind. The first is to modify the pintles so that the rudder can slide upwards up the pintle rods I imagine about 12 inches. You would need a lock to hold it down for sailing and the balance area in front of the pintle line may preclude this possibility.
My TS has a swinging rudder in aluminium cheeks. This has a large balance area which goes under the hull and high aspect. I use a large bolt through the cheeks to hold the rudder down and to clamp the cheeks together to reduce slop in the helm. The rudder can be swung up clear of the water but is a bit vulnerable extending aft so far when swung up.
Another alternative is the dropping blade into a rudder box. The blade box must be canted forward at the bottom so that when down a portion of the blade is forward of the pintles giving balance.
Both the last 2 options are rather expensive and the box can be made in cast aluminium or fabricated from SS tubing and plate.
A last alternative might be to chop some of the bottom of the rudder off and replace with foam and fibreglass (thin) such that it is frangible and will be destroyed rather than damage the rest of the rudder pintles and hull. This last idea only if there is just a slight possibility of damage when drying out. good luck let us know what you decide will

 

[ex-Gladys]

An option that may work is the very neat desOliver Lee did for the Anderson 26. The rudder is a fixed blade, byt the "pintle is a long stainless tube about 2" dia that runs through three gudgeons on the boat and the same on the rudder. A line through a block on the rudder lifts. The issue with pivoted rudders is the problem of slop developing within the cheeks... big thing with Racing dinghies....

 

[gjeffery]

Thanks for those thoughts. My first thought was to modify the pintles and slide the rudder up when drying out, much as described by botheras. This is precluded due to the balance area; the leading edge is about 10 mm forward of the transom. This would be possible if the rudder was "stood off" from the transom, but that involves more work, and risk, than I want take. I don't want to sail a prototype, and would prefer to buy a proven solution!

The rudder is too big and heavy to be taken off he boat completely, each time the boat dries.

A rudder box, from an experienced manufacturer , is a possibility.

My main concern is to avoid over stressing and working the transom, although, thankfully I have not heard tales of boats sinking due to their transoms falling off. The concept of a sacrificial blade tip sounds good. I think the rudder is made of laminated ply sheets, and fixing a sacrificial tip may not be straightforward.

I also suspect that takin say 75 to 100 mm from the tip of the rudder would not greatly affect the handling, but would mitigate most problems when drying out.

Overall, I cannot understand why boat designers produce twin keel boats with ruddfers having the full draught, but offer no provision to protect the rudder when the boat dries out. It would be reassuring to know that boat designers model these issues, and stress the boat to take the dynamic loads applied by the rudder to the transom. But I have to be convinced!

 

[graham]

The system on my boat is the same as on The anderson 26 but if the forward edge goes under the hull then it wont work for you.

if your boat steers well and allways keeps its grip on the water I would say you are right that removing 75 mm off the bottom would not have any detrimental effect.Certainly seems the easiest option.

When I dry out in mud I allways lash the tiller amidships as I think this reduces the pressure on the blade if the boat settles backwards a bit.If she slips sideways in the mud it can relieve the pressure by allowing the tiller to move.

 

[wicked]

My Evolution 26 has a high aspect ratio vertically lifting rudder. When the rudder blade is fully down balance is achieved by inserting a wedge in the front edge of the rudder box which kicks the leading edge of the rudder forward. Vertically lifting rudders are good if you need to steer the boat in very shallow water as you don't get the extreme weather helm associated with a swing up rudder that is not fully down.

I'll send youy a piccie if you need one.

Dave

 

[rex_seadog]

We have a twin keel Hunter Delta and on a firm, flat surface this can dry out without the rudder contacting the ground. However, the rudder can slide up within a rudder box which was useful when we inadvertently came to rest on a shingle bank and the boat sank down at the stern!! The design of the box allows the rudder to pivot slightly fore and aft to give some balance adjustment.

Just one thought - would it be possible to make a removable leg for the transom, which will protect the rudder? A bit like beaching legs but just the one. Would, I think, be easier to make a strong attachment point on the transom that at the sides. Surely simpler than a major redesign of the rudder?

 

[graham]

A couple of pictures of the rudder arrangement on my Anderson22.

There are 2 bearings bolted to the transom and 3 bearings fixed to the rudder.

A stainless rod goes through them all with the ruidder down,when the rudder is raised the top bearing on the rudder lifts off the top of the rod.

A small amount of blade in the water gives some limited control even with the rudder fully raised.

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2

If the balanced part of your rudder fouls the hull slightly you could pack the bearings bolted to the hull out on hardwood blocks to give a bit more clearance.