Conversion full crew racing yacht to double-handed

[Night Sky Yachts]

Hi all. My friend bought a 34 ft racing yacht for full crew and we are planning conversion for double-handed. Firstly, we have to add an autopilot, but the rudder tube is full from the bottom to the deck. We are planning to cut the rudder tube and seal this with a gaiter from Jefa Rudder and add the autopilot tiller like shown on the drawing. We don't want to mount the autopilot above the deck. Does anybody tried this kind of solution?

 

[gonzo]

You will have to calculate the forces paths. The rudder shaft tube is acting as a column joining the deck to the bottom.

 

[philSweet]

No, you have to start again. Get rid of the entire tube and rudder. You will need a new rudder with bigger diameter shaft and bearings, and a new tube to accommodate it. You will need to reinforce the hull skin out quite a distance - say 1/2 the length of the foil. The top and bottom bearings both go in the tube, followed by a proper seal. The tube needs to be supported. This is normally done with a full bulkhead, but can be done with a beam if necessary and if properly engineered as a system from the start. The top of the tube should be at least a couple inches above the waterline at anchor to prevent nuisance leaking. Then you need to resupport the aft deck since you removed it's primary support. You can't use the rudder shaft bearing to support the deck like that - it won't work.

The practical solution is to use a tiller-minder style autopilot on the deck. These should be mounted as close to the end of the tiller as you can manage - and check the maximum drive load and holding load compared to the tiller head torque rating.

Also, you will probably want a rudder that is about twice a large for the autostick to be effective.

 

[gonzo]

Another solution is to make a metal section of much larger diameter to join the two sections of existing tube. It would have a section cut on the front to allow the tiller to rotate. It can be a U shape channel.

 

[Night Sky Yachts]

Thank you for the answers.
Of course, I think about adding pillars and a partial bulkhead to stabilize the deck and the rudder tube. I attached a simple sketch.
@philSweet can you explain why you think that I need bigger bearings? Any source? In ISO 12215-8 I can't find that information.

 

[gonzo]

The bottom at the bottom of the rudder tube is usually thicker for reinforcement. The two diagonal tubes would be in a thinner section of the hull. Simply reinforcing the tube where you cut it will not change any of the force paths as designed.

 

[BoatBuildLog]

Are you mainly changing the deck layout and controls for double handing or are you planning bigger structural changes too ?

 

[BoatBuildLog]

Before you glass it, are you planning to fair that transition any more or is that roughly the final shape you are aiming for ?

 

[Night Sky Yachts]

Thanks a lot @gonzo you are right. I think the best idea is to make it like on the attached drawing as you suggested. The half tube will be glued with epoxy adhesive and laminated around the original rudder tube.
@BoatBuildLog we also plan to add water ballast tanks as equivalent to missing 6 crew members.

 

[philSweet]

Okay, but your seal is woefully inadequate. Your seal should be structurally equal to the hull above the waterline. Find a good packing gland to fit the shaft. Install the gland in a short piece of very heavy reinforced rubber hose and connect the hose to the tube with two heavy duty marine hose clamps that have pressed groves, not cut out grooves; or install a fitting in the tube and connect the hose to the fitting. You need about 1/8" radial compliance.

 

[montero]

Why am I afraid of such a rudder?

 

[Night Sky Yachts]

I'm planning to use a gaiter from Jefa Rudder. Don't worry, it's a proven solution. After modification will be even stronger than original.

 

[Rumars]

You would have to make the support tube a very large diameter to insure the gaiter never touches it. Unfortunately the thing can billow out like a baloon when full with water.
You could however install the gaiter on the autopilot tiller arm instead. Make a second piece for the shown support tube with a slit for the autopilot tiller surrounded by a round or oval flange. The tiller would need a round collar for the gaiter to seal around. The second piece of the support tube is sealed against the first one either by screws and sika, or you can permanently glue it in. This obviously depends on how you plan to attach the autopilot tiller to the rudder shaft (wich is another can of worms if the shaft is hollow).

Me I would take a simpler route, put a full bulkhead centered on the rudder tube, cut a big round hole where the autopilot tiller goes, add two knees to support the lower tube longitudinally. The upper remains of the original rudder tube don't neceserally need longitudinal support, but if it makes you happy you can also add to knees there.
I know, tabbing everything in would be a pain, but the end result is much stronger then even what's there now.

 

[Night Sky Yachts]

Thanks, @Rumars . I know that the gaiter could look like a balloon full of water, but we have a solution for that. We will add a vent line from the rudder tube to the transom to decrease pressure in the gaiter.
Your idea is OK, but please remember that the rudder sometimes we have to remove, so this seal system has to be easy to remove.
Putting the full bulkhead without removing the deck is impossible and not necessary. We just want to convert full crew racing yacht to double-handed racing yacht, not to the dreadnought.

 

[Rumars]

A ventline is a nice solution. Here's what I don't understand: if structural reinforcement of the deck isn't your goal, why bother with the molded tube and ventline at all. I doubt the deck relies on the rudder tube against collapsing. So it's just a matter of keeping the top of the lower part of the rudder tube against flexing. This can be achieved in several ways, depending on how you plan to install the autopilot mechanism. If you need a shelf across the boat for that, just extend the shelf to the tube and bond it to it with a few strips of glass. If not three knees spaced 60° around the tube will also do the job, an they are just three triangular pieces of ply or foam to be tabbed in.
This gives you the simplest solution while maintaining the most access to the seals and autopilot tiller arm.