Rudder change - please advise, who can

The biggest hassle with a trim tab is they must be locked in line with the rudder when backing.

Many of the self steering simply use a lift out trim tab .

The tab can cause "oversteer" when backing.

Nicest seems to be when the tab tiller can

1. be used as power steering instead of the tiller
2. be used by the vane or electric autopilot , for more sensitivity and a lower power requirement,
3.lock in place for backing
4 be used as a booster tab , lightning the load on the std tiller

Lots to do!

FF

 

Thanks for the comment. I’m ignorant of much of the technical detail that some of you more learned or experienced contributors mention. How and where is a trim tab like yours attached, and how controlled?
I think I will probably try hanging my rudder vertically with the top of the rudder stock where it is now and the bottom in a pintle bearing on an extension. Something like the sketch. I have in mind to weld stout s.s. straps to the stock extending forward, to which I can bolt a removable leading edge of the rudder, and see what the effects are. I could remove it, modify and replace, thus trying several options in size and shape, without needing to lift the boat each time. If, in the end, I can get no improvement, I’ll lift her and reverse the changes. It’s been suggested I move the rudder further aft and make it a spade rudder, but this raises construction difficulties, and would necessitate major changes to the aft cabin.
I take the point made by another contributor that the portion of the rudder forward of the stock on a long keeled boat will act as a brake. As I envision things the entire rudder acts that way, mitigated by the fact that the stern of the boat then moves in the direction the rudder is pointing. Which it wouldn’t do if the rudder were not tending to act as a brake. Also, I have difficulty imagining that the leading portion, of 1000 or 1500 sq cm, dragging at an angle to the direction of travel of a 17 tonne boat will brake it’s progress enough to notice. I concede that it might, though.
REgards, Barry

 

i dont see it posted maybe I missed it,
But how thick is the section forwards you could rebuild using a modern section, and how far is it from rudder top to hull.
There is only so much you can do, reef early on the main, shift the headstay forwards
I had a boat once that did zackly as your does, nightmare is ,nt it
Even with right and proper wheel and gearing, the boat will not steer, esp hard reaching? and the rudder stalls too? a proper section can help as many may have said
And you can not reduce area as she will not steer astern

 

I take the point made by another contributor that the portion of the rudder forward of the stock on a long keeled boat will act as a brake.

This is not true during most steering ,at a small angle of attack the rudder lead works for you.

Only when cranked way over , as in docking , will the rudder lead ( 10% or so) work as a break , and then its usually being hit with prop wash , so total area is the key to moving the stern with power.

The simplest I have seen is when the tab tiller is up the rudder stock , and there is simply two tillers . The main one , and a tiller that would look at home on a sailing dink.

The trick is in linkage to allow the tab tiller to be steered in the same direction as the main tiller , not backwards , to move the bow heading . A drop in notch holds the tab tiller during backing

FF

 

A hollow rudder shaft is the only way to get a trim tab to work in your boat. A second shaft inside the hollow rudder stock with a cross arm moving in slots near the base of the stock is attached by rods to a second cross arm at the base of the trim tab. The trim tab is attached by standard pintles to the back of the rudder. The trim tab can either be close to the rudder blade and faired in similat to the full keel to rudder junction, or for more tab lever arm be separated from the trailing edge with extension brackets and act with more force from less area of trim tab. For a cruising boat the first option may be better as the tab is more protected and less liable to be damaged. I would suggest that you extend the full depth of the keel below the prop back to the new rudder shaft and have balanced area on the rudder within the prop aperture. This will give some balance to the rudder, as well as then deflecting the whole of the prop wash, which will improve slow speed handling under power to a huge extent. The attached sketch shows what I mean.