Rudder& Self Steering Question

[big_s]

Hi all,
I have the rudder shown in the attached pic - hangs off the raked transom of a Samphire 26. I'm going to wrap it in some grp but thought I could take the opportunity to include some mods that would support self steering at the same time.

As I understand it, the best solution for a transom hung rudder is a trim tab. So my question is should I add a trim tab ...
a) aft of the rudder or
b) modify the rudder shape so that the trim tab would fall within the current outline of the rudder i.e. chop some off the aft edge and replace this space with the trim tab.

What should the dimensions of the trim tab be?
At what angle should it be mounted relative to the axis of rotation of the rudder? Parallel to this/perpendicular to the waterline/something else? ( The sloping line just above the white line towards the top of the pic is a few inches below and parallel to the waterline).

Many thanks for any advice/thoughts.

 

[jamie N]

I've fitted one to my Folkboat, and followed the principles set out in this article.
As well as that one, Alan of Wave Rover has a very good set of DIY plans available for a very modest amount of money.
Good luck as well, it's not too difficult.

 

[PlankWalker]

As I understand it, the best solution for a transom hung rudder is a trim tab .
That statement is not correct!
Ive always had transom hung rudders on my boats,
and for 10 years I had a trim tab.
For the last 20 years I've had a Servo Pendulum.
Hands down, the Servo Pendulum is far better.
It tracks far better than I can stear,
Whereas the trim tab would constantly go of course, then slowly come back on again.

 

[big_s]

As I understand it, the best solution for a transom hung rudder is a trim tab .
That statement is not correct!
Ive always had transom hung rudders on my boats,
and for 10 years I had a trim tab.
For the last 20 years I've had a Servo Pendulum.
Hands down, the Servo Pendulum is far better.
It tracks far better than I can stear,
Whereas the trim tab would constantly go of course, then slowly come back on again.

It was a statement of my understanding, not a statement of fact regarding trim tabs.
Can you elaborate please... what size of boat were these devices on? The boats referenced by Jamie N above have some similarity to a Samphire.
Also, could you explain how a trim tab would allow the boat to 'constantly go of course, then slowly come back on again'? What point of sail was this, or all points?
Ta.

 

[dansaskip]

Like PlankWalker both my boats had transom hung rudders - one was a 25 footer the other a 28 footer. Both have had servo pendulum steering gear. The first boat didn't come with any self steering so I fitted a Pacific Wind pilot which I bought second hand the 28 came with a monitor already fitted. Both of these self steering systems worked and track really well and I have done many thousands of miles with them. I don't think I would consider any other means of a self steering. The only disadvantage I can see is the cost but then the old adage of "you gets what you pays for" rings true.

 

[Blueboatman]

Don’t modify the boats rudder

Add a wind vane- pendulum servo or auxiliary unit. As available funds allow .

That’s my best advice

 

[srm]

- hangs off the raked transom of a Samphire 26.

The hull form with a longish keel and keel hung rudder will have good direction stability so a well designed trim tab system that is correctly set up will not have too much work to do and should manage the boat. The wind vane / trim tab turn ratios are critical to accurate course keeping. Do not reduce the rudder area as the trim tab moves the rudder for you by turning in the opposite sense to the rudder blade. However, if fitting a trim tab I would modify the rudder shape to give a straight, near vertical, trailing edge and more area at the bottom as this will be more efficient.

As others have said a servo pendulum gear will generate more power and is more responsive than a trim tab and would be my choice on your boat. It will also be easier to set up than a trim tab system.

The key to using any wind vane steering gear is good sail balance for the wind direction as they will only apply a small amount of helm to bring the boat back on course. They can not be expected to fight an unbalanced boat in the way an electric autopilot can.

the 28 came with a monitor already fitted.

Wow, that looks like overkill. My Monitor gear has managed a 32 ft Prout cat and my current 35 ft longish keel boat for me and I would not be without it. However, I bought it from its first owner who used it for an Atlantic circuit on a 50ft Colin Archer type. The higher the freeboard and the longer the paddle arm the more power it generates.