Transom mounted rudder

[Seeing AndrewH’s thread on his new Sloice reminds me of the issue of how best to make and mount the rudder. I would like to explore different ideas on what the ideal properties are and debate possible solutions. I am new to sailing but have been building and battling combat warships for 9 years, rc modelling for more than 20, and researching sail and Footy for about 3 years. It seems to me that the ideal (and we will limit this thread to transom mount) rudder needs to be light, accurate with no slop, reliable, easily maintained and “strong enough” for our small ships which several members remind me tend to be overbuilt. To that end I have seen a number of setups made from an aluminum bracket cut from square tubing pinned to a balsa or ply rudder blade often with some harder wood at the blade’s pivot points.


A piece of shaped Aluminum is glued to the top to serve as the horn for pushrod attachment point. I may be a slow builder but it takes a while to cut square stock, file and shape, smooth edges and get everything drilled to my satisfaction. While this is a big part of the fun of modelling for some, it is a pain for others. The process looks something like this.

transom rudder mount 001.jpg
I have been learning to make urethane parts for ship detailing and the end products seem quite strong enough for our purposes in Footy. I had the privilege of meeting Gary Sanderson on our holiday in London this summer and saw how he made parts. I also had the opportunity to see how well they work. Gary is a wonderful host and teacher. He gave my son and I our first official sailing lesson using Duck and Thintrekker. We had a great evening. On the trip home, I drew up designs for parts that could accomplish the same thing with moldings. I wanted a part set that is easier to make than fiberglass or carbon fiber/resin technology. The result is this:

transom rudder mount 003.jpg

the transom mount is simply glued on. CA, poly glue, and epoxy all work. It could also be attached with small screws. the rudder piece in this example was put together with CA and will be coated with West Systems epoxy after shaping. The balsa blank is quickly created in 4 cuts - very simple. I have made samples in 4 and 5mm widths. The horn is molded in the 4mm part and must be added to the current 5mm molded part.

Ok. there it is for thoughts, discussion, criticisms. What is good about it? What is bad about it? What could be done better?

Nate G

That’s one way to recycle old aluminum stuff. The only problem is that people don’t just put their old aluminum doors & windows out to the curb anymore (the window company recycles it for you.)

Actually, no recycling here. I buy 3/4 inch square Aluminum tubing at the local hardware store or did before coming up with the molded idea. it is a standard item.

If you put the boat in the box on the diaginal, does in “sailing trim” mean that it must have room to turn to full rudder in both directions (full rudder being how much it can turn when actually sailing)? I seem to remember a post implying this. If it fits in the slot, then it doesn’t need to turn.

We recently had a skipper experimenting with stern rudders and his went right to the corner and could not turn. Thanks for your comments.

Hi Frank,

This is mentioned in the new rule under paragraph B1, where item B4 (rudders) is exempted from the “in racing trim” definition. This reflects an interpretation on the earlier rule, made by the powers that be in Footydom.

Bill Nielsen
Oakland Park (Ft. Lauderdale), FL USA
AMYA #0835
Footy #835

Hi guys,

B4 permits a rudder to extend beyond the box through the slot.
B5 exempts a rudder that extends through the slot from having to rotate.

Any number of rudders that fit inside the box fall under the “in racing trim” clause, so they must be able to rotate to the full extent used in racing.

My latest Cobra Mk3 is a diagonal design. I had to mount the rudder about 1/4 inch inboard from the stern in order to get the full motion I want while racing.

Your skipper, FFrank, should modify his rudder to allow full motion.

Bill H

Correct me if I am wrong, but in the old Footy rules that will be in effect at the NCR there is no definition of racing trim included. So, my understanding of those rules does not require inboard rudders to rotate or rigs for that matter. The newly adopted international rules do define racing trim clearly in B.1. of the Primary Measurement Rule section. I think that absent a printed definition that most folks assume that racing trim would mean in a close hauled position since this is how most other boat classes are measured at regattas, unless they are required to have their rigs removed for measurement.

My understanding of the ( I hate to say this) intent of the way the rules were/are crafted is that if the ship is placed square in the box, it gets the benefit of a rudder with a backwards extension of 51 mm beyond the box. if placed any other way, then the rudder must fit inside the box at least when aimed straight back.

Thus unless the rule interpretations change such that I can put a transom mounted rudder on say Moonshadow or full length Voortrekker, etc. for extra moment angle to maneuver the ship, This way of handling the Mechanicals of the ship is limited to true less than 12 inch hulls. I have cut My Voortrekker hull down to 11 7/8th inches so as to use a transom mounted rudder. This was per my discussions with Gary when I got the hulll to " give it a try" and see if it will work any better.

Good point sailtwister-

I’ve never seen any requirements in other boat classes to have the boat parts to be excersized while getting measured. Everything, like you said, is measured while closehauled (pulled in tight, on the centreline, etc.)

But IMO, I think the intent of the racing trim requirement for the Footy class was to keep things small & manageable (or to fit in the measurement box) so that the boat doesn’t blow up into something obtuse. :scared:

If it does fit in the box, it ought to be able to move (especially inboard rudders) so that shouldn’t be a problem either way. If it did fit into or through thte rudder slot, then there’s no way for it to turn, is there?

Smiles - There are so many different answers. Let’s get rid of lawyers writing rules and put this stuff in plain English for all to understand without confusion.

Niel, the definition wasn’t in the old rules, but the Tech Committee interpreted the “in racing trim” phrase to mean full motion used in racing.

That said, since Orlando is our first NCR, there’s bound to be some boats that are not fully compliant as a result of misunderstandings of the nuances of the rules.

I have to measure all boats participating in the AMYA NCR, as stated in the bylaws. In the spirit of learning,however, I intend to point out all infractions that I see, but not disqualify someone for minor errors. Flagrant violations, of course, will have to be disqualified. I will use my best judgement, and strive to be fair.

Bill H

Nothing would thrill me more, FFrank…but the one thing that’s clear to me is that it won’t be clear to someone else!

Try writing a simple rule, post it here for fun, and see what different interpretations or unintended consequences come out. It ain’t easy.

Bill H

Hello Nate,

I really like your castings solution to the transom mounted rudder. I can’t see any obvious improvement as you appear to have got it just right. I particularly like seeing the rudder horn moulded into the part in one piece.

With regard to the strength of the casting material did you know that you can get casting resin in many different hardnesses. Some is almost like a hard rubber which will push tight onto a carbon rod for instance, often used for kite fittings. While others are harder and as strong as nylon. I have a chart somewhere I can email if you are interested.

Very nice work Nate.


Thanks Graham,
Re: the horn - I added that in the second round of test designs. It makes one less piece to have to assemble and the force required to deform the plastic is quite significant. as in you will break something else first.

Re: the plastic - I am aware that the chemistry exists to get a range of properties in the casting but have only tried the harder products so far. I would be interested in your list of options. I was concerned that the rubberier compounds would deform too easily under load and opted for the harder Alumilite and TAP products that I have experience with. There is some give to the material and I drill the rudder part to a slightly smaller hole for the brass rod so it fits snugly while the transom mount pivots on the rod easily with no appreciable slop.