I’ve at last had an opportunity to try the new rudders that I have fitted to my Iroquois IIA, Ambler.

Ambler’s original steering system used a wheel and  two very long cables to drive a pair of rudders fitted to massive skegs under the hulls. This equipment has been replaced by transom-mounted rudders, and I have added a pair of modest sugar-scoops to improve the water flow off the transom – they also improve the look of the boat. The MkIIA boats originally had petrol engines with outdrives, requiring the transoms to be raked forward at the bottom; Ambler’s sugar scoops match the rake of the bows rather better, I think:

 

 

 

 

 

 

 

The steering system incorporates a Simrad TP10 Tiller Pilot mounted fore-and-aft, operating through a push-rod and a lever mounted on the starboard rudder:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I regret that the low winter sun made it difficult to photograph these details, but I can send more pictures to anyone who is interested.

My initial impression during the trials was an amazing improvement in the responsiveness of the steering. It’s now possible to turn in a circle not much longer than the boat, and her response to the tiller is immediate. When sailing with full main and working jib I can feel a small amount of weather helm. Going to windward in a light breeze and flat sea the boat easily ran up to 7.5 knots and remained very controllable. If I let go of the tiller she turned into wind very quickly, and didn’t stop, but kept on going round. Certainly she is much less directionally stable than she was before, and of course that helps her responsiveness. It remains to be seen whether, in more severe conditions, she is too responsive. At no time is the load on the helm anything but light, as one would expect with such long tillers.

I found some small snags with the new set-up – for example, the rubber bungees holding the rudder blades down were not strong enough, and at first the rudders swung up at speeds over 5 knots. I put more tension on the downhauls and that fixed the problem.

Another issue is the method of controlling the rudders. For these trials I fitted two tiller extensions to the crosstube that connects the tillers, one on each side. That proved clumsy and needs further thought. A single long tiller extension would probably be better, and would allow the helmsman to sit or stand almost anywhere in the cockpit.

I also tried the boat under power and under the control of the Tiller Pilot, and again she performed without any problems. Under power I tried linking the outboard tiller to the steering crosstube, so the engine turned with the rudders. However, even with the engine locked straight ahead, the rudders are so responsive that I think this would rarely be necessary.

Previously the helm was totally without feedback, and I must say that it’s very nice to be able to feel the boat responding under one’s hand – she now sails much like a big dinghy.

So far, so good… I look forward to further trials in the spring.

Martin

New rudders for an Iroquois Mark 2A – part 2

 

This picture shows one of my new rudders temporarily fitted with its lifting blade and mounted on the new starboard rudder post.

The shape of the new rudder blades required some thought. The lifting blades of a typical Mark 1 Iroquois have an elegant rounded profile, tapered towards the tip, and a fairly thin section. Modern design practice favours high-lift sections which are much thicker, typically a symmetrical section such as the NACA 00XX series with squared-off tip. My new blades were made from three laminations of marine ply to a thickness of 40mm, a chord of 300mm and a length of 1000mm. I planed the sections to shape by eye. They are certainly not made exactly to a NACA 0013 profile, but they are somewhere near that section. These should be pretty powerful rudders, possibly too powerful. If so, it will be easy enough to reduce the length of the blades.

The stainless steel gudgeons were fabricated from 50mm x 6mm 316 grade stainless steel (thanks to Metal Supermarkets) and welded with a borrowed arc-welder. Although my welding skills haven’t been tested for more than 40 years, I found that an arc-welder is much easier to use than it was in the 1960s, so the welds aren’t too bad. The rudder hinge pins are lengths of 12mm stainless bar, and the lower gudgeons are arranged to incorporate the rudder blade hinge bolts for extra strength. The blades are fitted with uphauls and downhauls made from 3mm Spectra, with a bungee section in the downhaul to reduce the risk of damage when the blades are grounded.

My next post will look at the tillers and linking crossbar.

 

Martin