SUNMAID 20 RUDDER

AUTHOR: Alan Burney - NURGLER -102
First published July 200 in Sunlog #86

The original Sunmaid rudder box was fabricated from a marine ply laminated core and marine ply side cheeks. Chromium plated bronze pintle assemblies were secured to the timber by stainless steel screws and a fabricated stainless steel rudder cap served as a tiller mounting. Some rudders had a cast aluminium rod clamp as a blade control device and on others this clamp was fabricated from stainless steel sheet. The rudders were a very serviceable unit and, if the varnish was in good condition, they looked quite attractive. Unfortunately, many of them have not survived the ravages of time, weather exposure and rough handling by helmsmen and have failed completely, or simply split in such a way as to appear that failure is imminent. If the rudder blade is allowed to swing back just a few degrees in heavy weather, such that the effort at the tiller is increased (two hands on the tiller and two feet braced against the other side of the cockpit) then splitting of the cheek plates from the core is almost guaranteed.

There are several ways in which a replacement rudder can be made. One of the easiest methods is to replicate the original using quality marine plies and proper marine glue. For people accustomed to working in timber, this is a reasonable option. At least one of the rudder boxes seen around the launching ramps was completely fabricated from mild steel plate, fully welded and then heavily galvanised. Another rudder box which must not be overlooked is Webster Marine’s cast aluminium open web type rudder box, which is not cheap but is a proven alternative. The rudder box described in the following pages is the preferred option of a couple of members of committee and it has proved to be a solid and reliable replacement for the original. It is not difficult to make.

You will need:

Material: Two pieces of marine grade aluminium plate 6 mm thick, 500 x 300 mm - undamaged and flat. Marine plywood laminated to form the core. The thickness required will have to be determined from the rudder blade. It is about 41mm but take care to measure the blade in several spots around the area which will enter the rudder box cheeks. 41 mm can be fabricated from two x 19 mm and one 3 mm, 43 mm from two x 19 and one 5mm, etc. Use a good marine glue such as Epiglass or Blockey’s Resorcinal. Dimensions are 500 x 300 mm. Hardware - miscellaneous screws, bolts, nuts, washers, dome nuts, etc.

Tools: Bench drill and drill bits, power jig-saw with timber and metal cutting blades, wood plane, flat files, screwdrivers, spanners, clamps and sandpaper.

Step 1.
Mark out (See Fig 1.) and cut to shape the two side plates using the metal cutting blade in the power jig-saw. Clamp the two plates together and dress the edges clean with a file. Break all sharp edges. Note that many of the aluminium suppliers have a cutting service available and will supply the plates ready for drilling.

Step 2.
Cut the laminated marine plywood for the core into the same shape as the side plates (Fig 1.) using the power jig-saw with the timber cutting blade. Clean up the edges with the plane and finish with sandpaper. Use the finished shape of the metal side plates as a guide.

Step 3.
Clamp the plywood core between the aluminium plates, carefully aligning the edges at the top and both sides. Drill three 9/32” diameter holes at positions A, B and C (Fig 3.). Fit three 1/4” diameter hexagon head SS bolts, cut to length and tighten securely, using dome nuts. Remove the clamps.

Step 4.
Position the existing SS rudder cap on the top of the rudder box making sure the front edge is in line with the leading edge of the rudder box. Insert the tiller and check for a neat fit before clamping the rudder cap in position. Using existing holes in the cap as a guide, drill through three holes 7/32” diameter. Drill from both sides to ensure entry and exit holes line up with those in the rudder cap, then open up the holes through the timber section later. Fit 3/16” diameter roundhead or hexagon head screws, cut them to length, and fasten with dome nuts.

Step 5
Place the upper pintle bracket in position (Fig 4) making sure it is fully home against the forward side of the rudder assembly and that the hole in the bracket lines up with the hole in the rudder cap. Check that the pintle is parallel to the face of the rudder box. Note that the thickness of the rudder box is less than the space between the side cheeks of the pintle bracket and packers will be required to make up the gaps on each side. Use aluminium, stainless steel or an engineering plastic such as UHMWP or similar for packers but do not try to squeeze the side cheeks closer together. Clamp the pintle bracket in position and drill two holes 9/32” diameter through the timber (work from both sides as in Step 4) to match the holes in the rudder cap and pintle bracket. Fit two 1/4” diameter roundhead or hexagon head bolts, cut to length and secured with dome nuts.

Step 6
Carefully measure the distance between the top faces of the gudgeons on the boat’s transom. This distance is used to position the lower pintle bracket relative to the top one. Set the lower pintle in position and, as before, use suitable packers to match the thickness of the rudder box to the distance between the bracket’s side plates but do not try to squeeze the side plates in. Make sure the bracket is hard up against the front of the rudder box and that it is square to the front face and the correct distance from the upper bracket. Drill the two holes through the aluminium side plates from both sides and continue the rudder blade pivot bolt hole through the timber core.

NOTE: Check the details of the holes used in the original rudder. 5/16” diameter appears to be the standard size for the rudder’s pivot bolt, but at least one rudder in the fleet uses a 3/8” rudder blade pivot bolt. Also, the smaller holes in the bracket may be tapped to accept 1/4” countersunk screws inserted from within the rudder blade space. This method was used when the side plates were timber. These should now be opened out to 9/32” diameter and countersunk from the outside, and the corresponding holes in the rudder box side plates tapped to receive short CSK screws. The rudder blade pivot bolt (5/16” or 3/8” diameter) is a hexagon head stainless bolt, cut to length, and secured with a stainless steel “Nyloc” nut.

Step 7
Dismantle the rudder box assembly and partly re-assemble it using one side plate, the laminated plywood core and sufficient fasteners to properly locate the two together. Use a long bolt in place of the rudder blade pivot bolt and set the assembly on the bench with the aluminium plate on the bottom and the long bolt standing vertical. Place the rudder blade in position over the temporary pivot bolt and swing it from the up to the down position, marking on the plywood core the blade clearance required. Note when marking out the clearance that the top of the rudder blade is not a true circular arc. Mark also the areas on the core where the rudder blade will be stopped in the both the fully up and fully down positions. Dismantle again and cut out the shape of the plywood core with the jig-saw. Clean up the cut and partly re-assemble to check the blade clearance.

Step 8
Depending on the fittings used on the particular rudder there may be additional holes to be drilled, for the blade control clamp for instance, after which the aluminium side plates should be treated to prevent corrosion. Marine grade anodising is the preferred option. Powder coating is an alternative method but not as durable as anodising. The yellow pages will help you find a supplier in your area.

Step 9
While the aluminium plates are away being anodised, the plywood core should be sandpapered smooth and treated with a good coat of Everdure or Bote Kote and several coats of a marine grade of varnish. There is also an opportunity at this time to send the pintles and gudgeons out for chromium plating, if thought necessary.

Step 10
Assemble the three pieces of the rudder box with a liberal coating of Silastic between the side plates and the timber core. Tighten all bolts, working evenly around the rudder box. Insert the blade and check the clearance as it is swung through the full range of movement. Ideally, the blade should be free to move up and down without any noticeable side clearance. If necessary, plastic packing washers about 6” diameter can be cut from perspex sheet of a suitable thickness and used to make a smooth fit between the blade and the rudder box.

Step 11
The blade control clamp should have been chosen and any holes required for it before anodising. it the clamp and swing the rudder blade through the full range of movement to check the extreme positions. In the fully down position the most forward point of the blade at the bottom should be at least 70 mm forward of a straight line projected downwards from the face of the rudder box. When fully up the blade should be at least horizontal. The dimensions given apply to the rudder box made for Sunmaid No 102. There may be some minor variations for other Sunmaids.

The completed rudder assembly is hardly a thing of rare beauty or outstanding elegance but it is a rugged device which will stand a great deal of abuse. The rudder box is slightly heavier than the original timber one but this adds very little to the total weight of the rudder assembly.

SUNMAID 20 CENTREPLATE

AUTHOR: Alan Burney - NURGLER -102
First published June 1998 in Sunlog #78

During a routine replacement of the centreplate cable on Sunmaid 102, it was found that the loop welded to the top of the plate was corroded and worn to the point where failure was imminent.

Issue No 46 of Sunlog (June 1989) carried an article on the removal, repair and replacement of a centreplate by one of our Queensland members. The article also detailed the dimensions of his particular plate and it was considered that a new plate could be fabricated to this drawing as a “slip-in” replacement. However, after learning of a late model Sunmaid’s centreplate dimensional differences to the drawing, it was decided to err on the side of caution and remove No 102’s plate prior to any manufacture.

Fortunately, having the facility of a five tonne crane and a fork lift truck available, we avoided having to dig a trench and drag the boat from the trailer, as was done in Issue No 46. Using webbing slings, the boat was lifted clear, the trailer removed and it was observed we had an airship - an awesome sight! 650 mm from ground to skeg will provide enough clearance for working.

Removal of the plate was achieved by first lowering it to the normal “down” position using the on board winch. An automotive trolley jack was positioned midway along the plate and a rope with a slip knot tied around the boat to support the front end of the plate should the jack move. The pivot bolt was removed and the front end lowered to the ground. With the jack removed, the rear end was lowered to the horizontal, again using the on board winch. It is not necessary to remove the aft stop pin as the plate will move forward far enough to clear it. The shackle connecting the cable was removed and the plate pulled clear.

Inspection showed that apart from the rusted loop, the only other corrosion was a 12 mm strip of rust along the rear edge. The condition of the plate after some 20 years of use is testament to the quality of the original manufacture. A new loop of 8 mm dia mild steel was welded in place, the rust ground off and the plate delivered to the galvanisers.

Refitting was the reverse of the removal procedure. With the boat raised and the cable attached, the aft end of the plate was lifted into position by the on board winch. The trolley jack and rope were placed as before, the front end was lifted and the pivot bolt replaced using marine sealant.

The dimensions of this plate were found to be generally similar to those shown on the Queensland drawing but differ in the overall height and the position of the pivot hole. While the two plates MAY fit into the same boat, enough doubt exists to warrant removal and/or measurement prior to replacement of any Sunmaid centreplate. A dimensional check can be made with the keel in place by measuring the distance from the centre of the pivot bolt to the aft stop pin and subtracting 3 to 5 mm for clearance to give the radius. Similarly, the height could be measured in situ through the inspection port or with the top timber trim removed from the keel case. A new centreplate would probably be a rare requirement, unless one were to drop it off into 20 fathoms of Western Port mud. We suggest that removal, repair and re-galvanising is a simpler option and a lot less expensive.

The article “Replacing the Centreplate Cable in your Sunmaid” may also be suspect in the area of the cable and shackle. On Sunmaid No 102 we have found the 5 mm wire rope to be too thick and use the 4 mm - 6x19 galvanised wire rope instead. Likewise, the RF615 Ronstan slotted pin shackle tends to jamb in the centreplate case and we use the RF614 narrow shackle instead.

For galvanising we suggest you shop around. ABB in Wellington Road, Clayton, 9560 9944, had the best price at $60.00 for regalvanising the plate and two Danforth anchors. However, they do not do chain, etc. Dimensions of the plate from No 102 are shown on the next page together with the dimensions of the plate from the Queensland Sunmaid.