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.