Saildrives
Regular maintenance is especially important with saildrives as they are less forgiving than in-line transmissions for any lack of attention. Best practice is to check the saildrive fluid level before every engine start-up, along with the engine oil. This is more important in saildrives than regular gearboxes because water can leak unnoticed into the lower unit and water, especially salt water, can seriously damage the lower unit through corrosion and by preventing lubrication – presence of water means the absence of oil. If seals fail, corrosive raw water, (salt or fresh) can enter under pressure into the lower unit, mix with the gear oil and cause extensive damage. Seals can only be checked with the vessel out of the water; so while afloat the saildrive’s oil dipstick should be checked regularly for signs of emulsification – water mixed with oil looks ‘milky’ or ‘like mayonnaise’. The gear oil should be changed once a year or according to the manufacturer’s recommendation.
SEAL OF APPROVAL
If the vessel is out of the water, check for fine fishing line or netting caught in the gap between the propeller and saildrive anode or housing. Line can damage the oil seals and rubber hub fitted in many saildrive propellers.
The diaphragm sealing membrane between the hull and the saildrive leg, and prevents water coming into the boat, should last 5-10 years depending on servicing. Replacing it is typically a dealeronly procedure.
CORROSION AND ANODES
Saildrives can be quickly eaten away by corrosion because their aluminium casing is galvanically very active, much more active than a bronze through-hull or an exposed steel keel. In addition, the aluminium housing of the lower unit has only a slightly lower electrical potential than materials typically used as anodes (including aluminium) so the margin of protection is small. Any compromise in protection is likely to allow corrosion. Use the correct anodes for the vessel’s location – magnesium only in fresh water, zinc in salt or brackish water and aluminium in all types. Magnesium will be consumed too quickly in salt water; zinc is too inactive in fresh water. Don’t mix anode metals or assume that anodes installed by the previous owner or dealer are correct for the current location. A saildrive may have three anodes – on the upper unit inside the boat, the lower unit/leg and on the propeller cone. Replace each when they are 50% consumed (or likely to be during the season).
Saildrive anodes are sized to protect only the saildrive and the original propeller; installing a feathering (bronze) prop with greater surface area can increase the cathodic load on the anode – so protection will need to be increased or the anode will likely need to be changed more often.
PAINT
Paint coverage is part of a saildrive’s anti-corrosion regime. Any scratches increase the area of metal to be protected by the anodes, which will be consumed faster. Best practice is to touch-up any damage or scratches immediately. Use two-part epoxy sealer/paint if the original manufacturer’s paint is not available. Two-part underwater epoxy paint is available so a boat does not need to be hauled for touch-ups. Use only an antifoul paint that has been formulated specifically for aluminum outboards, saildrives or sterndrives. Avoid paint with (cuprous) copper oxide as this will promote galvanic action.
It’s also worth giving the gaiter a quick glance, as this protects the top of the saildrive leg and the diaphragm from damage and helps create a smoother flow. If reapir is necessary, either reglue or replace.