10 tips for your next outboard motor installation

Repowering or fitting a new marine engine to your boat? Here are 10 essential tips for that outboard motor installation.

10 tips for your next outboard motor installation
One trend these days is to put bigger outboard motors on boats. While it’s tempting to go for maximum power, keep it sensible and check the hull’s horsepower and weight capacity.

Our Haines Hunter V19R project boat was in need of an outboard motor. After some extensive research we narrowed the choice down to a new 200hp Yamaha F200G four-cylinder four-stroke outboard motor, kindly supplied by Yamaha Australia.

We entrusted this job to MY Marine. Based at Melbourne’s Mornington Peninsula, the crew there are well versed in all facets of marine engine fits. Michael Rozakis (below) heads an experienced team of tradespeople, all of whom have been around the marine industry most of their lives.

Here are 10 of his most essential tips for a new outboard motor installation.



1: Check the transom

There is a trend to put bigger outboard engines on boats, so keep it sensible and check your horsepower and weight capacity for the hull. Too big will void insurance, damage the hull and threaten safety and predictability. While four-stroke outboard motors have in the past been considerably heavier, outboard manufacturers are now designing lighter engines to reduce this problem and increase efficiency. Regardless, you don’t want to change the entire hull construction, weight distribution, etc. merely to cater for a few more unwarranted horsepower. Most boat manufacturers nowadays design boats to take heavier engines with transom heights, increased buoyancy, thickness and materials.


2: Your dealer will know if it’s a bad idea

There are still boats that are not suitable for repowering. Many older transoms aren’t that thick and strong and the extra weight can put back pressure on the exhaust relief, drowning or stifling the engine. We have generally done away with 20in (long shaft) transoms (now 25 or even 30in) for all installations of 90hp and over.


3: New outboards have torque

Don’t underestimate the increased torque of newer engines. Many have extra drag and sometimes more cavitation plates causing increased torque twist.


4: Is it the correct height?

Be sure you set the engine at the correct height. The guideline is that the cavitation plate (the horizontal planning plate above the propeller) should be around 10 to 25mm above the straightedge line of the keel. You need to watch out for broken and disrupted water flows from keels, etc. Four-stroke outboard engines often need smaller props to get them working hard for maximum efficiency in the torque range.


5: Fit a backing plate

Install a suitable backing plate between the engine and the hull. It doesn’t need to be huge and a 6 to 10mm polyethylene bit will do. It aids insulation from non-aligned metals on aluminium and spreads the load like a big washer, and can help reduce some vibrations.


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6: Have fun with the sealant

More sealant is generally better. There are tremendous silicone/Sika products nowadays that are good for the life of the engine, but be sure not to use an acidic cure on aluminium. Seal the threads on all mounting bolts to stop non-aligned metal electrolysis and water seepage. Don’t over-tighten the engine mounting bolts, especially on fibreglass. Once fibreglass is fractured it absorbs water.


7: You’ll love hydraulic steering

Upgrade your steering when you change an engine. The rule of thumb is to consider hydraulic steering on all installations of 115hp outboard motors and more. Many people see the advantages such as increased safety, reduced maintenance and increased drivability from hydraulic steering. This means hydraulic steering is being fitted to much smaller engines.


Visit our archive of hundreds of outboard motor reviews (and diesel marine engines).


8: Where’s that water coming from?

Consider safety factors such as water ingress through older slop-stoppers, etc. Deep-vee boats with 20in transoms and cable steering often require the rubber slopstoppers (rubber seal through the engine well for steering, cables etc.) to be below the transom height causing major safety implications with water able to run inside the transom undetected.


9: Plan your instruments

Lay out your instrument and rigging plan. Place switches and gauges in sensible and visible spots, taking into account other accessories and instrumentation requirements. NMEA 2000 gauges are great (digital engine readouts through multifunction displays), but we still love our analogues as well. Consider the handset position, its engagement arc, comfort positioning, obstructions such as upholstery, etc. Note that most handsets come with friction settings, and setting them too light can be dangerous in sloppy seas. New style cabling is much better now with Teflon coatings.


10: Everything should be neat

Ensure your fit-up is tidy and secure. Cable-tie or clamp all cables, lines and hosing. Keep batteries off the floor and wet decks if possible and ensure that everything is very secure. A neat boat is a safe boat.


See the full version of this story in Trade-A-Boat #455, July / August 2014. Why not subscribe today?


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