Mercury Super 15

In the January 2000 issue of Trailer Boat we brought you a three-year evaluation of the two-stroke loopcharged Yamaha 15F, followed by a run-down on its crossflow Mariner/Mercury and OMC competition in the May issue. All of these motors are designed specifically for amateur anglers and will Dead Slow Troll (DST) for hours without missing a beat.

But Mercury Marine has come up with an inexpensive alternative for anglers who aren't necessarily interested in trolling. It's a derated and rebadged Tohatsu M18E2 and as of April, the motors were priced at hundreds of dollars below the direct competition and even Mercury Marine's crossflow 15!

Designed more for commercial usage, the Super 15 has a torquey and fuel-efficient loopcharged powerhead, dual cooling water intakes and a very simple undercowl layout. It also has a zinc anode on the transom bracket and steering pivot tube in addition to one beneath the anti-ventilation plate.

Compared to its direct Yamaha and crossflow Mariner/Mercury and OMC competition, it lacks features such as an upfront gearshift, multiple shallow-water drive settings and low casting-over profile. But then, as my experienced co-tester Jillian and I found out, it has better mid-range torque.

In April we tried a Super 15 on a Bermuda 375 Dolphin dinghy, a much bigger hull than the other 15s were tested on. Set on the second trim hole to compensate for my 110kg bulk and a 25lt fueltank aft, spinning the standard 8.8-inch pitch alloy prop, my Lowrance GPS showed a DST speed of 2.9kmh on 800rpm. However, we found vibration levels at these revs were too high to endure for any length of time.

Above 2000rpm, the motor smoothed out and was a little rougher than the Yamaha 15F, although the Dolphin's rigid composite welded/riveted construction helped a bit. Over the years I've found this type of construction to absorb vibration much better than all-welded tinnies, where there's a fair amount of harmonic vibration and drumming of the unsupported topsides sheeting.

Pushing our 320kg total, the demo motor achieved a clean plane at 18.7kmh on only one-third throttle and 3500rpm. At 4000rpm the motor cruised effortlessly at 25.0kmh, and consumed 4.1lt/hr.

Set on the fourth hole (there are six trim positions) for best all-round planing performance, the Wide Open Throttle (WOT) average was 37.7kmh on 5590rpm, consuming 7.6lt/hr. Though higher than the Yamaha 15F, this fuel consumption was lower than the crossflow competition.

The antiventilation plate was located midway between the Dolphin's hull and external keel bottoms, but surprisingly, there was no prop ventilation through hard-over figures of eight at 4000rpm.

Starting the Super 15 was an easy one-hand pull once the throttle and choke were correctly set. The motor warmed quickly from cold, although below 2000rpm it was smoky on the 25:1 break-in mix. Providing the antiventilation plate was kept at least three-quarters immersed on the shallow-water drive setting, no cooling water starvation occurred and the pilot water discharge was clearly visible at all speeds. However, more thought could have been put into the tilt set/release lever.

Overall Jillian and I found the motor user-friendly with the tiller arm well placed in relation to our seating position, while the emergency ignition cut-off switch lanyard didn't get in the way of steering the motor.

Servicing the Super 15 is straightforward, with a bowl-type fuel filter fitted and excellent spark plug and mechanical ignition timing advance access. Recommended maintenance intervals are at 50 and 100 hours after the first 10 for the first year, then every 100 hours or once a year thereafter.

For anglers who want an inexpensive 15hp outboard to get them quickly from one fishing spot to another, the Super 15 is unbeatable. It should also be very reliable - one angler I know clocked up 800 hours on his Tohatsu 18 without having to do any more than change the gear oil and spark plugs!