Suzuki DT15

Suzuki's sweet 15

Earlier this year I tested a Suzuki DT9.9 on a fairly hefty 3.8m Blue Fin dinghy and found that, despite the engine providing less than 40 per cent of the hull's rated power, it performed well because the hull loading was limited to two adults and basic gear.

But had the hull been carrying three adults we would have needed at least a 15 to provide reasonable planing performance and, perhaps, even a 20 or 25 had a flat floor been fitted.

Suzuki's DT15 is an uprated version of the 9.9 that develops 51 per cent more power for no additional weight and doesn't use 51 per cent more fuel to achieve this output. The reason is that most carbie loopcharged outboards don't suffer de-rating well, and allowing the engine to deliver the power it was designed originally to do makes for a sweeter-running engine across the entire rev range.

Instead of mounting the demo 15 on a 3.8m hull, a 3.75m Horizon 375 Angler dinghy was used, which is about the size that most anglers would mount a 15 on. The Angler is a significantly smaller hull than the 3.8 Blue Fin and weighs only 80kg compared to 95 for the latter.

This allowed us to use the standard 10-inch pitch Suzuki alloy prop and the boat/engine combination provided excellent performance compared to the adequate performance of the DT9.9 on the Blue Fin. As with the 9.9 it started easily hot or cold, warmed quickly from cold and blew oil smoke only below about 2000rpm, despite running on a 25:1 break-in mix of ULP and TC-W3 oil.

Pushing a total of 330kg, including two hefty adults (the same as the Blue Fin with lighter adults), the 15 trolled us at 3.7kmh and 800rpm using 0.7lt/h. In comparison, the 9.9 spinning an eight-inch prop trolled us at 3.2kmh and 800rpm using 0.6lt/h. With the trim rod set on the third position (out of five) to provide an effective compromise between easy planing and reasonable Wide Open Throttle performance, a clean plane was achieved at 18.6kmh, higher than the Blue Fin because of the greater hull loading relative to planing surface area but at 3500rpm. The Blue Fin planed at 17.3kmh and 3600rpm.

Cruising at two thirds throttle or 4500rpm the average was 28.6kmh using 4.7lt/h compared to 23.7kmh and 4.1lt/h at 4700rpm for the same throttle opening. Through full lock figure of eight turns at these revs no prop ventilation occurred.

The 15 accelerated harder out to WOT where the averages were 40.8kmh and 5600rpm using 7.2lt/h, compared to 33.0kmh and 6.3lt/h at 5700rpm and, unlike the 9.9, the 15 was propped just where it should be for good performance and fuel efficiency, right at the top of the recommended WOT rev range.

As with the 9.9 the carbie induction roar made the Suzy a bit raucous at these revs but, again, not annoying and vibration levels at or near WOT were the same as the 9.9. However, as with the Blue Fin the bow was starting to bury at this speed and for long runs downwind at or near WOT the fourth trim position would reduce hull drag.

Powerhead access is the same as the 9.9 and very good, with a large bowl-type fuel filter provided to reduce possible fuel contamination. Recommended servicing intervals are every 50 hours or six months after the initial 20-hour service and the waterpump impeller should be replaced every 100 hours or yearly.

Because the DT15 has not been subjected to current emissions testing it's automatically rated "High Emission" under the Australian OEDA emissions compliance scheme, even though technically it should be a "1 Star" engine because of its loopcharged powerhead. The warranty is two years for recreational applications.