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Author Topic:   Improve 170 SuperSport for Water Skiing

jaycon posted 01-30-2014 10:37 AM ET (US)
Hi. We've a 2010 Boston Whaler SuperSport 170 with a Mercury 90 FOURSTROKE as supplied new.
Gear Ratio: 2.33:1
Propeller: 12 3/4” x 21” Black Max
<http://www.bostonwhaler.com/boat_graphics/eprowebsitemedia/2904/EnginePerformance/2014/323850_EnginePerf.pdf>
Per the factory supplied performance specs (and our observation) it will reach a top speed of 45-MPH at WOT 5,800-RPM.
The problem: with a few people on the boat and one average-sized adult male slalom skier, the boat is slow to reach 30 to 35-MPH, and is easily slowed two to three MPH with each aggressive cut of the skier. What are our options to improve the ski-ability of the boat? We're considering trading the Mercury for a higher horsepower two-stroke-power-cycle outboard engine.
Tom W Clark posted 01-30-2014 11:01 AM ET (US)
Try a 19" HighFive or TrophyPlus propeller before you do anything else.
jaycon posted 01-30-2014 12:02 PM ET (US)
Thanks Tom. I've got a co-owner on this boat that is determined to bolt on more horsepower. I'm hoping to reason with him and try your suggestion first. He is willing to eat the [cost] of a new motor so I might not argue too much with him.
Tom W Clark posted 01-30-2014 12:28 PM ET (US)
I'd spend a few hundred dollars on a good propeller before I went out and spent $8,000 for a new Mercury 115 FourStroke.
The SuperSport 170 in only rated for 90 HP.
Tom W Clark posted 01-30-2014 12:39 PM ET (US)
Additional propeller thoughts:
The idea behind the HighFive and Trophy Plus is more blade area and, in the case of the Trophy Plus, larger diameter.
Precision Propeller makes some good high blade area three blades designed for pontoon boats but which have proven to work well on some Whaler models, too, because of their excellent stern lifting qualities. However, they do not make this model is a pitch higher than 15" which is not nearly enough for this motor.
Mercury offers virtually nothing in a three blade that will help, but Precision does make a three blade with a large diameter designed for intermediate gearcase Suzukis. This propeller will also fit the intermediate gearcase Mercurys.
Available in even pitches, a 14" x 18" might be just the ticket, and at an economical price too. You can even reuse the Flo-Torq hub kit in the BlackMax to save more money.
russellbailey posted 01-30-2014 02:23 PM ET (US)
Tom has great propeller suggestions and knows propeller and boat combinations very well, certainly better than me. I have skied a lot as it is the main thing we do with our boats, and that seems less common for participants here. So, take my comments with that background.
If I'm reading the chart right, you are turning about 4500 rpm at 35 mph. The only way to improve your ability to maintain speed in a hard cut is to get that rpm at 35 mph up where the engine makes more power.
Suppose you want to get to 5500 rpm at 35 mph. I think conventional wisdom is about 400 rpm per 2". So, for 1000 rpm you'd want to drop about 5" of pitch. So, I like Tom's idea, but I'd be tempted to go for a bigger drop - like to a 16" pitch. You'll lose top end but if your goal is waterskiing that may be an ok tradeoff. And if your engine won't prevent it automatically you'll have to avoid over-revving the engine. I skied a lot behind a 70 hp Evinrude on a 15 Whaler, and we used a 15" pitch propeller, while most used 19" pitch. For us it worked well and we did not need the top end.
But no matter how you are propped, you'll still drop some speed on a hard cut with a 70 (mine) or 90 hp engine. Even on my Outrage 25 with twin 150s, when a good slalom skier really lays down a hard cut, I can hear the engines change sound pitch and slow rpm very slightly, though the speed moves so little I can't see a noticeable change. I'd guess that you'd have to move to a 150 hp V-6 engine before the engine would have enough reserve power to not really slow noticeably on a hard cut by a slalom skier, and that is most likely too much power for your boat (at least for most people).
jaycon posted 01-30-2014 03:01 PM ET (US)
Thanks RussellBailey. The friend I share the Supersport with has a 22' outrage with whalerdrive and Yamaha 300 hpdi. The 22' just throws up such a wake at 30-35 that it's no fun to ski behind.
I think you guys are right on with your suggestions about props...thanks again.
Tom W Clark posted 01-30-2014 03:13 PM ET (US)
http://continuouswave.com/ubb/Forum2/HTML/021884.html
russellbailey posted 01-31-2014 10:45 AM ET (US)
jaycon, yes, we don't slalom ski much behind the Outrage 25 either as the wake is just too big to do that reasonably. The big wake is great for wakeboarding and kneeboarding however, which is what we do mostly.
sosmerc posted 02-01-2014 01:57 AM ET (US)
A couple of thoughts:
The 90hp and 115hp FourStroke Mercs are essentially the same engine (same displacement, same gear ratio, same weight) The 115 is rated to turn more rpm.
So, in my opinion, you would be better off to prop your 90hp to turn 6000 rpm WITH YOUR HEAVIEST load onboard. I don't believe they make a HighFive anymore for the small gearcase that you have, but they do make a 4 Blade aluminum called the Nemesis that would be a relatively inexpensive prop to try. 13 X 17 might be the ticket.
You might also gain some by making sure the engine is mounted up at least a couple of holes above the factory setting which is usually pretty conservative (meaning too low, causing UN-necessary drag and unwanted steering effort.
Are you using a ski pylon? If you don't have a pylon, you may also want to consider the Turboswing...check it out.
http://www.turboswing.com/usa/waterskiing/
Tom W Clark posted 02-01-2014 10:22 AM ET (US)
The small tube HighFive was discontinued in 2012, but that doesn't mean that there aren't still plenty of them out there for purchase, both new and used.

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Author	Topic: Improve 170 SuperSport for Water Skiing
jaycon	posted 01-30-2014 10:37 AM ET (US) Hi. We've a 2010 Boston Whaler SuperSport 170 with a Mercury 90 FOURSTROKE as supplied new. Gear Ratio: 2.33:1 Propeller: 12 3/4” x 21” Black Max <http://www.bostonwhaler.com/boat_graphics/eprowebsitemedia/2904/EnginePerformance/2014/323850_EnginePerf.pdf> Per the factory supplied performance specs (and our observation) it will reach a top speed of 45-MPH at WOT 5,800-RPM. The problem: with a few people on the boat and one average-sized adult male slalom skier, the boat is slow to reach 30 to 35-MPH, and is easily slowed two to three MPH with each aggressive cut of the skier. What are our options to improve the ski-ability of the boat? We're considering trading the Mercury for a higher horsepower two-stroke-power-cycle outboard engine.
Tom W Clark	posted 01-30-2014 11:01 AM ET (US) Try a 19" HighFive or TrophyPlus propeller before you do anything else.
jaycon	posted 01-30-2014 12:02 PM ET (US) Thanks Tom. I've got a co-owner on this boat that is determined to bolt on more horsepower. I'm hoping to reason with him and try your suggestion first. He is willing to eat the [cost] of a new motor so I might not argue too much with him.
Tom W Clark	posted 01-30-2014 12:28 PM ET (US) I'd spend a few hundred dollars on a good propeller before I went out and spent $8,000 for a new Mercury 115 FourStroke. The SuperSport 170 in only rated for 90 HP.
Tom W Clark	posted 01-30-2014 12:39 PM ET (US) Additional propeller thoughts: The idea behind the HighFive and Trophy Plus is more blade area and, in the case of the Trophy Plus, larger diameter. Precision Propeller makes some good high blade area three blades designed for pontoon boats but which have proven to work well on some Whaler models, too, because of their excellent stern lifting qualities. However, they do not make this model is a pitch higher than 15" which is not nearly enough for this motor. Mercury offers virtually nothing in a three blade that will help, but Precision does make a three blade with a large diameter designed for intermediate gearcase Suzukis. This propeller will also fit the intermediate gearcase Mercurys. Available in even pitches, a 14" x 18" might be just the ticket, and at an economical price too. You can even reuse the Flo-Torq hub kit in the BlackMax to save more money.
russellbailey	posted 01-30-2014 02:23 PM ET (US) Tom has great propeller suggestions and knows propeller and boat combinations very well, certainly better than me. I have skied a lot as it is the main thing we do with our boats, and that seems less common for participants here. So, take my comments with that background. If I'm reading the chart right, you are turning about 4500 rpm at 35 mph. The only way to improve your ability to maintain speed in a hard cut is to get that rpm at 35 mph up where the engine makes more power. Suppose you want to get to 5500 rpm at 35 mph. I think conventional wisdom is about 400 rpm per 2". So, for 1000 rpm you'd want to drop about 5" of pitch. So, I like Tom's idea, but I'd be tempted to go for a bigger drop - like to a 16" pitch. You'll lose top end but if your goal is waterskiing that may be an ok tradeoff. And if your engine won't prevent it automatically you'll have to avoid over-revving the engine. I skied a lot behind a 70 hp Evinrude on a 15 Whaler, and we used a 15" pitch propeller, while most used 19" pitch. For us it worked well and we did not need the top end. But no matter how you are propped, you'll still drop some speed on a hard cut with a 70 (mine) or 90 hp engine. Even on my Outrage 25 with twin 150s, when a good slalom skier really lays down a hard cut, I can hear the engines change sound pitch and slow rpm very slightly, though the speed moves so little I can't see a noticeable change. I'd guess that you'd have to move to a 150 hp V-6 engine before the engine would have enough reserve power to not really slow noticeably on a hard cut by a slalom skier, and that is most likely too much power for your boat (at least for most people).
jaycon	posted 01-30-2014 03:01 PM ET (US) Thanks RussellBailey. The friend I share the Supersport with has a 22' outrage with whalerdrive and Yamaha 300 hpdi. The 22' just throws up such a wake at 30-35 that it's no fun to ski behind. I think you guys are right on with your suggestions about props...thanks again.
Tom W Clark	posted 01-30-2014 03:13 PM ET (US) http://continuouswave.com/ubb/Forum2/HTML/021884.html
russellbailey	posted 01-31-2014 10:45 AM ET (US) jaycon, yes, we don't slalom ski much behind the Outrage 25 either as the wake is just too big to do that reasonably. The big wake is great for wakeboarding and kneeboarding however, which is what we do mostly.
sosmerc	posted 02-01-2014 01:57 AM ET (US) A couple of thoughts: The 90hp and 115hp FourStroke Mercs are essentially the same engine (same displacement, same gear ratio, same weight) The 115 is rated to turn more rpm. So, in my opinion, you would be better off to prop your 90hp to turn 6000 rpm WITH YOUR HEAVIEST load onboard. I don't believe they make a HighFive anymore for the small gearcase that you have, but they do make a 4 Blade aluminum called the Nemesis that would be a relatively inexpensive prop to try. 13 X 17 might be the ticket. You might also gain some by making sure the engine is mounted up at least a couple of holes above the factory setting which is usually pretty conservative (meaning too low, causing UN-necessary drag and unwanted steering effort. Are you using a ski pylon? If you don't have a pylon, you may also want to consider the Turboswing...check it out. http://www.turboswing.com/usa/waterskiing/
Tom W Clark	posted 02-01-2014 10:22 AM ET (US) The small tube HighFive was discontinued in 2012, but that doesn't mean that there aren't still plenty of them out there for purchase, both new and used.