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Author Topic:   1989 SUPER SPORT 17, E-TEC 90

LewByrd posted 09-10-2008 08:12 PM ET (US)
I recently bought a 1989 Super Sport 17 that had been re-powered with a E-TEC 90 25-inch shaft (V6 lower unit). The previous owner apparently got a deal on the engine and to compensate for the 25-inch shaft installed a fixed jack plate which sets the engine back about five inches. The engine is mounted as high up as possible which puts the anti-ventilation plate about an inch above the bottom or keel. It had a Stiletto 14.25 x 17-inch pitch and would only turn up about 4,500-RPM and 31-MPH. The local propeller guy suggested I try a 14.25 x 15-inch pitch, which I did. It performed exactly the same as with the 17-inch pitch. I can get about 200-RPM more by really trimming it up, but the boat starts to [have a oscilation of the bow up and down]. It also pulls really hard to the right at any speed.
What propeller should I try next? I'd like to get about 1,000-RPM more engine speed and increase boat speed to something close to what everyone else is getting, 40-MPH. Thanks for the help.
jimh posted 09-10-2008 08:25 PM ET (US)
With the current mounting and engine height, where does the anti-ventilation plate run with respect to the surface of the water when the boat is on plane?
Tom W Clark posted 09-10-2008 08:26 PM ET (US)
Mark,
That is the wrong motor for that boat. It would be much better with the 20" shaft length and the 2:1 gear ratio intermediate lower unit.
As it is now, the motor is too low. It should be raised two more inches.
When you switched to the 14-1/4" x 15" prop, was it a three blade Stiletto as well or some other brand/model? We normally prop the 17' Whalers with E-TEC 90s with the 13-1/4" x 15" Stiletto Advantage and see 40-42 MPH.
With that big ol' V-6 gearcase and its 2.25:1 gear ratio you are going to have to go to a 17" Stiletto or a 19" BRP/OMC SST/Viper to get your speed up if you can after raising the motor. You want the engine speed to be 5000-5200 RPM.
The pull to the right is a result of the lower unit being large, too deep and probably with the trim tab set incorrectly. Try moving the trailing edge of the trim tab to starboard and then go run the boat. You want the steering effort to be neutral at normal cruising speed and motor trim angles.
LewByrd posted 09-11-2008 07:57 AM ET (US)
I'll have to check the height of the anti cavitation plate with respect to the water today.

Regarding engine mounting height, I can only go up one inch which I'll also do this morn and seatrial. The only way to get 2" would be to remount the bracket which require modifying the bracket by drilling new mounting holes to get it up (because the existing top holes would be above transom).
Both props are 3 blade stiletto, agin I'll try them both after raising the engine and will post the results.
Would it make any sense to have a prop shop modify one of the stilettos by reducing the diameter to 13 1/4? I don't think a 13 1/4 is available as a standard prop for the V6 case.
Tohsgib posted 09-11-2008 11:09 AM ET (US)
Can you raise the engine on the bracket? What hole is the engine mounted in? If you can't get anymore height it would be easier to put a longer rear plate on the bracket then to remove and redrill I think.
LewByrd posted 09-11-2008 12:11 PM ET (US)
Wow, what a difference an inch made, she now turns up to 5000 rpm at wot and goes 40.2 mph on the gps with the stiletto 14.25d 17p prop(with a 5 knot wind,2 knot current, 200 lb captain 16 gal gas). Planes at about 2700 rpm. Cruise 32 mph at 4200 into wind and current- I'm happy with that so I didn't try the 15 pitch, I suspect I'd get a few more rpm with same speed. I took some pitures of the set up prior to launching if anyone is interested in seeing the boat and engine mount. Breaks down as follows:
1000 rpm - 4.1 mph
2000 rpm - 7.2 mph
3000 rpm - 21.8 mph
4000 rpm - 31 mph
5000 rpm - 40.1 mph WOT
The only question I have is how to reduce the porposing, I can't get as much boat out of the water as I think I should be able to before she starts to porpose a little. Thanks for the help.
Tom W Clark posted 09-11-2008 01:51 PM ET (US)
OK, that is the performance I would expect for that boat.
Most folks do not appreciate the difference the correct motor mounting height can make but I have to admit I am rather surprised that one inch could make *that* much difference.
I also suspect your motor should be higher if you can figure out a way to do it.
ratherwhalering posted 09-11-2008 05:47 PM ET (US)
Mark, that's not bad for 5000 RPM. I have a 1987 17-Montauk with a 2004 E-TEC 90 and I'm seeing 39.5 RPM at 5000 RPM with a Stiletto 13.25 x 15 Stiletto Advantage I.
Tohsgib posted 09-12-2008 09:33 AM ET (US)
And they scoffed at my mere 70hp Suzuki which would also do 39.5mph.
ratherwhalering posted 09-12-2008 01:50 PM ET (US)
Yeah, Nick, but did I mention she does 42.5 at 5500 RPM? That's 3mph faster for those of us who are counting :-)

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Author	Topic: 1989 SUPER SPORT 17, E-TEC 90
LewByrd	posted 09-10-2008 08:12 PM ET (US) I recently bought a 1989 Super Sport 17 that had been re-powered with a E-TEC 90 25-inch shaft (V6 lower unit). The previous owner apparently got a deal on the engine and to compensate for the 25-inch shaft installed a fixed jack plate which sets the engine back about five inches. The engine is mounted as high up as possible which puts the anti-ventilation plate about an inch above the bottom or keel. It had a Stiletto 14.25 x 17-inch pitch and would only turn up about 4,500-RPM and 31-MPH. The local propeller guy suggested I try a 14.25 x 15-inch pitch, which I did. It performed exactly the same as with the 17-inch pitch. I can get about 200-RPM more by really trimming it up, but the boat starts to [have a oscilation of the bow up and down]. It also pulls really hard to the right at any speed. What propeller should I try next? I'd like to get about 1,000-RPM more engine speed and increase boat speed to something close to what everyone else is getting, 40-MPH. Thanks for the help.
jimh	posted 09-10-2008 08:25 PM ET (US) With the current mounting and engine height, where does the anti-ventilation plate run with respect to the surface of the water when the boat is on plane?
Tom W Clark	posted 09-10-2008 08:26 PM ET (US) Mark, That is the wrong motor for that boat. It would be much better with the 20" shaft length and the 2:1 gear ratio intermediate lower unit. As it is now, the motor is too low. It should be raised two more inches. When you switched to the 14-1/4" x 15" prop, was it a three blade Stiletto as well or some other brand/model? We normally prop the 17' Whalers with E-TEC 90s with the 13-1/4" x 15" Stiletto Advantage and see 40-42 MPH. With that big ol' V-6 gearcase and its 2.25:1 gear ratio you are going to have to go to a 17" Stiletto or a 19" BRP/OMC SST/Viper to get your speed up if you can after raising the motor. You want the engine speed to be 5000-5200 RPM. The pull to the right is a result of the lower unit being large, too deep and probably with the trim tab set incorrectly. Try moving the trailing edge of the trim tab to starboard and then go run the boat. You want the steering effort to be neutral at normal cruising speed and motor trim angles.
LewByrd	posted 09-11-2008 07:57 AM ET (US) I'll have to check the height of the anti cavitation plate with respect to the water today. Regarding engine mounting height, I can only go up one inch which I'll also do this morn and seatrial. The only way to get 2" would be to remount the bracket which require modifying the bracket by drilling new mounting holes to get it up (because the existing top holes would be above transom). Both props are 3 blade stiletto, agin I'll try them both after raising the engine and will post the results. Would it make any sense to have a prop shop modify one of the stilettos by reducing the diameter to 13 1/4? I don't think a 13 1/4 is available as a standard prop for the V6 case.
Tohsgib	posted 09-11-2008 11:09 AM ET (US) Can you raise the engine on the bracket? What hole is the engine mounted in? If you can't get anymore height it would be easier to put a longer rear plate on the bracket then to remove and redrill I think.
LewByrd	posted 09-11-2008 12:11 PM ET (US) Wow, what a difference an inch made, she now turns up to 5000 rpm at wot and goes 40.2 mph on the gps with the stiletto 14.25d 17p prop(with a 5 knot wind,2 knot current, 200 lb captain 16 gal gas). Planes at about 2700 rpm. Cruise 32 mph at 4200 into wind and current- I'm happy with that so I didn't try the 15 pitch, I suspect I'd get a few more rpm with same speed. I took some pitures of the set up prior to launching if anyone is interested in seeing the boat and engine mount. Breaks down as follows: 1000 rpm - 4.1 mph 2000 rpm - 7.2 mph 3000 rpm - 21.8 mph 4000 rpm - 31 mph 5000 rpm - 40.1 mph WOT The only question I have is how to reduce the porposing, I can't get as much boat out of the water as I think I should be able to before she starts to porpose a little. Thanks for the help.
Tom W Clark	posted 09-11-2008 01:51 PM ET (US) OK, that is the performance I would expect for that boat. Most folks do not appreciate the difference the correct motor mounting height can make but I have to admit I am rather surprised that one inch could make that much difference. I also suspect your motor should be higher if you can figure out a way to do it.
ratherwhalering	posted 09-11-2008 05:47 PM ET (US) Mark, that's not bad for 5000 RPM. I have a 1987 17-Montauk with a 2004 E-TEC 90 and I'm seeing 39.5 RPM at 5000 RPM with a Stiletto 13.25 x 15 Stiletto Advantage I.
Tohsgib	posted 09-12-2008 09:33 AM ET (US) And they scoffed at my mere 70hp Suzuki which would also do 39.5mph.
ratherwhalering	posted 09-12-2008 01:50 PM ET (US) Yeah, Nick, but did I mention she does 42.5 at 5500 RPM? That's 3mph faster for those of us who are counting :-)