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Author Topic:   15 Super Sport/Johnson 48 SPL Performance
Peter posted 05-03-2003 09:18 PM ET (US)   Profile for Peter   Send Email to Peter  
Took my new to me 1987 15 Super Sport/Johnson 48 SPL out for a little exercise today. At wide open throttle, the GPS read about 36.5 mph over numerous runs. One run read 38 - 39 mph when the boat felt like it was "getting air". The 48 is spinning a 11 3/4 by 17 aluminum prop. I don't have a tachometer so I don't know WOT rpm. How does this performance compare with other 15s with 50hp?

Overall, the boat is quite a thrill to drive compared to my 22 Revenge. The ride seems much smoother than what I remember from my many days behind the wheel of a 13 sport. I'd say the ride characteristics are a bit similar to my former 18 Outrage, probably due to the sharp bow entry.

At the end of the exercise, I was left thinking that this boat could be dangerous in the wrong hands if propelled with a 70hp motor.

jonha posted 05-04-2003 04:16 PM ET (US)     Profile for jonha    
peter, what is a johnson spl. My 15sport will do about 33mph with a Merc 50. repowering with 50 Merc efi-4stroke. 50 hp on this boat seems plenty for me. jonha
Peter posted 05-04-2003 05:13 PM ET (US)     Profile for Peter  Send Email to Peter     
The 48 SPL (Special) was a no frills 50hp motor offered by OMC back in the late 1980s and possibly early 1990s. To keep the price down, it came without variable ratio oil injection (a plus in my opinion) and without power trim or tilt (a feature I wish it had).

This particular configuration seems a little odd to me in that the original buyer spent more for the deluxe Super Sport interior and then compromised on a no frills motor. Perhaps it was way to keep the price in a certain range or to avoid VRO.

skred posted 05-05-2003 08:34 AM ET (US)     Profile for skred  Send Email to skred     
My 15CC with a 50 Merc 4-cycle gps's at 36-39 mph with my 245 lbs, normal 6 gal fuel and takle, etc. So I'd say you were right there...
jimh posted 05-05-2003 09:26 AM ET (US)     Profile for jimh  Send Email to jimh     
According to tests conducted by Boston Whaler and reproduced in the Reference section of the website in an article on the 15-foot hull, you should expect speeds of about 34-MPH with approximately 50-HP.

Since these tests were likely conducted with engines rated at the powerhead, you might want to adjust the horsepower down slightly when interpreting them to better correlate with today's prop shaft rated engines.

Peter posted 05-05-2003 12:10 PM ET (US)     Profile for Peter  Send Email to Peter     
Thanks Jim. I looked at the Reference section and was looking for a few more data points.

It seems that my engine performs satisfactorily at wide open throttle based on the data here and in the Reference section. (Now if I could just get it to idle smoother I'd be a happy camper -- suggestions welcome).

The rig I purchased did not come with any instrumentation. However, entering the known speed, propeller pitch and gear ratio and propeller slip at about 5 percent into the propeller calculator, I was able to estimate the WOT engine speed to be about 5500 rpm give or take 100 rpm. This is at the upper end of the factory specified range for this motor.

For those interested in this performance data, the engine trim pin was set to the 2nd hole (the one immediately adjacent to the furthest in position). There was 190lbs of persons, 50lbs of battery and about 70lbs of fuel aboard. The bottom is painted but relatively smooth.

where2 posted 05-05-2003 12:59 PM ET (US)     Profile for where2  Send Email to where2     
"this boat could be dangerous in the wrong hands if propelled with a 70hp motor." If you thought it was getting light when you hit 38mph, you ought to feel it at 48mph... At 48mph, it feels like any little gust of wind will send it tumbling end over end. It probably isn't safe for an unexperienced 15 year old. However, 22mph in a 10' Zodiac which weighed 73lbs, with a 70lbs engine, a 3 gallon gas tank, and a 110lbs fifteen year old wasn't far from being as unsafe as my 15' with a 70hp engine. The Zodiac was probably more likely to go airborn with a little gust of wind, due to the hull area to weight ratio.
jonha posted 05-05-2003 03:12 PM ET (US)     Profile for jonha    
skred- my 15ss is at this time being re powered with the merc 50efi fourstroke. my old engine was a 50 merc 2 stroke. what can i expect. thanks jonha
skred posted 05-06-2003 07:57 AM ET (US)     Profile for skred  Send Email to skred     

I switched out a '85 Yamaha 70 2-stroke for the '01 Merc 50 4-stroke (Carbs). As mentioned above, I get close to 40 mph gps with the load described, and with 2 people, I get about 33 mph WOT. This is only 5 mph shy of what the Yamaha 70 produced. I get about twice the fuel economy, no smoke, VERY quiet running, smooth idling, instant starting, and plenty of hole shot. I still have to verify the pitch as a 15 - the dealer said that's what he remembered installing. I haven't found the stamp on the prop yet. If you were planning on more than 400 lbs of passengers, and more than 12 gallons of fuel, a lot of tackle, etc., I might suggest looking at the 60 hp - IF the price didn't jump more than a couple hundred. I am totally pleased with my choice.

jonha posted 05-06-2003 08:28 AM ET (US)     Profile for jonha    
thanks skred. my new 50merc is being installed at this time. i don't fish i just ride around and let people look at my the way do you have one of those under the seat 12 gal tanks? jonha
Florida15 posted 05-06-2003 02:27 PM ET (US)     Profile for Florida15    
With two batteries, 10 gallons of fuel,
fishing gear and 2 passengers weighing about 420 pounds my 15' hits around 34 mph
by GPS. That's with a 1981 50 hp Johnson.
Bigshot posted 05-09-2003 04:20 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Numbers sound right, get a tach anyway. Also keep your eyes peeled on E-Bay for the same size in Stainless, they are oddballs so you can get one cheap(under $125). My 15 with a 1988 48spl moved pretty darn good and I would say 37mph or so. With the 60 and the 19"ss I think 41-42+ at roughly 5900(redline on 60's were 6k). Yes with a 70 and 48+mph she is downright exhilerating to say the least.
Peter posted 05-14-2003 07:32 AM ET (US)     Profile for Peter  Send Email to Peter     
Thanks Bigshot.

I have a Teleflex tach but need to hook it up. Would you know whether it can be plugged into the receptacle in the control box assuming I can get the right connector?

skred posted 05-14-2003 07:54 AM ET (US)     Profile for skred  Send Email to skred     

My 15 has pedestal seats replacing the thwart seat/rail arrangement that came on the 15CC. It had a standard 6-gallon plastic tank at the stern. Plan 1: I'm installing hinges on the front of my console with latches at the back, and installing a 12- or more gallon tank under the console. Flip 2 latches, swing the console forward, and fill the tank. I like the weight forward idea since I'm in the mid-200's myself. Alternate Plan 2: I may replace the pedestal seats with an RPS, and put a tank under the RPS. Lots of other owners have the 12-gallon underseat tank (having raised the seat 2-4 inches) and it's a nice setup.

Bigshot posted 05-16-2003 12:22 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Tach will conect to receptacle on bottom aft of control box if side mount. I believe it is just a 3 prong connector. Take it to a dealer and have them wire the tach then slide it on, make sure it works first. Might just be easier to buy one on e-bay new for $35 or so.
dee457 posted 07-11-2004 10:51 PM ET (US)     Profile for dee457  Send Email to dee457     
Does anybody know if it's possible to install Power Trim and Tilt on a '96 48SPL Evinrude? Cost?
Florida15 posted 07-11-2004 11:09 PM ET (US)     Profile for Florida15    
You can get a CMC power tilt for about $439 at Cabela's.
Don't know about a factory set-up.
high sierra posted 07-12-2004 10:25 PM ET (US)     Profile for high sierra  Send Email to high sierra     
I use a CMC tilt and trim on my 15 with a 40 Johnson. Best thing I ever did to the boat so save my back. High sierra
15ftlover posted 07-12-2004 10:31 PM ET (US)     Profile for 15ftlover  Send Email to 15ftlover     
I was at Lake Murray SC on July 4th. 15ft striper and merc 4stroke 60EFI smallfoot with 14 pitch heavily cupped SS prop, full 12 gallons. 1st time with new motor all by by myself (170lbs)! I could not keep the boat at WOT because the boat just became too unstable in the 6 inch chop. Above 36mph it began to waddle on the hull pad as the lateral chines would skip off the chop-really that "chine walking" feels like you are going to laterally pitch out of the boat as it begins to tailwag. Any solutions? The cavitation plate is just even with the bottom of the hull (no bottom paint) Horseing around put huge grin on my 34 year old face. I would be very uncomfortable to let a novice drive this combo near WOT. Add another passenger and the effect is much reduced.
Bigshot posted 07-13-2004 11:32 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
My 15 w/70 would hit 48 on a good day...36mph...hell she's still stable at that speed ;)
Peter posted 07-13-2004 12:56 PM ET (US)     Profile for Peter  Send Email to Peter     
Depending on how the motor is trimmed, it starts to become a bit unstable with one person at about 39 MPH.

As a follow on to this thread started more than a year ago, about a month after the post, I had an opportunity to repower with a slightly used 2003 Yamaha 70 2-stroke for a a truly great price (happen to be in the right place at the right time with cash and it didn't fall off a truck). Of course I jumped on it.

The difference in performance between running the 15 foot hull with a 50 and a 70 is remarkable. The 20 extra horsepower coupled with the power trim and tilt push the boat over the 36 MPH threshold where it really becomes lively and a bit of a handful. Top speed with my setup is in the neighborhood of 42 to 43 MPH with a single person, 12 gallons of fuel, engine mounted all the way down turning an aluminum 13 x 19 propeller. There are not too many times during the day when its smooth enough to run the boat at WOT to see what it will really do.

scaleplane posted 07-13-2004 01:08 PM ET (US)     Profile for scaleplane  Send Email to scaleplane     
My 1976 15' Sport with a 2003 40HP Johnson two-stroke runs about 31MPH by GPS with two people and a 6-gallon tank.
BrianF posted 07-14-2004 04:29 PM ET (US)     Profile for BrianF  Send Email to BrianF     
What do you suggest for my 15 sport to pull a 200lb skier with three adults in the boat? My son complains that with the load our 60 evenrude is not enough to pull him up. Will changing the pitch on the prop do the trick?
Bigshot posted 07-15-2004 04:12 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
2 things...3 adults are not helping anything, leave some on shore, all you want is a spotter. Changing the pitch for skiing will be VERY helpfull. Whatever you are running now, go down a size and change when you are gonna ski.
Over the LINE posted 07-16-2004 08:19 AM ET (US)     Profile for Over the LINE  Send Email to Over the LINE     
Yes, I put Power Tilt on a 48spl. Price the tilt unit, from a parts dept, or net (I think around $500-$600, but don't quote me). Besides running wires and hooking up a switch, the power tilt should be a bolt on replacement for the manual hydraulic tilt you have now.

Word of warning, If you look at your motor now, you will see a large stainless pin holding the tilt unit on. These pins like to become completely frozen in place, especially on salt water boats. The only reason I did mine was because the manual unit went bad and I had to replace it anyway.

Good Luck

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