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  Performance observations 15' Sport & 50 hp 4strk

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Author Topic:   Performance observations 15' Sport & 50 hp 4strk
mnboater posted 08-05-2003 12:01 PM ET (US)   Profile for mnboater   Send Email to mnboater  
I recently installed a 99 Yamaha T50 4 stroke on my Whaler 15 Sport. For those not familiar with the T50, it is the Yamaha equivalent to the Merc Big Foot. It uses the 4 gear case and swings a 13 or larger prop. The motor, while used, has limited running hrs and is in very good cosmetic and mechanical condition. It was sitting for 2 years and only needed the carbs cleaning and synced to bring to top operating condition. I will put forth an observation on my use of 4 stroke outboards ( I have an 01 - 25hp, a 99 - 50 hp, and a 00 - 100 hp on my different boats) the are very susceptible to jet varnishing, and in particular the pilot jets. . The jet opening are very small in comparison to the 2 stokes. If you are not going to be using the motor for a couple of weeks or more, run the carbs dry. Once the varnish starts to form it can become accumulative.

I had 2 major concerns with the T50 installation the added 59 lbs. of weight over the Pro 50 it replaced and the extra lower unit drag associated with the 4 gear case. The added weight of the T50 lowered the stern about 2 but it floats above the engine well drains. Even with me alone in the pilot seat, just a small amount of water enters the engine well. I am very happy with at-rest water line. The drag associated with the larger gear case proved to of no concern for me. The boat performance is equal to the Pro 50 it replaced and in some areas, an improvement. The basic motor specifications are:

50 HP 4 stroke
5,000 6,000 Max operating RPM
2.33/1 lower unit ratio
current propeller 13 X 16 Yamaha OEM stainless large blade area w/no cup

GPS speed with 1 person (light chop) 36.5 mph @ 5950 rpm - approx. 5.3% slip
GPS speed with 2 persons (light chop) 33.4 mph @ 5700 rpm - approx. 10% slip
Seating for the 2 person configuration was 1 on forward seat and 1 on rear seat

The above speeds are very close to what I was experiencing with the Pro 50 2 stroke. What impressed me the most was the ability to hold a power setting, my established speed, and hold high trim angles to break wakes. The 4 stroke did not exhibit the tendency to fall off plane and slow way down when you back off the throttle a little to cushion the big wakes. It would have immediate throttle response to power over the waves and resume full plane. The mid range power band 2500 3200 felt much stronger and made the weekend boating much more enjoyable. The engine is proving to be much more economical than I ever expected. Based on the type of river running I do: cruise @ 3000 3200 RPM / slow for no wake zones / drop from cruise to 2000 rpm for large wakes / accelerate to cruise / some flat out running, etc. I burned 8.3 gal in 10.7 hrs. and covered 78.6 miles by GPS. About 3 hrs. of the running were with 4 people on board. This was not an economy run but a typical weekend usage from Friday night through Sunday night.

I will add the typical caveat the above information is based upon my boat and my operating conditions. Your application may not produce the same results.

Jim Grinde

David Jenkins posted 08-05-2003 01:17 PM ET (US)     Profile for David Jenkins  Send Email to David Jenkins     
Thanks for the informative post. How high is the engine mounted?
mnboater posted 08-05-2003 02:55 PM ET (US)     Profile for mnboater  Send Email to mnboater     
The motor is mounted 1.375 above the transom. When I project the keel line rearward it is on the top surface of the anti-ventilation plate. I drilled 1" lower holes in the motor bracket to get the extra lift. No problem with the top holes but the lower slots cannot be used because they are below the motor well. I didn't want to add holes to the transom. I can drill one set 3/4" lower on the transom bracket but as it is, I like the leverage the trim has over the bow attitude. I am not using a doelfin or the like and can use full range of motor trim and it will not porpoise. It holds trim more like a bass boat when on the step.

Jim Grinde

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