CONTINUOUSWAVE

[Moderator's note: this post has been moved to the PERFORMANCE forum for discusison.]

I may re-power my 1985 SPORT CENTER CONSOLE 15 with a used 2013 Yamaha T50LA High-Thrust engine that has a dry weight of 262-lbs.

Q1: will a 262-lbs 2013 Yamaha T50LA be too heavy for a 1985 SPORT CENTER CONSOLE 15?

Q2: will the lower gearing—higher numerical gear ratio—of the used 2013 T50LA High-Thrust engine cause the engine to be a bad fit for the 1985 SPORT CENTER CONSOLE 15?

i just want to the boat to be able accelerate onto plane with a full load of people. I don't care if the [boat speed] will [exceed] 30 [MPH]

Please help readers help you with your inquiry by providing more information:

Q3: what is the model year of the boat?

Q4: what is the current engine that is to be replaced, and what was its dry weight?

Q5: what was the maximum boat speed with the current engine?

Q6: how many passengers and what will be their total weight for your "full load of people"?

Q7: what is the gear ratio of the T50LA?

ASIDE: having owned and enjoyed a 1976 SPORT 15 with a 1976 Mercury 50-HP four-cylinder in-line two-stroke-power-cycle engine for several years, I recall the top boat speed with two adults aboard was about 35-MPH. The most people aboard at any time was two adults. We did bring a 50-lbs dog aboard once, but she did not take well to boating and never made a second voyage.

jimh wrote:Q3: what is the model year of the boat?

[The model year of the SPORT CENTER CONSOLE 15 is 19]85. [Please use four-digits for designating a year.]

jimh wrote:Q4: what is the current engine that is to be replaced, and what was its dry weight?

[The previous engine was a] Honda BF30 [with dry weight of] 152-lbs

jimh wrote:Q5: what was the maximum boat speed with the current engine?

{With the 30-HP engine] I am guessing the maximum boat speed with one person was about 27-MPH. The boat [could not accelerate onto plane] with more than one adult aboard

The top speed with one person was fine, but my concern is the SPORT CENTER CONSOLE 15 will not [accelerate onto plane] with multiple adults aboard.

jimh wrote:Q6: how many passengers and what will be their total weight for your "full load of people"?

The maximum anticipated total passenger weight aboard will be about 800-lbs

jimh wrote:Q7: what is the gear ratio of the T50LA?

[The gear ratio of the Yamaha T50LA is] 2.33:1

I'm certain the T50LA would have plenty of power for my use. However, as it is designed for pushing pontoons, I don't know if [its] heavier weight and larger gearcase and propeller (compared to the standard 50-HP) would cause handling problem or be unsale for the SPORT CENTER CONSOLE 15.

My initial concern is the significant increase in engine weight of about 110-lbs, with the new engine at 262-lbs and the current engine on 152-lbs. This added engine weight will increase draft in the stern and affect the static trim of the hull.

The "high-thrust" model probably has a large gear case with a larger propeller aperture. This allows the propeller to be a larger diameter and also a larger pitch.

I am estimating that with the 50-HP engine and its added weight making the boat with one person about 1450-lbs, the top boat speed will be about 33.4-MPH. Assuming engine speed would be 5800-RPM, a propeller with 16-pitch should get you close to that speed.

Now add 600-lbs additional passenger weight, and the top boat speed will decrease to 28-MPH. You need the engine to be able to accelerate into the upper end of its full-throttle range to make rated power, so we assume at least 5500-RPM will be necessary to get 50-HP generated. Now we need a 14-pitch propeller to make this work.

Your problem is the massive variation in passenger weight you want to accommodate. In small boats where the hull itself only weighs maybe 600-lbs, you cannot expect adding 600-lbs of people will be possible and not need to change the propeller pitch.

Of course, you could try operating all the time with the 14-pitch propeller, but you will have to watch the engine speed so it does not exceed the maximum allowed RPM.

Thanks,

I don't know what "you cannot expect adding 600-lbs of people will be possible and not need to change the propeller pitch" is referring to, that is not my goal. Nor is reaching 33.4 miles per hour my goal. My goal is just getting on plane and handling well.

Thanks for the further information listing performance goals that you are not interesting in achieving.

Best of luck achieving your actual goals. Please report the performance you actually do achieve and details of the engine and propeller you end up using when you complete the re-powering.

For advice on how to report performance data, see the article pinned at the top of this forum on that topic.