1980 SUPER SPORT 15 Yamaha Re-power

Optimizing the performance of Boston Whaler boats
Bobg
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1980 SUPER SPORT 15 Yamaha Re-power

Postby Bobg » Sat Jan 26, 2019 5:29 pm

I have a 1980 SUPER SPORT 15. When the 2003 Yamaha 70 two-stroke-power-cycle outboard engines needs replacement, what Yamaha engine should be used?

Is a [Yamaha four-stroke-power-cycle 70-HP that was later specified to weigh 253-lbs] too heavy?

Thanks for the help.
Bob

frontier
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Re: 1980 SUPER SPORT 15 Yamaha Re-power

Postby frontier » Sat Jan 26, 2019 8:37 pm

You already have one of the best outboards ever made - the classic 70HP three-cylinder two-stroke Yamaha. It weighs 228-lbs and is the perfect match for your classic SUPER SPORT 15. You may be disappointed--and have a much lighter wallet--if you install a new four-stroke-power-cycle 70-HP outboard engine--especially in low-end torque. Those classic 60-, 70-, and 90-HP three-cylinder Yamaha outboards are near bulletproof and will last forever if given proper care.

TFrere
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Re: 1980 SUPER SPORT 15 Yamaha Re-power

Postby TFrere » Sun Jan 27, 2019 10:14 am

I have a 1985 Sport 15 with a Yamaha F70.

18B8F469-17ED-4606-91A3-FAD41A6C8860.jpeg
Fig. 1. SPORT 15 on trailer with Yamaha F70
18B8F469-17ED-4606-91A3-FAD41A6C8860.jpeg (53.75 KiB) Viewed 2677 times


[A SPORT 15 and a Yamaha F70] feels like the perfect match to me. [The SPORT 15] jumps up on step quickly and wide open boat speed is about 43-MPH. I have both a nine-gallon Moeller fuel tank and a starting battery in the stern of the boat. [The SPORT 15] seems to float fine.
1985 15’ Sport with Yamaha F70

jimh
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Re: 1980 SUPER SPORT 15 Yamaha Re-power

Postby jimh » Mon Jan 28, 2019 10:37 am

It is hard to predict in the future when the current engine needs replacement, how much a Yamaha 70-HP four-stroke-power-cycle engine will weigh. Those engines have been getting steadily lighter in weight.

If you want to use 253-lbs as the benchmark weight for a new outboard that in the future you might buy to re-power the boat, then we can consider if 253-lbs is too much engine weight for a1980 SUPER SPORT 15.

Boston Whaler never published specifications for a 1980 SUPER SPORT 15 for maximum engine weight, so there is really no authoritative source for a hard and fast weight limit. Several years ago an attempt was made to impute maximum engine weights for Boston Whaler hulls that were not rated by using ratings that were later specified for similar hulls. See

Maximum Engine Weight
http://continuouswave.com/ubb/Forum4/HTML/002449.html

In that analysis the imputed maximum transom weight for a SPORT 15 hull was calculated to be 249-lbs. Given the approximation of the method, I would infer that an engine that weighed 253-lbs would not be "too heavy." Yes, it is barely above the imputed limit for transom weight, but so close that I would not consider it to be over-weight.

On that basis, at some time in the future when your present engine needs replacement, and if you should be able to find a Yamaha four-stroke-power-cycle engine that weights 253-lbs or less, then that future engine will be right at the maximum transom weight limit (as imputed by calculation from other models).

A simpler way to get this answer might have been to ask what is the recommended maximum transom weight for a 1980 SUPER SPORT 15.

dtmackey
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Re: 1980 SUPER SPORT 15 Yamaha Re-power

Postby dtmackey » Mon Jan 28, 2019 10:08 pm

I have the same Yamaha [70-HP] two-stroke-power-cycle engine on my 15-footer, and I feel [that engine is] a great set-up for the boat. If I decide to ever replace, it would be the new Yamaha F70.

Consider the Johnson and Evinrude 70-HP two-stroke-power-cycle outboard engines weighed 250-lbs with power trim, and condiser thet countless 15-footers were rigged with those engines by Boston Whaler dealers; I can't image [the weight of those engines] being a concernl. Once you include the weight of the oil reservoir tank on the older Johnson and Evinrude engines, the [total engine] weight is several pounds more than the Yamaha [F70]

D-

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Dutchman
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Re: 1980 SUPER SPORT 15 Yamaha Re-power

Postby Dutchman » Tue Jan 29, 2019 8:51 am

Move the fuel tank and the battery out of the stern; don't have somebody as heavy as me on board. Like Jim said 250 or 260-lbs is not over weight. You must just adjust your weight distribution in the boat, either the crew or equipment.
EJO
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El Rollo
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Re: 1980 SUPER SPORT 15 Yamaha Re-power

Postby El Rollo » Tue Jan 29, 2019 9:06 am

I had a Yamaha 70 two-stroke-power-cycle outboard engine on my 1988 Super Sport before I re-powered with a Yamaha F70. Based on what other options were available at the time of purchase, I am 100-percent satisfied with my decision. In my opinion the Yamaha F70 is not too heavy for the classic 15-foot Boston Whaler boat.

To be very honest, the only thing that I miss about the 70-HP two-stroke-power-cycle engine was that small power band where the motor would really 'light-up--for lack of a better description. But since I spent less than one-percent of my operating time in that RPM range, it was not a factor.

The F70 is smooth, quiet, powerful, and a joy to operate. I use mine primarily for fishing on lakes, bays, and rivers. I have pulled three kids on a tow-behind toy with no problem, and use it for cruising frequently.

The one downside tp the Yamaha F70 compared to the older Yamaha 70 two-stroke-poower-cycle engine is cost of ownership. I realize cost is not the topic of this conversation, but I feel it is worth mentioning. If you have scheduled services, or repairs performed at an authorized Yamaha dealer, with a brick and mortar location, be prepared for sticker shock on service fees. I now perform all my own basic maintenance and have cut my bills more than halfl--just something to keep in mind if you are planning on using the engine frequently. A 100-hour services come faster than you think.

The ability to use Yamaha's Command Link digital gauges is also a nice feature.

The Yamaha F70 is in an entirely different class than the original Yamaha 70 two-stroke-power-cycle outboard engine. If you want to save some money and don't mind adding oil, hearing a bit more noise, smelling a little smoke, and having a rougher running engine, then keep that two-stroke alive. They are great performing engines. The F70 is just more refined, if refinement is of value to you.

Hope this helps a little. Good luck with your decision.