Page 1 of 1

1980 SUPER SPORT 15 Yamaha Re-power

Posted: Sat Jan 26, 2019 5:29 pm
by Bobg
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.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Sat Jan 26, 2019 8:37 pm
by frontier
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.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Sun Jan 27, 2019 10:14 am
by TFrere
I have a 1985 Sport 15 with a Yamaha F70.

Fig. 1. SPORT 15 on trailer with Yamaha F70
18B8F469-17ED-4606-91A3-FAD41A6C8860.jpeg (53.75 KiB) Viewed 10701 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.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Mon Jan 28, 2019 10:37 am
by jimh
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

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.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Mon Jan 28, 2019 10:08 pm
by dtmackey
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]


Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Tue Jan 29, 2019 8:51 am
by Dutchman
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.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Tue Jan 29, 2019 9:06 am
by El Rollo
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.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Wed Mar 18, 2020 7:35 pm
by Quincycarrega
Recently [I] re-powered my 1989 15-footer with a Suzuki DF90.

Fig. 2. Suzuki DF90 on a 15-footer.
15Repower.jpg (4.24 KiB) Viewed 2440 times

I did a lot of research. I was very hesitant at first [to put on the Suzuki DF 90] due to [its] weight. But, I am very pleased with the decision. The Suzuki DF90 engine is a little heavy, but the boat runs great--and we have a lot of fun

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Thu Mar 19, 2020 7:55 am
by jimh
Considering that a Suzuki DF90 with 20-inch shaft weighs 341-lbs, its weight is far greater than a reasonable maximum weight for the classic Boston Whaler SPORT 15 boat. It is also too much horsepower. The hull is rated only for 70-HP.

I don't understand how your research led you to believe that a 90-HP engine that weighs 341-lbs would be suitable for the 15-footer. As noted above a Yamaha F70 seems like a much better match.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Thu Mar 19, 2020 11:00 am
by biggiefl
I have been on several 15-footers with 115-HP engines.

One man's goal is another man's concern, but a moot point in my opinion.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Sat Mar 21, 2020 9:22 am
by jimh
There is a tendency in human nature that after you spend $11,000 on a new engine for your boat that you will be pleased with the outcome. I don't think I have ever read an account of a boater spending $11,000 on a new outboard engine, and then announcing that he made a big mistake in buying that engine, that is was too much power, that it was too heavy. People just don't act like that.

There is no doubt that someone, somewhere, has put an engine on a classic 15-foot Boston Whaler skiff that had more than 70-HP, or that an engine that weighed substantially more than a c.1976 70-HP two-stroke-power-cycle engine would have weighed was put on the transom of a 15-footer. You can justify putting on an engine with more than the rated horsepower or much more weight the boat was initially designed for in many ways, but there is no debate possible that the rated maximum is 70-HP and that in the era when the boat was designed a 70-HP outboard engine would have weighed about 250-lbs. An OMC three-cylinder 70-HP engine--itself a classic design--only weighed 237-lbs in the [manual tilt] model and 250-lbs in the [electric tilt-trim]model. That engine was probably the most popular 70-HP of the era when the 15-foot hull was designed.

A 90-HP on a boat rated for 70-HP is a 128-percent of the maximum power. People might like to point to other boats being over-powered, say putting a 300-HP engine on a boat rated for 250-HP, but that would only be 120-percent over-powering. I have 225-HP on my boat, which is rated for 400-HP, so it is only powered at 56-percent of rated maximum. I have never felt like there was a need for any more power on the boat--its top speed is 44-MPH and I have never sustained that speed for more than a minute or two in 15 years of running the boat.

Also, in 1976 the horsepower of an outboard engine was generally not rated at the propeller shaft. Rating outboard horsepower at the propeller shaft did not become standard until the ICOMIA 28-83 standard (here "83" means 1983) came into use. A c.1976 boat design rated for 70-HP would mean the propeller shaft horsepower would have been more like 65-HP. If we assume a modern outboard engine rated for 90-HP has 90-HP at the propeller shaft, then the over-powering is more like 90/65 or 138-percent.

The above is what my research shows on this question.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Mon Mar 23, 2020 12:00 pm
by biggiefl
One correction for above. The 237lbs is a manual tilt, not manual start. I do not believe they made a manual start model with remote steering, tiller only. There have been many different weights on the OMC 70hp over the decades as shows here:

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Mon Mar 23, 2020 2:40 pm
by jimh
NICK--yes, thanks for the correction.

A good source for the weight of older outboard engines is this thread:

Weight of Older Outboard Engines

and that thread was hyperlinked in my comments above regarding the weight of the OMC 70-HP.

Also, the very popular Yamaha 70-HP carburetor two-stroke-power-cycle engine was more or less an exact copy of the OMC engine. A very experienced OMC dealer told me that the Yamaha castings contained certain protrusions or bosses from the OMC engine block casting that were completely unused and unnecessary. The Yamaha engine was really a clone of the OMC design, but probably with some refinements. A lot of those Yamaha 70 two-stroke carburetor engines are still around, and they may be still in production, I think, for sales outside the USA. It is a classic engine for a classic boat.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Thu Mar 26, 2020 10:58 am
by dtmackey
A comparison among the Yamaha to Evinrude/Johnson 70 in the 2 stroke offerings:

Yamaha 70
72mm X 69.5mm Bore and stroke

Early Johnson/Evinrude 70
76.2mm X 59.5mm Bore and stroke
803cc displacement (approx)

Later (post 86 I believe) Johnson/Evinruide 70
80.9mm X 59.54mm Bore and stroke
918cc displacement

While all great motors and close in weight and design, the Yamaha has superior carbration, a better muffler system making it a quieter motor and also a better oil injection system and self contained under the cowl removing the need for a separate tank and hoses.

I've run all these motors and rebuilt as number of them over the years and wouldn't hesitate to select from this group of motors.


Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Thu Mar 26, 2020 11:12 am
by biggiefl
That Yamaha copied or used OMC power heads as a template for their outboards when they started production is well known. They also used a copy of Mercury lower units which--outside of the "clunk" going into gear on larger motors---are MUCH easier to service. Not sure why they went with a steel shift rod instead of stainless steel, as that steel shift rod was a pain to fix.

The two-cylinder Yamaha 55-HP was so close to the OMC engine that I think Yamaha were sued.

Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Wed Apr 01, 2020 11:00 am
by dtmackey
A little off topic, but an interesting read on Yamaha development and failures as they targeted the U.S. market for V6 production and sales. Some may find this interesting.

It goes on for several pages and you can tab forward at the bottom.


Re: 1980 SUPER SPORT 15 Yamaha Re-power

Posted: Wed Apr 01, 2020 11:45 am
by biggiefl
Good read!