1989 SUPER SPORT 15 2023 Yamaha F70

Optimizing the performance of Boston Whaler boats
rich_
Posts: 2
Joined: Wed May 17, 2023 12:45 pm

1989 SUPER SPORT 15 2023 Yamaha F70

Postby rich_ » Wed May 17, 2023 9:37 pm

I have a 1989 SUPER SPORT 15 with a 2023 Yamaha F70 mounted in the 3rd hole (two open on top) and PowerTech RED 13.25 x 15-pitch propeller. At an engine speed of 6,200-RPM the GPS boat speed obtained in choppy water is 38.7-MPH.

My 1989 SUPER SPORT 15 boat is a little heavier than a typical SUPER SPORT because the wood interior was changed to ipe wood instead of mahogany. This SS 15 could probably use a good drying out because the stern drain tube was leaking for a few weeks.

The previous 1993 Yamaha 70-HP two-stroke-power-cycle engine with a Quicksiver Laser II 20 pitch prop seemed faster than the new 2023 Yamaha F70 engine it was re-powered with, but I never had true GPS readings on the old setup to compare.

The new 2023 Yamaha F70 engine is quiet and sips fuel.

[Separated from another thread on the performance of a different boat and engine—Moderator.] <edited in an attempt to not be so critiqued by the moderator>

dtmackey
Posts: 759
Joined: Thu Sep 28, 2017 9:29 pm

Re: 1989 SUPER SPORT 15 2023 Yamaha F70

Postby dtmackey » Wed Jul 05, 2023 2:21 pm

rich_ wrote:I have a 1989 SUPER SPORT 15 with a 2023 Yamaha F70 mounted in the 3rd hole (two open on top) and PowerTech RED 13.25 x 15-pitch propeller. At an engine speed of 6,200-RPM the GPS boat speed obtained in choppy water is 38.7-MPH.

My 1989 SUPER SPORT 15 boat is a little heavier than a typical SUPER SPORT because the wood interior was changed to ipe wood instead of mahogany. This SS 15 could probably use a good drying out because the stern drain tube was leaking for a few weeks.

The previous 1993 Yamaha 70-HP two-stroke-power-cycle engine with a Quicksiver Laser II 20 pitch prop seemed faster than the new 2023 Yamaha F70 engine it was re-powered with, but I never had true GPS readings on the old setup to compare.

The new 2023 Yamaha F70 engine is quiet and sips fuel.

[Separated from another thread on the performance of a different boat and engine—Moderator.] <edited in an attempt to not be so critiqued by the moderator>


I have 1988 15 SuperSport. I re-powered from a Yamaha 70 two-stroke engine to a new Yamaha F70 four stroke engine. I was running a Powertech 17-pitch on the last engine and also use that on the new engine. The two-stroke-power-cycle engine gave a boat speed of 42-MPH; the F70 engine runs a touch faster and accelerates to the rev limiter with just me in the boat. I know the boat speed would increase if I gave the engine more propeller to turn. I also added a hydraulic jack plate with the F70.


I've been temped to try an 18-pitch or 19-pitch propeller, but I don't want to lose any bottom end power; the F70 is very soft on power down low and the two-stroke-power-cycle engine had much more “grunt” popping the boat onto plane.

I'm surprised your 2S motor could pull a 20" pitch prop and curious what your RPMs were at top end, as I'm betting is was lower than optimal.

ON YOUR CURRENT SETUP - you are running with too little pitch and hitting the rev limiter well before the peak horsepower of the motor. Change to a propeller with 17-pitch; you should pick up 3-MPH boat speed increase.

ALSO, make sure the engine is mounted as high as possible as the 15-footer hull responds quite well to an engine that's mounted high. I've done plenty of experimenting over five years with my boat.

I haven't been on this site in six months, thus a late to respond to your thread.

I am interested in hearing more on your setup.

D-

User avatar
Phil T
Posts: 2624
Joined: Thu Oct 22, 2015 6:08 pm
Location: Was Maine. Temporarily Kentucky

Re: 1989 SUPER SPORT 15 2023 Yamaha F70

Postby Phil T » Wed Jul 05, 2023 5:40 pm

Stay with the same brand and model of propeller but buy a new propeller with a pitch greater by 2-inches

Note: the engine speed maximum at full throttle is 6300-RPM
1992 Outrage 17
2019 E-TEC 90
2018 LoadRite 18280096VT
Member since 2003