SUPER SPORT 15 with F70A

Optimizing the performance of Boston Whaler boats
spatlennon
Posts: 3
Joined: Fri Jul 31, 2020 10:52 am

SUPER SPORT 15 with F70A

Postby spatlennon » Fri Sep 03, 2021 3:23 pm

I re-powered a1984 SUPER SPORT 15 with a Yamaha F70A and a PowerTech SCD3 13-1/4 x 17-pitch propeller. The F70 engine mounting height is [unclear as "highest possible"].

The engine has only five hours run time and is still in its break-in period. More engine runtime will be needed before [the SUPER SPORT 15 boat can be tested for] ride at full-throttle. At about 3/4-throttle with the engine trimmed “up” the hull starts to chine-walk.

In a future article I will report engine speed and boat speed data.

whaler 2.jpg
Fig. 1. SUPER SPORT 15 boat.
whaler 2.jpg (219.9 KiB) Viewed 2519 times


[Moderator's note: separated from another thread discussing another boat and another repower. For engine mounting height descriptions, please use the form recommended.]

dtmackey
Posts: 745
Joined: Thu Sep 28, 2017 9:29 pm

Re: SUPER SPORT 15 with F70A

Postby dtmackey » Mon Sep 06, 2021 9:27 pm

You should see about 42-43mph on GPS. I mounted my F70 on a hydraulic jackplate with a 4" setback and run it a full 6" above the transom lip and it's perfect. The boat will go from idle to full throttle with no prop ventilation and then you can trim it out from there. I see 45.1mph, but I need an SCD prop as others that run them see slightly better performance (with jackplate). In rough water I drop the motor about 1.5" and it will maintain prop bite in white cap rough water.

Based on your pic the engine appears to be mounted on the top hole which is ideal on the 15. As far as break in, you should be able to run full throttle as long as it's not for extended periods. I think I'm at 25 hours on my F70.

Report back as I'm interested to hear your numbers based on the SCD prop. I know others that are running a worked SCD 18" and seeing 47-48mph.

D-

TFrere
Posts: 40
Joined: Wed Sep 05, 2018 11:16 pm
Location: Lafayette, LA

Re: SUPER SPORT 15 with F70A

Postby TFrere » Fri Jan 28, 2022 12:24 pm

I own a 1985 Sport 15 with a 2014 Yamaha F70LA with a PowerTech SCD3 propeller with 17-pitch. The F70LA engine is mounted two-holes up. The boat accelerates to 43-MPH at full throttle with a light load. The SPORT 15 hull will chine walk at 43-MPH, so I don’t stay there long.

I contacted Ken Reeves with PropGods about my setup. I mentioned that others are running [their engines at a mounting height of] three-holes up. Ken told me to try raising the engine to three-holes up as that would likely eliminate some of the chine walk. I have not made the change yet but will do so soon.
1985 15’ Sport with Yamaha F70

dtmackey
Posts: 745
Joined: Thu Sep 28, 2017 9:29 pm

Re: SUPER SPORT 15 with F70A

Postby dtmackey » Wed Feb 02, 2022 10:32 pm

[For recommended engine mounting height for the 15-foot hulls] the generic response is "three-holes-up."

Many of us have been experimenting and actually have the 15-foot hull and F70 motor, and you can go to a mounting height of all-the-way-up [i.e. four-holes-up] with no problems. I run a jack plate and run the height up a full 6-inches, which is well above the three- hole-up recommendation. The engine does just fine.

By raising the engine you decrease the drag by having less lower unit in the water. Less drag makes a difference in the steering and overall feel of the boat.

With a jack plate when I set [engine mounting height] to a lower position and get on a plane, and then start raising the engine. You can hear the engine RPM come up and see the speed increase while the boat has a better attitude in the water. It's hard to explain, but others have run boat and agree.

With a 17-pitch propeller the engine accelerates to right on the rev limiter at full-throttle.

I've discussed this with other 15-footer owners. They run 18 or 19-pitch pitch propellers and see boat speeds of 45 to 46-MPH, and the hull shows no chine walk.

D-

jimh
Posts: 10566
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: SUPER SPORT 15 with F70A

Postby jimh » Thu Feb 03, 2022 9:00 am

The originator of this thread has not been active on the website since September of 2021. I hope he returns some day to read all of the excellent information that was offered in response to his question, and also to fulfill his promise to post updated performance information.

TFrere
Posts: 40
Joined: Wed Sep 05, 2018 11:16 pm
Location: Lafayette, LA

Re: SUPER SPORT 15 with F70A

Postby TFrere » Tue Aug 02, 2022 11:59 am

TFrere wrote:I own a 1985 Sport 15 with a 2014 Yamaha F70LA with a PowerTech SCD3 propeller with 17-pitch. The F70LA engine is mounted two-holes up. The boat accelerates to 43-MPH at full throttle with a light load. The SPORT 15 hull will chine walk at 43-MPH, so I don’t stay there long.

I contacted Ken Reeves with PropGods about my setup. I mentioned that others are running [their engines at a mounting height of] three-holes up. Ken told me to try raising the engine to three-holes up as that would likely eliminate some of the chine walk. I have not made the change yet but will do so soon.


Update: I raised my Yamaha F70 on my 1985 15 Sport to the top position (3 holes up). I test ran it and hit the rev limiter at 6500 RPMs at a speed of 44 mph. I had a very light load so I want to try with more weight in the boat before I re-pitch my SCD3 from 17” to 19” pitch.

My observations:
• The boat still had some chine walk but it was less pronounced than before raising the motor. I suppose a jack plate or extending the strakes would eliminate all chine walk.
• I found it hard to believe that I gained 500 RPMs by raising the motor a single notch upward.
•The boat felt fine and the prop never cavitated even while turning at high speeds.
•I appreciate all of the discussions and experience on this topic. While I rarely run my boat at wide open throttle, I like to have it dialed in for maximum efficiency and maximum speed if I need it.
1985 15’ Sport with Yamaha F70

dtmackey
Posts: 745
Joined: Thu Sep 28, 2017 9:29 pm

Re: SUPER SPORT 15 with F70A

Postby dtmackey » Wed Aug 03, 2022 4:23 pm

TFrere wrote:
TFrere wrote:I own a 1985 Sport 15 with a 2014 Yamaha F70LA with a PowerTech SCD3 propeller with 17-pitch. The F70LA engine is mounted two-holes up. The boat accelerates to 43-MPH at full throttle with a light load. The SPORT 15 hull will chine walk at 43-MPH, so I don’t stay there long.

I contacted Ken Reeves with PropGods about my setup. I mentioned that others are running [their engines at a mounting height of] three-holes up. Ken told me to try raising the engine to three-holes up as that would likely eliminate some of the chine walk. I have not made the change yet but will do so soon.


Update: I raised my Yamaha F70 on my 1985 15 Sport to the top position (3 holes up). I test ran it and hit the rev limiter at 6500 RPMs at a speed of 44 mph. I had a very light load so I want to try with more weight in the boat before I re-pitch my SCD3 from 17” to 19” pitch.

My observations:
• The boat still had some chine walk but it was less pronounced than before raising the motor. I suppose a jack plate or extending the strakes would eliminate all chine walk.
• I found it hard to believe that I gained 500 RPMs by raising the motor a single notch upward.
•The boat felt fine and the prop never cavitated even while turning at high speeds.
•I appreciate all of the discussions and experience on this topic. While I rarely run my boat at wide open throttle, I like to have it dialed in for maximum efficiency and maximum speed if I need it.


Great numbers. The 15' hull responds very nice to raising the motor and you can raise it more than many people think and improve the ride and handling. I can run my F70 a full 6" above the transom on the jackplate. I do need to get an SCD prop as those are ideal and I'm torn between an 18 or 19" pitch, so I'd be interested in your feedback if you jump up in pitch.

D-

TFrere
Posts: 40
Joined: Wed Sep 05, 2018 11:16 pm
Location: Lafayette, LA

Re: SUPER SPORT 15 with F70A

Postby TFrere » Thu Aug 04, 2022 9:13 am

Thank you DT.

I raised the F70 engine mounting height on my boat based upon your experience.

I would love to have a jack plate but as a recent retiree, I have become more frugal.

I will post results after further testing and possibly a re-pitch of my SCD3 propeller.
1985 15’ Sport with Yamaha F70