Classic 15 with F70 performance

Optimizing the performance of Boston Whaler boats
TFrere
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Joined: Wed Sep 05, 2018 11:16 pm
Location: Lafayette, LA

Classic 15 with F70 performance

Postby TFrere » Wed Aug 07, 2019 9:56 am

This past weekend, my adult daughter and I took my 1985 15’ Sport with Yamaha F70 out for a ride. At the beginning of summer I installed a PowerTech SCD3 13.35” x 17” prop but hadn’t truly tested it. My motor is mounted 2 holes up. We had about 8 gallons of gas, light gear, 325 in crew (me 200, her 125) we were able to hit 43 mph. However, the boat was getting pretty squirrely at that speed so we couldn’t stay there long. I quickly had to trim down to stop the chine walking.
Previously I was running a 13.25” x 17” Stiletto Advantage 1. I don’t see a difference in top speed but I’m running about 300 RPMs higher with the PowerTech (6100 vs 5800). The boat also seems to plane faster and I feel as though I can remain on step at lower speeds.

I did a bit of research on the Classic 15-footers and found that some have extended the strakes on the keel all the way to the transom. This modification seems to stabilize the boat at high speeds. I am considering this modification even though I do not run on the top end very often. Has anyone done this modification? If so, what are your experiences?
Thanks
1985 15’ Sport with Yamaha F70

biggiefl
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Re: Classic 15 with F70 performance

Postby biggiefl » Wed Aug 07, 2019 10:51 am

I think you have read everything there is about that mod between here and the other site. As James has stated only a handful have been done. I would advise contacting James and his friend who does the strake modifications as I doubt anyone here is going to have anything additional to comment.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

El Rollo
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Re: Classic 15 with F70 performance

Postby El Rollo » Wed Aug 07, 2019 12:47 pm

Sounds like you've got your 15 dialed-in nicely.

That Powertech propeller seems like it's working great.


I remember seeing somewhere a pretty detailed post with step-by-step pictures of someone extending the strakes on a classic 15. I'm not sure which site it was on, but I seem to remember the person was in the pacific northwest perhaps. The person seemed to know what he was doing, as the quality of his work looked to be top-notch.

jimh
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Re: Classic 15 with F70 performance

Postby jimh » Thu Aug 08, 2019 7:45 am

TFrere wrote:...I...found that some have extended the strakes on the keel all the way to the transom. This modification seems to stabilize the boat at high speeds. I am considering this modification even though I do not run on the top end very often. Has anyone done this modification? If so, what are your experiences?


In a post in the Old Forum at

http://continuouswave.com/ubb/Forum3/HTML/020289.html

a user ("Bowser") described the addition of new strakes on the hull bottom and the extension of the runners on his classic 15-foot hull. He provided this image:

15HullStrakes.jpg
Fig. 1. Bottom of Boston Whaler classic 15-foot hull modified to extend runners and add strakes.
15HullStrakes.jpg (22.96 KiB) Viewed 10003 times


The original comments stated:

I think this picture shows best what we did to stabilize the hull. We stretched the lower strakes to the back and instead of building a pad we put [two] runners in the center that work as a virtual pad without effecting the ride depth. ...[W]e have confidence...that the design will work without a hitch...had it out this weekend and...it felt very stable....


It is also noted in the thread that the user "Bowser" is the owner of IMAGE MARINE. On a social media website the telephone number is listed as (727) 612-1805. You may be able to communicate with him via telephone about the outcome of the modification. He also comments later in another discussion that the boat was "Stable as a surgeon's hand."

The entire thread should be read as it has many interesting comments about the 15-foot hull, its design, and modifications to improve stability at high speeds.

In another thread in the Old Forum at

http://continuouswave.com/ubb/Forum3/HTML/020588.html

there is further discussion about adding strakes, and there are links to photo-images of the process of adding strakes. These three links show the process:

https://www.dropbox.com/s/goq4706652z6oe4/Photo%20Nov%2001%2C%202%2044%2012%20AM.jpg

https://www.dropbox.com/s/fvolcxb86t9nhzv/Photo%20Nov%2002%2C%204%2054%2053%20PM.jpg

https://www.dropbox.com/s/kbsp1bnq4qxz01s/Photo%20Nov%2002%2C%204%2055%2005%20PM.jpg

TFrere
Posts: 43
Joined: Wed Sep 05, 2018 11:16 pm
Location: Lafayette, LA

Re: Classic 15 with F70 performance

Postby TFrere » Thu Aug 08, 2019 8:04 am

Great information--Thank you
1985 15’ Sport with Yamaha F70

biggiefl
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Re: Classic 15 with F70 performance

Postby biggiefl » Thu Aug 08, 2019 11:04 am

His name is James.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).

jimh
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Re: Classic 15 with F70 performance

Postby jimh » Thu Aug 08, 2019 12:19 pm

James Bowser?

biggiefl
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Re: Classic 15 with F70 performance

Postby biggiefl » Thu Aug 08, 2019 1:14 pm

He came to my last Homosassa rendezvous with the 15' and a 9' Tender. Can't remember last name.
On my 24th Whaler. Currently in the stable: 86 18' Outrage, 81 13' Sport(original owner), 87 11' Sport, 69 Squall(for sale cheap).