06 suntracker 21' signature repower 50hp to 115hp 4 strokes

[DirtinLa]

What kinds of speed increases can I anticipate.

By myself I can top out at around 16 with my 50HP Mercury 4 stroke non-bigfoot motor.

Looking at a 2013 yamaha f115 four stroke... prop-less.

Top speed to expect and prop recommendations please!!!!

Thanx in advance as always,

-=Fred=-

[Marc K]

What is the diameter of your pontoons? If you have 24" pontoon tubes (or larger) and you find the right prop, and you keep your bow weight down, I would think that you will run in the 30's.

My 25' Crest was built in 1999 with two little 23" diameter pontoon tubes and is powered by the original 2000 Yamaha F115. Mine is a front-heavy boat so my nosecones do not really lift at all with 115 HP - I plow continuously. Best I can do is 27 MPH running empty. With four adults and ice chests onboard plus two adults riding our tube, it's 25 MPH maximum. All of that is running at 5800 to 6000 RPM Wide open, which I prefer to do for only short periods.

When I load it up with 10-12 people plus gear, I get only 18 MPH wide open at 5900 RPM and 14 MPH at 4500 RPM. That 4 MPH difference almost doubles my fuel burn rate. Seeing my bow wake tells you why!

A big improvement for you will be cruising at a decent speed without needing to always run it wide open!
My Yamaha four-stroke uses about 10 gallons per hour wide open at 5,900 to 6,000.
That drops to about 5.8 gallons per hour at 4500 RPM which still gives me around 20 MPH with a "normal' load of people.

Heck, 3200 RPM lets me pull two adults (and their ice chest ) on our tube at 12 MPH and use only 6 gallons of gas for the 25 mile round trip up to the Tiki Bar and back again.

[Motor7]

I'm thinking about 25mph empty....

[DirtinLa]

24" pontoons with the lfter rails up front

[DirtinLa]

any recommendations on props?

[Steiner]

A 115 on a boat that size should move on out. Yamaha's standard prop for that motor on a pontoon is the Talon GP aluminum 13-5/8 x 14. Yamaha has performance bulletins online. The data on the F115 is pretty light, but they do show a 3000+ lb 23' pontoon running 26.2 mph with that setup and a smaller tritoon running 36.

[DirtinLa]

any chance of getting a link please?

[Marc K]

any recommendations on props?

FWIW, my prop is a Yamaha part number Y-2 15K 6E5 and is marked 13.5" x 15.
I believe that I am propped about right for my boat because I run 5800 to 6000 wide open.

Marc

[Steiner]

any chance of getting a link please?

There are actually a lot more bulletins than I thought. Was looking on my phone so the list might not have populated right. Several different props used. When I was shopping, I made a spreadsheet with all the info to make it easier to compare.

https://yamahaoutboards.com/en-us/home/ ... -bulletins

Use the filters for the 75-115hp range. Once the list loads you can click on the engine column to sort it. Click twice and it should sort in descending order so 115 will be at the top.
https://yamahaoutboards.com/en-us/home/ ... -bulletins

[Rick McC.]

I can’t imagine any two log ‘toon hitting 30 MPH no matter what the engine; unless the toons have lifting strakes to make them planing, rather than displacement, hulls.

[ROLAND]

I could very well be wrong, but personally I don't believe you would get near 30 mph... I would guess in the mid 20's. I base that on my son has a 22 foot bennington with a 115 hp 4 stroke. I have a 20 foot bennington with a 75 hp 4 stroke... when my boat was newer and the toons were clean, I could hit approx. 24 mph on a smooth lake... and my son's boat can barely out run mine with his 115. Probably because his boat is so much heavier at 22 feet.