Pontoon Boat & Deck Boat Forum

New to me, so I don't have any base line to start from. What prop would you reccomend for this boat:

24' Tri Toon, 25" tubes, six-6" full length lifting strakes, motor set back 18" + 6" jack plate (24" total, 5" up & down), motor (for now) will be a 1984 Johnson 140.

Motor came from a little 17' speed boat so I will need to replace the prop I'm sure right away. Stainless is not out of the question, just depends on what I can find. Suggestions?

Does that 140 have the 13 or 15 spline lower unit?

The 13 spline (small V-4) lower unit has a gear ratio of 2.00

Some 140's had the larger lower unit with a 15 spline shaft which can use V-6 props. The 15 spline unit ratio is 2.25 to turn larger dia. props.

If your best guess of top end is about 30 mph you'd be looking at a 13 pitch (v-4 13 spline) prop,or a 15 pitch (v-6 15 spline) prop
'' 27 mph 11 pitch (v-4) / 13 pitch (v-6)
'' 35 mph 15 pitch (v-4) / 17 pitch (v-6)

This a ball-parking, but a place to start......

Without any base numbers I am going to guess a 15p prop. Make sure you order from someone that offers a prop exchange program so if you are too far off you can swap them out.

I would agree with Rick. A 15 works well on my Tri toon with a 135. I think it would be a good place to start.

Hmmm....I'll have to check the splines today. How does the the diameter play in? My buddy has a 15p (13-spline) but it's a 12.25. I have seen others as big as 13.5? Thanks for the input!

Woody wrote:I would agree with Rick. A 15 works well on my Tri toon with a 135. I think it would be a good place to start.

+1 I'm running a stock 17 on mine, but gonna try a SS 15 after I fix/replace my tach

The_Hellbilly wrote:

Woody wrote:+1 I'm running a stock 17 on mine, but gonna try a SS 15 after I fix/replace my tach

So, do you know what kind of RPM's you're turning with the 17 ?

ToonGuy wrote:Hmmm....I'll have to check the splines today. How does the the diameter play in? My buddy has a 15p (13-spline) but it's a 12.25. I have seen others as big as 13.5? Thanks for the input!

Good question,

In short it effects the slip ratio in the equation. If pitch is true,a 12.5" dia. will turn more rpms than a 14" dia. prop of the same pitch. So, you can to a point factor that in at around 100-150 rpms per 1/4" change in diameter.

Here's a fun tool to play with when testing props,or ball parking a starting place. http://go-fast.com/Prop_Slip_Calculator.htm Find your gear ratio and start plugging in numbers.

Keep in mind that not everybody measures pitch the same. Especially with today's progressive pitch profiles. One company's 15 pitch may be anothers 16. But with known props a guy can dial it in.

I running a 14.5" x 17 pitch 4 blade on my V6

Post some pics of your boat!!

Woody wrote:

So, do you know what kind of RPM's you're turning with the 17 ?

Just a hair less than 6k. FWIW: my toon with the current furniture setup is REALLY heavy. I currently run in the mid 30's light, 30-32mph loaded down, and ran in the high 20's with a log full of water. (all gps verified) I'm hoping the right prop and maybe a setback will get me to 40mph. My biggest issue is that my motor is right at the azz-end of my toon, intstead of set back 12-24 inches as is the current trend.

[quote="The_Hellbilly My biggest issue is that my motor is right at the azz-end of my toon, intstead of set back 12-24 inches as is the current trend.[/quote]


Me too. I would like to change that someday. I don't have strakes either, but will eventually add them also.

I hae the 13 spline unit. So I'm thinking a middle of the road dia. 15p to start with. I do NO water sports, the boat is just used to cruise (mostly to the sand bar and back ). I'm usually lightly loaded (4-5 people, and my tank is only 19 gal. max). Whatcha think?

FWIW: That's where I plan on starting

Well, I'm picking up a 12.25x15 new OEM aluminum for $70, I think it's a good starting point.

Isn't 12.25 a little small? Just goin on what I hear but "on a toon go as big as you can get and then pitch for rpm. Just throwing that in there for conversation....