What pitch prop for Carolina Skiff J14 with Yamaha15 2 stoke?

[adcampbe]

I recently bought a Carolina Skiff J14 with a 2 stroke Yamaha 15 hp. With two in the boat, one in back running the tiller motor and one sitting up near the front deck, the boat will not plane. With just me in the back running the tiller the boat will struggle and struggle, but finally get up on plane. Prop is currently a 9 1/4 x 11. I think I need a lower pitch, but don't know if I should buy a 9 pitch or 10. Anybody have suggestions?

 

[QBhoy]

Have you presumably explored the easy things like trim of the motor ? Is it a long or a short shaft and which should it be ? Long or short ?
sorry to ask, if you have already.

 

[adcampbe]

I have tried different trim settings. Currently I have the motor trimmed as far down as it can go to try to keep the bow down. The motor is a short shaft. I might be able to raise it up about an inch to get the anti cavitation plate even with the bottome of the boat.

 

[QBhoy]

You might just be a little over propped actually. When it does eventually plane...does it still seem a little low on rpm ?

 

[WesNewell]

Info I found says it's rated for up to 30hp. A lower pitch prop may help, but at only half it's max hp rating it's not going to be a speed demon.

 

[Sea Rider]

With tiller, manual trim motors the trim must be set at 90 deg at whichever trim hole dials so. Perfect to have a driver at the tiller, a boating mate sitting up front. (1) To get the max HP out of that motor must prop it right to run towards it's max wot rpm range factory stated which is 5500 rpm. Assume the current motor's shaft lenght (whether 15 or 20) is what the boat manufacturer designed it to run with ?

For a correct prop maximization will need to buy a cheap induction tach (2) install it next to the tiller grip, adjust the firing sequence to 2 cylinder, 2 sparks per revolution, go for a wot run on flat calm water cond and report the max wot rpm the motor achieved with 2 up, with current prop surely the motor runs extremely lugged.

To determine if there's a correct motor/transon height match will be ideal once the combo it's on plane to visually check (3) if there's any water splash in/out transom going on, prop aertion on choppy water cond and very important at which lower leg height if the water flow is currently passing by, is it right under the upper small plate or towards the AV lower plate. Report your findings.

As the under powered 15 HP motor is powering a large boat would suggest based on a wild guess to drop at least 2 pitches to an alum 3 blade niner to increase wot revs, but with an installed tach will be able to fine tune a better pitch prop to run towards the full wot rpm range with a fixed load of 2 up.

If that boat floats high, has an efficient hull shape with min hull drag, correctly propped wiill be able to achieve a faster plane as loaded than before.

Happy Boating​

 

[dingbat]

The boat is badly under powered at 15 HP

A good friend has one with 25 HP that he uses to crab.
Runs pretty good with one onboard. Has a hard time planing with 2-#200 guys on board.

 

[Sea Rider]

Touche, that combo is badly under powered, as the OP already counts with a 15 HP it's a matter to impove its water performance and take the max out of that 15 HP. Won't be a speed demon but will plane much faster than before which is the purpose of the post. Let's see what the OP has to say...

Dingbat, if your friend has hard time planing his combo with 2 up his 25 HP motor is definitely not running healthy, has a awful motor/transom match, badly deck load distribution, running at the lugging side of the wot rpm range or a cocktail of all 4 mentioned situations.

A top prop maximization it's the way to go when running larger/heavier boats with underpowered portable motors which nobody does....

Happy Boating​

 

[dingbat]

Dingbat, if your friend has hard time planing his combo with 2 up his 25 HP motor is definitely not running healthy, has a awful motor/transom match, badly deck load distribution, running at the lugging side of the wot rpm range or a cocktail of all 4 mentioned situations.
​

No, he has not sent the prop out for blue printing. Nothing wrong with the motor....

Carolina Skiffs are utility boats. A flat bottomed boat built for shallow, back bay use. A fiberglass Jon boat by all measures.

Very popular with the locals as a stable crabbing platform, Although the 16’ is much more popular.
Works well for the purpose but a total dog from a “performance” stand point out.

Two guys and gear pretty much maxes out its #685 load capacity

 

[Sea Rider]

I like boating myself with larger boats along underpowered motors for such applications. Water Performance for me it's achieving the best prop thrust in all water conditions while my motors with maximized props runs at their max wot rpm range. With underpowered motors you can't possibly ask for demon speeds, must content yourself with the max speed achieved with that particular hull and HP motor.

Worst case scenarion : Don't pretend going for a prop maxization for the motor to run towards their max wot rpm range with 2 up and next week decide that you want to go boating with 5 up and achieve the exact same water performance as with 2 up.

Happy Boating​

 

[JimS123]

Info I found says it's rated for up to 30hp. A lower pitch prop may help, but at only half it's max hp rating it's not going to be a speed demon.

Our 13 1/2' tinny is rated for 25. We ran an Evinrude 9.5 2-stroke with an 8" pitch prop for many years. At the time I believe an 8" was the lowest available. With just me aboard it would pop up quite nicely. With 2 moderately fat adults and 2 skinny pre-teenagers the boat would plane just fine. It didn't "pop right up", but it didn't lug and drag on either. To reiterate, that's FOUR people aboard with total weight right at the boat's capacity, with less than half the rated HP.

After the kids left the nest and bought boats of their own I got greedy and put a 25 on her. Scary performance....that motor came off in a hurry. I ended up settling on an 18, which I considered optimum for the hull. In later years I went back to the 9.5 just because the boat ran so nice with it.

Sure, the 9.5 was underpowered. Did we care? No. It was a fun boat. It was our vacation traveling boat. Our at home family boat had a tach, the prop was rpm optimized and the motor height was way up there. I charted fuel usage and speed along the way. But the little tinny had the motor all the way down and why bother with a tach? It's just a little toy boat. I knew it needed a lower pitch prop because of the small size and high load, so it got a brand new Michigan right off the bat.

Sometimes we all get too stressed over the little things. To the OP - level the AV plate parallel with the keel and put on a 9" prop. That will be your "optimum" until you move to a bigger motor.

 

[Sea Rider]

During that boating era was out of this world to install a dial tach for small portable tiller motor use along little prop options to choose from. Moons back owned a 15 HP 2 stroke Evinrude 96 motor and there were only 3 props which were cataloged as : light, medium and heavy to go for depending on application and load.

Now a days motor manufacturers gives extreme importance about their motors revving within their respective wot rpm range stated by each, but most boaters don't care as long their boat whichever model and size it's being powered with works for them.

For my particular open water boating its no fun running an underpowered motor powering a larger boat when now a days with an installed tach and the right prop can get the max HP cowl rated out of them. Something unthinkable years back dealing with portable motors.

Happy Boating​

 

[JimS123]

A real boat - like a fiberglass or aluminum runabout with a relatively high HP motor - has literally dozens of prop styles and sizes to chose from. It's fun to optimize and get her running optimally.

A toy boat - like a little fishing boat with a little clamp on outboard - has maybe 3 props to chose from. Small, medium and high capacity......LOL. It's just simpler to pick what the book says and have fun out with the family. Not to say that putting on an induction tach isn't worthwhile, but with so few options you might make an improvement, but ya ainta gonna dialherin tight.

 

[Sea Rider]

Now a days the prop selection for oldie motors has been highly increased. While there were only 3 pitches to choose from for say an Evi 96-15 HP motor now you have 8 and with an installed induction tach will be possible to dial their max wot rpm with the correct pitch. Doesn't matter if powering a toy boat or a sailboat, the motor must rev inside the wot rpm range each manufacturer calls for to get the max out of them.

Happy Boating​

 

[JimS123]

I was wrong. I like Michigans. My old catalog showed 3 pitches. I just looked at their current offerings in their online catalog and now they only carry 2.

I realize some people like Solases. I tried one once and didn't like it.

Regardless, you have to love those online prop selection tools. I fit my data into the Mercury Marine tool and it spit out the data, including rpms, and it was spot on.