What size motor for a Carolina Skiff J12?

[BrianOGrady]

Started my Craigslist engine search for the J12, I have read that people will put anything from 9.9HP to 25HP.

I will have 2 adults and a child most of them time with me, we will be mostly on a small creek or small lake with no HP restrictions.

Anyone have any experience with these boats/motor combo's?

 

[gm280]

I would suggest what ever the capacity plate states as maximum. You can always throttle back, but you can't go faster then the available HP will allow. And with three folks in the boat, the extra power will be used. JMHO!

 

[Scott Danforth]

I believe the capacity plate has 15hp as max.

 

[BrianOGrady]

I believe the capacity plate has 15hp as max.

Capacity plate is completely faded away. I have read 15hp is max, but looking for any real world experiences

 

[Scott Danforth]

Capacity plate is completely faded away. I have read 15hp is max, but looking for any real world experiences

In the eyes of the local LEO, insurance companies and the Federal Law that the US Coast Guard uses for OB HP calculations will say 15.

 

[BrianOGrady]

In the eyes of the local LEO, insurance companies and the Federal Law that the US Coast Guard uses for OB HP calculations will say 15.

thanks, I wonder how a 9.9 will push it with two people?

 

[Scott Danforth]

It probably won't plane, however it will move it just fine

 

[boobie]

I always go for the max hp allowed. You can never have too much. Been there.!!

 

[igotit]

J12 as stated 15hp max
I used to have a j12 15 years ago with 25 tohatsu,57 mph with 2 teens in it.
Id run a 2x2 betwen motor and mount bracket to surface drive the motor,30hp wheel not to exceed 5600 rpms wot.

Scary on full throttle turns.
I also tried a 15 tohatsu on the j12,18 mph with 2 teens weighting $300 lbs total.
Not bad

 

[steelespike]

The 25 and 30 99 - 01 use the same prop with the same ratio.
Speed at 5600 calculates at about 33 mph. Perhaps your Speedometer was in error.

 

[igotit]

Perhaps the math provided is in error,i was clocked by moving cars.....traffic.the bayou ran along a hiway,speed limit 55 mph.easily walk away many cars.
Mind blowing to know that both my dads vehicles speedometers were over 20 mph off.

The 30 wheel i use had more pitch than the 25 wheel.
All your math cant change my mind about what i owned,did in my youth.
The question was about performance on a j12,i simply stated my motor experience with the j12.

 

[steelespike]

J12 as stated 15hp max
I used to have a j12 15 years ago with 25 tohatsu,57 mph with 2 teens in it.
Id run a 2x2 betwen motor and mount bracket to surface drive the motor,30hp wheel not to exceed 5600 rpms wot.

Scary on full throttle turns.
I also tried a 15 tohatsu on the j12,18 mph with 2 teens weighting $300 lbs total.
Not bad

30 hp, 5800- rpm,15"ss prop, 1.85 ratio,12% slip = 39.2.
Calculate for rpm: 57 mph,15"ss prop,8% slip,1.85 ratio= 8000 rpm.
A 30 Tohatsu can't turn a 15" prop to 8000.

 

[igotit]

No disrespect

Im positive my j12 with ol 2 stroke tohatsu did 57 mph for 8 years of service before finally selling it.
My water patrol buddys boat done 53 mph all day,id walk away from him all day aswell.

Your not factoring in weight of boat and gear,viscosity of water,wind.....all of that throws a little wrench in that math.
A typical 25hp 2 stroke ran as intended will push a standard 14x48 allweld aluminium hull around 35 mph.
If you think my j12/25 tohatsu story is hard to believe.if it eases your mind,my brother recalls 52 mph.
You should hear my 1963 3.9 mercury on a old 14x42 rivited hull doing 24 mph story.
I have plenty friends to verify it.
Ive got nothing to prove here....what do you gain by standing your ground and makin me out to be full of bs.

Try this math out.
1975 70hp johnson,14 pitch wheel,5200 rpm.
Now tell me how fast is my boat running....without knowing its weight,or water conditions.
All ill state...its a 17x54 factory aluminium hull.
Ill report back with the actual speed after your reply.

My point is that math formula is and estimate,not set in stone.

 

[Sea Rider]

A Tohatsu 30 can theoretically turn 8K with wrong prop pitch size, but will pull all rods out while at full grip. I'll second math formula is only an estimate, many tech parameters are not being considered in real world outings.

Happy Boating

 

[igotit]

I agree 100%
Acording to the math formula....if i get a 25hp to turn 6k rpm with 14p prop....ill do (example )32 mph.
Right.
Even if its installed on a 6000 lb 20 ft cargo barge.....the math claims 33 mph....so thats gotta be my speed.the boat doesnt affect the math.
I call bs

I believe a j12 weights in around 300lbs,no deck or seats,with 2 teen boys,6 gal tank...assuming its full....my total weight was 550 lbs.
Thats hardly any weight for a 25 to push around.

 

[steelespike]

No disrespect

Im positive my j12 with ol 2 stroke tohatsu did 57 mph for 8 years of service before finally selling it.
My water patrol buddys boat done 53 mph all day,id walk away from him all day aswell.

Your not factoring in weight of boat and gear,viscosity of water,wind.....all of that throws a little wrench in that math.
A typical 25hp 2 stroke ran as intended will push a standard 14x48 allweld aluminium hull around 35 mph.
If you think my j12/25 tohatsu story is hard to believe.if it eases your mind,my brother recalls 52 mph.
You should hear my 1963 3.9 mercury on a old 14x42 rivited hull doing 24 mph story.
I have plenty friends to verify it.
Ive got nothing to prove here....what do you gain by standing your ground and makin me out to be full of bs.

Try this math out.
1975 70hp johnson,14 pitch wheel,5200 rpm.
Now tell me how fast is my boat running....without knowing its weight,or water conditions.
All ill state...its a 17x54 factory aluminium hull.
Ill report back with the actual speed after your reply.

My point is that math formula is and estimate,not set in stone.

One of the first things we usually ask is brand,size and dry weight when figuring performance numbers.
Then motor size ,ratio and present prop and light load performance.
You can't say I have a boat with a 70 what size prop do I need?
With the correct info we can estimate any one of the 5 specific numbers required for "prop"calculations.

 

[Sea Rider]

A friend of mine has a 2 strokes Tohatsu 30 HP on a very light boat, with 2 medium weight boaters the engine is only producing 4850 wot revs at full grip when should be doing max 5850 rpm. The issue is that current engine was factory delivered with a 9.9 x 13 pitch when should have been delivered with same diam but with 11 prop pitch. 2 + pitches sizes makes the whole 1 K RPM difference. Will test that combo with a GPS and check max speed on flat calm water cond. I'm skeptic if possible tu run at 35 MPH or even close.

When running at 52 MPH, which was the prop pitch used and wot rpm reading of that 25 HP at full grip ?

Happy Boating.

 

[igotit]

I dont remember exact size,it was a michigan straight back 14 pitch.....thats all i remember.....that was back in 1997 when i got that wheel.bought it used was told it was for a 30 tohatsu,i always surface drived my motor to play in shallows.