Please help with my setup. 16ft superboat with 12” JP w/120 Johnson. Only 40mph?
#1
Please help with my setup. 16ft superboat with 12” JP w/120 Johnson. Only 40mph?
Had the boat 10 years now but recently changed the motor. Previous motor was a 1.6ltr 110 v4 vro Johnson with raker prop. Boat did 50mph exactly as a center console then I converted to dual console(maybe added at the most 100lbs) swapped the old 1.6 for a 2.0 v4 Johnson 120hp from early nineties. Was expecting in the high 50’s low 60’s but instead topped out at 41. Motor has good compression and is in great mechanical condition.
Any ideas why a small motor with less displacement was able to push the boat 10mph faster than the newer 120?
is it running on all cylinders?
is the extra weight the issue?
is the shaft longer? Should I raise the motor?
the boat has a 12” manually adjustable jack plate.
aslo from what I researched the newer motor is 65lbs heavier. With the same raker prop that was on the older motor I’m only turning 5000k. With another mid range prop I had lying around the boat pushes 6200 rpm and does 39mph almost the same speed. I’m at a loss
experienced people please help!!!
thanks in advance
Any ideas why a small motor with less displacement was able to push the boat 10mph faster than the newer 120?
is it running on all cylinders?
is the extra weight the issue?
is the shaft longer? Should I raise the motor?
the boat has a 12” manually adjustable jack plate.
aslo from what I researched the newer motor is 65lbs heavier. With the same raker prop that was on the older motor I’m only turning 5000k. With another mid range prop I had lying around the boat pushes 6200 rpm and does 39mph almost the same speed. I’m at a loss
experienced people please help!!!
thanks in advance
Last edited by PoshDesignNY; 09-15-2020 at 06:50 PM.
#3
Charter Member # 55
Charter Member
Not that we don't want you here but you would probably get a lot more advice on https://www.screamandfly.com/forum.php. It is geared more toward smaller boats with OB's.
The following 2 users liked this post by Griff:
PA.WOODCHUCK (09-16-2020), TomZ (09-16-2020)
#4
With all the additional weight. (from console conversion, bigger motor, larger battery) I’m thinking the boat doesn’t lift as well increasing hull/shaft drag in the water, because the raker prop is a high range prop not much low or mid torque it prob can’t lift the boats extra weight. I’m think’n
thank you in advance
btw, this is also posted at screamandfly, just trying to get as much advice as possible. Infact OSO responded before SAF
#5
Registered
What rpm's where you running with the old setup? adding 100lbs forward on a 16 foot boat is a lot. How does it react to trim old to new?
#6
#7
Registered
a few extra hp is fighting the added weight (which you are probably underestimating the true number).... have you run a traditional prop with an appropriate pitch to start as a base line at the proper max rpm?
Raker props are a top end rpm on a light boat prop - you don't really have that anymore and your slip #'s are probably through the roof
Raker props are a top end rpm on a light boat prop - you don't really have that anymore and your slip #'s are probably through the roof
#8
Registered
Move the battery to the back of the boat.
Should be faster than old motor.
Rakers are great props. I’ve run tons of them on everything.
Check compression.
If your no longer carrying the bow at speed, you probably added more weight than you thought (as already stated) or moved it farther forward.
Neither of which would a 16’ boat liked.
Both of your motors are great motors.
My brother had an old 16’ OB yrs ago. It was heavy and slow.
Was trying to convince himself he was OK with 30 mph.
W/him at full throttle I got up and walked to the back of the boat.
It picked up 3 mph!
He was blown away.
He asked if I knew it would do that 😉
Should be faster than old motor.
Rakers are great props. I’ve run tons of them on everything.
Check compression.
If your no longer carrying the bow at speed, you probably added more weight than you thought (as already stated) or moved it farther forward.
Neither of which would a 16’ boat liked.
Both of your motors are great motors.
My brother had an old 16’ OB yrs ago. It was heavy and slow.
Was trying to convince himself he was OK with 30 mph.
W/him at full throttle I got up and walked to the back of the boat.
It picked up 3 mph!
He was blown away.
He asked if I knew it would do that 😉
Last edited by Twin O/B Sonic; 09-16-2020 at 04:21 PM.
The following 2 users liked this post by Twin O/B Sonic:
resurrected (09-17-2020), ThisIsLivin (09-16-2020)
#9
Registered
6000k with old setup, I def lost 1000k with the new. Trim for the new setup doesn’t raise the bow as high, also because of the extra motor weight I moved the batt from aft to more than mid way forward to help balance. Should mention it’s a heavy pig 1000 deep cycle, used a smaller 650in the old setup. You thinking weight is the major factor? Even with the newer motors extra hp and displacement?
#10
a few extra hp is fighting the added weight (which you are probably underestimating the true number).... have you run a traditional prop with an appropriate pitch to start as a base line at the proper max rpm?
Raker props are a top end rpm on a light boat prop - you don't really have that anymore and your slip #'s are probably through the roof
Raker props are a top end rpm on a light boat prop - you don't really have that anymore and your slip #'s are probably through the roof
Like it is said many time ‘setup is everything’
I still feel like it maybe running on only 3 cyl, maybe a spark wire or coil. It’s not running rough but that maybe because of that heavy ass flywheel.
think about it!
the new motor is a 2.0, the old a 1.6, 3cyl working on the 2.0 is only a 1.5, almost a 1.6 like the old motor.
did notice one day that 1 plug looked perfect and the other 3 looked normal. Might have to look back into that and track down the problem cyl. And FYI my old 110 had only about 100psi and the new motor has min 125psi across. One day I felt the boat jolt forward at speed like it was just let loose of it’s restraints but that was only once.
when I read about heavier boats with similar hp going 50 I feel like I should be doing 60 especially with this superboat, it’s so simple there is nothing to the boat
also with the raker on the new motor it is unusually slow to plane even with 2 people, the mid range prop I have now gives it an amazing hole shot about 3 seconds to 30mph. Another reason I feel it’s not getting full power.
Get a smaller battery move it to the back. Where is your tank? I had a 16' Larson Senza with a very modified Chrysler 115, great boat but the 18 gallon tank was in the front and really hurt top end. I just pulled 2 giant subs out of the back end of my 28' Velocity and it totally changed the ride. I now run morey trim than I used to, I'm now trying to find ways to move weight to the rear.
Last edited by PoshDesignNY; 09-16-2020 at 05:37 PM.