1436 with 15hp Johnson speed questions

[aarolar]

I am struggling to get what I think is appropriate speed from my 1436 Lake Lowe with a 1992 Johnson 15hp on it. With just two adults (200lbs each) fuel and starting battery I am only able to run about 15mph. Previous owner of this motor had it on a similar boat and claimed it was running nearly 28mph. So far I've moved the motor up so the cavitation plate is above the bottom by 3/4" and got zero gains. It's running a 9-1/2 x 10 prop.

 

[LDUBS]

My initial gut reason was that 28 mph would be a tall order. However, I note several claims on the internet of similar set ups in the low to mid 20's. Hopefully someone with a similar set up will chime in.

 

[aarolar]

My initial gut reason was that 28 mph would be a tall order. However, I note several claims on the internet of similar set ups in the low to mid 20's. Hopefully someone with a similar set up will chime in.

My previous experience says I think it is possible lightly loaded it should definitely be doing better than 15

 

[airshot]

NOT 28 mph unless they are guessing !! I have had a couple 14' V bottoms that won't go 28 with minimal equipment. I would venture someone had a 15 hp hood on a 20 hp motor to get 28 mph. The flat bottom has more friction drag on the water than a V bottom on plane. From personal experience ( I have had a bunch of small boats in my 60 plus years of boating) if that 15 hp is running perfect, you might see 22/24 with one person, tops 20 with two adults on a flat bottom. You might gain another 2-3 mph on a V bottom. I base that on accurate GPS readings not a pressure speedo or a poor quality phone app. Accurate speed readings need 5 satellites for real accuracy, only three sats can drop accuracy by 20-25% which is what phones typically use.

 

[Ga Aquadog]

I am struggling to get what I think is appropriate speed from my 1436 Lake Lowe with a 1992 Johnson 15hp on it. With just two adults (200lbs each) fuel and starting battery I am only able to run about 15mph. Previous owner of this motor had it on a similar boat and claimed it was running nearly 28mph. So far I've moved the motor up so the cavitation plate is above the bottom by 3/4" and got zero gains. It's running a 9-1/2 x 10 prop.

I think it might have to do with total weight in the boat. I wonder how much weight the previous owner had in it.

 

[flatheadsteve]

I get 9mph out of my 1436 with 5hp 2 stroke. 8mph with 2 200lb adults and a 110lb kid. I got 23 on my 1648 with a 20hp 4 stroke. I'd pick up a cheap tachometer and check rpm. Prop hub could be slipping or maybe the prop is just too big and the motor is struggling to turn it.

 

[thill]

I've always seen 18 MPH or so with a 15 HP, but that's with older motors.

 

[Weldorthemagnificent]

Like mentioned, it's all guesswork until you get rpm reading. But my years on the water are telling me that 15 pushing two solid men on a narrow boat ain't horrible. Put a 150lb guy and a kid up front and you'll get into the 20's.

 

[aarolar]

Like mentioned, it's all guesswork until you get rpm reading. But my years on the water are telling me that 15 pushing two solid men on a narrow boat ain't horrible. Put a 150lb guy and a kid up front and you'll get into the 20's.

Even with just me in the boat I only hit 17mph matter of fact with me and my father (200 and 250) and a half a 48 quart cooler full of water it ran 15mph.

 

[fwman1]

My 1436 started out with a 6 hp. It would barely do 11 mph. A tach, two props, and some rearranging and it would do 14. You want to be on plane at the upper end of the rpm range of the engine. It could be that you have one prop for loaded down, and a different prop for running light. Tilt pin also needs to be at the best setting.

 

[LaqueRatt]

Best/easiest/cheapest way to tell how fast you're going in a small tinny? I'm curious, but not wanting to spend a fortune to find out.

 

[aarolar]

Have a tach hooked up headed to the river this afternoon see what happens

 

[airshot]

Best/easiest/cheapest way to tell how fast you're going in a small tinny? I'm curious, but not wanting to spend a fortune to find out.

Phone app if you have a smart phone or a handheld gps. There some cheap ones out there now....I have a couple old Garmin 12 units I let folks use to get speeds, even taped one onto my R/C car ro get speed readings. GPS is going to give you your most accurate speed...

 

[sonny.barile]

I had a 13 ft v hull aluminum with a 15 hp 4 stroke Yamaha tiller that would hit 28 + mph. My Tohatsu 9.8 would do almost as well………It’s all about having the right prop, rpm, and engine height…..Not to mention that each boat and how you load/balance it is different. If you want to dial it in for your specific scenario, it’s going to be a little work…….

 

[Crazyboat]

Small boat/motor packages are finicky when it comes to weight, hull condition, prop selection, prop condition, how well the motor runs, current etc. anything above 20 isn't bad, above 25 is real good. Under light loads, you lose MPH as weight goes up.