14mph speed

[Lil Willie]

I have a 2005 Sun Tracker pontoon with. 2005 Johnson 50hp 4 stroke motor. It will not go over 14-15 miles per hour. I have put a new fuel tank, line and pump bubble as well as 4 new spark plugs. Still doesn't seem like it is as fast as it was last year. Any suggestions?

 

[Lil Willie]

I have a 2005 Sun Tracker pontoon with. 2005 Johnson 50hp 4 stroke motor. It will not go over 14-15 miles per hour. I have put a new fuel tank, line and pump bubble as well as 4 new spark plugs. Still doesn't seem like it is as fast as it was last year. Any suggestions?

Might also add it is 21ft long.

 

[Scott Danforth]

If your RPM is the same, but your speed is down, look at load, and if the logs have water in them

 

[Lil Willie]

If your RPM is the same, but your speed is down, look at load, and if the logs have water in them

The rpms are the same. It's not winding up, still running smoothly and the toons are empty.

 

[HotTommy]

Are you comparing tachometer RPM from last year to now? What were they?

Here's the basic science. Top speed is determined by the maximum power output of the engine and the total drag (water and wind) of the boat. The propeller allows you match the point where your engine produces its maximum safe power to the speed at which that amount of power is required to move the boat. So, if your boat is slower now than before, one or more of three things has happened. One, your engine is not producing as much power as before (e.g., lower RPM, lower compression, reduced fuel flow, etc.). Two, your boat has more drag than before (e.g., heavier load, added bimini top, motor lower than before, boating into a headwind or strong current, etc.). Three, the propeller has become less efficient (e.g, damaged blades).

In order to know which of these many things is the root cause, you (and we) will need more specific information. Otherwise, we're just guessing.

 

[ahicks]

I would add a few more factors. First would be the condition of the logs. If they're all crudded up, that's a lot of drag. Another big deal - weight, especially if misplaced. (too much on front, or rear). Doesn't take a lot. What about the prop condition? Trim angle?

Best case, in my experience anyway, is for that boat to do something in the high teens - IF - it's lightly loaded, as in just you on board. Point being, everything needs to be just right for that to happen. Dirty 'toons, a nicked prop, and a little extra weight, together can add up to just not enough poop to get the boat up on top, where it can pick up a couple MPH. -Al

 

[HotTommy]

ahicks makes good points and I'd like to expand on one of them. Suppose a boat engine makes peak horsepower at 5500 RPM and the boat is setup to reach maximum speed at that RPM when conditions are ideal. If you take that boat out on a day when there is a 5 MPH headwind, the extra drag may prevent the boat from reaching a speed that allows 5500 RPM. That means the engine is now producing less than maximum horsepower. So in this case the effect of the headwind is amplified by a drop in power making the drop in top speed even greater. That illustrates why it is difficult to diagnose the many "its not as fast as last year" threads we see. Unless there is an obvious cause (e.g., I gained 100 pounds during the pandemic), it can be a tricky problem.

 

[Rabbit929]

whats the possibility that your fuel is of ****-poor quality, after sitting all winter? Octane in modern fuels drops fast during storage, which would lead to it feeling sluggish.
The other thing to check is to make sure your hub isn't beginning to slip. Put a mark on it, run it, and see if your marks still lined up.