CONTINUOUSWAVE

This summer I picked up a 2000 Dauntless [22] with a 2000 Mercury OptiMax 225. I was continually able to get a top boat speed of 47 or 48-MPH at an engine speed of 5800-RPM at full throttle, with just myself aboard and with my wife and daughter on the boat.

Recently the boat speed was unable to get over 42-MPH, but the engine speed was still at 5,800-RPM. I have made three outings, by myself and with the family. and boat speed is repeatedly maxing out around 41 to 42-MPH.

I did add fuel to the boat but only about 30-gallons. All speed readings are [Speed Over Ground] by GPS receiver.

Yesterday I intentionally went out and back on the same track, trying to get over 42-MPH; the speed was consistent.

The only other change was the addition of a strainer scoop for the live well water intake. It was missing when I purchased the boat.

It was speculated that the water intake strainer could be causing aeration or some other water flow disruption over the propeller. But the water intake scoop and strainer is in the factory location, so this seems unlikely to me.

The hull and engine are clean; the boat is kept on a trailer between use.

The fact that the engine speed is the same throws me off.

[Give me your] thoughts.

My next plan is to remove the strainer for a test run.

If you are reaching the same WOT engine speed, I would proffer the following variables are affecting performance:

- sea state
- wind
- current
- air temp
- relative humidity
- strainer
- boat weight (daughter growing, fuel load, gear etc.)

Since the engine is a Mercury, you probably have a Mercury propeller that is using a FLO-TORQ hub. Check the hub to see if there is any sign that the plastic coupling between the propeller shaft and the propeller hub is slipping. Look for circumferential scratches on the surface of the propeller that bears on the thrust washer. Look for signs of distortion on the plastic hub. There is 225-HP being transmitted through that small surface of the plastic, and it could be slipping.

The airy water explanation sounds plausible to me. I expect that the through-hull and stainer are probably rather close to the keel centerline. If they are located in the aft live well, they would be close to the engine.

The only water pick-up scoop and strainer I have seen on a Boston Whaler was installed very far forward, near the center console on an OUTRAGE 25 hull with twin engines on a long set-back bracket, thus plenty of separation between the pick-up strainer and the engine gear cases.

Q1: What is the location of the water inlet scoop-strainer relative to keel center line and to bow and stern?

The water pick up strainer on the 2000 Dauntless 22 is only about two-feet forward of the transom and about six-inches from centerline. It is in the original location as factory designed. Perhaps the original was a lower profile than the one I used, which is only raised about half-an-inch--but I can easily picture a flatter more recessed strainer.

I'm going to do some searching for the original part number: found the part number and the factory part looks identical to what is on the boat now.

Don't want to be Captain Obvious here (but): remove the strainer and take it for a run.

Did you hit a button and change [the speed units on the chart plotter display] to knots from MPH? That would be about correct as 42-knots is 48-MPH.

Lastly--check the propeller, too.

ASIDE: I have always admired the lines and look of that DAUNTLESS 22 center console boat.

Q2: Is the sea strainer in line with the prop's path and is it causing disturbance in the water flow to the prop?

"The only other change was the addition of a strainer scoop"

Q3: Is the sea strainer cover an original item Whaler installed part?

Q4: did you add it?

Q5: In other words is it like original now or did you add something new?

Q6: What was missing when you got the boat?

I would take off [the part you added] and run [the boat]. I am thinking [the cause of the speed reduction is the propeller is running in aerating water and] not [caused by an increase in] drag.
Archie

Please post a photo or a link to a photo that shows the strainer device you installed.

From the wonderfully organized and amazingly complete selection of factory drawings made available by Boston Whaler under their RESOURCES tab at WHALER.COM, I found a drawing at

http://bostonwhaler.com.s3.amazonaws.co ... 4-2000.pdf

that shows the through-hull rigging on a 2000 DAUNTLESS 22. Here is an excerpt from the drawing:



Q7: Does the strainer you installed look like the one seen above at callout 15?

Q8: Did you orient the strainer as shown in the assembly drawing, with the vertical open grating toward the bow?