Boston Whaler has published performance data for a 2010 DAUNTLESS 230 with the VERADO 250, available at
http://bostonwhaler.com.s3.amazonaws.com/resources/230-Dauntless-Performance-2010.pdfThe test data was collected with an ENERTIA 18 propeller, and with rather warm weather, 86-degree air temperature and 82-degree water temperature, although probably saltwater. The VERADO was able to accelerate to 6,250-RPM and the boat speed was an impressive 51.9-MPH.
You report that your engine can only accelerate to 5,300-RPM, almost 1,000-RPM less than in the factory test report. In the factory test data there is no mention of a hardtop on the boat, so I will assume it does not have one. You describe your boat as having a "T-top." According to the specification sheet at
http://bostonwhaler.com.s3.amazonaws.com/resources/230-Dauntless-Spec-Sheet-2010.pdfthe T-Top was an option.
In general, the Mercury ENERTIA propeller has been found to be an excellent choice for use with the Mercury VERADO engine. The ENERTIA was designed specifically to produce more boat speed than other propellers, and does that by allowing the engine to reach higher engine speeds. I would not look for a different propeller type; the ENERTIA was the propeller of choice for Boston Whaler for their boat.
We have to look for reasons why your boat is not reaching the same engine speeds as the boat in the performance test. There are several possible causes.
The presence of a T-Top adds air drag, which will increase the load on the engine, and the added drag could cause the engine to not be able to accelerate to the same speed as on the boat in the test report that has no T-Top. I would expect the addition of the T-Top to cut down the top speed of the boat and reduce the engine speed range at full throttle. I would not think it would cut off almost 1,000-RPM, but that is just my speculation. It would be useful to get performance data about the 230 DAUNTLESS with the T-Top. I recommend you contact Boston Whaler customer service to see if they have any data on that situation. The difference in boat speed in the factory test between engine speeds of 5,300-RPM and 6,250-RPM is almost 10-MPH. That is quite a speed loss to be attributed completely to the added loading of the T-Top.
If you are not experienced with the operation of planing-hull outboard boats at speeds of 50-MPH, it is possible that you have not adjusted the engine trim for optimum speed. Perhaps your boat could exhibit more speed if the engine trim were carefully adjusted. Let us know your level of experience with operating outboard engine boats at this speed range.
Reduced engine speed could be due to damage to the propeller. Inspect the propeller to verify there is no damage to the blades, and the condition of the propeller is as-new. Any deformation or slight damage to the propeller could cause a reduction in boat speed.
Since the boat has the OEM propeller and an OEM accessory, it would be reasonable to assume that Boston Whaler expected that combination to work properly. Your report tends to show the engine is not accelerating into its expected top speed range. Verify that the Verado engine is in good tune and operating properly. Perhaps the engine needs some attention and service. It might be running on only five cylinders due to a bad individual cylinder spark coil (called "pencil coils"); these spark coils are know to be a problem.
Like many modern engines, the VERADO is not particularly designed for the owner to perform a lot of the necessary maintenance and service. While the engine has electronic diagnostics, they use proprietary electronic tools that are very expensive. Even among Mercury dealers, special training and specialized tools must be purchased in order to properly diagnose and service the VERADO engine, and not all Mercury dealers have undertaken the expense of those tools and training; those dealers cannot provide VERADO service.
It is a good practice for any owner of any modern outboard engine to have a relationship with an authorized service dealer that has a staff of properly trained technicians and a service department that specializes in the particular brand and model of engine to be serviced. Outboards are no longer the realm of the shade-tree-mechanic.
As an owner of a seven-year-old VERADO engine, you probably should do some reading at the website dedicated to VERADO engines, veradoclub.com. In much the same way that continuouswave is focused on Boston Whaler boats, veradoclub is focused on the VERADO engine. You can do a lot of reading there without having to join the club, and I would expect you'd find some good information.