CONTINUOUSWAVE

I re-powered my 2000 Outrage 21 with a Honda 250-HP outboard.

GIve me a propeller recommendation.

The engine is mounted [please describe the engine mounting height as explained in the article Engine Mounting Height. Do not attempt to describe the location of particular hole in the engine mounting bracket.--jimh]

I have no performance data.

There are three Group-24 batteries for the trolling motor for a total of five batteries.

The Honda calculator recommended a three-bladed SOLAS LEXOR propeller, 15.25-inch by 19-pitch, based on data entry:
Dry weigh = 3000-lbs
Gear Weight = 1000-lbs
Fuel Volume = 125-gallons
Motor weight (added automatically) = 622-lbs.

[The engine is mounted] on the [please describe the engine mounting height as explained in the article Engine Mounting Height". Do not attempt to describe the location of particular hole in the engine mounting bracket.--jimh]

The propeller that was used on the previous engine is a 15-inch by 17-pitch.

The previous engine was a 200-HP OptiMax.

Please describe the engine mounting height as explained in the article Engine Mounting Height". Do not attempt to describe the location of particular hole in the engine mounting bracket. Read the linked article and reply with one of these possibilities:

• lowest possible mounting height
• one-hole up from lowest
• two holes up from lowest
• three holes up from lowest
• four holes up from lowest

A "hole" is a unit of measurement equal to 0.75-inches, the spacing of the holes.

What is the gear ratio of the HONDA 250?

What is the maximum engine speed recommended for that engine by HONDA?

Do you have ANY data about the boat speed at a particular engine speed with the new HONDA 250 engine?

Do you have ANY data about top boat speed with the 200-HP engine?

Propeller selection is part science and part art.

Key elements are

• the lower unit gear ratio,
• engine wide-open throttle (WOT),
• and target WOT speed

Given you do not include the year of purchased for the engine, I will presume the Honda 250 is the current BF250 model that has a lower unit gear ratio of 2:1 and a WOT limit of 6300-RPM/

Recommendations for the BF 250 installed on Boston Whaler's include:

17-pitch MIRAGEplus at two-hole-up mounting
18-pitch Enertia
17-pitch REVOLUTION4

I would start with the 17-pitch MIRAGEplus propeller.

[The engine mounting height is] the lowest mounting possible.

The engine type is a HONDA BF250.

The maximum engine speed is 6,300-RPM.

I would use your current propeller, if that propeller will fit. Then go from there.

I would raise the engine to a two-holes-up from lowest mounting.

Using the Crouch method for speed prediction and these inputs:

LBS = 4750 (from data supplied by the OP)
HP =250
Hull Factor = 190 (typical for a fast Boston Whaler moderate V-hull boat)

the predicted top speed is 44-MPH.

Using a propeller calculator with input

RPM = 6000
RATIO = 2
SLIP = 10
MPH = 44 (i.e., the predicted top speed possible)

and solving for PITCH, the propeller pitch is calculated as 17.2-pitch.

I think starting with a Mercury MIRAGEplus 17-pitch three-blade propeller is a good suggestion.

The second recommendation for the MIRAGEplus propeller came from:

http://continuouswave.com/ubb/Forum4/HTML/007768.html

Scroll down about two-thirds through the thread.

The Honda 250 has a 2:1 gear ratio and a 5300 to 6300 RPM [full-throttle] operating range. The suggested operating range is 2,500 to 4,500-RPM. I rarely run my 2013 250 Honda above 4,500-RPM as the fuel mileage drops off appreciably above that.

I would think you could turn a 21" pitch. I'm running a 15.25 x 17-pitch four-blade on my 1993 23 Walkaround. Engine speed at full-throttle is 5,800-RPM.

A lot more boat at length 23-feet 9-inches, dry weight 4400, fuel capacity 150 (about 1000-lbs), and gear weight around 1000-lbs. And the boat has a T-Top.

A Powertech OFS4 15.25 x 17 four-blade propeller gives top speed 39 to 40 [MPH] at 5800-RPM. The boat jumps on plane. Fuel mileage 2.3 to 3.0 MPG across operating speed of 12 to 28-MPH and about 3300- to 4500-RPM.

A Yamaha 17-pitch three-blade stainless (I think it was a saltwater series 2) gave top boat speed of 41 to 42 [MPH] at 6300-RPM. Planing time was decent. To hold plane is harder than with [the OFS4] four-blade propeller. Fuel mileage was around 2.5-MPG

Running a 15.25 x 19 Solas three-blade the top speed was 40 to 41]MPH at 5400-RPM. [The acceleration from a standing start was], doggy. Fuel mileage was less than 2.5-MPG. The boat tended to fall off plane at slower speeds.

I would stick with a 17" Mirage as it is a more aggressive prop than others. The suggestion to run a 21 would not work. 4 strokes like to be propped at the higher bad of the redline, not lower or else you will have planning problems and poor economy as sited above. The old mindset that running lower rpms means better economy does not work on modern engines. Some engines will get very close in MPG over a pretty long range of cruise speeds. Again, I think using your old prop would be a good start.

Thank you for all the suggestions.