REVENGE V-22 Re-power

[colderbythelake]

I am re-powering a c.1980 Revenge V-22 with a dry weight is 2,350 lbs with a Yamaha VF175XA.

Give me recommendations for a propeller.

ASIDE: The outboard engine dealer has had no success getting information for a propeller from Boston Whaler.

This REVENGE V-22 has a fuel tank capacity of 70-gallons. The boat is set up for fishing on Lake Superior. There is a 9.9-HP auxiliary engine made by Yamaha. There are two batteries in the stern. In the aft cockpit there is a live well that may hold 20-gallons.

There is seating for two and a removable jump seat.

Across the stern there is a steel mounting bar on which three electric downriggers are mounted. There is a steel radar arch with more rod holders. There is canvas with aluminum frames. The anchor is aluminum. The electronics are usual. As much as 100-lbs of additional gear is possible.

[jimh]

The outboard engine dealer has had no success getting information for a propeller from Boston Whaler.

This should not be a surprise. You are asking about a boat made 43-years ago. There is no possible basis to assume that Boston Whaler would have any test data for a 43-year-old boat with a 2023 modern engine manufactured by a competitor company. All modern Boston Whaler boats are rigged only with Mercury engines, as both Boston Whaler and Mercury are operating division of the Brunswick corporation.

There is no reader who can make a guess at the TOTAL BOAT WEIGHT that would be more accurate than you can deduce by your own knowledge of the boat weight, the engine weight, and the weight of gear, fuel, and people who will be aboard the boat in normal operation.

If you can give a reasonable figure for the total boat weight, then a reasonable figure can be estimated for the expected boat speed with 175-HP.

For purposes of starting a discussion, I assume the the total boat weight will be 4,500-lbs. The expected speed at full power can be estimated with the Crouch Method, assuming a hull factor of 190. See the calculator I have created at

CROUCH'S CALCULATOR
https://continuouswave.com/calculators/crouchCalc.php

I now continue with these inputs to the Crouch's Calculator
HP =175
LBS = 4500
HULL FACTOR = 190
MPH = TO BE CALCULATED

The calculated maximum boat speed according to the Crouch method is then

37.5-MPH

Now you must provide the following information about the engine:

GEAR RATIO
MAXIMUM ENGINE SPEED AT FULL THROTTLE

For purposes of starting a discussion I will assume the engine gear ratio 1.86:1 and the maximum engine speed is 6,000-RPM

A propeller can be calculated with my PROPELLER CALCULATOR using input on the engine information, the anticipated boat speed as already calculated, and the anticipated propeller SLIP. For more about the method of pitch calculation see my calculator and the basis on which it works at

PROPELLER CALCULATOR
https://continuouswave.com/calculators/propCalc.php

I now continue with these inputs to my propeller calculator
RPM = 6000
RATIO = 1.86
PITCH = TO BE CALCULATED
SLIP = 15
MPH = 37.5 (as predicted for the hull, power, and weight using the Crouch method)

Now, based on all the ASSUMPTIONS made as described above, the calculated pitch is then 14.4-inches.

For general use a three-bladed stainless steel propeller that is as large in diameter as the propeller aperture can accommodate with a pitch of 14-inches should be TESTED on the basis that the propeller can be returned if the boat performance is not satisfactory. You may find that a propeller of 14-pitch is difficult to find, so an alternative first trial run pitch is 13-inches.

The next step you must complete is to give the boat a thorough sea-trail with the initial propeller selection, and then report all related data. For advice on what data to collect in a test run of a new propeller, boat, and engine combination, read the article pinned at the top of this forum:

Propeller Testing: What Data to Collect; How to Evaluate that Data
https://continuouswave.com/forum/viewto ... f=7&t=7196

[jimh]

What engine mounting height have you INSTRUCTED the engine dealer to install the engine on the transom?

[colderbythelake]

Thank you for your helpful and informative reply. You asked a question re: engine mounting height. Can you be more specific as to factors that need to be considered?