CONTINUOUSWAVE

Give me performance data for a 1986 OUTRAGE 25 with a 250-HP and with a 300-HP engine.

BACKSTORY

I currently have a 1986 OUTRAGE 25/with a HONDA BF250 engine and a four-bladed propeller. I plan to re-power soon. I am kicking around the idea of moving up to 300-HP.

The present top speed is 44-MPH with a light load. Fuel economy peaks at 4.1-MPG at 24-MPH. At 35-MPH fuel economy is 3.0-MPG

I do not have any actual data that I myself have compiled about an OUTRAGE 25 with 250-HP or 300-HP, but I can make a prediction on the speed increase that will occur if your boat is re-powered with a 300-HP engine from its speeds with its current 250-HP engine.

My prediction is based on the work of naval architect George Crouch who developed a formula for predicting the planing speed for moderate V-hull boats based on their weight and horsepower, along with a coefficient that encapsulates the hull form and speed units.

Using your data for 250-HP, to predict for 300-HP will be quite simple. The only assumption will be that the total boat weight will remain the same. The top speed will increase by the ratio of the horsepower change to the 0.5-exponent.

As your boat is now able to reach 44-MPH with the 250-HP engine, with a 300-HP engine the top speed would be expected to increase to (300/250)^0.5 * 44 = 48-MPH.

I have developed a calculator based on these principles. See

Crouch's Calculator
https://continuouswave.com/calculators/crouchCalc.php

In your instance, it is really not necessary to know the weight or the hull coefficient, as the only element assumed to change is the horsepower. If the new 300-HP weighs more than the current HONDA BF250 (which would be hard to imagine it could), then the increased performance would be reduced due to the extra weight.

For the classic OUTRAGE hulls of the 1980's the hull coefficient is generally thought to be in the range of 180 to perhaps 190.

My calculator can also deduce the total boat weight, so assuming the hull coefficient were 180, your total boat weight is about 4,180-lbs, based on the power and speeds you report.

ASIDE: generally the price of an outboard engine is in proportion to its horsepower. I would consider if the 4-MPH anticipated increase in absolute best top speed will be worth what I would expect will be an increase in cost for the 300-HP compared to the 250-HP engine. Unless you are habitually running the boat at full-throttle, the amount of time spent at either 44-MPH or 48-MPH is probably only a small portion of the total time underway, maybe less than 5-percent if your use is typical.

Another consideration: to realize the added 4-MPH you may have to optimize the propeller for the 300-HP engine. Buying a new stainless steel propeller is going to cost an additional $600, so add that cost to the engine cost for the extra 50-HP you will be getting.

bcoastal wrote:Fuel economy peaks at 4.1-MPG at 24-MPH.

Your fuel economy data is very impressive. With 140-gallons of fuel tank capacity, your range at cruising speed would be about 550-miles. Even at 24-MPH that is underway for almost 23-hours, a very impressive endurance.

That 140-gallon fuel tank was likely intended for a c.1986 boat powered by twin 225-HP engines using two-stroke-power-cycle design with carburetors, which would be quite less fuel efficient than your single HONDA BF250. A full tank of 140-gallons would add about 875-lbs to the boat. That is a lot of added weight which will also affect top speed potential.

Good points. I will probably stick with a 250-HP engine, since that is all that is offered by Honda. And I do like my Honda mechanic.

I changed out my 140-gallon tank for a 100-gallon tank when I replaced it. The back was left open to drain water. I thought a 100-gallon capacity fuel tank was enough—and it is.

ASIDE: To hear you’ve been keeping that 1986 OUTRAGE 25 going is very good news. That hull is a really great design, the big-dog of trailerable classic-era Boston Whaler center consoles (and REVENGE models). The next step up in classic-era hulls was the 27-footer, which is much bigger, heavier, needs a lot of twin engine power, and cannot be easily trailered because it is very heavy so it needs a very big trailer and big truck, and the rig too wide for legal road use without permitting.