1996 225 Mercury Offshore (carb)

[Fletch170]

Quick question, I think I'm going with a 19 inch pitch prop. What is the proper (pun intended) diameter for the 225, on a deep v, heavier boat?

Also, we have a lot of shallow sandy bottoms up here....I'm concerned with screwing up a $400 stainless wheel. For this application, what are the pros and cons of running an aluminum prop? Outside of a possible annoying "hum" I got with the Solas prop on the 17 AS.

Kind regards,

Christian

[Fletch170]

The Mercury website is suggesting a "black max" aluminum prop with 21 inch pitch, and 14.25 diameter. Scott, do you remember the dry weight of the 2100 cc? I believe it was around 2200 pounds??

[gran398]

Hi Fletch,

I'd definitely run a stainless wheel. Most damage occurs in oyster rock around these parts, and normally you hit it with a rounded file you're good. Running them aground in sand just keeps them polished up pretty

Re the weight, seems like you're right there...#2250 sticks in my mind.

Ran an old 175 cross-flow Evinrude on mine. Not a speed-burner, upper 30's WOT. But that little boat would leave behind anything under 25 feet in the ocean.

CAN'T WAIT for you to run her!

[Fletch170]

Cool, I'll look around for a decent used one. Found a 21" 13.75 Mercury prop that looks the part for 180 bucks.

[Fletch170]

So, Ive done a lot of research on how much fuel this thing is going to burn. I know the answer is "A Lot", but I'm getting responses all over the map. Guys who are running twins, getting one MPG...but I have to assume each engine is working less to make a cruise speed. I have seen guys running boats around the weight and size saying they are only getting about 1MPG.

I know this is a loaded question, as there are variables, but is 1MPG really all i'll get from this thing?

Right now, I'm planning on a 21 inch prop, 14.65 diameter prop. Boat with fuel/ gear and motor will be around 3300 pounds. 22 degrees of deadrise.

Thoughts?

[fitz73222]

At full throttle, a carb'd two stroke outboard will burn 10% of it's rated HP in gallons per hour. This is a long standing equation that has stood the test of time. There really isnt a 1-1 ratio of throttle setting relative to fuel burn at lower rpm's since every hull and propeller combination have different sweet spots for speed over mpg. It seem for most applications, 4000-4200 seems to be the best mpg for the average outboard. This is why a flow scan (or equivalent) is so handy for these discussions. I would say you you should be seeing 2-2.5 mpg at cruise which is reasonable.

[Capt. Bob]

My 200hp Yamaha has an average of 2.45 mpg as per my flow scan. The ideal spot is indeed 4200 rpm.

[Fletch170]

 :You_Rock_Emoticon:

Thanks guys. Everything I read about this 225 offshore says it has a smoking and drinking problem:) I'm OK with that, because, according to the reviews, it's a very reliable motor. I've done all the things to make sure it stays that way.

I dont know if a flow scan really makes sense for me, Sure, it's cool, but $500 is a lot for one of the flowscan models. Is there any less expensive, decent alternatives?

I'm am looking down the barrel of a pretty expensive build list, (Seastar, t top, Simrad NSS7, Starboard doors and trim work, Coosa for the transom....etc) you can see why a flow meter might be down on the list:)

[Fletch170]

Whats up guys, pretty simple question here, that I cant seem to hammer out by searching the internet.

I got a temp gauge, which came with a sender unit. I see the bung were it is inseted at the bottom of the jacket.

So, the overheat sensor measures the temp of the head itself, not the water, correct? I want to make sure im not supposed to just piggyback those wires. Thoughts?

[Capt. Bob]

So, the overheat sensor measures the temp of the head itself, not the water, correct? I want to make sure im not supposed to just piggyback those wires. Thoughts?

I can't speak for your Merc but on my Yamaha, the sensors are pressed into the heads and you can remove them by hand. They make contact with the head case rather than the actual water itself. I have two plugs, one each on top of the heads that allows the install of a water temp sensor on the right side and a water pressure "sensor/fitting" on the left. These both would be in contact with the actual water. I'm thinking your setup is similar. They would not be wired together (temp to sensor)

Good luck.

[fitz73222]

The temp sensor measures and responds to cylinder head temp and feeds the overheat signal to the temp gage in the form of a resistance measurment. This can be attached to your tan wire, already in your wiring harness.

[Fletch170]

Understood. I'm guessing though, water temp would be a better indicator as to what the motor is doing?

[Capt. Bob]

So, the overheat sensor measures the temp of the head itself, not the water, correct? I want to make sure im not supposed to just piggyback those wires. Thoughts?

I can't speak for your Merc but on my Yamaha, the sensors are pressed into the heads and you can remove them by hand. They make contact with the head case rather than the actual water itself.

My bad, the "sensors" I was referring to are thermal switches that complete a ground when they reach a specified temperature range, thus sounding the alarm horn. I thought that was the wire you were referring to. The sensor that came with your gauge would have its own wire to act as Fitz described. On my Yamaha two are required, one each for the two alarm switches (I'm assuming they are connected to one main wire in the harness) and another dedicated to the gauge sensor itself (if you had an optional temp gauge).

[Fletch170]

Thanks Guys! I figured they were seperate, but I wanted to be sure. As always, I appreciate the help.

-Fletch