another estimate of fuel usage.

[viper1]

A 3.0 Merc. cruse in a 221 Islander Hard top. Prop approx 22 pitch. Says it will run at 35 or so with 4 men and gear.

 

[Chris1956]

I would think that boat/motor combo be near wide open, to achieve that speed. I would therefore expect poor economy.

 

[viper1]

According to owner. He opens up till its on plane, which he says is quickly. Then backs off to any where between 20-25 . Claims he got 4 day trips, out 13 mile and trolled 4-5 hours and back on less then 40 gal. Not sure what that would come out to though.

 

[Mischief Managed]

If it truly tops out at 35 with 140 HP, it should get around 4.5 to 5 MPG from 20 to 25 MPH.

 

[thumpar]

What is the WOT? 22 pitch seems a little steep for that combo.

 

[viper1]

Well he says 2 Large adults, 2 regular size and equipment 35 MPH by GPS. I asked what he considered large and medium. Large 250+ and medium 150 avg. I also got 3 props with it. The one now he said was a 22 pitch the other were less.
Now my 191 had same setup. And i could get 30 with 3 people and gear. of use large. I did great on gas. But most times i cruised on plain around 20-22 too! For the gas mileage.

 

[steelespike]

At 4 mpg it would be about 26 gallons for the 4 trips out and back.Leaving about 14 gallons for trolling.
I do wonder about a 22" prop lugging the motor.What is the wot rpm and gps speed,lightly loaded?

 

[viper1]

LOL! 22 pitch not 2 inch on the prop. Cant give you the rest, as i just got the boat. Just trying to get an idea, also killing time before may 1st. We troll around 2-3 MPH i would think trolling it would really milk the gas.

 

[airdvr1227]

I'd be surprised if a 3.0L could push anything with a 22 pitch screw.

 

[thumpar]

Not speed WOT. RPM WOT is what is needed. You need to make sure the motor is not lugging. If anything you want to be underpropped more than overpropped.

 

[Watermann]

Your going to just have to run the set up starting with a full tank and see how she does to have any certainty about it. About all we could do is SWAG it.

Yeah a 22"p prop sounds to me like it's a couple inches too much. I believe most boats of your size running the 4 banger are at a 19"p, maybe 20"p.

 

[achris]

Yeah, I'm with everyone else. Those numbers are NOT right.... I've just run my prop calculator and something is off.

If the boat is getting 35mph with a 22" prop, the max revs are at around 4000, which is way too low (that engine should be doing 4400 to 4800 at wide open throttle)....
If it is making the right revs with a 22" prop, (which in a 22' boat I would SERIOUSLY question!) then the speed will be more in the order of 42mph...
To make the right revs at 35mph it would have to be running a 17" or 19" prop....

But the big kicker is 140hp in a 22' boat... 35 yes, but not mph, more likely kph.... But running a 22" prop, NO WAY! Think more in the order of 15 or 17"....

Chris......

 

[viper1]

Well like i said just going what he said. I really don't understand the revs verses pitch. Id would think lower rpms would be better. But now i'm all confused!
lol! He gave me two other lower pitches. But said top end was lower. Is there a way i could figure this out of water?

 

[achris]

Well like i said just going what he said. I really don't understand the revs verses pitch. Id would think lower rpms would be better. But now i'm all confused!

The engine manufacturer quotes a rev range that the engine must achieve at WOT (Wide Open Throttle). For a Mercruiser 3 litre it's 4400 to 4800rpm..

The way to achieve those revs is to take the boat for a test run. If the maximum revs are too low, you need less pitch in the prop (reduces the load and the revs rises)... If you run with too higher a pitch prop you WILL burn valves and detonate pistons. The engine is 'lugging'...

lol! He gave me two other lower pitches. But said top end was lower. Is there a way i could figure this out of water?

No....

Only way is to put them on and test run the boat in the water.

Before you buy, make sure you go for a test run. Make sure the boat performs as advertised, and that it is making the max revs range at WOT. If it isn't and he's been running it that way for a while, it will have done damage to the engine.... (that's not a 'maybe', that a 'for certain')

Chris......

 

[viper1]

Well I would but seems i always shop in the winter. And it cost me on one boat so far as i had to install a new engine. Piston rod pin cut a grove into a cyl. Not And i'm a mechanic too! Just started on Boats a few years ago. I understand the specs. But not totally with boats. And pitch i have no experience with. He said this engine ran smooth with the prop that's on and attained plane quickly. I checked the boat out rather well And every thing was maintained well. So i'm thinking hes telling the truth to the best of his ability. I know my 191 rarely got above 3000 rpm. But figured the prop pitch was to low. But i kept it that way as it allowed me to troll as low as 1.4 MPH and top End was about 30 MPH Wish I could tell you what the pitch was on that prop but i can't. But it got extremely good mileage. And purred at all speeds. I did think the idle was a bit high. But the only complaint i had. And at trolling speed it wasnt gallons per hour, it was more like hours per gallon. Guess I was hoping to hear the same.
Oh yes and i to expected a 6 or a small 8 in this. Actually this year im told had a choice of 6 engines...

 

[achris]

Personally, If I can't drive a boat or car I'm about to buy, I walk away... Especially a boat! And why is shopping in winter a problem?

Also, as I said, and numerous others, the numbers don't work... Something's awry... In which case, don't walk away, RUN.. :bolt:

Chris......

EDIT: Dive over to the props forums and have a read... There's plenty about the relationship between pitch (the amount the prop will move forward in one revolution) and the engines' maximum achievable revs....

 

[viper1]

Well I have enough confidence in my skills that if a boat is structurally sound and checks out to me. Then its more about the savings. Every one knows Boats are the biggest money pits. As they say the two best days in a boat owners life is day 1 and day of sale. LOL! But i bought because i wanted one for so long and the price was good enough to warrant a risk. If i was the drive and put gas in type I would agree. But im more into working on them and fixing them up to what i want. A new boat would never make me happy. And another reason is, have you ever tried talking a man out of his boat cheaply while hes doing good catching fish, or sking with some pretty ladies? LOL!

 

[thumpar]

If the prop is too big on a boat and it can't reach full WOT the engine is lugging. It doesn't matter if you only run at a low RPM and never try to get to WOT it is still lugging the engine and it will ruin it. It is OK to be underpropped as long as you don't overrev the engine but don't overprop.

 

[viper1]

Prop is right size. The question is pitch.

 

[thumpar]

When I wrote to big I meant to big in pitch.