330 Express Performance

[Knot'N Line]

Looking for opinions. I have an 05 330 Express with twin Yamaha F250's. The props are 15 x 15 SWS. In good sea condition and all trimmed up I get about 1.2 mpg which seems to be in the normal range. My concern is that I am running 4700 to 4800 rpm to get that. The performance charts on the Grady website show lower rpm, but without a painted bottom or enclosure. They also use a 15 3/4 x 15 SWS prop.

I guess my questions are:

Should I be concerned about running at that rpm?

Would changing props from 15 to 15 3/4 lower the optimal rpm range?

Just trying to see what the experts think.

Thanks for reading.

 

[seasick]

I am not sure what you are asking. Is the fuel burn number your maximum across all revs or is that the range where you usually cruise? I would expect the sweet spot for fuel burn to be at lower revs. How are you getting the burn numbers?
What are the WOT rev values? That will be a better figure to use to see if you are over/under propped.
Finally, there is no magical answer. prop selections is always a trade-off between performance characteristics and fuel burn

 

[magicalbill]

Seasick;
I think he's asking if he should be worried about spinning the mils up in that high RPM range all the time; will it prematurely wear the engines out?

I have 3 friends in my Grady group that have the exact same boat and powerplants. They run similar fuel burn numbers to yours and rev the engines 47-4800 all the time. The 250's I think, were all that was available then for power. I would certainly opt for the 350's or 300's if I was equipping one for me today.

Props? I'm no expert, but I can say, as I did above, that your numbers match up with my friends boats, so I would consider it normal.

Concerns about the RPM's? Frankly, I would be, but others do it and it seems to be alrite. Just keep 'em serviced.

 

[ElyseM]

i agree with the comments. i get the same fuel burn over almost a 10 mph range. low end equals low rpm and high to high. i trim out both tabs and engine to achieve best performance. pay closer attention next time you are out to see whether you can replicate what i am saying. and yes, different props will yield different results from the performance bulletin. good luck, ron

 

[seasick]

Seasick;
I think he's asking if he should be worried about spinning the mils up in that high RPM range all the time; will it prematurely wear the engines out?

I have 3 friends in my Grady group that have the exact same boat and powerplants. They run similar fuel burn numbers to yours and rev the engines 47-4800 all the time. The 250's I think, were all that was available then for power. I would certainly opt for the 350's or 300's if I was equipping one for me today.

Props? I'm no expert, but I can say, as I did above, that your numbers match up with my friends boats, so I would consider it normal.

Concerns about the RPM's? Frankly, I would be, but others do it and it seems to be alrite. Just keep 'em serviced.

What speeds do your friends get at 4700 revs? I am curious.

 

[Knot'N Line]

Thanks for the reply Seasick. Believe it or not, I don't know the WOT. The fuel burn comes from the fuel management gauges on the boat. I am just trying to determine if running at 47-4800 is too high or if I should dial that down with different props.

 

[Knot'N Line]

My speeds at 47-4800 is around 28 mph. 30 in smooth water.

 

[alfa1023]

Similar performance as above, with fuel burn and speed varying a little dependent on load and condition. Props are 15 3/4 X 15 Yamaha SWSII. My sweet spot for GPH seems to be in the 4600 - 4800 rpm range getting around 1.2 mpg, running anywhere from 28 to 32 mph (heavy load, offshore waves to light load inshore smooth).

Running at continuous 4800 rpm seems unnerving, but - several Yamaha mechanics have told me that is better on the motor than running slower/lower rpms, which is actually making the motors work harder with this big/heavy boat.

 

[family affair]

If your props have ever been serviced, it is not unlikely for them to be a little "off". If you really think you are over revving from what Grady tested, try getting the props cupped. Way cheaper than new props and the result could be just as good.

 

[magicalbill]

Seasick;
All of my buddies boats get roughly 30MPH at 4700.

 

[NOTHING ELSE MATTERS]

You are under propped. You need 15 3/4 prop for your boat. I bet you revving more than 6000 RPMS.
Had the same boat(2007) with the same motors and i was getting 1.2-1.3 at 30-32 mph.

 

[grady33]

Went canyon fishing yesterday and burned about 185 gallons on a 180 mile round trip. Headsea entire way out and rough seas for part of say. We ran a little hard coming home...and I was getting 28-30 burning 32-34 GPH give or take. No idea on rpm.

 

[chub2000]

I have the same setup with 4 blade props. I always seem to get 1mpg at all rpm ranges.

 

[Knot'N Line]

I have to give Grady White credit. I submitted the same questions as above on their website and a tech rep called me to discuss performance. He was very helpfully and informative. I'm not sure many other major companies would do that for an 8 year old product. Way to go GW!