DF300 prop question

[JNoel81]

I just repowered my 24' Grady White Explorer with a new 300 Suzuki rigged with a 18.5 pitch prop. On a very light load and trimmed out all the way, I am at 5650-5700 at the most. My fuel mileage is not quite what I expected at 2.5mpg, which is not bad, but I have read from several other getting 3+mpg with the same set up. My mechanic who rigged the motor says if it is hitting 5700 then it is fine at the bottom end of the max range. Any thoughts or suggestions on going down to a 17 pitch? Thanks

[MPUSMC_68]

DF300 Prop Question

There is a web site called Propgods.com
When I repowered my Hydrasports 230 from a 200hp Johnson to a
Suzuki DF250 I was able to get assistance from Ken at PropGods.com.
I purchased a Mercury Rev4 21 pitch prop from Ken. Initial run resulted in a speed of 42mph at 5600 rpm max. This is a decent point, but I'll probably need to raise the engine up one hole for a slight increase in rpm.
Then I can figure out the fuel enconomy.
All said I was pleased with the help that I received at PropGods.com

[hrly-lvr]

I'm using a 20X16 prop. on a 24 Pro-line and get the same readings, my understanding is the fuel will increase as the motor breaks in. But going from a 2 stroke (1.1 MPG) to 4 stroke I'm already happy (2.6 MPG). I only have 14 hours on motor.

I won't change prop's I also concerted that option, but choose to wait until I have more hours and tested in different conditions. (amount of people, gear and seas)

With six people, fishing gear, scuba tanks (4), approx. 80 gals. of fuel and food, I was still able to obtain 42 MPH on plain.

Video: http://www.youtube.com/watch?v=1BsJr...ature=youtu.be

[noelm007]

If you are going to load with 6 people and all their dive hear, then perhaps the next size prop down might be a good option, also be 100% sure your motor is as high as it will go without problems.

[hrly-lvr]

Well I took the boat back to the dealer and they raised the motor up 2 holes and changed the prop to 16x18 1/2, 3 blade and it was like having a different boat....

It got up on plane faster, 51.1 WOT @ 6100 RPMS....

[barrell]

I just repowered my 24' Grady White Explorer with a new 300 Suzuki rigged with a 18.5 pitch prop. On a very light load and trimmed out all the way, I am at 5650-5700 at the most. My fuel mileage is not quite what I expected at 2.5mpg, which is not bad, but I have read from several other getting 3+mpg with the same set up. My mechanic who rigged the motor says if it is hitting 5700 then it is fine at the bottom end of the max range. Any thoughts or suggestions on going down to a 17 pitch? Thanks

Ive had three suzukis and they tend to gain about 200 rpms after 100 hours. So I wouldn't mess with props until that time. I always like my motors to reach redline with the prop. I know running at 6300 scares a lot of people who baby their motors but Ive put thousands of hours on my motors with zero problems.

[300HP32168]

Well I took the boat back to the dealer and they raised the motor up 2 holes and changed the prop to 16x18 1/2, 3 blade and it was like having a different boat....

It got up on plane faster, 51.1 WOT @ 6100 RPMS....

I have the same boat and motor.

So of the 5 holes... which position is your motor installed now?

I have tried a 3x16x17, 18.5, and 20p. Top speed was 48mph at 6200 with the 18.5.

I have a BAD vibration just above idle and just above 4000 rpm. Do you have any?

[Moonlighter]

If you talk to Ken at Propgods.com or any other experts at a prop company, they will tell you that the first thing to do before you play with props is get the engine set at the optimum height, and, there's only one way to be certain of that:

Do an on-water test where you get the boat to a fast cruise speed, (say 3/4 throttle) trimmed out to the normal sweet spot, and go down the back and have a look over there and see where the anti-ventilation plate is. If it is skimming the surface or visible and getting splashed, it is good.

But if it is underwater, where you can't see it, it is too low, it causes unnecessary drag, stuffs fuel economy and can badly affect how the motor and boat sits in the water under power. An engine too low can result in a boat that handles like a dog. Porpoising is one effect.

The engine needs to be lifted until you can see ithe anti-vent plate as described above. We usually put some red sticky dots on the top of the trailing end of the anti-vent plate so we can see it easier from the boat.

Then, once engine height is set right, re-check the revs you are getting at WOT trimmed out as far as possible.

If you really want to be certain about the prop selection, you should record speed and fuel economy at every 500rpm interval from idle to WOT, record the minimum planing speed, and time how long it takes to go from idle to WOT (or to say5000 rom) when you give her full throttle. This data takes all the guesswork out of which prop performs better across the rev range. Done this myself a number of times, as have guys in our fishing club, and it is invaluable data that will see you making an informed decision about the right prop for your boat.

Do not listen to people who say that you can measure engine height above keel etc when the boat is out of the water and find optimum height that way. At best, that method is a rough guide. The only way to be CERTAIN is by the on water test described above.

To get the best out of these engines you really need to be hitting at least 6000rpm at WOT in light-ship mode. Better if its a bit more. In my opinion, anything under 5900 with only a light load on board will not get you the best performance and economy from almost all props. Even on my DF115 I have it propped to hit 6200 and even loaded up I can hit 6000. My local Zuke dealer says that is perfect. That's how he sets up them all.

Yes, you do find that after a couple hundred hours these engines loosen up and you can pick up 100 or so rpm. But by then you will also have managed to stow extra load on board too! A bit of cupping to the prop at that point in time soon gets things back into the perfect zone if you so desire.

[300HP32168]

It's just under the surface. Of the 5 mounting holes it's in the center position.

I have worked with Ken before. We ran several sets of props on a Contender I had.

[Moonlighter]

Good photo. Shows that it is too deep and needs to be lifted first, then play with props.

[300HP32168]

Did the early 300's have 5 mounting holes? The dealer used a Suzuki performance bulletin from 2006 that matches the hull and engine. It says third hole but it doesn't say how many holes there are obviously.