Propping out my Suzuki 300DF part two

[knotreel]

There will be part three undoubtedly but I hope that's it.

My last post on this subject was about the difficulties and results from my efforts to get my 300 DF's to run correctly on my boat, a 30' custom built CC. See knotreel.com for details of the build. The 300 DF's are replacing my old 225 Optimax's that in way's I am beginning to miss. I still love the motor and control part of the zukes but I seem to be foundering with drive issues, correct props, drive height and perhaps something else.

I have to say, I am confused. Since yesterday's fishing trip when I ran the Power Tech "bow lifters" ( OFX4 15" X 22P), "X" cut, raked and extra cupping, things have not gotten better. As we stepped the rpm's up things went OK till we got the throttles near WOT.

With the old 225 optimax's you could feel the boat get on the pad beginning about 50 mph. Above that things were fine up the max at 57 or so.

With the Zukes, it also gets on the pad at about 50 but can only go as couple of mph higher no matter what prop I have run, except it got to 56 mph briefly with the borrowed set of Turbo Ultimas 14 1/4 X 21's. This was when the motors were two bolt holes higher and my other props would barely plane the boat. I have not borrowed these props again to run them at present drive height. maybe I will.

Here is the results of the PowerTech 15 X 22P OFX4

tested heavy fishing loaded four people 125 gallons out of 200, 300# ice, gear etc.

rpm mph slip mpg

4400 39.5 .10 1.65

4600 41 .11 1.58

4750 42.5 .11 1.47

4850 43.5 .10 1.43

4900 45 .08 1.38

5100 45.5 .011 1.36

5900 52.5 .011 1.1 (not sure this was max)

Just for reference the Turbo Offshore 1's 15 1/4 X 24P tested

a couple weeks ago

tested with medium load, three people 110 gallons out of 200, gear, no ice

rpm,mph,slip mpg

3600 32 .19 1.95

3700 34 .16 1.9

4000 38 .13 1.8

4400 43 .11 1.7

4500 45 .08 1.6

4750 47 .09 1.5

4900 50 .11 1.4

5450* 53 * would have been more

the problem is that none of these tests have produced a WOT rpm that I can rely on. The boat goes out of control with the zukes about 52-53 no matter the prop except the small diameter Ultima's.

Here are some other pieces to the mystery,

the zukes don't seem the care about engine trim, trim all in, up 5%-12% you get all the same boat speed and rpm? above 15% boat slows. Mercs on same boat ran like a pig trimmed under, would gain about 10 mph and close to 400-500 rpm as you trimmed out, would trim out way past level with no lost speed and very little rpm gain.

Mercs held at speeds well above 50. Zukes go off above 50, port engine looses grip and boat turns to port, can correct but star will go then. That is the sensation I get. However instead of the a prop losing bite another possibility is the larger prop diameters are lifting stern and the drag of the forward lifting pad that "sets" the keel pad is now pressured more causing drag way up front and boat wants to swap ends. So i am thinking it's one or the other of these or a some of both? The lack of responsiveness to trim with these motors may figure in too as the mercs loved to be trimmed out a bunch when in the upper speeds.

Chine walking has been suggested but I don't get that idea running the boat but since I am confused I will not say that it is definitely not chine walking. We have tabbed down to try and stabilize it but no help. With the zukes you can get it up on the pad with out the hard port turn but as you push it a little more it goes off. When it goes to port you correct it with steering then you end up running a salomn course as you fight the port turn with steering input.

I am also questioning the water flow off the transom, the 16" wide keel pad is raised about 1 1/2" and it's dead rise is 12 deg and the hull bottom is at 25.5 deadrise. So you have a "notch" in the water flow. The motors are 27" c-c and the pads disturbance is in the prop swing, never was an issue before but....

My next step is to drop the engine down from 2 hole to first hole which will make vent. plate about + 1" height , merc's ran at + 4" !

After that fine tune toe-in.

After that, I will re-test the 14 1/4" dia Turbo props to see if the small D is still what I think I need.

After that, reverse the prop rotation, after that I am out of ideas.

I know my boat got good slip numbers at 45 mph with both of the above props but starts to fall off after that. I think the slip should not increase like that , the merc was, basically ,1mph to 100rpm but got better than that above 50 mph. The zukes start getting worse around 50, just the opposite?

Even though the 24P test might have got more rpm, say 5600-5700 at best, points to the boat needing a 22 or 23P. So, what this means the new 300DF zukes vs. the old 225 Opti's is my top speed will be maybe 1-2 mph better (maybe, at best) and cruise speed assuming I end up with 22p and run the zukes about 4500 where the fuel burn is ok, it will be 2-3 mph slower than the Opti's when they cruised at 4350-4400.

Sure the zukes run quieter, smoother, got better gages and controls and can plane the boat at slower speeds but come on, 600 hp vs. 450, I sure would have thought they would be faster than a pair of 225's?

However, all that said, I still think if I could get a set of 14 1/4 X23P or 24P Turbo fusions then all might look better.

Anybody got some?

[velocity 30]

Hi I have a hull thats similar a 30 ft Velocity. The boat was new in 1985 and I had it built custom with a cc, most of their hulls are encosed. the weight is also 4k net. The boat was deliverd with 2 200hp mercs model before opti max after adjustments the boat would do 60mph wot at 4000rpms the speed was 40mph with 4 people and full dive gear 12 tanks etc. at that speed the milage was better than 2mpg. all this was great but the motors were mounted hi for better performance. i blew 5 powerheads in a three year period and the warrenty was coming to an end so I upgraded to 2 300hp evinrudes,these moters were about 400pounds heavier total and the boat was a pig with the rudes. after wedges all types of props etc had to put motors all the way under,tabs full down and throw the controls forward rapidly to get up on plane. boat would finally do 70 after full throtle but at a cost the milage dropped to 1mpg at around 40mph when we were lucky most of the time it was about .9 or so. keep them for 3 years and down graded to 2 175 rudes boat would do 52 got about 1.5 mpg.kept these until recently bought a couple of used 250HPDIs having issues with these now but have already blown a powerhead anyway weight makes a significant difference the hull also has a pad and the transom is notched so their are similarities. also mercs seem to get the most out of horsepower but often have reliability issues. Doesnt suzuki claim to accept larger diameter props? Steve Stepp of velocity motors can probably shine a lot of light on your problems when I bought the Velocity he was telling me that a .250 radius on the chine would have an effect on handling etc. velocity 30

[ken2]

I thought you were going to try some Rev 4's.

I saw a picture of one in your last thread.

[knotreel]

I thought you were going to try some Rev 4's.

I saw a picture of one in your last thread.

I have run the rev4 as part of a mis-mash "break-in" set of props. I bought (2) 26P B1's ,not a set, and one was a good 26 the other was a reman modified that was about a 23 with non stock blades. I got the 23p Rev4 to run on the boat with the goofy B1 while I was between props as I am now. THe Rev 4 is possible but looking at its design, it seems similiar to some of the others I have run, but that the Rev4 is still a possiblity, I guess. But I have some other thing I want tot try first.