knotreel

I am trying to re-prop my boat (30' offshore CC) after repowering with DF 300 Suzuki's replacing a pair of 225 Merc Optimax's. I was running a pair of 14 1/4" X 21P Turbo Ultima 4B. With the lower gear ratio of the suzuki's at 2.08 vs. the 1.75 of the merc and with a few more hp I needed to go to a prop with more pitch and tests so far have indicated a 23 or 24P would be about right. Now the problem is most of the offshore props in 4B are built for a heavy and larger boats than mine and seem to favor stern lift. My boat is a lightweight custom built one off with a full lenght keel pad and speeds above 50mph the boat starts to ride the pad. These stern lifting props are creating havoc with boat handling making the boat go out of control sorta like a dunken sallom skier. I believe these new problems are a being caused by the lack of choices in the props I am familiar with to choose anything other than stern lift. I was going to return to the turbo 14 1/4" D in the Fusion line up they offered in higher pitches but this line is now dropped and these are not available. the old trusty Turbo Ultima B4 is not made above 21P.
I ran some Turbo Offshore 1's, 15 X 24P and they did good at cruise but I couldn't stay in the throttle over 50-51 mph.
These were "stern lifting props" , I have run B1 and Rev4's and these have not helped but the B1 test was not a good one due to some condition issues of the set I tested, so I am not sure the B1's were a problem in the handling area.
Can anybody sugest a 4B that can run on an outboard that is available in 23 or 24P that is bow lifting? or at least something with minimal stern lift.

throttleup

You have a limited choice of props. The Suzuki motors need the larger diameter props, about 16" or so. Powertech makes props for the Suzuki applications in the proper diameter. I would call them, they also have an exchange program.

knotreel

Thanks, I am thinking of using a four blade and I think suzuki's 4B's are 15"D or so. Anyway, I just got a set of PowerTech OFX4's these are 15 1/4" X22P 4B and look like bow lifers. They are higher rack than the others I tried, lots more cup and cut leading blade edges. They do have an unusual look and they may work. I am not sure about the pitch but that issue is put to rest with a test run.

bbladesprops

With respect, larger diameters aren't the best way to get bow lift. If fact, larger diameters would be a backwards step for you.

Engine height adjustments and proper propeller geometry adjustments could get you where you need to be.

B

knotreel

I was trying for smaller diameter and the best running prop so far was the 14 1/4" D X 21P Turbo Ultima4 but the pitch was about 2" too little by my estimation. I tried to order 23's in that prop but LH is only available up to 21" so that's out. And, the Turbo Fusion line that is 14 1/4" D is not in production anymore so I don't know any other small D props to try, the Rev4 is not running good either. My engine is now on 2 hole , down from 4 hole where I began. I only have one hole down to go and ventilation plates are just above the water flow now. Got any recomendations on a small D prop?
If my test this week on the Powertech OFX does not work then I am out of ideas except try the bottom hole.

bbladesprops

Custom built propellers (from current stock castings) to your needs, post specific stock prop base lines are the best.

Accurate numbers in similar conditions are a must.

B

throttleup

Based on the hull description and the boat handling issues you are having I wonder if what you are encountering is chine walking? If you are not familiar with pad bottom boats and chine walk it can be a little scarry.

Once you have mastered the art of driving a boat on it's pad it's like riding a bike, you don't really even think about it when you are on the pad.

I'm not sure if what you need is a bow lifting prop.

ChristianGott

hi...
a "full length pad" ? i would have to agree with the chine walk analysis. do you have quality tabs and hydraulic steering?
they both will truly help....$.02...
c

knotreel

I have to say, since I am confused , I am not sure if chine walking or some form of it might not be part of the problem. At at several points so far I was sure I knew why this thing is not going right. Now 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 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
r's 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 meduim load
3600 32 .19
3700 34 .16
4000 38 .13
4400 43 .11
4500 45 .08
4750 47 .09
4900 50 .11
5450* 53 * would have been more

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 trimed out, would trim out way past level with no lost speed and very little rpm gain.
Mercs held at speeds 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 but 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. 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.
I have Dana Marine 12 X 24 planes
and hydraulic steering
Since I am confused I will not say that chine walking is not it. But we have tabbed down to try and stabilize it but no help. It does not feel the same as is does when it gets on the pad. 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 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 distirbance 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.
Only thing I know is my boat got good slip numbers at 45 mph but starts to fall off after that. I think it should not fall off, the merc was, basically ,1 to 1 speed vs rpm but was above that as you got over 50 mph. The zukes the opposite?

ChristianGott

let's see a picture of the bottom, transom, etc. maybe we'll see something that will get us thinking...have you checked the hull for defects like a hook, or twisted strake or chine? a prop shouldn't have such a "cure-all" effect....i'm thinking the bottom might be the culprit....