Need help with four blade that is "bow lifter"
 

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.

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.

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.

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

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.

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

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.

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

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?

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....

You can take a look at a bunch of pictures on my website about the design and build, there are pictures of the bottom an a lot of other bs. Website is knotreel.com THe hull is Corecell foam cored has huge stringers and is about as strong and stiff as a brick. I have looked at it but never gave any defects any thought as the running surface is perfect as far as I can tell. Chines and all strakes still have sharp edges I didn't think much about the hull as it ran fine, no problem with the Optimaxs that I just removed. All this started with the new engines just installed a month ago. I will take a closer look though as anything is possible I guess.
The engines are set back from the transom 31" to the brackets and props are 47" back from transom.
I have been told the Suzuki likes to run deep but +1" set back 47" that is crazy. Maybe I should get some JB weld and redo the nose cones.
I have said the mercs and hull ran good before but all high speed stuff was done a goodly trim up, these zukes can't be even trimmed to level with the hull which is about 17% on the trim gage and I mostly run them at about 7-9% trim which is considerably under. Maybe the mercs would have got the bow lift pad too wet and lifted the stern if they could not be trimmed either. These are things that are bothering me and thinking maybe this maybe that, I have to just go down the bottom hole and re test then that issue will be done because no matter what I can't see me dropping below +1".

Consider you added 200 lbs to the transom with the Suzuki motors compared to the 225 Opti's. You are going to need something to pick up the transom. Stern lifting props might work.

An easy way to test what's going on would be to add some weight to the bow. Try adding 50 lbs or so and see what happens, if handling improves add a little more. You also need to keep in mind the Suzuki props are turning lower rpm which is the reason most of the props for those motors are a larger diameter than what you would typically use for an outboard.

Just something to consider.

Well thanks for all the sugestions, Bow lift stern, stern lift I really don't know? Thought i did but what I have decided to do is re-borrow the set of 14 1/4" X21P Turbo Ultima4's that I had on the boat with the merc's and briefly borrowed to made an offshore trip when my junk set of "break-in" props would not plane the boat. This was when the motors were in the fourth hole, up two holes from the present. They ran about as good as the props I have tested at the hole two. It will, I hope, be enlightening to see if they run at all speeds in hole two. If they do, then I guess I will have to have a set made from larger diameter props, probably the turbo offshore4's as these are available in their really cool "t-loc" hub that can not spin.
I am thinking these would be 23P.
So I will make that test later this week. Then if that fails i will go two the bottom hole and try some more.
This kind of stuff is what can happen when you build your own boat, very frustarting I will say.

the first thing you need to do is take a long straight edge and verify that your bottom is still straight. do all the running surfaces, not just the pad. the next thing i would try would be a s blade prop that has both stern and bow lifting traits. i run a hydromotive 5 blade p 5x. generally the more blades, the less a boat will chine walk. from your handling experiences, it sounds like you need both stern and bow lift. hope this helps,

Pics from his site...

I thought some one said this was a padded bottom. I don't see a pad on the bottom of this boat but I guess I could be missing something. Also the step/notched transom has a very small deviation from the bottom of the hull. I have seen this type of set up create handling issues. This could create a skiddish feeling at high speeds, kind of like riding on marbles.

I happen to have a RH and LH Fusion 4 in 23 pitch on my test shelf if you are interested.

Brett

Sorry for not getting back but I was planning on some more testing before I came back.
About the bottom, it is dead straight. It is a 25.5 degree deadrise at transom and has a 16" wide keel pad that runs from stern up to where entry starts. This pad is 12 degree dead rise at the transom.
I was interested in the fusions as I was told that they were virtually the same as Ultima's. Here is what happened with my new "set". I ordered a 23 RH Ultima4 and picked up a 23 LH Fusion. I did this because Fusions are no longer made and Ultima4 is only available in RH in pitches above 21". So believing they had the same blade I got this "set". Well, they do run similarly up to a point but the blade shapes are not the same , the Fusion does not have the round ear design I wanted.
My latest two tests were a re-test on the 21P Turbo Ultima4's and the test of my new "wackly" set.
The Ultima's tested great with real good slip numbers that got better as speed increased in the upper ranges rather than worse as some of the others did. at mid range these got to 5% range and went in 4% range around 50mph.
Now I just tested my wackly set and these got down to 6% around 45 mph but got a little worse as speed went over this.
With a lot more seat time in the boat I now think I know what is going on. I believe the Suzuki's must be buried deep to run properly and my boat can not keep them buried as the boat rides up on the raised pad. The boat gets on the pad as you approach 50 mph and is really up over 50. My mercs loved this, my suzuki's hate this.
It is not chine walking, the port prop is coming loose and drive shifts to star and boat turns to port then the "s" curves are all me trying to correct. When the port comes loose the engine really doesn't always gain that much rpm, sometimes just a hundred or a little more. The nifty Suzuki syncronizers were fooling me earlier.
The Fusions that I though I wanted, I not too sure now as the lastest test where the fusion is on the port, indicated that the problem is worse than when two Ultima's are on the the motors.
So, I am dropping to the bottom hole and re-test. The Ventilation plate is now 2 1/4" up and going down to the bottom hole which will put me at 1 1/2" up.

After that some ideas I have are:

reverse the lower units to turn in
try some PTC4 power techs ( look like Ultimas in pictures?)
get a custom made LH prop to match the Ultima

My boat used to get to almost 60 mph with the 225 optimax's and now it's like trying to break the sound barrier which is about 50-51mph with the 300 zukes. This sucks!
BB, I might want to test the Fusions but more likely I think it will end up being a custom made Ultima4. I guess you could make one from a blank or maybe use a Turbo OffshoreI which would have plenty of extra blade to work with in cutting down plus have the T-loc hub?
Well first I have more work to do.
Thanks to all who have offered your advice. I don't think I am confused now but still looking to have that "ah ha" moment.
Ron
PS, my earlier conplaints of lack of responsiveness to trim and not able to trim out beyond level (19%) has been cured with the Ultima4"s .