Propping out my DF 300 Suzuki

[PatrickG]

You can do what you want, but unless your boat is capable of running over 70 mph you don't need to even look at 24 pitch props.

[knotreel]

You can do what you want, but unless your boat is capable of running over 70 mph you don't need to even look at 24 pitch props.

My calculator tells me that 24P @ 6000 rpm = 61.2 assuming the same slip I got at 50 mph. If you aren't familiar with the 300 zukes you might not realize their gear ratio is 2.08:1 instead of the usual 1.75:1 or 1.86:1 that most older engines had. Assuming that the 24's had a D of 14 1/4" instead of the 15" that I tested and assuming that boat handling issues hadn't aborted the WOT runs the 24P should have got in the high 5000's. As it was the 15"D's looked like they would have got close to 5700 or more likely 5600 except for the boat handling. 70 is not what I was expecting but around 60 should be doable since the boat would run around 60 light loaded with the old 225 opti's.

You had sugested 21P's but as I said when I tested some 21's it easily got 6300 and I guess would have gotten to the rev limiter but I didn't let it go past 6300, so I think 21's are not what I need? Right now pitch is not the thing I am thinking about a lot, I have to get a prop that will get to WOT without the boat going out of control.

[Hawkeye]

I ran the 21P already, engines are down two holes from the merc height, I only have one hole left and ventilation plate is getting very close to the water. I think the curve ball that the raised keel pad has thrown into the picky zuke gear case issue has eliminated some of the options that otherwise would be good approaches. As I said I am hardheaded and have THE props on order. I will post results in a few weeks.

Ventalation plate should be right at the water on a boat your size. Go down to the last hole..

[knotreel]

Ventalation plate should be right at the water on a boat your size. Go down to the last hole..

I may have to do that but right now I am focusing on getting some bow lifting props or at least some with lesser stern lift. If this doesn't work out then it will be down to bottom hole and/or three blade props. The boat liked four blades with the opti's but that was when I could trim out as far as I wanted which is not the case now. I will be testing the power tech next week and Power tech is recomending a prop that they think will lift the bow vs stern. It is their OFX4 witch they describe as having "a high aspect ratio X cut geometery" which I don't know what that means and the more familiar things like moderatly high rack and aggressive cupping. The rack and cupping sound good but high aspect X cut is new to me.

Well , I will just run them and see what happens.

At the height the motors are now the ventilation plates are barely visable, really just shadows in the spray.

I am not completely sure what is going on now but earlier with the props that have gone badly, I was definately getting ventilation when I was two holes up but i am thinking it is not just ventialtion anymore since I have lowered the motors. About 50 mph the hull was always ran a very low trim and with a little extra stern lift I think it might be trying to "swap ends" as it's running trim flattens out. The hull has a small forward pad area that is meant to "set the keel pad" or in other words the idea was to have a small lifting area at the beginning of the full lenght keel pad that keeps the hull and keel pad at and angle of attack. This feature was added to counteract the very low forward lift of the hull and sets the point where the hull contacts the water as more or less a constant. It is effective in setting the forward contact but I guess it does add some drag at a fixed point pretty far forward, funny it was meant to reduce drag and it might do that but may be complicating things with these motors as oppesed to the mercs that I could tirm out and lighten the front as I needed.

[PatrickG]

Actually I was thinking the gear ratio was slighly higher than that. I should have looked it up before I posted that. I find that Suzuki props tend to have a lot of cupping in the prop. I get several hundred RPMs less running a Suzuki prop. I agree with you since it is a 2.08 gear ratio that 21's wouldn't be enough. I would think 23 is the ticket and 24's would be good for light loads. Probably somewhere around 22 pitch with a Suzuki prop.

[DreamWeaver21]

Have you tired swapping the gear cases? I have heard that can correct (or worsen) a handling issue. But since you are experimenting anyhow, why not try? Not sure if there is any reason you couldn't on Zukes.

[knotreel]

What I understand about swapping the gear cases is, amount other things, you get more stern lift which is what I think I don't need and trying to avoid. However my analysis could be all wrong. I will run this next set of props which are to say the least, different looking and then start looking at options like what you sugest if things don't get better.

Another point about swapping is the zukes with their shift by wire, the electric motors or servos that shift the units are controlled by wire and the port and star is setup by a laptop at the dealer. Maybe just swapping the ECU would allow me to swap the gear cases around? It am sure it can be done some way? either by swapping the ECUs, or swapping some harness plugs or reprograming with the laptop.

I will test my new "bow lifting four blade" props, the PowerTech OFX1 show below.

this is the blade showing the added cup that goes around the tip and the "X" cut which is the removal of the blades leading edge

this shows the OFX Powertech(left) next to Rev4 (right)

Well, I will run these thursday on an offshore trip, should be a good test, the blades do look smaller,m if fact the 15"D OFX appears smaller than the 14 5/8" Rev 4. But enought of that, test and see.