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I posted them. "The Pig" on here was the guy who hung over the back of his boat to take those pics.
One thing to note.
When your looking at the plate. You need to be at a fast cruise speed, AND trim the boat the way you normally would.
If they are trimmed all the way in, the motors will look lower then they really are.
So trim the boat to wherever it likes to run, before you look.
These photo were taken in 1 foot seas going 34-35mph at 4050-4100RPM with Zuke 4 Blade 15x20 with 180gal of gas with 20gal of water with two adults and two kids. Gears were 3 tanks and 1 set scuba gear.
At 35-36mph cruise I get about 1.5-1.6MPG
At 52-53mph WOT I get 1.0-1.1MPG
I think it is time to setup an appt with you to see if this can be improved. Given the current price of gas. Shouldn't take too long to break even. Do you think there still room for improvement?
If you have a trailer, you can do the job yourself. I just did mine a few weeks ago and it's way easier than I thought it would be. Mine looked much the same as yours in the pic, but to play it conservative, I only went up one hole to start with. Here's what I did
Lower the front of your trailer and fit a suitable wooden block under the skeg of your motor, raise the trailer until the skeg touches the block. Now loosen the bottom bolts holding the motor on the boat and remove the top ones. Start to raise the front of the trailer which will lower the transom and raise the motor until the next set of holes lines up, reinstal the top bolts. Now with the motor's weight still sitting on the block back all the nuts on all 4 bolts to the end of the bolts, this will allow room to get back there and clean out all the old sealant. Apply new sealant and let it set up for a an hour or two, this will help create a gasket rather than just squeeze all the sealant out when the bolts are tightend down.
Although, I haven't really had a chance to get real results with changing my motor height due to a power head replacement, there still seems to be an improvement in efficiency so far, I'll know for sure when I'm done with the 10 hr break in.
As you can see for the data. For whatever reason. I am getting worser performance (not to mention worser MPG) from raising the motor two hole up. Only gain is top end which is useless.
A seat of pant feel. I think I lost a little bite on the holeshot because the prop is now more out of the water. Instead of feeling the motor get up to speed normally and biting. Now the rpm climbs much quicker and I can feel the prob cavitating a bit. Once the boat is fully on plane the prob does begin to bite again.
Maybe I need a different prop? Just to be on the safe side. I will get the stock zuke prop computer scan within the next few weeks. And maybe add a little more cupping to reduce the slip.
I am going to go out on a limb here and say you are still too low. You have now brought them up just enough that the anti-ventilation plate is causing turbulence and that is causing prop slip. Before the plate was burried ad although it was dragging, it was running cleanly under water. Now, it right at the surface, not above it. You can see the water is actually cleaner in the before pics.
Some hulls do just seem to like the engines burried though. Lets see what Ken thinks...
As for clean water. Here is another viewing angle. I think the clean water was because the before photo was taken on a smoother day.
So if I can get out this weekend I will take another set of photo in the bay where there is minimal chop for comparison.
One more piece of info: The before photo was taken with the engine trim at ~55. The after photo was taken with the engine trim at ~10. If that makes any differences.
After the prop scan. It is time to buy new prop or put it back down to hole #3. (There is no more room to go up and I am not excited about putting more hole into the transom)
Put the engine where it performs like you want it to. Dont get too hung up on being too low or too high. It seems like hole 3 or 4 is going to be your sweet spot. Every boat and engine/prop combination can be different. You get it too high and you will get easy blow out in rougher water and loose quick handling in turns.
If the Props are cavitating, drop it down a hole. It looks to me like you have it too high, now in some of the pics up top.
As mentioned by Hawkeye, every combo is different, so get it like you want it. The seat of pant feel you mentioned is the boat trying to ride high and probably "bow proud" and you will lose all your out of the hole performance and feel slippage and normally it is tough to get the engines to stay in synch. From the pics I see, I would head back down with them a notch at a time. Something tells me when you frop it down one hole, you may hit the sweet spot. Also, don't hesitate to call the factory and ask where the engones should set on that boat.
Im curious if the same theory applies to a cat because of the different hull design compared to a monohull? Are the motors centered behind the hull or in the center?
They "look" like they are the correct height but obviously the numbers are not as good.
Suzuki 3 blades sometimes ventilate pretty badly when run very high.
And as said above, sometimes certain boats just like the motors lower.
Check your IM's
You could drop them down one or two holes, or go with different props.
The first option is obviously cheaper.
FYI, I'm currently thinking about raising my motor also. Cannot see the cavitation plate clearly when running, but its slightly under the surface, however, there may be some benefit leaving it where its at.
23' Sea Vee with 30" Zuke DF250 running a Rev 4 21P prop. Motor at highest setting. 36" setback from transom to start of lower unit. Cavitation plate 1.5" above bottom of hull plane when at optimal trim (slightly positive trim). Running (unloaded) 30 smph @ 4200 rpm, 45 smph @ 6100 rpm (recommended upper range WOT). Don't have floscan but average trip GPS mileage/consumption is about 2.1-2.2 mpg.
Now, having said all of that, I am inclined to raise the motor 1 more inch, however I noticed one thing offshore the past two trips: in 3 ft seas I rarely cavitate, and I maintain a good cruise speed with these conditions. Although I could raise the motor slightly and obtain better mileage, I may suffer on rough water performance. Still thinking about it, before I do anything I would have to make some adapter plates to allow a couple notches higher (don't want any more setback with a jack plate).
Cats do seem to be a little different. My single-engine ProKat [I know apples-to-oranges with UaVaj's] so far does better with an aluminum 3-blade Evinrude "ordinary" prop than two different Power Tech 4-blade stainless props. Talking with Power Tech, we've decided the problem is that the PT props are stern-lifting and that is the opposite of what this hull likes. The 3-blade is more of a bow-lifting prop and so keeps the stern down in cleaner water and also keeps more of the hull out of the water.
FYI, I'm currently thinking about raising my motor also. Cannot see the cavitation plate clearly when running, but its slightly under the surface, however, there may be some benefit leaving it where its at.
23' Sea Vee with 30" Zuke DF250 running a Rev 4 21P prop. Motor at highest setting. 36" setback from transom to start of lower unit. Cavitation plate 1.5" above bottom of hull plane when at optimal trim (slightly positive trim). Running (unloaded) 30 smph @ 4200 rpm, 45 smph @ 6100 rpm (recommended upper range WOT). Don't have floscan but average trip GPS mileage/consumption is about 2.1-2.2 mpg.
Now, having said all of that, I am inclined to raise the motor 1 more inch, however I noticed one thing offshore the past two trips: in 3 ft seas I rarely cavitate, and I maintain a good cruise speed with these conditions. Although I could raise the motor slightly and obtain better mileage, I may suffer on rough water performance. Still thinking about it, before I do anything I would have to make some adapter plates to allow a couple notches higher (don't want any more setback with a jack plate).
With 36" of set back and only 1.5" above the bottom hull plane, that is pretty low. I have a 29" set back, with a df250 25" shaft and the cav plate is 3.5" above the hull plane. I am running a stock 16x21.5 3 blade SS suzuki prop. I have great rough or any water performance.
With 36" of set back and only 1.5" above the bottom hull plane, that is pretty low. I have a 29" set back, with a df250 25" shaft and the cav plate is 3.5" above the hull plane. I am running a stock 16x21.5 3 blade SS suzuki prop. I have great rough or any water performance.
Thanks, that is the kind of feedback I was hoping for. I am designing adapter plates that will allow an additional 1.5 to 2.5 inches. My initial target was 3" above, but based on your data I may initially shoot higher. If you don't mind, what size boat and what kind of fuel consumption and performance numbers are you running with that motor?
Engine Height
