HELP NEEDED ON MOTOR HEIGHT

[hooker67]

HI

I have just had a new 300 Verado fitted to my 250 explorer and I think they have stuffed up the stetup as it cavitates really bad, doesn't get out of the water quick and as soon as its on the plane and the front dips the motor cavitates. My first trip out I need to sit on 16kn with the motor trimmed all the way down with the bow in the air to get it to work to go anywhere as ones it jumped on the plane it would just cavitate
Can someone give me a photo of the height it should be at. I think is should be lower to suit the bottom of the boat but from a bit of research it might need to be lifted to suit the height of the step in the hull. The motor is a 25' leg and has been installed all the way down and has no more adjustment to be positioned further down as it is sitting hard on the transom.
Any help would be great.
I have called the people who have installed it and they are very apologetic and have told me to get it back down there and they will sort it out but I would like to have some more information before sending it to them. I'm in Australia and there are not many Aquasports over here or stepped hull boats

Thanks

[Aswaff400]

any pics of the motor/transom? what prop are you running?

[hooker67]

I will get some today and I am not sure of the prop
This is the one I have from picking it up so its not a good photo. will get some with a straight edge today

[wingtime]

Two questions. 

1) does your transom have the step down notch in it (transom top drops about 3" lower than the outer portion)

2) what hole is the top bolt in? If you have the notch it should be in the second hole from the top.

[fitz73222]

Not to worry,
The hull type isn't as important as where is the anti-ventilation plate relative to the bottom of the boat. Don't get hung up on which holes on the engine the bolts run through. The only time it matters is if you cannot raise or lower the the mounting height to correct the problem. Your hull however has the engine mounted much further back than the actual boat bottom in an integrated offset in the hull which allows the engine to run higher than if it was mounted closer to the actual hull bottom. First, your engine is ventilating not cavitating. Cavitation is something entirely different. You are simply getting surface air into the propeller area causing the prop to lose bite and slip. Engine height is usually the cause for this, meaning it's too high and getting surface air or turbulence into the propeller. The interim correction for this is to lower the engine. If that doesn't solve the problem then propeller choices are next. A prop with a higher degree of "cup" helps the prop grab turbulent or air infused water and hold on to it before it exits the blade tip. Prop choices are vast and some props work much better than others at higher engine heights. As Aaron suggests, an understanding of the current set up will help us understand the current set up condition. From there we can start to work on solutions.

[hooker67]

Yes, it dose step down about 3”. I have attached some old photos with the old motor. I don't think the motor can come down any further as its sitting hard down on the transom so I don't have any room to lower it. I am just concerned they are going to tell me I need to put a spacer on the outboard leg and it will be another $5000.
I did know about ventilating but sometimes people don't understand what you are saying and it just seam that everyone uses cavitation for the terminology not ventilation

[hooker67]

[fitz73222]

Hi Hooker67,
One more question that may be relevant. By any chance did you happen to add or relocate a transducer for a bottom unit that puts it in the path of the gearcase or propeller? I've seen where this can add enough interference ahead of the gearcase to cause the propeller to ventilate. The minimum distance a transducer should be located is 4" outward of the prop radius to keep the turbulence away from the prop area.

[wingtime]

Ok I strongly doubt your motor is to high then. There has to be another cause going on here. Do you have a gopro camera? If you do mount it so you can see where the cavitation plate is riding when running on a plane.

[Blue Agave]

I am just concerned they are going to tell me I need to put a spacer on the outboard leg and it will be another $5000.

Regarding a spacer, if the new motor is the same shaft length as the old motor than no spacer should be required.

[hooker67]

Hi Hooker67,
One more question that may be relevant. By any chance did you happen to add or relocate a transducer for a bottom unit that puts it in the path of the gearcase or propeller? I've seen where this can add enough interference ahead of the gearcase to cause the propeller to ventilate. The minimum distance a transducer should be located is 4" outward of the prop radius to keep the turbulence away from the prop area.

Had a call back from the dealer who fit the motor and he has blamed the transducers as I did install another one but I thought is was far enough away. He also changed the prop to a 4 bald and said he could get it to ventilate now and had it up to 41kn. Will be picking it up today and taking bit for a run.
Will let you all know the outcome. 

[fitz73222]

I'm assuming you meant the dealer could NOT get it to ventilate?

[Aswaff400]

i bet he swapped it to the mercury revolution 4. they work well in cases where the prop will easily ventilate, they have a ton of bite, i have found they almost work better letting them ventilate a little bit, especially for holeshots

[hooker67]

Had it out twice on the weekend and its a different motor getting just over 40kn WOT and a good cruise at 4500rm at 26kn. I have always like a four blade prop as that what I had on my last boat.