Motor height question

[Holeshot458]

I have a 1988 Bass Tracker V17 with a 1988 45hp Mariner with trim. I've been reading a lot of the threads and articles on outboard motor height. So I decided to check the relationship of my prop to the bottom of my boat. After leveling everything out, I found that my prop is 7" below my transom. My anti-vent. plate is .25" below the transom.
Would I benefit from raising the motor 3"? Would I benefit from adding a small (4") jackplate? Or would it all be a waste of time with this particular boat and motor combination?
I'm turning 5600rpm at WOT right now. I haven't pulled the prop yet to see what the pitch is. (there is no identification visible on prop, so I think it is hidden under the prop nut washer)
Would raising the motor help me gain some speed and efficiency?

 

[Bondo]

Re: Motor height question

Would raising the motor help me gain some speed and efficiency?

Ayuh,.... Possibly.....

But,.....
4" would be Too Much I believe........
I think if you went an Inch, Maybe 2 might be alright......

 

[steelespike]

Re: Motor height question

Operating range of your motor is 5,000-5,500.So your right at the max.
Your antivent plate is at a good starting point.
45 hp is pretty small for that boat.Raising the motor could help performance
a little.Usually best to raise it about 1/4 inch at a time until just before ventilation becomes a problem.Just add 1/4 inch sticks on the top of the transom.You'll be lucky to get 1 inch.One inch could get you a couple of miles per hour.Be sure it pumps water and the clamps have a good grip.Once you are set you will probably need to change the prop and this may give you the chance to gain a little more speed and height.Usually a change to a stainless prop will combat ventilation.

 

[Texasmark]

Re: Motor height question

Numbers are usually cast into one end or the other of the hub.

Don't know where you are headed. You are above max rpm's right now. I guess your plan is to optimize your setup and then put some more pitch in the prop to bring the rpm's back into perspective.

Mark

 

[Holeshot458]

Re: Motor height question

I guess your plan is to optimize your setup and then put some more pitch in the prop to bring the rpm's back into perspective.

Mark

That is exactly what I am trying to do. Does that sound like a good plan? To raise then prop?

I realize this setup isn't going to break any speed records, but I figure I can at least get everything to running as efficiently as is possible. And raising the motor is free!
The motor is bolted to the transom and the holes are approximately .6" apart. I have 3" to work with.
The boat has a water pressure gauge, so I can keep that with in specs.
I do know at WOT and trimmed the anti-vent. plate is, at least, 1.5" under water. Is that where it should be?

Thanks for your help.

 

[steelespike]

Re: Motor height question

Anti vent plate position is where you have the best performance with the least ventilation.If the motor has clamps use them and drill new holes once you have the best setup.If only bolts check the mount there may be slots that will let you fine tune the setup.If you meant the holes are 6 tenths of an inch apart then try one hole.Keep in mind that if it seems better but vents
you may be able to solve it with a prop.

 

[Texasmark]

Re: Motor height question

Every setup is different, but just shooting from the hip, if you are 1.5" below the hull you are at least 2" too low....just shooting from the hip. What you want to know is where is this plate when you are at WOT. It would be out of the water somewhat for best performance.

Next thing is you should expect some blowout once you jack her up. Question is, how much and when. Like on my boat I am half an inch above the bottom and am runnign a HP SS prop. I can be running WOT and get into a hard turn (deliberately) and the engine will pickup about 200 rpm's. But it will not blow out. It will hold this rpm till I change something.....light straighten back out and then it goes back to normal. It does not blow out at all in rough water as I slow down and tuck her in and there is plenty of water there to grab.

On some boats, with their current prop, they blow out completely, engine races and boat settles into the water, and have to dump the throttle and pick it back up to recover. In my opinion, the design/type of the prop is main thing involved there.

So, when you get all that figured out, you can go to the archives and lookup some of Walleyehed's prop info and find yourself a HP SS prop and get what you are looking for.

My 2c

Mark

 

[Holeshot458]

Re: Motor height question

Texasmark

The anti-vent. plate is 1.5" below the water at WOT and trimmed out. So, from what you are saying, I must be too low.

I think I need to raise it this weekend.

Thanks everyone for your help.

 

[Texasmark]

Re: Motor height question

Absolutely. You ought to at least see half an inch of water under it if not more....if you can stand it. But I'm not the expert. I just know what works for me, what I have read from others that have spent a lifetime on the subject, and what makes sense.

Mark

 

[Holeshot458]

Re: Motor height question

Mark
I raised it 2 holes and am going to see what that gets me.
I'm not sure when I will be able to get it back in the water again.
Never know what the weather will be here from day to day!

Thanks again for your help.