Outboard Motor Height

[pjbass]

I have 1996 Stratos 280 SF Fish & Ski boat with 1988 Johnson VRO 140HP that has a 25-inch shaft and 14.5 x 19 prop. The cavitation plate is set well below the keel of the boat (approx. 2 inches). I am new to this boat and motor and learning threw the forums to understand it. I took the boat out for a test run and notice that the water was spraying in a upward direction, splashing between transcom and motor. It seems to me that it was a trim issue so I adjusted the trim upward enough for the bow to lift but still having the same effect. The maximum boat was 36 mph at 4100 rpm. To me, its dragging! I know its supposed to be at 5000 rpm. Can anyone tell me if the motor is to low?

 

[roscoe]

Re: Outboard Motor Height

It is to low.
Raise it 3-4 inches.

 

[tashasdaddy]

Re: Outboard Motor Height

agreed, you may need something similar to this. they are also available in hydrolic. http://www.iboats.com/T_H_Marine_Pr...23903806--list_time.1178655216--view_id.40131

 

[pjbass]

Re: Outboard Motor Height

Thank you both for the advice. I raised the motor as high as it can go and the cavitation plate is still an 1 inch below the keel. Again, it was spraying upward onto the back of my stern. By raising the motor, do you think this will stop? So if raising the motor will stop the splashing, can I still use my trim with this jack plate?

 

[tashasdaddy]

Re: Outboard Motor Height

yes, you are just getting the motor where it belongs. you need to come up 2 more inches.

 

[Vortec MAX]

Re: Outboard Motor Height

I think I have the same problem. I have a small 12 foot aluminum Starcraft fishing boat and a Johnson 7.5 HP long shaft motor. I bought them together. The boat will only go 6 MPH. It seems like it is dragging badly. The transom flexes under the torque of the motor, but it just pokes along.

Suggestions??? Scrap everything and start fresh???

 

[Silvertip]

Re: Outboard Motor Height

Both engines appear to have the wrong shaft length for the boat. Short (15-inch) for the 12 footer and Long (20-inch) for the Stratos. The Stratos may need a jack plate to solve the problem. Fix it before you destroy the engine. 4100 RPM at WOT constitutes severe lugging.

 

[studlymandingo]

Re: Outboard Motor Height

The jack plate will most likely give you additional performance enhancements beyond just getting the motor height up. By having the lower-unit further from the hull, it runs in less turbulent water, you should get lots more lift which reduces drag.

I have a jack-plate coming for my boat, supposed to be here today in fact.

Good luck and keep us posted with your project.​

 

[pjbass]

Re: Outboard Motor Height

Thank you you all! I'm definitely going to purchase it!

 

[Vortec MAX]

Re: Outboard Motor Height

I am going to convert my motor to a short shaft. It will cost around 300 bucks. It looks like the plate above the prop will still be below the bottom of the boat, even after converting to short shaft. Will this be OK? It looks like it will be two or three inches below the bottom of the boat still. Right now it is about 7 or 8 inches below.

Mike

 

[pjbass]

Re: Outboard Motor Height

Jack plate fixed part of the problem, which was my biggest problem, splashing upwards. Now, I"m still having the issue with the RPM. My speed is now at 40 mph but my RPM is still at 4100 rpm at WOT. It should be at 5000 rpm. So, what's next? Change prop?