Prop depth/water flow questions

[controlu]

When running at high speed, water shoots UP each side of the motor right up to the engine cover. The engine is a '03 Johnson 50 hp two cylinder two stroke mounted on the center "pontoon" motor mount. The motor mount has a flat bottom with no "wings" on the side.
It looks like the motor (transferred from another pontoon boat) is sitting too deep but it is mounted as high as it will go and when I try to trim it up it starts to cavatate. So, just where should the water be hitting the lower part of the engine when at speed?or is a problem with the water flow under/around the motor mount?

 

[tashasdaddy]

Re: Prop depth/water flow questions

sound like the same problem i had, long shaft on short shaft transom. i just built a jack plate to raise the motor.

 

[controlu]

Re: Prop depth/water flow questions

Looks like the same setup except I thought I had a short shaft motor judging by what I found here. http://smalloutboards.com/shaft.htm
I like the jack plate idea though. When you are at high speed, just where does the water hit the motor?

 

[tashasdaddy]

Re: Prop depth/water flow questions

i can't really tell you, because there is so much backwash. all i know is that i mounted it higher, and had to cut 3/4 of an inch off the plate, to keep from ventilating.

 

[bsl528]

Re: Prop depth/water flow questions

if your motor is mounted on the center toon of a triple toon boat the anti cavitation plate on the motor should be flush with the bottom of the toon.

 

[controlu]

Re: Prop depth/water flow questions

Problem solved!! The motor mount section was flat bottomed. I made a "V" plate that tapered from the edges to a two inch drop at the center and presto, no more problem.

 

[pontoonokie]

Re: Prop depth/water flow questions

ok .. how much of the lower unit needs to be below the transom mount? i am new to the pontoon boats.. i am thinking my shaft on my motor may be to long
thanks ..