Ventilation on corners 40 HP evinrude on 16 FT Aluminum runabout

[Thornes-Del16]

Hey Guys,
I took my project boat out for the first time last weekend. I noticed that im loosing "traction" when im cornering or trying to accelerate quickly. I know it may be possible that the engine is a little low on the transom, but i wouldnt think it would cause that much of an issue. I have attached some photos for you guys to look.

Let me know what your thoughts are

 

[MH Hawker]

its not low its high

 

[Scott Danforth]

^+1....what he said

been on a few boats that if you want to turn fast, you drop the motor trim all the way down to get it to bite, and as you finish the turn, mash throttle while raising trim

 

[Chinewalker]

Between the motor being flush with the bottom of the boat, and the keel sitting down below the bottom like it is, there's a lot of turbulence ahead of the prop and it's right near the surface. Those two factors are contributing to your blowout issue. Sometimes can be handled with a better prop choice - something with a cup to it that holds its bite better. For your purposes, might be better off either lowering the motor or tucking it under a little bit as cupped props are going to be hard to find.

 

[Sea Rider]

That's a manual trim OB, right ? If so just remove alum u shape between transom and OB swivel bracket so OB sits further down. Go for a wot spin trimmed at seen on pics, should have 0 prop aereation or slight minimum that will need to live with it as OB can't be lowered any more without modifuying transom height. Anyway don't make close tight turns at speed....

Happy Boating

 

[Thornes-Del16]

That's a manual trim OB, right ? If so just remove alum u shape between transom and OB swivel bracket so OB sits further down. Go for a wot spin trimmed at seen on pics, should have 0 prop aereation or slight minimum that will need to live with it as OB can't be lowered any more without modifuying transom height. Anyway don't make close tight turns at speed....

Happy Boating

Ok, Ill try removing the aluminum block i put on the transom. I only installed it as the transom hight is 20" and the engine measures close to 23".
The PO had put a block in aswell so i figured it was needed to run properly.

Thanks,
Rob

 

[Sea Rider]

Rob,

As won't know which is the ideal OB/transom height for that old OB, check modified pic to illustrate better.


If with prop aeration at close turns and on choppy waters, water flow at speed is passing right over AV plate (red line) if you remove alum block to lower OB downward and depending on its height, flow will pass around middle yellow line which is much better than red line. Ideal is to skim right under blue line, right under protruding angled edge.

With deck weight evenly distributed, OB trimmed at 90?, check water flow passing by at plane by pulling head over transom to have a look on what's going on at lower tail, report your findings at which line is flow passing by..

Happy Boating

 

[jimmbo]

You have a couple of issues.
One, that is a tin boat, and they generally will have a Keel extending all the way to the transom. So your motor anti-ventilation plate has to be even or lower with the depth of the keel, not with the bottom of the hull as in a glass boat.
Next is the fact that the propellers for that engine are not performance props in any sense of the word. No progressive pitch, no rake, and no cupping. So they have to be buried in the water to avoid blowing out.

OMC did tend to make their engines with slightly longer than 15" or 20" transom lengths. Probably to bury the prop deeper to cover less than great propeller design.