outboard shaft length

[paul watki]

Hi, Hope someone can answer this.I want to : replace an outboard with a newer 4 stroke. when choosing the shaft length what are the measurments if any to be adhered to. Is it the distance from the keel to the mounting plate or maybe mount plate to water line or is there a standard minimum/maximum the prop should be underwater.If the prop is to shallow it will cavitate but what effect on the engine and boat performance will a prop that is well below the keel have.<br />Thanks

 

[Dhadley]

Re: outboard shaft length

Measure your transom from the top to even with the keel or pad -- whichever you have assuming its not a tunnel boat.<br /><br />A typical 20" transom is usually about 20 3/4". 5 more for a 25" and 5 more for a 30".

 

[Dhadley]

Re: outboard shaft length

How true! <br /><br />The lucky ones get more than they need. A manual jackplate is the easy answer. The ones who really get "shafted" are the guys who end up with a shorter motor than they need!

 

[paul watki]

Re: outboard shaft length

No worrys about the engine, it will be used but I will be looking for nearly new with a warranty left on it, probably from a dealer.<br />Went out and had a measure, from top of the transom to the keel is about 18". Assuming the engine has a cavitation plate above the prop at what depth should this plate be below the keel?<br />Also what effect would a longshaft have if used on a transom more suited to a standard shaft.<br />Thanks<br />Update, read a few other posts,oops! should have done that first It seems the cavitation plate should be as close to level with the keel of the boat,best to delete,save peoples time.

 

[DJ]

Re: outboard shaft length

pw.<br /><br />Check out the engines right here at iboats.<br /><br /><br /> http://www.boatmotors.com/ <br /><br />They are fully warranted.

 

[lark2004]

Re: outboard shaft length

cavitation plate should be level with keel, longer just means more drag (less performance) due to more leg being in the water than is needed.