Long shaft conversion

[jd8251]

I have an '83 Evinrude 140 that I want to convert to a long shaft because the current length shaft (20") causes the prop to cavitate with a three bladed prop installed. A four bladed prop causes much less cavitation but the hole shot is BAD! I want to get the 3 bladed prop deeper in the water so it does not cavitate and I found the conversion kit right here locally.

Looking for advice on this idea before I go buy the kit for $200 and find out it doesn't work like I think. Will it just create so much more drag that the conversion is not worth the cost or is this a sound idea?? I do mostly tubing and skiing with the boat and not concerned about top end to much.

For anyone else looking for a conversion kit I found this one at Budget Boats in Chesapeake VA. You can Google them and find out their contact info.

 

[Chris1956]

Re: Long shaft conversion

If that motor is a 20" shaft, it is already a long shaft. You want an extra long shaft, whch is 25".

Where does the antiventilation plate sit with respect to the bottom of the hull? Does the boat have a keel or any other hull design that might cause ventilation?

 

[jd8251]

Re: Long shaft conversion

From what I can tell the Evinrude comes in 20", 25" and 30" models. They call the 30" model the extra long one. The boat has a very shallow V aluminum hull which of course sits higher in the water than a fiberglass hull so I am thinking that is why the prop cavitates immediately. The anti-cavitation plate sits almost flush with the bottom of the boat. The transom measures just over 22 inches and the motor sits as low as it will go.

 

[jd8251]

Re: Long shaft conversion

OK just found out that there are 4 lengths with the 30" being extra extra long and the 15" being the short shaft as you said. At any rate, still need to know if converting it to a 25" shaft is going to fix my cavitation/hole shot issue.

 

[Chris1956]

Re: Long shaft conversion

I have no way to tell you if lengthening the shaft will fix the ventilation issue. Most boats would tolerate a 2" difference in transom length, that you have.

An adjustable jackplate is another possible remedy. Is your prop cupped? Sometimes using a prop with more cup is the answer as well.