1991 johnson v8 300 gt counter rotating prop selection

[varvatos]

Hi everyone,<br />I am new to this forum and thank everyone in advance for all the help they will provide me with.<br /><br />I just purchased a Johnson V8 300hp gt counter rotating and am now trying to find out how to determin the right propeller for this monster. I have a 30ft boat, which i would like to equip with that motor. it has a deep V hull and wheighs around 1200 kilogram (1.2 tons). i don't know much more about it. Can someone help me determine what prop I will need to put on the motor??<br />Thanks a bunch

 

[ob]

Re: 1991 johnson v8 300 gt counter rotating prop selection

First thing you'll want to do is to mount the engine at it's optimal height on transom.Start with the engines lower unit anti-ventilation plate even with the mean bottom of boat leaving up and down adjustment hole positions of transom bracket.Your final prop selection will need to be based on which diameter and pitch will allow your engine to attain it's max wide open throttle rpm.I believe that will be in the neighborhood of 6000 with an average payload.See if you can hook up with a dealer or propshop that will allow you to test a few different props until your final selection can be determined.I'm guessing that your starting point will be a 15 1/2 dia. X 15" pitch.Prop selection and optimal engine height placement is what your goal is for best all round operation and engine longevity.

 

[Dhadley]

Re: 1991 johnson v8 300 gt counter rotating prop selection

The rev limiter on that motor should be at 6700. Don't be afraid to turn it up but do be afraid to lug it. 6000 should be about the lowest target rpm with an average load.<br /><br />A GT (or XP) should be a 20" motor. Keep in mind the 20" V8's are actually 23". I take it from your post that it's a single on a 30' boat. Depending on how it's set up (bracket mount, transom mount, jack mount etc) it's probably set up for a 25" motor. The 20" V8 is probably a good match given the actual mid section length.

 

[varvatos]

Re: 1991 johnson v8 300 gt counter rotating prop selection

Thanks guys. As far as I know the back of my boat is 25 inches high. the motor has a 30 inch shaft, as I was told from the seller. I actually haven't seen the motor yet and the boat is in europe. it is going to be hard for me to test props so i am trying to find out if there is any way to work around this issue or if i am going to have to buy several props, and which once if so?