Correct Pitch Prop

[78Glastron150Rude]

I'm new to the forum by you helped me & Tim_in_Indiana rebuild my carbs. Thanks<br />I'm working on finding the correct prop for my boat. It's a 1978 Glastron HVT175 Fish/Ski w/ 1984 150hp Evinrude, We bypassed the VRO and are mixing fuel 50:1. the boat came with a 14 1/2 x 24 3 blade prop with a M with a square around it is the only makers mark I can find. It would run 5600 RPM at 40mph (gps) or so @ WOT. I borrowed a 4 blade Renegade 13 1/2x 25 and ran 45 @ 5800-6000 rpm @ 3/4 Throttle. Any suggestions.<br />Thanks

 

[walleyehed]

Re: Correct Pitch Prop

Your 14-1/2X24 is an OMC Raker...good prop if you need alot of bow lift.<br />I'm going to run some numbers and post back...something isn't looking right here.

 

[78Glastron150Rude]

Re: Correct Pitch Prop

The only other thing different was with the raker you call it. It had a plate between the prop and lower unit. I had to remove that plate to get the Renegade to fit. It was like that plate on the raker was causing exhaust back up.

 

[walleyehed]

Re: Correct Pitch Prop

If your speeds are true GPS readings, your tach is "WAY" off. At the RPM listed,you should be in the upper 50's to low 60's in MPH<br />With your type of boat, and figuring a semi-std slip ratio of around 12% (The Raker is capable of much, much better), at 40MPH, I show your engine RPM to be only 3800-4000, and the Renegade would indicate about 4300-4500RPM. Bad news there...<br />Are you positive the GPS is MPH, or is it in KTS??<br />Also, there shouldn't be that much RPM difference between those 2 props...you leave a fairly wide range of RPM.<br />If you can confirm the GPS readings by truck or car with speedo, we have engine problems.

 

[walleyehed]

Re: Correct Pitch Prop

Are you talking about a thrust washer on the prop shaft ahead of the prop, or an exhaust seal ring ON the prop where it meets the lower unit gearcase???

 

[78Glastron150Rude]

Re: Correct Pitch Prop

I would guess the exhaust seal ring was on the raker and I had to take it off to fit the Renegade. The speedo in my boat and GPS are within one MPH or so different.

 

[walleyehed]

Re: Correct Pitch Prop

well, #1, that may not be a Raker but the box with the "M" in it usually is OMC's logo.<br />Here is the problem I see with your numbers...If we know the GPS is good and we can trust those speed numbers, the pitch of props you are using at those speeds indicates #1, the tach IS way off, but #2, with a conservative slip ratio figured in, I'd say we have some serious engine problems...<br />"IF" the tach was correct, we would have a slip ratio of between 37 and 40%....not a good thing unless you have a barge for a boat.<br />I would perform a compression test first and see what we have in all 6. Pay close attention to all plugs as you remove them as to color, wet, dry, etc...also, can you tell us what plugs you are using?? And how about fuel...are you using fresh 87 octane or something different??

 

[78Glastron150Rude]

Re: Correct Pitch Prop

I reinstalled the "Raker" last night went for another run. Got 6000RPM at 48mph everything was the same as before me and my old lady fishing gear. Gas tank was at 3/4 full though. The gas was the only thing different. I wonder when the raker prop was put on if the washer between the prop and the lower unit was on backwards before allowing the hub to spin inside the prop. I took the renegade back the washer wouldn't fit inside the Renegade because of the differences in diameter of the prop.

 

[78Glastron150Rude]

Re: Correct Pitch Prop

I'm using Champion UL77V theres a sticker on the motor that says what the model of spark plug is and it's what I installed. I believe the above model is correct.

 

[78Glastron150Rude]

Re: Correct Pitch Prop

Do you know what the gear ratio is on 1984 150hp 75th anniversary Evinrude?

 

[walleyehed]

Re: Correct Pitch Prop

I'm going to send a pic of a Raker AND the thrust washer that should be on the shaft in front of it... the washer is the same for the Renegade as well. I think we are talking of 2 different items.<br />I'm pretty sure your gear ratio is 1.87:1 and the UL77V should be fine.<br />Pics to come after I go take them...