Prop to pad height johnson 150

[phoenixgold2100]

Hey guys I have a 99 stratos 273 vindicator 17'3 6" jack plate and a 3blade 24 raker prop johnson 150
I am trying to get some info on prop to pad height and what prop i should run. I think the prop is 4.5" from pad at the moment. I'm not concerned with holeshot performance i want as much top speed as possible. I have read these boats like to "walk" so any tips on how to avoid that. I have a hot foot and trim at the wheel. this is my first boat and ive read they can do close to 70 with the right set up i'm just wondering what that set up would be. thanks.

 

[Texasmark]

Re: Prop to pad height johnson 150

With a BB and especially with a jack plate, the proper height is that of the anti vent plate vs the pad. Normally you would put a strait edge on the bottom of the boat (conventional hull) and an engine mount would be such that the AV plate would be around 1-1.5" above or below the bottom, depending on variables in boats, engines, and usage.

With the BB riding on the pad, not the "bottom" per se, and with the pads usually set back several inches forward of the transom, and with the additional distance of the jack plate, the AV plate will have to be several inches higher; like that 4.5" number could be the correct number for the vertical distance of the AV plate above an extension of the pad (strait edge ruler).

Reason being is that when properly running on the pad, the boat has a bow high attitude of 15-ish degrees and if the bow is up, the aft end is down. So to keep your prop at the surface, you have to jack it up. Trial and error is the best bet.

I think Mr. D. Hadley uses the rule of thumb of 1" up for every 1" of setback from the end of the pad to the front of the AV plate.

He's the expert and seems to be semi-retired on here, but said he visits often. If you ping him you may get an accurate answer. I am just passing on what I know about the subject by association on here.

HTH,
Mark

 

[jestor68]

Re: Prop to pad height johnson 150

The way we do it here in Georgia is by the pad to prop shaft center line dimension. You generally begin with a dimension of (prop shaft center line) 3-1/2 inches below the pad and work from there.

We usually adjust in 1/2 inch increments until we experience too much ventilation, then drop beck to the last setting. We usually add an inch of height for each 6 inches of set back; but that doesn't matter, as it's factored into the 3-1/2 inch starting point.

The correct pitch depends upon the WOT rpm. You're shooting for 5500 rpm Expect 60-61 mph with a 150. In fact a 24 pitch with a 1.86 gear ratio at 5500 rpm with 10% slip equals 60 mph.

 

[phoenixgold2100]

Re: Prop to pad height johnson 150

i put a level on the cavitation plate measured to a level floor measured from the pad to floor then subtract. I read on some posts that 3.25 to 3" below the pad is right. There are guys on youtube with this set up touching 70 with a 150 on gps I have also read that these engine rpm max is 6200? 6000?

 

[jestor68]

Re: Prop to pad height johnson 150

Forget the cavitation plate. Measure (1) pad to floor. Measure (2) prop shaft to floor. Subtract 2 from 1. That is how far below the pad your prop shaft is. Shoot for 3-1/2 inches to start.

Your Johnson 150 has a recommended WOT rpm range of 4500-5500 rpm.

Is there a data plate on the front/top of the mounting bracket that has the full throttle operating range on it?

 

[phoenixgold2100]

Re: Prop to pad height johnson 150

No such plate on mine.. Start with 3-1/2? so it's at 4-1/2 right now is that too deep?

 

[Texasmark]

Re: Prop to pad height johnson 150

No such plate on mine.. Start with 3-1/2? so it's at 4-1/2 right now is that too deep?

He is talking about the prop shaft. What are you talking about with your 4 1/2 dimension?

If you were like me you were talking about the AV plate/top of the prop being 4 1/2 above the pad which is right at the same dimension for a 14" dia prop measurement vs the prop shaft being 3 1/2 below the pad (his way of doing it)...about 8" difference in the same measurement, just a different way of getting the same answer.....engine height vs pad location.

When you measure the pad and the engine heights I assume he wants the pad parallel with the floor and your engine in the vertical to the floor position. Otherwise the angle of the pad off the floor will mess up the measurement of the prop shaft dimension to the floor. The higher the bow up angle, the lower the prop shaft, or whatever method you use will be to the floor and the higher the error.

On your comment initially about walking, I assume you are referring to chine walking. That is where the boat becomes unstable and starts rocking back and forth dipping one chine (intersection of the side of the boat and bottom) in the water and then the other. The faster you go the faster and deeper it gets. Question is, will you flip your boat first, or it will pass as a result of powering beyond it. If powering beyond it is the answer just think, you get to go through that getting up and coming down.

I had a Ranger pad boat but it had no pad setback as is common today, and no jack plate. I was at about 55 mph on my first outing with a new boat, when mine started and it scared me resulting in me throttling back and not attempting to reach nor exceed that speed again. Actually I took the prop back to the dealer and got a prop with less pitch so that 50 was as fast as I could go.

On rpms, I don't know about OMC but I ran my tower at 6000 every chance I got even though WOT rating was 5000-5500. I ran it 7 years that way and my BIL still has it and I guess still doing the same thing. That's where the rpms were when I had the trim right and in a reasonably calm water straightaway with no nearby boaters.

HTH,
Mark

 

[dan02gt]

Re: Prop to pad height johnson 150

The way we do it here in Georgia is by the pad to prop shaft center line dimension. You generally begin with a dimension of (prop shaft center line) 3-1/2 inches below the pad and work from there.

We usually adjust in 1/2 inch increments until we experience too much ventilation, then drop beck to the last setting. We usually add an inch of height for each 6 inches of set back; but that doesn't matter, as it's factored into the 3-1/2 inch starting point.

The correct pitch depends upon the WOT rpm. You're shooting for 5500 rpm Expect 60-61 mph with a 150. In fact a 24 pitch with a 1.86 gear ratio at 5500 rpm with 10% slip equals 60 mph.

This is good advice and low 60's is all you can expect from that setup.

My brother had a '93 Javelin 379 with Johnson 150 when we were teenagers and it would run low 60's. We installed a 5.5" plate and jacked the motor up till it stopped chine walking. I'm not sure want the final prop shaft to pad measurement was but I think it was between 3.5''-3" below the pad.

Those hulls are prone to chine walk but with some seat time you'll learn how to drive it. You don't power through it. You use small steering inputs to keep it balanced on the pad. Start slow and work your way up driving it. Also balancing your weight in the boat will help minimize.

 

[phoenixgold2100]

Re: Prop to pad height johnson 150

I just measured again prop center line to pad is 4.5 so do you think i should put it at 3.5 and try it? or leave it there drive it and adjust? I just got this boat and haven't driven it yet. actually never really driven anything more than a 4.5 hp merc that i grew up on.

 

[jestor68]

Re: Prop to pad height johnson 150

You have never driven a pad hull before? I really hope you know someone who can go with and give you some pointers on how to drive this boat. Engine kill lanyards were first developed especially for bass boats.

I would leave it alone for now until you have a hundred hours of seat time.

 

[Texasmark]

Re: Prop to pad height johnson 150

You have never driven a pad hull before? I really hope you know someone who can go with and give you some pointers on how to drive this boat. Engine kill lanyards were first developed especially for bass boats.

I would leave it alone for now until you have a hundred hours of seat time.

+1 and I haven't driven the really fast ones and have been boating for over 50 years. Read the caption below my answer and heed!!!!!!!

 

[phoenixgold2100]

Re: Prop to pad height johnson 150

+1 and I haven't driven the really fast ones and have been boating for over 50 years. Read the caption below my answer and heed!!!!!!!

Naw never driven a boat like this before... Well with a steering wheel lol. My neighbor at the cottage has a ae-21 with a 2.4 merc on it tri hull I think so i'm not sure if he'll be able to help me or not. I'm just going to take it easy and see how it goes if it's crazy i'll back off I don't really expect it to be that crazy thou. As for prop height i'll leave it at 4.5 and adjust after a few runs. I have a rapid jack and it adjusts in .25 inch so it wont be too hard to count the clicks and set it up or back down.