17ft glastron prop help *Updated ran new prop*

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smoedog

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I have a 92 17ft glastron with a 4.3 alpha one gen 2 outdrive (serial number 0D667511).. The previous previous owner put a hi-five prop (part number 48-815760-21)

Right now it's painfully slow... GPS is showing 30-31mph @ 4000 rpm at maybe 1/3 throttle. WOT yields about 5600 rpm. Any suggestions. I am 8 use the boat to cruise and pull a tube.. Butit is painfully slow
 
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steelespike

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

My limited experience I think a high 5 does better on very powerful boats.
Please read "read this first" at the top of the prop main page.
What is the hp We need the speed at 5600 run it only as long as it takes for a quick speed.
If the tach is accurate your 800 over the max rating.I think the 4000 is actually 3400-3500.
I believed the tach is wrong. You might note the switch on the back and operate it a few times to clean the contacts.
Perhaps borrow a shop tach to verify your tach.
 
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smoedog

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

Ill grab another tach to verify but at 4000 im only at 1/3 throttle so the motor isn't working hard. i tried getting an accurate reading at 5600 but i didn't want to hold it at that speed very long. I thought I saw between 38-40.
 
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steelespike

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

At 4800 a well setup 4.3 with the proper pitch in a 17 footer would be about 50 mph I think you can see that at 5600 it should be considerably faster.The high 5 could actually be holding you back both speed and rpm.
We will need the pitch of the high 5 so we have one more actual number for the calculator.
 
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smoedog

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

researching the part number I gave earlier, the it appears to be a 21pitch 13.25" prop
 
Bondo

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

smoedog said:
I have a 92 17ft glastron with a 4.3 alpha one gen 2 outdrive (serial number 0D667511).. The previous previous owner put a hi-five prop (part number 48-815760-21)

Right now it's painfully slow... GPS is showing 30-31mph @ 4000 rpm at maybe 1/3 throttle. WOT yields about 5600 rpm. Any suggestions. I am 8 use the boat to cruise and pull a tube.. Butit is painfully slow
Click to expand...

Ayuh,.... If yer turnin' those kinda rpms with a 21" prop,....

I'm gonna Guess that, that boat had a 3.0l motor originally,... 'n it's Still got the 1.98:1 gears in the drive....

If so,.... Yer gonna need to regear it, before you find any decent results with yer prop search...

They don't make props to make up that kinda difference...
 
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steelespike

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

Bond-o said:
Ayuh,.... If yer turnin' those kinda rpms with a 21" prop,....

I'm gonna Guess that, that boat had a 3.0l motor originally,... 'n it's Still got the 1.98:1 gears in the drive....

If so,.... Yer gonna need to regear it, before you find any decent results with yer prop search...

They don't make props to make up that kinda difference...
Click to expand...
Good point but he's claiming he saw 38-40 at 5600. The calculator says a 21" with 1.98 at 5600 produces about 50.
At 4800 21" with a 1.98 nets about 43. 1.84 is about 46 at 4800. But we can't be sure what it is turning at this point.
It does seem that a 21 on a 17 footer would over rev but if it was we should see the speeds indicated.
 
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smoedog

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

The outdrive has 1.84r stamped on it. I before I go and rip the out drive off and count turns ill see if I can get another tach
 
Bondo

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

smoedog said:
I had my suspicion about this boat being repowered after I had to pull the motor to get to the young pipe laser weekend and saw that the federal motor mounts were shimmering with some pressure treated 2$4bs that look like they were cut in a hurry.. I'll go see if I can find the ratio of my drive... What ratio should I have?
Click to expand...

Ayuh,.... Generally the 4.3l runs 1.84:1 gears in a Big boat, 'n 1.65:1 in little hulls....

I'd think either would work in yer boat, but the 1.65s would probably be Better...
 
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smoedog

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

You I guess they repowered it from a big boat since it has 1.84 gears
 
Bondo

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

smoedog said:
You I guess they repowered it from a big boat since it has 1.84 gears
Click to expand...

Ayuh,... It might work Ok, with a 23" or more likely a 25" prop...
 
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smoedog

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

Well I borrowed a 26p Laser 2 from a guy who was selling it and tried it out. At 4000 rpm i was only running 32-33mph on GPS. Thats only a 1-2mph increase over the high five 21p I have been running. But on the top end it brought my rpms down to 5100-5200 rpm and i was getting 45-46 mph so I was happy. But a couple times after I got trimmed out, It felt like the prop lost traction and the rear of the boat came "loose" (sorry I'm a car guy), So I don't know what that was about, Idea's?

But the hole shot was horrible. It took a long time to get up onto plane, so I was worried if i could even get up with my family on board pulling my tube.

I am going to pick up a laser tach this weekend to verify the rpms. I think for know I'm just gonna look for a 25p 4 blade for cheap and wait till the off season to put the 1.65 gears in the outdrive, since everything else I read on here about comparable setups are running in the 40's with 19p props.

Any input or am i way off track? Or should I just pickup the laser 2 for the 150 the guy was gonna sell it for and go from there.
 
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steelespike

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

I think your tach is whacky At 5200 rpm 1.84 ratio 26" prop 10% slip would go 62 mph at 20% slip about 56 mph. 46 mph @ 10% indicates about 3800. 20% 4300
 
spdracr39

spdracr39

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

Could someone have changed his gears and not marked the drive ?
 
Texasmark

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

Not butting in but a vented prop can really help hole shot on a bass boat. I have no experience with I/O's and ports. Maybe steel or bond can help on that. What the holes do is to deliberately force the prop to ventilate reducing the load on the engine and allowing it to develop it's rpms rapidly which develops its HP rapidly and the hole shot is much faster.

Hole size is important as you need large enough holes to get some ventilation, but not so large as to cause the engine to run away. Once up and running they seal off by the prop wash and you don't know they are there other than sometimes in rough water you may do a little slipping, but trimming in a tad usually corrects that and for me, I like more of the boat in the water when rough, to utilize the V of the hull for smooth running so trimming in and slowing down comes naturally.

So, you get the best of both worlds, a prop that acts like a low pitch prop in the hole and a high pitch at WOT. Neat.

HTH,
Mark
 
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smoedog

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

spdracr39 said:
Could someone have changed his gears and not marked the drive ?
Click to expand...

Well I am gonna get a laser tach to verify rpms. If nothing comes up with that I'll pull the out drive IRS spin the motor by hand to verify the gears. It's just frustrating because something is up and can't understand why this boat is so slow
 
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steelespike

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Re: 17ft glastron prop help

Re: 17ft glastron prop help

Your not butting in; Can't make any progress without input from everyone.
As I understand it vented props aren't as effective on an I/O.
 
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smoedog

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Re: 17ft glastron prop help *Updated ran new prop*

Well i got a multimeter from autozone that would read rpm by hookng the positive lead to the negative post on the coil and the negative lead to a ground. Well my readings were good till i got to around 4k and then the meter got real inconsitant and started giving off random numbers.

So has anyone had success with a harbor freight laser tach?
 
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steelespike

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Re: 17ft glastron prop help *Updated ran new prop*

As I understand it the problem with the laser tach is you have to aim it at a spot say on the flywheel. In a boat while possible won't be easy.
Has anyone suggested the Tinytach.? $47 and will work on your motor and any future motors.Be sure to read all info before a purchase.
 
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