MPH question....

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Bubba

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I've got a 03' HP170 with a yammi 90horse 2-stroke. I'm just wondering what kind of mph I should be seeing? I had my buddy gps us one day using his phone and it was giving a reading of 35-36(maybe 1/2 tank gas...two guys-400-425lbs, and average gear). I kinda thought it should be getting at least 40mph, or am I mistaken? Just wondering if the position of my motor could be off or what could be my problem(if any)? Before my speedo hole got plugged...it read right at 40...with a reading of about 42 being the fastest I had seen it, but my speedo hole is plugged now so I can't judge by it...but I know they are typically off anyways. Still got the stock aluminum prop(13x19).

Any of you guys know if what i'm getting is about right, or if does it seem kinda low to you guys? Just wondering if my motor might be positioned wrong, or what?
 
you should be doing better than that.. i do 34mph with GPS on my Smokercraft with a Johnson 50 SPL 1998 model..
 
do you know if your getting the proper rpms,maybe it's not going wide open or wrong prop?
 
Zum said:
do you know if your getting the proper rpms,maybe it's not going wide open or wrong prop?


I'm pretty sure its got the factory prop on it. Average rpm's run right around 5K...give or take 100...the recomended rpm range is 4500-5000.
 
Bubba - Below is a link to the Performance sheet on your particular 2003 model boat with a 80HP 4-Stroke. Given the 4-strokes are about 100lbs heavier and depending on the particular load you are hauling, I would think you should be getting somewhere between 38-44MPH out of yours. You might want to consider trying out a new prop or investing in a jack plate if you don't already have one.

https://www.fishingworld.com/G3Boats/Performance/bulletins/2002-april23-HP170wF80TLRA.pdf

Hope this helps!
 
Thanks Brian, I've never seen that one before. That's kinda what I was thinking...that one has a 80 4-stroke(about 100lbs heavier and 10 less horsepower) and its getting 39mph. That one is showing the same kind of prop as mine too on the 4-stroke(13x19).

Could that guy you were telling me about at Madisonville tell me what could possibly be my problem? And tell me how mine should be set up?
 
Bubba said:
Could that guy you were telling me about at Madisonville tell me what could possibly be my problem? And tell me how mine should be set up?

No problem. I know Mad. Marine would be a good place to start... ask to speak with Matt. Did you by chance test the compression on that motor when you bought it? How was it? I don't want to scare you... just covering all my basis here. It could be several different things or combination. If I had to guess at this point a Prop or Jackplate would be the answer. Matt might have some other ideas though. Give him a ring.
 
G3_Guy said:
Bubba said:
Could that guy you were telling me about at Madisonville tell me what could possibly be my problem? And tell me how mine should be set up?

No problem. I know Mad. Marine would be a good place to start... ask to speak with Matt. Did you by chance test the compression on that motor when you bought it? How was it? I don't want to scare you... just covering all my basis here. It could be several different things or combination. If I had to guess at this point a Prop or Jackplate would be the answer. Matt might have some other ideas though. Give him a ring.


I don't think its anything with the motor mechanically....its gave me no signs at all that something isn't right mechanically as far as running. Plus, it didn't appear to have been used much at all because it was spotless under the cowl.

One thing I am pretty sure about(from what i've looked on other forums from other people) is that G3 doesn't recommend a jackplate on anything other than the HP200's...At least thats what i've read from other G3 owners that have looked into it...they said it will void the warranty on anything but the 200's.

So i'm guessing it could be either the position of my motor(on the transom), or the prop...or both.

Thanks. I'll see about giving him a call this week!
 
Bubba said:
One thing I am pretty sure about(from what i've looked on other forums from other people) is that G3 doesn't recommend a jackplate on anything other than the HP200's...At least thats what i've read from other G3 owners that have looked into it...they said it will void the warranty on anything but the 200's.

This makes absolutely no sense to me... I talked to my regional sales rep and he wasnt sure about it. I've got a call into home office now. There should be absolutely no reason to void the warranty when it comes standard on the 200. I'll let you know what I find out.
 
G3_Guy said:
Bubba said:
One thing I am pretty sure about(from what i've looked on other forums from other people) is that G3 doesn't recommend a jackplate on anything other than the HP200's...At least thats what i've read from other G3 owners that have looked into it...they said it will void the warranty on anything but the 200's.

This makes absolutely no sense to me... I talked to my regional sales rep and he wasnt sure about it. I've got a call into home office now. There should be absolutely no reason to void the warranty when it comes standard on the 200. I'll let you know what I find out.


It seemed kinda odd to me too, but evedentally thats what a few other owners have been told...but like I said, thats just what i've read. The HP170, 180, and 200 are all the same exact hull(from what I understand) other than just the length, so I wouldnt understand how a jackplate would bother them and not a 200. :-k

You Da Man! =D>
 
I've heard that G3 will void your warranty for hanging a jack plate on one as well.

The boat in my sig is a Triton 170DS SC and it will run 47mph @ 5600 rpm with the same loading as you describe. I have a 90hp 2 stroke Merc and a 13 1/2 x 22 Laser II.

Your recommended rmps sound low to me. The other guys that I have seen talk about Yamaha's were all running over 5k.
 
Quackrstackr said:
Your recommended rmps sound low to me. The other guys that I have seen talk about Yamaha's were all running over 5k.

Quackrstackr is right on the RPMs... you should be turning around 5300 - 5500 with the particular motor.

I'll let you know about the warranty as soon as I hear from the factory.
 
G3_Guy said:
Quackrstackr said:
Your recommended rmps sound low to me. The other guys that I have seen talk about Yamaha's were all running over 5k.

Quackrstackr is right on the RPMs... you should be turning around 5300 - 5500 with the particular motor.

I'll let you know about the warranty as soon as I hear from the factory.


I'm not so much worried about the warranty...just that it could have the potential to mess up my boat. Mine hasn't got any warranty left on it anyway...just kinda curious as to why they don't reccomend a jp.

I may try to give madisonville a call today and see what he thinks.
 
I just spoke with Roger at the home office in MO and he said that the rumors were in fact truth... HP 170 and 180 model boats are not warrantied if a jack-plate is installed on them. I asked why, since it was a standard feature on the HP200 and the response was that the HP170 & 180 model boats had not been tested with JPs and approved by their engineering team but that the HP200 had.

Since the HP 170 & 180 are the exact same material and structural design as the 200, the likelihood of damaging your boat by having one on it should be extremely small..if at all existent. However, thats a decision you'll have to make for yourself.

As for the warranty on your boat, there might be some left on it. You should be able to give name of the previous owner and the serial # off of your boat to the guys at Madisonville Marine and they could tell you for certain if there was any left or not.
 
G3_Guy said:
I just spoke with Roger at the home office in MO and he said that the rumors were in fact truth... HP 170 and 180 model boats are not warrantied if a jack-plate is installed on them. I asked why, since it was a standard feature on the HP200 and the response was that the HP170 & 180 model boats had not been tested with JPs and approved by their engineering team but that the HP200 had.

Since the HP 170 & 180 are the exact same material and structural design as the 200, the likelihood of damaging your boat by having one on it should be extremely small..if at all existent. However, thats a decision you'll have to make for yourself.

As for the warranty on your boat, there might be some left on it. You should be able to give name of the previous owner and the serial # off of your boat to the guys at Madisonville Marine and they could tell you for certain if there was any left or not.


Yeah, I checked on the warranty when I bought it. There were only like a couple months left when I bought it...so I didn't bother. Mine(being an 03') doesn't have the lifetime hull warranty like the new ones do.


Thanks for looking into that! I'm kinda thinking like you though...if I decided I want to put a JP on it, I wouldn't see how it could hurt since they are the same as the 200's. But I don't know if I wanna worry with going that far on it right now anyway. I'm gonna see about taking my buddy out with me with his phone(Blackberry with GPS) and do some figures and see what kinda rpm's i'm running at optimum speed. Then go from there in deciding if I need to look into a new prop. I'd like to see it be able to hit at least 40. After I do that, if I can't figure out anything i'll probably wait and see what Madisonville have to say about it...and if I need to think about a new prop.
 
What set of holes is your engine mounted in currently? It could be mounted too low.

I'm not familiar with recommended pitch sizes for a Yamaha to be able to suggest what to go to but I know that Yamaha will use a smaller pitch than a Merc. because of the gear ratio difference.

There are a lot of different prop calculators out there that should get you in the ballpark of what you need to be running.

I would try to tune in the prop before adding a jack plate.

Your rpm and speed just sounds like a prop problem that may not be improved much with a jack plate.

Our boats are roughly the same dims with pad hulls and near identical weights with the same hp. and mine doesn't have a jack plate. You should be doing better than what you are currently running.
 
Quackrstackr said:
What set of holes is your engine mounted in currently? It could be mounted too low.

I'm not familiar with recommended pitch sizes for a Yamaha to be able to suggest what to go to but I know that Yamaha will use a smaller pitch than a Merc. because of the gear ratio difference.

There are a lot of different prop calculators out there that should get you in the ballpark of what you need to be running.

I would try to tune in the prop before adding a jack plate.

Your rpm and speed just sounds like a prop problem that may not be improved much with a jack plate.

Our boats are roughly the same dims with pad hulls and near identical weights with the same hp. and mine doesn't have a jack plate. You should be doing better than what you are currently running.


My motor is set all the way down on top of the transom(top hole). It's hard to compare exactly what I should be running as there isn't many people with the same exact setup as me....but like you said...I'm kinda thinking it should be running a little better than it is. I'm gonna try to get some readings on my rpm's/speed and stuff, then do some looking into what prop or motor position mine be better suited for me.

Not saying this is absolutely the problem, but what exactly would changing my motor height do for me(considering not changing props)? Will it allow my engine to turn a few more rpms?(basically what lowering my prop pitch would do?)
 
It should pick up on the speed as you won't be pushing as much of your lower unit through the water. It may bump your rpm's up a bit as well.

I think your motor is too low.

Most boats have the motor mounted on the next set of holes down, leaving a gap above the transom. The motor mount tends to pinch the transom when set all of the way down.
 
Let me get a couple things straight as far as props now...

What exactly will increasing the prop diameter do?(Like if I went to a 13 1/4" or 13 1/2" diameter) Increase/descrease rpms? More take-off, More speed, or both?

And lowering the pitch of the prop increases the Rpms, correct?
 
Increasing diameter will drop your rpm's. I don't know how much effect it has on speed but it supposedly helps in load carrying ability while staying on plane.

Decreasing pitch will increase rpm.

There's the whole stainless vs aluminum thing too. You can turn a bigger ss prop than aluminum at the same rpm because of decreased flex and usually thinner blades.
 

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