# aluminum vs steel prop



## mean16 (Jul 13, 2010)

i can get a 3 blade aluminum for $60 or a 3 blade steel for $120
what are the pros and cons of either prop and which would you go with?


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## Quackrstackr (Jul 13, 2010)

Pros of SS: you can run less pitch because of no blade flex, much more durable
Pros of AL: cheap, possibly some degree of l/u protection from prop strikes (debatable)


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## Captain Ahab (Jul 13, 2010)

Quackrstackr said:


> Pros of SS: you can run less pitch because of no blade flex, much more durable
> Pros of AL: cheap, possibly some degree of l/u protection from prop strikes (debatable)



That is it in a nutshell



You will get more out of a SS prop - what are you putting it on?


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## nyjay75 (Jul 13, 2010)

If your gonna be around rocks and stumps, go with alluminum. If not you stand a good chance of snapping a shaft.


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## Quackrstackr (Jul 13, 2010)

Aluminum props are not a cure all for l/u failures because of prop strikes. I've run both. Either of them can cause l/u damage. People have a preconceived notion that a ss prop is going to detonate your lower unit every time that you hit something but an aluminum will shed blades before it happens... it simply is not true.

An outboard isn't a mud motor that is designed for that kind of abuse, regardless of prop material.


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## mean16 (Jul 13, 2010)

7.5 mercury on a 1636 monark
it is really slow right now with the 2 blade that is ate up from shallow rivers

what would be the best pitch?


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## crazymanme2 (Jul 13, 2010)

That horse power on that boat I wouldn't go over 9 pitch.You don't want to over prop your motor.That is the quickest way to ruin it.You want it to run the max rpm's that it was designed for.


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## Whoopbass (Jul 13, 2010)

Your little 7.5hp motor is not going to be any faster with a SS prop. 200 hp motors only see a few mph gain.
Your boat is 16' right? 7.5hp is not much motor for that boat. 
I like to think that aluminum props offer more LU protection then SS but its just a guess. I have gone through my share of aluminum props because of rocks in shallow rivers and never had any LU issues.

Another thing....I can almost guarantee your boat won't be any faster with a brand new prop of any material versus the beat up prop that you have. I have ran some gawd awful beat up props on my 25 hp and my boat speed never seemed to increase after a brand new prop install.


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## mean16 (Jul 13, 2010)

that is the exact opposite of what the dealers tell me... and then again they are looking for a quick sale, but they have said it will make a big difference in speed. i watched a video of a 7.5 merc on youtube plane a 16' v-bottom. i hope it makes a difference because it is so slow it seems more of a pain in the rear than it's worth somethimes, and reverse is even worse. i think going from 2 blade to a 3 blade will make some difference though, guess we'll see. probably go with the aluminum though because of the cost difference and if i decide to put it on the river it would be somewhat safer for the motor


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## Quackrstackr (Jul 14, 2010)

2 blade props are more efficient than 3 blade. That's why you see a lot of those on small hp motors. 3 blades get better bite.


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## perchin (Jul 14, 2010)

Mean16...... I'm going to be doing the same thing. My 9.8hp has a two blade prop, and I want to switch to a 3 blade prop. One of our neighboors switched his 2 blade to a SS 3 blade and can now plane a 16' Lund, with the same motor as me. Problem I'm having is finding someone who still makes em'. :x As far as efficiency..... I could care less.


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## mean16 (Jul 14, 2010)

what do you mean as far as efficiency? i just want to get to the honey holes faster than i am now with out harming the motor. i have been around bass boats all of my life thanks to my grandfather, but this is my first jon boat and i am learning something new everyday.


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## perchin (Jul 14, 2010)

mean16 said:


> what do you mean as far as efficiency? i just want to get to the honey holes faster than i am now with out harming the motor. i have been around bass boats all of my life thanks to my grandfather, but this is my first jon boat and i am learning something new everyday.



I mean as far as gas mileage. Its not too often I buy a toy, just to worry about its fuel consumption.


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## Quackrstackr (Jul 14, 2010)

All things being equal, a 2 blade should be faster and more efficient than a 3 blade because of reduced drag and friction, less rotating mass, etc.

It just depends on what you want. More blades equals more low end performance and less blades equals better top end.

Notice on most trolling motor props that their 2 blade versions are usually marketed as "power props" while their 3 or even 4 blades are general purpose or weed whacker props.


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## perchin (Jul 14, 2010)

Quackrstackr said:


> All things being equal, a 2 blade should be faster and more efficient than a 3 blade because of reduced drag and friction, less rotating mass, etc.
> 
> It just depends on what you want. More blades equals more low end performance and less blades equals better top end.
> 
> Notice on most trolling motor props that their 2 blade versions are usually marketed as "power props" while their 3 or even 4 blades are general purpose or weed whacker props.



yes... all things being equal. Although when we are talking about a 7.5hp that will not get onto plane with a 2 blade prop, if the 3 blade prop gets it on plane, then it is definatley going to go faster, and also be more efficient, not just plowing wide open. Although I don't think a 7.5hp anything is going to get a 16' on plane. So???


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## Quackrstackr (Jul 14, 2010)

Hey, I'm just telling you guys the physics of prop design and how it pertains to properly sized motors.

I can't help it that you both need motors that are actually suited to the task instead of trying to make them something that they are not. You can't make a silk purse out of a sow's ear. :lol:


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## Captain Ahab (Jul 14, 2010)

mean16 said:


> 7.5 mercury on a 1636 monark
> it is really slow right now with the 2 blade that is ate up from shallow rivers
> 
> what would be the best pitch?




I woudl not waste the money on a SS prop for a motor of that size. Instead, get a few different aluminum or even composite props with different pitch and blades and see which gets you what you want with your motor, hull and weight


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## lckstckn2smknbrls (Jul 14, 2010)

What ever prop you get I suggest getting some type of prop protector. I have a Mac's River Runner on my motor.


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## Quackrstackr (Jul 14, 2010)

Captain Ahab said:


> mean16 said:
> 
> 
> > 7.5 mercury on a 1636 monark
> ...



Wise man.

If repeated prop strikes on rocks are a concern, I wouldn't get a ss prop regardless of motor size just from the refurb/replacement aspect of it. There's nothing cheap about ss props no matter how you slice it.

In that same thought process... beware of the composite props and rocks. Those are pretty much toast after one strike unless you can find one of the ones with replaceable blades to fit your motor.


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## WTL (Jul 14, 2010)

I was looking for a SS prop the other day, just out of curiosity, and I'm not even sure they make one for mine? Do yall eer see SS props for the old style hub, 9" OMCs? I think my motor was on a sailboat before me, so certainly repropping it is worth considering.


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## Zum (Jul 14, 2010)

Holy pie man...easy
Pretty sure it was meant to be funny,with some truth in there as well.
Must be hot down there,chill.


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## Brine (Jul 14, 2010)

Just clocked in.....







cleaning in progress.....


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## mean16 (Jul 14, 2010)

i'm not wanting to make something out of nothing here, just getting opinions. the guy with the props also has a good used 2 blade that i could get but i have been told a 3 blade is the way to go. like i said in previous posts i'm new to jon boats and small motors, i'm just looking for the best bang for my buck. this 7.5 has to push the boat faster than it does now, i'm not kidding when i say it's slow at full throttle 5-7mph at a guess. with the prop being ate up as bad as it is i only ran it at about half throttle. i just got the boat this past friday and the motor 2 weeks ago. the day i got the motor i put it on a 1430 i had and it did ok with a person on the front bench but the boat was a suicide boat, a good gust of wind is all it would have taken and i would have been swimmin' so i sold it thursday and got this 1636. i just want to go faster than 5mph so what is my best option 2 or 3 blade?


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## Brine (Jul 14, 2010)




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## Brine (Jul 14, 2010)

I'll be interested to hear your results. I've got a 7.5 I'm using on a 16 footer myself. Won't be water testing it for a while though.


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## Zum (Jul 14, 2010)

Lol,Brine.
I'm guessing like someone suggested before,a 3 blade with enough pitch to get you close to planeing.
You'll be running your motor at it highest rpm's and it still may not plane.
If you don't plane you'll never get much for speed,,,not sure if your motor is big enough.
Maybe someones running close to the same setup,they'd could be more help.


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## Brine (Jul 14, 2010)

I suspect you're right Zum. I fish 90% electric only but a few state parks that have 9.9 restrictions, and seeing how the 7.5 was a gift from an x-member on here.....It'll have to do. :LOL2:


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## Rat (Jul 14, 2010)

For all out high end you need the two blade; for hole shots you need the three blade - all else being equal. But all else is rarely equal. 

A two blade prop will give more vibration in the lower RPM range; if you troll with the gas motor this will equal more stress on the drive train and transom. A three blade is better balanced and will perform better at low RPM and, generally, through the whole RPM range up to about 2/3 throttle where the characteristics of the two blade really begin to outperform. 

The trick is to get a good hole shot with good top end, quality 3 blade props will do this much better than 2 blade props. A three blade prop can be 'massaged' by a prop shop to perform better through the whole range than a factory 2 blade; of course the same can be said of a custom 2 blade as well. 

Considering the use of the boat and the fact that 'most' of us go out pretty loaded I would start with a good 3 blade prop and tune it from there. Using a Dole-Fin or equivalent will allow you to jump on plane quicker as well as give you some better steering control while on plane. They can cause more drag lowering top end slightly if the motor height isn't perfect tho; but the trade-off is usually worth it. Playing with the diameter and the pitch of the prop will get you where you need to be with your motor. Ideally you want to get out of the hole as fast as you can and get the most top end speed while hitting the RPM your motor suggests. 

The real key is getting the right pitch and diameter for WOT and then 'massaging' the prop for better low end performance or to negate ventilation. This is probably more than you want to do on such a small craft though. 

IMO 2 blade props should only be used on high speed hulls designed for super high top end speeds, and trolling-motors. 

Some good pointers I learned about all this long ago:
1) Make sure your motor is as high as it can be; get as much of the lower unit out of the water as you can. Mine is high enough that it ventilates in tight turns, which is fine with me; it means I can get as much out of her on a straight run as I can. 
2) Use a Dole-Fin or trim tabs, they work very well at getting stern heavy boats out and on plane fast. A Dole-Fin will also halp with steering while running on plane.
3) Get the right diameter and pitch prop. Start with the factory sized prop and adjust from there; you will need a GPS (for speed) and a tach for RPMS to dial a new prop in right. 
4) Do all this with the normal load of the boat. It doesn't do much good to prop the hull with just yu in it and then add 800 pounds of people and gear; you will be under proped then.


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## Waterwings (Jul 14, 2010)

:-k All of this makes me glad I fish electric-only 8)


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## mean16 (Jul 14, 2010)

thanks for the info man. i'm registering the boat and trailer tomorrow and will get the prop next week (payday) is it normally pretty expensive for a shop to work on them? the guy said i can go from 8-11 pitch at the same cost but he said a 10 would probably be best. i don't know much about this stuff so what would you say? the boat is pretty heavy and most of the time i will have about 400-500lbs plus the weight of the motor on the boat for now, but i would like to deck the floor one of these days


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## mean16 (Jul 14, 2010)

here is my project... don't laugh!
https://i325.photobucket.com/albums/k390/1996gmcjimmy/1636%20monark/1636.jpg
the prop
https://i325.photobucket.com/albums/k390/1996gmcjimmy/1636%20monark/prop1.jpg
some nice seats i picked up for $24 each from the same guy with the prop
https://i325.photobucket.com/albums/k390/1996gmcjimmy/1636%20monark/seat.jpg


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## mean16 (Jul 14, 2010)

how can i find out what year the motor is?


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## Brine (Jul 14, 2010)

Nothing to laugh at Man. Nice rig.

FYI, in your photobucket account when you choose to upload pics, there is a option to upload them to a specific size. Click the more options link right below the Upload button, then choose the 640 x 480 one, and your pics can then be posted straight to the site.

Also, I'm pretty sure you can check the serial number on the motor and cross reference the year it was made. If you need help, there are enough motorheads on here to help ya out. 

Good luck!


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## Quackrstackr (Jul 14, 2010)

Yikes. :shock: 

After looking at your prop, I'm going to go out on a limb and say regardless of what you do.. you will see an improvement.


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## Whoopbass (Jul 15, 2010)

Quackrstackr said:


> Yikes. :shock:
> 
> After looking at your prop, I'm going to go out on a limb and say regardless of what you do.. you will see an improvement.



You really think so? The prop doesn't look that bad to me. Looks like its just missing some paint and the edges are pretty worn.
I'm still sticking with there is no way to get any noticeable performance out of that motor (i'm assuming its running fine). It might seem a tad faster the first or second time he's out but its going to turn back into a slug soon and he's going to want more power which will mean a new outboard like a 15-25 hp.
I've ran props with gouges, large nicks and pieces out of them and a then replaced them with a new prop and the performance was always the same. 

I would buy a cheap compression gauge and see what it reads before I dumped money into that motor. That motor should be able to plane that bare bones boat out with just you in it but when you start adding weight that motor is just to small.
That's a 1970's motor by the looks of it. Find your serial # and then compare it to this: https://stores.ebay.com/Outboardnuts/Mercury-Year-Lookup.html


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## Rat (Jul 15, 2010)

That prop doesn't look to be in bad shape really, but who knows if it is even close to being the correct prop for that hull. I think you will be happier with a good 3 blade prop. I just realized that this thread was about Alu vs SS. I would stay with Aluminum on this motor; just because a SS will cost more than the entire motor is worth! Really on a small craft with moderate speeds an Alum. prop is fine and I doubt you will see a difference in the two alloys. Keep the 2 blade in the boat as a spare and throw in some cotter pins as well and whatever else you need to change the prop.


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## Quackrstackr (Jul 15, 2010)

I was just going by the blade geometry and a quick picture search for equivalent props.

My trolling motor has more aggressive blade geometry. :lol:


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## mean16 (Jul 15, 2010)

the guy showed me a good 2 blade and there is a big difference in the width across the blades and length of blades compaired to mine. aluminum 3 blade to come next week! think i might paint my boat trailer and truck matching camo


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## Quackrstackr (Jul 15, 2010)

mean16 said:


> the guy showed me a good 2 blade and there is a big difference in the width across the blades and length of blades compaired to mine.



That's what I was thinking.

Your prop looks just like what a mud motor prop looks like after several hours of grinding through mud and debris... and when it is time to replace them.


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## perchin (Jul 15, 2010)

mean16,
what supplier did you order from? I have not been able to locate one yet.


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## mean16 (Jul 15, 2010)

local dealer, if you like i can get you some information when i go out there next week


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## perchin (Jul 15, 2010)

mean16 said:


> local dealer, if you like i can get you some information when i go out there next week



That would be great... thanks man. Its a 1966 9.8hp (110 model) Merc. All of my local shops say they can no longer get them, if yours can I be glad to order through them.

Thanks again.


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## mean16 (Jul 17, 2010)

i have the guys cell number i will call him tomorrow.

took the boat out this evening caught a 4' gar on on a 3" perch as i was reeling in, man them suckers put up one heck of a fight! took the camera with but flash wouldn't work so pictures didn't turn out. rewired the trailer today and it worked good until i loaded the boat and then nothing... 2 hours later i'm home!


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## mean16 (Jul 20, 2010)

sorry man no luck on a prop for ya, he said you never know what will come through the door though. if you'd be interested in a good used 3 blade he'll let me know if anything comes up that is direct fit/interchangeable


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## mean16 (Jul 23, 2010)

got one! the guy ordered me a 10 pitch and the company sent an 8. don't know what the difference is between the two or how they will act but i got it for $63.72 out the door. they said if i don't like the 8 pitch bring it back and they will order me a 10. was going to the lake this evening but my babysitter just backed out on me, i'll let ya'll know results when i can get on the water!


updaterop wouldn't turn w/o hitting the motor, it's a 9.25 and i need a 8.75 or so (if they make that)


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## Quackrstackr (Jul 23, 2010)

Sounds like they ordered the wrong prop all the way around or the wherever they ordered it from really screwed up.


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## mean16 (Jul 24, 2010)

i think your right... i have searched the net pretty good and came up empty handed. this one is a solas "amita 3" and has a extra wide blade design for 4 stroke motors, but thats not what i need. very nice prop, i wish it would have worked. i'm beginning to wonder if i can even get a 3 blade for a 71-72' 7.5 merc, guess i'll take this one back and take the motor with me in the morning.


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## mean16 (Jul 26, 2010)

well i took the 3 blade back to the dealer today and he had a 2 blade that fit my 7.5 so i snached it up for $20 which saved me $43.75. the origional prop is a 6 pitch and this one has a 9 pitch. whats going to be the difference between the two? i called iboats service center and they only had parts for a 1976 and mine is a 1971 so i guess they wouldn't interchange and the mercury service guy thought i was dumb or something because he didn't know why i would even want to put a 3 blade on such a small motor.


any luck perchin?

here they are side by side
https://i325.photobucket.com/albums/k390/1996gmcjimmy/props.jpg


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## Quackrstackr (Jul 26, 2010)

That all depends on how much of a load your boat is for that motor.

Theoretically, it will be faster... if the motor can handle it.

You will drop somewhere in the neighborhood of 600 rpm with a jump in pitch that steep.


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## perchin (Jul 26, 2010)

no luck here ...... honestly i've been waiting to see what your results were before i made an order from the same place . i've been hoping it made a noticeable difference on yours , then on my 10hp. that would make a difference . Hmmm. i've also been looking for a 15hp without any luck so far.


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## Zum (Jul 26, 2010)

Wow,that one looks pretty wide(longer)as well.
Is it going to spin without hitting?
Like mentioned before,if your motor has the power,in theroy you should go faster.


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## Zum (Jul 26, 2010)

mean16 said:


> well i took the 3 blade back to the dealer today and he had a 2 blade that fit my 7.5 so i snached it up for $20 which saved me $43.75. the origional prop is a 6 pitch and this one has a 9 pitch. whats going to be the difference between the two? i called iboats service center and they only had parts for a 1976 and mine is a 1971 so i guess they wouldn't interchange and the mercury service guy thought i was dumb or something because he didn't know why i would even want to put a 3 blade on such a small motor.
> 
> 
> any luck perchin?
> ...


I found this link,to me it says that the 68-85 all take the same type prop?
Opps forgot the link https://www.propcopropellers.com/mercury_Outboard_Propellers.htm
I say this because then the 1976 prop on iboats(3 blade/3 different pitches) should fit./
Also found this link about a guy with a similar motor(81 I think)and he found a 4 blade prop(Solas part number (1113-100-07)).
Heres the article,I only read the first 2 paragraphs.
https://www.sailingtalks.com/forums/archive/index.php/t-29192.html


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## Quackrstackr (Jul 26, 2010)

Although the shaft splines look the same, that looks to be a bigger hub diameter.


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## mean16 (Jul 26, 2010)

i thought so too but it is flared out at the front then goes to the same diameter as the old one. about 1/4" of the rear goes into the l/u as the original did too. i put it on at the shop before i bought it, it spun freely and the shop owner also inspected it, but it is quite a bit larger. 

i also have the reverse problem as mentioned in the link above. i was hoping it was just because of the crappy prop i had on there. what is he talking about drilling a hole in the exhaust chamber? i just started to camo the boat and wasn't planning on taking it out until it was done but i don't think i can wait that long.

thanks for the info zum, i picked this one up cheap enough where i can research this and maybe get in contact with solas and find a 3 blade made for speed instead of thrust


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## Quackrstackr (Jul 26, 2010)

I must have missed the discussion about drilling a hole but that is normally done to help get your boat on plane with high pitch props.

Mercury puts ventilation holes on many of their props for their larger motors as standard. I can't remember if mine has 3 or 4 holes in it. I have them all plugged with solid plugs because I don't have planing issues.

The holes let a small amount of exhaust gas out which will ventilate your prop and get your rpm's up to help it plane. Once you get up to speed, the water pressure causes the holes to seal off.

My motor acts like it has a spun hub with the largest diameter set of plugs in the holes until it bites.


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## mean16 (Jul 28, 2010)

with this old boat and motor i'd be happy if it came colse to plane, any improvement would be better than what i had.
Quackrstackr i'd take a kick in the face for your boat #-o


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## Quackrstackr (Jul 28, 2010)

If you're ever in this neck of the woods give me a shout and we'll take it out.


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## mean16 (Jul 28, 2010)

hows the deer huntin' over there?


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## Quackrstackr (Jul 28, 2010)

Just depends on who you talk to and where you are.

We have some nice deer but there's no wallhanger behind every tree like the hunting media is protraying us to have.


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## mean16 (Jul 29, 2010)

wasn't the "amish buck" killed in ky? that was a big sucker


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## Quackrstackr (Jul 29, 2010)

Yeah.

Killed within rock throwing distance of a friend's farm.

But they've owned that farm for years and never seen anything that even begins to approach that deer. That's kinda what I was referring to.


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## mean16 (Aug 1, 2010)

the big fellers are few and far in between around these parts, they are here but very stealthly like all of em' 


took the boat out this weekend with the new 2 blade and man what a difference. was very close to plane with just myself. i'm around 200 my grandfather is around 270 and the boat was loaded with gear and it was still 10 times faster than it was before with just me. i'm still going to keep my eye out for a 3 blade but i'm ok with what i have for the time being. i also adjusted the trim on the motor today and ran it for a bit but i didn't notice a difference. i only moved it up 2 pens because i didn't want it to get too far out of the water. would it be ok to go up another spot or two or should i just leave well enough alone?


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## Zum (Aug 2, 2010)

I always tinker with stuff like that.
Just make sure it pumps good water.


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## mean16 (Aug 3, 2010)

as it sets now it looks like i can see the top of the cavation plate at full speed, not quite out of the water but close


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