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Discussion Starter · #1 ·
I need some schooling on prop pitch. I recently bought a used boat with a 1998 Force 120 on it. I took it to the lake and it feels really sluggish to me. With two people, two dogs, a cooler and a full livewell it barely gets on plane. I did a compression check and it's better than I expected. It's a 4 cyl and from top to bottom I got 140, 145, 150 and 152. That's an average of 146 and within the total deviation of 10%. I was told the carbs were re-built, new reeds and new plugs. The motor sounds good.

So, I'm questioning the prop becase the boat feels to me like a truck with oversized tires and a small motor.
The numbers on the prop are 13"x21-19. I called the manufacturer of the boat and they said the boat was shipped with a 12.5"x23.

I don't really understand how the numbers work on the pitch. Could this much difference make the boat feel the way I described?
 

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i ahve an 18ft skeeter wit ha 21pitch,its almost too much for my 115,if you were a big guy it miggt not plane out with full load
 

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my 115 probably has the same amount of power your force has cause the forces are tested for hp at the powerhead not the prop,or so i have read off of bbc
 

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Discussion Starter · #7 ·
So is the 13"x21-19 prop a variable pitch? Is that a taller, or higher speed prop than the 12.5"x23?
 

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I'm 100% sure it is...

Try going with a smaller pitch... I'll also suggest trying a 4 blade..

I'm sure if you take it somewhere else like SC, Rosey, Plez, etc... It'll run good!
ya go 4 blade i would just not as good of topend speed,pm stickbait he may knoow
 

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ya go 4 blade i would just not as good of topend speed,pm stickbait he may knoow


My boat runs faster with a 4 blade due to the bow lift and less drag... But WTF would I know... I'm not a teenie bopper that knows everything.

I guess if you're concern about running 33 with a 4blade instead of 34 with a 3 blade on your skeeter then so it be.


Each hull is different.
 

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Just a quick question on the subject what are the pros and cons of running a 4 blade rather that a 3 blade? My boat came with a 4 blade on it.
 

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Just a quick question on the subject what are the pros and cons of running a 4 blade rather that a 3 blade? My boat came with a 4 blade on it.
generally speaking

4 blade- hole shot, bow lift, handeling

3 blade- top end speed... that's all i can think of...
 

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+1, good info there. Somewhere I have a pamphlet from North American Prop. Service. It has some of the same info. and a list of which props are are recommended for each of the manufacturers according to size, year, model, etc. If I remember correctly, this current one goes back 20+ yrs. If I can't find, I'll call back home and see if another can be sent out to me.
 

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Discussion Starter · #16 ·
Good info there, thanks! That explains the pitch. I always thought the pitch was measured in degrees. This system makes it easier to understand. The first number is the prop diameter, and the second is how many inches the boat would theoretically move forward with one complete revolution of the prop, with no slip.
So my prop is marked 13x21 but, the 21 has a dash stamped on it and there is a 19 steel stamped after the crossed off 21. So I'm guessing that a prop shop re-pitched the prop to a 19, right?

My next question is about hydrofoils. My last boat was a while back. It had an I/O with a 4.3litre V6 and had bad bow rise until it was on plane. I put a hydrofoil on the cavitation plate and that fixed the problem. One of those seems like it would help. Is there a reason you don't see them on many bass boats?
They sell these at Sportsmans Warehouse. Are they worth having? http://www.sesport.com/5_29.asp



Ok if you want to learn about props this will tell you all you want to know. It will also explaine what the differences are and why props do what they do. Hope this helps. Tom

http://sites.mercurymarine.com/portal/page?_pageid=126,48572,126_49259&_dad=portal&_schema=PORTAL
 

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OHHHHHH Lower Unit how right you are. A four blade will lift the whole boat stern first which in turns makes the boat flater...............................
 

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Good info there, thanks! That explains the pitch. I always thought the pitch was measured in degrees. This system makes it easier to understand. The first number is the prop diameter, and the second is how many inches the boat would theoretically move forward with one complete revolution of the prop, with no slip.
So my prop is marked 13x21 but, the 21 has a dash stamped on it and there is a 19 steel stamped after the crossed off 21. So I'm guessing that a prop shop re-pitched the prop to a 19, right?

That would be correct if the prop shop did their part.

My next question is about hydrofoils. My last boat was a while back. It had an I/O with a 4.3litre V6 and had bad bow rise until it was on plane. I put a hydrofoil on the cavitation plate and that fixed the problem. One of those seems like it would help. Is there a reason you don't see them on many bass boats?
They sell these at Sportsmans Warehouse. Are they worth having? http://www.sesport.com/5_29.asp
To each their own and depending on application sometimes there is a little to be gained with a hydro-foil. Typically on heavier, underpowered, or sluggish out of the hole boats people install them thinking it's going to make a boat perform better or faster. In some cases it does, but not typically a very noticeable difference to most people.

If your boat is mechanically correct is the starting point regardless of Hydro-foil or not. This includes proper motor height and propeller size. As mentioned altitude affects performance more than one thinks. The stock motor set up from the factory is good from sea level to 2500'. Going above that dropping prop pitch is a quick inexpensive way to gain back performance. If somebody knows they will be doing most or all of their boating at higher altitudes rejetting, high altitude gears in the drive, and other adjustments can be done to set the motor up.
 

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Discussion Starter · #20 ·
My old boat was a 87 Reinell 175A. Without the hydrofoil it would yank a slalom skier out of the water, but they had to hang on for a bit. After, I could pull two with no problem. I think your probably right about not needing it if the boat is set up well, but for $39 it does have me curious if it would help at higher altitudes. Living in Tucson I'll probably go to patty a lot, but not enough to make major changes that sacrifice performance at the lower lakes. For the price, it may be worth having for patty, and taking it off otherwise. Cheaper than a prop...

Another question is the reeds. I was told it has Boysen reeds. From my old dirt bike days we always used Boysen (dual stage) reeds to bring back some bottom end on high RPM motors. Max RPM is supposed to be 5250. Seems like dual stage reeds could be harder to open since it's not really a high RPM motor. But then, my dirt bike days were a while back. Maybe Boysen has single stage reeds these days. What's the favorite boat motor reeds these days?
 
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