1998 Force/Mercury 75 hp Prop size?

[RussellW]

I lost my original prop and replaced it with a 10 inch diameter 17 pitch 3 blade aluminum. The boat has a much slower hole shot now and maximum speed. Top speed two people 30 vs 38 before. With 3 people and a full livewell I can not even get it on plane whereas before it was not a problem. The motor is a 75 hp and it pushes a 17 foot 6 inch Challenger bass boat.
What size prop should I go to next?
Thanks for your help.

Russ

 

[hwsiii]

Re: 1998 Force/Mercury 75 hp Prop size?

Russ, you might try reading this, as a 10" diameter prop is not normally large enough to have enough surface area to push a boat that size. I have to assume you meant about a 13" diameter, because you should have noticed the change in RPM between the two props. I use a larger diameter than that on my 40 HP Force.

You might try reading these articles to have a better understanding of what is happening.

http://forums.iboats.com/showthread.php?t=369057

http://forums.iboats.com/showthread.php?t=381820

And if you have any more questions just repost back here and I will be glad to help you.



H

 

[RussellW]

Re: 1998 Force/Mercury 75 hp Prop size?

H,
Thanks for the quick reply and information. I have not read it yet. It is a 10" diameter prop. I had asked at a local marina what size to get for this boat and that is what they ended up ordering for me. Though it does say on the box that this prop fits up to a 75 HP. But obviously not pushing a boat this size. That will teach me to get the correct size on my own before trusting others knowledge.
I will read the info you provided and see if I can figure it out. I was hoping to shortcut it a little with this post. If you have any thoughts on what size diameter and pitch I should go with I would appreciate it. The "full throttle RPM range" according to the owners manual is 4750 - 5250. When running it with two people maxed out I think I was getting more like 4400.
Thanks for your help.

Russ

 

[hwsiii]

Re: 1998 Force/Mercury 75 hp Prop size?

Russ, exactly who is the manufacturer and what is the model number of the prop.



H

 

[RussellW]

Re: 1998 Force/Mercury 75 hp Prop size?

H,
The manufacturer is Quicksilver. It is a Black Diamond QA 2088R17. Note that I had edited my original post with some more info. Whoops not the original post but my reply.
Thanks.

Russ

 

[Frank Acampora]

Re: 1998 Force/Mercury 75 hp Prop size?

You are WAY overpropped. That engine uses a 10 X 13, 10 X 14 prop or (max) 10 X 15 prop. It is the same prop used by the 40 Mercs and you can buy any brand--it does not need to be Quicksilver. Reason? Merc made that year 75 and put a small Merc lower unit on it.

First 75 I worked on was the same size bass boat. I thought it would be a dog with that itty-bitty prop, but it went like a scalded cat. Apparently, Merc did their homework on this one.

 

[RussellW]

Re: 1998 Force/Mercury 75 hp Prop size?

Any tips on how I go about finding out exactly what the original prop for that motor and boat was?
Thanks.

Russ

 

[weerix]

Re: 1998 Force/Mercury 75 hp Prop size?

Hello,

I have a Mariner 75 HP of 1992 and I think you have to fit a 13 1/4 x 17
Oem no 4877344a4017p
thats the original on a 75 HP motor of mercury/mariner
I'm looking for the best on my motor in stainless steel
I'm reading a lot this moment to find out which one.

 

[Frank Acampora]

Re: 1998 Force/Mercury 75 hp Prop size?

Russ: Since the general rule of thumb is that 2 inches of pitch will change rpm by about 400 and since you really want to run near the top of the rpm range (especially with that engine), at 4400, you need to gain about 800 rpm. Dropping 4 pitches would probably put you in the correct area. So, a 10 X 13 would most likely be correct or close to it.

However, it is a difficult call on line. You really need to experiment. See if the dealer has any loaner props and try a 10 X 13 and a 10 X14 to see which is best for your set-up before buying.