Need advise for best overall performance?

[pataterchip]

I have a 97 18' Nitro fish and ski. I use it mainly for fishing for fun.
The boat has a 2001 mercury 60HP bigfoot on it and is underpowered.
it has a 13 3/4"Dia x 15" pitch Michigan wheel 3 blade aluminum prop on it.
It has a really hard time planeing and I usually have to trim it up/out to get it to WOT but once it is planeing and trimmed up/out it will run roughly 5000 rpm maybe less (I don?t trust my tach) and my manual shows 6K as max.

I would like to know if a 14" Dia x 13" pitch 4 blade aluminum prop would be better for overall performance?

Also would like to know what the performance differences are between 3 and 4 blade prop for my application?

 

[QC]

Re: Need advise for best overall performance?

Well you need to verify your tach before you can really make any changes with any confidence . . . If your tach is right then you might gain a little hole shot and some RPM with the change you noted. Typically a 4 blade will cut RPM a little but a 2 inch drop in pitch should raise it more, so you should end up going the right direction.

 

[steelespike]

Re: Need advise for best overall performance?

The Big foot is a missmatch on a relatively light boat but to me something doesn't add up.My indications are the Nitro went out after 88. But tell us the weight and typical load.What is max speed?The big foot would normally require higher pitches on a relatively light boat.To me the sluggish hole shot and 15"pitch don't add up. Also 5,000 is low to me. If you were to try to get to 6000 you would need a 10" prop thats close to what you would run on a big pontoon.I would check that the throttle opens all the way,do a compression check.Be sure motor is in excellent tune.Check the tach,is the antivent plate (just above the prop)about even with the bottom of the boat?That would be the set up starting point.

 

[Silvertip]

Re: Need advise for best overall performance?

I would also make sure the engine is making full power. Changing props does not help an engine in a poor state of tune. A Big Foot motor has a 2.33:1 gearset and should twist a 15P prop with no problem. My 40 Evinrude ran best with a 15P on a 17 foot boat and it had 200 less CCs than your Merc. You should not need to drop to a 13P.

 

[john from md]

Re: Need advise for best overall performance?

I suggest that, no matter what you do with your prop, you should get a set of smart tabs. They will get you on a plane at a much lower speed and make the boat more stable as well.

As to your prop, you should go to michigan propellers page. They have all the info needed to determine if you need a pitch/diameter change. There are a lot of variables and it is not as straight forward as you would think.

Also, as Silvertip has said, make sure the engine is doing it's best. Has it been decarbed recently? have the carbs been set up? If not, you should take these actions before making a prop change.

Regards,
John

 

[pataterchip]

Re: Need advise for best overall performance?

I hooked up another tach and calibrated the one in the dash so it is reading correctly now. And the carbs were just gone through and cleaned and sent to a mercury authorized shop for syncing and tuneing. The motor was given a clean bill of health and is running quite well my problems are simple haveing to much weight in a boat that is under powered. I am working on re-powering the boat ( I really like this boat) but due to expense i need to get what I have as good as it can be.
I will lokk into smart tabs thanks fo the advice guys.

 

[steelespike]

Re: Need advise for best overall performance?

Don't forget the vertical height;it could mean a little better hole shot and up to 2 mph more speed,if you can gain an inch in height.And if you go with something like a Hustler turning point you coul get a smidge more height and speed.Don't forget one change at a time.How much weight are you carrying?

 

[pataterchip]

Re: Need advise for best overall performance?

I got the 13" pitch prop that I ordered but have not tried it yet, I will post results as soon as I do. I am also looking into trim tabs, that seems like a good idea regardless of the prop questions.

What do you mean by Vertical height? Are you referring to raising the whole motor ie... bolting it higher on the transom? What would this gain please explain.

 

[steelespike]

Re: Need advise for best overall performance?

Raising the motor gets less motor to drag through the water.Less resistance.
The anti vent plate(just above prop) even with the bottom of the boat is considered a starting point.As I said as little as an inch increase could net a couple of mph and a slight improvement in hole shot.Most larger motors have holes in the mounting bracket to adjust height.Don't change the height until you test the new prop.

 

[Silvertip]

Re: Need advise for best overall performance?

What speed were you running with the 15P prop at 5000 RPM? When you try the new prop, make sure you have the same load as before and again, provide us with WOT RPM and speed. I still fail to believe that that engine with a 15P prop cannot exceed 5000 RPM unless this boat is extremely heavy. Look at the capacity plate and tell us what the maximum rated HP is for this boat.

 

[steelespike]

Re: Need advise for best overall performance?

I hooked up another tach and calibrated the one in the dash so it is reading correctly now. And the carbs were just gone through and cleaned and sent to a mercury authorized shop for syncing and tuneing. The motor was given a clean bill of health and is running quite well my problems are simple haveing to much weight in a boat that is under powered. I am working on re-powering the boat ( I really like this boat) but due to expense i need to get what I have as good as it can be.
I will lokk into smart tabs thanks fo the advice guys.

Yes you are underpowered but the big foot is intended to perform well under those conditions.What kind of weight are you pushing,And what speed are you getting at 5,000?Without the weight,max rpm and speed there is no way to know if the setup is performing normally.

 

[pataterchip]

Re: Need advise for best overall performance?

I put on the 14" Dia X 13" pitch and ran it at the lake, it ran well much better than it did with the 15" I can provide the MPH speed still working on why that gauge doesn?t work. But 5400 RPM was as fast as I could push it I would guess around 30 MPH. I called Nitro and they informed me that the max HP for my boat is 150, and that completely dry the boat weighs 1600 Lbs, It is worth mentioning that this weekend i had 650 Lbs worth of people with fishing gear and an ice chest full of beer and ice The boat was full of fuel aprox 15 gallons with along with trolling motor, anchor tackle box etc...
I was pleased with the performance considering I know the boat is under powered, It will suffice for now. It did take a little longer than I expected to get to WOT and plane well.

 

[john from md]

Re: Need advise for best overall performance?

If you put a set of smart tabs on it you will get even better performance. They get you up on a plane faster and make the most out of the power that you have.

Regards,

John