Prop Help Needed

[Bilmus]

For years I have suffered with an exceptionally slow boat. Recently in talking to a friend, he indicated that the prop and not the engine might be the issue. The background data is: Bass tracker 16' deep V aluminum side console fishing boat. 40 horse 2002 Mercury pro series outboard engine. By myself the boat will reach plane and take off, with my kids and the fishwell full, we are passed by pontoon boats. The boat never reaches plane. The engine runs great, starts right up with no hesitation and runs well. The current prop is 10.5 x 13P. The max RPMS the engine will reach is 4500, the listed max RPMs is 5500 so the max RPM's that I can acheive with the current prop is ~ 1000 below what the engine will allow.

Thoughts or help would be appreciated.

 

[rndn]

Re: Prop Help Needed

First off, Welcome to the iboats.com forum!!

You are correct that you need to gain 1000 rpm's, but I doubt your prop is the problem. For each 1 inch of pitch change you should move your rpm's by about 200. So if you drop 2 inches in pitch, you should raise your rpm's by 400. I find it very hard to believe you need to drop 5 inches of pitch and of more suspect is possibly your motor is mounted too low and causing excessive drag in the water. As a good starting point, where is the anti-cavitation plate in comparison to the bottom of the hull? You would lower the motor all of the way for the measurement. Does your motor have hydraulic or electric tilt and trim? Does the prop look like it's in like new or close to new condition? For the entire time you have had this boat/motor package, has it always been slow with a load? What boat do you have and what is the maximum suggested horse power rating on the coast guard tag?

 

[Bilmus]

Re: Prop Help Needed

I will follow up on your questions when I get home tonight. Some of the background, I can answer now.

1. Where is the anti-cavitation plate in comparison to the bottom of the hull? I will measure it when I get home. I do have a trolling plate mounted to the motor. We suffered poor performance before the plate was mounted but I could easily remove it to see if there is a definable change.
2. Does your motor have hydraulic or electric tilt and trim? Yes.

3. Does the prop look like it's in like new or close to new condition? This prop was installed in 2002. It is not the original prop, the original prop was dinged and taken off for repair. It was the sampe prop Dia and Pitch. I have the repaired prop, never re-installed it. The current prop has a small nick in 1 blade where I ran into a shoal last winter on the local lake. The ding is small as I saw the ground coming up, killed the engine and was almost stopped when the blade hit. The performance issues predated this prop and ding.

4. For the entire time you have had this boat/motor package, has it always been slow with a load? Yes, we are the original owners.

5. What boat do you have: BassTracker deep V aluminum fishing boat with side console; Pro Guide? V-16 SC.
6. What is the maximum suggested horse power rating on the coast guard tag? I will check when I get home.

Also, thank you for your time on this.

 

[rndn]

Re: Prop Help Needed

Thanks for the information and you're very welcome for the information and time thus far. I will keep checking this post and wait for you to post the additional information.

 

[steelespike]

Re: Prop Help Needed

That is a lot of boat for a 40 so setup,weight and weight placement is critical.
if your tank and battery are in the rear move some thing forward even if only to the mid way point. minimize load.aluminum cans,less ice in a styrofoam cooler kept shaded,a light effective anchor like a Danforth.
As suggested motor height can be critical.A good starting point is with the antvent plate even with the bottom of the boat.Raise the motor a hole at a time to a point just before venting becomes a problem.A setting just on the edge of venting should work best.Sometimes you have to trim in for turns to get a setting best for straight line.An inch up could gain about 2mph under ideal conditions.If this allows you to plane with a load it could double your loaded speed.This should also improve your rpm.Let us know how you make out.

 

[Bilmus]

Re: Prop Help Needed

Okay, the rest of the data is:

1. I have 1.5" of clearance between the top of the prop and the bottom of the anti-cavitation plate.

2. The moter is set as low as it can be, there are 3 holes with the bolts in the top one. I can raise the motor by ~ 1.5" if I go to the bottom hole.

3. The bottom of the prop appears to be 15" below the bottom of the boat. The anti-cavitation plate is in line with the bottom of the boat.

4. The "Happy Troller" trolling plate extends 11" behind the anti-cavitation plate and is 10" wide. I can pull a handle and it will drop down into place behind the prop. It is normally locked in a straight back position. I have used it twice int he last year.

5. The coast guard sticker is gone. I will call Bass tracker and try to confirm the max HP. I did note on the 2008 model which looks to be the same boat with a few minor changes (location of the minnow buckets, etc) calls out a Max HP of 75 for the boat.

 

[rndn]

Re: Prop Help Needed

You should try to raise the motor one hole at a time and see if it performs better. The thing to pay very close attention is to make sure you are still pumping water at the higher mounting locations. You should be but just make sure. It does sound like it's mounted too low and you may be a bit over-propped which would cause it to not be able to plane with a load on the boat.