Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

[JanKsterS]

Hi, I am new here. I've got a 14ft Grumman bass boat with a 1998 2-stroke 9.9hp Johnson on it. The prop right now is a 9.25" Diameter, 8 pitch. I feel like the boat isn't getting up out of the water fully with 2 people sitting in the driver seats. When my girl sits on the bow, we seem to plane out better. Initially I thought the prop may be too low of pitch so I tried out a 10 pitch, but that bogged the motor down. Now I am thinking two things; either I need to leave the 8 pitch on and adjust the trim, or I need to drop to a 7 pitch. I see people on the lake going 3-4mph faster than I am, and I am in a 14ft aluminum hull boat! What do you guys think? I know the smartest thing to do would be to get a tach and optimize it that way, but I dont have the time or money.

Here are my weights:

Boat: 425lbs
Motor: Approx 100lbs
2 People: 350lbs
Gear: Approx 75-100lbs

Total Max Weight: 975lbs

 

[steelespike]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

It would help if you get us the gps speed lightly loaded and loaded.some cells have a gps app. Of course weight and a weight placement is very important,
As is the motor trim. Definately try different trim settings.
If your boat is 425 lbs Is that the boat dry weight,no motor?
425 lbs dry weight is not a light aluminum boat.I have a 18 foot bare utility that is 330 lbs. dry weight.
My 18 full up weight with me in the boat is about 900 to 1,000 lbs. I run a 50 hp and the boat has a big foot print to help get the boat up on the water. If you empty the boat and get us the gps speed with you alone it would help evaluate your setup.
On a light reasonably fast boat the 9.9 should make over 20 mph of course a load will slow it easily.
Some aluminum boats while light often have lots of keels, jon boats sometimes have 5 keels, and many rivets and their shape sometimes isn't too slick.If your boat is what I call a small 14 It may struggle with added weight.
Very likely you have your gas tank in the back and maybe a battery and yourself. Perhaps a 6 gallon metal tank when a 3 gallon plastic tank would probably do fine. A 9.9 will run about an hour on a gallon at wot.
You can save weight with a couple of plastic paddles instead of wooden oars,A styrofoam cooler instaed of molded plastic.
Metal instead of glass bottles, A light danforth style anchor instead of a heavy iron anchor.

 

[JanKsterS]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

Thanks for the reply.

"If your boat is 425 lbs Is that the boat dry weight,no motor?"

I was incorrect with my boat weight, I also forgot some factors. According to the website below, the weight of my boat with no equipment is 325lbs.

Boat: 1994 Grumman by OMC GV1465SP Super Pro

Figure the 9.9 is 100 lbs, the 3 gallon gas (I switched it out with the 6 gallon that was in there) full should weigh 25lbs. I have 2 batteries, one in the front, one in the bow - these weigh approx 40 lbs each. On the tip of the bow I have a light duty Evinrude electric motor, I'd estimate that weighs about 50lbs. I just put a Bimini top on the boat, I'd guess that weighs only 25lbs. Myself, 205lbs. My tackle and cooler, 75lbs.

All together I am getting...... 885lbs.

If you empty the boat and get us the gps speed with you alone it would help evaluate your setup.

I will do that this weekend and get the numbers here ASAP.

Here are some pics of my boat without the bimini top on it.

http://cdnmedia.endeavorsuite.com/i...4-4d14-9f70-f5fd06be0afe.jpg?v=20130409082024

http://cdnmedia.endeavorsuite.com/i...9-45fb-b90e-023c8d466f40.jpg?v=20130409082025

 

[steelespike]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

Unfortunately I think your boat is a 1465 SP And the NADA guide says its 465 lbs Those built ins are really nice but add some weight.
Infact all of the similar models are 465. You might be over estimating some of your equipment.
Hopefully you can get the speed of a loaded run as well. Remind me of your prop pitch.

 

[pootnic]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

A nice decked out 14' boat,console,acouple people,batteries,trolling motor,bimini,etc...
I'd be happy just to plane with a 9.9hp,that a lot of boat for that size motor.

 

[JanKsterS]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

Okay, so this past weekend I got out. I ended up adjusting the trim a little; I angled the prop one slot closer to the transom. This seemed to really help out with planing, especially when I was out by myself. I did also try adjusting to the slot closest to the transom, but it seemed to bury the bow a little too much.

Fully loaded (myself, my girl, tackle, gear, some food) we were doing a constant 14mph. I forgot the GPS when I went out alone with minimal gear, but it was significantly faster. I would say I was going about 18-19mph. I definitely plane out better when alone.

I am wondering if a higher thrust prop (possibly a 10"dia by 7pitch) could help me out at all. Right now I have a 9.25"x8p

 

[JanKsterS]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

....anyone?

I ended up ordering a 10x7 3 blade after doing a bunch of research. I'll let anyone who cares know how it turns out this weekend.

 

[Sea Rider]

Re: Prop selection for Johnson 9.9HP on a 14ft Grumman V-bottom?

A hardline hour/tach only costs $ 35.00 bucks, this must have device will stop wild guessings & wrong prop purchases. A 9.9 Engine is too poor to plane fast 975 Lbs total weight. What's the max HP factory recommended for that alum boat ? definitely not a 9.9; are we talking about a 25/30 HP ? If that's so, meed a minimum of 70% of max rated HP to perform as expected. If that horse is same as 9.9 Evi model, you can update it to a 15 HP for less than $ 170 to have a punchier engine and pass anyone out there at lake boating with a 9.9.

Both 9.9 & 15 runs 5000-5000 at wot, a prop pitch delivering at least 5500 with medium loaded boat would be ideal. Trim engine to be perpendicular to water level once boat is floating, place fiancee at bow to ballance better boat. Check engine leg at back transom while passing through water flow, must not have in/out water splashes on straight courses nor aireation/cavitation issues at close turns.

Happy Boating