|
|
Posts: 20281
Location: oswego, il | I was wondering if anyone knows just how much rpm you can gain by gpoing down in pitch number. Granted, I don't have much boat but from last year to this year, my kids have gained enough weight that now the boat won't plane with 3 people. I have a 14' princecraft with a 25hp johnson. It runs ok, put new plugs in it, it just won't get up. It has a 10x13 prop and I think i can only go one pitch higher to a 14 but i see I can get down to a 9. I see 4 blade props are available too. I just need to the boat to get up and i think the motor will keep it there.
With me, it used to go 28 on the sonar, 3 people would go 23 and 4 would go 13 and not plane. Now it goes 23, 13 and 13 respecively with the same people it did last year, granted there is more weight now but not a huge amount.
I had two comparables while up north. A 16ft lund rebel with a 30hp honda, 3 people no problem getting up on plane immediately. It has to be a heavier boat. Another has a sea nympth 16ft with a counsole and a 35 johnson whch is the same motor as mine. Easily a heavier boat. 2 people and it got up fine on plane.
The other thing is it really sucks the gas. As measured on my gazeteer, I can roughly go 16 miles on 6 gallons of gas. I would think a 96' johnson 25 should do better than that.
Edited by ToddM 7/1/2007 8:24 PM
|
|
| |
|
Posts: 31
| Todd,
Not sure about a smaller outboard like yours, But on my 225HP Yamaha I am dropping from a 27" Pitch prop to a 26" pitch prop and I am told I will gain approx 300-400 RPM. With the 27 I was only turning 5500 RPM at approx 67 MPH with the 26 I should be almost 6000 and in the low 70's.
Fuel mileage does sound a bit low, You think your a little underpowered with that 25?
Bill |
|
| |
|
Posts: 20281
Location: oswego, il | Zero it, that's it, the boat is only rated for a 30. I see bigger heavier boats getting it done with a 25. My brother bought the boat new, it's never gotten up on plane well and I put a fin on it which helped a ton. I am looking at changing the prop as a possible solution. One dealer told me to put a 4 blade composite prop on, he had luck with a 25hp that carried a load. Thanks for your input. |
|
| |
|
Posts: 375
Location: In the slop! | Todd, try the compprop with 11 inch pitch. That's what we run on the duck boat, planes a lot better with a heavy load than the 13. |
|
| |
|
Location: Athens, Ohio | I've been advised to stay away from composite props except to carry as an emergency spare. Adding the fin should have helped.
BassBoatCentral has a Johnson owners page and also a set up specialist, you might try over there, too. m |
|
| |
|
Posts: 167
Location: Fonda IA | Just went through this with my 18 foot tiller alumacraft with a 60 horse.When I was loaded with 3 to 4 people I was dogged out and could not get on plane.I was running a 13 pitch with a max RPM of 5600.I went to a 11 pitch gain 600 rpm's and the power to pick up 4 people in the boat.I lost 3 miles an hour of my top end but being able to get up and go,is worth that.My biggest problem was when I'am walleye fishing with 3 to 4 people in the boat and a full livewall.Which the 11 pitch solved I just lay off the gas alittle now run about 5800 RPM's for around 26 mph. Hope's this helps.Dennis Blume |
|
| |
|
Posts: 375
Location: In the slop! | Mikie, for a big outboard I would agree with you. But, for that size, compprops work great! They will not stand up to a lot of abuse however. On the plus side, they are pretty cheap. |
|
| |
|
Posts: 20281
Location: oswego, il | Sledge51, I was thinking of the comp prop but I do fish one place where it won't last at all. What do you think about an aluminum 4 blade prop? Bass pro sells them in the same pitches. |
|
| |
|
Posts: 375
Location: In the slop! | I don't have any experience with them but would think it would work just as well. Dropping the pitch two inches is what is most important. |
|
| |
|
Posts: 20281
Location: oswego, il | Well it turns out the 4 blade aluminum is only available for certain engines so I ordered the comp prop. If this works, I will get a spare and and a 3 blade aluminum in that same pitch(11 is what I got) or a 10 for the place I need a sturdier prop. |
|
| |
|
Posts: 20281
Location: oswego, il | I am still frustrated. I put the 11 pitch comp prop on and I gained rpms but nothing else. Ran the same speed as before. I put the motor out one notch and gained almost 2mph but it still won't plane but with just me in it and with just me it still runs the same speed as before. My buddy has an old merc 25, i am going to put that on to see if it is the motor. I it is, it's been that way since it was new. |
|
| |
|
Posts: 32958
Location: Rhinelander, Wisconsin | The further trimmed out the slower the hole shot, Todd. You want that motor tucked in as far as you can get it.
A composite prop flexes more than an aluminum, which flexes more than a stainless. One pitch down should pick up about 250 RPM. About 500 with two. However, in order to be able to get the higher RPM and better hole shot, you need to either go to an 11 pitch aluminum prop or a stainless if what you had was a 13 pitch aluminum, IMHO. |
|
| |
|
Posts: 20281
Location: oswego, il | Steve, my thinking was to see what this prop would do, then buy an aluminum in the same pitch as the comp prop was 1/2 the price. I had the motor in the first hole, all the way down and it was no help either. I was hoping an 11 4-blade would get the boat up and that maybe that was really my problem. As it seems now, I am so far off from being planed out that I am not even sure an 11 pitch aluminum will do it. With two people in the boat and some gear, my boat does not have 3ft of hull out of the water. I did not even have a musky box, just 5 planos in the livewell. |
|
| |
|
Posts: 20281
Location: oswego, il | This boat is driving me crazy. The only difference in it from last weekend to before is that I have run about 1/2 tank with amsoil. We started out, same gear/people ect as last weekend and she buzzed up on plane to 21mph. About 2 miles into the run, it slowed down off plane to 14mph never lfting the throttle. The next time, it would not plane, same 14mph speed and then the next time it buzzed up[ to 21mph on plane again. The next time, would not plane, my buddy was drinving, he shook the motor back and forth, then it got up on plane. The motor does not run rough or act up. |
|
| |
|
Posts: 375
Location: In the slop! | Todd, it sounds like you may have crap in your carberators. I had a 70 horse Evinrude that acted like that, had the carbs rebuilt, end of problem. |
|
| |
|
Posts: 5874
| You are losing power somehow. I would suspect jets in the carbs amy be plugged, but it could be weak coils, or spark plugs loaded up. You should be able to hear a change in rpm's when running at 21 vs 14. I support the move to Synthetic oil, and that may provide a clue to look at the plugs for signs of fouling. I'd rplace the plugs, and carefully gap them, then see how she runs.
Edited by Shep 7/17/2007 9:43 AM
|
|
| |
|
Posts: 1462
Location: Davenport, IA | My 25 Johnson went from 28 mph to 18 mph top speed after putting on a hydrofoil. It sounded like it would not rev high enough. Also, the hydrofoil made it take 5x longer to get on a plane. |
|
| |
|
| You may have coil going bad causing bad spark on one cylinder. |
|
| |
|
Posts: 20281
Location: oswego, il | I did put new plugs in it, actually the old plugs did not look bad. This motor has had issues planing this boat since my brother bought it new. It could be a bad carb ,coil, maybe some sort of timing advance? I notice some drop in rpm but nothing like you would think. My brother bought this boat from a dealer getting out of the boat business. It was a new 96 bought in 98. Perhaps the motor sat around too long or something was wrong right from the factory. I actually would not mind converting it to a 30, I wonder what the difference is, Would be cool if it was just the carb.
Edited by ToddM 7/17/2007 9:56 PM
|
|
| |
Blade pitch