Issues getting boat on plane

[traybore]

I have a 16ft bass tracker with a 40HP and 13P prop. Trolling motor and battery in the front as well and a 15Lb anchor and anchor winch.

With myself and one other in the back of the boat it jumps on plane immediately and runs around 28MPH. When I add two more people (total weight about 220LB) toward the front, it plows and will barely make it to 18MPH. Obviously weight is an issue, but my question is can this be corrected by dropping the prop down to a 12 or 11P? Or is this only correctable by moving weight around?

I don't want to spend money on another prop if its not going to make a difference.

Thanks!

 

[acabtp]

prop changes can be easily calculated, but we need more info first.

what motor do you have? we need to know the WOT RPM range and the lower unit gear ratio
what RPM are you running wide open w/ just two people? if you don't have a tach, get a tinytach and measure, important
28 mph is your max speed? that's measured with a GPS (like your phone) and not a paddlewheel sensor/pitot tube? (paddlewheels are very inaccurate)
what RPM are you running wide open w/ all four people when you are going 18?

without this info, it's all just a guess, and nobody can give you good advice. if you are already towards the top of your WOT range with your 13P, propping down will let you overrev the motor when lightly loaded (bad).

 

[lovedr79]

I was having a similar problem. I went down in pitch and went with a 4 blade prop.

 

[traybore]

Motor is a 40HP Mariner, mid 80's(model 40ELTO). It is actually made by Yamaha, I believe. I do not have a tach. My "tiny tach" shows around 6700RPM with 4 in the boat, I did not check with just myself, but I am not at all confident in the reading. WOT RPM for the motor is supposed to be 5000-5500. Speed was measured by GPS. I was planning on keeping two props. One for when I am heavily loaded i.e 4 people and gear, the other for myself and maybe one other passenger. I realize an accurate tach reading is required for final prop choice, I was just asking more generally if a prop change could solve the problem or if I need to look more at weight distribution? Thanks for your reply's!

 

[acabtp]

yeah if you don't mind swapping the props out that makes things easier. i'd second the suggestion of the four blade for the heavier load then.

 

[traybore]

I know almost nothing about props. What is the advantage to a 4 blade as opposed to 3 blade? If I drop pitch to 12 or 11, will a 4 blade perform better than a 3 blade of the same pitch under the heavier load? Thanks!

 

[jonboatboy]

Dude obviously the extra weight is lugging down the boat. Trackers are heavy aluminum boats anyway but yes if you drop a pitch or two in props when hauling extra people it will take care or your problem. A four prop in the same pitch will only help your hole shot but will not help your plane problem. Get a 11p and I think that'll do you. As far as getting you top speed that you get now I don't you'll get it but you should get up out of the water easier with the extra people. Been there done that and got a T shirt.

 

[traybore]

That's what I wanted to know. I am not worried about top speed, I fish for fun with my wife and family, don't care how fast I get there. Just want to plane properly and not plow so much. I will drop the pitch on the prop when carrying extra people...

 

[turbotodd]

a 4 blade will generally get the boat on plane quicker, faster, hold plane at a lower RPM (so you can cruise at less throttle), runs smoother than a 3 blade, BUT you lose a little top speed. In a situation like yours, I'd say a 4 blade would help a TON. I'd probably recommend an 11" 4 blade.

IIRC that would be a twin cylinder powerhead. Is it possible that the tinytach that is installed right now could be reading double your actual RPM due to an improper tachometer or perhaps an install error? Sometimes the wire end will get a little loose on mine and it will "read" from both plug wires. I always know because the tach shows about 10,000 RPM (when it's only running 5000). The reason I ask about your tach is because I wasn't aware that those engines would actually run 6700 RPM (IIRC, they were rev-limited at around 6000). So if it were reading double speed, and you're showing 6700, the actual engine rpm would be right around 3350-ish....which would be indicative of a horribly overpropped situation, which would also explain why it won't get on plane with some weight in the boat.

Need to know the gearcase ratio, correct RPM to give an educated guess. But sounds like you would benefit by dropping back to about 11" pitch and 4 blades. I know I prefer 4 blades over 3 and I actually have a 4 blade 10" that I will put on my boat if we are loading heavy.

 

[traybore]

consensus seems to be 11P and 4 blades. I will give that a shot. You are probably correct on the tiny tach reading double, would make a lot more sense. As you said the engine does have a rev limiter.