would a different prop help

[junedawg]

i recently bought a brand new Suzuki DF20ATL2 and installed it on a 14 foot bass boat. i previously had a 50hp on there. i was hoping that this would be enough to get me on a plane to do some fishing on some lakes and rivers in my area. what i have discovered is, if it is just me on the boat, i have to kind of lean forward in the boat until it gets to about 13 or 14 mph for it to be on a plane, and then i can sit back down in back, and it maxes out around 18-20 mph. This is a speed i'm very comfortable with.

The problem is, i cant have a 2nd person in the boat and achieve anything much over 10mph, which at that speed im popping a wheelie the whole time. I was curious, i have read a couple things that make me think its possible if i bought a prop other than what came with the boat i could get a little more out of it. does anyone have any opinions or reccomendations on this? or would i be wasting my money?

the prop on there now says 9-1/4x9

Thanks in advance

 

[Scott Danforth]

first, welcome aboard

second, what RPM is the motor turning?

third, what is the boat rated at. generally you want to be between 75% and 100% of the rating. going from a 50 to a 20 you may not have enough motor, or you may need to drop pitch...... goes back to the RPM question.

 

[junedawg]

this is kind of an old boat, it is missing the transom plate, or whatever it is called that tells me the rating. also, i dont have a tach, so im not too sure what RPM its hitting

 

[Texasmark]

If you would have said a 14' Alumacraft or Starcraft aluminum open fishing boat you probably wouldn't be posting this thread. Rule of thumb around here is 75% of rated engine power for the boat. Even if the 50 was BIA max rating (which I doubt given the mils that some 14' BBs run, you are less than half. Engine power is measured at wide open throttle...WOT. Numbers are usually around 5k RPM give or take some range. You prop for the upper part of that range recommended by the mfgr. for your engine.

The prop that comes with the engine, when furnished....norm on smaller engines, is a general performance prop since the mfgr knows not the application. Had you put that 20 on a boat like I mentioned, you would be up running 25, nicely on plane with your second passenger and all your gear.

In short, you are probably going to have to come down significantly on your pitch and one would assume that your tilt pin is adjusted all the way down (closest to the transom) helping to have prop thrust push the stern up and the bow down.

I bought a little LED tach with reflective strips for 30 bucks give or take. I bought it for my lawn mower and other small engines but it would work on your engine just fine. Just put a reflective strip on the flywheel and follow the manual for operation for your engine.

Get an RPM number when you and your companion are attempting to get on plane, look up your engines WOT operating range, find out the pitch of your current prop....sales literature may show it if the prop isn't marked, and drop pitch 1" per 150-200 rpm you need to get your RPMs up where they belong. You will find that it's not a linear scale so if you are a thousand RPM low, you don't need to go 6" down in pitch.

Once you unload the engine ( by backing off the pitch with another prop) it will perform more efficiently providing more thrust and that, along with getting the boat to level out (on plane) reduces the drag which enhances the engine which increases the RPMs which enhances the speed which reduces the drag etc. So you may only need to go down 3 or 4".

With that said, once you get your problem solved for 2 folks you will have to keep your throttle scaled back when alone to keep from over revving. That's my opinion.

 

[Sea Rider]

What need to do in such case is : If plan boating with a fixed load, say 2 up. Go for a wot spin on flat calm water cond with the second soul sitting up front, it at bow much better. Need to know what's the max wot rpm the motor achieved as loaded, compare those numbers with the min-max wot rpm range factory stated, will know how over propped the motor is for your application. What's the current prop pitch of the motor.

All portable range motors delivered with a installed prop are delivered with medium pitched props and if runing a underpowered motor on a large boat will need to go asap for less prop pitches to rev much higher as of now and be able to plane the boat out and faster.

As you don't count with a tach won't be possible to max prop your motor, not even by ear sound doesn't matter if having a musician ear LOL !! Would recommend to buy a Hardline hour tach model HR-8061-2 It's for 2-4 strokes 2 cylinder motors.

Besides a prop maximization will be good to perform a motor/transom height optimization and check if the motor is powering the boat at the sweet spot, combine it with a prop maximization and will do the trick.. Have done so many times and has worked 99.99% of the time....

Happy Boating

 

[junedawg]

thanks for the responses, i agree, i have little doubt the motor is undersized for the boat. the motor that was on there previously was an old evinrude electric shift nightmare. and so i bought this little 20 new to get rid of the headaches, and get me back on the water. In the meantime, im saving up for a 14 or 16 ft gillgetter or something similar that calls for a motor approx this size.

the existing prop is a 9 pitch, so from what i can tell 7 is about as low as you can go? looks like i can get one for around $60, and then if i understand correctly, if it does help me do what im hoping, i should just be cautious when its just me in the boat not to "overdo it"? honestly, buying a tach for $30-40 seems a little silly if the prop is just $60? or would it be reckless just to try the new prop?

 

[Sea Rider]

Wow, have seen and received nonsense answers but yours flew out of this world. See it his way :That new 20 HP motor cost money which wasn't peanuts cost. The correct way to take care of your costly investment is to prop the motor right with a tach to dial the best prop pitch as not to overrev, faster plane on water at a nice crusing speed, along keeping the count of the total run hours which will be useful for future preventive and corrective maintenances as well .

The issue is that isn't known how many max wot revs the motor achieved to recommend a less prop pitch, it's not as simple as to say, well due to being a spend the less money scenario go straight for the 7th pitch and voila. Boating it's not a exact science, will have to fine tune the motor to your particular boat which is unique, that's if wanting to get the max HP cowl rated out of it which seems it's not your case. BTW, who said that Boating was a Cheap Sport....

Happy Boating

 

[junedawg]

ok, well question on this tach issue. when i got this motor it had a wiring harness on it to simply plug into battery cables and remote. there were also a few "extra" wires. i contacted the dealer as to what these were for, and they said that on the different models for this motor those would be connected to other accessories such as a tach. would having those wires simplify hooking this up? or would they only truly work if i had a different model of the motor?

 

[Texasmark]

The tach wire on early 2000 mid range engines from a Commander 2000 or 3000 control is grey and on pin 5 of the 8 pin round connector that attaches to the engine. Accompanying wires, external to the plug include tan for alarms and blue and green with white stripes for power trim.

 

[Sea Rider]

Will need a much costly tach if plan using the internal provided cables along a central console if counting with one. if like tiller steering better buy an induction hour/tach as suggested. Install it as factory recommended, it's as simple as winding 4-5 pick up cable rounds on any spark plug cable, select the firing sequense and voila. Can insntall it next to the throttle grip to read it at a distance..

Happy Boating