Trouble planing out

[cbrevelle]

I have a 16 ft. Bass Tracker III with a 70 HP Johnson. It seems like it take a long time or lots of acceleration to get it to plane. If I try to run at a modest speed in an area with potential stumps, I can hardly see over the front. I was thinking I may need to lower the motor pin adjustment to "plow" more at low speed, but now I'm thinking maybe the prop pitch may make a difference. My question is: Will reducing the pitch of the prop help me plane the boat at slower speeds (though higher rpms)? Thanks.

 

[JB]

Re: Trouble planing out

Click here <br /><br />Good luck.

 

[DJ]

Re: Trouble planing out

orleans53,<br /><br />Prop pitch is part of the equation, but not all of it.<br /><br />What is your maximum RPM at wide open throttle?<br /><br />Do you have power trim?<br /><br />Of no trim, what notch are you running the engine at now?

 

[cbrevelle]

Re: Trouble planing out

I'm running at about 5500 rpm wide open... I do have power trim, but I trim it all the way down hoping that will help(?). I have the pin in the last (closest to the boat) hole.

 

[Solittle]

Re: Trouble planing out

Where is the cavitation plate relative to the bottom?

 

[Bondo]

Re: Trouble planing out

Smart Tabs...........<br /><br />Big Ones...............

 

[jsfinn]

Re: Trouble planing out

I had a good conversation today with NautiJohn who works for the manufacuture of Smart Tabs. An important thing I picked up from him durring our conversation is that if you rely on your prop to give you lift, you'll lose forward thrust which makes you lose speed.<br /><br />There have been tons of posts on this board about how great smart tabs are and none about how bad they are.<br /><br />I've never used them but I am ordering a set for my boat and have all the confidence in the world that they are going to do everything everyone raves about.<br /><br />Call NautiJohn. If you search the forum for "Smart Tabs" you'll find his email address and number. He'll tell you exactly what you need and why.<br /><br />Let us know what you work out!

 

[Link]

Re: Trouble planing out

JB it's most likely my blond CPU but the banner didn't work for me so I'll add this<br /><br /> http://www.iboats.com/mall/index.cgi?&keywords=smart+tabs <br /><br />Grrrrrr

 

[Jdeagro]

Re: Trouble planing out

oleans53;<br /><br />when you speak of lowering the motor, it could be that you are talking about the trim adjustment (either with the electric tilt/trim or the pin / bar stop) or actualy moving the motor down on the mounting brackets. <br /><br />Moving the motor down will only put the prop deeper in the water and make the bow rise higher. As Dhadley refers to it as the X dimension. You want to push the boat forward as close to the center line of the boat as possible. The more you lower the motor the more you are pushing from below the boat ( this becomes a leverage arm to raise the bow). <br /><br />If your are talking about trim, you are correct as far as getting on plane. The problem here is that the motor must come back up to 0 trim once the boat is on plane. If not the lower position will continue to push the bow down and the boat will bow steer not to mention other issues.<br /><br />If you do not have tilt trim, the best bet is to put the motor trim in the center hole, and install Smart Tabs, or other trim tabs.<br /><br />I personally do not beleave in using the prop to alter or adjust the boat attitude, as this is an inefficient use ro misuse of prop thrust. If you go down in pitch unnecessarily, it will be like running arround town with your car in 1st gear constantly. You will get better acceleration but loose fuel economy and top end.

 

[Solittle]

Re: Trouble planing out

Again - - Where is the cavitation plate relative to the bottom? It needs to be even with or slightly above. Sounds like you are way above. A 16' boat with a 70 turning 5500 rpm should jump out of the hole & fly.

 

[cbrevelle]

Re: Trouble planing out

By "lowering" the motor, I meant the trim. The cavitation plate is level with the bottom of the boat. I don't want to change that. I also found out this weekend from the fellow who had the boat before me that he thought the prop pich was a little shallow for the boat (it runs at higher rpm that it should at full throttle). So far, it sounds like smart tabs may help. Maybe I'm just used to boats with less weight in the rear than this one. I've always like sitting up front and using a stick to steer -- especially in Louisiana, so I can see the stumps before I run over them. Thanks for your input on this.

 

[Dave Abrahamson]

Re: Trouble planing out

I have found that with power tilt/trim, you do not need the bracket pin at all. The motor is resting on the trim rams most of the time anyway. That way you get the full range of motion of the PTT.<br />Ever think of trying a hydrofoil on the motor? I did and it made a world of difference for only 30 bucks or so.<br />(I may have opened up a can of worms with that last suggestion)<br /><br />Dave

 

[Jdeagro]

Re: Trouble planing out

Dave;<br /><br />For once I keep my mouth shut, but if you or anyone else would like a copy of a tech booklet on Boat Balance & Performance" free send me an e-mail to John@NauticusInc.com

 

[Dhadley]

Re: Trouble planing out

No matter which 70 hp motor you have 5500 is too low. I would expect a lousy holeshot and performance just as you describe. I would suspect that the motor is mounted too low if the AV plate is level with the bottom but that largely depends on the style and design of your prop. Your target rpm should be 6000 with an average load.<br /><br />With the motor mounted that low I would not be suprised if adding a fin (which is not a hydrafoil) might cause some starnge handling. I also suspect that the balance is very positive aft in percentage. <br /><br />Since you mentioned you are not going to raise the motor (????), you are limited to a prop change to get the rpms up but will most likely lose efficiency. Without raising the motor I would not suggest a fin, even the small ones. <br /><br />That pretty much leaves your options to the tabs and playing with the balance of the load in the boat. I suspect the Smart Tabs will do everything you expect as far as the boats ride attitude. <br /><br />As for your prop change I would suggest something like a Stiletto that has real good overall lift. But again, without the option to raise the motor, even a Stiletto may not be the best choice. Without the option of raising the motor I would definately not recommend anything like a Turbo. You'd be spending money on technology you arent going to take advantage of.<br /><br />Keep us informed!

 

[rickdb1boat]

Re: Trouble planing out

I'd try the hydrafoil and see how it goes. It will keep you on plane at lower speeds. Better hole shot, too. Cheap fix for now and if you want to change back or go with the tabs, no big deal. Remove it and fill in the holes with marinetex. You may be able to raise the motor then for better performance..

 

[Jdeagro]

Re: Trouble planing out

If DHadley says bring the motor up, I would bring it up. If he says you need to target on 6000 rpms then that should be the target. Raising the motor is likely to increase the rpms, a prop change is likely to increase the rpms, and Smart Tabs wil increase the rpms, so where to start.<br /><br />My Guess is to raise the motor first ( I would deffer to DHadley for how much) then, Smart Tabs because the running attitude and the hull efficiency will let the motor rev higher, then prop to perfection.<br /><br />What is Dhadley's opinion?

 

[cbrevelle]

Re: Trouble planing out

OK, I'm starting to get confused... I was told by the previous owner of the boat that my motor should not be running at 6000 rpm; that it was "over-revving". Second, I was under the impression (not sure where I heard/read it) that the cavitation plate should be level with the boat bottom. Is this wrong?<br />Also, I'm not sure I know what a hydrofoil is or does. (lots of questions, I know, but ya'll are helping me understand this better). Thanks.

 

[Dhadley]

Re: Trouble planing out

We target that rpm with either of the E/J motors and they live longer. What is "over-reving" on a two stroke? There are no lifters to float. There are no pushrods to bend. There are no valves to hit the piston. As long as there is a load on the prop the rpms are simply limited (ultimately) by the ammount of air/fuel it can pump in and out. In the stock classes the guys are turning those motors well over 7000. <br /><br />Raising the motor will help correct the rpm issue -- ie engine life.<br /><br />Getting the rpm's up will also help with overall efficiency which means holeshot, mid range and top end. Fuel consumption should improve also.<br /><br />In this case I believe a fin and/or tabs will help correct the ride attitude issue but only if thy are installed properly. Without raising the motor I dont believe the fin would be installed properly.<br /><br />As for the motor height, we always start somewhere even or above depending on the prop. Test from there.

 

[quantumleap]

Re: Trouble planing out

Dhadley: I repect your opinion and have a question regarding rpm's- I have been told that on my mariner 125 2+2 that going over the recommeded 4850-5250 rpm range is very detrimental to this engine, but you make it sound as though you believe that rpm limits are somewhat relative to air/fuel. I have a prop I really like that gives great performance but allows my engine to run a 5400 rpms. Do you see this as a problem? I know it it harder on a motor to run it at too low of a rpm than too high. Your opinion please. Sorry, don't mean to highjack the thread, but I though this is relevant to the topic.

 

[Dhadley]

Re: Trouble planing out

We've found that rpm tends to be the friend of a 2 stroke. Low rpm (lugging) is their enemy. <br /><br />There are plenty of these stock motors that are on boats that turn a lot of rpm. I bet you cant find one of those motors that have coked a piston and broke a ring. Yet we see that all the time with the same motor thats "overpropped". Horrible and incorrect term but thats the common term. <br /><br />It all has to do with combustion temps. Think of your little family car that gets 25 mpg. Now start towing a 25' Tubcraft. How long would you expect the motor to last?