Aluminum Bass Boat front jumping up and down on water

[XoDiViAoX]

hi,

i have a 1998 bass america made my polar kraft, it is called an eagle 15 and has a johnson 50hp motor. my dad bought this boat practically brand new 10 years ago and we used it for a matter of months and just now got it back out to use. the front of the boat doesn't ride smooth, it jumpsg up and down on the water starting at about 20 - 25 mph and does it worse when you get up to about 30 - 35 . i was wondering, is this normal for an aluminum bass boat like this, or is there something you can do to make it ride smoothe?

when i go to the johnson website and look the engine up it says the motor has "power tilt/trim" but it seems to only have tilt, because you can tilt the motor with a push of a button, and i don't know what trim is, but if there is a button for it we've never found it.

we've never messed with the tilt on the motor while driving up and down the river, only tilt it to haul on the trailer.

if anyone has any suggestions on this, they would be greatly appreciated. thanks

 

[j_martin]

Re: Aluminum Bass Boat front jumping up and down on water

If you tilt it down, you'll notice that it moves fairly fast to a certain point, then slows down. That slow range is the trim range. The hydraulics are stiffer there, and will stand up to the thrust of the engine. In operation you trim the engine to the conditions and speed you want to run.

That hopping you describe is called porpoising. A boat will porpoise if the trim angle is too high for the speed and weight distribution.

There may be a stop pin to limit the minimum trim angle. You may have to move that pin.

Moving weight forward helps.

Bottom line is engine trim and boat loading are all part of the game. You just need to learn the ropes.

On my 150 hp bass bote, I trim the engine all the way in for the hole shot, then trim it out to maximum for top speed. It tends to hop a couple of times going through the 30 - 40 mph range, which takes about a second and a half. If I'm taking the 80 year old preacher fishing and need to hold the speed down, I throw 150 - 200 lbs of sand bags in the bow.

hope it helps
john

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

"trim the engine all the way in for the hole shot, then trim it out to maximum for top speed."

when you say trim it out to maximum for top speed, does that mean to run the motor down as far as it will go? like so the motor and the prop is 90 degrees with the boat?

 

[Lyle29464]

Re: Aluminum Bass Boat front jumping up and down on water

can you post a picture of the side of your motor?

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

yeah, i'll take some tomorrow when it's daylight outside so you can see them good. anything in particular i need to get a picture of? or just the whole motor?

 

[roncoop75]

Re: Aluminum Bass Boat front jumping up and down on water

"trim the engine all the way in for the hole shot, then trim it out to maximum for top speed."

when you say trim it out to maximum for top speed, does that mean to run the motor down as far as it will go? like so the motor and the prop is 90 degrees with the boat?

No, that's how you would start out. IOW, start out with the engine trimmed all the way down, ie. vertical, prop tucked under the boat as far as you can get it. When you get up on plane you trim up which pushes the prop back away from the boat and up towards the surface. As you trim up, the bow comes up you have less hull in the water therefore less drag and your speed picks up.

 

[Lyle29464]

Re: Aluminum Bass Boat front jumping up and down on water

I wanted to look at the side of the motor to see if you have a rod in the trim adjustment and if so what hole it is in plus they did make a tilt only after market unit. I wanted to see if you have that or the regular tilt and trim.

all of the advice above is great and you can do that. You will need to see what hole the rod is in. Plus you must know if you really have power trim.
if the rod is not in the front hole you need to move it at lease one hole foreward.

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

i took these today, in the third picture i took that thing off when i took my trim motor off, i have yet to figure out what it suppose to do.

also the reason those wires are like that is because one of my relays are bad and i'm waiting for it in the mail before i hook it all back up and im just using a jumper box to run the trim up and down at the moment

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

i've never known that i needed to trim the engine up, but i will try it next time i put it in the water, would you think that would fix the porpoising? or is it probably from other causes?

 

[Fisher3491]

Re: Aluminum Bass Boat front jumping up and down on water

If I understand, your boat is porpoising with the motor all the way down.

That being the case, trimming up will only make it worse.

Sounds like a weight distribution problem. Can you move some weight further forward? Or add some weight to the bow and see if that fixes your problem.

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

I'll try that, thanks. The prop didn't look very good so I ordered a new one. If the new prop doesn't fix the problem I will try shifting some weight to the front and try that next time we put it in the water. We're well under the weight limit on this boat, and I looked at the hull and it's perfect, no hooks or dents or anything.

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

I got the new prop, took it out to the water today and still porpoises bad, i can't run it wide open or trim the motor up at all while driving down the water. I had my passenger sit on the front of the boat and it helped, but I didn't feel that was too safe so I didn't get up too much speed.

The engine has plenty of power, it takes no time to get on a plane when you give it the throttle, but it just has the porpoising problems...

the engine is down as far as it will go, will raising the whole outboard motor up a notch or two help?

i think i've located the trim pin, it's at the very bottom of the tilt n trim cylinder, and there are 3 different holes for the pin to go threw, and it's in the hole closest to the rear of the boat. if i moved the pin to the hole farthest away from the boat, would that help?

 

[roncoop75]

Re: Aluminum Bass Boat front jumping up and down on water

if i moved the pin to the hole farthest away from the boat, would that help?

Generally, that would tend to make things worse. Motor height could be part of it also.

Edit: With the motor down, take a picture of where the cavitation plate is in relation to the bottom of the boat. Post the picture in this thread.

 

[WIMUSKY]

Re: Aluminum Bass Boat front jumping up and down on water

Generally, that would tend to make things worse. Motor height could be part of it also.
Edit: With the motor down, take a picture of where the cavitation plate is in relation to the bottom of the boat. Post the picture in this thread.

In the one pic you can see the motor is mounted in it's lowest position. May need to raise it... Another pic, as mentioned, will help determine if that's the case....

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

i dont know if i measured right, but i held the level where i showed in the pic underneath the boat and thats where i took the pics of the level in relation to the cavatation plate and the cavitation plate is 1" or so below the top of the level

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

heres one more pic i took it only lets you upload 5 at a time

 

[TerryMSU]

Re: Aluminum Bass Boat front jumping up and down on water

Here is how I trim my motor. I remember that the switch is directly related to how the front of the boat behaves. If the front of the boat is trying to run too high, I push the down button. Running too high makes the boat porpose. When I am just starting out, I trim the motor down (using the down button). This tries to force the prop shaft back under the stern of the boat. When I am running at full throttle, I hit the up button which pushes the prop shaft out and to the rear. I do this until it just starts to porpose and then i run it back down (and under the stern) until the porposing just stops. This is where the boat gets its maximum speed.

TerryMSU

 

[WIMUSKY]

Re: Aluminum Bass Boat front jumping up and down on water

Your motor is sitting too low in the water. The cavitation plate needs to come up "at least" even with the bottom of the hull. I would raise it up 2 mounting holes(3 holes if the plate is still below the hull). That will still leave you 1 more if you need to go higher. Then test it. You should notice a difference.

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

thanks for the info, got it moved up 2 holes without any problems, gonna try it out tomorrow hope it fixes the porpoising

 

[XoDiViAoX]

Re: Aluminum Bass Boat front jumping up and down on water

helped some, but still does it ... starts doing it at 25MPH or 4500 RPM with a 15 pitch prop, gonna raise motor another hole(all the way up), try another prop, and add a stabilizer ... if i raise motor all the way up what do i need to look for to make sure i dont have it raised too high?