is motor installed correctly? have porpoising problem at higher rpms

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

here is a pic of the boat if it helps.

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

what airshot meant, is: is the hull straight along the back half of the bottom and gradually start to curve up at the front or is it deformed, damaged, bent... if you have even a slight roller coaster down there you will have problems... Like say if someone hit a log at speed and pushed the bottom up 1/2" a few feet in front of the transom

i gotcha now,,,no it is straight,,and not bent,,looks suprisingly good underneath considering the boat is a 90 model. no bends and no damage underneath.

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

I would definitely move the other batt and the gas tank as far forward as possible

but thats how it came from the factory,,, both are kinda hid and out of the way back there,,not sure where in the heck i could put them if i moved them up front..

 

[jestor68]

Re: is motor installed correctly? have porpoising problem at higher rpms

Placing a couple of 50 lb sacks of play sand in the bow compartment should help balance out the boat and get rid of the porpoising.

If that doesn't work(it should), putting a Doel Fin on the motor will make it go away.

 

[smokeonthewater]

Re: is motor installed correctly? have porpoising problem at higher rpms

but thats how it came from the factory,,, both are kinda hid and out of the way back there,,not sure where in the heck i could put them if i moved them up front..

ok...

I would steer away from the doel fin suggested above. smart tabs are only slightly more money and SOOOO much better without any of the scary side effects that the fins sometimes have..... Usually porpoising is not caused from the engine too high but maybe .... 2" could be a little much but usually the symptom of having the engine too high is prop blowout (high rpm) that's why I asked if rpm varied or not. It wouldn't hurt to play with engine height as it is a nearly free change.... use 3m 4200 on bolts and not silicone

If you back off of the throttle just a little does it smooth out or do you have to slow down a lot?

 

[beardeddone]

Re: is motor installed correctly? have porpoising problem at higher rpms

I had this happen once on a 17' Tracker I had a number of years ago, it had a 90 Merc on the back and no matter what I did as far as trim goes it would porpoise until I put a hydrofoil stabilizer on the motor, it went up on plane like it should and never porpoised again, some people don't like them and don't think there needed, but I sure did and still do and it worked for me, jmho

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

the motor is not all the way down on transom..if you look at the pics below. there is a gap between the bracket and the transom lip... but IF the motor was all the way down the steering arm would hit the transom lip... see below pics..

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

ok...

I would steer away from the doel fin suggested above. smart tabs are only slightly more money and SOOOO much better without any of the scary side effects that the fins sometimes have..... Usually porpoising is not caused from the engine too high but maybe .... 2" could be a little much but usually the symptom of having the engine too high is prop blowout (high rpm) that's why I asked if rpm varied or not. It wouldn't hurt to play with engine height as it is a nearly free change.... use 3m 4200 on bolts and not silicone

If you back off of the throttle just a little does it smooth out or do you have to slow down a lot?

it will not fully go away by backing off the throttle,,, it just lessens the jumping of the bow.

 

[smokeonthewater]

Re: is motor installed correctly? have porpoising problem at higher rpms

Is your motor mounted straight up and down or is it leaning to the side?... there is no reason that the end of the steering cable should be angled down to the transom like that...

that probably wouldn't cause porpoising but......

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

Is your motor mounted straight up and down or is it leaning to the side?... there is no reason that the end of the steering cable should be angled down to the transom like that...

that probably wouldn't cause porpoising but......

one side appears to be a little lower,,, but looking at the engine cover it looks level.... but the side where the steering arm comes out appears to be a little lower than the other.

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

but never the less if i lower the motor all the way down on the transom it will surely hit the steering cable..

 

[smokeonthewater]

Re: is motor installed correctly? have porpoising problem at higher rpms

It's already hitting.... There is a mark where it hits when you turn right

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

It's already hitting.... There is a mark where it hits when you turn right

its not hitting...theres about a 1/2 " gap before it will hit,,,what your seeing in the pic is a faded out sticker thats torn a little making it look like a rub mark.. i just turned it full lock to lock and it does'nt rub..

 

[greenpathy]

Re: is motor installed correctly? have porpoising problem at higher rpms

look at the very 1st pic ( the most recent ones of the transom) i just posted and look down at the arm,,,you will see a small gap there...

 

[EddiePetty]

Re: is motor installed correctly? have porpoising problem at higher rpms

The reason the steering arm is hitting/close to hitting the transom AND the motor is NOT fully seated is due to that darn wedge!

Get rid of the wedge, lower the motor and let's try again.

 

[ondarvr]

Re: is motor installed correctly? have porpoising problem at higher rpms

Lowering the motor can increase the porpoising, the lower it is the more leverage it has on the hull and it will push the bow higher. Raising the motor typically reduces porpoising. If your prop isn't sucking air you don't need to lower it.

 

[generator12]

Re: is motor installed correctly? have porpoising problem at higher rpms

what water conditions? does this happen on glass or just in the chop?

have you moved all possible weight forward? IE batts fuel tanks anchor etc.... anything heavy you carry

What condition is the prop in?


While we need to look for any problems first, when all is said and done, a set of smart tabs will surely stop this and allow you to trim up a little for more speed...

Smoke has it. Smart tabs help with several things, including speed-to-plane and low speed steering. But often unmentioned is that they can help with porpoising by providing lift to the stern to keep the hull more level, just as you do with weight in the front.

I suggest you do a search of the forum for "smart tabs" and read the comments. I think you'll find some help there.

 

[roscoe]

Re: is motor installed correctly? have porpoising problem at higher rpms

the motor is not all the way down on transom..if you look at the pics below. there is a gap between the bracket and the transom lip... but IF the motor was all the way down the steering arm would hit the transom lip... see below pics..

If you remove that wedge from the transom, you will likely be able to lower the motor without the steering arm hitting the transom.

But it looks like you could only lower it 3/4" anyway.


I'd say get the smart tabs.

 

[snowman48047]

Re: is motor installed correctly? have porpoising problem at higher rpms

I am not going to claim I'm a pro at this, but c'mon guys, this is a 17' with a 50hp. In NO WAY should he need to add stabilizers like a doel-fin or tabs nor should he need to relocate batteries and weight forward. If this were the case then boats would be like this from the factories. IMO start with mounting motor with the correct length shaft (which he appears to have) CORRECTLY to the transom.

Removing the wedge will properly place the clamp on the transom forward of current position and justy a bit lower. This also looks like it will eliminate the potential steering arm rubbing issue by moving it slightly forward of the transom cap. Who says the PO mounted the motor correctly?

 

[steelespike]

Re: is motor installed correctly? have porpoising problem at higher rpms

I think the wedge is there for a reason, as first stated, it is so the motor can be trimmed in(down) more.
As far as the bottom If it was pushed up(hook) near the transom it would pull the bow dowm.
You could check for slight rocker in the bottom .
A 3 or 4 ft straight edge laid between the keels will help find rocker if any.
May not be much, barely visible.
The Smart tabs should help. They need to be applied carefully a little at a time just to a point the porpoising stops.
Too aggressive and the boat will lay down like its stuck to the water creating strange handling and too much drag.
You might consider a 4 blade prop.Should reduce the porpoising,will improve hole shot,stay on plane better
at reduced throttle,seem smoother,will resist venting and should respond better at speed and around the dock.
Top speed may be reduced slightly.