is motor installed correctly? have porpoising problem at higher rpms

[greenpathy]

boat use to have a johnson on it and someone put this nissan on it,,they bumped the horsepower up 10hp, but just wondering if the motor is installed correctly... it runs really good and strong, but i can not trim out the porpoising issue at high speeds.. the only way i can control it is have a friend sit almost at the very front of the boat... when i'm boating by myself thats not an option..any ideas of how i can control this issue??? the boat is a 17ft aluminum sea nymph with a 50hp nissan.. you can see in the pics there some sort of metal wedge installed in between the motor bracket and boat transom.... just wondering if its suppose to be there and why...

 

[Don S]

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

but i can not trim out the porpoising issue at high speeds..

It may be just how you typed it out, but when porpoising, you trim down (in) not up (out).

If that isn't the problem, it's not obvious from your pictures but when the cavitation plate of the drive is running parallel to the bottom of the boat, is it above or below the transom?

 

[EddiePetty]

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

That wedge is there to increase the mount of 'IN' trim.......which reduces porpoising.
From the pictures it appears you have a manually trimmed engine and currently trimmed at the closes 'IN' or bow down position.
With the engine trimmed down, place a yardstick edgewise along the hull and measure the distance from the upper edge of the yardstick to the ventilation(anti) plate. Report that dimension either even to, above or below the hull plane. Also note if the ventilation plate is parallel to the hull.

 

[smokeonthewater]

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

Can't tell for sure from the pics but it looks like the motor is too low.... possibly a long shaft on a short transom....


lower the motor to running position.... you may need to lower the trailer tongue or jack up the trailer... then look along the anti vent plate (just over the prop) and make sure it is even with or slightly above the keel (lowest part of the boat)

 

[greenpathy]

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

lowered the motor to running position and the anti vent plate was above the keel..

 

[greenpathy]

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

i did not lower the engine all the way down,,,will go do so now...1 sec..

 

[smokeonthewater]

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

what hp is the engine and what is the boat rated for?

 

[greenpathy]

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

motor was trimmed all the way down and the plate was about 2 inches above the keel.

 

[greenpathy]

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

what hp is the engine and what is the boat rated for?

the boat is rated for a max of 60hp according to the tag, and the engine on it now is a 50hp nissan.

 

[greenpathy]

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

That wedge is there to increase the mount of 'IN' trim.......which reduces porpoising.
From the pictures it appears you have a manually trimmed engine and currently trimmed at the closes 'IN' or bow down position.
With the engine trimmed down, place a yardstick edgewise along the hull and measure the distance from the upper edge of the yardstick to the ventilation(anti) plate. Report that dimension either even to, above or below the hull plane. Also note if the ventilation plate is parallel to the hull.

the ventilation plate was not parallel to the hull

 

[smokeonthewater]

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

when boat porpoises does the motor rev up and down or remain fairly constant?

 

[airshot]

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

If I may suggest...trim the motor until the anti-venalation plate is parallel to the bottom of the hull, then check to see if the venalation plate is above or below the bottom of the boat. Also sight down the hull from the stern and see if the hull (keel) is straight or does the hull (keel) have an arch to it, commonly refered to as a hook in the hull. If their is a hook that curves into the hull that itself will cause porposing.
Just a couple suggestions, keep us posted..

Airshot

 

[Don S]

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

motor was trimmed all the way down and the plate was about 2 inches above the keel.

That is not trimmed all the way down in your picture. The motor should be down so it's resting against the cross pin in your picture.

 

[greenpathy]

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

when boat porpoises does the motor rev up and down or remain fairly constant?

motor remains constant...its almost like there is not enough weight to hold the front down.. like the boat is too light in the bow.. like i said when someone is sitting at the bow area,,all is good,,,when they return to middle(which is where the seats are) the boat slowly starts porpoising and gets worse and worse till it almost wants to leap clean out of the water , unless u back off the throttle...i hate it....

 

[greenpathy]

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

That is not trimmed all the way down in your picture. The motor should be down so it's resting against the cross pin in your picture.

in the pic no it wasnt...i went back and trimmed it down after reading the suggestions.

 

[smokeonthewater]

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...

 

[greenpathy]

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

If I may suggest...trim the motor until the anti-venalation plate is parallel to the bottom of the hull, then check to see if the venalation plate is above or below the bottom of the boat. Also sight down the hull from the stern and see if the hull (keel) is straight or does the hull (keel) have an arch to it, commonly refered to as a hook in the hull. If their is a hook that curves into the hull that itself will cause porposing.
Just a couple suggestions, keep us posted..

Airshot

with the motor trimmed parallel, it is above the keel, no matter how you trim it all the up or down it is always above the keel, under the bottom of the boat when sighting, the boat has 4 runners (or whatever you call it) 2 per side that run almost 10 feet in lengh, 2 per side..

 

[greenpathy]

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...

happens on glass or chop... both just as bad, battery for cranking on back corner, gass tank in other back corner,,battery for trolling motor up front. anchor up front, prop is in excellent condition.

 

[smokeonthewater]

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

 

[smokeonthewater]

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

happens on glass or chop... both just as bad, battery for cranking on back corner, gass tank in other back corner,,battery for trolling motor up front. anchor up front, prop is in excellent condition.

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