tri-hull bounce

[paul33]

I have a 1980 16ft Canaventure with 115HP Evinrude outboard. When I get it on plane it starts to Bob or Hop as I speed up. I've tried adjusting the trim but to no avail. I've never had it full open in a straight line, bobbing gets worse.would weight in the front bow help? Or maybe motor is oversized?

 

[oops!]

Re: tri-hull bounce

Hi Paul.......Welcome to iboats !


That problem is called porpoising....

Like a dolphin...the bow "hops" up and down it makes a smooth ride very difficult at times.

There are many reasons for porpoising.

Motor too high on transom....
Transom angle incorrect...
Motor angle incorrect.
Motor too heavy.

The most common is a mistake on the trim of the motor.

Most of the higher powered motors have tilt and trim.
When your boat is starting away from the dock....the trim is usually set as low as it can go.
This forces the bow of the boat down for easier handling around the dock.
The boat will run fine with this adjustment, but it is not the most efficient as far as speed or fuel economy is concerned

When the boat is on plane.......click the trim button up by a series of short touches to the button.....as you do this the angle of attack of the motor changes. This will cause the rpms to increase.....too high....and the boat will cavatate as the prop comes out of the water.

Just before cavitation....the bow will start to hop.....as the angle of attack pushes the hull upward......then the weight of the hull over comes thrust....and the bow comes down.....then bounces back up.....and so on.

The trick is... to adjust the trim so that the rpm raises just a wee bit.....and the boat picks up speed while running at the same throttle.
The bow will stay level.....and flat.....its a very smooth ride......just a little touch of the trim ....and the bow will hop again.

Now.......If the bow is hopping while the trim is in the full down position......The problem is one that is listed above....and we would need to see pics of the boat on the trailer while the motor is in the full down position.

Before we discuss the advantages of add ons like trim tabs......Lets get you set up correctly.

I hope this helps

Cheers
oops

 

[smokeonthewater]

Re: tri-hull bounce

other possible causes are motor too low IE 20" or 25" motor on 15" transom, and an aftermarket foil or fin on the lower unit can also sometimes cause handling issues like this.
Stay with us and we'll get you sorted out.

 

[steelespike]

Re: tri-hull bounce

I think some motors have a base manual setting to aid in getting it so the trim can be low enough.
If the boat was poorly stored it might have a deformed bottom put a 3 or 4 ft satraight edge along the bottom
looking for a bulge in the area ahead of the transom.Also a poor rebuild of the hull may have created a bulge.
If the transom was replaced and not given enough angle I think around 13degrees from verticle.

 

[Texasmark]

Re: tri-hull bounce

The problem in attempting to solve problems herein is FACTS. We read a post and assume a response based upon our experiences/training/whatever. After numerous responses are received we find out that you are running a 1.6 hp single cylinder on a 30' boat and you expect it to plane out and pull half a dozen water skiers.

FACTS, FACTS, FACTS. YOU WANT A USEABLE ANSWER GIVE US SOME FACTS.....WE CAN'T READ YOUR MIND.

MARK

 

[chriscraft254]

Re: tri-hull bounce

^^^huh? he has the hp and boat listed.

Op, are you tucking the motor in all the way when throttling up? If the motor is trimmed up it will cause it to porpoise. Might need some smart tabs. Water logged foam can cause you porpoising also if it is soaked aftward. also,whats the rated hp for the boat, might be to heavy of a mtor sitting on her. Pitch of prop?

 

[southkogs]

Re: tri-hull bounce

I have a 1980 16ft Canaventure with 115HP Evinrude outboard ... Or maybe motor is oversized?

Just to throw another log on the fire: what HP is your boat rated at? My last 15 was rated at 100HP max. If yours is rated that way, you might be overpowered a little. If your capacity gives you all 115 horses, then you can rule that out.

Unless you meant oversized as in "it's just a fatty."

EDIT: sorry, I didn't read Chris' post close enough. ^^^ "...what he said." ^^^

 

[paul33]

Re: tri-hull bounce

Sorry guys I have a 9 year old goalie in competitive hockey so its been nuts this past week.
First I want to thank you guys for all the responses

Here's a little more info, this is my first boat. So I'm trying to keep up to speed with all the info I'm getting.
Boat has a rating of 90HP by the info of plate on boat, so not sure if this Is my biggest issue.
When motor is fully down and just moving thru slow zones bow is really high of course until I speed up and it gets on plane. Again I hope I am using correct terms.

The motor also has rubber fins attached to sides of lower leg, I was told these were put on to cause bigger wake?
I took those off to see if that was part of the issue. It made the porpoising somewhat worse.
Boat gets on plane well and turns awesome, just in a straightline it porpoises so bad almost comes out of water even if lake is calm.
I've tried trimming up and down thru full movement, I may be adjusting it to quick.

I will post some pics tonight thks

 

[oops!]

Re: tri-hull bounce

Sorry guys I have a 9 year old goalie in competitive hockey so its been nuts this past week.

Are you a canuck?....we need more goalies....keep at it

When motor is fully down and just moving thru slow zones bow is really high of course until I speed up and it gets on plane. Again I hope I am using correct terms

just explain it in your own words.....we can figgure it out bud.......no worries.

but the above statement leads me to believe your motor is set at an improper angle.....
a bow way up in the air is just about on plane......this should not happen in a no wake zone.

we will need the pics

 

[chriscraft254]

Re: tri-hull bounce

Boat has a rating of 90HP by the info of plate on boat, so not sure if this Is my biggest issue.
When motor is fully down and just moving thru slow zones bow is really high of course until I speed up and it gets on plane. Again I hope I am using correct terms.

The motor also has rubber fins attached to sides of lower leg, I was told these were put on to cause bigger wake?
I took those off to see if that was part of the issue. It made the porpoising somewhat worse.
Boat gets on plane well and turns awesome, just in a straightline it porpoises so bad almost comes out of water even if lake is calm.
I've tried trimming up and down thru full movement, I may be adjusting it to quick.

I will post some pics tonight thks

The fins your talking about are called dol-fins or hydrofoil. They are a cheap source of adding lift to the stern so the boat can plane better. first thing is you need to find the hp rating plate on the boat if you haven't already.

Different Canaventures were rated for different hp motors. Like the open bow compared to closed bow I believe. Anyway check it out and be sure. What boat do you have, open bow? Its important on these boats. If it is over powered, the weight of the bigger motor, though probably not much can effect a small boat.

Also like I mentioned, if the boat wasn't kept dry, you may be riding around with a couple extra pounds of water weight due to soaked foam in the lower part of the hull. Any inspection plates towards the stern for inspection of the bilge?

If the boat is riding low at idel or slow speeds with bow up even before throttling up, the above is my guess. If it is only an issue when getting on plane or after on plane, Your motor is probably set to low.

Take some pictures of the outdrive in relation to the very bottoom (keel of the boat) and post them up. The anti-ventilation plate should be about even or an inch above the keel of the boat when tucked in or at 90 degrees witht he hull.

We can help you further with pics uploaded.

Is your motor long shaft or short shaft and what kind was the boat suppose to have?

Chances are , you can invest in some smart tabs by nauticus and make the porpoising go away. But lets figure out why it is porpoising first.

 

[LippCJ7]

Re: tri-hull bounce

Gentlemen lets stay focused here, we all know that Hockey threads seem to take over this site and then Ego's get involved followed by betting and then Sinister avatar plots against boaters of other nations, next thing you know we have a political discussion and the thread gets locked....


I knew a Canadian Moderator was going to be an issue....

 

[oops!]

Re: tri-hull bounce

Gentlemen lets stay focused here, we all know that Hockey threads seem to take over this site and then Ego's get involved followed by betting and then Sinister avatar plots against boaters of other nations, next thing you know we have a political discussion and the thread gets locked....


I knew a Canadian Moderator was going to be an issue....

HEH...HEH....HEH......the puck stop here (evil grin) unless the other mods come along....then i run and cower like a little girl !

 

[LippCJ7]

Re: tri-hull bounce

oops I love ya buddy!


especially when ezmobee keeps closing the threads I post in that are 5 years old.....

 

[southkogs]

Re: tri-hull bounce

Sorry guys I have a 9 year old goalie in competitive hockey so its been nuts this past week.

Cool! I have a nephew who is a defenseman!

Boat has a rating of 90HP by the info of plate on boat

I'm gonna' suggest that this is a starting point. You're 25hp overpowered on a 16' boat. On some hulls that's not a big deal, but on others it can be huge.

Can you confirm that you meant to say you typically don't run at Wide Open Throttle (WOT) because it's a little scary to drive like that (my translation of your post)?

 

[cyclops2]

Re: tri-hull bounce

A 1980 boat & a HEAVY 115 horses with 2 full gas tanks in the back. Seat is about 3/4 back ?

Foam flotation space got a load of water in it. Driver is 200 to 300.


Yup

Got 2 just like that in our place. Boston Whalers. The water is 3" from pouring in over the stern & sinking the boat. Those 2 guys are spending hundreds to go fast in boats that were bargains.

 

[Thalasso]

Re: tri-hull bounce

A 1980 boat & a HEAVY 115 horses with 2 full gas tanks in the back. Seat is about 3/4 back ?

Foam flotation space got a load of water in it. Driver is 200 to 300.


Yup

Got 2 just like that in our place. Boston Whalers. The water is 3" from pouring in over the stern & sinking the boat. Those 2 guys are spending hundreds to go fast in boats that were bargains.

Don't they claim, you can't sink a Whaler?

 

[cyclops2]

Re: tri-hull bounce

Well 1 of the engines is taller than me. 6' 1". Old motor. Rattle can paint job.

 

[paul33]

Re: tri-hull bounce

Hey Guys,

This is only pic i have of boat.

The nameplate on boat says 90hp max, it is an open bow also.

sorry if I am repeating myself, as I am leaving boat launch bow is riding real high until i can increase speed and get it to plane then it starts to porpoise and get worse unless i turn or slow down.

i understand if i need a better pic of motor and transom. but she's -20 here and shes locked up in storage for winter.

 

[chriscraft254]

Re: tri-hull bounce

Wow, thats a pretty old boat. Nice! We will have to see a picture of it with the motor down to make a proper assessment of wether the motor is mounted to low or two high. I would invest in some smart tabs for that boat anyway. They will always help a stern motor mounted boat perform better imo.

 

[Triton II]

Re: tri-hull bounce

Hi Paul, I suspect that your 115 is too heavy for the transom so she's sitting bow high even trimmed fully in. Once on the plane the centre of lift moves backwards causing the bow to drop, however the thrust line is still far from ideal and is trying to lift the bow, the bow lifts, the motor rpm increases and causes the boat to accelerate, the centre of lift moves further back lowering the bow again, the thrust line starts to lift it again... repeat ad nauseum. As oops stated in an earlier post, this is called porpoising. One cheap and quick way to see if this most probably mismatched motor/boat combination can be made to behave is to put a couple of people in the bow of the boat and try to make her plane. If this stops the bow lift then you will know for sure the weight on your transom is too much for your boat. Give it a go once the water softens!

TII