Aquasport 19-1 porpoising in calm water

[lac8362]

My 19-1 starts to porpoising when i reach a speed exceeding 20 mpg Its pretty bad i was wondering if any one else has had this problem and a remedy. I was thinking of a dolphin hydrofoil thx for any help.

[Blue Agave]

Your best bet is trim tabs.

[wingtime]

A dolphin will cause even more troubles...  you don't want any type of lift on the motor itself...  imagine the boat trying to balance on that hydrofoil...  it is unstable and will want to flop over to one side or the other...  as Fernando suggested trim tabs are the solution...   some have had luck with the smart tabs...  but full trim tabs will give you the best control over the boat.

[pete]

You might try trimming the motor all the way down,or moving some weight,like batteries from the stern to the console.Usually can be corrected by engine tilt or weight distribution.

[gran398]

You might try trimming the motor all the way down,or moving some weight,like batteries from the stern to the console.Usually can be corrected by engine tilt or weight distribution.

Pete's right, the first solution would be the batts moved forward. Also, is the bilge dry?

[lac8362]

the motor was trimmed all the way down i'll attach some pictures of the motor position below

[Blue Agave]

By the looks of it, it appears that your motor is mounted too low on the transom.  The cavitation plate on the motor appears to be below the bottom of the boat.  This is probably part of the problem, I would raise the motor so that when it's trimmed down the cavitation plate is about half an inch above the bottom of the boat.  I would also invest in a set of trim tabs, you will not be disappointed.

[wingtime]

Good eye Fern!  I'd say the motor is a tad low as well..  you should be able to place a straight edge on the bottom of the hull and at the very least the cavitation plate should be level with it or about a half an inch higher...  also you my want to try moving your motor trim pin out a notch...  looks like it trims in a bit tight making for too much bow down trim.

[lac8362]

looks after placing a level to the bottom it measures 1 1/2 inches short of the desired location is this enough to create this porpoising effect?



also is this a good location to move the pin to?



I also noticed  the transom was cut down about one inch may have been from another outboard or to allow for steering cables they do look a little tight



do you guys think i could just get away with trims or will raising the engine up 2 inches putting the cav plate 1/2 above the bottom fix this problem also what are some decent trims for this model aqua 19-1 gull

[gran398]

Make those adjustments first...then see how she does.

[Blue Agave]

Each hole on the mounting bracket is approximately 3/4". Raising it two holes should give you an inch and a half.  Do you have a water pressure gauge?  After you raise the motor you'll want to make sure that the motor is getting enough water. When the boat is up to speed have someone drive and go back and look at the position of the cavitation plate. At planing speed the cavitation plate should be visible, should be riding across the top of the surface.

[fitz73222]

I'd say your engine height is perfect for that hull. You are running a relatively stock propeller with very little cup. Porpoising can be caused by the propeller trying to grab water, loosing bite and falling down. I would say a 115 on your boat should swing a 15"-17" propeller at 5300-5600 rpms. I would really consider a Stiletto propeller, 3 blade, nice cup with good bite. We need to know what the engine is turning wide open, what pitch and brand of propeller you are running, very slight positive trim to establish a pitch base line. You want to be in the upper 50% of the rated maximum RPM. An example would be if the engine is rated at 5250-5750 we need to be a 5500-5600 for the optimum RPM. This allows the engine to breathe in its sweet spot that gives the best overall performance for hole shot and wide open speed. I agree that weight distribution, trim angle, and propeller design has a lot to do with a porpoising issue, so be aware of proper weight distribution and other factors. One of our board members DHadley should be able to help you with a nice prop selection.

Fitz

[wingtime]

I'd say that motor is a tad low...  costing you speed and fuel since the water will be hitting the lower unit above the cavitation plate..  It may be causing your problem but I doubt it.  try moving up the pin...  can't hurt wither it will help or not.   Also how many bolts are holding your motor on?  am I seeing things or is there no bolt in the lower position?

[Blue Agave]

I'd say that motor is a tad low...  costing you speed and fuel since the water will be hitting the lower unit above the cavitation plate..  It may be causing your problem but I doubt it.  try moving up the pin...  can't hurt wither it will help or not.   Also how many bolts are holding your motor on?  am I seeing things or is there no bolt in the lower position?

There should be four bolts securing the motor to the boat!  I'd raise the motor and attach with four bolts. And as Fitz mentioned the prop is also a variable.

[lac8362]

there are 4 bolts but not through the bottom mount kinda strange im going to bolt it up 1/ 1/2 inches 2 spaces and pull the pin out 1 space ill see if i can tell what the prop is pitch and all any info on good trim tabs would be helpful