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help for a new guy

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Jacked Up Foot
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SAFARI RICK

Well-known member
I was wanting some input on setting the jacks in my boat. The guy that build it has taken ill so it hard to get in touch with him. I have been told 2 differtent things about the jacks.I've been told to make the bottom of the hull as flat as possible and I've been told to put a small amount of bow in it (Eggshape was the word used).I'm starting to porpoise at about 30 mph. Ya see I was told that by setting the jacks right the porpoiseing could be stopped. Any input would be greatly appreciated. And yes I could buy a trim tab but I know myself and it would just be torn off the first time I forget to put it up before running dry and I WILL FORGET. Thanks SAFARI RICK
 
Are you running aluminum or fiberglass hull? - Just don't know if you can do it to fiberglass - I am assuming you can't.

So I am also assuming you have an aluminum hull.

Most jacks are set between the middle t-bar runner and the motor stand directly beneath the motor. However, most stands with jacks have bracing on the motor stand that keep the jack from bending the middle portions of the stand upwards. Turn the jack and it forces the bottom out slightly - just do little adjustments then try it.

Did the boat just start to porpoise or has it always done it? Engine angle can make a boat porpoise as well. Just like a motor trim on an outboard. If it just started it, I would guess a jack could help. If it always has done it, engine angle could be the issue and a jack will not help.


Good Luck
 
You can run them on fiberglass but I don't know what it really does. I personally have a boat with them in it.
 
I have occasionally used jacks to reshape the hull so it runs best dry, then use a trim tab to take out porpoising. Keep in mind as the load in the boat changes, the porpoise speed and dry run ability both will change. Load distribution effects it as well. I always make sure I have about 1/4 of a bubble down slant at the prop end of the engine, for a starting point, using a carpenters level.

Best dry run shape and best flat running in water are kinda opposites in hull shape. Both jacks and tabs work fine on glass or metal. Key is to have one under the motor and one under the front legs of the seatstand or thereabouts.

Definately the good advice says go slow and easy with the jacks, you can damage your hull and, if not built correctly, can damage the motorstand or seat package as well.

Best of luck. If you have someone close who knows, ask them to help ya do it.

Scotty
 
THANKS FOR THE INPUT FROM EVERYONE. FIRST OFF THE HULL IS 12FT ALM. THE BOAT IS BRAND NEW AND THE JACKS ARE ALREADY BUILT IN THE BOAT. WHAT I'M LOOKING FOR IS IF ANYONE HAS HAD ANY EXPERIENCE SETTING THEM SUCH AS DO I NEED MORE IN THE FRONT JACK THEN THE BACK OR DO THEY BOTH NEED TO BE SET ALMOST THE SAME OR SOMETHING ALONG THAT LINE. I'M SPENDING THE ENTIRE NEXT WEEK ON THE RIVER AND WILL HAVE PLENTY IF TIME TO MESS AROUND WITH IT. I HAVE THE MOTOR SET COMPLETLY LEVEL AT THIS POINT SO I'M GOING TO GIVE THAT A FEW TWEEKS TO SEE IF THAT HELPS. I SET THE BOAT UP TO RUN DRY BUT I'LD LIKE TO BE ABLE TO GO ALITTLE FASTER ON THE WATER( STILL HAVE ALOT OF PEDAL LEFT DOING 30 MPH) NOT LOOKING FOR THE FASTEST JUST ALITTLE MORE THEN I'M GETTING, THANKS AGAIN FOR THE INPUT. SAFARI RICK
 
Ok Ill give it a shot, but since I wont be there I bear no responcibility if you break your bottom.

FOR DRY: Imagine in your minds eye an egg shaped ball right under the front of the seat package. The motor is angled down slightly so it picks up the back end a little (really just lightenes it) and pushes forward so you are riding on just this ball in the front of the boat. Less bottom on the ground the easier your going to move. This ball will make the boat poprpoise in the water so step II is on order.....

Anti Porpoise: Again imagine in your minds eye whats happening in a porpoise, you add trim tab at the back of the boat to keep the nose down on this ball you have created. Too much trim tab and your boat will DART to one side or the other !

Thyere's an advantage to doing it this way and that is that in skinny water, you will have the ability to snap it around and change directions in the blink of an eye. Youll look good and youll be able to maneuver quickly. In sweeping turns you may even need to counter-steer some.

Theres a disadvantage too, that same snap in turning will catch you off guard on a high plane in deep water when the wind kicks up, you better be able to control it. I slow my rudder responses WAY down for this setup so I dont over-control at high speeds.

Anti porpoise ONLY: leave the front jack under the front of the seat package alone and put some down pressure on the back one under the motor. SMALL adjustments at a time and run it. Youll find a point where it helps. You will also find this way that when you change the weight and the weight distribution youll be back to porpoising again. This is why I use an electric trim tab I can adjust as needed in the water. Its a double barreled hassle to guess how the load is going to change and readjust the jacks or your load, plus jacking back and forth will untimately fatigue the metal in the bottom of your boat then ya got a real problem.

REMEMBER: EVERYTHING IN MODERATION, TAKE IT SLOW AND EASY MAKING ADJUSTMENTS. Maybe 1/4 turn at a time and try it. Maybe someone else can contribute here. There may be other ways to set up a bottom, this is just how "I" do it, and why I do it that way.

EDIT: I keep thinking of things to say. I gather form the topic, you are new to airboats so keep this in mind. You can take a basically safe, stable boat and jack it around to the point it is INCREDIBLY dangerous and unsafe for a new operator. An airboat has no conscience and can and will kill you. Learn to operate it safely first and get a bunch of hours under your belt before you try changing things very much.

Hope it helps, and be careful

Scotty
 
Whitebear - No reason to beam that Scotty up and out of here. Damn fine answer on how jacks work. And I like that advice at the end.

Both jacks and trimtabs can turn a boat that is very easy to drive into and almost unpredictable and possibly deadly machine.

Having a airboat catch a chime and doing an unexpected 180 during a turn or in trail with little safety margins is a very SCARY situation. Faster you are going the faster she will swap ends and can easily roll.

Trying a small adjustment and testing on shallow, deep, and skinny water is the way to go.
 
THANKS FOR ALL THE INPUT GOING TO GIVE IT A GO OVER NEXT WEEK BUT JUST TO LET YA KNOW MY MOTTO HAS AND WILL CONTINUE TO BE SLOW AND CAREFUL. ONLY BEEN OUT WITH IT A COUPLE OF TIMES AND SO FAR 50% OF THE TIME I'VE EITHER HAD TO HELP WITH A SUNK BOAT OR HELPED TO PULL ONE IN. WAKE UP CALL WHEN SOMEONE MORE EXPERIANCED THEN MYSELF SINKS THIER BOAT IN DEEP WATER RIGHT NEXT TO YOU.-SAFARI RICK
 
Give Dave a call att Alumatech.He is probably one of the best around when it comes to jacks.
 
my 2 cents worth keep the bottom of the boat as flat as u can.
put as much weight like anckors tool box cooler in the front of the boat.
set the motor approx 1 inch higher in the rear as the boat is heavier in the rear so motor should be almost parallel to water when flying.
if it still pourpeses then move the gas tank forward maybie 6 inches
at a try. most boats are built with the tank to far back.
the last few boats i built i made the tank brackets so they can be adjusted.
i c clamp the bracket to the rib until it is set up just right.
these ideas have been suggested to me thru the years by old timers who
never used trim tabs because they are unstable at high speeds when
making turns plus u do tare em off on dry ground.
also i have learned to always make the front seat the drivers seat.
this is espically true in short boats 12 ft and under.
hope you get er done.
 
Rick your motto is the only one to have --- I've been in the seat of airboats for over 15 years and I learn something new every time out. and every time I think that I can show off a little bit it reminds me what is relay in control . you have excellent information on the bottom jacks and how to adjust them .I was told many years ago that the main purpose for the jacks is to keep the bottom in the shape that best fits your running train. As for the porpising On the transom of your aluminum boat ware the transom meets the bottom ---The bottom should stick out past the transom around 1 inch. If you take a large pipe or crescent wrench and bend this bottom tab down 1/32" all across the back it should stop the porpoising. Again as previously stated --go slow with the adjustments and try one at a time so you know what each dose for the boats performance.
When I'm doing this type of experimenting i keep a log book of each step so that next year after several rocks and logs I can easily recheck to see if everything is still adjusted correctly.
If you bend that tab to far then the nose (bow) of the boat will not come up to go on plain but will plow the water.
If this works for you then take a small carpenter square --place it against the transom and measure the the amount of bend that your boat works well at. as dry unloading and loading along with rocks can effect this bend.
Good luck --Be safe -- respect others --and have fun
 
Swamproot has a great post here. This is a perfect way to set up a well balanced neutral handeling boat. You can slso use the battery to move weight around. Keep in mind as the tank empties you lose weight no matter where it is located. Were I setting up a new boat for a new customer this is how I would balance it. Jacks and tabs are for altering the way a boat will handle and should always be used from the starting point of a properly balanced neutral handeling perspective.

I also couldnt agree more with the operator up front. You have a better feel and perspective of where you are going.

Old timers had to learn it the hard way and they didnt have the luxuries we have or the options we have to day on our boats. Remember they had small motors and narrow short hulls and setup was way more critical for them. The lessons they learned though are just as applicable and important today.

If it isnt balanced to begin with all your doing is covering up deficiencies with jacks n tabs.

In my above post I was trying to show a new person not what to do, but How the different things he can do will affect what his boat will do. The more experiece we get the more we are able to deal with deviating from from a basic setup. When we do deviate it is good to understand what the thing we change will do to the handeling and why we want to do it. There is likely no ONE RIGHT WAY for everyone. One person likes quick rudders another likes slow rudders, one runs more dry and another person only runs deep water, and yet another loves to just play in a marsh.

Rick your getting good advice here and hopefully it contributes to good understanding :)

Scotty
 
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