T&T or JP

Discussion in 'Boat Yard Basics' started by oysterbreath, Jan 23, 2012.

  1. oysterbreath

    oysterbreath Well-Known Member

    If you could only have ONE on your microskiff (25hp merc 4stroke motor)...which would it be Trim and tilt or Jack plate?
     
  2. Brett

    Brett > PRO STAFF <

    T-n-T over jp.

    Allows thrust angle adjustment to fit sea conditions and load.
    I can bolt the engine to the transom at near optimum height
    as I have no need for every last drop of performance. That last 1/2 inch
    of vertical adjustment isn't going to cause me to lose any sleep.
    But the ability to tilt the engine to shallow water drive or clear of the water
    is more important to my needs as a shallow water fisherman.
     

  3. cutrunner

    cutrunner Cert. Yamaha technician

  4. Is that not too much set back!?
     
  5. oysterbreath

    oysterbreath Well-Known Member

    I think the designer of cut runners boat calls for a setback wide enough to hide below slot redfish in. Lol
     
  6. oysterbreath

    oysterbreath Well-Known Member

    I see your point Brett but my question is this:

    When you are coming up on shallow water while under power, let’s say you’ve encountered a series of sand bars, are you better off trimming the boat or raising the motor?

    I mean, if you trim the boat you raise the bow thus causing more cavitation. So then you begin to actually draft MORE in the transom unless you also have trim tabs to compensate. WITHOUT trim tabs, trimming your motor in this situation is contrary to your desire to clear the sandbar. In this case, which I think is a typical case, wouldn’t it be more conducive to raise the motor to clear it from bumping while still being able to power your craft? Blowout could be possible but the trimming alternative would create increased cavitation and wouldn’t tuck your motor as well either.

    Also If you are going to run a long expanse of shallow water in a no wake zone or at idle speed you’ll be running slow but you’ll want to still run level which means you can’t trim too much. Not trimming enough in this case leaves your lower unit exposed to subsurface obstacles. Trimming more…well, that leads to cavitation and deeper drafting and your transom right? But if you raise the motor…well you might blowout if you over do it but your lower unit is safe and you are still level right?

    Now, before you reply, please realize that I’m an armchair boatsmen! I have LITTLE real world experience. I can design a battleship but I’d drive a zodiac into a seawall! lol

    ______________________________________________________________________
     
  7. Excellent question! I'm interested in this. Its almost like how shallow can I go when goin at idle speeds and on plane with a JP or a TT.
     
  8. Brett

    Brett > PRO STAFF <

    On a small skiff with limited horsepower, total draft on plane is the controlling factor.
    Three numbers affect how shallow you can run.

    1) The distance from the top of the water inlet to the bottom of the skeg/blades.
    2) Hull draft on plane (which works out to about the same as at rest)
    3) How far the engine hangs below the bottom of the hull and still maintains water pressure.

    A flat bottom aluminum jon boat with a 15 hp outboard is going to draft about 15 inches on plane.
    That's the 4 inches of hull draft and 11 inches from the inlet to skeg.
    My flat bottom tunnel skiff can run in 12 inches because the top of the tunnel ends up level
    with the natural adjacent water level . So  the inlet to skeg distance controls.
    My old 19' whaler outrage had a 14 inch draft and 14 inch inlet to skeg, yet with it trimmed back
    could scoot across 24 inch depth water. Wasn't the most efficient running angle, lost speed
    and threw a rooster tail but it let me run the stake channels from Flamingo marina
    to Man-O-War channel behind the rest of the high performance flats boats. I could run shallower
    but had to make a wide turn to tilt the hull and angle the skeg to one side.
    I could get across a 20 inch deep bar if I needed to. But, this was not over grass bottom, only sand and mud.

    Find the channel, stay in the deeper water. If you have experience in the area
    and can read water depth while running, I'd still rather have PTT than a JP.
    That same whaler with the 14 inch draft could idle across 15 inch depths with
    the outboard tilted up to shallow water drive. I don't think a jackplate would lift the engine
    high enough to get the bullet above the bottom of the hull, so idle depth with a jp
    would have been 20 plus inches. I've had to idle long distances in a small skiff
    and as long as the inlet was below water level, I could run shallower by tilting than lifting.
    Especially with a stock prop.
     
  9. cutrunner

    cutrunner Cert. Yamaha technician

    Haha wanna know how to really do it?? (this is what i do). When i know im about to encounter some serious shallowness, i punch it. WFO!, trim that sucker out, cavitate!, PUT THE MOTOR ON TILT MODE (SHALLOW WATER DRIVE), and make one big gradual turn. If you still hot hard enough to fall off plain, ha well, you better hope higher tide is coming
     
  10. So it seems if you want to idle through shallow water it's best to have a tunnel.

    My problem is I'm in Louisiana and I like to get back up in the cuts where it's a foot deep or so and the bottoms are pure mud with SOME shell. Most of the time I just troll into the area, but once Im done fishing I crank up the engine and drive out.

    Im POSSIBLY in the market for a good boat for fishing these Louisiana marshes but I just can't seem to find the right one. :mad:
     
  11. Brett

    Brett > PRO STAFF <

    Tunnel jet outboard maybe?
    Have a few in my area that go places that regular flats boats can't.
    17' Aluminum tunnel hull, 60 hp yami jet, even oysters don't scare 'em.
     
  12. oysterbreath

    oysterbreath Well-Known Member

    Thanks Brett. That's something to chew on. But now I have another question. banter on T&T vs JP could go on till the end of time. The argument ends up being, "have both usually!" But since you brought up the jet drive. Doesn't having a jet drive negate the need for either? A motor with built-in T&T, a cupped blade, AND an add on jack plate cost how much more than a jet drive? The Jet drive would need NONE of those items -assuming manual tilt is fine with the owner? Is that an accurate line of thought? I know you loose some power and fuel efficiency going to a jet drive but my current line of thinking is....maybe a jet drive ain't so expensive after all with all things considered?


    Edit: how much of an issue is clogging the jet drive though?
     
  13. Brett

    Brett > PRO STAFF <

    Jet drives are specialty outboards strictly for running shallow.
    Not particularly efficient in a chop or in heavily vegetated areas.

    previous posts

    http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1232027473

    http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1305032174

    http://www.microskiff.com/cgi-bin/yabb2/YaBB.pl?num=1285539672/35#35