Buying or Building a Z Drive?

Discussion in 'Propulsion' started by Pceditorpro, Dec 3, 2018.

  1. Pceditorpro
    Joined: Dec 2018
    Posts: 1
    Likes: 0, Points: 1
    Location: Massachusetts

    Pceditorpro New Member

    I'm getting ready to start building my first boat. It will just be a 24ft flat bottom skiff. Mostly used for recreational lobster fishing and helping friends move some docks around. When I started studying for this I decided on a few things first I wanted more of a learning opportunity then just buying things off the shelf like a simple outboard and after repairing boats for a living for the last 7 years I may be a little paranoid when it comes to reliability. I wanted to build twin Z drive pods that will be set off the stern like an outboard would be placed. I was thinking of powering theses via shaft driven. I have read a lot about people using hydraulics but they seam to only be worth it on something much bigger. For power-plants I was thinking of using 2 350 Chevys I was given by a friend when he moved. They just got back from the machine shop ready to be assembled. This is probably way to much power but I have them and trying to find parts should be relatively straight forward. I guess the first thing to ask is where is the best place to find information on Z drives for this application? Do they sell something that I can use or do I need to make something? If I need to make them are their any good plans to work off of? In general what do you thing? I'm kinda looking to just bounce some idea around on this.
  2. Barry
    Joined: Mar 2002
    Posts: 1,001
    Likes: 52, Points: 48, Legacy Rep: 158

    Barry Senior Member

    and why not just an IO, especially if you are going to mount them on the stern
    No rudder, vectored thrust with the turn of the outboard unit

    Volvo even has a computer controlled joystick positioning device to help with docking if that is why you would want a Z pod that turns.
    In a 24 foot flat bottom boat, 600 plus horsepower?
  3. Mr Efficiency
    Joined: Oct 2010
    Posts: 6,805
    Likes: 180, Points: 63, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    :eek: One of those engines would be far too much for a flat bottom 24 footer. And unless they are marinized, simply forget about that power option ( a single 350 )

  4. Barry
    Joined: Mar 2002
    Posts: 1,001
    Likes: 52, Points: 48, Legacy Rep: 158

    Barry Senior Member

    What is the beam? If it is a trailerable width of 8 feet, it will make the installation of twins difficult plus hard to work on.
    A 5.7 set up with outdrive is about 1100 pounds, a pair of them 2200 pounds, in the back of a 24 boat with an 8 foot beam, this is excessive.

    Unless your engines already come with the marinized components required to make the engines legal and safe, the cost to complete these blocks will be excessive.

    It appears that your selection of twin 350s is revolving around the fact that you have been given a couple of blocks, perhaps you are trying to build this boat as economical as possible.
    So on a tight budget, an option would be as follows. Locate 1 (one) used stern drive assembly from someone who has upgraded his boat that has a worn out engine. Craigs list, kijiji,
    etc and install one of your blocks into it, rebuild the stern drive portion, (depending on the extent of the rebuild maybe 3500 US). If you want a get home engine, install a 25 hp Yamaha, they
    have a new lightweight version of them, I think about 120 pounds.

    Marinizing a 350 engine,
    You should have bronze/brass frost plugs, marine starter, carburetor, fuel pump, distributor, flame arrestor, alternator, raw water pump. Generally, the cam is ground for marine
    applications as you are looking to produce more horsepower at lower rpm, ie higher lift/or duration. This stuff is expensive and that is the reason I suggested the used sterndrive set up
    as these components will come attached

    If you are going ahead with two engines, against advice, Add to one engine the cost to make it a reverse rotation engine, timing gear set, distributor, Lots of bucks here

    An expensive heat exchanger, not absolutely required but the best way to cool your engine.

    And flat bottom. We have built many 12 degree jet boat hulls to be able to run in shallow water, but have occasionally taken them into larger waves and even at 12 degrees in short even 2-3
    foot waves the ride is kidney killing. Why would you want a flat bottom?

    We had a 10,000 pound 26 foot cabin cruiser back around 1981, 10 foot beam, with one 5.7 stern drive, suspect about a 22 degree deadrise, this boat would cruise easily at 28 knots
    at about 3300 rpm. One engine, heavy boat, full cabin, black water, regular water, 140 gallons of fuel,

    Anyway you said that you wanted to bounce some ideas around and with a flat bottom boat you will,
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.