out leg power

Discussion in 'Sterndrives' started by kcmd, Jul 23, 2009.

  1. kcmd
    Joined: Jan 2005
    Posts: 24
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cornwall uk

    kcmd Junior Member

    Hi guy's i have an old pp jet drive on my 19 ft fast fisher coupled to a Nissan 2.7 turbo diesal, how much work is needed to fit a out leg, will this give me more power then the jet ? can the gearbox in the outleg have its cogs with prop changed to get more speed and what out leg would you advise me to have any help would be very greatfall .
  2. CDK
    Joined: Aug 2007
    Posts: 3,324
    Likes: 148, Points: 63, Legacy Rep: 1819
    Location: Adriatic sea

    CDK retired engineer

    Impossible to answer that question without a picture of the engine bay.
    A Mercuiser Alpha-1 has the advantage of an integrated gearshift but requires relocation of the engine to the stern. A Sternpower leg with a ZF gearbox may fit without such an operation.
    Either way speed and acceleration will improve considerably.

    Contact Lancing Marine, Mike Bellamy, in Sussex or look at lancingmarine.com
  3. baeckmo
    Joined: Jun 2009
    Posts: 1,524
    Likes: 506, Points: 113, Legacy Rep: 1165
    Location: Sweden

    baeckmo Hydrodynamics

    Which PP is it? The coupling flange on almost all PP jets is very close to the transom. Depending on what kind of shaft coupling is used, the engine should not be far from its position with an Alpha or Bravo installation. If you want to keep the Nissan engine, Mercruiser has a connecting part (for use with a cardan shaft), that fits with a standard SAE flange (for BW, Hurth gears) on the engine.

    There are also "pirate" transmission parts for Volvo 290 drives on the market, likewise fitting a standard SAE bell housing, so it is not a miracle job to do. And, as CDK points out, the jet efficiency is bad at speeds below about 25-30 knots, even if the PP,s were better than most in the low speed range.
  4. kcmd
    Joined: Jan 2005
    Posts: 24
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cornwall uk

    kcmd Junior Member

    Thanks guys very helpfull
  5. kcmd
    Joined: Jan 2005
    Posts: 24
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cornwall uk

    kcmd Junior Member

    This is my connection coupling and shaft for my Nissan ,engine in pic was replaced with newer engine fitted in engine bay.The engine is the lengeth of the coupling from the stern.

    Attached Files:

  6. Frosty

    Frosty Previous Member

    Is it in a Dateline Bikini or a Bounty?

    You know that the metal straps around the donut are to be removed once fitted?
  7. marshmat
    Joined: Apr 2005
    Posts: 4,127
    Likes: 149, Points: 63, Legacy Rep: 2043
    Location: Ontario

    marshmat Senior Member


    Switching to a sterndrive is probably feasible, but it could be quite a lot of work. Especially if you have to modify the transom. I'm not sure at what angle your transom is raked back- sometimes with jets it's 0 or 5 degrees. Most sterndrives are intended for a transom that rakes back a little more sharply- otherwise they may have trouble trimming down enough to get you on plane.

    I'm not a huge fan of the Alpha, mainly because of horror stories that keep circulating about them breaking down, needing early rebuilding, or cracking their bellows and letting water into the boat. In small single-prop drives, the Volvo SX would be my choice. Sternpower and Konrad make substantially beefier, industrial-grade drives that might be overkill for your 2.7L motor but are said to be darn near indestructible.

    Switching to a prop would probably bring some benefits- more efficient, for one- while also having some downsides. Hitting debris, for one. It's also worth noting that one of the reasons commonly cited for choosing a jet is because they tend to maintain roughly constant efficiency over a wide range of boat weight, ie. they don't tend to bog the engine down when the boat is heavy in the way a prop tends to.

    For a jet to come near a prop drive's efficiency at low to intermediate speeds, it needs to be quite large in diameter. Most sport boat pumps are rather on the small side, producing a narrower and higher-velocity stream. That's fine for speed but can hurt at the low end. If you often run at low planing speeds, the prop might be a substantial improvement over the jet.

  8. kcmd
    Joined: Jan 2005
    Posts: 24
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: cornwall uk

    kcmd Junior Member

    the engine and jet is fitted to a 19 ft fast worker built in cornwall uk.
    Thanks for all the help guys plesure writeing to you all.
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.