Shaft angle for old inboard project

Discussion in 'Inboards' started by Luchog, Dec 6, 2005.

  1. Luchog
    Joined: Dec 2005
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    Location: Rosario, Argentina

    Luchog Junior Member

    I'm currently refitting an old 19 feet boat originally designed for a 6 cilinder engine and remote v-drive unit.
    I want to install a V8 wich is about 300lbs heavier than the 6cilinder engine, and was told to install the engine on the center of the boat using a direct drive transmision, because of bow raising issues.
    For this I must modify shaft angle to fit the center of the boat, therefore the propeller will "kick" more water downside.
    I was wondering what effects it could have on overall performance/navigation.

    Here is a pic of two boats, the one on top is just like mine with a Remote V-drive installed, watch the narrow shaft angle.
    The one below is a different hull that has a direct drive unit and wider shaft angle like I would install.
    Any advise or comments are most appreciated
    Thanks
     

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  2. woodboat
    Joined: Nov 2003
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    woodboat Senior Member

    The struts come in standard sizes. http://www.glen-l.com/inboard-hdw/struts.html#0127
    I would mark where you want to mount the engine then determine your approximate angle. I would however mount the strut then insert the shaft to determine the actual spot to cut the hull.
    I prefer Vdrives and weight in the stern. It is very easy to add trim tabs and push the nose over. It is very difficult to get the bow to raise if you mount the engine too far forward.
     
  3. Luchog
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    Luchog Junior Member

    My first worry is not nose diving but general tracking/turning since the boat's gravity centre will be moved forward.
    Thus ignore what effect different strut angles may have on navigation and power efficiency

    I fear the engine on the stern to be too much weight and start taking water in when power-turning even with trim tabs
    This is a project ski/wakeboard boat.
     
  4. Jango
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    Jango Senior Enthusiast

    Moving the Cg forward can cause problems especially the faster you go.

    Since your boat was probably designed for a Vee Drive and rear engine placement, I would assume the bottoms widest point is at the Transom. Conventional Inline Inboards are normally widest near the Motor or Cg (further forward)
    .
    The combination of increased shaft angle and forward Cg can cause the Boat to bounce especially with increased power. The increased angle provides more Lift BEHIND the Motor tending to lift the back of the boat out of the water.

    I would, as a previous Poster suggested, Stay with the rear Engine Vee Drive. Some of the 300 lb will move forward since a V8 is shorter than a straight 6. Shouldn't be a problem in a 19' Boat
     
  5. Luchog
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    Luchog Junior Member

    Jango you're right, the bottoms widest point is at the transom. how does it affect??
    Wider strut angle/lift behind wouldnt prevent the bouncing??
    I was told someone installed a 5.7lts (as i want) in V-drive config. on one of this boats and the bouncing was awful.
    Thanks for the imput so far
     
  6. Jango
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    Jango Senior Enthusiast

    Luchog,
    To provide proper balance, Boat bottom design takes into consideration weight distribution. Normally, bottoms are widest at the transom IF the motor is located there. The wider the bottom (more surface area), the more LIFT.

    At higher speeds, If you move the motor (center of gravity) forward, the REAR of the boat will want to LIFT out of the water causing a bounce. Further adding to this problem is the increased shaft angle necessary with an in-line drive.

    Wide bottom at the rear, together with moving the motor forward (CG) and shaft angle will also tend to make the Bow "Plow."

    Higher speed Ski and Off shore boats locate their motors Aft.
     
  7. woodboat
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    woodboat Senior Member

  8. Luchog
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    Luchog Junior Member

    All of this is really helpful, keep it coming please.
    If I add a fixed position flap on the centre of the transom, how long should it be and in wich angle?? I was thinking about the same as the transom's botton as a continuation of the hull.
    Would an extra feet help bow rising issues??
     
  9. gonzo
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    gonzo Senior Member

    What engines are you swapping? 300lbs seems like a lot. Also, if you are taking out a VeeDrive, the difference shouldn't be so much.
     
  10. Luchog
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    Luchog Junior Member

    The boat was originally designed with a 6 inline 3.6lts, 133 or 166hp in mind.
    A 4.3 V8 190hp was available at that time (1974), but it wasnt worth for the weight/power relation.
    I want to install a 5.7Gm Crusader in it, 270hp.
     
  11. gonzo
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    gonzo Senior Member

    If this is a new engine, the added weight, if any, will be minimal. There may be more than one problem. First, is the boat capable of handling the extra power? Second, will changing the weight distribution affect the ride so bad that it will be worse than before? If it can handle the extra power, keeping the vee-drive would be the best option. The length of the engines is about the same. The mounts are different though.
     
  12. Luchog
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    Luchog Junior Member

    The engine I want to install is 1979, so I guees it would not qualify as "new".
    My worries are bouncing and turning

    Jango mentioned stern lifting/bouncing at higher speeds,
    This boat will be used for wakeboarding mostly, so I doubt it will ever reach speeds greater than 30-35 milles, so should I still worry??
     
  13. gonzo
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    gonzo Senior Member

    Do you still have the vee-drive. That would be the ideal thing, to keep the engine in the original location. So, do you ski in the Parana River?
     
  14. Luchog
    Joined: Dec 2005
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    Location: Rosario, Argentina

    Luchog Junior Member

    I have just bought a 1:1 velvet Drive and I'm now looking for a 1.5 reduction Remote V-drive unit, there is a national brand that runs up to 300hp. It suits my application well.
    Yes, I wakeboard in the Parana River, have you ever been here?
    btw, I've checked your site, I wish I could get my hands on some of that stuff you work with.
     

  15. cyclops
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    cyclops Senior Member

    Why not got to a commerical meat place that has a scale you could use to weigh the 6 cyl. motor in the boat. Just lift it and let it down . You then have the weight. 5.7L weights are known. Then you know if there is little difference.
    Keep the transmission and V drive design if you can afford it. Struts can be cut and rewelded or brased to new shaft angles and then plated new.
     
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