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Mercury Outboard Powered 65' Motoryacht (no joke!)

Discussion in 'Popular Yacht Topics' started by YachtForums, Jul 12, 2011.

  1. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    I concur. In "Voyaging Under Power" by Beebe, if one takes the time to sift through all the technical bits, a larger and heavier boat than the subject of this thread can do 8 knots requiring roughly 160 HP. One of those ~250 HP Mercs would up that to almost 9.
    Too, if the owner had installed two aft-installed thrusters facing north/south, and ran them off the (presumably) twin gensets, he'd get diesel economy and possibly a longer lifespan than the handgrenades, er, Mercs.
  2. Capt J

    Capt J Senior Member

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    It is indeed possible to do 9 knots on a larger boat with less horsepower, if it is a displacement hull. I once worked on a 97' Steel motoryacht (displacement hull) 8.5' draft and twin 250 hp gardener diesels......at cruise utilizing 400 HP, it did 9-10 knots.

    The Azimut has a planing hull, which is going to take more HP to push it 9 knots, than a displacement hull. These Mercury's are only 185 cubic inches, so how much torque do they actually make?
  3. K1W1

    K1W1 Senior Member

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    Hi,

    For the second time in this thread I will suggest that you find out what the word Torque actually means.

    The engines in the photo will have enough torque to turn the props attached to them.
  4. Capt J

    Capt J Senior Member

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    Yes, I agree the engines will turn the props attached to them. But do the engines actually have enough propellor torque to safely maneuver a boat of that size in tight situations with wind and current. Do they have the amount of torque to be able to spin the boat on it's axis, stop the boat in a reasonable amount of time, etc.

    Of course they will eventually get the boat up to hull speed, but on inland waters a lot of times you don't have 1/2 a mile to do so.
  5. Marmot

    Marmot Senior Member

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    There is a difference between torque and thrust.

    It is possible to deliver enough torque to a propeller to break the shaft but not produce any thrust at all.

    Sorry J but it sounds like you have fallen victim to the marketing folks.
  6. tirekicker11

    tirekicker11 Senior Member

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    Allright Marmot, could you (or K1W1) enlighten us with a bit of your knowledge.
    J is not the only one confused here.
  7. Marmot

    Marmot Senior Member

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    Torque is the force that tends to rotate an object around its axis or a pivot. If you attached a bar that extended one foot from the center of a propeller shaft and placed a one pound weight on it you would apply a force (torque) of 1lb-ft or 1 foot pound however you want to say it.

    A reciprocating steam engine, an electric motor, or a hydraulic motor will deliver its maximum torque to that shaft when it is stalled, not rotating, even if a propeller was attached to the other end. At the same time it will not produce a single horsepower or fraction thereof as long as the shaft is not turning no matter how powerful it is rated or how much torque it can produce.

    I'll let K1W1 provide the propeller section of the lecture.
  8. NYCAP123

    NYCAP123 Senior Member

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    As Marmot pointed out, Capt J was referring to thrust or bite, the ability of those props to grab the water and propel the object as opposed to just moving water, something I was wondering about as well with those little OB props. I'm sure there's enough torque and thrust to keep the boat going once it's moving, but getting it moving from a dead stop or stopping it once in motion could get interesting. I sort of wish they were bringing it down the New River under its own power. I suspect that the turns by Little Florida would show if theory translates to practice in very dramatic fashion.
  9. Capt Bill11

    Capt Bill11 Senior Member

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    Lack of the ability to build up thrust quick enough, is exactly why I don't believe they would ever try to bring it down the river under it's own power. What with other boats moving around on the river and all the boats lining the river, unless you ringed the boat with a large inflatable collar, it would be pretty irresponsible as well.

    In fact they may tow it right out the inlet.
  10. Capt J

    Capt J Senior Member

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    Yes, that is the definition of Torque. The Mercury's do not have enough Torque to spin a propellor with hardly any pitch around it's axis when trying to push a boat as heavy as this. You are also limited to 15" diameter propellors because of the distance between the propshaft and gearcase. And running 15" diameter propellors versus the 36" diameter propellors the boat origionally had, is going to take 2 years (disclaimer: not literally) to get the boat moving at a decent speed to even properly maneuver it in any close quarters.

    The size of the propellor the Mercury can turn and achieve it's HP and recommended maximum RPM, depends on how much torque the motor makes. If the motors only make 200lbs of torque each, then they are probably only going to be able to spin propellors with 8-10" of pitch on them. These engines are 7200 RPM engines, and don't start developing hardly any torque until they are turning about 3500 rpms. So the amount of torque the engines produce, directly effects how much propellor pitch the engines can turn and achieve rpm's getting into the HP zone of these motors, and that directly effects how much propellor thrust you will have to push the boat, and that directly effects how fast those engines will push the boat.

    However, 1- 750 HP diesel that produces a lot more torque than all 3 Mercury's installed on this boat with the proper propellor with a lot more diameter and probably more pitch, would push the boat faster and accelerate it faster to that speed as well as being a heck of a lot more efficient.

    Why is it that you have to put everything into Scientific talk on here, when most of the readers can directly understand the message that I am conveying.
  11. Marmot

    Marmot Senior Member

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    That wasn't "scientific talk" it is high school mechanics. I find technical illiteracy among machinery operators annoying and when misinformation is repeated often enough it breeds more.

    There are readers who don't know any better who might believe it when someone repeatedly writes that torque is what moves a boat.

    Because I naively hoped that a Son of Magellan would avoid mangling the principles which motor his boat.

    Thrust moves the boat. Thrust is produced by a propeller when it accelerates a mass of water. You don't even need a propeller to accelerate a mass of water to create thrust and move a boat. You don't need a single inch pound of torque to move a boat.

    You are correct that those small diameter high speed propellers will not produce enough thrust to safely maneuver that boat at low speed. Those engines can produce enough power to drive the boat but not in the rpm range needed to turn a large enough propeller to produce sufficient thrust to operate it safely in the New River.
  12. Capt Ralph

    Capt Ralph Senior Member

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    Sea Drives on a Huck?

    Any of you kids remember, about 25 years ago, some new Huckins build with 5 OMC Sea Drives on its transom?
    I remember it in some magazine.
    The thought was HP per weight on a plaining hull. I think the owner finally gave up and put some proper power in her a few years later.

    I always thought the 2.5 was in minutes?
  13. CTdave

    CTdave Senior Member

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    Surface drives! She'll kick up a great rooster tail for the 30 minutes that they live.
    I'd love to see video of it in ANY sort of sea. The triplets will be submerged constantly.
    I wish he had them hooked up to a giant tiller LOL LOL. I could drive & Carl could throttle (bending over each engine to manually throttle)
    Priceless!

  14. SHAZAM

    SHAZAM Senior Member

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    Funny you mention a "tiller", I just saw a 40 something Merritt with a huge tiller being towed down the river. I'll try to find it tomorrow and get some photos.
  15. 99fxst99

    99fxst99 New Member

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    Did it get underway yet?
  16. Yachtjocky

    Yachtjocky Senior Member

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    Any News

    Anybody got any news about this vessel, did it make it back to Texas.
  17. Yachtjocky

    Yachtjocky Senior Member

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    Update

    I was in the boatyard yesterday and the yacht is now in the water but not going anywhere. Apparently different Captains and crew have shown up, taken one look and left even a crew employed full time in Texas by the owner came, looked and left.

    The tow boat also sent from Texas turns out to be an old house boat with little free board. :cool:
  18. sunray09

    sunray09 New Member

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    Million Dollar Mistakes

    Perhaps a little Coast Guard Inspection is in order.
    Since this is obviously about "saving money".
    Everyone here is well aware of the pitfalls of saving money or going the cheap route. It can be bloody expensive.
    The sea makes ZERO allowance for stupidity and the full range of natural laws are in force at all times. Its all well and good for us to laugh about this KLUGE but if it puts to sea in a state that puts lives at risk..then there is little money to be made or saved that is worth a persons life.
    Perhaps the Coast Guard can apply the OUNCE of PREVENTION.

    This boat and owner are quickly gaining a reputation in Maritime History that the wiser man would seek to avoid. The only way I would set foot on that yacht is if the entire continent of the USA was on fire..and even then I would want a lifejacket and an oak paddle as big bloody stick to hit the captain with when the inevitable occurs!!
  19. Laurence

    Laurence Senior Member

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    New Crew

    I'm sure there are Rednecks here in Alabama that would be glad to help out for a buck or two. LOL
  20. BLouder

    BLouder New Member

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    any word on this mess? I just want to see video of him leaving the dock, cause Idon't think its gonna go much further!