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Thread: reverse rotation?

  1. #1
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    Default reverse rotation?

    I have a used 28x10.5 ft fiberform that I am re-powering. It has twin 350's now that are old, tired and have sat for about 2 years. I am going to buy rebuilt 350's and upgrade to 300hp. My question is if I need to have them in reverse rotation. I thought you for sure needed it and the way it used to be done was at the motor. I thought the way it is now, the rotation is changed in the outdrive so you just have standard rotation motors. I talked to a few manufactures, mechanics and knowledgeable others and they all said different things (of course). I have alpha one outdrives. The props that are on them look to be the same rotation, so I assume they were spinning the same way. I can not tell if the motors are reverse because I can not read the firing order or serial numbers. It does not really matter what is on there now anyway. I am more interested in what should be on there later.

    So what is the deal? Does a boat that big need to have reverse rotatation?

    If so, how is it done. At the motor or in the out drive?

    Sorry if this has been hashed over before. Like everybody says, the search function is a mess.

  2. #2
    Member Cap'n Ron's Avatar
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    If the props are the same, you do not have counter (reverse) rotation in one of them. It is done in the outdrive, not the motor. The purpose of counter-rotation is to eliminate steering torque at low speeds...it is very desireable when manipulating in tight spaces, like in a harbor or approaching a mooring buoy. Some have it, some don't. It is more expensive, and if you need parts, some of them are specific to the normal or counter outdrive. I have in on my twin outboards and really appreciate it. I don't know if it makes any difference in the power or fuel efficiency, someone will likely have an opinion on that.

    There is a place in Michigan where I bought an aftermarket Alpha one outdrive that was guaranteed for 3 years, even if you hit a rock! It uses all inter-replaceable OE parts, if you want to check them out, PM me. For $1200 I bought a brand new outdrive vs a lot more than that for an OE rebuild...it went right on and worked perfectly, they are built in a factory in Florida. A new outdrive by Mercury is about /$3500 I think. The shipping to AK was maybe $100, might have been less, it's been a couple of years.

  3. #3
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    Really, nobody has an opinion on twin engine boats? I thought a bunch of people would chime in. Thanks Cap't Ron.

  4. #4
    Member hoose35's Avatar
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    I don't know how the Alpha outdrives work, but I am pretty sure on my old boat with a volvo 280, you could easily change the rotation for left or right handed props by rearranging the shifting mechanism, meaning a left hand rotation engine could be used with a righthand prop with the direction change happening in the outdrive, not the engine. Like stated earlier, if you have the same props, then neither your engine nor outdrives are counter rotating, but they probably should be, maybe whoever had the boat first changed the direction in one of the outdrives to make them the same so they did not have to buy a counter rotating prop. You should be able to find out if your engines are counter rotating by turning them over and seeing if they both go the same direction, if they are countering, then you should next find out if you can make your outdrives counter because if you are going with new engines, the best way I think to do it is have to left hand rotation engines (standard) and make your outdrives counter if you can. I have a 28' boat that I am repowering, but it has v-drives, not outdrives. I bought a right hand rotation engine and it was 1200 dollars more than the left hand rotating engine. Hope this helps
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  5. #5

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    I have twin Volvo 280s powered by small-block GM V8s. There is a RH and a LH prop, and the reverse rotation is generated through the outdrive shifting mechanisms, not the engines.

    Think of it as one prop always running in "reverse" (as far as the shifting mechanism is concerned), but since the prop direction is also reversed on that side, the net result is *forward*.

    If I'm running on one engine, the boat tracks straight but turns much better *away* from the operating engine. I believe this is a function of the push from the turning propeller being on the outside of the turning radius, rather than which way the prop is rotating.

  6. #6

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    As I understand it, Twin propped boats with the props spinning in the same direction has a tedancy to pull the stern slightly in the direction of the prop spin. Essential causing a slight "crab walk" for lack of better terms. This uses slightly more fuel and less speed.
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