Aluminum jet to outboard conversion

Discussion in 'Boat Design' started by LouReed, Mar 23, 2015.

  1. LouReed
    Joined: Mar 2015
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    LouReed New Member

    Hi All, I'm new to this site, so thanks in advance for all the great info! I have a 1988 Almar jet boat that I'm looking to convert to an outboard. It's a super beefy boat, so I'm not concerned with transom strength 1 bit, but I'd like some input on how far back my outboard should be mounted from the transom. I've seen other posts that say 1" for every foot of hull...so 19.5" to the gearcase. I'm thinking about doing a 14" jackplate, and using 4" aluminum tube to build a little better bracket and also integrate a swim platform. Any input you guys can provide for an offshore bracket would be greatly appreciated!!
     
  2. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    Tell us more about the boat. Is it an offshore setup, or more of a rocky river setup? Does it have a jet tunnel?

    I suggest you contact the mfr. and get their input/advice.

    Personally, I wouldn't go over 10" on the setback. I don't think you'll see much performance gain relative to hanging the motor back that far - it will place additional stresses on the transom and hull (regardless of how beefy it is), and may upset the balance of the boat to where you are too stern-heavy. If it is a planing hull, you may want to also raise the motor substantially as you bring it back (roughly one inch up for every three inches setback).

    If there is any sort of jet tunnel built into the hull, then you will want the outboard as close as possible to the transom, and you will probably find the addition of a powered jackplate to be beneficial.
     
  3. LouReed
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    LouReed New Member

    It's a rocky river set up, but it's got 15 degrees of dead rise so it's very similar to the ThunderJet and Alumaweld outboard models currently offered. It does have a 12"-ish flat section at the transom where the jet intake currently is however. I'll see if I can attach some pics...

    The boats currently sold look like they have around 24" of set back, especially the Wooldridge boats. I will for sure be using a jack plate, probably a Bob's Machine Shop plate.
     

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  4. Village_Idiot
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    Village_Idiot Senior Member

    Ok, if it's just a flat pad, then that is just a planing pad, so you can use setback. 24" sure seems like a lot of setback (just to be clear, setback is the distance from the transom that the motor is mounted; standard setback is zero), but if that's what similar boats are using in your application, you may be able to get away with it. Again, I would contact the mfr. for their recommendations.
     

  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    You only want, imo, enough set-back that will enable clearance to fully tilt the outboard.
     
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