17ft custom aluminum jet sled plans. Better built than bought.

Discussion in 'Boat Design' started by TwinSled, Sep 10, 2018.

  1. TwinSled
    Joined: Sep 2018
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    Location: Montana

    TwinSled Junior Member

    Hello all! I am new to the forum, but in the last year have become obsessed with welded aluminum river boats. I recently moved to eastern Montana, amd reside not 400 yards from the Yellowstone river.
    I have been scouring the web for an aluminum jet boat for the last 6 months, but have found that either a used boat costs too much, and doesn't fit my needs, or a custom ordered jet boat would basically cost my soul.

    I have come to the conclusion that I am going to custom fabricate my "perfect" hull, and outfit it with twin jet outboards. (Just because I can.)

    I have become very partial to the design of the Wooldridge Alaskan, and plan to build a hull with a 2 piece windshield very similar to that. This boat will primarily be used on the Yellowstone river, but will also see the waters of Fort Peck reservoir every so often.

    So in order to have a tailored hull, I need the side panels (or gunnels) to be 3 to 4 inches taller than the ones of a wooldridge, and also need to have the windshield and dash moved forward almost a foot from the wooldridge to increase sight while running the river in low light conditions.

    This boat will need to be equipped with a large livewell/baitwell, and have storage compartments along with port or starboard rod lockers.

    When it comes to propulsion, I have always dreamed of having a twin outboard setup. To me, nothing looks sharper than two outboards hanging off a transom.
    In order to have an appropriate amount of horsepower, I planned on running either 50hp Tohatsu's, or 40hp yamaha's or Mercs. I thought Tohatsu may be the best dollar value.

    A little background about myself, I took welding courses years ago in college and have been hobby welding ever since. I've always had a fiery passion for fabrication, but only have accessibility to a hobart 190 handler with an aluminum spool gun setup.

    I am looking for some insight from some people who have undertaken this project, and have a couple question like,
    What thickness aluminum should be used?
    What is the best way of getting the "semi V" hull shape like wooldridge's?
    When it comes to the side panels or "gunnels" how does a fella go about getting the curved sides with the "upward curving" bow?
    Thank you
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Can't find any plans that suit ? Twin jet outboards will be expensive to run, all jet outboards are thirsty, what with the losses in the pump, but twins are always using more fuel than a single giving the same performance. So you have a double whammy there. You are probably best not to get involved with guessing or garnering info on hull design, if you can buy suitable plans, one problem you may have is needing a stout bottom, on a boat subject to hard knocks and scrapes, like a river jet boat, that might not be catered to in available boat plans. I also imagine that twin jets may have issues in getting continuous "clean" water into their intakes, so any projections on the bottom that might act to protect from grounding, could interfere with the inflow. Have you seen many twin jet outboard boats there ?
     
  3. TwinSled
    Joined: Sep 2018
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    TwinSled Junior Member

    Well, I can't say that I haven't found any plans per say, I haven't really looked into purchasing plans, I have a couple sketches and rough designs on paper for a Wooldridge style hull.

    When it comes to the twin outboards, I have seen two rigs ever, one when I was a very young lad, and the second setup, I actually had the opportunity to speak with the owner. He had a 15ft modified V jon boat style hull, with 2 30hp jets off the transom.

    He modified the hull himself by adding two jet tunnels (which almost forces "clean" water into the intakes, and lifts the jet foot up inside the hull a couple of inches) When I spoke to the gentleman, he explained to me that getting up on step with the twin 30hp jets was incredibly fast and he was able to have incredible control in the "skinny'' waters. He also stated that he was still able to get on step and have good control with just one of the outboards. He (like me) strongly believes in the "redundancy factor."

    I have always been a fan of redundancy, always having a backup. Especially when traveling 50 to 60 miles downstream from the launch. I have heard a number of horror stories about people getting stranded on the river. I do not want to be one of them.

    I figured, that on a 17 foot hull, twin 50s or twin 60s would be able to push the boat very efficiently, and in an emergency situation, still be able to maneuver with a single engine.

    Being that this is going to be a custom hull, I had already thought of a large in-hull fuel cell. Size to be determined.

    Another item brought to mind is the "skeg" type rails on the underside of the hull. I had an idea that welding 1x1 angle aluminum would be sufficient.
     
  4. TwinSled
    Joined: Sep 2018
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    TwinSled Junior Member

    When it comes to the expenses of twin outboards, I get it. I have been shut down, put out, and steam rolled by all the reasons not to run twins in the past, and all the downsides boil down to money, more money. Oh well!

    Ive just gotten fed up with the ridiculous price tags manufacturers slap on their products, and people who have a 19-somethin-or-another, beat to heck aluminum can for sale, and think that their boat is worth almost what they want for a new one.

    I would just like to build something that is tailor made to suit my every need is all. (Without having to sell my soul to the devil buying new or used)
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    I was just a bit concerned those skegs might cause flow problems into your jets, with a twin rig. You could just opt for heavy plate on the bottom, with close spaced internal framing, and have a "clean" bottom. I understand your desire for a back-up, 100 %, you don't want dramas that can be avoided. The thing about plate boats, without pressings or swaging, is weight, it can build up, and you will need heavy plate on the bottom to avoid dishing from bumping bottom obstacle.
     
  6. TwinSled
    Joined: Sep 2018
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    TwinSled Junior Member

    I wasn't sure which would be the way to go about the underside of the hull.

    If a fairly thick slick, flat bottom will be sufficient, then done and done. I read that modified jet tunnels would also act as a skeg and assist in turning.

    Yes, ever since I was a young lad, I was a firm believer in twin outboards, for the redundancy, and they look sharp.
     
  7. Mr Efficiency
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    Mr Efficiency Senior Member

    This is the boat ? Twins very wide apart, must be near flat bottom aft, or the intakes would be out of the water.
     
  8. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

  9. TwinSled
    Joined: Sep 2018
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    Location: Montana

    TwinSled Junior Member

    Something very similar to this Mr Efficiency. Very similar.
    Modifications include:
    Overall length shortened 2 feet
    Windshield and dash moved forward one foot
    Sidewall height increased 3 or 4 inches.
    And with the twin jets, they will be moved in closer to the center beam, and having two jet tunnels, the jet foot will be allowed to be raised up into the hull an inch or two (out of harms way) and the jet tunnels will force "clean" un-aggitated water into the jet intakes
     

  10. Barry
    Joined: Mar 2002
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    Barry Senior Member

    There is an inherent problem with a tunnel though it does help get the shoe up an inch or so.
    Assume the boat is running in a straight line, the transom is ventilated ie the water is coming off the bottom of the boat and if you look over the back you can see down to the bottom plate.
    The tunnel will be "full" of water.
    Then if you turn tight and left, the right side of the tunnel can become ventilated, ie the upstream leading edge and you can ventilate the pump, lose "grip" and control. The engine will over rev with the lack of load on the impellor until the boat slows down.

    If the shoe is below the bottom of the boat, without a tunnel this rarely happens.

    Of course slower turns will in most cases not cause this to happen.

    On the outboard jets that we built, we minimized this effect by welding on 1 1/2 inch strips to the shoe to increase the captured inlet area somewhat and it also provided a bit of a
    crash plate as these would bend and keep the shoe from cracking. Sorry, I looked and could not find any old pictures but perhaps it is something that can be found on the jet forums

    We also extended the tunnel back, then cut a partial circle into the top of the tunnel overhang to wrap slightly around the bottom of the pump. This reduced spray
    Again, sorry no pictures.

    The problem with the outboards jets is that when you go over a log or rock and the hull is lifted upwards, when you clear the rock at the transom, the boat drops and can hit directly on the shoe.
    Just some things to be aware of.

    If memory serves me right, our tunnels were about 24 inches long, from the transom to the leading edge, tapered up 1 1/2 to 2 inches. From the back of course it looks like an inverted channel.
    But the legs of the channel were at a 60 degree down angle from horizontal. The tunnel extension past the transom was a further 6 inches prox.

    On a narrow boat a tunnel will reduce some lift at the back and you might notice a nose high attitude as compared to say a regular outboard. With two tunnels, you will lose much more lift.
    The higher the nose, the deeper the transom, and you increase the draft somewhat. Going against the idea of a shallow running boat.

    I built a completely flat bottom 14 footer once and found that in rapids I would take some air into the pump and lose thrust. Additionally, the flat bottom was more prone to sliding
    on a tight turn. To reduce this, I welded on 4 2 per side 1 1/2 inch square tubing runners from the transom up maybe 2/3 rds of the length of the boat to give more directional
    stability. It worked quite well except for still taking in some air.

    A few years later, I did another, with a 6 degree V, gained better stability, used 1 inch solid runners for steering stability, and got rid of most of the air ingestion problems.

    If you do not really need the absolute minimum draft, I would not bother with tunnels, include some definite steering runners and use a 4 - 6 degree V
    Also, keep the beam as wide as you can at the chine. This is the easiest way to keep the boat higher in the water and carry some weight


    Thickness of the hull, 1/4 bottom, 1/8 inch sides. I would just look at the various manufacturers to see what they use. 1/4 seems like a lot for the bottom but if you go less, then you will need more stringers to strengthen the floor, which adds weight.
    Again, just look at boat that have been built from the major manufacturers as they often spec thicknesses etc.
     
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