moving Pontoon boat outboard transom forward

Discussion in 'Boat Design' started by MRee, Jul 11, 2019.

  1. MRee
    Joined: Jul 2019
    Posts: 2
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    Location: Lake Champlain

    MRee New Member

    I have been mulling over 'one last' project in my early 70's. I have been a sailor and windsurfer since the 80's and a kayaker since the 90's and a kiter since 2001. I've owned and enjoyed sailing multiple sailboats over the years. My only power boats have been a couple dinghies and a 14' aluminum fishing boat.

    I could only find one previous post that touches on this subject... I would like a marine support vessel that has a clear stern deck 6 foot by 8 foot 6 inches wide and a swim platform pivot-mounted to the sterns of both pontoons (so it can be flipped up for transport and down for use). Having a clear aft deck means moving the outboard transom unit forward. I'm thinking about relocating it roughly 1/3 of the LOA distance back from the bow of the boat. Assumption: this will mean steering will be the opposite of a stern mounted motor (tiller pointed left to go left and right to go right). I realize that additional cross-members will need to be added to the forward deck area to match the existing support for the bolt-on transom unit. I'm looking at a 22-foot pontoon boat with 24" diameter pontoons. The boat would need enough power to cruise 12-15 mph and handle moderately rough wind/sea conditions, so I would hope to be able to use a mid-size motor around 40 h.p. (+/-).

    I have found someone willing to do the welding/fabrication needed to beef up the forward area where the transom frame will attach. I'm expecting trouble getting a boat business to sell and install a motor due to concerns about liability. I consider this a special use workboat where the owner assumes 100% responsibility from customization... but then I don't own a business.

    This subject seems to get strong reactions from individuals focused on the fact that 99.9% of Pontoon boats (all boats for that matter) have stern mounted motors. I appreciate and respect that reality, but it is not like this has never been tried... Mullet Skiffs are an example of forward mounted motors that function acceptably for the intended purpose.

    I'm looking for 'can-do' thinkers that are able to envision both complications and possible solutions and do not equate this project with "putting legs on snakes."

    Thanks for any input you might offer.
     
  2. KeithO
    Joined: Jul 2019
    Posts: 111
    Likes: 10, Points: 18
    Location: Michigan

    KeithO Senior Member

    Lots of fishing boats on the west coast of South Africa had outboard motors mounted in a well in the hull with the motor just behind the keel (fin type keel in a glass fiber sailboat style hull). I think the reason why they used outboard motors was because they were considerably cheaper than inboard motors of any description. The reason they were put in a well was because the motion closer to the middle of the boat was considerably reduced compared to the bow or stern. Thus less chance of burying the motor in a wave and drowning it or having the prop pulled out the water when the bow drops down into a trough. The west coast weather was notoriously bad, the water temperature was just a few degrees above freezing (due to an antarctic current) and the coastline was formidable rocky shores with very few safe harbors.

    For your application, the simplest solution would be to use a 3rd pontoon of reduced length, with the bows of all 3 pontoons being the same from forward., Then make a hole in the deck to facilitate access to the new motor location. Steering is going to be just like normal. The only difference would be that the stern of the vessel will not swing out in a wide arc when turning. If you had twin motors and mounted them to the front of the pontoons, it would be equivalent to a FWD car. But remember, the motor still has to point in the right direction, with the prop to the rear, so there is no point in trying to mount an outboard to the front of the pontoon. And the argument of reduced motion, especially vertical, for the center of the boat remains true. Its just not a convenient location for the factory when they are trying to cram as much as possible onto one of those things.

    One thing I am puzzled by: Pontoons are usually not very structurally strong. In a sea with waves more than a few feet high I dont think they would last very long at all since the entire raft section is generally held together with sheet metal screws and a few bolts ???
     
  3. ondarvr
    Joined: Dec 2005
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    Location: Monroe WA

    ondarvr Senior Member

    Not sure what advice you are looking for, if it fits your desires and needs just do it.

    Anything that needs a modification or adjustment can be handle after you see how it works.

    The maneuvering may be a bit odd at first, but you’ll get the hang of it.
     
    Last edited: Jul 12, 2019
  4. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Twin hulls generate a wake on both sides of the hulls. The interior side wakes can and do converge at some point aft of the bow. The convergence point is a function of boat speed . It is a matter of considerable concern when the hull wakes converge near the outboard leg. The result is miserably poor performance and sometimes a geyser of water shooting up into the air at or near the outboard.

    Before you decide where to put the new outboard location, do some experiments and observations to determine the least troublesome new location with regard to the speed that you usually use.. You could place the propulsion units far enough ahead of that wave train to be in front of the extreme turbulence area. If you do that then steering could become problematic or at least have you endure a learning curve.

    The problem with the converging wave train is not encountered with a monohull. Therefore the fact that mullet boats and others of the type can do this successfully does not apply to a multihull.
     
  5. Mr Efficiency
    Joined: Oct 2010
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    Location: Australia

    Mr Efficiency Senior Member

    Steering could be the problem, as the underwater profile of the boat changes under varying conditions, you may find you have no steerage, or even reversed. It isn't too hard to fit a fairing ahead of the motor leg to keep it protected. The handling is likely to be problematical, at least part of the time.
     
  6. MRee
    Joined: Jul 2019
    Posts: 2
    Likes: 0, Points: 1
    Location: Lake Champlain

    MRee New Member

    Thank you all for the prompt thoughtful and useful insights and things to consider. When I asked for more detailed projected cost for customizing the forward deck frame structure and relocating the transom unit, I realized that this project would be more costly than I expected. I also realized that while it will probably work for my intended function, the resale value after costly customizing might be 'even more' compromised for a pontoon boat (over a monohull). Plus, it was looking like local boat companies were reluctant to discuss an outboard motor sale involving a forward mounted outboard install. I haven't fully given up on the pontoon boat idea yet (mostly because I have a 22 x 8.5 clean pontoon boat in my 'Craigslist gunsight' but I'm also now looking at alternatives such as adapting boat plans from something like a Bateau FS-19 skiff (8' beam). I have not gotten far enough to learn whether boat plan companies have restrictions on the type and amount of 'customization' that can be applied to plans that you purchase. Adapting a forward outboard well and center-hull tunnel (aka... Mallet Skiff type design) might be another option, in which case I would lower the bar to 'good-enough' functional construction (used 40 hp tiller outboard) and revise the project as a grand experiment without resale objective (I've build a functional (53,000+ miles) light weight - extruded polystyrene core - fiberglass truck camper... so epoxy work is not something new).

    KeithO's idea of a shortened center pontoon seemed a bit less unconventional and would get the motor away from the stern but the deck well would likely end up encroaching on the clear 6' x 8.5' aft deck area that was/is a prime objective of the project. Again, thanks for the helpful information and for shedding light on likely problem areas.
     

  7. Mick007
    Joined: Sep 2019
    Posts: 1
    Likes: 0, Points: 1
    Location: Tulsa Ok

    Mick007 New Member

    I built a boat similar to what you're wanting about 10 years ago. I had the power lift motor structure welded to the middle of the boat in the box that was the center console with the captain's chair behind it. No steering was run to the motor just lift plate and power motor lift. I started with the cavitation plate set up to be level with the water at rest at mid travel of power Jack plate so I could lower it or raise it depending on whether the water was rough or I needed more speed on smooth water. And then the motor lift was retained to lift the motor into the console box for trailering. Steering was done through hydraulic linkage to rudder that was in the water at the rear of the boat. Worked well and was simple except when trying to dock at a snail's place. Recommending bow up to the dock and offloading a rope handler.
     
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