Need help with 23' pontoon boat design

Discussion in 'Boat Design' started by TobaccoFarmer91, Aug 24, 2011.

  1. TobaccoFarmer91
    Joined: Aug 2011
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    TobaccoFarmer91 New Member

    Hi guys, new to the forums, but not to boats! I've had this idea in my head for a while that I wanna build a pontoon boat, and I had a drew up a nice design a while ago, but looking at it now I think it needs revising. I want to build a 23' pontoon boat with a few special features:

    1-is its own trailer, has a set of wheels with air tight bearings and a trailer tongue up front that can be detached

    2-doubles as a light ferry, I want it to be able to carry a couple ATV's on the waterway

    3-has a ahrd top roof over the back half that can support a couple people

    4-has a fold up trampoline deck

    5-has roll up canvas sides so the back half becomes a cabin

    Here is my current design:

    I'm pretty sure that my buoyancy calculations are off. I figured that with 14 55ga. drums making up the pontoons, it would support ~6400lbs of weight, because each drum would displace 55 gallons of water, so 14 drums x 55 gallons x 8.33 lbs per gallon (8.556 for saltwater) = 6415, but that much weight would put the entire pontoon under water right? So realistically I should cut that figure in half if I want the waterline halfway up the drum right? And that made me think, this will be one heavy SOB, especially with 2 ATV's on it (~1500lbs), plus with the extra features (wheels, trailer tongue, top, trampoline deck) the boat itself will weigh a lot more than a regular 23' pontoon boat. Also the floor will have to be heavier to support cargo, so I though about adding a third pontoon. I can't decide how to do it though. I know most trimarans have the middle hull sticking out farther than the other 2, but this wouldn't work with my trailer tongue. Also I'm not sure about whether or not the middle pontoon would interfere with the outboard in any way? And another concern is the track width of the trailer wheels. Originally I was going to use an old tobacco trailer axle, which is kinda narrow and would put the wheels just inside the pontoons, but a third pontoon would mean I'd have to split the axle and just weld on a frame to support the spindles individually, and I think it would pull better with a wider track anyway, so I thought about removing a barrel so the wheel will be on the outer edge, like this:
    But then I though about how much the GVW will be with 2 atv's, so I figure a tandem wheel setup would be best (I could go with a single axle 8-lug setup, but the extra reinforcing would weigh alot, although not as much as 2 extra tires, wheels, hubs, and spindles I guess). Here's what I'm thinking now:

    My main concern is how should the middle pontoon be setup, shorter? longer? same length but moved forwards? I know it shouldn't be lower than the others cause that would cause it to wobble like a table with 1 short leg, but should it be higher or the same as the others? I though about making it higher so most of the weight would be on the outer pontoons, but it can't really be higher unless I mount the deck higher above the other 2. I also thought about having a smaller pontoon in the middle, like so short it wouldn't even touch the water unless the boat was loaded heavy, but then again that wouldn't support half as much weight as the others would.

    What do you guys think? Any help is greatly appreciated!
  2. Russ Kaiser
    Joined: Jul 2009
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    Location: Winston-Salem, NC

    Russ Kaiser Exuberant Amateur

    Tobacco Farmer,

    I can't help you at all but I wanted to let you know that I find your idea intriguing. The side deck idea is pretty ingenious, I don't know if that has been done before but it's an interesting concept. :idea:

    I assume that this will only be in the water for quick jaunts to barrier islands, is that correct? The first thing that comes to mind is that this will be so heavy it will probably need two axles and you will need a large deployable wheel off of the hitch to hold up the front when you go to jerk her out of the water. Also, you will have to winch her out and getting her mated to your towing vehicle is going to be a bear.

    Look, this thing is going to be a dog in the water anyway, so you may want to consider fabricating pontoons with a large or more square cross section to gain displacement. You probably have the barrels so that's why you're considering this. I have often gone down the road of making a project with what's on hand only being disappointed in how it turned out and kicking myself for not buying the right material up front.

    It might be easier to make your ferry a steel scow with the axels hanging in the water or rigging up some ingenious way to retract them into the hull.

    Anyway, good luck and keep us posted.
  3. Village_Idiot
    Joined: Oct 2007
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    Village_Idiot Senior Member

    I agree that you'd be much better off with a barge-style hull - much greater displacement at a lighter weight. Check out this link for ideas on a trailerable barge:
    1 person likes this.
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    BATAAN Senior Member

    Here's some ideas.

    Attached Files:

  5. Wavewacker
    Joined: Aug 2010
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    Wavewacker Senior Member

    LOL, you must have read one of my past posts somewhere about hauling my motorcycle on a boat that could be pulled by my motorcycle. I would not have my wheels down at all times, but guess you could. Are your plans to pull the boat/trailer on the highway or just pull out and going slow in a local area? Here, we need a trailer license and that needs to be made and inspected as a trailer frame and welded tounge (but I did get one passed with a removable tounge that slid in and pinned in place).

    There are trailer wheels with a torsion bar that bolts on to the side of the fram and does not need a full axel, that's what I was thinking of using.

    So far, the best set up seems to be using inflatable pontoons. I'd suggest you consider building simple barge style wood pontoons, butt joints and glass tape as they can be incorporated into the decking. Attaching round drums, which has been done here, are difficult to attached being strapped. There is alot of strain on those attachments with a moving barge, especially running aground.

    My idea was to build a light weight tubular trailer with retracable wheels, then cover it with a deck and attach pontoons that could be fitted as needed or that would swing up and down to be carried on the trailer. Depending on where the wheels were, if the pontoons swing down lower, the wheels could be afixed.

    I had a tendency to build heavy which is the wrong way to go. Since you want a trailer aspect, you need to build off the framing and keep it as light as possible and the pontoons sized for the displacement required.

    I may have missed it, but if you are simply using the barge to cross a 50' wide still water area, that would be one thing, crossing a river with any significant current under power will be another. The pros here will probably advise to build for the waters you intend to travel.

    Mounting your canvas tent and curtains would be pretty simple. :D
  6. philSweet
    Joined: May 2008
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    philSweet Senior Member

    What are the roading requirements? highway speed with 2 ATVS on board?
  7. Chase_B
    Joined: Aug 2011
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    Chase_B Junior Member

    I built a pontoon boat with retractable wheels and hitch, has over 5000 miles on the road as trailer mode,..1 deer test at 60 mph( which the suspension with stood with flying colors :) ) and many hours of some fantastic fishing,..and it weighs 300 lbs dry.
    all aluminum
  8. TobaccoFarmer91
    Joined: Aug 2011
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    TobaccoFarmer91 New Member

    I really like the pipe barge design, but I don"t think it will work with my wheels plan. I think I'm gonna stick with my triple pontoon design though, cause I've got tons of barrels laying around. I have a pretty good idea of how I'm going to connect them and how the frame will be built, and I plan on using the same deck plan as my first design, but I need to know if my current design will have problems. Will it be a problem for the middle pontoon to be shorter than the outer 2? or does it even to be shorter? I thought that it would have to be spaced forward so it wouldn't interfere with the motor.
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Make the pontoons all the same length and the same depth. Calculate your maximum full up weight, worst case situation, then double it as your 50% (immersed) floatation requirement. You'll not be very pleased with the preformance of a drum pontoon and it'll be heavy with huge corrosion issues too, but some have done it. In all honesty, you'll be better off just making some flat bottom pontoons. If using steel, it'll still be heavy, though likely not as much as a stack of drums, especially if the pontoons are sized and reinforced properly (you'll only need two as well). With the drum pontoons I've seen, all have had attachment and corrosion issues.
  10. philSweet
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    philSweet Senior Member

    My concern is that if this is roadable, it must all be IAW Nation Hwy Saftey Sds, which treats a vehicle differently than the cargo on a trailer. Will it pass inspection? Basically, it should be a vehicle that floats more than a boat that goes down the road. Hopefully, this is an irrelevant concern for you.
  11. viking north
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    viking north VINLAND

    Some where back in the history of popular mechanics there were a full set of plans for such a vehicle. The idea using drums isn't really a bad one. My dock float design is such a set up using 20gal. plastic drums strapped inside siding contractors cat walks.The cat walks are inverted and the drums fit snugly into them. I have made up fiberglass bow noses to slide on over the two front drums. I also have a central hatched floor opening over which is mounted a winch used as a mooring lift. It is driven by a small outboard and easily decoupled from the docks gangway, where it sets as a float 99% of the time. 55 gal ( Canada) plastic drums could also be use but you would have to make up a custom frame in place of the cat walks. The individual drums serve as individual watertight compartments and several can be used as fuel and fresh water tanks. If one was to become really inventive you could use the drum pontoon set up as a base for a male fiberglass mold by running longitudionals attached to 3/4 ply bulkheads between the drums-- wrap the whole assembly in say 1/8 ply and glass her over. Oops--i have to stop now --such is the mind of a mad scientist :) --

    A yacht is not defined by the vessel but by the care and love of her owner --
    Last edited: Aug 28, 2011
  12. Poida
    Joined: Apr 2006
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    Poida Senior Member

    Doubts have been raised about getting the pontoon trailer registered for the road.

    You may be able to buy an old registered trailer and add the pontoon to it, or make the trailer part and get it registered first.

    It would of course be desirable to get a boat trailer. Dunno about where you are, but here a boat can be considered, "part of the trailer" for fixing lights rego details etc.

    Once you have the licensed trailer you can basically stick what you like on it.

    Cops don't always know all of the regulations concerning trailers anyway.
  13. TobaccoFarmer91
    Joined: Aug 2011
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    TobaccoFarmer91 New Member

    I've built a few trailers before, and most of em I don't even bother to put tags on (benefits of being a farmer, in NC there are exemptions to almost every traffic law for farm equipment. Hell I've pulled tobacco trailers down the road with ATV's before.) I have had a couple inspected though, and I'm pretty sure if that rolling barge thing will pass mine will, It'll be a lot sturdier anyway. All they really look for in a homemade trailer is if it has the correct number of lights in the right place and if it's structurally sound. And I'll probably be required to have brakes for a tandem trailer this heavy. If I keep the pontoons the same length like PAR said, and take 2 barrels out of each side for the tandem wheels, I'll have 17 barrels, at 55 gallons each that's displacing 935 gallons, half of that's 467.5 gallons, times 8.33 lbs per gallon is 3894 lbs, so that's the max the boat and cargo can weigh. My 4 wheelers are 900lbs and 500lbs, so that's 1400lbs of ATV, plus 2-4 people (~600lbs) is 2000 lbs. So that means the boat itself can weigh 1800lbs. That may be a little lower than what I'm looking for, but I have built a trailer around this size (25') that only weighs 1000lbs, and it was steel channel frame and 5/8 OSB plywood decking. The only steel on this boat will be the drums and a piece of angle running the length of the pontoons to weld them to, and the reinforcing straps. The rest will be aluminum channel or angle. I'll do a structural drawing later once I've decided on the pontoons. That brings up another question, I can't decide on decking material. I won't want plywood and marine carpet because I wanna be able to leave it outside with no cover to worry about. I actually thought about thin marine plywood and linoleum with a hard wood look, but I've seen linoleum shrink in weather before. Then I thought about 1.5"x6" decking boards, because I've got a huge stack of them laying around, but I worry about my boat being as bad as the deck on my house in 5 years. Any suggestions?

    Funny story about how I came up with this idea, I actually jerry rigged a floating trailer one time. One year the river overflowed over the bridge, and cut off my buddy from 3 of his big fields (the next nearest bridge was 40miles away, a hell of a journey on a tractor). So we took a 20' steel trailer, chained 10 of those square 250gallon ISB tanks to it, loaded a small ford tractor on it pulled it to the edge of the river, backed it in, unhooked it and tied it off to a tree. Then we went and got my 19' rinker to pull it with, put it in at the nearest ramp, went to where we backed the trailer in and tied to it, pulled it a mile down the river and a quarter mile up a flooded field until we got to the waters edge, tied the boat off to a tree, jumped in the trailer and 4 of us rowed it as close to shore as we could get it. The chains that held the tanks on were a little slack, so the trailer bottom was about 2' under the waterline, but that don't matter to a tractor cause the wheels are tall. Then we just drove the tractor off, hooked up to the equipment that was already in the field and went to work, haha. At the end of the day we left the trailer tied to a tree and drove the boat home. When the water went down a few weeks later we drove the truck to the next bridge, drove to the field and the trailer was sitting there on its wheels , still tied to the tree. We just hooked it up, flipped the tanks inside it and drove off. I couldn't believe it worked, lol.

  14. Chase_B
    Joined: Aug 2011
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    Chase_B Junior Member

    I had no problem registering my pontoon boat with built in trailer ,..I took it right to the State where they inspected it and approved my registration as a boat with built in trailer,..I have only the boat registration numbers on the boat ,..not trailer tags needed.
    The difference is , in MO , pontoon is concidered like a wood splittler on wheels, do not need to register it to be towed on public roads,..because it is not carrying a cargo,..just itself,.. I'm sure each state has different rules concerning this,..
    I just moved out here from NC not far from camp lejuene and in NC I always see trailers going down the road without tags on them,..but then in NH ,..the trailer better have current tags on it you will be ticketed,..
    The best approach ,..I had called the state in advance and asked them how I would register my boat with built in trailer , I knew it would be registered as a boat only ,..prior to building it,..and I would be able to tow it on public roads legally once the boat was registered .
    What it boils down to , satify the state ,..they made their revenue off my boat by me registering it,..but I beat the system and added a built in trailer.., I am not mass producing this boat with built in trailer , it being home built ,..the legistics of it are very open,.. I do have tail lights for road use installed and clearance lights even though it is only 6'10" wide,..along with NAV lights for when the boat is on the water.
    I purposely built the boat exactly 12 foot long so that I did not have to meet any coast guard rules,..if I had made it longer ,..then I would have to follow both road and boat rules to the letter,..and hope the 2 different set of rules didn't null each other, a boat can be any width as long as it is in the water,..where as a trailer can be up to 102" wide before it needs a permit to be transported on road ways ,..and a 10 foot wide boat needs a permit to be transported over the road on a trailer as well ( keep in mind ,..the state in which your transporting the loads determines max width,..some will allow up to 12' wide without permit ,..but require flashing lights , flags attached to corners and a wide load sign strapped acrossed the stern )
    Do a little home work and check into the area/state for which you live or plan on using your boat with built in trailer , can save you allot of time,.. it paid off for me :)
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