Pontoon - Workboat Conversion

Discussion in 'Boat Design' started by Pontoonworkboat, Mar 28, 2009.

  1. Pontoonworkboat
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    Pontoonworkboat Junior Member

    Hi Everyone,

    I am starting a small construction company that will service and install moorings on a remote lake.

    I recently purchased a 24' pontoon boat with a 2600lb weight capacity.

    I am trying to figure out the best way of installing a 1,000 block without damaging the frame of my boat. I have a coupe of thoughts but I'm not sure what would work the best, and what would be the safest method of doing this. Any input or experience you could share would be appreciated.

    My first thought was to take 3 8' long 4x4's and screw them down to a dolly on either end. Load the block on the middle of the 4x4 and that would dispense the weight over the pontoons. Run 2x4's the length of the deck on either side as a track to ensure the block would go straight off the front of the boat.

    Another idea was to mount a jib crane to the deck of the pontoon boat. This idea makes me nervous because I'm not really sure how I would support and secure the crane without ripping my deck up and destroying the frame.

    My other thought was I could put to gantry cranes mounted to the deck. Again they would be mounted over the pontoons. Mount one in the front, and one mid to rear near the the stern. Than mount an I-beam running from one to the other in the center of the two gantry cranes. Attached to the i-beam would be an electric winch to pick up the block and lower the block into the water. At the front of the boat I would have to build some sort of ramp to lower the block onto which would allow it to slide past the bow and into the water.

    Does anyone have any experience with moving heavy loads using a pontoon boat?

    Thanks in advance for any thoughts you guys may have!
     
  2. ThomD
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    ThomD Senior Member

    I think that anything that involves rolling it on and off, as in your first example, would be the lowest risk and lowest tech option. It's hard to know in detail what will or won't work without knowing what you boat looks like and what the docks at either end are like, in detail.

    After that, I like the gantry crane system where you have something that looks like a coat rack, and the I-beam allows one to use a sliding block that will move the load from one end to the other, allowing one to effectively weight, and then unweight either end.
     
  3. Pontoonworkboat
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    Pontoonworkboat Junior Member

    The track system was the way I was leaning as well. I will have to figure out a way to pull that 1000lb block off the bottom in case I had to take it back out of the water. Maybe setting up one gantry crane on the front with an electric winch and some sort of cable guide mounted to the bow pushing the winch's cable 3 or 4' past the bow, on hinges, so when the block got to that point it could come up past the bow without clipping it.

    In terms of the 1,000 block being loaded on the deck of the boat. Do you think a standard pontoon deck would be able to handle that type of load on its cross braces?

    (the boat is a 1988 princecraft, 24', max capacity is 2,600lbs. Sorry I couldn't find a picture)

    Do you think the dolly's positioned over the pontoons would be a safe way to transport and divide that type of load?

    I'm trying to keep my cost as low as possible with this business venture especially given the current state of the economy.
     
  4. peter radclyffe
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    peter radclyffe Senior Member

    WHAT IS A 1000 BLOCK
     
  5. Pontoonworkboat
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    Pontoonworkboat Junior Member

    1,000 block = mooring block.
     
  6. PAR
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    PAR Yacht Designer/Builder

    It sounds like you've got too small a boat to be snatching half ton mooring blocks off the bottom. It'll take a lot more then a 1,000 pounds of line pull to yank it clear of the bottom suction, second, the rig you'll be hoisting with will put huge point loading in just a few areas on your pontoon boat, likely breaking the deck bridging or pontoon attachments and lastly, by the time you do manage to get a block free you better hope it doesn't get you in "irons", which can happen fairly easily, at which point you'll have a half of ton of live load swing at the bottom of a long pendulum, which ain't no good for boat, gear or crew, trust me.

    In all honesty, I don't think you can rig your boat, power and crew it and stay within a comfortable safety margin. Look at it this way, 1,000 pounds worth of boat, engine, hoisting rig, gear and crew (this is way on the light side, but lets just say you can do it), 1,500 pounds of line pull trying to unstuck a block, where's you deck going to be? What's your safety margin? In other words you're maxed out and it's not even freed from the bottom yet. They it comes loose, all of a sudden like and the boat starts to roll from a passing wake or wind conditions, damn now you got a half a ton of block, dangling 40' or so below your boat attempting to march it all over the puddle you're on, of course testing the attachments of all your gear and boat in the process.

    I've pulled a fair share of blocks and they can bite you in the butt if you don't have a lot of boat and rig to manhandle them when they try to exert themselves or conditions are less then ideal for pulling blocks (it never is, that's why you're pulling them).
     
  7. Village_Idiot
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    Village_Idiot Senior Member

    If you are just moving blocks around with a pontoon boat, then that may be doable, but I would put an extra layer of plywood on the deck to help distribute the weight, and avoid the dollies as they would concentrate weight in specific areas. Twin gantry cranes should be used to take the majority of the weight off of the block while it is being transferred to the deck, but not necessarily all of the weight (whatever you are comfortable with the crane structure/pontoons supporting). Getting the weight laterally centered is critical, as is longitudinal positioning for correct running attitude, i.e. - weight centered just aft of midway. At that point, the weight must be fastened, because any movement of it while underway could spell disaster.

    If, as PAR suggests, you are snatching 1000-lb. weights from the bottom of a lake, then the pontoon boat is too small. You will need something on the order of a small barge (modular, perhaps, maybe 36' x 12' or 36' x 16') with an opening in the center of the deck to pull the weight through (with gantry cranes), then set the weight on the deck, again just aft of midships.
     
  8. Pontoonworkboat
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    Pontoonworkboat Junior Member

    I'm going to take your advice guys and forget about the removing of blocks for now. I can offer that service after I have built up my business enough to justify the cost of a barge.

    Structurally speaking, you guys believe a pontoon boat can handle a half ton mooring block on its deck if it has been reinforced?

    Village idiot, I was thinking of having the two dollies positioned over the pontoons on either side of the boat, 8 wheels per dolly. I was going to screw 3 - 8' 4x4's to the dollies on either end. Load the block in the center of the dollies.

    Do you think having the 500 pounds on a dolly with 8 wheels over the pontoons would be too much?

    *One important question about installing moorings for someone who has done this. If I just drop a mooring block into the water, would the concrete block break apart when it hits the sand, or are they pretty durable? My thoughts were after I dropped it in I would be able to reposition it into place with lift bags.

    Thank you for all the responses.

    -Mike
     
  9. PAR
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    PAR Yacht Designer/Builder

    No it usually will not break the blocks, but you shouldn't do this. As it falls to the bottom it can easily twist up it's pendant(s) with no guarantee it's going to land where you want it or facing right side up. Moving them around is a pain in the butt and not necessary. Hover over where you want it, lower it down and don't just cut it loose. The flogging pendant, flailing around on deck as the block rockets to the bottom, should be enough to keep you honest about the work involved.

    I wouldn't feel comfortable with a half ton block on that size pontoon boat. Yep, it would likely hold it, but damn, let it get sideways on you during the hoist and now you've got most of the weight on one pontoon and things will get wet shortly, probably suddenly there after.
     
  10. Village_Idiot
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    Village_Idiot Senior Member

    Well, I'm no engineer, but when you're talking that kind of weight on that kind of boat, you want it spread out as much as possible. With extra decking and heavy rails to distribute the weight, the dollies may be do-able. Look at the surface area of the dolly wheels and try to determine the psi that they will be putting on the deck. Remember that old idiom about a woman's high-heel shoe putting more pressure on pavement than an eighteen-wheeler's tire patch?

    What size are these pontoons, anyway? 25 inches? 27 inches?

    Once you have the weight loaded, you don't want to move it again until you are beached. Just reading between the lines, sounds like you might try dropping the weight off the boat into the water? - I would NOT do that with a pontoon boat, it'll likely capsize, or get someone hurt at the very least. Again, you need the hatch in the center of the boat (barge) to do heavy lifting in and out of the water at this scale.
     
  11. Typhoon
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    Typhoon Senior Member

    Guy I used to know had a 30ft catamaran party boat style of thing, converted to a flat deck. It was about 12ft wide at the gunwhales and I am guessing the hulls were around 28-32" wide. He used to do moorings with it, had a large slipway winch at the rear of teh boat and a massive bow roller on the front crossmember between the hulls.
    I was on board one day when we salvaged a 30ft Scarab in 20m of water, was a dead lift on the slipway winch. The boat handled the weight no problems.
    It was powered by two 45hp Honda four strokes and would do 14kts all day, any load. Was a fantastic platform, low freeboard, stable, only issue was sensitivity to fore and aft loading.
    Anyway, when doing mooring work, he could pull all the gear up, leaving teh block hanging off the bow roller for inspection, and because the winch was at the rear of the boat, all the heavy tackle would come aboard for inspection/repairs and be easily accesible on a nice wide deck
    As for mooring blocks, they should contain steel reinforcement to spread the laoad from the ground tackle, the ones I have seen made had a steel lattice in them (just rebar and concrete mesh). Used to cast them up in a box trailer with a plastic liner dropped into it first.
    The blocks of choice for smaller boats over here are train wheels.

    Regards, Andrew.
     
  12. Pontoonworkboat
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    Pontoonworkboat Junior Member

    Thank you everyone for the replies!

    I agree with PAR and VI about it being dangerous to be attempting to move this kind of weight with this boat. (that's why I'm posing these question to you guys.)

    My original plan was to build a track that the dollies would run on, and they would run straight off the boat. While under way the block and dollies would be secured and not moving. I was going to fabricate a 45 degree angle ramp on the bow to help the blocks into the water and hopefully prevent them from flipping over. To overcome the issue of it landing top side down, I was planning on attaching a 10' chain to the block so I could just attach my lift bag to it, re position the block right side up and where I wanted to put it. Attach the mooring chain and be done.

    It sounds like from your experiences if I let the block come off the front of the boat straight I still run a chance of capsizing the vessel which is the last thing I want to do. I was concerned with the bow being pushed down by the block and bobbing up hard when the block came off the boat, I wasn't originally concerned with the boat flipping though.

    Would my setup work for a smaller swim raft mooring? I assume 250 pounds would not be a problem because that would be similar to myself jumping off the bow. A 500 pound block might be a little more dangerous but do you guys think that would be a safe amount of weight to drop in the fashion I described above.

    I was really trying to avoid incurring extra cost of starting up this business. The mooring services was really just an additional service and not my main focus so I can drop it (no pun intended.)

    I also did come up with a means of testing out the way the boat handles the weight without loading a block. I have a lot of 40 gallon trash barrels, I was going to put them on the dolly setup I'm building and see how the boat handles with the weight, what happens when I move it. This way if the boat starts to tip the barrels will simply empty and my boat will stay right side up. Any thoughts on that plan?

    As a back up / kicker engine do you guys think a 2005 Johnson 3.5 hp would move this 24' boat? Should I be looking for a larger engine? This is going to be used only in the event of an engine failure to get the boat back to the marina to avoid paying the $250-300 tow charge. The engine will cost 350-450. I'm just not sure if the 3.5 could even move a boat this size. The engine weighs about 30 pounds so I was also looking at it in terms of something light that I could build a custom bracket for the back of the boat that wouldn't add to much weight.

    Thanks again guys

    -PW
     
  13. Typhoon
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    Typhoon Senior Member

    The boat I referred to in my previous post would carry the blocks hooked up to the winch and just slung between the hulls up against the bridgedeck. No problems at all transporting that way. The bow roller was around 4ft from teh very tip of the bows. The large winch and engines at teh rear of teh boat more than counterbalanced the weight.
    There was never any question as to the boat's stability with such a load. The key was the slipway winch, which allowed smooth and controlled movement of the weight of the block up and down.
    I'd suggest carrying your loads this way, forget cranes and hoists on such a small boat. For all teh initial outlay of your gear ent, the large winch option looks very good. All you ened is something that'll store teh length of rop equivalent to the depth of water you'll be working in. You just snatch the mooring you are lifting, wihcn up say 12ft, belay to deck, snatch fuurther along mooring line etc. To release just do the opposite, or wind your mooring tackle onto teh drum beforehand, attach block to your mooring tackle in shallow water (wading depth) winch up for transport and release smoothly when you are in position.

    Regards, Andrew.
     
  14. Village_Idiot
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    Village_Idiot Senior Member

    Well, if you do everything very carefully, I don't think you would have a problem. It's just that, with that kind of weight, you can't afford to be sloppy. One wrong move, one weak tie-down or broken cleat, etc. and someone could get seriously hurt. I doubt you would capsize the boat - just think of it as four big 250-lb. guys jumping off the front of the boat all at once - if their weight is exactly centered, shouldn't affect boat much other than some longitudinal rocking. If the weight is off-center, then you'll get rocking in all four directions.

    Larger pontoons would increase your safety factor. 27-inchers would be way better than 24-inchers. By the same token, the pontoons should be U-shaped rather than cylindrical for this application. The problem with cylindrical is that once they are halfway submerged, their rate of buoyancy decreases, which can lead to unpredictability and be very unnerving for the captain.

    Again, as long as you take utmost care, it should be do-able. Make sure the weight is just aft of midships while underway, and don't move the weight until boat is NOT underway. I also wouldn't attempt such a task if there was a chance of decent waves in the vicinity.
     

  15. weelilboats
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    weelilboats New Member

    why put the mooring blocks on the boat at all just make a simple pontoon raft out of steel pipe or barrels much safer to use an unmanned platform to do that kind of thing you could load it and the mooring block onto a flat trailer and launch it at a boat ramp then tow it to where u want it placed
     
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