How much Horse Power do you think this needs?????

Discussion in 'Boat Design' started by Ravencry, Mar 29, 2009.

  1. Ravencry
    Joined: Mar 2009
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    Location: Iquitos

    Ravencry Junior Member

    wide and short.jpg
    Hey guys, This is my question. I need a boat that can hold around 5500LB and plane off. This is the design that I was thinking of. I would probably make it out of wood, seeing that I live in the Jungles of Peru and wood is cheap. My problem is that I would not want to buy a outboard and then not have enough Horse Power. That would be a waste of money. The weight would consist of: Motor, Gas, 12 people, luggage, roof, and the weight of the boat, which I approximate around 1700LB, this all equals out to around 5500LB. I don't need to fly, but I would want it to go over 20 MPH. I want enough Horse Power but not to much. I don't need to go over 35 MPH. Thanks for your help and your pearls of wisdom. Ravencry
     
  2. Willallison
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    Willallison Senior Member

    Lets leave the question of power and weight for a moment and look at your design. The 1st thing that strikes me is that you've shown a boat that has round chines throughout, which is less than ideal for the application that you're describing.
    Also the sections are all quite round up forward, so this boat would pound terribly in any chop.
    I would suggest that you'd be far better off buying a set of stock plans. There are any number available that would suit your needs.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Nothing personal Ravencry, but your efforts with FreeShip haven't produced a viable craft for your application. It has so many issues wrong with it, that I will not bother going into them. Considering your designing skill level, you should be strongly urged to take Will's advise and find a set of plans.
     
  4. Ravencry
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    Ravencry Junior Member

    I was going for a design that the Long tail boats from Asia have. This boat would be on river, so chop is not so much a problem. I have read that a flatter bottom would make planing easier, and since I am trying to go with as little HP as possible I wanted something that would plane more readily seeing that I it would be carrying so much weight. But if the design is faulty, I am man enough to take the criticism and go another route. Ravencry
     
  5. Willallison
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    Willallison Senior Member

    Attaboy .....
    Without putting too much thought into it, my 1st reaction would be to go for a flat bottomed punt. It would plane at the lowest speed, have the greatest load carrying capability and be by far the easiest to build. It might get a bit hairy at 20 knots, but if you could settle for 15 it would certainly be worth considering
     
  6. PAR
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    PAR Yacht Designer/Builder

    The punt shape or better a classic jon boat would be suitable, though it'll pound if driven too hard. It'll climb up quickly and with moderate power, if you keep it narrow.

    I'd be inclined to lean toward a Garvey shape if not a conventional pointy bow, for your needs.

    Considering you design skills, I'd still strongly recommend a set of plans. FreeShip and other low cost or free software packages will draw up a very efficient or inefficient shapes, depending on what you input. Unfortunately, it doesn't tell you the difference between the good ones and the bad, nor does it handle any of the structural requirements. This is where the design skills come to play. In other words, there's no substitute (or software) for understanding the concepts, principles and dynamics involved.
     
  7. tom28571
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    tom28571 Senior Member

    I agree with the others. This is not a good starting point. Best to throw it out and look elsewhere for plans. There are several sources for free plans for situations like yours. The UN has some plans for fishing boats that would be suitable. These can be constructed of plywood or planks.

    http://www.craftacraft.com/fao_fish...tom_boats_of_planked_and_plywood_construction

    Garveys are too wet for me. I'd prefer something that can turn a bit of water up forward. On a river, a flat bottom can work out just fine. What you have to do is force the bow down. It naturally wants to lift up and that is what causes most of its pounding tendencies. Below is a link to a boat that impresses me. It is flat bottom but regularly makes long runs in the Pacific off California. It's worth some serious study. If you blow up one of the photos and look carefully at the trim tab on the stern, you can see what lifts the stern and drives the bow down. I've had some discussions with Brad, the designer, and think he has found a reasonable solution that will also work well for you, although you need a larger size to carry the loads you want. I use similar technology as part of some of my designs. This system also makes for more stable behavior for varying loads and is less sensitive to fore and aft placement of loads.

    http://www.oceanskiffjournal.com/index.php/osj/1EMPS/610/P0/

    110hp should give you 20mph with this boat if it is built with a good flattish bottom. You don't want to run at wide open throttle, so 125 to 150 is more likely to work better if that big load is hauled a lot. At lighter loads, the 110 would be more reasonable in fuel use. I'd give it a pointed bow with some flare and upsweep and effective spray deflecting rails on the sides. A waterline length of 23' to 25' and waterline beam of 8' should be about right.
     
  8. daiquiri
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    daiquiri Engineering and Design

    I think you could find some inspiration (and understand better the appropriate hull form for your needs) at this page:
    http://www.working-boats.co.uk/
     
  9. lewisboats
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    lewisboats Obsessed Member

    My thought is....Panga or Panga like. Add a bit of a hook...say 3/4" to the aft 6 ft of the bottom to act as a trim tab to keep the nose down. Look at how a SkiffAmerica20 planes nice and flat...Adams has 3/4" hook and still gets about 25 mph out of a 25 hp. As far as engine size...You should have more engine than you really need...so you aren't constantly running it maxed out...it'll last much longer and give you much less trouble, plus you have some in reserve to counter a heavy current, heavy passengers etc.
     
  10. Ravencry
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    Ravencry Junior Member

    skiff.jpg
    This might be a better design.
    It will hold 2.6tons at a 13 inch draft. Its 29feet long and has around an 8foot beam. I am thinking of around a 115hp or 150hp outboard.
     
  11. tom28571
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    tom28571 Senior Member

    It will never make the speed you asked for with that load and power.
     
  12. Ravencry
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    Ravencry Junior Member

    What must I do!!!!!!! =(


    =)
     
  13. lewisboats
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    lewisboats Obsessed Member

    Here...something like this: 28.5 ft long, 2250 lbs cap, 7.71 ft beam 125-150 hp about 8" draft.
    Shallow vee, decent planning performance, shallow draft and good forward wave cutting with the forefoot. 1/2" ply x 2 for the bottom plus framing, 1/2" for the sides. Basically a Panga...used and abused for many a decade all over the Carib...can't go wrong. Use 8" 1x butt blocks at all joints, epoxy if you can get it, framing with chine logs (internal) and a bit of FG tape to seal the edges.

    Steve
     

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  14. tom28571
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    tom28571 Senior Member

    Lewis,

    I think the form is ok and well suited to what raven wants. Certainly easier to build than the one he shows. Don't think it can carry the loads he will have at the speeds he wants though. 12 passengers are likely to have baggage and other gear plus maybe a few animals to transport along the river. His earlier guess of total displacement at 5500# might be realistic and this hull probably won't support that while planing at 20kts. It needs more bottom which means more beam. Better input of real needs and conditions are needed to refine it. If these 12 people are tourists, You gotta figure that they may move about to look at stuff on one side or the other and that needs more beam for stability also.

    If the boat is going to need to load and offload on river banks, it would do well to have a pram style bow with a drop ramp. This design can have that without much change.
     

  15. Ravencry
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    Ravencry Junior Member

    2654948.jpg n525366949_1407893_277266.jpg First off, Thanks for the suggestions, this is helping me learn a lot and get a better Idea of what I can get away with. A basic trip would look like this: When a group comes in from the states I will try to keep the group below 8 people. Add a two or three translators and my self. I work with volunteers that come to help the Indigenous that live on the rivers. From Iquitos the closest group is the Yagua. Their closest village is around 50 miles down river on the Amazon. The farthest villages what we have people at are around 300 miles Away, one-way. My objective in travel is to get them there in a timely fashion. Most people in the US can not get off work for more that 10 or 12 days. That means One day of travel from the US, another to get to Iquitos and then another by river, and then back. Half your time is spent in travel and not helping the people. We are currently having to hire a boat and driver. This boat is a Fugimori, pictures above, This aluminum boat has a 60hp 2-stroke yamaha. With 11 people, luggage and 160gallons of gas we get a wopping, 15mph at full blast. The last trip was 18hrs long at 15mph avg. and was 280 miles long. We used over 135 gallons of gas. I have around $20,000 that was graciously donated to get a boat and motor, this will mostly go into the motor. I am just trying to be a good steward of that money. You guys are helping me do that, so I really appreciate it.
     
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