High Speed Narrowboat

Discussion in 'Boat Design' started by Nick Ireland, May 21, 2003.

  1. messabout
    Joined: Jan 2006
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    Location: Lakeland Fl USA

    messabout Senior Member

    Jimburden: Am I reading this correctly? You say that inflated hoses inside the tubes would increase the flotation????.

    My arithmetic has each 16 inch tube, if fully submerged, displacing 5200 pounds of fresh water. Less than that if the ends are conical. If the tubes weigh 1300/2 = 650 then the positive buoyancy will be about 4600 each. Please help me understand how we'd have 6000 positive per tube. That's not all. It is a convention to have pontoon boats with round flotation members submerged at less than half the diameter.

  2. jimburden
    Joined: Oct 2015
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    Location: Lincoln NE

    jimburden Junior Member

    The .190' wall 16 inch PVC pipes weight 280 pounds per forty foot section. The thiner walls are resiliant. I have never tried to crush one to see what the breaking limit is. PVC pipe walls up to about 7/16 inch thick are available in 16 inch to over 24 inches. You can Get the size charts from Kroy and Diamond Plastics The foam weights about 2 pounds per cubic foot to about three times that for about three times the strength at about 60 PSI compression at yield and under 1% water absorption. The foam backs up the plastic but both yield to many hard object impacts instead of resisting solidly then breaking. A rubber raft is an inflated tube. Lay flat industrial discharge hose is like tough rubber raft tubes hundreds of feet long if you want. In a SWATH hull you could change the buoyancy by using a blower to suck air out the lay flat tube goes flat, blow air in the tube can be up to about 16 additional inches down to about an inch in diameter. For as long as I am aware most fire hose and some garden hose has been available in smaller diameter lay flat hoses under about 6 inches. For inflated masts some Kevlar lay flat fire hose is available in burst strengths up to about 1,100 PSI and inflated to 250 PSI might make impact resistant spars These tubes in the higher 250 PSI pressure range and 16 inches in diameter with a, if I remember right a 3/8 th inch wall thickness can make full length hull bumpers.

    An aside is the idea for regular lock and concrete pier using boats is to install wheels on the barge corners so control in tight situations does not require throwing fender tubes over the side. The boat could roll endlessly along walls instead of scraping. I've never seen this done but suspect some canal boats have tried this also to avoid bank suction problems in very narrow straight walled channels. Just some ideas or possibilities.
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