Long Narrow Planing Hulls

Discussion in 'Boat Design' started by Randerso, Sep 8, 2006.

  1. Randerso
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    Randerso Junior Member

    Several years ago I had a friend who owned a 62 foot "commuter" built in 1926 in Detroit. She had a planing hull with an 8 foot beam. Originally she was powered with God's own heavy Sterling gas engines (one of which is now in the Smithsonian). When I knew her she had a pair of Chrysler 318s for power. At the time I had a very light, flat underbody 40 footer powered by a pair of 327 chevys. The 62 foot commuter could run rings around my "modern" 40 footer while looking absolutely wonderful in the process.

    Here is my questions - is anyone building long, narrow, fast yachts today? It seems that if the commuter could outrun my shorter boat with similar power, that this peformance atribute would also net better fuel efficiency - all else being equal. If this hull type is not being consider, why not?
     
  2. Gene Rosson
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    Gene Rosson New Member

    The long narrow boat has much to recommend it. One of the virtues is that on a pound per pound basis, it can be propelled with less power than short fat boats. Dave Gerr elaborates on this in one of his books; The Nature Of Boats. Phil Bolger has done several homely but effective boats that are long and narrow. Owners have reported outstanding performance with modest power.

    Among the reasons that the long narrow boat is not often seen is a matter of public perception. The ill informed boat buyer is attracted to what he considers cutting edge moderniity. That would be a futuristic looking fiberglass thing that is top heavy, grossly overpowered, overpriced, wide hulled, floating condominium wannabe. Some of them even have a spoiler or wing like appendages presumably to create downforce like a race car or maybe because it is sporty looking. Boat manufacturers build what the public will buy. The buying public would condemn the long efficient boat as an antique style that is obvious (to them) inferior. Another factor is dockage fee that is usually charged by the foot of boat length. Add to that the long boat cannot easily be spun around in its' own length when one chooses to show off. If the boat is to be trailerable, there is a limit to the practical length. Interior accomodation is spread out over the longer boat in such a way that it will be percieved as inconvenient.

    A pretty safe generality is that the skinny boat will be more comfortable to ride in a chop than a short fat one. I'll take one of the long ones myself because I have had experience with both types.
     
  3. tom28571
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    tom28571 Senior Member

    Yes, a long skinny boat has much to recommend it. So why don't you see more of them?

    It may be because, being so long, it can't be trailered easily or legally and slip rental is charged by length. My dock built 20 years ago cost less to build than a year's slip rental for a 40 footer locally.

    Maybe people that can afford a big slip have enough money not to worry about how efficient the boat is and want all the room that goes with a beamy boat.

    That's two reasons and there are probably others.
     
  4. FAST FRED
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    FAST FRED Senior Member

    Besides slip rental, and boatyard charges,the "modern" marine motorist frequently wants all the "comforts " of home.

    So 3 story monster boats with Oxygen Tents" on top give the "required" room , even in as little as 30-35 ft.

    These boats are fine weather cruisers with 15K frequently being too much weather to move the cottage from the slip.

    Merly unpluging the shore power is "heroic" for many.

    Many of the LSB are semi displacement and are just really EZ to push tp SQ rt LWL X 3 , rather than the usual 1.34 of fat boats due to smaller wavemaking.

    FAST FRED
     
  5. bbsboat
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    bbsboat Junior Member

    what Oxygen Tents is?
     
  6. marshmat
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    marshmat Senior Member

    Sad, but so true. I was amazed a few weeks ago, walking the docks wishing my boat was actually in the water, to find a 'yacht' of perhaps 40 feet LOA and a beam of close to sixteen feet, with the flybridge a good twenty feet off the water. The engines were likely around 400 horses a piece, and the hull, though glossy, flexed noticeably as people walked around and the boat banged its fenders against the dock. The glasswork was huge, and so thin and poorly mounted that I would have been afraid to take this boat out in anything over a Force 3. There's a surprising number of such floating condos here- beamy, tall, heavy, and with an AVS of perhaps sixty degrees. Sometimes I would swear the engines are more for ballast than propulsion as some of these things can't go over eight knots without sticking the bow 20 degrees in the air.
    Guess the boat-buying public doesn't always recognize just what they're buying.

    In my books, a fast boat ought to get its speed from efficient design. Long and thin is a great way to get speed without wasting much energy. I think a very big part of the problem is the way marinas assess their fees. Most are designed for short fat monohulls, and impose huge financial penalties on long slim monos or cats of any sort.

    I'm not sure what your regs are down in Florida; here, as long as boat and trailer together weigh less than 4.6 tonnes and aren't overwide, it's probably trailerable on a standard licence. Get a Class A licence and you can trailer almost anything at all up to, IIRC, around sixty feet or so if it's not overwide.

    As an example of just how much efficiency can be gained by long and slim over short and fat, look at the Dashew FPB 83. On twin 150 hp, the 40-tonne yacht can cross oceans at ten knots with ease. More 'conventional' fat hulls of the same displacement and accomodation, would require at least double the power to make that cruise speed, and would probably be a lot less comfortable in rough seas.
     
  7. skyl4rk
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    skyl4rk Junior Member

    Does anyone have an example of a long, narrow powerboat that would run fast with low power?
     
  8. Crag Cay
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    Crag Cay Senior Member

  9. Randerso
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    Randerso Junior Member

    If you go to (http://www.jclass.com/charter3.asp) and scroll down to PAM you will see the boat my friend used to own that started this thread. There are also may other similar vessels.
     
  10. Randerso
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    Randerso Junior Member

    OK - I just read the rest of information available on the PAM on the web site I posted. I notice that she was almost derilict in Ft. Lauderdale when the current owner found her. Bless his heart. When I knew her (1982) she was in Bristol Fashion. The friend that owned her then could do anything to perfection - from engine overhaul to varnish. I remember that the decks reminded me of a bowling alley. He was perpetually varnishing PAM. He would start at the bow - and by the time he got to the stearn the bow needed another coat. This is the main reason he sold her. Had he known she would be neglected later on - I suspect he would still own her.
     
  11. skyl4rk
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    skyl4rk Junior Member

    What would be a good bottom shape for this type of boat: moderate vee forward, tapering to a shallow vee aft with little to no rocker?
     
  12. FAST FRED
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    FAST FRED Senior Member

    "what Oxygen Tents is?"

    Those are also known as Flying Bridges ,
    they become Oxygen Tents when full inclosed with acres if plastic & canvass.

    Most of the older commuters were round bottomed , as there still semidisplacement hulls.

    They will have a long water contact at speed , usually at a low angle of attack.

    Pure plaining required the wide box boats , and a flatish after surface.

    Perhaps a higher top speed , but with a HUGE fuel bill.

    FAST FRED
     
  13. Randerso
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    Randerso Junior Member

    PAM has soft chines, a vertical stem and a large concave pad just forward of the transom to provide lift. At speed she ran pretty flat with her forefoot in the water. Just like Fred predicts. She really looked impressive at 30 knots with this running attitude and curling bow wave - just like a destroyer at flank speed.
     
  14. SamSam
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    SamSam Senior Member

    I'm not sure what you mean by fast, but this is sort of like your 'Whaleback'. Sam
    http://markvdesigns.tripod.com/boatbuilding/
     

  15. skyl4rk
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    skyl4rk Junior Member

    Dashew's pages on his unsailboat got me thinking (danger!). I wonder if a smaller version of his boat would work with low power, I am thinking one or two Bukh diesel saildrives (about 10 hp each). Or inboard diesels using small diesel engines, Yanmar or Beta single cylinders. Maybe 6 foot beam, 36 foot LOA. Purpose is to allow comfortable passages at 5 to 10 kts across Lake Michigan from the Michigan side to Chicago or Milwaukee (80 miles of open water, often rough), with modest but comfortable accomodations.

    I have been telling myself that Whaleback is the last boat I will build. But I seem to have the disease.
     
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