small boat opinions

Discussion in 'Boat Design' started by JLIMA, Oct 22, 2009.

  1. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    Before I say anything about your latest sketch, would you offer some rationale for the bottom hull form? Did you just lay down some lines on the CAD or is there some operational logic behind the form?
     
  2. JLIMA
    Joined: Oct 2009
    Posts: 123
    Likes: 4, Points: 0, Legacy Rep: 130
    Location: New Bedford Ma.

    JLIMA crazed throttleman

    Tom about the hull form, my logic was to keep the hull shallow aft so as i can use my short shaft outboard, I kept the bow a good deal on the fine side because the bay can toss a steep chop and i was trying to smooth the ride, not to mention I kinda have a thing for the lines of the old time Maine lobster boats. The added ease of planking in ply wood dictated that she be a chined hull. I use a mooring and have a bum leg which makes boarding a higher sided vessel painful from a small dingy (I'm too cheap to pay for a slip). I'm not in a hurry to go anywhere so low planing speed or even high displacement is fine for me, as long as I have room to put all my crap and I do carry a lot of crap. The last 2 influences were ease of build and the space i have to build in. Just wondering if there was a reason you asked (like you thought there could be an issue with the design) or are you just curious to my thought process? Either way it's a good question.
     
  3. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    I can get no idea what is goin on from that picture , how about a screen shot of the lines plan , or just all fews in freeships
     
  4. JLIMA
    Joined: Oct 2009
    Posts: 123
    Likes: 4, Points: 0, Legacy Rep: 130
    Location: New Bedford Ma.

    JLIMA crazed throttleman

    That is just an idea sketch i haven't finished the lines plan for it yet but as soon asIi'm done they'll be up.
     
  5. JLIMA
    Joined: Oct 2009
    Posts: 123
    Likes: 4, Points: 0, Legacy Rep: 130
    Location: New Bedford Ma.

    JLIMA crazed throttleman

    So here's the basic lines plan for her not a complete idea yet just something I was considering for a while figured i might as well post it too, and as of right now not the idea i want to go with although it was suggested i might try to do a flat bottom I would be concerned with pounding so thats not an idea I'm entertaining at the moment. But i haven't made up my mind as to what idea to go with.
     

    Attached Files:

  6. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    Ok, here are a couple thoughts about the latest sketch. A fine bow and a wide flat stern can be a problem and can even be quite dangerous. It is a receipt for boaching when running downwind in waves. The boat surfs into the back of the wave ahead and digs in. The following wave (if even slightly off angle) will want to slew the stern sideways and because there is nothing to stop it, the result can be a broach or even capsize. This is probably the cause of most serious operational mishaps in powerboats. Lobster boats have huge keel/skegs in an attempt to prevent this and are not all that fine forward anyway.

    When quartering into waves upwind, the fine bow will enter a wave, which wants to push the bow aside. With no hull appendages to resist this, the result is a sharp lurch sideways. It's all too common and I owned a boat like this before learning that it was a terrible design. It was actually necessary to hold on tight to avoid being thrown sideways in these conditions.

    You need more buoyancy forward and more directional stability aft. It's a compromise, but you need to know what the results are of compromising in either direction.
     
  7. apex1

    apex1 Guest

    Is this going to be a "how to become a NA in a few hours" ? If so, may I subsrcibe also?
    And is it possible to step in at the next level? Cos I know already how to play with Freeship.
     
  8. DBM
    Joined: Oct 2009
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Potomac River, VA

    DBM Junior Member

    Your design is starting to resemble a 50's era ChrisCraft Sportsman with a mild v in the bottom - which is not a bad design.
     

    Attached Files:

  9. Easy Rider
    Joined: Oct 2009
    Posts: 920
    Likes: 46, Points: 0, Legacy Rep: 732
    Location: NW Washington State USA

    Easy Rider Senior Member

    JLIMA,

    I really like Tom's comments and I'd like him to critique a design of my own but I don't know how to present it here. I'll learn and present it later.
    About yours I;d like to add a point. Your boat's a planing hull and planing hulls ride on their bottoms amidships or slightly forward and at that point your bottom is taking the seas and where it's quite flat and the forefoot is out of the water doing no good at all. I thing we can all learn a great deal talking and studying other people's designs. I offer "atkinboatplans.com" as an excellent place to study.

    Easy Rider
     
  10. tom28571
    Joined: Dec 2001
    Posts: 2,474
    Likes: 116, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    You're way ahead of me. I don't know how to run any computer design programs.
     
  11. apex1

    apex1 Guest

  12. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

    There was an article in an edition of Woodenboat that was about three people who designed boats by eye .Very impressive .
     
  13. JLIMA
    Joined: Oct 2009
    Posts: 123
    Likes: 4, Points: 0, Legacy Rep: 130
    Location: New Bedford Ma.

    JLIMA crazed throttleman

    I had some one pm me saying i should consider a flat bottom and they recommended a sort of a dory with a widened transom. I have concerns that with the chop that usually develops it will pound excessively. Is there a way around excessive pounding or would it just be more prudent to just finish tweaking the idea i have already?
     
  14. Oftengoofenoff
    Joined: Oct 2009
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Silverdale Wa.

    Oftengoofenoff Junior Member

    abds
    l
     

    Attached Files:


  15. Easy Rider
    Joined: Oct 2009
    Posts: 920
    Likes: 46, Points: 0, Legacy Rep: 732
    Location: NW Washington State USA

    Easy Rider Senior Member

    JLIMA,

    More deadrise, longer and narrower, soft chines, weight, flatter running attitude, extremely narrow multihull and longer WLL will help. Running a V bottomed boat into head seas at 20 to 30 degrees may present a relatively flat part of the bottom to the seas causing pounding that may be less w a flat bottom. Sound seems to amplify the effects of pounding and could intensify the experience so a quiet running boat may seem to pound less. When I designed a boat to address this issue I chose to use deadrise to solve the problem and I sorta went multihull to do it. The entire bottom of the "Easy Rider" had a deadrise of 45 degrees. Ray Hunt used deadrise to solve the same problem and countless other boat designers since. One may even use suspended seats like trucks to lessen the effects. I know of no solutions that don't offer significant penalties that offer significant benefits to the problem of pounding.

    Easy Rider
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.