My Dingy Is A Piece Of Crap- Help!

Discussion in 'Boat Design' started by ecflyer, Nov 16, 2009.

  1. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    I havebuilt a dingy out of 1/4" ply for my yacht and it's a piece of s**t. It's an 11' design w/ front 2' sliced off to yield a slightly squared looking bow. The keel is one continuouse curve from bow to stern somewhat like the football shilouette. Depth is 17" beam is 49" lenght 9'. This boat will not plane with a 4 hp. It plows thru the water at 1-2 mph and if I try to turn, green water spills over the corner of the transome. I could not put a larger motor on it as the stern would sink at the dock. This dingy was designed to sail or row. Is that where the problem lies? Are ocean rated dingy's designed differently w/rounded keel to better transite the surf? I hate this piece of crap and want to build a new dingy. I have been in factory alum boats 14' long that my 4 hp easily planned and achieved speeds of 12 mph and not this 1-2 mph my piece of crap is yeilding. By the way, my dingy plans were designed by a navel architect.

    Earl
     
  2. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    Go find a Grumman Aluninum Dink, either the rowing or sailing model.

    About 75 lbs , EZ to haul aboard ,not hassled by dragging up a rocky beach.

    Hard to find , but worth any amount of effort.

    FF
     
  3. sabahcat
    Joined: Dec 2008
    Posts: 792
    Likes: 28, Points: 0, Legacy Rep: 273
    Location: australia

    sabahcat Senior Member

    Why that one in particular?

    [​IMG]

    This is a 14 but is it really any different to any other tinnie?
     
  4. Manie B
    Joined: Sep 2006
    Posts: 2,041
    Likes: 117, Points: 63, Legacy Rep: 1818
    Location: Cape Town South Africa

    Manie B Senior Member

    please post pics

    if it was designed for sail it will never plane as conventionally with an outboard

    it doen't seem the designers fault - seems like wrong application
    lets see the pics first
     
  5. Manie B
    Joined: Sep 2006
    Posts: 2,041
    Likes: 117, Points: 63, Legacy Rep: 1818
    Location: Cape Town South Africa

    Manie B Senior Member

    = rocker

    not for planing
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 479, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yes, because the dinghy was intended to row or sail, it's screwed when it comes to powering past a few MPH. It'll just stick it's nose in the air and cuss at you.

    To get the boat to plane off, the whole aft end of the boat (on the bottom from midship back) needs to be a different shape. Generally if you straighten out the bottom panel from it's maximum depth at midship, leaving it straight and extending the sides down to meet the lower bottom panel, then yep, she'll plane off, but now it's screwed for rowing and sailing.

    Welcome to the world of yacht design, where nothing doesn't come at a cost. Yacht tenders are typically designed to be rowed and to carry a hefty load. This makes them "pigs" in most regards. They're really too fat to row well, too short to sail well and have the wrong rocker to power well. You can make them better to a degree, depending on how much length you can live with, but they will always be a boat trying to do too many jobs to be really good at much.

    In other words, if you want to plane off and scoot along at say 12 MPH (actually much faster if you want with your 4 HP), then you have to kiss off rowing and sailing performance. She'll scoot under power pretty good, but will row and sail like a, well, like a pig. You have to pick one. You can have a sort of hybrid (piggish) boat, but like I said, it'll sort of sail and row okay and power not bad (but not real good either). This type of hull requires more thought in design.

    You could also put a ventilation plate fin on the outboard (if you can find one small enough to fit the leg). This may offer enough area to keep the bow down and get you up to semi plane speeds (6 to 8 MPH). Another option would be to put a "whale tail" on it, which is an extension often seen on fishing boats to prevent them from squatting under excessive power. A wing, mounted below the boat is another possibility, again to offer enough area so the boat can settle down and plane on it.
     
    1 person likes this.
  7. alan white
    Joined: Mar 2007
    Posts: 3,731
    Likes: 121, Points: 0, Legacy Rep: 1404
    Location: maine

    alan white Senior Member

    In any case, unless you get an inflatable, a yacht tender should be built such that it won't damage the mother ship. Nothing worse than being tethered to a hard-nosed battering ram.
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 479, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Alan makes a good point. Tenders are not the easiest thing in the world to design. I've done a few and the difficulties are surprising for such a small piece of boat. Making the sheer match the deck crown for instance, so it can straddle the fore deck neatly. Placing the thwart low enough in the boat so when it's stowed over the hatch it does "center stand" on it. All sorts of little buggers that can drive a designer nuts, plus make it work as a boat too.
     
  9. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 170, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Cheeeezzzzz. At least Earl got a direct and to the point answer for a change. Usually someone after post no 413 comes up and says ok, now I get it, you mean to tell me... :eek:

    You won't win any races with a 4hp either.

    Get a duckie.
     

    Attached Files:

  10. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 479, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Water just sheds off it's . . .
     
  11. messabout
    Joined: Jan 2006
    Posts: 3,127
    Likes: 294, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    With a screen name like ECflyer, one would suppose that you may be a speed freak. Your dinghy is not likely to be a piece of s#*t! The boat that you describe is a pram type dink. It is great for rowing from the mooring to the dock, it will carry a substantial load, it will fetch your anchor to or from a place the big boat dare not go. It is a purpose designed piece of work. It was never intended to go fast. If you had done your homework you would not have met disappointment. If you are compelled to go fast, then you need a different type of boat. If you can find or build a three point hydro, then you can really go fast with the 4 HP motor. The hydro is not very well suited for hauling anchors however. It has long been discovered that the grand scheme of things prohibits us from having it both ways.
     
    1 person likes this.
  12. ecflyer
    Joined: Jan 2009
    Posts: 81
    Likes: 4, Points: 0, Legacy Rep: 72
    Location: Green Bay, Wisconsin

    ecflyer Junior Member

    Messabout!
    You are partially correct when you guessed w/name like E C Flyer that I like speed. My initials are E. C. and I am a commercial pilot so I do like 200-600 mph in the air. As far as my dingy is concerned, I'd just like to go a little faster than 1-2 mph. In fact, I'd be tickle'd pink if I could just barely plane, so yes, I will build a different dink with the aft keel flattened out as reccomended by some of the very helpful gents in this blog.
    Have a Great Day!
    Earl
     
  13. FAST FRED
    Joined: Oct 2002
    Posts: 4,519
    Likes: 110, Points: 63, Legacy Rep: 1009
    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    No the Grumman wont plane , but a tiny kicker does fine at 5 or 6K , the speed the condom dinks run in confused seas in a usually not sucessful attempt to stay dry.

    A huge advantage is the very easy to move hull form.

    Rowing is fast , but for folks with 1st mates that can't repair an outboard , the small electric trolling motor does just fine.

    A cruise can be ruined IF the 1st mate feels "TRAPPED ABOARD" , and a modest battery will provide many trips ashore with out effort.

    FF
     
  14. jimm
    Joined: Sep 2007
    Posts: 37
    Likes: 1, Points: 18, Legacy Rep: 23
    Location: us

    jimm designer MID

    I designed and manufactured 2 dinghy models,an 8' LOA x4' wide tunnel hull and a shortened version 6'9" LOA same width. The 8' will do 15k in flat water with 165 lb person driven by a 5hp. A 7hp would take it to 24Kor 10K with 2 adults. The shortened version 6'9" would do 4K with a 3.2hp or a 5hp. but no faster. I just posted the pictures. I built over 40 of these and the they sold about the same volume. The shorter version fit easily on the fore deck of most sail boats. Light weight was a key factor,90 lb for 8' and 75 lb for the 6'8".
     

    Attached Files:

    Last edited: Nov 20, 2009

  15. Chuck Losness
    Joined: Apr 2008
    Posts: 311
    Likes: 39, Points: 28, Legacy Rep: 135
    Location: Central CA

    Chuck Losness Senior Member

    I made a hard dinghy a couple of years ago from Sam Devlin's guppy design. The design is a rowing/sailing dinghy which I modified with Sam's blessing to power/rowing. No thought being given to sailing. The modification consisted of eliminating all shape in the back half of the boat and just letting the plywood hull panels run straight. I also contoured the sheerline to fit on the foredeck of my Gulfstar 37 and inset the transom to provide more room around the mast when stored on deck and to provide support for the outboard. Much like you see on an inflatable. Sam uses this transom design on some of his other dinghy designs.
    I could not be more pleased with my dinghy. It has exceeded all my expectations. It just jumps onto a plan with an 8hp nissan outboard. I tried a 9.9hp outboard and it was so fast it was scary. It also rows very well with no engine on the back. And it tows well too.
    LOA 9'10" Beam 4' All up weight is just over 100lbs. without the engine or fuel tank
     

    Attached Files:

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.