thoughts on a 16ft offshore yacht concept

Discussion in 'Boat Design' started by misteringer, Aug 15, 2014.

  1. misteringer
    Joined: Aug 2014
    Posts: 6
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Auckland

    misteringer Junior Member

    I have noticed that most offshore capable yachts are heavy, slow classic looking yachts (take the flicka 20 for example) why aren't there any light or medium displacement boats with planing hulls under 20ft out there crossing oceans? I recently came up with the idea of a sort of shrunk down mini 6.50. I am thinking about a boat that would be easy for people to build at home, have a medium displacement (to make sure it doesn't fall apart around you), yet still have racing potential. I haven't drawn up any sketches or plans, but I will try to explain everything the best I can.
    Approximate specifications:
    LOA - 4.8M
    LWL - 4.5M
    beam: 2.5m
    Draft: around 1.8-2m (personally I would like to have a deep keel to help make up for the short length) I would like to think that the boat could be trailered, with a lifting bulb keel that would be bolted down once the boat is in the water. The interior would be relatively small so its occupants don't get thrown around too much. also, there wouldn't be windows, instead just small hatches so if the boat is rolled it would be as watertight as possible, and there would still be some forum of ventilation. I know I didn't give much information but this is currently just an idea in my head and would like to know what everyone else thinks about it. All responses are appreciated.
     
  2. gonzo
    Joined: Aug 2002
    Posts: 13,732
    Likes: 419, Points: 93, Legacy Rep: 2031
    Location: Milwaukee, WI

    gonzo Senior Member

    Since you are talking of occupants, in plural, make the calculations of the weight of them plus supplies. Then figure how a boat that size can carry that weight at the very low speed it can reach. The boat won't plane with the heavy load you propose, so it will go very slow.
     
  3. tom28571
    Joined: Dec 2001
    Posts: 2,471
    Likes: 113, Points: 63, Legacy Rep: 1728
    Location: Oriental, NC

    tom28571 Senior Member

    Yes, that's one major reason.
     
  4. DCockey
    Joined: Oct 2009
    Posts: 4,415
    Likes: 214, Points: 63, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Try sketching your idea on graph paper.
     
  5. bregalad
    Joined: Dec 2010
    Posts: 110
    Likes: 5, Points: 18, Legacy Rep: 36
    Location: Georgia

    bregalad Senior Member

    There are/have been some.
    Webb Chiles is halfway across the Pacific in his Moore 24. Not quite as small as you are suggesting, but at 2000 lbs. every bit a light disp. flyer.
    In the modern era the first was Sopranino. Sailed across the Atlantic in the 50's. Less than 20' long, less than 6' beam and very lightly built.
    Most people want more room and greater carrying capacity. Those requirements quickly make a short boat heavy.
     
  6. frank smith
    Joined: Oct 2009
    Posts: 980
    Likes: 14, Points: 28, Legacy Rep: 185
    Location: usa

    frank smith Senior Member

  7. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 472, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    The basic problem with small passage makers is simply volume. You have to have enough stores to get you there, alive, well equipped, well fed, well hydrated, with a margin of safety, in case you get becalmed or have an issue. This requires a fair bit of capacity, which in a small platform just makes for a fat boat.

    Lets assume you want to travel across the Atlantic, 3,000 miles, with a crew of two, on a boat with a 18' LWL. Sailing or motoring at 1.35 S/L ratio (displacement speed) the full way, you're doing 6.5 MPH, so a bit more then 19 days in route. Now how much food will you need, where will you store it, ditto water (about 320 pounds for two, plus it's containers). What equipment, what in terms of reserves will you carry. How about fuel to cook with, stay warm, maybe even motor along.

    Designing any boat is about having the volume to handle the capacities you'll require, for the worst case or at least the expected passages, the design is intended to make.

    As to planing across the ocean. Have you ever done this? Sure it's fun for a while, but after just a few hours, you've taken a beating and you need to return to a more sedate state. Lets assume you have a sailboat capable of full plane speeds, near 20 MPH. Lets also assume you can maintain this speed the whole way across (you can't, but lets try). This is approaching world record time at 150 hours (6.25 days) and you'll be so whipped from the pounding, it'll take a few days for you to stand upright after the trip.

    I have a design (Discrete) that is a real off shore capable yacht (http://paryachts.blogspot.com/p/sail.html at the bottom of the page) and she's 18' on deck. She's a bit heavy for an 18' boat at 1.1 tons, but she's intended for off shore work, so can carry the stores necessary and have a motion that is tolerable in heavy seas, on a small craft. A light 18' boat would be in 1,200 pound range, while average would be in the 1,700 - 1,800 pound range. So, comparatively, my Discrete is considerably lighter than a 2.4 ton Flicka. Small boats are disadvantaged in this regard, with Flicka being over 400 D/L. Discrete is in the mid 300 range, but this isn't as telling as you might think, because small craft proportionately have higher D/L's than larger.

    Lastly, small craft in big seas can get the crap kicked out of them in short order, so they have to be tough. Anyone considering deep blue water in a small boat should do this simple test. Buy an 8' inflatable dinghy from Wal-Mart, blow it up and toss it in the nearest ocean surf. Climb aboard and paddle out to the breakers and see how well you do. You'll quickly find the motion is intolerable, usually in just a few minutes. Now picture yourself in a small boat, with seas bigger than the length of your boat, much farther from shore than you can swim back to. The motion in a small, light boat can overwhelm you in minutes. This is why (well one reason anyway) Flicka and other craft like her are hefty, for their length.
     
  8. keysdisease
    Joined: Mar 2006
    Posts: 794
    Likes: 43, Points: 28, Legacy Rep: 324
    Location: South Florida USA

    keysdisease Senior Member

    I don't think anyone can help you meet these expectations within your size constraints

    :cool:
     
  9. SukiSolo
    Joined: Dec 2012
    Posts: 1,270
    Likes: 25, Points: 0, Legacy Rep: 271
    Location: Hampshire UK

    SukiSolo Senior Member

    Agree with above posts. I don't think I'd like to take anything much smaller than a Farr 727 (24') or similar out in deep blue water. The reasons above, especially well highlighted by PAR outline why.

    The link below gives some good UK designed home build boats, for offshore, close to your requirements, but not strictly blue water.

    http://www.bluelightning.co.uk/
     
  10. Tad
    Joined: Mar 2002
    Posts: 2,302
    Likes: 182, Points: 73, Legacy Rep: 2281
    Location: Flattop Islands

    Tad Boat Designer


  11. jehardiman
    Joined: Aug 2004
    Posts: 2,489
    Likes: 202, Points: 63, Legacy Rep: 2040
    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    You need to do a study of the Midget Ocean Racing Association (MORA) boats from the San Francisco Bay Area. Many more boats than you think out there and the smallest of them are ~21-24 ft (6.5-7.5m) for very good reasons. I assume you have read John Guzzwell's "Trekka Round the World"? It is a pretty good example about the difference between "minimalist crusing" and a foolhardy stunt that some of the "micro crusiers" have attempted. That said, with proper prudent seamanship, almost any size vessel is "offshore capable"...look what Bligh did...but unless you are a masochist or racing it gets old in a hurry.

    As PAR notes, offshore, very few small boats are able to maintain planing speeds just because of the physics of the wind close to the sea. Blanketing and back clumbing, give way to crest instability knockdown and wild surfing which, enjoyable for an afternoon, but dangeriously tiring after a day or two. And well offshore, there is only a small window in the wind/seaway interaction that supports wind of the proper speed with the necessary seaway.

    In short handed crusing the maxim is reef early and often, while sailing a small boat fast offshore is very tiring and you need to be able to trim and switch the sails constantly which is why ocean racers, even the 21-24 footers have lots of crew, usually 6 or so. Additionally, if you look at most offshore races or crusing flotillas, they pick the track and season to minimize upwind work and seaway.

    IMO, when all is said and done, I think the minimum size for an offshore cruiser is 26-30 feet, and the dream boat on my board over the years has grown to 40 ft.
     
    Last edited: Aug 15, 2014
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.