27' 60/40 motorsailer

Discussion in 'Boat Design' started by DavidBoat, Dec 26, 2009.

  1. DavidBoat
    Joined: Aug 2009
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    Location: Huntersville NC

    DavidBoat Junior Member

    I am designing a 27' motorsailer that would be a 60% motor/ 40% sailer.
    Based on a Thoosa type electric propulsion with a sailing arrangment for fun, recharge of batteries and emrgency get home propulsion.
    I hoping to acheive a +10 knot semiplaning hull form that can provide decent sailing capability.
    I'm obviously not talking about sailing close to the wind and all sacrifices would be on the sailing end.
    A low gaff rigged sail configuration is what I'm thinking....

    The main problems are hull form and capability to carry sail with minimal displacement.

    This seems to be an age old design problem that has to have at least been close to being solved by much smarter and more experienced people than myself.

    Can you design a semiplaning hull form capable of actually carrying sail with some efficiency?

    Wanting it all much?
  2. DavidBoat
    Joined: Aug 2009
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    Location: Huntersville NC

    DavidBoat Junior Member

    More Detail - the Skinny

    :) My first post was a little light on what I was thinking for the details so for the purposes of attempting to really attract true consideration here's the skinny.

    Design for Intercoastal Cruising and Venturing to the Fishing Grounds on good day

      • 27' LOA
      • 8' Beam
      • Shoal Draft (less than 2' board up)
      • South of 4,000 lbs displacement with 750 lbs battery/ballast
      • Plywood/Epoxy Construction with Ply bulkheads, 1x3 oak stringers/intermediate frames
      • Swing keel
      • Thoosa electric motor w/48v bank
    The accomodations are for an extended weekend.
    Simple Stove
    Semi-enclosed steering compartment

    Oh yeah....trailerable too.

    Is there a design that successfully crosses the line from a stable easy moving displacement hull to something that can ride the wave past hull speed (in good conditions) but yet provide sailing capability?

    Somebody must have done this in a plywood design.
    I'm thinking Caulkins Bartender meets Dory type of Hull.

    Names....Frankenstein, Abomination, oh yeah female names....
  3. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Mrs. Frankenstein, Miss Abomination?

    The Bartender is a dory type hull. If you could mount about 1250 sq. ft. of sail area on a 22' Bartender (not likely) you'd be able to plane in the mid teens.

    The problem with craft that can plane is they need power (lots of it). More specifically, they need a fairly high power to weight ratio. You can use a light weight hull and rig, like a Laser and get by with a small amount of sail area. You'll get the boat well over 2 S/L ratio, though this particular hull does have some shape limitations, it's in semi plane mode. It gets there with a light weight package.

    Toss in a motor, battery banks, weekend accommodations and now the boat needs a lot of sail area, because the weight has jumped tremendously.

    I see several problems in your requirements. You estimate you'll sacrifice sailing performance to do 10+ knots. Okay, but this means you'll do 10+ knots on batteries which are heavy as hell, particularly on a boat that is going to be weight sensitive. 27' at two tons is light, which means very little reserve or battery range, so maybe the sailing thing should be reconsidered, or maybe the target speed or maybe the weight.

    These conflicts will haunt a design. It's a common set of problems, trying to do too much in one package. The usual result is a product that doesn't do any of the things it's designed for very well. It'll sail okay, but not great, it'll motor on batteries okay, but it's range will be limited from the weight restrictions and speed requirements.

    I'd recommend you try to refine your goals a little more in an effort to define the hull form.

    Having a 27' powerboat that can putter at 10 knots all day on a 5 gallon jug of fuel isn't that uncommon. Having 27' sailboat that travels at 8 knots under sail alone isn't uncommon. You'll have to accept the compromises that come with these two craft, but mixing them generally doesn't work out so good, one usually is the burden of the other. The economical powerboat will be narrow, so you can tow it, but the weekend accommodations will be tight. This is the price of efficiency. Tossing batteries in the bilge is great, you can motor in little noise, but the power output will usually be considerably less then conventional gas engines for their weight, then there's the range issue again.

    In short, there are many designers working on this complicated set of issues. I have efficient sail and power designs, as have many others, but frankly battery development is what's holding everything up and has been for several decades now. There have been some great advances, but these need to be in place longer with more market approval before the prices will come down. Your best bet would be to contact a designer and have a custom design worked up to suit your clearly very specific and specialized needs.
  4. DavidBoat
    Joined: Aug 2009
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    Location: Huntersville NC

    DavidBoat Junior Member

    Par, thanks for the well reasoned reply.
    I've thought a lot about the design parameters and the goal is an electric boat that can carry sail and make "recharge speed" under sail.
    If I get rich I'll find room for a small generator for recharge power as well.

    The main goal is electric propulsion, but I'd like to have the sailing rig for recharging the batteries and fun!
    The range would then be the life of the battery and not how much gas I could carry.
    I'm figuring 4 battery (spare no expense here) bank with a Thoosa 7000 (7.2 KW) motor.

    I'm attaching a hull form I'm working on for your perusal.
    I'm at the following specs-

    27'4" LOA
    25'2" LWL
    3800# Disp.
    12" draft
    Carlson's Hull Designer estimates a 6.7 kt hull speed

    Any suggestions on modifications for hull form for sail would be appreciated.
    I'm still figuring swing keel location and sail plan, but the keel / rudder shown is what I'm aiming for.

    Attached Files:

  5. apex1

    apex1 Guest

    If you ARE rich, you can afford to save a little bit of energy while sailing.
    If you´re not, pay the price.

    Electric propulsion on a boat, yacht or ship does not happen as long as the north pole grows no palm trees!

    All your idiotic thoughts have been handled here and in thousands of (more sophisticated, esoteric) Forums worldwide.

    NOT WORTH TALKING is the result.

    Of course you know better. You know how all the technology is suppressed by ignorant idiots like me.

    The commercial fleet and the fishery worldwide does not even think about it.

    All idiots and ignorant, clear enough.

    Go dream on...........

  6. DavidBoat
    Joined: Aug 2009
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    DavidBoat Junior Member

    Wow Apex!
    When you leave an oil slick, you really leave a stinky one.

    Believe it or not, Electric propulsion will work.
    Sure batteries need to get better, but for someone not living off of the boat commercially, I'll be happy with the best result I can get 12 months from now when I'm done. (12....how's that for optimism)

    Any way thanks for kindly dropping in.
  7. apex1

    apex1 Guest

    At least I leave something.

    When you disappear no one will notice!

    Well, your neighbours may be disturbed when your widow is celebrating the fifth month.
  8. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Currently, electric propulsion does work, but you have to make several concessions. The biggest two, assuming displacement speeds with an efficient hull form, are range and hull volume.

    If you are willing to live with quite restricted range and no elbow room inside the boat, then you've got a project.

    The drawing you've provided will be restricted to 1.35 S/L ratio only. You're not going faster then that, with that shape and your beam/length ratio could be taller for more efficiency.

    The basic problem revolves around the weight of storage (batteries). You can go light with minimal storage capacity, but your range is also short. You can increase the capacity with a generator, which can be driven a few different ways. PV panels are another option, of course with a whole new set of issues.

    This storage weight issue means you have to relinquish a lot of boat to the batteries, which cuts into living spaces. Further screwing with the issue is a need for efficient hull shapes, which tend to be narrow and light. Narrow, light hulls have limited elbow room and hauling capacity. Mutli hulls have been an answer for some folks, though the same rules apply and the same issues exist.

    In the end, this is a very specialized type of yacht. You may be able to cobble your way through designing a fairly inefficient sail or powerboat hull, but a yacht with the cleverness necessary to perform as you're describing, requires considerable expertise in hull form, systems coordination, stiff/light weight structures, etc. This is well beyond the engineering ability of the self educated novice or amateur designer. An especially efficient stock sail design will be moderately successful, a semi custom or full blown custom much more so. Of course this means a professionally worked up design.
  9. Zappi
    Joined: Oct 2008
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    Zappi Senior Member

    Wow Dick, you have some serious social issues. Do you drive a jacked up pickemup truck???

  10. DavidBoat
    Joined: Aug 2009
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    Location: Huntersville NC

    DavidBoat Junior Member

    Past Designs to compare

    I appreciate the advice and will take it to heart and ego.
    While I'd love to design this myself, to reach the performance I'd like and end up with an efficient electric hull that can carry sail, I think I need a professional.
    I'm an architect and you'd think I would know this already....

    Do you have advice on a past design or stock plan from a designer that approaches a solution for my objectives?
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