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Thread: Design for a small motor boat?

  1. #1
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    Default Design for a small motor boat?

    I am fairly new to wooden boats in general and am looking for a design for a smaller motor dinghy or skiff. Should have an inboard motor, be at around 14-17 feet, lapstrake design.

    When researching on the web I was inspired by designs Hvalsoe 16 rowboat
    http://farm3.static.flickr.com/2157/...ed53bf102d.jpg
    http://erichvalsoe.googlepages.com/13and16

    Any ideas on combining the aesthetics of the Hvalsoe with an inboard motor?

  2. #2
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    Default Re: Design for a small motor boat?

    You looking to build, or buy? Say some more. Are you hoping to row this boat with relative ease? There are a lot of good little, lightly-powered, skiffs out there. A favorite of mine, though it couldn't be construed as a row boat, is the mid to late fifties Lyman Islander. It grew a bit, from 17 to 18. A similar form, but not lapstrake, is some of Harry Bryan's skiffs, if you want a more modern iteration.

    The Lymans, I can attest to this because I did a bit of work on them, were very nice creations. A four cylinder gas Gray, which pushed the bote onto a plane with just enough power to make it work efficiently. It got going maybe seventeen knots. Yet just at the balance so it was fairly stingy with gas. Incredible materials. Old growth fir ply over white oak frames. Small dex fore and aft of good mahogany ply. I've sung their virtues before.
    So many questions, so little time.

  3. #3
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    Default Re: Design for a small motor boat?



    I was just looking at this website (again) yesterday...

    http://www.batritningar.se/default.a...Page=Boatplans

    Look under "Motorsnipa" (above)
    and
    Belkingseka
    Last edited by Greg P H; 12-02-2008 at 12:59 PM.
    We think we are living on a planet that is floating around the sun. It isn't true, there is no planet and there is no sun. There isn't anything, it's just pure consciousness and nothing more.


  4. #4
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    Default Re: Design for a small motor boat?

    You'll be hard pressed to find a boat with an inboard in that size range, and most will be very old plans. Damn few small inboards being made these days -- everyone puts an outboard on the transom or in a well.

    Big Question = WHY an inboard?

    And DON'T take a pulling/rowboat design and try to convert it for inboard power -=- hull shape and many other elements are dead wrong for it.

    There are lots of plans that meet your requirements without you having to learn some expensive and frustrating lessons about marine design the very hard way...

    Check out the Atkin designs -
    http://www.atkinboatplans.com/
    "The enemies of reason have a certain blind look."
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  5. #5
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    Default Re: Design for a small motor boat?

    If you're looking to buy, this beautifully restored Canadian Launch is for sale by one of the Ol' Coots:

    http://www.flickr.com/photos/jkohnen...7605761327936/

    http://farm4.static.flickr.com/3107/...b707f703_o.jpg

    And I'd second what my smarter twin, Thorne, says about the Atkin designs. They were prolific, so there should be a good selection for you to choose from.

  6. #6
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    Default Re: Design for a small motor boat?

    I'll be interested in hearing other people's comments on this. As to actually putting a (very) small inboard in an Hv 16 hull, in terms of the center of gravity, it would have to replace the centerboard trunk towards its aft end. Somewhat more robust parameters is probably what you want - you really have to define your use of the boat - but there is no reason that a small inboard launch cannot have some of the aesthetics that you enjoy with the 16. The HV 16 is fine ended, though with good reserve bouyancy and strong haunches, for rowing and sailing - weight distribution is important, either evenly distributed through, or focused in the middle of the boat. She will squat with one person perched on the transom or with much thrust coming from inboard propulsion. With the addition of an inboard, displacement - ie weight and capacity, as well as trim is most important. Poulsbo Boats look like small tugboats, but they are really very trim sensitive and easily overpowered. You can also bat this around with me on the PM board. Nevertheless, good to open the question up to forumites.

  7. #7
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    Default Re: Design for a small motor boat?

    Thanks for all the replies so far.
    Ishmael: I am planning on building the boat.
    Thorne: I am thinking inboard rather for aesthetics.
    I very much like the Atkin designs. Thanks.

  8. #8
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    Default Re: Design for a small motor boat?

    Quote Originally Posted by aklimo View Post
    I am thinking inboard rather for aesthetics.
    I
    The Handy Billy, though a bit longer is a very handsome boat. Something along those lines could be incorporated into a smaller boat.

    I like the idea of a small diesel propelling a small displacement craft, but part of the problem as I see it is that the placement of the motor is right smack in the middle of the boat, greatly limiting your usable space.
    Steve Martinsen

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    Default Re: Design for a small motor boat?

    How about a 16' Poulsbo Boat. Lines and offsets are available from the Center For Wooden Boats in Seattle. I haven't seen a lapstrake version, only carvel.

  10. #10
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    Default Re: Design for a small motor boat?

    Barrett Faneuf, of "I'll just build two Welsford Navigators at the same time" fame, also built a lovely little launch with an inboard that might meet your needs -

    http://barrettfaneuf.livejournal.com/21264.html#cutid1
    "The enemies of reason have a certain blind look."
    Doctor Jacquin to Lieutenant D'Hubert, in Ridley Scott's first major film _The Duellists_.

  11. #11
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    Default Re: Design for a small motor boat?

    From Selway-Fisher http://www.selway-fisher.com/Mcup16.htm


    NEW15'1" PORT PEGASUS ROWING & MOTOR BOAT
    <SPAN style="mso-default-font-family: Arial; mso-ascii-font-family: Arial; mso-latin-font-family: Arial; mso-greek-font-family: Arial; mso-cyrillic-font-family: Arial; mso-hebrew-font-family: Arial; mso-arabic-font-family: Arial; language: EN-GB; mso-ansi-language: EN-GB"><FONT face=Arial color=#000080 size=2>The Port Pegasus is a clinker boat which may be used as a pure rowing boat or fitted with a small diesel (ie Farymann 7.5) as a small motor launch with classic appearance.

  12. #12
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    Default Re: Design for a small motor boat?

    An entirely different kind of launch - the Disappearing Propeller Boat, AKA Dippy or Dispro. An overgrown double ended pulling boat with inboard and exotic propshaft arrangement. Somewhat long and narrow, maybe 17' at the minimum, probably not what you had in mind.

  13. #13
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    Default Re: Design for a small motor boat?

    "Now and then we had a hope that if we lived and were good, God would permit us to be pirates." ~ Mark Twain


  14. #14
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    Default Re: Design for a small motor boat?

    I'm completing a Payne Yellowtail - a 14' boat that meets your definition, but mine has been strip planked rather than lapstrake (most seem to be lapstrake)

    http://www.payneyachts.com/motor_launches.htm

    Here's one running a small 6hp Kubota diesel



    My engine is a smaller 3 1/2 hp single cylinder 1930's engine, located further back so that I can put a gaff rig on as well.

    This is his 4.5m (15') boat

    Carpe the living sh!t out of the Diem

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  15. #15
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    Default Re: Design for a small motor boat?

    I'll second Harry Bryan's Rambler. She is so sweet:








  16. #16
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    Default Re: Design for a small motor boat?

    Steve,

    I thinks it's funny that the little movie of Rambler has no sound. The small diesel would distract a bit I guess (whackity-whackity-whackity!)

    The design would lend itself to electric power. It reminds me of the auto-boat era.
    "Now and then we had a hope that if we lived and were good, God would permit us to be pirates." ~ Mark Twain


  17. #17
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    Default Re: Design for a small motor boat?

    aklimo,
    you might want to keep in mind the noise factor with an inboard (especially a diesel) in a small boat. A lightweight lapstrake hull will act as a sound board verses a heavily constructed hull with a lot of mass to absorb some of the sound. Unless you power it with a tucky-tucky antique engine you will need lots of sound deadning insulation.
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  18. #18
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    Default Re: Design for a small motor boat?

    Since you value aesthetics highly you might consider electric power as rbgarr suggested. No noise is a great feature for plesant cruising and the motor itself is so small you can fit it in without intruding into the boat's interior space nearly as much as an ICE. The batteries can go out-of-sight under the seats and/or fore and aft decks, wherever their weight keeps the boat floating level.

    The negative of electric power is high weight and short range. In a 15' wl boat you would be limited to displacement speeds (under 6 mph) and range with a reasonable battery bank (4 12v 100 ah, 250# total) would be about 3 or 4 hours at 4 or 5 mph.

    If the range and speed constraints are acceptable it would be a good solution. You also have to be able to plug it in to recharge. Would not work on a mooring but no problem for a boat on a trailer in your garage.

    You can see my electric launch here www.wolfEboats.com

    Small gasoline marine inboard motors are non-existant. An air cooled lawnmower type engine is inexpensive but awfully noisy. A water cooled marine diesel is a good functional solution but still noisy and quite expensive. If I were you and couldn't live with electric's constraints I'd find a design with an outboard hidden in a well. There are lapstrake sailboats (Oughtred, Selway-Fisher, Wellsford and other designers) that could be built with out the rig and a motor well. A modern 4-stroke outboard is very quiet and if you are OK going slow you only need about 5 hp.
    Denny Wolfe
    www.wolfEboats.com

  19. #19
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    Default Re: Design for a small motor boat?

    Another problem with lawnmower engines is that they are usually vertical shaft (but lawn tractors may be different?). And most garden engines are air cooled, so you have the noise problem. How hard would it be to convert an engine to water cooling? I guess you could solder a water jacket around the cylinder head and run water through that. But you still have the problem of fitting the water pump to the engine...

    What about scooter engines?
    1947 Nordic Folkboat "Nina"

  20. #20
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    Default Re: Design for a small motor boat?

    Quote Originally Posted by BarnacleGrim View Post
    Another problem with lawnmower engines is that they are usually vertical shaft (but lawn tractors may be different?). And most garden engines are air cooled, so you have the noise problem. How hard would it be to convert an engine to water cooling? I guess you could solder a water jacket around the cylinder head and run water through that. But you still have the problem of fitting the water pump to the engine...

    What about scooter engines?
    The big problem with any small displacement engine is that it must operate in a specific RPM band to generate enough torque to carry a load. Usually that RPM range is too high for driving a boat propeller. Some type of gear or vee belt system is needed to get the prop shaft spinning slow enough. Gear boxes can be expensive and belt drives require space and must be covered for safety. There have been builders here who have built their own speed reducers but isn't something that can be quickly put together.
    If you can find a suitable small implement motor with a built in gear reduction you are half-way there but new motors aren't all that cheap.
    Many small air-cooled motors are die cast aluminum. You certainly can't solder on them and welding on such alloys, if it can be done, would require someone with a high skill level.

  21. #21
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    Default Re: Design for a small motor boat?

    Quote Originally Posted by mcdenny View Post

    Small gasoline marine inboard motors are non-existant. An air cooled lawnmower type engine is inexpensive but awfully noisy. A water cooled marine diesel is a good functional solution but still noisy and quite expensive. If I were you and couldn't live with electric's constraints I'd find a design with an outboard hidden in a well. There are lapstrake sailboats (Oughtred, Selway-Fisher, Wellsford and other designers) that could be built with out the rig and a motor well. A modern 4-stroke outboard is very quiet and if you are OK going slow you only need about 5 hp.
    All very good points though I must disagree with the small gas engine thing: Kohler's Aegis line of liquid cooled motors are available from 20-30 Hp and are remarkably quiet, and stingy on fuel; something on the order of 1.3 GPH for the smallest size. So if you have a boat that can run 18 Kt, you're getting something like 20 statute MPG from a boat, which is spectacular.

    The Atkins' boats are big favorites here at WBF. If your size limit were a little bigger I'd suggest looking at Sergeant Faunce but maybe that's my own little peccadillo.

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