1 man mini boat

Discussion in 'Projects & Proposals' started by Sockie, Dec 28, 2019.

  1. Sockie
    Joined: Dec 2019
    Posts: 11
    Likes: 0, Points: 1
    Location: Brisbane, Queensland, Australia

    Sockie Junior Member

    Hi all,

    I've been thinking about building a 1 man mini boat along the lines of the rapid whale but want to make one better.

    It will be an extended project with the plan to slowly acquire materials required as I need them.

    First step is obviously to design a hull and plan everything to go inside it.

    I want it to be inboard, electric jet impeller driven as I'm not looking for a speed boat, I just want a mini cruiser I can run around the bay in at around 6-12 knots and do some light fishing. It doesn't need to plane.

    Plan is to run under the lower power limit for registration requirements so I can not worry about paying to register it and can just go to the ramp with it on my roof racks and go for a day on the water.
    I can run up to 3000 watts which (according to my calculations which may be completely wrong) is more than enough to achieve the speeds I am aiming for with the right impeller setup.

    Being an ultra small vessel (max 5ft long) stability is going to be a main focus for the hull design and I feel that I will need to do something out of the ordinary to maximise the stability.

    I was thinking of something along the lines of a deep vee bow transitioning to a tunnel hull stern to allow for maximum stability where the driver and electrics will sit at the stern and the forward cutting ability of a deep vee bow.
    My first question is has anyone had any experience with a hull design like this and what advice would you give for proportions based on a 5ft overall length regarding the transition from vee to tunnel hull.
    I want to either use 1x 2800w electric impeller and mount the jet outlet in the centre of the rear tunnel hull and utilise a steering nozzle as the primary steering device OR use 2x 1200-1500w electric impellers mounted as far from centre as possible in the rear tunnel hull and use differential thrust as the primary steering method.
    I am interested to know opinions of the differences between these setups and pros and cons of each.

    If worst comes to worst and Jet is not the ideal solution, I'd then choose to go with a single centre propeller, shaft driven from a direct coupled 2800w electric motor.
    I am interested to hear opinions on this drive method too.

    Primary hull construction is planned to be zip and stitch plywood constructuon with 2 skin design filled with buoyancy material such as construction foam.
    Joints are to all be fibreglassed for waterproofing, rigidity and durability.


    I'm not interested in anyone's opinion telling me NOT to do this build.
    Whilst I respect everyone's opinions, I feel that this is a place to share lessons learned and experience rather than bagging on other's ideas. Unfortunately I have had a number of very rude and aggressive comments on other forums about this project which is the reason I have come here to discuss it.

    Any help with planning, design and ideas or even just as a sounding board is greatly appreciated and I thank you all in advance.

    Cheers!

    Sockie
     
  2. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,048
    Likes: 634, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    5 feet is ridiculously short, in shark-infested Moreton Bay, that might look from below like a turtle sunning itself....and chomp ! 8 feet, or not worth thinking about, and then only for close inshore in good conditions. There are plenty who fish from kayaks, and frankly not real smart, as sharks are attracted to the smell of bait, and hooked fish.
     
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  3. bajansailor
    Joined: Oct 2007
    Posts: 1,303
    Likes: 375, Points: 83, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Welcome to the Forum Sockie.
    Unfortunately (for you) I (like Mr E) am also urging you to NOT do this build.
    The reason why you had those 'rude and aggressive' comments on other forums is that your proposal is quite simply totally hare brained.
    If it was viable, somebody would have done it, and be offering plans for building it.
    A 5' long vessel that is suitably 'boat shaped' to achieve the speed that you are desiring is not going to have the required displacement to support you, nor is it going to have the necessary stability to stop you from immediately capsizing when you step into it.
    And as Mr E says, you will appear to be ideal shark food from underneath.
    If you REALLY want to build a boat, buy a set of plans for a proven design that is capable of doing the intended task.

    Edit - google is wonderful (again). I was wondering what you meant by a 'rapid whale boat' - and here it is.
    Mini Boat - Rapid Whale http://rapidwhale.com/mini-boat.php
    Notice how the drivers in these boats are wearing lifejackets?
    Please don't even think about going fishing in something like this that is a foot shorter, with an inboard engine, and batteries - not much room for you as well.......

    Just wondering if you posted this Sockie?
    Scaling designs for mini boat :: Builders' Forum https://www.clcboats.com/forum/clcforum/thread/45371.html
     
    Last edited: Dec 29, 2019
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  4. kapnD
    Joined: Jan 2003
    Posts: 713
    Likes: 83, Points: 28, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    Great ideas, Sockie, go for it!
    Be sure to post up pictures of your progress, and get someone to video the event on launch day!
    And pass the pipe to the left please.
     
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  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,048
    Likes: 634, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Just imagine you scaled a "fat" 10 foot dinghy down to five feet, it would be one-eighth the size, volumetrically, of that 10 footer. Do you want to be one of eight people in the ten foot dinghy ? That is the task you are setting.
     
    Last edited: Dec 29, 2019
  6. BlueBell
    Joined: May 2017
    Posts: 1,316
    Likes: 263, Points: 83
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Sockie,

    Welcome to the forum.
    I like you.
    Don't build this little vessel please.
    But do build something similar, just 3 or 4 times longer.
    OR
    Get a stubby kayak, a "Shortie".

    EDIT: Oops, I told you not to build it. Do you want me to delete my post?
     
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  7. BlueBell
    Joined: May 2017
    Posts: 1,316
    Likes: 263, Points: 83
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Okay, I've reconsidered, disregard my last.
    Build it, post a bunch of build videos and photos.
    Differential thrust would be the way to go, no rudders.
    This is going to be great!
    Cheers
     
    bajansailor likes this.
  8. GIOVD
    Joined: Nov 2009
    Posts: 6
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Canada

    GIOVD Junior Member

    Hello sailor Sockie,
    In 2014 I did a hand sketch near to you idea. Please take a look :)
    upload_2019-12-29_14-38-4.png
    You need remember that the plywood minimum sizes is 8'x'4x1/4"
    Here is the render that faster I did:
    upload_2019-12-29_14-40-16.png
    Hydrostatics &Stability is very simple. I need little time for do that.
    If I remember was a MESH Engine. I will look.
    The color reed if for easy cost guard identification.
    I hope inspire you keeping the safety first,
    GIOV
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,048
    Likes: 634, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    GIOVD, that one won't fit on his car's roof racks, as stipulated.
     
  10. BlueBell
    Joined: May 2017
    Posts: 1,316
    Likes: 263, Points: 83
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    SOCKIE, come on, build it man.
    A stabilized monohull, what could possibly go wrong.
    Do it! Do it! Do it!
    What's your budget and how small a place do you have to build it in?
    60" ( 5' ) is nothing, you could build that in your kitchen!
    And what is your expected completion date?
     
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  11. kapnD
    Joined: Jan 2003
    Posts: 713
    Likes: 83, Points: 28, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    I don’t see room for a jet drive in there, space and weight are at their absolutely most premium in a vessel so small.
    Where will the batteries go?
    A modified electric trolling motor would solve many problems offered by an inboard driven shaft.
    A wash deck with a sealed hull would be a good idea, like a plastic kayak.
    Speaking of plastic kayaks, you might be on the water next week by just modding one and adding the trolling motor!
     
    bajansailor likes this.
  12. fishwics
    Joined: Mar 2004
    Posts: 33
    Likes: 1, Points: 8, Legacy Rep: 10
    Location: UK

    fishwics Quiet member

    6 knots might just be do-able with an 8ft boat; even then I'd have worries about the weight of engine and battery to achieve a reasonable endurance. 12 knots is totally out of the question. (You'd need a good 10hp for that, something like the Torqueedo Cruise 10, and the weight would be prohibitive)
    My experience (with small RIBs) is that you want to go over the water rather than through it, so you don't need a deep-vee bow, but rather something flatter that will lift. I'd be looking at a shape rather like an Oz Puddle Duck Racer (which is a sailing dinghy but no reason why it couldn't take an electric outboard). For that matter you could build a PDR hull unmodified.
    It won't be ocean-worthy, nor will it go through a surf (I don't know what conditions are like where you are), but OK for flattish water.
    Just my 2c
    Simon
     
  13. Sockie
    Joined: Dec 2019
    Posts: 11
    Likes: 0, Points: 1
    Location: Brisbane, Queensland, Australia

    Sockie Junior Member

    Nope, not me...

    Whilst I appreciate the concerns some commenters have raised, I am not going into this half cocked....

    Kayak fishing is extremely popular in the area and Mr Efficiency, sharks in the bay have never been an issue...
    I dive and kayak and fish regularly..... never had issues with sharks. In the canal estates maybe... but out in the bay the sharks don't bother anyone unless you are looking for them. As a diver and regular kayaker, I am in theor domain ALOT and rarely see them. Haven't seen one locally for several years
    I am wanting to essentially make this but with my own hull design to further increase stability and buoyancy.
    The rapid whale is a design that remains afloat even when completely submerged. Regardless, anyone in any craft this small is a ***** if they dont wear a life jacket.... I always wear mine when kayaking with mates in the 6 footer sea kayaks (we fish off them too and have not even seen a shark locally for years).
    My idea is to purchase the rapid whale plans and then modify the rear of the hull to accommodate an onboard motor rather than the water snake.
    I am leaning more towards the inboard electric + prop design rather than the jet impeller design purely to allow for easy engineering of reverse gear. Different electric motors for each application means that I can afford a reversible motor if I prop drive....

    Again, I understand where you are coming from however, I have a mate who has a 6ft kayak with a chonda 4hp prop driven long tail and he achieves 12-14knots flat out.
    The difference between the chonda and my electric plan is torque curve and this is incredibly important as you all would know.

    The 4hp gx120 copy only achieves peak torque and HP OVER 3000rpm meaning it requires a centrifugal clutch and reduction gears to drive the prop at an appropriate rotation speed whereas, electric has full torque and power as soon as voltage is applied. I can have 3kw of power turning on instantly rather than ramping up meaning faster acceleration AND less energy consumption once cruising.


    I have also been looking into a solar solution for the upper forward deck to charge the auxiliary power.


    A few have asked where everything will go.

    Current plan is motor batteries under seat, motor and controller between legs in almost centre or just forward of centre (encased in removable hard casing for safety) and auxiliary battery up in the bow for ballast/balancing and used to run uhf, lights and stereo.

    Project is still in concept stage and I plan to take my sweet time building it once I start.

    Need the approval from the ministry sister of war and finance first so probably wont be kicking off until I can have the entire design proofed and costed (hence the modifying of the rapid whale design).

    Worst case scenario, I'll just make an inboard version of a rapid whale.

    Full build video series is planned as a YouTube series
     
  14. Mr Efficiency
    Joined: Oct 2010
    Posts: 9,048
    Likes: 634, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Where exactly are you intending to use it, on the bay ?
     

  15. Sockie
    Joined: Dec 2019
    Posts: 11
    Likes: 0, Points: 1
    Location: Brisbane, Queensland, Australia

    Sockie Junior Member

    Essentially, I feel that anywhere I can Kayak, I can take this thing. I'm not about to head ro New Zealand nor peave protected waters of moreton bay. I live redlands bayside so probably between wello and redland bay and maybe out to Russell where my mate lives.

    Often fish around coochie in the kayak so majority of use would be around coochie and vicky put

    All in all, I believe that if its calm enough for a 6 foot kayak, its calm enough for a 6 foot electric boat.

    Have been looking more into the single motor prop option and it looks more promising than jets given the size and displacement.

    After looking online I have found a 24v 2.8kw motor that draws 40A startup and 1.2A constant. It is reversible and controllable meaning that I can utilise a 60A ESC safely and I can also get away with standard 12v deep cycle batteries.

    2x 12v 140AH batteries in series will provide enough power to run the motor on startup current for 3.5 hours. This is obviously a worst case scenario as the motor is only ever taking the full 40A for a maximum of 1 second when starting under load.

    This means that the average current draw would be more like 10A across a full day's scooting and fishing and so calculates at 14 hours or runtime on a full charge. This is before I even factor in solar charging.

    This motor setup is about 6 times more powerful than the trolling motor used in the rapid whale design.

    I know that this doesn't translate to 6 times the speed due to the laws of fluid dynamics.

    To double the speed you need 4 times the power (or ratio of 1:2 speed vs power required). Reversing this means 4 units of power = 1 unit of speed or 2:1 power vs speed. This being said, 6 times the power results in 3 times the speed.

    The rapidwhale has a top speed of 4mph or 3.47kts

    3x4=12mph or 10.4kts max with the planned electric motor.

    I believe that with the correct hull design, I can comfortably cruise at 8kts and can definitely achieve the 10kts maximum especially with the boost function on the ESC.

    This setup also will not require registration due to the output being less than 3kw.


    Now back to my original question.....
    People with plywood zip stitch and epoxy experience, should I stick with the rapidwhale hull and modify for the inboard motor prop drive? Or modify it as per my OP?
     
    Last edited: Jan 3, 2020
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