Cheap to run, cheap to build electro plywood cruiser ?

Discussion in 'Boat Design' started by ASM, May 8, 2008.

  1. ASM
    Joined: Sep 2005
    Posts: 146
    Likes: 2, Points: 0, Legacy Rep: 56
    Location: The Netherlands

    ASM Senior Member

    Hello all,

    I have been a member for a while now on this forum and have read many threads with interest. After substracting/consuming a lot of the (wise) information from this forum and designers sites, I have come up with a simple plywood cored, electro driven inland cruising boat for family/weekend use.

    It is roughly 8 m long, 2.5 m wide, with a keel box to hold the batteries and motor. The salon top can be covered in solar panels, the big side windows aft could be of the opening type like in cars (manually of course ! no powerrrr).

    Since I am no naval architect at all, could you give me some usefull feadback on the initial sketches and see where I made huge mistakes or if I am on the right track ? I am planning to build a 1:10 scale model just to see if it floats and its stabililty.

    Thanks !

    Attached Files:

  2. Guest625101138

    Guest625101138 Previous Member

    What do you want to carry - displacement?
    What speed do you want to travel at?
    What range are you hoping for?
    What conditions do you intend to operate in?

    The design has merit. It may be possible to do better.

    It is worthwhile building a model but it pays to do a bit more design first. Most important thing is to have a realistic displacement.

    Rick W.
  3. ASM
    Joined: Sep 2005
    Posts: 146
    Likes: 2, Points: 0, Legacy Rep: 56
    Location: The Netherlands

    ASM Senior Member


    To be used as a day cruiser/weekender, inland waterways, maybe occasionally along coast line, but that option falls if that means to much adjustments or changes.

    Approx weight on board: 500 kg (6 persons + light luggage)

    Hull design speed (~7.5 knots ?) with a little margin for upstream, 'rough' water.
    Range would be approx. 6 hours of running at 6 knots or so, solar panels to give a bit of extra range and ppower on board for electrocnics.

    Displacement empty: 2 tons ( I do not know if that is possible for this sort of construction, I can imagine that the superstructure can be made from foam cored panel, which in combination with batteries in keel keeps te cog nicely low and therfor a stable boat)

    Conditions, mild, it's a family nice wheather boat....

    Straight shaftline, propeller surrounded by a steerable nozzle.
  4. Knut Sand
    Joined: Apr 2003
    Posts: 471
    Likes: 30, Points: 28, Legacy Rep: 451
    Location: Kristiansand, Norway

    Knut Sand Senior Member

    I had an aricle lying around somewhere, believe it was in the Wooden boat magazine, Think it was on the frontpage also. May be a little over a year ago, or so? I'll try to look around for it. They had an article about a electric boat like that, trailerable, beam approx 7-8 feet maybe, long sleek and narrow, ply design(?) epoxy sheated, it was quite ok looking also. Maybe some other will remember this?
  5. Guest625101138

    Guest625101138 Previous Member

    I did a rendering of the hull based on a somewhat different underbody that I think would give good efficiency at 6kts for the other constraints specified. The hull displaces 2.5 tonne and is 8.4m long.

    With a 14" 3-bladed prop, the hull shown would require 2.5kW to do 6kts but power rises steeply above that speed. It takes 10kW to do 7.5kts.

    I believe a two tonne boat would not be difficult to achieve. If you are considering composite construction for deck then why not use for the rest.

    Using VRLA batteries you will get say 20kWh for 500kg and this is the size you need to get fair battery efficiency at 6kts. Would have a range of around 45nm.

    If you are happy to plod along at 5kts then range goes out to about 120nm.

    An 8m boat of this beam and displacement will start to makes waves above 5kts and that takes energy.

    If you want to do 6kts efficiently then you need longer hulls - say 10m or go for a catamaran.

    This was the first pass so it may be possible to get better.

    With things like this I normally start with the most efficient hull for the speed and displacement without any constraint and then decide what each feature costs in terms of performance. For example the optimum 2.5t hull will require 600W to do 6kts with a good prop.

    Rick W.

    Attached Files:

    • ASM8.jpg
      File size:
      35.2 KB
  6. ASM
    Joined: Sep 2005
    Posts: 146
    Likes: 2, Points: 0, Legacy Rep: 56
    Location: The Netherlands

    ASM Senior Member


    wauw you'r quick, thank s for this very impressive answer. As I saw your comments on several othe items ont his forum and your website, I kinda hoped you would be the one to reply........ is this your preffesion or are you just a big enthousiast ?

    Will it be a big advantage to reduce the weight by 0.5 t ? and reducing the keel box in width ? I guess the waterflow towards the prop becomes more efficient then and together with a thrusttube around teh prop it should give some more efficiency, thus pushing the power graph a bit upwards in speed ?

    Would it be very bold to send you the hull sections as in the attached JPEG with my thread, or do you consider the minimal differences of minor importance ? (so with a little bit of optimization on the hull, one expects an improvement, but the figures as calculated still stand and might end up with a little more power reserve, so in fact a worse case scenario ?)

    I understand your philosophy, and I already started with a narrower hull, but considered space and ease of building (so relative square flat sections) important to sacrifice in performance.

    Another thing I do not have the knowledge for is the situation that the 5 kts is a good optiomal cruising speed, but what happens to the power requirement when you run in a very strong countercurrent or wind ? Does it rise exponential ?

    Thanks again...
  7. Knut Sand
    Joined: Apr 2003
    Posts: 471
    Likes: 30, Points: 28, Legacy Rep: 451
    Location: Kristiansand, Norway

    Knut Sand Senior Member


    Impressed by the details given by Rick here.

    The atricle in the Magazine was WoodenBoat, August 2005, not a year ago then... (The speed of time.....Ok, lets face it, all... we have to live when we do it, cos' when we're dead, we're gonna be dead for a long time).

    Boats name is Nomad III, Article was "Considerations for a sun-powered cruiser".

    Link here:
  8. ASM
    Joined: Sep 2005
    Posts: 146
    Likes: 2, Points: 0, Legacy Rep: 56
    Location: The Netherlands

    ASM Senior Member

    HI Knut

    Thanks for the link, I had that one for 2 years now, also one of the inspirations and a proof that it is possible. I feel electric boating will become big in the years to come, and in The Netherlands where we have 14 million people and recent studies showed 1 in 10 own a boat of some sort..... and since we are a cheapcheap type of persons, the diesel fuel price will be painfull. We also have much more displacement craft compared to f.i. US so the potential for electric boats is big.

    The downside with electric craft so far is the lack of 'sexyness', the ones available over here are scarce or or just plain ugly..... or are re-engined diesel ones, so bad publicity for the electric propulsion since they were not designed for such a propusion in the first place (WEIGHT !!)

    BUt, there are some initial step in the right direction, look at:

    you see my point of view to devellop and electric family vessel ? Just for myself, but who knows if people are interested.....
  9. Guest625101138

    Guest625101138 Previous Member

    I could not resist looking at something more like the optimum hull based on the concept.

    The attached is 10.5m long. It will require about 700W to do 6kts. So a large improvement over the other one. Hitting 7.5kts requires only 1.5kW.

    The hull is effectively a trimaran. I expect performance would drop considerably in heavy weather because the side wings would be submerged quite a lot.

    It is not all that different to what you drew initially.

    The difference with this second one to the first one is that it will rely on the outboard hull for stability. However sitting 500kg of batteries in the keel will certainly help to keep it upright.

    I would say building a model of this will be interesting. You might get a lot of interested folk.

    Rick W.

    Attached Files:

  10. Guest625101138

    Guest625101138 Previous Member

    Boating is my hobby.

    You should be able to get reasonable section drawing off the lineplan if you want them.

    At this stage I think it is still an idea in development.

    The length is really the big factor from an efficiency perspective. WEight comes into it but if you can stay around hull speed or below then there are big benefits.

    The design has huge potential. It is sort of taking the Atkin hull another step.

    I am not certain about the seaworthiness for heavy weather but once you stick 500kg in the bottom of a small boat it really stiffens it up.

    If you are serious about the model I will do more work on it. You should be able to get Delftship and I can give you the file so you can play with it.

    As you can see if you go longer you can reduce power required and therefore battery weight.

    I also think 6kts is a good cruise speed.

    If you determine what are really hard constraints then it can be pushed and pulled to suit.

    Rick W.
  11. ASM
    Joined: Sep 2005
    Posts: 146
    Likes: 2, Points: 0, Legacy Rep: 56
    Location: The Netherlands

    ASM Senior Member

    Thanks for all your input and I also think it has huge potential as this kind of electric vessel is not on the market at the moment and suits a big crowd needs.

    The trimaran concept is already in (sort of) devellopment:

    Though the website is not up yet for the featherline brnad, it is under construction for almost 1.5 years now....

    I will be on a short holiday this weekend and thin kthings over, will come back early next week on this !
  12. messabout
    Joined: Jan 2006
    Posts: 3,281
    Likes: 426, Points: 83, Legacy Rep: 1279
    Location: Lakeland Fl USA

    messabout Senior Member

    I can see but little advantage in doing the under body as a faux trimaran. Much simpler to let it be a box keel with flat or slight deadrise outer section. I reckon it ought to have some aft rocker to get the transom reasonably clear of the water. I'd also pinch the transom in a bit. In a chop or when traversing wakes the aft corner of the boat will dig in such a way as to make temporary drag. A narrower transom is also structurally stronger as well as lighter. Keep the ends of this boat as light as is practical.

    The advantage of the sections that you have drawn are structural. That is to say that the width of the flat sections are smaller and will require less framing than a wider flat section. On the other hand the larger number of corners (chines) will increase eddymaking and contribute to drag. In a boat of this sort we are trying to keep wetted surface and drag to a minimum.

    My attic is the resting place of a model of this very type. The model is about one meter long and was propelled by an electric motor with radio control. Care was given to maintain similitude as regards displacement. The model performed very well at S/L ratios of less than about 1.2. Pressing the speed much beyond that caused a big wave train, clumsy behavior and rapidly drained batteries.
  13. Guest625101138

    Guest625101138 Previous Member

    This is in early stages. It was 10minutes of work. I am sure it can be improved. Looking at the lineplan I can see 3 changes already that would make it easier to build and one possibility to reduce the ama drag.

    Would like to see a photo of your model and more comments on how it performed. Even better would be a video clip of it at economic speed and also with wave making.

    Rick W.
  14. rwatson
    Joined: Aug 2007
    Posts: 5,956
    Likes: 341, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    That design takes me straight to Phil Bolger - even looks like the boat he designed
    Check out

    You can get the plans for $400 at

    Phil Bolger,
    P.O. Box 1209
    Gloucester MA 01930

  15. afrhydro
    Joined: Mar 2008
    Posts: 243
    Likes: 12, Points: 0, Legacy Rep: 245
    Location: port charlotte fl

    afrhydro Senior Member

    i built this boat for electric power plant
    but I'm still working the bugs out
    so I'm testing it with gas motors now

    for me its already to go just battery money and controller money is my problem

    Attached Files:

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.