Low power day boat - protected waters.

Discussion in 'Boat Design' started by kerosene, Jun 25, 2014.

  1. gonzo
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    gonzo Senior Member

    These are built in England. They are CE certified for 12 passengers (did it myself). With an electric trolling motor it does about 4 knots for one hour with a size 27 battery
     

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  2. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Fiberglass cuts fast and easy with a grinder and abrasive cutoff disks for cutting metal.
    why is this possibly of advantage to you?
    If you found an old, used fiberglass boat with SOME of the parameters you want and got it cheap? Modify it. if it has a deadrise bottom and you want it flat for shallows, cut off the original and put on a flat bottom. If you want to be REALLY cheap, invert the cutoff bottom and reuse it, reglass the cut lines.. A tunnel hull. Sorta. You'd have to be careful the cutting was symmetrical both sides, so, it would fit reinstalled upside down.
    Boat too long? Chop off the pointy bow and make a pram hull of it.
    Too WIDE? hmmm. well, uh; Look for a different boat! :D
     
  3. alan craig
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    alan craig Senior Member

    Kerosene, I just did a back-of-envelope calculation for electric power. If the hull needs 1200w to do 6kt then you could assume 2400w required from the batteries allowing for prop inefficiency etc. This means 12Kwh of energy for a 5 hour round trip so about 15Kwh of installed battery would be required (you can't use all the energy in a lead acid battery), which would weigh about 360kg. It's not impossible but a small four stroke outboard might be better.
    Your hull shape looks nice; a stretched Rescue Minor might also work.
     
  4. tom kane
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    tom kane Senior Member

    Lower powerday boat-protected waters

    To really enjoy safe and enjoyable boating and camping you need an easily managed boat and only be a fair weather sailor. There will be other days and you need a quick and safe passage home by land in case of bad winds which is the real problem in camping and boating.
     

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  5. philSweet
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    philSweet Senior Member

    Following along on Alan's thoughts, I would want to know how you envision the electric drive to be done. If Torqeedo OB and cheap wet led deep cycles that can be used anywhere and replaced anywhere, then figuring out where to put 700-800# of batteries (my estimate) in a small boat is near the front of the design spiral. On the other hand, they could greatly help with stability, and might mean that for a given feel and sense of heft, you could go narrower on the beam than a 4 stroke OB version. At any rate, primitive hulls and electric drive don't usually go together because the initial price of the electric setup suggests a more sophisticated hull as part of the trade-off.

    What sort of recharging are you thinking about? That has a huge bearing on system cost and battery choice. Keeping with the dead simple series 27 deep cycle batteries at 36 or 48 volts, the charging system alone could cost as much as an outboard - or you could use a golf cart charger for $600 or so. If you are going to go electric, you really need to pick out the components of that first, and design the hull specifically to accommodate (and take advantage of) it's space and weight requirements. With a small gas OB, you can afford to be a lot more cavalier regarding the hull.

    As ballast, I figure batteries have a density of about 2 based on the volume you reserve to put them in. If you plan to line the battery box with lead sheeting, that can go up a bit to 2.3 or so. You need very good access to the batteries and traction batteries should be thoroughly rinsed down with fresh water regularly. I'd probably go with an automatic watering system as well.

    If by a cuddy cabin, you mean two adults can sit facing each other in the cuddy, with the kids further forward, I suggest you start by drawing the cross section through the seating area and wrap the boat around that. I figure 66" separation between the back of their heads, and about 4' to the top of their heads, with an additional 8" clearance required on the centerline. Maybe some other members can confirm or improve upon these numbers.
     
  6. alan craig
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    alan craig Senior Member

    I can confirm that my leisure batteries for a small electric boat have a density of 2.3, and I agree that it would be a great idea if designing for a lead acid battery electric boat to take advantage of the weight as ballast.

    What does series 27 mean? Here in the UK lead batteries are just referred to by their Amp hour capacity.
     
  7. kerosene
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    kerosene Senior Member

    thanks everyone. Tom's boats have the right low key attitude.

    As nice of an idea electric drivetrain it might just not make any sense and seriously handicap the vessel. Even if going for self made setup - with a lot of time invested - and thus improved efficiency the battery bank is quite limiting.

    5hp Honda can be rigged with remote steering and will offer tons more flexibility in terms of range and speed.
     
  8. kerosene
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    kerosene Senior Member

    size 27, at least one I found was 105 Amphours (at 20h rate). with more googling it seems that it really does vary (saw 86-105Ah).
     
  9. Horsley-Anarak
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    Horsley-Anarak Junior Member

  10. tom kane
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    tom kane Senior Member

  11. BobE
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    BobE Junior Member

  12. tom kane
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    tom kane Senior Member

    I have been searching for the Popular Mechanics book which gave me the basis for the boat I built for shallow water camping shown in my no 19 post left side image with retractable shaft drive.
    It was called lilypad in PM mag, a flat bottom punt styled roomy craft which I changed to a 6 inch constant dead rise bottom continued right up to the quarterdeck.
    It was the most comfortable boat to do all-round boating very stable and easy to handle and safe in heavy sea conditions.If any one has seen that mag I would love to know about it. I built it right side up to start so I could see how to easily modify the plan then turned bottom up to do the bottom. The transom and some forward frames were built first then the rest was designed and added as needed just on a flat concrete floor.
     
  13. SamSam
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    SamSam Senior Member

    I don't know if you've seen this, but if you know the approximate time of publication, it shouldn't be too hard to find.

    http://books.google.com/books?id=ZNsDAAAAMBAJ&source=gbs_slider_gbs_user_shelves_1004_homepage

    Here's the main site...

    http://books.google.com/books?as_list=BDa7KskMQrpXLnYTzlJs3GhQqK0khMkhWhzxW_AFvWVcie6AD2Q
     
  14. tom kane
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    tom kane Senior Member

    Low power day boat-protected waters

    Thank`s SamSam I have been browsing through online PM book`s many times but not come up with edition with lilypad build yet.I have tried lots of search words it is possible it may have been a similar publication (can not remember what) that I found the article in a friends mag.
    I would love my old build boat back so great to use and keep tidy and no costly maintenance.It was built from saving up David Brown tractor cases which the timber was probably imported into the UK from USA so it travel well and I still have several pieces so the design had to suit the free timber and the ply was 3/8 thick and the boat had to fit on a standard trailer.
     

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    Last edited: Mar 2, 2015

  15. BobE
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    BobE Junior Member

    I saw that last article I posted while looking at a little ice shanty in the Feb, 1960 issue. It reminded me of this thread.
    I have a popular mechanics encyclopedia set from the 70's. All the articles in it came out of the magazine. There is one particular pontoon boat article that I was telling someone about. I tried to look for it in google books so I could give them a link, but it wasn't there. However, there just happened to be someone on ebay selling the issue that article was in and they had listed the article in their description. I can't remember which issue it was now, but when I looked it up in google books the pages the pontoon article was supposed to be on were missing :confused:
    I wasn't about to give away part of my full set. So. I took pictures of that article and put it on scribd.
    https://www.scribd.com/doc/228527225/Pontoon-Boat-for-Summer-Fun
    Maybe somebody ripped out their favorite boat building articles sometime before google came along with their scanners...
     
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