Bolger Bantam : Direct 50 % scaled up version........

Discussion in 'Boat Design' started by boat fan, Sep 7, 2009.

  1. boat fan
    Joined: Sep 2008
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    boat fan Senior Member

    WoW ! Many thank s Rick for taking the time to reply .

    I think I understand that concept Rick.It was the larger central "box" on the Bantam

    Rick , do you think this would make the boat more sensitive to rocking at anchor ? I`m thinking wakes from passing

    I would think 30 ft max is "doable" within a reasonable time frame if the boat is not too complex of form or shape. I`m not set up for steel construction , but partial to wood /plywood ( plank on frame or even stich and glue or a combination of ) i have the tools for that.

    The load carrying target....I `m not real sure about that Rick I think I will have to research similar boats and see what is required for a couple to liveaboard .plus maybe a spare double for the occasional visit by grown up kids ....

    It`s very kind of you all to reply to this.Thank you again.

  2. boat fan
    Joined: Sep 2008
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    boat fan Senior Member


    Thank you PAR I`m going to study those drawings for a while in order to get a handle on the kind of displacement required to float what I think I will need...

    You are all most kind !
  3. Matt.D
    Joined: Oct 2007
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    Matt.D Junior Member

    Gday Boat fan , I build houseboats up on the gold coast. I build in steel and have just taken on a new product that coats the steel renders it rust proof and has anit foul propities so u never need to pull it out the water.
    Have a look at my webpage
    I have a 40ftr on the go at present but can build what ever size u like and to any stage. Ignore the price guild on there as things r a bit slow at mo so will do u a very good price save u a lot of time and headacke!
    Feel free to give me a call 0405184081
  4. Guest625101138

    Guest625101138 Previous Member

    The boat will flop roll if the outboard hulls are set too high and you are beam-to. This is annoying. The hulls can be shaped for gradual immersion to cover the normal loading range to avoid this.

    My only hands-on experience with this hull configuration is in pedal boats up to 7.2m long. My objective with these is to minimise drag while having a stable and comfortable platform. This is the latest variant:
    At this scale the motion is better beam-to than a catamaran of similar beam. The roll over the crest of a wave is not as severe as the cat due to the combination of roll inertia and the small waterplane of the central hull.

    You have not indicated the speed you are aiming for. At some point a catamaran will provide lower drag for the displacement than the stabilised monohull. As target speed goes up it can be advantageous to load the outboard hulls to make a trimaran. This concept from Marshmat evolved along these lines:

    Rick W
  5. boat fan
    Joined: Sep 2008
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    boat fan Senior Member

    Yes, I think I understand Rick. That suggests flare to the outside hulls to me..possibly a vee bottom , or both

    As to speed Rick :Not in a great hurry :D

    Having said that , the NSW central / South East QLD coast offers some lovely waters to explore.Trouble is , so has the Sunshine coast , a little far to go with a slow boat between harbours.Not good if you get caught by bad weather.

    If you had a boat wider than 8 ft trailing width it would be handy if you could push a little harder to reach safety along the way.Given prudence and caution and a favourable weather window , it may be "doable."

    If on those rare occasions you were required to throw some extra $100.00 bank notes over the stern in the form of fuel receipts , in order to get there be it I guess.:rolleyes:

    Is there a specific thread relating to the efficiency issues you mentioned , particularly about when a catamaran becomes more efficient than say the stabilized mono or Tri. ?

    I`m asking because it would save you from having to repeat all this again...I could see that becoming rather tedious very quickly...:rolleyes:


    That pedal boat of yours looks VERY efficient Rick !
  6. Guest625101138

    Guest625101138 Previous Member

    I do not know any thread that covers the specific issue of what hull configuration provides the lowest drag for set contraints. The analysis does not take that long if the displacement and design speed are estimated accurately or specified.

    The ideas I am working on are for safe coastal cruising and are self-righting so beam is restricted to achieve this. I also want something that is trailerable and easily handled by one person.

    Your fast cruise requirement probably translates to around 12 to 15kts given the coastal hops in NSW. Once on the Queensland coast shelter is never far away.

    The best basic configuration will get down to the weight. Lighter will favour the stabilised monohull. Building really light is expensive when it comes to carbon fibre for example. But it would pay you to get some experience with foam/glass composite in flat panel. My view is that this is easier than wood to build light and strong and it requires less maintenance.

    There are existing designs along the lines of the stabilised monohull if you search around. One might suit your requirement. I would be wary about simple scaling of an existing design because there are bound to be unintended structural weaknesses.

    Any boat that you aim to live aboard will have a cost similar to a small house to build. You need to be reasonably clear on what you want from it before embarking unless you have that sort of money as petty cash. If you just want to go boating then taking a close look at the second hand market pays right now.

    Rick W
  7. Guest625101138

    Guest625101138 Previous Member

  8. boat fan
    Joined: Sep 2008
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    boat fan Senior Member

    Thank you Rick.

    I think your speed estimate of 12 - 15 knts is spot on.

    You know , these days I cut lawns that no one plays on , maintain a pool that no one really swims in , keep the gardens looking good for passers by ,
    and as there is only two of us here now , we really only use one end of this house .We have " stuff " and furniture and floor space we don`t need.

    The car gets little use , we use bikes more and more...

    We have both come to the conclusion that it would be quite "liberating "
    to lose all that "stuff"....:D

    I don`t think carbon will be included in any future build Rick...I`m not that dedicated to pair down weight . Foam could be a possibility , insulation built in .....Maybe resin infusion on a vac. table ??

    Given the land prices these days , I think you could probably do this for less than a house .

    I`m off to the displacement powerboat thread ......:D

    Best regards , BF
  9. Guest625101138

    Guest625101138 Previous Member

    I was not including the land. Given the land prices in some locations you would be building a boat that would be anti-social in the extreme. Something like the floating gnomes seen constantly adorning the marinas these days. (Shane Warne and his ex have just paid AUD3.5M for a block in Melbourne. It has a house but that will be bulldozed to make way for his new palace.)

    There is quite a lot of detail on flat panel construction on this thread:

    This photo series goes into more detail on the actual panels albeit in CF but same process for glass:
    The associated blogs cover a lot of building detail. The workmanship has been first class although neither of the guys involved have built a boat in this style before. That said they have experience with CF in planes. bikes and moulded boats. It would come close to the most expensive boat per unit weight you will find. Materials alone in the hull cost a small fortune and the end result weighs about 60kg without any fixed fittings.

    I shifted my focus from chores around the garden to making little boats about 7 years ago. The garden is now littered with boat hulls and the garage has some decent metal working tools. The garden became a source of frustration and disappointment once the drought set in here in Melbourne. I am lucky to drag the mower out once a month and then it is primarily a convenient source of exercise.


  10. Guest625101138

    Guest625101138 Previous Member

    I will also make some comment on losing all that "stuff".

    My father always wanted to do that but my mother kept him connected to the reality on his smoking related health issues. On the other hand there were two acquaintances of my family who had better health and more obliging partners who took the plunge. Sold their houses and purchased houseboats to mooch around Moreton Bay.

    One got out within six months as life was too monotonous. For the second couple, the first two or three years were quite enjoyable most of the time. Moreton Bay is wonderful to mooch around. However their time on the water was a period of dramatic property inflation. As the boat maintenance costs mounted and they could no longer afford it they found the boat value had deflated substantially and house prices had inflated. They could no longer trade their way back into land-based accommodation - even a little unit. They ended up living with a daughter until shoved off to aged care.

    So if you make the big move make sure you have an escape route under your control. Do not count on any value returning from the boat.

    I get immense satisfaction from my pedal boats. If you like bike riding you will love pedal boating. It is way less stressful. You get the endorphin high without any stress.

    My wife has never tried one of my boats but she did have a go on a friends two person Nauticraft last year and found it enjoyable. She held around 5kph with Mike photgraphing me zooming around in his racing boat. We spent about 3 hours on the water and an hour or so having lunch in a waterside restaurant: Union RW 2008-05-24/index.html
    The NSW and Queensland coast has a wonderful array of rivers and protected waterways that suit pedal boats. My style is to enjoy the exercise and serenity on the water and then accept the comfort and security of a hotel room (This is what I do for the Murray Marathon). If you do the maths, the earnings from $100k in a steady investment, that would be spent on a decent live-aboard boat, will pay for quite a few nights in 3 or 4 star motel rooms in the coastal towns. Could be a way to work into boat building and enjoying the water before you make the big plunge.

    Rick W
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