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

[boat fan]

Intended use : Sheltered estuaries , lakes , inlets , and rivers along Australia`s East coast.

Scaled up 50 % , as is ....please comment , good , bad ......neither......
or .......Stupid Idea..............:D .
http://f1.grp.yahoofs.com/v1/cK-kStolMZOlps--_wVdi97wCYiH_1IT8IG2hO3qr5NHEAGlLjilzp1JRJqXveQGLY6SlQ9XnxYtiml08XmS6DONYzD-i27_YLj8dw/Bantam%20%23654%20Houseboat/bantam.jpg

[boat fan]

http://4.bp.blogspot.com/_a3OWaTvBM3g/SQRhubCo_QI/AAAAAAAAA0E/7b_YsBov56A/s1600/IMGP3749.JPG

http://www.boatdesign.net/forums/attachments/boat-design/22798d1214543711-catamaran-living-aboard-bantam1.jpg

http://www.boatdesign.net/forums/attachments/boat-design/22800d1214543752-catamaran-living-aboard-bantam3.jpg


http://www.boatdesign.net/forums/attachments/boat-design/22799d1214543731-catamaran-living-aboard-bantam2.jpg

http://4.bp.blogspot.com/_a3OWaTvBM3g/SQRhubCo_QI/AAAAAAAAA0E/7b_YsBov56A/s1600/IMGP3749.JPG
Edit...pictures not showing...

[lewisboats]

bunch of additional displacement... but otherwise interestingly revised

[boat fan]

bunch of additional displacement... but otherwise interestingly revised

Yes ...Agreed.

Is that necessarily bad though ? I`m thinking the additional buoyancy of the hulls would carry the extra materials ( weight ) of the larger boat.

[GAZZABO]

I seem to remember reading somewhere it was OK to plus or minus 20% on an existing design without altering the factors to much to make the design perform differently. I remember a friend spacing out the frames of a Roberts from 60 to 85 ft and was surprised that the angle of the stem raked a lot more!( there are frames in the bow area!)

[boat fan]

I remember a friend spacing out the frames of a Roberts from 60 to 85 ft and was surprised that the angle of the stem raked a lot more!( there are frames in the bow area!)

Yes I think you would have to be careful doing something like that.
I would not have the nerve to alter a project of that magnitude.
Better to choose an existing design , or get a N A to draw what works....

Scaling a large and beamy monohull opens a pandora`s box when you consider the changes induced by heeling waterlines , wetted surface areas and reserve buoyancy etc..etc..
Thank god there are people that know how to work those calculations .A job for the experts no doubt.:D

What I`m particularly interested in with the Bantam is the behavior of the vessel if scaled up.It seems to me , given that the hulls are little more than elongated pointy boxes , the boat should function as before .

I`m hoping some of the designers on this forum will give some insight ...

I think most of them would consider this particular boat a little too "crude" to be worthy of comment , after all long elongated box hulls are not that " sexy " by most people`s standards.I still like it for its utalitarian simplicity and despite it`s scaled up size , I do believe it would not present any great difficulties for a dedicated home builder with tool skills.

Best regards ..BF:)

[PAR]

The laws of mechanical similitude will apply here and you'll be quite disappointed with the results.

These laws also apply to the loads on the structure as well.

What does all this mean, well simply, put you'll be converting this one ton boat to a 4 ton boat, so you can kiss off any idea of powering it with a little 25 HP outboard or easy trailering.

It would be much easier to just find a 24' design that more closely satisfies your needs.

[boat fan]

The laws of mechanical similitude will apply here and you'll be quite disappointed with the results.

These laws also apply to the loads on the structure as well.

What does all this mean, well simply, put you'll be converting this one ton boat to a 4 ton boat, so you can kiss off any idea of powering it with a little 25 HP outboard or easy trailering.

It would be much easier to just find a 24' design that more closely satisfies your needs.

Thank you PAR.

This is what I need to know.

Unfortunately there seems very little on offer as far as plans go ...
some scow houseboats perhaps...

When you say " you'll be quite disappointed with the results " ,
are you referring to speed , handling , fuel economy or other , or all the above ?

I must admit the increased loads worry me more than a little.

So whats " out there " for a modest self build houseboat / pontoon boat 25 - 30 ft if anything....?

[liki]

o whats " out there " for a modest self build houseboat / pontoon boat 25 - 30 ft if anything....?

http://bateau.com/proddetail.php?prod=GT27 perhaps?

[boat fan]

http://bateau.com/proddetail.php?prod=GT27 perhaps?

Yes thank you liki.

I have looked at that one too.

Probably a good way to go.

[Guest625101138]

.,.....
I think most of them would consider this particular boat a little too "crude" to be worthy of comment , after all long elongated box hulls are not that " sexy " by most people`s standards.I still like it for its utalitarian simplicity and despite it`s scaled up size , I do believe it would not present any great difficulties for a dedicated home builder with tool skills.

Best regards ..BF:)

There is nothing wrong with hard chines. A lot is written about the fundamental advantage of a half circle hull form to get the minimum wetted surface but this is only part of the story.

When you start to get into wave making it is the slenderness that counts. So a section that produces large volume for beam is advantageous.

My view is the best shape for low power at modest speed is a stabilised monohull. It takes this Bolger concept to the extreme. The outboard hulls normally sit above the water level and only come into play to provide stability. You can get very easily driven hulls.

If you set some design criteria such as length, beam and target load carrying plus accommodation I can give you a hull shape to think about.

Here are a couple along these lines:
http://www.boatdesign.net/gallery/showphoto.php/photo/15019/size/big/cat//ppuser/18624
http://www.boatdesign.net/gallery/showphoto.php/photo/14408/size/big/cat//ppuser/18624

Rick W

[PAR]

You may like my RYD-23.2 design. It's 26' on deck, 7' beam and does well with modest outboard power. You can see several of the configurations for this hull. It has twin skegs aft to permit her to take to ground bolt upright and the engine lives in an enclosed well out of sight, no smell and much reduced noise.

Or you may consider a larger version of the same idea. RYD-29.6 is available in three beams 7', 8' and 9'. The 7' (a) and 9' (c) versions are shown. The 7' version is very efficient and requires little power to get to hull speed. The 9' version is a bit more decadent, but has considerably more internal volume (elbow room).

All are hard chine, simply built and will make fine power cruisers.

[wardd]

par do you have a web site?

[messabout]

Par; Nice presentation of a superbly practical boat. I reckon that the smaller one would prosper with modest (spell economical) motive force. It would be near perfect for cruising the Harris Chain, the St. Johns from Sanford to Jacksonville, and other liesurely cruising. She could do a mile in ten minutes with almost no fuss, wake, or noise. Ahh, Paradise. To hell with Donzis, metalflake bassers and jet skis.

[PAR]

Nope, I haven't gotten around to a web site. Hell, I'm lucky to get the grass cut before I get yelled at. Drop me an email if interested.

The narrow version of 29.6 is an especially efficient shape. Long drawn out lines make for easy motion, no wakes and small fuel bills. It's a little big for most folks to feel comfortable with any more, but it's a size that was once very common for commuting and short trips. You do have a lack of elbow room for all the efficiency, but everything is a trade off. This would be a good hybrid or electric power craft.

RYD 23.2 is a little more bang for the buck. It's a size most can be comfortable with, can tow with a mid size car and will not force you to get a second mortgage to pay off the building materials.

The wide version of 29.6 is an attractive riverboat. There's a model of this one under construction by a fellow in North Carolina, that I can't wait to see. It would make a nice bachelor pad.

[boat fan]

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



When you start to get into wave making it is the slenderness that counts. So a section that produces large volume for beam is advantageous......
Rick W


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

The outboard hulls normally sit above the water level and only come into play to provide stability.

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

If you set some design criteria such as length, beam and target load carrying plus accommodation I can give you a hull shape to think about.

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.

[boat fan]

http://www.boatdesign.net/forums/attachments/boat-design/34755d1252413191-bolger-bantam-direct-50-scaled-up-version-ryd-232all.jpg



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 !

[Matt.D]

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
www.myspace.com/budgethouseboats
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

[Guest625101138]

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

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:
http://www.boatdesign.net/gallery/showphoto.php/photo/15138/size/big/cat//ppuser/18624
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:
http://www.boatdesign.net/forums/attachments/projects-proposals/31875d1242837935-trailer-cruiser-revisited-trimaran-019-stbd-qtr.png

Rick W

[boat fan]

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.
Rick W

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


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:

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 .....so 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:

http://www.boatdesign.net/gallery/showphoto.php/photo/15138/size/big/cat/ppuser/18624

That pedal boat of yours looks VERY efficient Rick !

[Guest625101138]

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

[Guest625101138]

This thread covers the topic of hull configuration for a 5 to 6m boat with design speed of 10kts:
http://www.boatdesign.net/forums/boat-design/hull-design-small-displacement-boat-28618-5.html
In this case a catamaran is lowest drag but Martin likes the connected look achievable with the tri and, in its best form, is not much different to the cat. The idea is still evolving and he is yet to post the latest rendering.

Rick W

[boat fan]

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

[Guest625101138]

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


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:
http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-8.html

This photo series goes into more detail on the actual panels albeit in CF but same process for glass:
http://picasaweb.google.com/adventuresofgreg/ExpeditionBoatBuilding#
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.

Rick

[Guest625101138]

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:
http://snorlax.lampi.org/images/Lake%20Union%20RW%202008-05-24/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