FAT BOY DESIGN "what do you think ?"

[Buckie]

Hi Guy's ...can anyone see the obvious faults with this design ?
I'm sure there are some but me not being very Boaty...hmm

I plan to build it, its called "FAT BOY" just as soon as I can find somewhere cheap to rent.

I've a few questions though, which I'm hoping you can help.
What is the normal range of a cruiser.
Is 1" thick the norm for gelcoat and 1" fibreglass, plus fibreglass/gelcoat inner.
Is there a standard width/beam for entry into marinas. (Fat Boy is 4m)






Cheer's guy's

[Nojjan]

I think it is fantastic, please go ahead and build. Just make sure to update the forum on progress. Please post a video on the sea-trial...

[Frosty]

Forgive me for pointing them out, but the obvious faults are what exactly?

[Buckie]

I was expecting people to say this looks wrong or having 2 fin things will just slow it down...We had a little compertition to design a 30-40 foot boat, it had to be stable in rough water but had to be fast through the water and look good. I done this during a wild life program about Whales, it only took the length of the documentary to do in Ms Paint, obviosly it will now have to be done in a CAD proggie but should begin by the end of the year,I'll run a video of the build too right through to sea trials....

cheer's

[SamSam]

It looks wrong for having 2 fin things that will just slow it down. What is all that structure below the waterline supposed to do? The top view looks fine, the front view looks pornographic, the side view makes me wonder what is all that structure below the waterline supposed to do? You might want to build a model and try that first.

[marshmat]

Hi Buckie,
Definitely think about building a model. It's difficult enough to simply visualize a shape like that, let alone predict how it will behave.
To be honest, I don't think it would look out of place in the shuttle bay of the Starship Enterprise. If it's intended for on-water use, you might find it helpful to drop by the local boatyard around winter haul-out time and take a look at the undersides of boats that see similar types of use to what you're thinking of doing with it. You'll find that hull shapes have evolved particular combinations of attributes, which are different depending on what the boat is meant to do. Working from something that is known to perform well, will likely prove less expensive and frustrating in the long run than trying to create something radical and new out of thin air.

[Buckie]

I never thought about a model...cheer's I'll get on to it right away. I live on a marina and there are plenty of boats out of the water all with different types of hulls. the underside , as I explained was for room, and glide through the water, just like a whale, or so I think, In rough weather you dont see a whale rolling about, so I thought it must be its shape, but I'll see what the model shows up...

cheers

[Frosty]

You finished with the rafts now then?

[PAR]

I'm not sure what you're attempting to accomplish, but I can see dozens of things wrong with this hull configuration, the least of which will be the huge HP requirements just to push such a burdensome craft at displacement speeds, let alone any faster. What is your target top speed and calculated displacement, say with full tanks, a full compliment of crew and supplies? I can only imagine what kind of wave train this shape would produce, but it will very likely be dragging quite a hole.

[rwatson]

Top marks for creativity. It would be a great PR stunt if you left it on the trailer.
I think the previous comments about its actually working , and the suggestions to build a model are a very kind way of letting you know it aint going to work as a boat though.
Do the model by all means - I think you will look back on it in years to come as an imaginative start to a great design career.

[Jratte]

The problem with designing a boat like a whale is that it isn't going to move like a whale. A whale is generally spending it's time with most if not all of it's body and mass below water. You don't see them bouncing around in high seas because they stay below water where it is much calmer. Whales are not designed as surface vessels. Also they use their body to provide propulsion. This dictates it's shape as much as it living under water. If you want to build a submersible vessel that will propel itself in the manner of a whale then by all means look to the whale for design ideas. For surface vessels, and your first or one of your first forays into design, well all I can say is "if it ain't broke, don't fix it" and "don't reinvent the wheel." Basically take a look at other boats that meet the goals you are trying to accomplish and see how they met those challenges, especially if you intend to build from the design.

On the other hand if you never intend to move past the drawing/model stage then by all means, draw all the curvy lines you wish. You may not discover and wildly new Naval Architecture principles but you may better understand existing ones. Best of luck.

[tom28571]

While basic principles should not stifle creativity, they should, at least, provide guidelines of what is possible. Since you asked, what are "obvious faults" with your sketch, here is one. Notice that I don't call it a design, but a sketch.

Look at what part of the boat must be under water to make the boat stable at rest, and draw a waterline. Then calculate or estimate the displacement required to make the boat float at that level.

That should offer some clue as to one obvious fault.

[lewisboats]

What Tom is suggesting is that for every cubic foot of water the underwater part of the hull displaces or occupies it has to weigh 64 lbs in salt water. Assuming that the waterline is above all the bumps and bulges but below the "nose" in the bow...you have a massive amount of displacement for the size of the boat... on the order of 70 + tonnes (2240 lbs/tonne)! I arrived at this figure by multiplying the length by the beam by half the height then dividing the result by 2 ...multiplying it by 64 and then dividing by 2240. Actually...my eye suggests that dividing by 2 is being generous...but anyways.
to push this to hull speed... which by the shape would only run around 6.5 kts {1X sq root of hull in ft =6.5} I would expect you would need significant more hp than something that is a bit more friction and resistance friendly. I would be willing to bet whatever I might make during the rest of my working life that you couldn't PUT enough horsepower into that to get it to plane.

Steve

[tom28571]

Steve, I was trying to be generous and thought the displacement would be less than you state.

No matter, and not wishing to insult Bucky, I do expect that it would be a slug of the first order. With all that weight and all those convex underwater surfaces, a lot of power would not only not cause it to plane but would more likely suck it to the bottom. Best to find out now before any real resources are wasted.

Aesthetics is a very subjective issue and I won't offer any opinion on that.

suck = negative lift or reduced pressure

Keep at it, Bucky, but get some fundamentals on board.

Best Tom

[lewisboats]

Even if it was half what I came up with...that's still 35 tonnes or over 78 THOUSAND pounds or 35000 Kilos in a 42.25 ft boat...Burdensome is an understatement! A couple of 1000hp turbo diesels to push it might give it a fifth of that displacement. Time for a bit of Study in the subject...as you suggest.

Steve