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Old 08-28-2016, 10:50 PM
standman standman is offline
 
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50' Length by 16' Beam Power boat

I would like to build a 50' x 16'. It needs to achieve a cruising of 20 knots and max at 25 knots and able to carry up to 5 tons. There will be occasional chop up to 3 ft. Shallow draft would be ideal ( 3 ft. max). I am considering sort of this tunnel hull. I'm not sure if it is termed correctly. Has anyone tried this? better off with a cat or stabilized monohull?
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  #2  
Old 08-28-2016, 10:57 PM
Mr Efficiency Mr Efficiency is online now
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Is that what is sometimes called a "monomaran" ? I have been in a somewhat smaller boat roughly along those lines, which was inclined to wander around annoyingly if the sea was on or near the beam.
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Old 08-29-2016, 04:31 AM
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PAR PAR is offline
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Welcome to the forum.

That's a really poor set of hull shapes to employ on a 25 knot boat, particularly a large one. I find little redeeming about it, frankly.

Establish the goals of the boat first, then see if they can be met with a known design. Once you've found it, buy the plans. Designing 50' yachts or working craft isn't easy, unless you want little more than a barge, don't care how much it'll cost to build and it doesn't matter much how well it'll perform. If you do care about these things, you'll need some pretty specific and serious engineering skills. How's your math?
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Old 08-29-2016, 04:39 AM
TANSL TANSL is online now
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The construction of a hull with such complicated shapes, so hard to build, with a so irregular curve of frames areas, should be justified by the urgent need to achieve a very particular goal. Besides the aesthetic reasons that might influence your decision, could you explain what is that, so special, that you want to get?
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Old 08-29-2016, 05:03 AM
standman standman is offline
 
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Thanks for the welcome PAR. Read a lot here, but just now posted. I have "established" my goals.

TANSL - It will definitely be a challenge to build. With that aside, I just wanted to get opinions if the shape makes it more stable. Will the cat like stern generate lift or just create more drag. Will the lines create too much turbulence? For ease of build was thinking of just doing a 50x12' mono with a variable deadrise. FYI- Aesthetics is not considered.
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Old 08-29-2016, 05:29 AM
TANSL TANSL is online now
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Irregularities in the submerged hull could create problems, hydrodynamics does not improve.
If you need large initial stability, go to a catamaran.
If you need a high tons per centimeter of immersion, go to a monohull.
If the various loading conditions give rise to very different displacements, do not use a catamaran.
Whatever the stability of the hull, you can not know if it is enough until you know how you want to load the boat. You could get problems due to low stability or at too high stability (large righting arm).
Therefore, untill knowing what is what you want to do with the ship, no one can give valid advice on the type of hull and its shapes.
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Old 08-29-2016, 02:52 PM
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Quote:
Originally Posted by standman View Post
. . . I have "established" my goals . . .
If you post them, we can offer more definitive comments about the suitability of your hull, though honestly, that shape has nothing going for it, particularly if you want to hit 25 knots. Simply put, I doubt you'll be able to drive that bulbous forefoot over the bow wave, without huge amounts of power, which seems self defeating at best, on a 50' boat with a 25 knot requirement.
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Old 08-29-2016, 03:07 PM
Squidly-Diddly Squidly-Diddly is offline
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How about a scaled up Panga (outboard), or Lobster Boat (inboard)?

Sounds like you would be hauling cargo, so a very big Panga sounds right.

Wiki says the 28' models can carry up to 5 tons.

If you don't need to worry about waves over 3', maybe stretch an existing 28' design about 4'.

Then you will get a well sorted out boat and save lots of fuel and building and design costs.



http://no1pdfplans.de.vu/diyboatplan...at-plans-4.jpg
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Old 08-29-2016, 06:58 PM
standman standman is offline
 
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I need to use a diesel inboard. Lobster boats have a deeper draft.
50' x 16' can do 50 by 12'
cruising of 20 knots and max at 25 knots
able to carry up to 5 tons.
handle occasional chop up to 3 ft.
Shallow draft 3 ft. max - i know i can use jet drives, but would rather not
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Old 08-29-2016, 08:03 PM
tom28571 tom28571 is offline
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OK, taken as a whole, it is a strange shape that does not have much potential to carry 5 ton at 25kts. The buoyancy distribution is not ikeanything I'ver seen. What the reason for the strange transition between such contrasting hull shapes could be escapes me. On the other hand, if the forward shape were caried well aft and blended into a more normal tunnel shape, it would not look so different from other fairly common hulls.
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Old 08-29-2016, 09:41 PM
Mr Efficiency Mr Efficiency is online now
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50' with 20+ knots, 5 ton load capacity, will need a sizeable engine.
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Old 08-29-2016, 10:58 PM
JSL JSL is offline
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All good advice from Par & Tansl
One idea, consider a conventional planing hull with twin diesels & props in partial tunnels. Done a few from 40 to 60 ft for whale watch etc.
one problem is that 20-25 knots on this size boat is around minimum planing speed & not that efficient but that you just have to live with.
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Old 08-29-2016, 11:33 PM
Stumble Stumble is offline
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I would guess almost any currently available 50' displacement power catamaran would work fine. Just strip the cabin and other cruising type gear and install cargo handeling gear instead. You should have more than enough cargo capacity.
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  #14  
Old 08-29-2016, 11:42 PM
Mr Efficiency Mr Efficiency is online now
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Originally Posted by Stumble View Post
I would guess almost any currently available 50' displacement power catamaran would work fine. Just strip the cabin and other cruising type gear and install cargo handeling gear instead. You should have more than enough cargo capacity.
He wants a single diesel ?
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