Shanty boat build - self design BBC materials

Power Boats only. Please include the boat type in your question.
jbo_c
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Re: Shanty boat build - self design BBC materials

Post by jbo_c »

Thanks for the info ‘Nemo. We’re going to look into going for three nights in October or November. Our daughter lives in Orlando, so it will be a good way to break up a week long visit.

Love the pics.

Jbo

silentneko
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Re: Shanty boat build - self design BBC materials

Post by silentneko »

TomW1 wrote: Sun Jul 25, 2021 4:50 pm jbo a 9.9HP will be enough for you. I ran the numbers through my calculators and you would be fine. I assumed a weight of 4500lbs with the shanty, people, safety gear, food, and everything else. A 9.9 will be perfect and will allow you to cruise at a 5-6 mph without stressing the engine, top speed is 9mph. A 15 will give you a little safety margin with a top speed of 12. I used Yamaha outboards for my calculations. Mercury also has a 9.9HP Pro Kicker EFI.

I used 4500obs as Jauques listed 3000lbs as the DWL for the XF22 so I may even be light for your boat. You will need to keep a spread sheet to determine what your final weight is or weigh it on a scale once finished.

Wishing you the best and post pictures as you go.

Tom
Not to try and argue your calculations, but since he won't have enough power to plane won't he be restricted to hull length based displacement speeds? Assuming he has about 20ft at the waterline I don't thing he will be able to exceed 6mph with that low a HP outboard.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe, and an FS17.

jbo_c
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Re: Shanty boat build - self design BBC materials

Post by jbo_c »

Yes, if I stick with a displacement hull, I’ll be restricted on speed. Think Tom was referring to if I chose to use one of Jacques’ designs(XF or HB).

Then, in theory, I could run in a transition phase(incredibly inefficiently) and beat hull speed.

Jbo

TomW1
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Re: Shanty boat build - self design BBC materials

Post by TomW1 »

My calculations take any boat into account, once they go into it, it doesn't cares who the design comes from and depend on the inputs. Both boat and motor. Any flat bottom boat can be considered a planing boat by its design. To make it a displacement boat you you just reduce the HP. That is the advantage of a flat hull. My calculator I used your boat at 22' with a 20' water line at 4500lbs and a 9.9HP motor. It also showed ideal displacement speed of 6.5mph one of the calculations it throws out. So your puttering along at what you want will be fine.

Silentneko my calculators throw out many different calculations from max speed to best cruise speed for displacement boats. I don't control what they say but they are accurate.

jbo I still think you should build the XF22 hull as it fits your needs perfectly only 6" wider and already a proven design you don't have to mess around with, the design of your stringer widths/length, bottom strength, frame distances, etc. that is all taken care of for you. Just build everything to the height of the front and rear decks and put some type of railings like a house boat would have around the edge.

Well my thoughts worth 2 cents today and nothing tomorrow, :lol:

Tom,
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

jbo_c
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Re: Shanty boat build - self design BBC materials

Post by jbo_c »

So, Tom, a question I keep coming back to in one form or another:

How much efficiency is lost on a flat bottom that is immersed vs one that is designed specifically for displacement with the transom above the water line?

Put another way, if a person is building a boat specifically for displacement speed, why would he build a planing hull?

Jbo

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Re: Shanty boat build - self design BBC materials

Post by silentneko »

Best reason I can think of is draft. The flat bottom, or shallow V hulls will give you the ability to load up weight without a huge penalty. Cruising around its not needed, but finding safe harbor or gunkholes and beaching it's an advantage. Personally I'd build a planing hull just so I can exceed hull speed to outrun a storm, but I'll be running the coasts and might need to make long runs on occasion. Either way if your running a smaller motor and not stressing it then it will have great efficiency.
Built: 15ft Skiff, 16ft Skiff, Modified Cheap Canoe, and an FS17.

TomW1
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Re: Shanty boat build - self design BBC materials

Post by TomW1 »

He is correct the flat hull is more efficient. Add a keel, strakes, and spray rails on the edges to help in steering and maintaining straight line way on.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

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Re: Shanty boat build - self design BBC materials

Post by jbo_c »

TomW1 wrote: Tue Jul 27, 2021 12:59 am He is correct the flat hull is more efficient. Add a keel, strakes, and spray rails on the edges to help in steering and maintaining straight line way on.

Tom
So why would anything be built on a “displacement hull” then?

I’m not trying to be argumentative. Just want to understand. I’ve always read/learned/been told that displacement hulls were the most efficient because the immersed transom on a planing boat creates drag at displacement speeds. Has physics changed over the last few years? (That last one was in jest.)

Jbo

fallguy1000
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Re: Shanty boat build - self design BBC materials

Post by fallguy1000 »

Xf22 requires too much horsepower with 70 at Mertens low end recommended.

The gt23 is a great design with a larger displacement houseboat hull option.

The xf22 is the wrong hull for what he wants.

Build a gt23 houseboat version; power it with the old evinrude 18 until you decide or must replace.

I had an old Evinrude 18 and it died when I forgot to add oil to a 6 gallon tank fill up. Broke the crank right in half.
My boat build is here -------->

viewtopic.php?f=12&t=62495

fallguy1000
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Re: Shanty boat build - self design BBC materials

Post by fallguy1000 »

jbo_c wrote: Tue Jul 27, 2021 9:03 am
TomW1 wrote: Tue Jul 27, 2021 12:59 am He is correct the flat hull is more efficient. Add a keel, strakes, and spray rails on the edges to help in steering and maintaining straight line way on.

Tom
So why would anything be built on a “displacement hull” then?

I’m not trying to be argumentative. Just want to understand. I’ve always read/learned/been told that displacement hulls were the most efficient because the immersed transom on a planing boat creates drag at displacement speeds. Has physics changed over the last few years? (That last one was in jest.)

Jbo
A displacement hull is not designed for speed, but for loading. Big people, water tanks, waste tanks, kitchen sink, kitchen stove. Sure, a planing hull can have all that, but the engine power requirements are great and then fuel burn is as well.

A planing hull is not right for your plan. Tom is mistaken, but he is a great guy and offers lotsa help on props for people and we can give him a break here.
My boat build is here -------->

viewtopic.php?f=12&t=62495

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