What floats your boat.

That's what makes the boat float which is to make the structure light as possible such as the Myark folding trailer barge pictured is manufactured from 3mm 5083 with strips of 5083 cut into 50mm X3 mm for the stringers placed 80mm apart and making the cross members also from 3mm 5083 placed 800 mm apart.

This cuts the weight down and with the flat bottom area that allows to float in less than 2'' of water with out load, with two 30 hp out boards it plans at 25 knots because its practically siting on top of water already, how ever it needs a slight kick up on the bottom of the back hull so it rides level with the water surface when front rises when planning.

 

w

Post #6 includes other needs to be discussed with customer.
The boat is to be used for family,camping, fishing, water skiing and general family fun.The boat must be robust and capable of dragging up beaches.
The boat must be capable of being used to sleep two and live aboard.
Propulsion main unit to be four cylinder petrol inboard engine closed water cooling (suggest the need for handling under power).

 

I have just had a talk with the customer and he does not want a flat bottom boat, he says there is lots of rocks on the beaches he uses and thinks that a flat bottom boat will be damaged by the pressure points of these rocks all over the flat bottom when people are sleeping and living in the boat. He suggests that a hull bottom with a 6 inch dead-rise
v form will allow the weight of the boat and contents to sit on the beach along the length of the hull. He says he can put a couple of logs or sand each side of the hull to make it stable and also he can put driftwood under the bottom of the boat to move it up the beach if needed. He says he does not want a deep keel or any rub strips on the bottom of the boat just a half round metal strip to run on the trailer rollers..So a flat bottom boat is out.

 

what floats your boat

You have a big fat bottom there myark with plenty of buoyancy.Buoyancy is king especially with a life jacket to add to a body to help lift it up in the water.

 

Because Myark folding trailer barges are able to carry the towing vehicle such as a camper van or some circumstances a luxury caravan, its able to beach in shallow waters allowing the vehicle to be driven off the deck such as a small island as in the youtube movie demonstrates http://www.youtube.com/watch?v=DDfSuAtiVkQ
How ever as you say if the load is on the deck and is beached and rocks are under hull, it can damage,
My solution for this was to place similar to which scaffolder uses and have wind up scaffolding tubes in each corner of he hull.

For example on high tide say at great barrier island in a paradise bay, beach the barge then pin the scaffolding poles in each corner and make the deck level and when the tides go out then the barge stays level and no rock and roll, also because the scaffolding is adjustable it can also raise the front end so when tide does come back in the hull is completely out of the water and boat is always level.

 

For the same mass, a flat bottom will have shallower draft. There's no way around this.

I think you should consider taking your own advice...

If you provide a comparison drawing (like the two I gave above) I'll explain them for you.

Just as long as he's ok with the fact that this will increase draft compared to a flat bottom.

 

Rather late in the day I found the relevant paragraph on teachengineering.org.

The last sentence which refers to the plank that was eight feet long, nine inches wide, and 2 inches high, .... the plank would have six square feet of area ....... only one square foot the block has. It is clear that to keep it as simple as possible they were only considering the special case of an object with vertical sides and the area referred is that of a flat base.

In order that some good might come of this debate I shall be emailing teachengineering.org to inform them of the confusion that has arisen.

 

Tom is the "customer" you mention a real, live person other than yourself? Or is the "customer" either fictional or yourself, Tom Kane?

 

Less draft thru more compressed area.
Nail a carpet, a shaggy under your boat !

pogo

 

Leave your boat alone in the water long enough and nature will happily oblige.

 

This thread has been thrashed unmercifully. Correct information is blended with the not so correct. So far I have managed to stay out of the pissing contest. I reckon I will stick my oar in here too.

Here are some fundamental examples that are not based on any ones opinion. Just plain old arithmetic that is not subject to argument.

Let us draw some mental pictures of a floating object. That object could be part of a boat. To keep things simple I want to build a vessel that will support 100 pounds, an easy number. I know that I am going to push (displace) 100 pounds of water out of the way. I know that in fresh water I will need an enclosed volume of 2,770 cubic inches.

Let the chine beam be 48 inches, let the constant section be 20 inches long. I have a flat bottomed box 48 by 20 inches and in order to get the volume I need for 100 pounds the box will sink into the water two and seven eighths inches (2 7/8") SO we have a draft of 2 7/8" The wetted surface of the box will be 7.46 square feet. Therefore the unit pressure on the skin will be 13.36 pounds per square foot.

Case 2: Let the section of the boat have a vee bottom with ....say a one on four dead rise...that's about 14 degrees. The beam is still 48" but the draft will become 5.75 inches. Wetted surface will be 6.85 square feet. Unit pressure will be 14.55 pounds per square foot of skin.

Case 3: We could make a flat bottomed boat section with radius chines. Let the chines have a radius of 3.125 inches and so the draft will be 3 1/8 inches. Wet surface will be 7.16 square feet and unit pressure will be 13.96 pounds per square foot.

Case 4: Let the section have an arc bottom whose lowest point extends 4.25 inches below the chine. We have a draft of 4 1/4 inches. The ends of the arc join the sides at the waterline. (The radius of the arc is 68.3 inches) We are displacing 100 pounds with our 20 inch long section that has a chine beam of 48 inches. Wetted surface will be 6.79 square feet, and unit pressure will be 14.72 pounds per square foot.

It is easy to see that different section shapes, all designed to support a load of 100 pounds, vary in draft, wetted surface, and unit pressure on the skin. The only constant is that we have displaced 2,770 Cubic inches of water in every case.

Aside note for anyone who gives a hoot: The radius of an arc, like a cambered bottom or deck can be found by using this simple device. R = (4D^2 + B^2)/8B Where D = draft or maximum camber and B = beam or extent of the arc line (the chord). Calculating the area of the arced section needs some mental gymnastics but not enough to induce a headache. But many of you guys know all that

Where do we get 2770 for volume....easy. Divide 100 pounds by the constant 0.03611 = 2770 cubic inches. Derive the constant by figuring out how much water a cubic inch will displace. Divide 62.4 pounds per cubic foot of fresh water by 1728 cubic inches which gives us the constant 0.03611 pounds per cubic inch. A handy number to remember when drawing little boats on napkins at the club bar..

 

The images show typical heavy design flat bottom boats with keel and rub strips that are not needed if you want a shallow draft boat and just add to the weight and draft, note painted water line.
A shallow v bottom could be stronger and lighter,more comfortable in rough seas and be just as shallow draft with out the deep keel.

Without these keels and rub strips the flat bottom boat would be damaged all over the bottom and is hard to drag across sand and other surfaces among other disadvantages such as bad rocker design which cause more pounding in
rough waters.

 

We are discussing boat design for What Floats Your Boat and customers are real for a good light shallow draft boats that has many improvements over traditional copy cat design.

I have been involved with Traditional Small Craft Groups and Wooden Boat Groups for years and seen many beautiful craft built that would take your breath away. And they are still designing and building boats brought into new technology.

 

I don`t think "they" will take much notice of you.
Where would you suggest we can find " FACTUAL" information for our discussion other than teachengineering.org.

 

Quote: "If teachengineering.org can not teach our engineering students with the correct information. Where can we turn to get it right." (sic)

You could turn to those of us who teach engineering students for a living.