Flat bottoms seaworthy?

[Gilmarine]

We make fishing boats for deep sea fishing - with a flat bottom. The fishermen are really satisfied. Does rough seas require a V-bottom? (the flat bottom is required to beach the boats safely) www.geocities.com/gilmarine2003/

[fede]

Deep V hulls where introduced to correct a problem flat bottms used to have, when moving at 30 knots on sea with a flat bottom the boat offers a big flat surface almost parallel to the sea that bumps really hard when going from wave to wave.
The V opens the wave smoothly and let the hull go back into sea smoothly.
But even when moving slowly the V offers some pros in rough waters.

So is a flat bottom required? as I wrote in the other post it depends on what is the speed and what kind of waters is the boat going to be used in.
I can't see any flat bottom pro (when comapared to V) other than a lot more Hydrodinamic lift...but you might benefit from that only in very very calm waters.
Flat makes turning at high speeds more difficult also.

I guess that if it's open ocean waters you might wanna think about V bottom!!!

[Gilmarine]

The problem is, that flat bottom is required. For the fishermen, the boat has to be able to land on the beach. For recreational use, "beach-hopping" would only be possible with a flat bottom craft. History has proved that military landing crafts has made it over rough ocean, and here in Lisbon we have more than 300 boats of this size, working every day in seas up to 10 ft. Any comments on safety experience anybody? www.geocities.com/gilmarine2003/

[PAR]

Flat bottom craft of all sizes have been plying the ways for many hundreds of years.

For your workboat needs a flat bottom vessel can be designed to more than suit your needs. On the other hand, bilge keels on a "V" bottomed design may be of some use as well.

At the loads and speeds expected from typical fishing craft, a flat bottom will save you time and money in construction, will carry more over the same LWL a "V" might have and will provide the beaching ability necessary.

[MikeJohns]

A flat base is OK in a displacement hull, best if there is still a V section overall with a flat bottom to the V. This flat is best if it runs out before the bow otherwise the forefoot will pound. Only really suitable for metal construction.

[Gilmarine]

Fully agree with you MikeJohns. In Morocco, we made a series of 17' boats vith deep V in the front and almost flat 2/3 to the back. It could be beached safely and was soft in the sea as well. The problem is the customers, they want exactly a specific design, otherwise they dont buy. Since they are risking their lives everyday on the ocean, they should know? Anyway, the only problems in the sea with this model occurs when we have large waves from the side. www.geocities.com/gilmarine2003/

[Tall Timber]

Flat/shallow vee = shallow draft, high mileage, pounding on plane quicker rolling action and less resistances to lateral motion, easy beaching doesn't flop over when beached.

deep vee = smoother ride during planing but higher fuel consumption.

Our area has lots of aluminum jet boats that plane in rivers that have stretches that are 6 inches deep and deep vee's for crossing out and into the pacific and for big river use.

[lobsterman]

after viewing your website i would have to say that i am very impressed with your designs + vessels,they certainly look to be a very seaworthy vessels for rough surf launch and recovery, i was just wondering if the beam of your vessels designed for customers is constrained by an over the road width / trailering restrictions,as i have a design of a somewhat flat bottomed boat but it has a length to width ratio of only 2 to 1 (40' length X 20' width) and is designed to be a large capacity displacement boat that would bring itself onto a plane quickly, in order to achieve this and to overcome some of the adverse effects of a flat bottom, i have incorporated four shallow air cavity chambers brokenup into quadrents under the hull, these create an air cushion ride on a plane and it also creates a stabilizing effect when operated in the displacement mode in addition these air pockets would help to avoid the pounding and slamming of flat bottomed designs, also these air cavities can be pressurized with water or air in order to negate the effects of suction created in soft beach sand launchings ( you won't have to wait for the tide to come in as much,just bubble your hull free of the sand or the suction of the beach) i hope this helps. Patrick M.

[Gilmarine]

Since we are making custom artisan fishing boats, we have to sell what the customers wants. It is not unusual that we encounter a fifth generation fisherman customer. You cant really argue in that environment. Your comments are interesting though, because it would improve the working conditions while the style / shape is maintained. Since we are looking for a 500-vessel order for Africa, based on the overall concept of this vessel, I should send you a private mail?