I want to show you a little reportage of the construction of my custom alloy boat .
First of all, the requires:
HULL: I usually sail in the west coast of Sardinia, Italy. Here, for the 80% of the year there is a strong wind , the Mistral, who blows from the 10 am to the 19 pm, and it reaches force 6/7 Beaufort. The resultant sea state is always rough, steep waves of 1.5+ m that some years ago broke also my old Boston whaler 13 's hull. Too rough for a comfortable ride also in boats like Boston Whaler Outrages , WhiteSharks, the unique boats that can ride comfortably in this little maelstrom are Regulators, Mako, and some high-deadrised inflatable boat. (more similar to a SAR boat than a leisure boat..) I wanted a boat that gives a great ride through this waves, not suffering head wind; that should have a dry ride, and also that would be faster than the "not alloy" similar boats with a greater MPG.
I wanted 40+ knots of max speed with a 200 hp outboard, and a 25/27 kn cruising speed also in this 5 ft rough sea, even head sea.
Then, like whaler boats, the boat MUST had to be UNSINKABLE.
DECK LAYOUT : I rarely go fishing, but I like the offshore center console American boats. The unique thing that I don't like in these boat is the "nude" deck: no bow sundress area, no cabin, no place to lunch
... I wanted a big deck with sundress area, a 2 people room under the deck, and a aft area to place a big lunch table for 6 peoples... 
I established a vacuum space in the hull, to use as a 400 L water ballast tank, useful in heavy seas or for the live bait when fishing.
SO,
I designed a high flared (dry ride) bow , and a V variable hull with a entry deadrise of 60°, 34° midship, 23° transom, with 2 strikes for each side and a lateral chine , plus 2 "winglets" to decrease roll when afloat.
The other important thing , to control seakeeping, is to place well the center of gravity CG and center of buoyancy CB: I calculate every weight, included engine and screws, to place CG on the same vertical position of CB, to have a perfect trim angle (0° ! ) and a correct plane angle. Besides, the long. position of CG was lightly advanced, to give more soft ride in the waves and allow a lower minimum plane speed, near 4% forward 1/3LWL .
I also placed a enclosed transom bracket to increase speed and engine trim feeling.
The material? Alloy, of course, ALU 5083 : the material that gave the maximum strenght/weight/performance ratio: fully customizable, more durable than NON ALLOY's/plastic, more simple than wooden-epoxy, less maintenance, low costs.
BOAT SPECS:
material: Alloy 5083 H111
thickness: 12mm(6+6) transom, 6mm hull and stringers, 4 mm sides , strikes,deck and t-top tubes.
Lh: 23 ft (7.05m)
B: 2.48 m (trailerable)
D: 1.71 m
Weight finished: 1350 kg .
Carrying: 7 px
Power: from 135 to 300 hp.
Performances (with a 200 hp optimax) : cruising 26.5/27 kn , max 45.5 Kn (52 MPH)
Fuel consumption: 26 L/H at cruising, 77 L/H @ WOT.
mileage at cruising speed: 1.05 NM / L ( 4 miles per gallon, if the gallon is 4 liters..)
Fuel tank: 300 L (300 NMiles of range at cruising speed)
Water ballast tank: 400 L
Water tank: 100 L
- placing and welding the hull plates
- 1 - Hull plating.jpg (94.84 KiB) Viewed 14519 times
- hull shape
- 2 -hull shape.jpg (92.01 KiB) Viewed 14518 times
- trans stringers
- 3 - transv stringers.jpg (99.79 KiB) Viewed 14519 times
- transom with a bend , helpful to increase strenght
- 4 transom.jpg (94.87 KiB) Viewed 14518 times
- strikers and bracket
- 5 - long strikers & bracket.jpg (93.9 KiB) Viewed 14519 times
Continues..
