What is the Importance of Hull Design?

There is a huge secret in the boat building industry; Whether your boat is a small one or a large one, there is nothing else that will make as much difference in your boating pleasure as the design of your hull.  And nothing else can make it go faster or perform better.

This may come as a surprise to many boat buyers who are used to owning cars of every type without having the exterior conditions actually affect their driving pleasure. However boat exterior conditions change constantly and widely depending on wind, tides, and current.

At Twin Vee, hull design is central to the design philosophy of Roger Dunshee, founder of Twin Vee and one the best small boat hull designers in the world today. The planing catamaran hull was picked because it offered the most complete package of benefits over V-hull designs currently popular. The advantages of a softer and dryer ride in heavy seas and chop was very important. Efficiency, stability and safety advantages over V-hull designs made the design choice easier. Twin Vee developed a super strong hull and because of it's design prowess in weight and balance, was able to create these features in a cat that was also fast. The result today is the best line of small boats on the market. These cats have the ocean going capability of V-hulls 25-30% larger. The ability to go through 4-5 feet chop at high speeds, comfortably, and safely, is a singular accomplishment in the boating industry.

The dedication of Twin Vee to hull designs is the reason that Twin Vee has developed strong customer loyalty and proven performance from Bermuda to Kona, in the world's biggest waters. An additional benefit that came with the package is that cats have a shallow draft. Twin Vee Cats have drafts from 7" (14&17), 8-10" (19&20), to 12-14"(22&26). This allows Twin Vee to perform very successfully in the shallow waters and flats of Florida, Texas, the Bahamas, Cape Cod and bays everywhere.

Additional work was done on the hull design to allow for single engine performance in Twin Vee cats 19 feet and lower. This was a significant accomplishment that has since become the industry standard.

Hull design is central to performance, comfort and speed among other things. But how can a potential buyer test the hull design? The answer is a test ride in different sea or chop conditions. The average sea state in the Atlantic is about 3 feet (higher from November to April). The average wind speed is about 10-11 knots, again higher in the winter (in Florida). If the buyer wanted to be able to go boating year round, then a test in 3-5 foot seas or wind speeds of around 15 knots or more would be called for. Any place where such conditions could be duplicated would suffice for test purposes. In any case, a test ride in calm, protected waters is inadequate.

Additionally, in the case of twin engines, it is important to test the planing ability of a boat with one engine turned off and tilted up. This test simulates an engine failure off-shore. Over 90% of V-hulls will fail this test, even with large engines, due to the inefficiency of the hull. By comparison, a 20 foot Twin Vee will plane with a single 50hp motor, and a 22 will plane with a single 70hp. The failure of a single engine to plane a boat is a safety issue.

The boat buying public has been kept in the dark about the importance of hull design. Twin Vee is a manufacturer that can be trusted to fully understand the issues surrounding hull performance and testing. It is proud of its pioneering development of the best small boat hulls in the world today. It's customers can have the most enjoyable boating experience at a most affordable price.


What are the Qualities and Concepts of Power Catamarans?

It seems new catamarans are entering the world of power boating every day. Numerous magazines have featured "cats" on their front page. What is making these boats so popular? By now, many know their qualities: soft ride, performance, comfort, and stability. Those fortunate enough to have experienced "the cat ride" swear they cannot go back to V-hulls.

We like to introduce boaters to "the cat ride." The recipe is easy but you've got to pick the weather! Sunny is nice, but not for demonstrating Twin Vee Cats. Make sure the wind is blowing at least 15 mph, then make your way to the inlet. Now you have the perfect mess that most boats (and boater's backs) loathe. Ahead, a 5' chop with plenty of white caps approaches and the cat smoothly slices the wave and moves up on the next one. The green face turns toward you with a surprised grin. "How in the heck...???" Makes a Twin Vee dealer's day every time.

Truly there is no bad cat in terms of ride, and even an average catamaran will compare favorably to a V-hull boat of the same size. However, to move a cat from average to great requires a special touch. If we've learned anything from years of testing multihulls, it is the great importance of reducing weight and creating balance to create great performance, comfort and SAFETY.

Today, we have many years of R&D on our several hulls. It is this R&D investment that has allowed Twin Vee to be the technological leader in developing the most affordable, softest riding, fastest and safest power catamarans on the market today.


What are some of the Definitions used in the Power Catamaran Industry?

Tunnel
All cats have one, although some are specifically called the tunnel hull. It's the space between the two hulls and the underwing or bridge deck, and is relied upon for lift.

Slamming (Called "pounding" on V-hulls)
Occurs when a wave is trapped inside the tunnel and hits the underwing. A lightweight, good design, and sustained speeds prevent slamming.

Sneezing
Exclusive to cats, it's a spray from the front of the tunnel back into the boat. Air compresses the water and creates a cushion. The air cannot escape out the back of the tunnel and thus is forced forward. Poor design and /or balance usually cause sneezing, and weight can sometimes be a factor. Thanks to our great hull design and attention to weight and balance, Twin Vee PowerCats are practically immune to sneezing.

Banking ("Leaning" for some)
The lateral attitude of a vessel, applicable to moving vehicles as well. V-hull boats, bicycles, and motorcycles bank into a turn. Powered catamarans on the other hand, are more similar to cars. They tend to bank out of the turn, and it takes a little getting used to!  If you think of your car as riding a bus standing up, it's the same idea.


Can you Explain Catamaran Hull Design Theories?

There are three types of hull designs for catamarans. Each design relies on the tunnel effect to some degree, and each can have innumerable variations within its type:

Tunnel Hulls
As the name implies, these boats rely on lift to operate from the bottom hull when compressing air into the tunnel. As you can imagine, this can only happen at high speeds, and this means that a lot of power is needed to bring the boat up to plane. A tunnel hull performs poorly at lower or trawling speed. Also, due to their mostly flat-paneled bottoms, the ride can be rough in waves.

Displacement Hulls
Displacement hulls depend on buoyancy. The volume of the hulls is a major contributing factor; the boat slices waves instead of punching them, and it does not come up on a plane. This accounts for the smooth ride. Some factors such as friction from the wetted area can limit the top speed and can also cause both slamming and sneezing.

Planning Hulls
These are hybrid hulls combing features of both tunnel and displacement hulls. They provide a smooth ride and top speed for less overhead. Twin Vee's proprietary asymmetrical bottoms do just that, plus control the amount and flow of water in the tunnel that the center propulsion requires.


Why is Weight so Important?

The catamaran hull shape, by nature, is easily driven through the water. It requires less power to attain the same speed as a V-hull. The largest single negative is weight and its location. It will impact comfort and safety since a heavy cat is low in the water. It will then suffer from underwing slamming, sneezing and slow steering reactions. A heavy cat also needs more power and more fuel (which adds even more weight!). The Domino effect is hard to stop. And since we are talking trailerables, the heavy cat will also need a heavier trailer and a bigger vehicle to tow the whole package!


Why do Twin Vee's 17 and 19 Footers Utilize a Single Engine?

Because they can!  The real answer is multi layered, and will depend on how you intend to use the boat. A day trip within 5 miles of land does not call for twins. A Florida/Bahamas crossing, Channel Islands, Catalina or Dry Tortuga trip will usually call for a twin setup. Single engine catamarans are asked for, and we have made it work where others have failed.


Isn't all this "State of the Art" Expensive?

No! Twin Vee's design philosophy is affordable power catamarans. If you want performance, strength, comfort, economy, dependability, durability, low maintenance and resale value all in one package, then isn't it nice that it's also affordable?


What is the Best Decking Material?

In many respects, wood is actually stronger than any material known, even so called space age material.

How can wood be stronger than Kevlar and graphite fibers? It is stronger, strange as it seems. The answer lies in understanding "strength." There are two critical types of strength: tensile and stiffness (the modulus of elasticity, or Young's modulus-E). Both are measured in pounds per square inch (psi). Following is a comparison of space age materials in order of "strongest" to "weakest".

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Strength of Materials




MATERIAL



TENSILE STRENGTH 
PSI



STIFFNESS 
or E PSI



WEIGHT 
LB / CU.FT.

Graphite 170,000 12,900,000 100
Spectra 168,000 9,400,000 82
Titanium 150,000

17,500,000

140
S-glass 128,000 5,500,000 95
Kevlar 90,000 3,200,000 80
Steel 60,000 30,000,000 495
Aluminum 40,000 10,400,000 168
E-glass 15,000 1,400,000 95
Douglas fir 12,400 1,950,000 32
 
It doesn't appear that wood is very strong in the above chart. But boats and most structures require the minimum weight for a given strength. So we must compare strength relative to weight by dividing the strength or stiffness by density, giving us the next two charts:
 


Tensile Strength vs. Weight

MATERIAL
PSI / LB./ CU.FT.

Spectra 2,049
Graphite 1,700
S-glass 1,347
Kevlar 1,125
Titanium 1,071
Douglas fir 388
Aluminum 238
E-glass 158
Steel 121


Stiffness vs. Weight


MATERIAL

PSI / LB./ CU.FT.
Graphite 129,000
Titanium 125,000
Spectra 114,000
Aluminum 61,905
Douglas fir 60,938
Steel 60,606
S-glass 57,895
Kevla 40,000
E-glass 14,737

 

  Wood has moved up in both charts, but is still behind. But because stiffness is more important in most structures, including boats, the structural efficiency must be measured. Here wood wins!  
 

Structural Efficiency Relative to Weight: 
Columns



MATERIAL

SQUARE ROOT OF PSI
LB. / CU.FT.
Douglas fir 44
Spectra 37
Graphite 36
Titanium 30
S-glass 25
Kevlar 22
Aluminum 19
E-glass 12
Steel 11

 

Structural Efficiency Relative to Weight: 
Beams and Panels


MATERIAL

SQUARE ROOT OF PSI
LB. / CU.FT.

Douglas Fir 3.91
Spectra 2.58
Graphite 2.38
S-glass 1.86
Titanium 1.86
Kevlar 1.84
Aluminum 1.30
E-glass 1.18
Steel 0.63

 

  Amazingly, and contrary to everything you've probably read and heard, wood is structurally far more efficient than any of the building materials known anywhere. In other words, you can build a lighter structure out of wood than of anything else, for the same stiffness.

In addition, wood has better durability under compressive loads and better resistance to degradation over time than "composites." The major exception is that untreated or unprotected wood can and will rot if exposed to water over an extended period of time. Twin Vee's treated decking material, MarineTech PTP, is protected completely and is given a Lifetime Warranty. Twin Vee has command of all materials and methods it uses, and stands behind it's products!

MarineTech PTP is manufactured by PlumCreek, a 7B+ Publicly Traded Company on the New York Stock Exchange.  PlumCreek is the second largest timberland owner in the United States, with 7.8 million acres located in the Northwestern, Southern, and Northeastern regions of the country.

Also, visit APA The Engineered Wood Association  for a more comprehensive discussion on why treated wood on a boat will not rot.

Other Information:

APA Letter to Twin Vee Marine, Inc. (Maryland Dealer)

Preservative-Treated Plywood for Boat Manufacturing Applications

Marine Grade Plywood

 
     

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Twin Vee Marine, Inc.