Design Features

THE MARINE INDUSTRY IS UN-REGULATEDBUYER BEWARE!

While there are many great boat builders in Australia and many great designs out there, the fact still remains that there are no requirements for independent checks on designs or construction methods.

So the term ‘Buyer Beware’ applies when you buy a new or used boat and it is up to you to do your research. The average small pleasure boat costs more than the family car and is a significant investment. We believe it is important that you know how your boat is designed and constructed so we have produced this page to give you enough basic information to ask questions and do your research before you part with your hard earned cash.

The famous quote below by John Ruskin sums it up perfectly

It is unwise to pay too much, but it is equally unwise to pay too little.

When you pay too much, you lose a little money. That is all. When you pay too little, you sometimes lose everything, because the thing you bought was incapable of doing the thing you bought it to do.

The common law of business balance prohibits paying a little and getting a lot. It can’t be done. If you deal with the lowest bidder, it is well to add something for the risk you run. And, if you do that, you’ll have enough to pay for something better.”

John Ruskin (8 February 1819 – 20 January 1900) English Author, Poet and Critic.

When you consider the cost of materials, labour and engines, getting your boat designed right is a small fraction of the total cost.
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Designed in 3D using the latest 3D CAD software, our DIY aluminium boat kits are built in the computer before they are physically built.  This allows us to develop the most efficient construction methods which saves time and money.  It also allows us to produce easy to understand 3D drawings.  Free Sample Drawings Available Here

Our comprehensive drawing set features 3D Assembly Instructions guiding you step by through the construction sequence.

Our aluminium kit boats are designed to cope with the choppy waters encountered off the Australian coastline and feature our exclusive “S” shaped inverted chine with variable deadrise hull.  This combination was made possible using advanced Naval Architecture software and results in a unique hull shape that is both stable and soft riding.

We have tested in the open waters in a 2.5m swell.  We tested into the swell, beam on to the swell and running with the swell.  The boat stayed dry, did not broach and maintained a comfortable 25 knots.

We have developed this web site to show case our designs and to give prospective boat owners some basic information on what to look for when choosing a boat.  See our Design Features page for more….

If you are hoping to see magazine cover style pictures of boats jumping over waves then sorry but we cant help you.  No matter what the deadrise of any hull, 1500kg of boat jumping over a wave is going to land hard.  For that reason we have designed our hulls to stay in the water and cut through the waves – not jump over them.

Our designs include many features aimed at improving performance and reliability.

Hull Shape

Our unique hull shape was designed from scratch using advanced naval architecture software. Our design brief was to develop a hull shape that is best suited to the conditions off the WA coast. Our hulls feature a variable deadrise combined with an inverted forward chine. This combination was chosen to give a balance between stability at rest, smooth water planing and rough water comfort. The inverted chine allows for a finer entry to increase comfort levels when heading into choppy seas. Below the waterline the flatter deadrise aft promotes stability and easy planing. Using advanced naval architecture software allows us to test each hull on the computer and fine tune the shape before any plate is cut. Once we are satisfied with the hull shape we can then extract the individual plate shapes for computer controlled cutting. Our design development costs are kept to a minimum since all the trial and error is done on the computer.

Designed by Degree Qualified Engineer

Aluminium is a great material for building boats since it is light weight and corrosion resistant. The down side is that it has a very poor fatigue resistance. That means that in areas of repeated vibrations, such as those caused by engines and sea chop, Aluminium is more prone to cracking than steel and other materials. This is why it is vital that your boat is designed by appropriately qualified & experienced people. When designed properly, the risk of cracking can be minimised. This is why we place so much importance on using CNC cutting to allow us to use stress relieving shapes. We can design the best shapes and cut them cost effectively.

Individual Design

As strange as it may seem, designing small aluminium boats is extremely complicated. Because they are so light they are very sensitive to weight changes and subtle hull shape changes. An incorrect hull shape can make the chines sit too deep in the water, resulting in difficulty in getting on the plane and increased running costs. Just as easily if the hull shape is too full, the chines will sit out of the water resulting in poor stability and handling. Finding the right balance of boat weight and hull shape takes time and skill. Have a look around and you will notice just how many small aluminium boats sit with their chines out of the water. For this reason each CNC Marine hull shape is specifically designed for the configuration offered. While it would be easier and cheaper to use the same hull shape and just extend it or swap a walkaround cabin for a half cabin, the result would be inferior performance and stability. The use of modern computer technology allows us to fine tune each hull shape in a cost effective way and do the job properly.

Designed Beyond The Standards

There is no standard independent check for recreational boat designs. It is up to you to do your research. We design our boats by referring to Australian Standard 1799, BV rules for High Speed Light Craft, DNV rules for High Speed Light Craft and the USL Code. In addition we then apply fundamental engineering principles in areas not covered by these rules such as stress relieving cutouts. We go beyond simply meeting the minimum requirements.

Solid Frame Construction

To maximise the strength and safety of your boat, our hull frames are full depth solid plate.
Unlike some manufacturers we do not use floating frames.

On CNC Marine boats each frame is welded to the bottom plate. The use of floating frames has no technical merit and is purely a cost saving measure.

SOLID FRAME CONSTRUCTION

Contoured Stiffeners

The software that we use allows us to develop longitudinal stiffeners that are cut to the exact shape of the hull bottom and are orientated perpendicular to the bottom plate at all times. This reduces the chance of the stiffener “tripping” and losing its strength. They are stitch welded to the bottom plate using DNV welding guidelines and are fully welded to each frame section. The cutout in the frame has a stress relieving contour on top to minimise the possibility of cracking. Our stiffeners are cut from plate which makes them 26% stronger than an extrusion. Some well known manufacturers only use standard flat bar extruded stiffeners that are not contoured and are not perpendicular to the plate, and therefore not as strong.

STIFFENERS CONTOURED TO HULL AND PERPENDICULAR TO THE PLATE

Built In Chines

We design our boats with chines that are built in the same way that larger commercial boats are built.
That is inserted between the bottom and side plates and fully welded inside and outside.
The alternative is to join the side and bottom plates directly and then cap the join with an extruded angle section. We will not design this way due to the risk of crevice corrosion. If this capped section should ever leak, damp salt would build up inside.

The area would then become oxygen deficient and corrosion would be accelerated.
Some builders that use the capped method drill drainage holes in the ends of capped chines to let water out if it ever leaks. The problem is that this also lets the salt water in. While the water would drain out, the salt will build up.

By building the chines our way, this problem is eliminated. The use of computer controlled cutting allows us to build in this way without extra cost. We don’t use reverse angled chines as we believe they increase running costs due to causing extra drag.

CHINE STYLE
ACTUAL CHINE

Welding Connections

Some builders use lap joints when joining frame halves and brackets. While this is acceptable in steel applications it is not good practice for aluminium. Classification societies do not allow lap joints in commercial vessels. We do not use lap joints anywhere.

CNC Cut

All plate parts for the boat are nested onto standard size plates and are cut using CNC controlled cutters. This allows us to minimise material wastage and ensure that the parts are the correct size and shape. It also allows us to use shapes that would be difficult to cut by hand, like for example our stress relieved stiffener cutout. It doesn’t cost any more to computer cut a simple shape or a complex shape so we can design the structure with intricate stress relieving shapes at no extra cost.

TYPICAL PLATE WITH PARTS READY FOR CUTTING - NOTE MINIMAL WASTAGE

Curved Edge Brackets

We could dedicate a whole web site to aluminium fatigue and how to avoid it. One important consideration is how stiffeners are bracketed. We only use brackets with curved edges that allow a smooth transition in stiffness. This minimises the risk of cracking the stiffener at the edge of the bracket. The use of this style of bracket is not common because it is easier to cut a straight edge bracket using a guillotine rather than cutting a curved edge bracket with a hand saw. Because we use CNC cutters we can cut superior curved brackets at no extra cost.

Marine Grade Aluminim

We only use DNV (or equivalent) certified marine grade plate.

The End Result

The result of the use of this modern technology in the design process is that properly engineered boats can be built quickly and with minimal distortion. This reduces residual stresses in the aluminium and hence reduces the risk of cracking problems. It also improves the look of the boat and reduces the costs associated with bogging before painting.

The end result – Higher Quality at no extra cost.
Remember it’s your money so do your research and ask questions before you buy!
Visit our FAQ Page for more helpful design information.