Boat Hull Construction...Build It Right!

What separates good or even superior boat hull construction techniques from less desirable and lower value cost cutting methods? Most boat hulls look primarily white with a colour accent that at first glance appear basically the same. Salespersons are going to tell you that their brand is built with quality....what would expect? Information in many boat manufacturer brochures is limited to down right skimpy on how they build their hulls and what materials they chose. This is done for a reason...don't ask...don't tell! The spin doctor's have been very busy lately with hull terms and descriptions sounding very catchy. Terms such as "Smoothride", "Duo Delta Conic", "Fastrack" and for the most part all of these are meaningless. Yes there is significant differences in ride and fuel efficiency for different hull shapes. The discussion of hull shape in itself is quite detailed and worthy of an article in itself.

So your family is going to The Toronto Boat Show or visiting boat dealers looking for a new cottage boat or a fine cruiser. How do I the buyer know what to look for outside of good it looks to me? How do I trust the salesperson is telling me the right things? How do I know that I am getting true value for the thousands I am preparing to spend? Very good questions not to mention the different hull shapes, running surfaces, boat transoms and power options. This is all very confusing..how do I make an informed decision?

All boats are not created equal! Difficult to judge when first looking at those shinny toys with most buyers looking primarily for perceived comfort first and overall visual appeal. Buyers forget or don't understand that overall comfort underway on the water is primarily a result of the hull quality and design and not how soft the seats are at rest at a show. Yes a Mercury Outboard or a Mercruiser sterndrive with the same features is the same on any boat. The quality, shape and technical aspects of the running surface and utilized construction will go along way to determining how well it will perform and how much fuel it will consume. One should consider operating costs as a prime consideration for purchase. This subjects usually makes salespeople run for cover. For this subject you may wish to look at information on Green Boating as well.

For those starting the buying process you should take a moment and review Boat Buying..Getting It Right! You will also find extensive information at Boater's Chat.

Hull Construction Methodology

There are two builing processes of construction fiberglass runabout, bowrider and crusiers hulls.

1. Tradional hand layup technology utilized in a number of forms.

2. VEC hull construction.

Tradional Hand Laid Construction

Traditional hand laid construction has been used extensively for over 30 years by most of the recognized brand names in boating. Recognized brands such as Monterey, Stingray, Campion, Searay, Chapparel, Regal and Cobalt use this process. Hand laid construction utilizes open mould technology to produce the hull laminate essentially with the laminate being built in layers by skilled labour. Differences occur in laminate materials chosen to be utilized, different coring materials, a wide range of gel coats, laminate thickness and the supporting structures. This is our preferred method of construction the reasons of which will be discussed below. I have also included just below a series of pictures which show the process.

VEC Construction

VEC construction which stands for vertual engineered composites has been utilized exclusively by Larson and Glasstron Boats for the last 5 to 7 years. This is closed mould technology where the hull components are added in liquid form only. Four Winns tried this process for some 250 boats and reverted back to hand laid construction. Glasstron is now manufactured with tradional hand laid construction for 2011. This leaves only Larson and Finncraft utilizing this technique for boat building.  The rights to VEC were sold to be used for bathroom fixtures and tractor hoods a few years ago. Limits to this process will not allow for larger format bowrider and cruisers to be constructed with this method. There continues to be available information on the web with regards to hull osmosis problems with this method.

Just What is Tradional Hand Laid Construction?

Below is a series of pictures with some attached desciption of the process. The utilized pictures were taken at the Stingray Boat plant in October of 2010. I have been in a great many boat manufacturing facilities over the years and the process where quality is a consideration is consistent among top brand manufacturers. All boat boat manufacturers purchase their engines at or near the same pricing. To manufacturer a boat with the same dimensions and power at a lower price the builder must cut costs on hull lamination, mechanical systems, windshields and upholstery. Dealer markup is not part of the equation as this is consistent in a competitive environment throughout the industry with the exception of Cobalt.

Immediately to the right is a picture of an open bottom hull ready to begin the process of lamination. The mould must be perfect with respect to flaws as the constructed hull will mirror its shape exactly. Before the initial first step which is gel coat ( outer hull colour) is applied the mould must be waxed with mould release wax. Key facets of the application are the quality, thickness, drying time in the mould and the number of pulls from the mould before it is rewaxed. Three to five is considered excellent and more results normally in small flaws in the outer surface as the finished laminated hull sticks to the mould surface and small sections break off. This results in required localized repairs further down the assembly line and a poorer overall cosmetic finish.

There are two types of gelcoat chemistries utilized...Vinyl Ester and Poly Ester. Properly applied in a system with the right resin and roving either will perform well. There is discussion that Vinyl Ester may be superior for osmotic protection (water absorption). I have been in this industry for over 25 years and have seen older 20 + year old Cutters, Grews, Dorals and Searays made with polyester that have absolutely no osmosis after that length of time. I have seen a 4 year old VEc hull with blisters that would make you cry. Outside of the marketing spin I consider the over synergy of the lamination and the effort put into the process the best representation of true value for the dollar and lasting enjoyment.

The boat mould has been prepared for spray application of the outer colour portion of the laminate also know as gel coat. The plastic wrap on the inside at the top of the mould is where the accent colour will be added latter. Gelcoats themselves come in an extremely wide range of quality. The quality of the outer hull colour is very important as this is what is in contact with the elements on a never ending basis. Superior gelcoats provide a higher level of protection against UV radiation or sun damage, water absorption (osmosis), get coat cracks ( poor gel, too thick gel, too much hull flex or improper drilling or screw application), crazing ( localized discolouration and or fading. The best colour for a fiberglass boat is white period. Accent colours should be localized to high on the sides under the gunnel moulding where only reflected light comes in contact. Dark colours on the top deck particularly red are prone to oxidative sun damage or fading.

After application of the gel coat which must be precisely applied to a very specific thickness we begin the process step by step of building the hull laminate thickness. In this picture the builder is applying gun roving. Gun roving comes in different quality but comes form the manufacturer in long strip form about 2" wide. The gun roving comes to the technician in a continuous band where at the point of application it is cut into needles of varying lengths. Properly applied gun roving provides strength to the laminate as well as preventing print through from the heavier woven roving to come later. The gun roving needles are applied randomly crisscrossing intermixed with fiberglass resin providing tremendous strength for the applied weight. The heavy woven roving has difficulties being applied flat in areas of high slope, narrow depressions and corners. Gun roving is appplied in these areas to provide the required hull strength.

In this picture if you look closely the technician is applying a second coat of gun roving over a layer of woven roving. The texture of the hull shows a weave on the top have of the hull just above the spray line. Both the gun roving and woven roving are overlapped at the keel for strength. gun roving once applied is hand rolled using a small spiked roller to remove any air voids. A coloured catalyst is normally added to the mix to aid visual inspections for voids or non uniform thickness. One boat builder states that VEc hulls or machine made hulls provide superior consistentcy. Machine process or VEC removes the heavy woven roving which provides the real meat to the hull strength. This in my opinion is marketing spin.

Immediately to the left is a picture of a outboard boat from the 90's undergoing a major hull restructure. I use this picture as it gives the reader a visual look at the start of a wood stringer system and shows the interlocking together of the hull sides and bottom. The shinny look to the wood is resin that has been applied to provide protection. Wood panel stringer systems today are much more complex than what is shown here with this boat. You could substitute fiberglass structures in a similar grid system. This boat had reqular plywood utilized during construction including a plywood floor which lasted over 15 years. Essentially all boats built today have wood incorporated in the structure ssomewhere or should. One of the reason for this other than superior stiffness is that fiberglass does not hold fasteners such as screws well.

A boat has a skeleton of a rigid grid structure to support the laminated bottom hull as it impacts the water surface. The hull bottom or running surface is subject to high levels of extreme stress from tons of water pounding on its surface continuously. There are no shock absorbers on a boat hull. Hull stringers provide the required rigidity to maintain the designed operating hull shape. Stringers must be intelocked to the floor structure and hull sides to distribute the energy coming from slicing through the water with its wave action. The stringer system can be made of wood, enginered boat panel, fiberglass, FRP (fiberglass reinforced plastic or a combination of the before mentioned. There has been a movement back to wood based stringer systems. Wood based stringers provide a higher level of hull stiffness which results in improved ride in rough water conditions. Typical fiberglass stringers are "C" shaped and constructed of woven roving with a hollow center. They are laminated to the hull bottom and foam filled to provide required strength to the stringer. The overall support structure with "C" shaped fiberglass type of stringer is not as complex and typically supports a lower square footage of the bottom hull as typically found in high quality wood stringers. There has been concern with fiberglass stringers coming loose over time from the hull bottom. Some manufacturers are incorporating the stringer system as part of the fiberglass liner to reduce the problem of adhesion with fiberglass stringers. One of the problems with this is that the unitzed floor and stringer system is placed into the bottom hull blind without being able to be checked for proper seating and adhesion. No system is perfect and much of what is told boat buyers by builders and salespersons is marketing spin. The real key is the quality and effort put into the process by the manufacturer and the importance they place on customer satisfaction in combination with long lifespan.

The floor and support stringers have been added and heavily glassed in place with heavy weight woven and gun roving. Shown the support structure or the beginning of the motor mounts for the engine to be installed later. Properly done the hull is a unitized structure bonded together for maximum mutual support. Yes in this case specially prepared and treated boat panel has been used in the construction. There was a movement away form wood floors and stringers in the 90's due to floor rot issues due to utilizing poor technique and regular plywoods. Boat panel is different in that each layer is protected before lamination with a preservative and the quality of the panel is far superior to normal plywoods. The most expensive bowrider and most cruisers have returned to wood panel stringers and flooring supports as they provide superior hull rigidity, less hull flex ( results in less joint problems and hull cracking) as well as holding the required fasteners tighter without loosing over time. A boat hull with less flex provides superior ride in rough water conditions as the designed hull shape remains true.

In this picture we look forward to the bow. You can see the flooring firmly bonded into place with a the cutout for the gas tank evident. The floor and the stringers under the floor which are built in an interlocking lattice structure support the hull below providing the required rigidity to prevent oilcanning (hull flex) and hull sides below or at the water line. You can see 12 creamy spots on the floor where floatation foam has been injected into the cavities below the flooring. The floatation foam has three main purposes. One is to meet safety standards for level floatation and the other is to provide additional hull support plus noise suppression. One of the problems in purchasing a boat is that this entire subject of hull construction is not discussed by either party or the purchaser is offered only slanted information to obtain a sale. The entire hull lamination process leaves a wide range of opportunities for manufacturer cost savings in labour, materials and quality as it is essentially invisible. The whole key is the quality and effort put into the lamination. The boat builder places less emphasis here and my production costs go down accordingly and then my retail price should also fall. Brand X is less....why?

Back to the transom area. Here you can see where the initial cut out for the drive leg of the sterndrive has been made. Quality of the cuts here is very important. Notice the black coating in this area for further protection and finishing purposes. All the edges here should be smooth. Behind the cutout and just above is the under deck support for the swim platform. Lots of detail work here as well.

I have included a picture of the lamination of the top deck to show it must go through the same process as the hull bottom. he top deck does not undergo the same pounding as the hull bottom it must be correctly constructed. I have seen top decks as thick as 3/8" in higher stress areas and overall 1/4" or better is considered good to excellent. I have also seen many of top decks only 1/8" thick that cannot hold screws properly and tend to show cracking. If you want to know a secret ask the boat salesperson if the top deck was scribed before attachment to the bottom hull. If they answer yes then ask why? The reason is that prevents those annoying get coat cracks from screws or fasteners holding the two decks together. Remember at a show some 40% of sales personnel are hired just for the show and are on commission or bonus.

After lamination is complete the bottom or top hull is pulled from the mould to continue down the production line. This is a Stingray hull and it is weighed to make sure it falls within acceptable quidelines for weight which is tight. This insures to the purchaser that all that should be done was done and they are receiving true value for their dollar.

To the left is a 3"hull top deck hull cutout for a blower. The overall thickness is 1/4" and you can see how dense the laminate is. This piece was taken from a 185 Stingray a 2010 model. The hull areas below this thicker.

Again the the left is a floor panel section showing the heavy layer on roving an mat (woven roving but a with less thickness in the weave) to protect the panel. This also clearly shows the overall quality of the laminated wood panel..how consistent and dense it is with no voids. The colour throughout demonstrates the preservative application during construction of the panel. Singray in this case applies the fiberglass liner over the protected wood panel for superior support in this model. Fiberglass liners which are very popular options or requests from today's boat buyers do present some issues as well as benefits. Cracking and small get coat cracks are common where insufficent underneath support of a too thin liner has been utilized. The main benefit is the clean cockpit interior without the headaches of fixed carpets.   Do not buy liners for the sole reason that there will be no issues with wood floors. Liners are noiser and when not properly installed or supported provide a situation or increased hull flex.  There is more labour involved in wood panel floors and stringers.

Hull Coring

A number of boat builders utilize different materials in addition to woven roving to provide laminate strength at minimal weight. Product such as "Nidacore", "Coremat" and "Spraycore" are used by Monterey. These are product names used in high stress or top deck areas which tend to be thinner and need some additional internal support.   Sprayfoam provides addition noise suppression to hull sides and appears to provide a thicker hull. The use of coring materials such as roving and Nidacore, Coremat and Spraycore do add value to the purchaser. Those companies utilizing only gun roving or fiberglass mat are doing so to save production costs.   If you are on a very small body of water with little of no wave action a simple hull lamination will work for you. However fading and finish deterioration will be your partner very shortly. Rough water applications call for a detailed hull lamination schedule.