Pontoon Floor Supports, M brackets, Joints

Boater's Chat Boat Buying Information Muskoka

Pontoon shopping….lots of choices out there!  Looking for a great deal on a pontoon boat at The 2015 Toronto Boat Show or an in season purchase?  Today we continue our discussion on pontoon chassis….the structural skeleton that you are paying thousands for and most buyers don’t spend much time considering.  I was setting up the Larson Booth at The Toronto Boat Show yesterday and man is there a stack on pontoons either at the show or on the way into the show.  Going to be very confusing for buyers unless they do some homework and can get past the flash marketing!  Today we continue on providing you the knowledge you need to make an informed pontoon buying decision at the Toronto Boat Show or that in season purchase.

Pontoon Supporting Structure….It May Not be Sexy But Man it is Important! 

In our last article on pontoon chassis we talked about structural rigidity, torsional stress and warranty.  Under the floor there are cross members made of aluminum or galvanized steel that function to bridge the pontoons together plus note that the pontoons are in excess of 6 feet apart on a 2 tube model.  These cross members are intended to provide stiff support to the large floor panel directly above in a pontoon boat.  A 20′ pontoon will have 5 or 6 sheets of 4′ x 8′ floor panel comprising the floor with 5 or 6 major seams.  Going past the treatment that the floor panel received for wet and dry rot during lamination,  there are two types.  Tongue and grove at the area of connection to the next panel or just a flat square edge.  Tongue and Grove costs more and provides a stronger locked together seam than the much more common butted up panel seam.  Tongue and grove joints for floor and roofing plywood is used in the majority of housing construction as it is significantly stronger and reduces flex in the area of a seam.  It is well-known that tongue and grove joints are stronger….way stronger!  Okay so what about pontoon boats?  The majority of today’s pontoons have an 8′ 6″ beam…..right.  Yes they do but tongue and grove floor panel is not made in 8′ 6″ lengths!  Oops!

Now that you know that….this means that essentially all pontoon builders are not using tongue and grove wood panel and are butt ending their floor panels together hopefully over a cross member.  Those floor panel joints have no ingrained support so they require significant structural support underneath hence the thought to have the joint over a cross member.  Then you get to the conversation about how the floor panel is connected to the cross members.  Screws, nuts and bolts, “Tech Screws” and any adhesives?  Choices of positioning the fasteners are…both sides of the seam or down through the seam itself with a large fastener with a larger head to pull down through the cross member?  Which is better nuts and bolts or “Tech Screws”.  My opinion on this is….”Tech Screws” on both sides of the seam.  Why “Tech Screws” over nuts and bolts?  “Tech Screws” have attached adhesives and the heat that is produced in applying the “Tech Screws” actually welds the screw into the cross member…it is not ever going to loosen or pull out and if done properly is applied to both sides of the seam!

Back to those floor panel seams.  Is there a chance to get tongue and grove floor panel in a pontoon?  Yes and only in an 8′ wide pontoon if the builder utilizes it or there is one builder that utilizes tongue and grove floor panel in a 8′ 6” wide pontoon.  That pontoon builder is Cypress Cay who in a brilliant  move uses 4″ aluminum extrusion on the edges that overlap top and bottom of the panel by one inch to get to 8′ 6″ of width.   I am using below a series of pictures of a pontoon cross-section of a Cypress Cay pontoon to illustrate the aspects of superior pontoon chassis construction.   In high quality build you may get variations of the below with the exception of the outer aluminum extrusion with is a patented exclusive Cypress Cay chassis component.

Wood floor panel if it has a weakness it would be considered at the exposed edges.  You can see from the picture that the floor panel is very tight and dense with little or no voids which is great.  In the case where a pontoon builder goes the extra mile and seals the seam and the panel edges this should be considered a superior protection step.   A few including Cypress Cay go another step and place sealing tape on top to the seam below the carpet or flooring.  There are two basic types of coverings for wood floor panel which are carpet in varying textures and qualities and a vinyl floor covering either a solid colour or perhaps a wood grain look.  Carpet may have a rich feel on the feet but it does hold moisture directly onto the wood panel until it dries and this process repeats itself each and every time the carpet gets wet.  This moisture will find its way into the panel and the seams.  One of the important points here is warranty.  Most pontoon panel has a limited lifetime warranty which may cover replacement for up to 10 years and prorate after that for an additional 10 years.  As a note a pontoon builder is expecting you to protect your floor and not leave the pontoon open to atmosphere when not in use.  Buyers should note that floor warranty does not normally cover delamination at the edges caused by continuous or intermittent water soaking which can cause expansion and contraction cycling as well as cracking or splitting at these areas.  This is why it is recommended that the seams be protected by more that one means.  Superior would be considered tongue and grove as it in itself helps seal the joint from water in combination with a sealing tape on the upper edge of the cross member before the panel is placed on top, them a sealant calking in the actual joint and finally a top water-resistant coating or tape product over the seam on the top of the floor.  Looking at pontoon floors from boats without a sealing caulking in the seams after a couple of seasons frequently you will notice that the seam itself appears to becoming more and more noticeable.  This is due to expansion and contraction of the wood floor panel at the edges of the joint due to water soaking as the panel starts to lose some of its compressed integrity in this area.

I frequently get asked why something other than wood panel is not used on a pontoon floor.  Most pontoon wood panel is 7 ply and no its is not all the same with respect to quality.  How can you tell that….essentially impossible which is good for the boat builder.  Wood panel quality is reflective of the quality of the wood utilized, how many voids, how rough the surfaces are and what bonding agents are.  One of the big differences is in the preservative used and whether each of the layers is treated before lamination or whether it is done after the lamination cycle to 7 layers.  The main reasons for the used of wood panel is cost and strength.  Metal floors have been tried…I remember Tracker a few years ago with a tongue and grove aluminum plank floor….but they have large issues with noise transfer and carpet coverings with their adhesion are a nightmare.  Cobalt Marker 1 pontoon new this year is using a glass liner but this pontoon is priced way over $100,000….not for most of us.

In my experience I recommend vinyl floor coverings as they eliminate any moisture sitting on and wicking into the wood floor panel.  As an added benefit the application of vinyl coverings causes the builder to provide essentially a perfect floor and panel joints as imperfections will show on vinyl floor coverings that do not show with carpet.   Be advised that some of the Seagrass type coverings may have some durability issues as they are foam backed based and the top vinyl is not very thick.   A solid one piece vinyl product will be more durable and does come in a solid colour or in a wood strip flooring look.  Next we deal with the third tube option!

A note on structural strength of the chassis.  Buyers have to understand the importance of structural rigidity in all boat hulls.  That fine car or truck of yours has a suspension to absorb road shock from bumps or pavement imperfections.  Compared to lake travel a road is as smooth as a sheet of glass.  The hull and it supporting structures have to absorb and deflect wave energy thousands of times.  There are not shock absorbers on a boat hull.  Poor seams, light duty and reduced cross member numbers and insufficient “M” brackets connecting the floor to the pontoons are very important to the overall structural rigidity of the hull.  You will find significant difference in pontoon boat weights due to reductions in build materials as more materials cost more money!