Aerodynamic and Hydrodynamic Performance
design for Powerboats

Figure 1 - Common pontoon boat designs are a tunnel hull/catamaran with two sponsons ('tubes') or a trimaran with three hulls (outboard sponsons + centerpod) called 'tri-toons'.

Figure 2 -Some fast pontoon boats have achieved super-performance and speeds in excess of 100mph!

Figure 3 -Tunnel height, pontoon diameter and tunnel width can optimze pontoon hull performance

Figure 4 -Tri-toon hull designs can provide additional stability and weight support to accomodate multi-engined, higher HP installations.

Figure 5 -Effective Deadrise can be evaluated by looking at all of the local deadrise angles throughout the full 'wetted surface' area of the circumference sector.

Figure 6 -Lifting Strakes on outboard pontoon sponsons and/or centerpod pontoon can improve 'effective deadrise' and overlal hydrodynamic lift efficiency

AR® has developed advanced analysis techniques that accurately calculate the performance features of 2-tube pontoon or 3-tube tri-toon catamaran hulls.

Pontoon boats are no longer just slow, heavy, multi-seated, displacement mode, 'party boats'.   Pontoon boats are no longer just slow, heavy, multi-seated, displacement mode, 'party boats'. Common pontoon boat designs are a tunnel hull/catamaran with two sponsons ('tubes') or a trimaran with three hulls (outboard sponsons + centerpod) called 'tri-toons'.  Pontoon boats commonly have 2 or 3 large-diameter round PVC/aluminum 'tubes' with large decks that accommodate many passengers.  the hull is effectively a 'tunnel hull' concept with little aerodynamic benefits from deck surfaces due most all of the upper surfaces allocated to seating or entertainment features. Availability of large hp outboard motors make even these heavier, entertainment-oriented boat capable of high speeds.  

Pontoon boats can be easily represented in TBDP/VBDP by modelling using the provided standard design template 'Round Pontoon Boat', or configuring a 'Tunnel Hull' with 'Sponson Type' = 'Round Pontoon'.  

Performance analysis of Pontoon style hulls, until now, has been very difficult to model.  Round pontoon-style sponsons behave much differently, hydrodynamically, than flat bottomed sponsons. For example,

• What is the 'deadrise' angle of planing surfaces when the sponsons are a 'Round Pontoon' shape?
• How does a centrally-located pontoon contribute to low speed and high speed performance?
• What if the center round pontoon height is different than the outboard round pontoons?
• Does 'strakes' on round pontoons affect lifting performance?  

AR® has developed unique engineering techniques that accurately represent the complex behaviour of round 'pontoon' sponsons and even and 'tri-toon' configurations.  A tricky challenge of performance analysis of the pontoon sponson design is this...  

Deadrise Changing - The round-bottomed sponson shape are not as efficient as flat-bottomed planing surfaces.  Even these round surfaces can generate 'planing-mode' hydrodynamic lift, and the wetted surface needed to support hull weight decreases as speed increases. As the hull rises with reducing planing surface, the portion of the round pontoon circumference that is wetted changes.  The portion of the wetted pontoon circumference that is high on the pontoon, say close to 90degree point on its radius, has a very high local deadrise - close to 90 degree deadrise!  The lowest point on the radius, close to the bottom or 0degree point of radius has a very low local deadrise.  When much of the pontoon radius is wetted, the effective deadrise is very difficult to calculate.  depending on where we look on the lifting surface circumference, some parts of the lifting surface have high local deadrise and some parts of the circumference have a low local deadrise.  But all of the 'wetted' surface area, from the 0 degree point of radius up to the highest degree point of the wetted radius (at bWidth_wet) are contributing to Lift and should be included in the analysis. The amount of the radius of the pontoon that is wetted changes with the hull speed.  

It's important to know what the deadrise is at each point on the circumference, and it's important to know how much of the pontoon circumference is wetted at any speed.  lower deadrise lifting surfaces have higher lift coefficients (CLW) generating higher lift, while higher deadrise surfaces have lower lift coefficients and generate lower lift.  

Let's say at some speed, the round pontoon is wetted from 0degree around to the 30degree point on the radius.  some of this surface is high deadrise and some is lower deadrise.  We can calculate the 'average effective deadrise' of the wetted section of the round pontoon by 'integrating' all the contributing elements of the wetted circumference.

Effective deadrise = ∫ f(x,b), …
   where x=pontoon radius, b=bWidth (wetted width)
   from a=radius (0 degrees) to b=wetted radius (degrees)

How it Works - Due to changing lifting surface shape of this design feature when the planing width 'bWidth' changes, the 'Effective Deadrise' angle of lifting surfaces is complex and variable.  This can affect all lifts/drags and other performance results. For example, for a 24ft-4in tri-toon hull with 2x25inch diameter outboard round pontoons and a 27inch diameter round centerpod pontoon, powered by 2X Merc 400hp outboards might see sponsons that perform as - at 75 mph the 'Pad Deadrise' AVERAGE effective deadrise is 13.6 degrees and at 50.0 mph the AVERAGE effective deadrise is 30.1 degrees. At 75 mph the 'Pod Deadrise' AVERAGE effective deadrise is 20.6 degrees and at 50.0 mph the AVERAGE effective deadrise is 30.1 degrees.  

Wetted Surfaces - Hydrodynamic drag is made up of 'Friction Drag', 'Induced Drag', 'Profile Drag', and 'Spray Drag'. With 'Round Pontoon' shaped lifting surfaces, the Friction drag analysis must accomodate an increased surface wetted area simply because of the circular surfaces, compared to conventional flat lifting surfaces.  Wetted width, bWidth, isn't just a straight surface on a pontoon configuration, so the wetted length of the circular arc that is defined by the bWidth is considered for calculating total wetted surface.  (see Figure 5, above).

Aerodynamic Lift of Pontoon boats - Pontoon style hulls are normally configured with large decks that accommodate many passengers, with exposed structures to reduce weight.  This style of construction makes the pontoon hull quite aerodynamically inefficient. There is some aero lift generated, however.  If high-performance is the design goal, there are design accommodations that can be addressed to optimize aero performance:

• Reduced deck area - increases aerodynamic potential if some deck surface area remains aerodynamically clean and uncluttered.
• Skinned tunnel roof - skinning over structural members that support the deck surface such that tunnel roof (underside of deck surface) is smooth and unobstructed
• Lifting strakes - effectively positioned strakes on (both) sides of round pontoons will increase 'effective deadrise' and improve hydrodynamic lift
• Reduced cockpit/center console width - will reduce cockpit drag and increase aerodynamically available deck surfaces.
• Reduced tunnel height - increases ground effect lift contribution 

Tritoon vs Pontoon - A tritoon is a triple-hull pontoon boat. Instead of having two large tubes beneath the deck, a tritoon has a third tube in the center that distributes weight more evenly over the water and provides additional hydrodynamic lift. This added stability and structure also means the boat can accomodate more weight, and more horsepower with multi-engine installations.

The 'Pod Height' of the center pontoon can be optimized for stablity, speed and handling, effectively reducing load on outboard sponsons at higher velocities.