Surf Canoe

Hi there,

Im an industrial design student in NZ for my project this year i'm looking at redesigning the surf canoe. See vids bellow for surf canoe.

http://www.youtube.com/watch?v=To8v...DvjVQa1PpcFNPiDcFSVsmHLfo1y2H1xyIChZVyXa_Ea4=

http://www.youtube.com/watch?v=S9WJ...DvjVQa1PpcFNPiDcFSVsmHEcVHSvu0RKuMfEzdcVKqR4=


The surf canoe is a race within the surf sport side of surflifesaving. The boats before about 10 years ago were single hull. They changed to cats as they are more stable and don't fill up with water.

I have come up with a few research questions which i thought i would put on here to see if anyone had info/ ideas on different areas. I am fresh to the boat design area but am eager to learn so any help would be much appreciated.

Questions are.

1. How can I make a faster hull that still performs in mixed surf conditions.
- I would like to be able to reduce bounce from the forces of paddling to achieve better boat run. Also looking at the bow area and how it could cut through waves better.

2 How can I make the boat pull waves and runners more easily.

3 How could I design the boat differently that it does not broach on waves as easily.
-see video canoe crashes ^ .These boats are near impossible in big surf (6ft+) to hold straight

4 How can I implement ergonomic principals in such a way that the design
encourages high paddling efficiency

5 How can the buoy turn be improved through an improved rudder system.

There is a few different restrictions on the boats allot of which are aimed at the single hull canoe. However here are the few which are relevant.
-LOA. min 5.5m max 6.5m
-External protusions- There is to be zero external protrusions to the hull. i.e skeg fins or keels.
-Seating To be incorperated in such a way paddlers paddle 2x2 abreast.

Any questions ill do my best to answer. Look forward to hearing your thoughts.
Cheers Kieran

 

Where are the rudder(s) ? Don't see any in the pix. If external protrusions are forbidden, what kind of rudder is/isn't allowed ? The only way I could see to control the broaching would be some kind of retractable rudder that could be kept raised when going out to sea.

 

Rudder

Yes there is a rudder system. It is controlled by the two back paddlers through one foot pedal each. It is sprung so the boat can beach. Im not sure if the white water from these larger waves is what causes the rudder to turn and broach or if its the force from the wave which turns the hulls.

 

Think of the boat (the bit in the water) as an arrow in flight, if the resistance to sideways motion is located behind the centre of gravity, it will run straight, but if it goes ahead of it, the boat can run off course. Watch what the lifesavers do on their surf skis when surfing in, they shift backward with their legs dragging in the water and the ski tilted up so it doesn't nosedive. You need some decent lateral plane right aft.

 

I would use old eskimo trick for their kayaks, they use wider transoms above the waterline. When going ashore in following water this transom presents a wide and nice area for the wave to push it forward. That should help.

Another idea for speeding up the boat is using hydrofoils. You got there a good speed and I think hydrofoils may lift the hulls a little upward. Theoretically it should reduce wetted area and friction. A hydrofoil shape below the waterline repeating the arms shape above should do the tripple chores:

(a) increase rigidity of the system and
(b) provide some uplift at higher speed and
(c) introducing some displacement in the hydrofoil will allow to make the main hulls thinner thus reducing the drag

I am pretty confident that you guys could make the hull body much lighter and slimmer in order to have less drag
I just read about "zero" protrusions. I think there is no regulation where to have the arm connecting two hulls. If you connect under water with hydrofoil shape it may OR may not benefit at all. It needs to be investigated.

Just my opinion.

 

Study the traditional Hawaiian surfing canoes. They have evolved in big surf over a very long time and are the best in the world.
Note that the sharp deep forefoot of your existing hulls is a surefire way to cause a broach. You also need extra buoyancy aft for surfing in.

 

See this paper to understand what happens with the wave and the boat http://www.kayakwaveology.com/wp-content/uploads/2010/09/CrossingTheBarBesier105.pdf

 

I'd be worried about my head or privates smacking into the other hull or

cross beams in a surf wipe out. Seems like gunnels have rather sharp edges.

 

Spoon bows and fish tails and the CG as far forward as you can get it. Low (or none) torsion on the crossbeams.

If the port hull and aft crossbeam were rigid and the stbd hull and fore crossbeam were rigid and each were connected to the opposite with a heim joint- that might work, but it might feel a bit odd.

Loose the rear rudder and replace with a fixed angle of attack bow rudder in each hull that extends and retracts. One pulls each way. Controlled by a man each side but interlocked so one goes up then the other goes down. Spring loaded to both up position and if anyone goes overboard, both retract (clutch disengages).

Of course #2 and #3 are mutually exclusive. That's life.

 

Thank you very much for your reply! However allot of it is beyond me could you please help me understand ?
How would low torsion on the cross beams help ?
What are fish tails ?
How would a fixed angle of attack bow rudder work ? Would that mean that it would not move? Like a keel of sorts ? Is that in relation to the broaching also?

Would weight behind the C.O.G be better for surfing ? Just going from surfboats and how when the crews catch waves the rowers all move to the rear of the boat ?
http://www.youtube.com/watch?v=iMelI777Y9o&feature=fvwrel

I have also come across an example of biomimicry where they have taken inspiration from the humpback whales fins. In which they have found "the tubercles on the flipper delay the stall angle by approximately 40%, while increasing lift and decreasing drag".
Along with it being used on windmill and helicopter blades they have made a surfboard fin. Would this technology also work on the bow of boat?
http://www.asknature.org/product/6b64f488c9d06dc65c46fa210e17844e

The technique for the buoy turn is the outside paddlers paddle hard and the front inside paddler does a bowrudder or draw stroke type movement to pull the nose around and back inside paddler digs their paddle in for the boat to pivot off. Was wondering if there was a front rudder that operated off the front cross beam that replicated the front paddlers stroke if it would be effective.

 

Yeah the hydrofoil is an interesting idea i wonder if four canoe paddlers could provide enough power for the craft that the hydrofoils would be effective or if they weren't then it would just make more resistance ?

I heard somewhere of a hobi cat that had an inverted v in the hulls which provided more lift ?