HPB Building Frequently Asked Questions
HPB Building Frequently Asked Questions
The building of Human Powered Boats is still an art form rather than a science. As such many things are tried in the name of building a more efficient human powered machine. Most of these things don't work too well. On the IHPVA HPB list, these things are discussed length. Victor Garza noted that it may be a good idea to list the stuff that works and doesn't work, as the same questions come up like clockwork every year or so.
Hulls  
Keels Weight required to keep boat upright is too high for most HPB use. No clear advantage.
Planing hulls Humans do not possess enough power to achieve planing speeds
Bidarkas Currently untested in HPB application. May be problem in shallows and weeds.
Tilting/pivoting drivetrains Works well to allow weed cleaning and shallow water ingress/egress. Increases complexity and weight.
Hydrofoil wings Work well and fast for short distances, riders cannot sustain flight for extended periods and at that time they are a liability.
Submerged Floatation Not practical - very hard to control floatation/balance.
Subsurface bulb bows  Offers 5 - 25% reduction in energy for larger vessels- 
not often exploited with HPBs.
Catamaran hulls Much more stable than a monohull but will have higher  wetted surface giving it more viscous drag compared with a monohull of the same displacement.
Propulsion / Drivetrain  
Air Propellers Work well for shallow water but are easily affected by wind and are bulky
Jet propulsion / squid drive No, losses too high. Efficiency probably less than 50%. May be acceptable in a very shallow water application. 
Surface piercing props Not practical
Paddlewheels Ok for some applications, but noisy and splashy
Variable pitch props Yes, if light, efficient and controllable on the fly
Folding props Yes, if light and efficient
Inboard power generation Converted to electric thrust Yes, if conversion is high efficiency, and a mechanical means of power transfer is difficult. Used in some subs.
Anticavitation plates  Useful for shallow props directly behind struts. Efficiency may suffer in other applications.
Weed shedding props Maybe in some applications where efficiency losses tolerable 
Weed cutting mechanisms for props Good luck has not been had with these, they jam
Kort nozzles Maybe for perfectly clear, non weedy water
Right angle gearboxes 
Light industrial right angle drives are suitable for HPB drives. There are a wide range of suppliers- Mitrpak, Zero-Max, Siti, TEA Transmissions. Low cost right angle drill drives have limited use due to lack of stiffness in the housing.
Flexible prop shafts It is possible to make curved shafts from flexible materials. Fatigue life will be a consideration if the stress range exceeds 40% of yield strength. Torsional rigidity is important for smooth power transmission.
Clipless pedals Make pedaling less tiring in the recumbent position. Need to make sure that feet can be twisted at any point for safety if capsized
Flywheels Not found to offer any benefit that offsets the added weight
Oscillation foil drive system Can be made efficient at cruising speed for displacement craft. Hobie Mirage is a commercial example.
Misc  
Engine (human) An elite male athlete can generate up to 20W/ kg of body weight for a few seconds. Continuous output for an elite athlete is around 6W/kg. The corresponding figures for an untrained but fit person is 12W/kg peak and 2.5W/kg continuous.
GPS These can be used to give instantaneous speed and most have the facility to download the track log for performance monitoring on a trip.
Windscreen & fairing Useful for wave protection but HPBs are too slow for a performance improvement. Used on Escapade but not very many others.

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