Although often refereed to as prop or jet drive, "Drive" is used to reference to the prime mover and "Propulsion" to what provides forward thrust. There is no universal answer as to which is better for ASVs. Both have benefits & drawbacks and each entails specific requirements and precautions. It often comes down to deciding which is the most suitable for your specific application, and there are number of variables to factor into the decision.

General Summary

The chart below is a general summary of trades between the two. Few of these criteria are absolute black & white, so additional narrative is included that might assist in the selection process.

This is often the deciding factor. If the study area prohibits the use of gasoline powered vessels, an eDrive may be the only viable alternative. Always be sure to review and understand rules and regulations of the proposed study area when planning a mission or selecting a vessel type - especially if there are multiple owners or land stewards across various levels of government.

When speaking in terms of endurance, consider not only the max duration of a typical deployment (minus reserve time) but also the turn-around time between launches (see Mission Planning below). Also consider actual use-cases when looking at deployment endurance - it may be nice to have 8 hours on the water, but if your deployment is dependent by tidal cycles, 4 hrs may be sufficient.

In high power systems such as the Jetyak or Yellowedge - with all things being equal - gas provides a greater power-to-weight ratio and the shortest turn-around between deployments. In a Jetyak it's quite common to get 8 hours of surveying on a 5-gal tank of fuel with just a few minutes required for re-fueling - which can be done from a chase boat if required. Five gallons of fuel weigh approximately 30 lbs; getting the equivalent endurance from a DC source would require several hundred pounds of high-energy batteries.

Mission planning for eDrive ASVs generally require greater attention to detail, as actual power consumption will vary with throttle position, water conditions and will de-rate in air temperatures below 20° C. Also for systems where batteries are not readily swappable, re-charge time needs to be factored when estimating mission efficiency. Non-swappable batteries will typically require the same amount of time to charge as the survey mission that discharged them. Again, this is a generalization - re-charge times can be much longer depending on the conditions they were depleted under. During mission planning always use data from test missions as a starting point in factoring approximate discharge and re-charge times.

Expedition Missions - where equipment is shipped weeks or months in advance to reach a remote site for critical vessel deployment entails detailed logistics. If regular 87-octane fuel is used for field generators, the same fuel can be provisioned for the Jetyak without any additional considerations, other than quantity. Typical LiFePO₄ eDrive battery systems are certified to UN38.3 safety standards, and UN3480 Class 9 shipping classifications. During Expedition Mission Planning be aware of the shipping implications involving Class 9 hazardous goods, as generally these are not permitted to be transported by air.

For Local Missions, fuel can be purchased as required with very little planning - oftentimes as an afterthought. However greater planning and considerations for battery charging apply. If intending to power the charger off a support vehicle, ensure the inverter and vehicle alternator can handle the charger load & duty cycle - and ensure the ASV and support vehicle can be co-located during charging.

When it's critical and time-sensitive to quickly get out on the water - eg to establish a baseline before a rapidly approaching storm - and assuming both systems are properly maintained - either can have an advantage - depending on the conditions.

eDrive ASVs can handle energetic post-storm waters without fouling air intake or exhaust ports at the cost of lower endurance. If these hazards are avoided, gas systems will generally have have longer endurance, which better supports extending a deployment if factors necessitate.

Benefits are typically neutral for a less critical deployments (eg post-storm assessment) provided vessel deployment can be deferred until favorable water conditions return.

A day of Jetyak operation typically require a 5-gallon Jerry can of 87-octane or higher regular unleaded fuel, universally available anywhere world-wide. Other typical safety gear for deployments are a 10 lb ABC fire extinguisher and some absorbent mats in the event of spillage.

eDrive systems require dedicated charging circuits and generator capacity (as well as fuel for the generator) if the ASV is intended to be used for multiple deployments in locations where AC power is not available. All eDrive systems provided by ISC will charge in less than 8 hours (some in less than 4 hours), and spare batteries for rapid swapping are an option.

As discussed above in Mission Planning, Class 9 hazardous goods are extremely difficult to ship by air. They are generally not allowed on any aircraft carrying passengers, and special provisions must be made between shipper and carrier if they are shipped by cargo-only aircraft.

The number of allowable cells in a single shipment, and how the cells are contained, as well as their charge state are all evolving and subject to conflicting interpretation. Suffice it to say, if planning to air-freight an eDrive ASV, plan on dealing with a logistics hurdle likely involving a moving target of paperwork at both shipment origin and destination, and be mindful that the additional restrictions may come up when return shipping.

eDrive systems produce zero emissions during operation, and have zero chance of leaking oil or spilling fuel into environmentally-sensitive study areas. We are confining this to emissions during operation, and not considering life-cycle implications of either option

eDrive systems are quieter than a 4 stroke gas engine for an equivalent power output. This can enable missions involving ocean acoustics without introducing unwanted background noise. This also has the added benefit of being less intrusive when deployed in populated areas.

eDrives are the hands-down winner. They can take a wave or constant spray and continue operating without risk of fouling air intakes or exhaust ports. A large wave event that causes stalling can hydrolock an gas engine - which in extreme cases can bend a rod resulting in catastrophic engine damage. These are never a concern with an eDrive.

In addition eDrive systems can operate at any angles indefinitely, whereas 4-stroke systems have max inclination angles of typically <25 degrees before oil starvation becomes a concern. Even when non-operational, tipping the nose up or down >30 degrees (eg during deployment) may result in fouling of the carbon fuel canister or other components evaporative recovery system, and dilute the oil with gasoline.

eDrives can also be integrated into completely sealed unsinkable and self-righting hulls - something not possible with gas engines. For insight into prop or jet drive fouling see the corresponding section in Propulsion Selection.

In discussing safety, consider not only the edge cases that result in fire, but also the ability to avoid dangerous situations in attempting to rescue a stalled or failed vessel. A Jetyak's engine can be swamped and disabled around obstacles whereas an eDrive in the same conditions may have kept operating. In this context the "safest" vessel is the one less prone at putting a field crew at risk having to embark on a recovery operation.

As far as fires, this is both somewhat subjective and controversial. Both gasoline and Lithium are highly volatile and need to be handled with care. Furthermore, for ASVs, it is not always directly applicable to use common ICE and EV powered vehicles as a basis of comparison.

Both systems if well maintained and not subject to catastrophic damage can be considered safe. However, in general, fires involving the quantities of gasoline required for Jetyak operations can usually be quickly brought under control - even if indoors - using common fire fighting gear and procedures.

Fires involving the high-capacity and extremely high energy-density Lithium-based battery chemistry used in the larger eDrive systems burn extremely fast and very hot. These require advanced fire-fighting techniques to bring under control and can remain a fire hazard days after being extinguished.

Generally speaking, short-term maintenance of 4-stroke small engines is relatively inexpensive and not that difficult (think of a lawnmower stored in a shed). Problems arise when ASVs are deployed in salt water and not cleaned or stored properly (i.e. run hard and hung-up wet), then expected to start right-up after extended storage. This is especially true if stored outdoors for extended periods.

Following the recommended maintenance and storage guidelines (as outlined in the Jetyak manual) should mitigate these problems and give the greatest chance of trouble-free start-up after seasonal storage. Do plan on normal small-engine maintenance - especially in salt-water environments.

eDrive systems also require cleaning and a fresh-water rinse, but other than periodic battery tendering have no ignition, carburetor or fuel delivery systems to maintain.

Small 4-stroke engines like the Kohler CH395 have a proven long-term track-record of maintainability. They have simple ignition systems that are easy to maintain, and carburetors can be field swapped in a matter of minutes, and parts are globally available from an OEM dealer network. They do require some basic knowledge and hand tools to maintain and tune, along with regular engine oil changes (as with any gas-powered vehicle) - but in knowledgeable hands these engines are renown for providing inexpensive trouble-free operation for years. However, salt water operation compounds degradation and strict maintenance is required to keep engines operating long-term.

eDrive systems do not have the same degradation issues - long-term battery capacity is the principal degradation. ICS eDrive battery systems are high-performance and durable, designed specifically for electric watercraft. For larger systems these are typically rated for 3000 charge cycles at 80% DOD (Depth of Discharge). For smaller systems LiPo batteries can be swapped-out once capacity is diminished similar to that of a typical UAV drone.