ROTAX Engines

A conversation among Whalers
jimh
Posts: 11670
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

ROTAX Engines

Postby jimh » Tue Aug 31, 2021 9:31 am

As a corollary to the recent discussion about the SEA DOO SWITCH boat as the new product from BRP that came from the their Project-M development, the new boat uses a ROTAX four-stroke-power-cycle engine, built by BRP's other engine maker, ROTAX of Austria.

ROTAX has been making modern small four-stroke-power-cycle engines for aircraft for 100 years. In terms of engine reliability, engine weight, and engine power-to-weight, an aircraft engine would seem to impose more stringent demands than an outboard engine. If an outboard engine fails in service, the boat continues to float, whereas an aircraft engine that fails in service presents a much more serious obstacle to a safe return to the ground.

These ROTAX engines are also quite fuel efficient, to the point that they have been used in military drone aircraft where long flight endurance is a very desirable characteristic. The smaller drones used a ROTAX 912 iS engine, which produces 100-HP using a four-cylinder-opposed design, uses fuel-injection and an electronic engine management module, has a rating of 2,000-hours between recommended overhaul, and has been see in some crashed drone wreckage photographs. For example, visit:

https://www.recreationalflying.com/uplo ... 1071c.jpeg

Once Bombardier found out that some non-US countries were using ROTAX engines in their military drones (notably Turkey), they stopped exporting them to those countries.

The 2,000-hours between recommended overhauls is also a very attractive specification. I don't know exactly what an aircraft engine "overhaul" consists in. (For some guidance, see the FAA Advisory on that topic.) In terms of service life, 2,000-hours would be reasonable for me as a recreational boater. My E-TEC engine is now in its 13th season of use and is still only at 535-hours of running time. Extrapolating my pattern or use of my boat to 2,000-hours suggests that I could get 48 seasons of recreational boating out of a ROTAX engine rated for that much use "between overhauls." However, I infer from the existence of "100-hour maintenance kits" that the ROTAX aircraft engine does need some attention every 100-hours.

The SEA DOO SWITCH uses a larger three-cylinder 1.630-liter engine which can produced up to 230-HP output without supercharging, and 300-HP with supercharging. For comparison, the Mercury four-cylinder in-line 1.7-liter VERADO with supercharging was sold at a top horsepower rating of 200-HP. To get 300-HP from the VERADO engines Mercury switched to a six-cylinder in-line 2.7-liter displacement engine, which they have since boosted to 400-HP in special race versions.

Even the non-supercharged 230-HP engine seems to be producing a lot of horsepower per liter of displacement: 140-HP per liter is no slouch.

Is there something from BRP in the future in the way of using their ROTAX engines in boats other than jet-skis? Again, one would have to think that putting a ROTAX engine on the transom of a BRP boat would be more profitable to the BRP corporation than buying engines from Brunswick to put on them.

Don SSDD
Posts: 313
Joined: Fri Oct 23, 2015 6:58 am
Location: Nova Scotia

Re: ROTAX Engines

Postby Don SSDD » Wed Sep 01, 2021 6:37 am

It seems the pricing on the Switch is reasonable considering it’s size and performance, which makes it appear the engine cost of the Rotax in it is reasonable. It will be interesting to see what BRP will do with the Rotax in future, possibly using one with a propeller instead of jet drive? I assume they are light weight and fuel efficient if used in drones.
1986 Outrage 18 with 2001 Honda 130 HP
Former Owner 1991 Guardian 19 with 1994 Evinrude V4 140HP
Former owner 1987 Montauk with 1998 Mercury 90HP
Nova Scotia

Jefecinco
Posts: 1592
Joined: Fri Oct 09, 2015 6:35 pm
Location: Gulf Shores, AL

Re: ROTAX Engines

Postby Jefecinco » Wed Sep 01, 2021 10:44 am

When I fist saw the Rotax name I assumed the engines were rotary as in the Wankel engines used in some Mazda vehicles. I was disappointed to learn they were just more or less ordinary in-line reciprocating engines. The appear to enjoy reliability and weight advantages.
Butch

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: ROTAX Engines

Postby dtmackey » Wed Sep 01, 2021 4:04 pm

Jefecinco wrote:When I fist saw the Rotax name I assumed the engines were rotary as in the Wankel engines used in some Mazda vehicles. I was disappointed to learn they were just more or less ordinary in-line reciprocating engines. The appear to enjoy reliability and weight advantages.


The older (1980s - 2000s) 2 stroke Rotax motors did emply a "rotary" technology, but this was a rotary valve in place of reed valves on an in-line reciporcating engine. SkiDoo used these and was a dominant force in snowmobile racing and the motors were nicknamed balogna cutters as the valve reminded many of a deli slicer.

D-

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: ROTAX Engines

Postby dtmackey » Wed Sep 01, 2021 4:12 pm

Don SSDD wrote:It seems the pricing on the Switch is reasonable considering it’s size and performance, which makes it appear the engine cost of the Rotax in it is reasonable. It will be interesting to see what BRP will do with the Rotax in future, possibly using one with a propeller instead of jet drive? I assume they are light weight and fuel efficient if used in drones.


I would image the efficiency using a prop would increase as jet drives are generally 30% less efficient than props on outboards. My guess is they will stick with jetdrives as the Switch seems geared towards watersports and jet drives are the safer propulsion. Having the drive unit in common with their SeaDoo Waverunner PWCs provides the perfect econmy of scale in manufacturing rather than a custom powerplant/drive unit.

D-

Tacky79
Posts: 130
Joined: Wed May 03, 2017 1:49 pm

Re: ROTAX Engines

Postby Tacky79 » Wed Sep 01, 2021 8:02 pm

I was just reading that older BMW F650GS motorcycles used a Rotax engine back in the late 1990's.
2017 Boston Whaler Montauk 190 w/ 150 Merc/Fish Pkg/Bowrail delete/aft seating
1979 Boston Whaler Harpoon 5.2 sailboat with sails and a tiller :D

jimh
Posts: 11670
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: ROTAX Engines

Postby jimh » Mon Sep 06, 2021 7:59 pm

dtmackey wrote:My guess is [SEADOO] will stick with jetdrives as the Switch seems geared towards watersports and jet drives are the safer propulsion.


The USCG 45-foot response boat uses jet drives. I believe one of the reasons was safer operation around persons in the water that were going to retrieved and brought aboard in a rescue operation. The waterjet drive also reduced the draft of the vessel, allowing it to operate in shallower water; this could be important to the USCG in try to reach vessels aground.

The efficiency of jet drives improves as the hull speed improves, from what I recall reading. Some very high speed military boats employ jet drives when they are at high boat speeds. At low boat speeds, under 20-MPH, a propeller drive will probably be more efficient than a water jet drive

Admittedly this literature is from a maker of water jet drives so naturally it contains favorable remarks, but it says, in part, that:

HamiltonJet waterjets are designed to be optimized for vessel speeds from 25 to 50 knots, dependent on application’s engineering variables including hull resistance and type, engine power rating and rpm, impeller rating, etc.

HIGH EFFICIENCY
--Propulsive coefficients as good or higher than the best propeller systems achievable at medium to high planing speeds

--Flexibility when using multiple waterjets may allow operators to continue to operate efficiently on fewer drives
Source: https://www.hamiltonjet.com/global/waterjet-overview

Also see a prior discussion of efficiency of jet drives at

https://continuouswave.com/ubb/Forum4/HTML/007832.html

dtmackey
Posts: 760
Joined: Thu Sep 28, 2017 9:29 pm

Re: ROTAX Engines

Postby dtmackey » Tue Sep 07, 2021 11:49 am

I read the old thread on jet drive efficiency and there's so many variables in the comparisions and information that people are referring to is apples to oranges which muddies the water on a true comparison. Comparing ferries or larger heavier commerical boats to a jetdrive and other drive systems is a moot point since the Switch is a small light recreational boat that couldn't be more different. It's true that jet drives can have a pump efficiency of up to 90% (in a perfect world), but that is at a specific RPM and usually in the very upper end of the RPM range where few people actually operate a boat. Jet drives are also less complex without lower unit gears, no lower unit that creates drag and a propeller that can be a safety hazard for some, not to mention generally less costly to implement in recreational watercraft.

If one could take a side by side comparision of 3 identical recreational boats with the various power options (outboard, jet and inboard) then a great comparision could be made, as with the test in the shared link. The results are what I expected and if jet drives were truely more efficient as some claim, then outboards with jet drive would have taken over the market, but they haven't because they are not and only have a very small target market that needs them for shallow running. In outboards motors, engine power takes a big hit when converted to jet HP, about a 30% hit.

Image

Boats are all the same and the dicrepency in length is due to an optional swim platform on the jetboat, but that's insignificant in the comparision.

Information is from a Boating Magazine comparision (Aug 28, 2017) and good reading.

https://www.boatingmag.com/boat-engine-comparison/

In a nutshell:

Image
Image

D-

jimh
Posts: 11670
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: ROTAX Engines

Postby jimh » Wed Sep 08, 2021 8:11 am

The ROTAX engine power shaft output can be connected to various methods of propulsion. It is not limited to water jet drives.

As I mentioned in my earlier remarks, the water jet drive efficiency is best at high planing speeds.

While at low speed displacement hull operation, the water jet loses efficiency, it has very good maneuvering ability.

A water jet propulsion system does not require the engine speed to be reduced to allow shifting into reverse. The reverse thrust from a water jet is usually very good. With a skilled operator who understands the water jet propulsion mechanism, a boat can be made to perform a180-degree turn in a very small circle.

With SEA DOO using water jet propulsion on the personal water craft products, their use of a water jet propulsion on the SWITCH is not a surprise. The water jet propulsion has another big advantage: no exposed propeller in the water. Without an exposed propeller, any swimmer in the water is much safer around a jet drive boat than around a propeller drive boat, particularly if the operator of the boat is a new boater. Another advantage, and again particularly for the new boater, is a jet drive won't have a propeller or engine skeg as the deepest draft projection on the hull. Many new boaters discover that having the propeller blade strike the bottom is an expensive learning exercise.

I am still interested to see what Project Ghost was about, and if there was any linkage to use of ROTAX engines in some new and novel propulsion system similar to an outboard engine, with the ability for the product to be bolted onto an existing boat transom and replace the conventional outboard with a much lower profile engine and drive system.