Rotary Power ?

[Gordy]

I came across this web site and this engine would fit just fine in the offshore fishing boat I plan to build AFTER I build a Belhaven and rebuild my small English roadster...and re-do the bath...and the kitchen...and a deck.

Well it's nice to think about anyway.

Does anyone know anything about these engines?

http://www.rotarymarine.com/index.html

[KWorkinger]

I have seen instances where rotary engines were coupled to water jets: a nice, small, light weight application for light-weight boats. However, I do not think that rotary engines are able to generate the torque needed to spin a traditional prop.

[Adam L]

I happen to go to school where Rotary Power Marine Corp is. A friend of mine actually worked part time for them for a while. Its basically a one man operation using the Mazda rotary block for marine applications. The package is great for jet drives because of the power to weight ratio, but the torque problems (mentioned above) limit it to only jets. The latest thing to come out of RPMC is a supercharged setup which is pretty cool. He also does some RX-7 rebuilds when business is slow. Rotary motors are probably best suited for smaller planing craft. Prices a pretty steep I believe and who knows about parts availability

[Rick Tyler]

Of *course* rotary engines can spin a prop. That's what reduction gears are for -- converting a high-revving high-horsepower engine into a lower-revving, higher-torque engine.

There is also no particular reason that someone couldn't build a bigger rotary engine with more power and torque. Well, one reason might be that it wouldn't be economical for the size of the market.

The twin rotor Mazda 13B engine specs are:

Displacement: 1308cc/80ci
Compression Ratio: 9.4:1
Output(hp): 135bhp @ 6000 rpm
Torque: 133lb-ft @ 2750 rpm

A Pleasurecraft SeaMaxx 5.0 liter gasoline marine engine makes 275HP and 305 lb-ft of torque.

I don't see why torque made by a piston engine is magical. A 4-rotor engine of the same specific output as the old Mazda 13B would make about 270 HP and 266 lb-ft of torque. This is not far from the power output of the much-larger piston engine.

Rotary engines have had some inherent engineering problems, mostly to do with meeting emissions controls and keeping the edges of the rotor sealed. Lack of torque is not a problem.

- Rick Tyler

[SailBoatDude]

Reciprocating mass is what develops torque. The relative lack of the substantial mass of the crank, rods, and pistons in a rotary means it's easier to slow down a loaded rotary power plant compared to a reciprocating engine typically found in gas and diesel arrangements.

The problem is, we need a power plant able to generate near max output under near full load conditions nearly all the time it's in operation. The rotary can't yet provide this and this is the kicker in rotary use in boats. The rotary lacks the mass and has to rely on torque multiplication through a transmission to get it to be reasonably efficient. This is why some are experimenting with jetdrives and rotaries. The jet needs to be overly spun to work and to over come it's own inefficiencies, and matting it to a power plant that also needs to be overly spun to develop the energy necessary is a natural joining.

Lets face facts, a jet needs near twice the engine displacement to develop the same power a conventional prop needs. If we take the 13B specs and translate them to conventional engines then everybody and their brother would be repowering with a rotary because on paper they are hands down winners. Lets see, 80 CID (a Harley engine) w/ 135 H.P @ 6,000 RPM & 133 @ 2,750 RPM right? It develops it's max torque at less then half it's horse power RPM. Assuming the HP curves and torque curves are relatively smooth it would put to shame most conventional engines. Now we know this isn't the case, but lets say the power curves have a nice smooth slope upward 'till max HP and torque are met (at their respective RPM's)

Now lets look at a 350 CID marine engine (over four times the displacement of the 13B) developing say 300 HP and 300 ft. lb. of torque. The V8 generates a bit better then twice the power, using over four times the displacement. The rotary on paper develops twice the power (per cubic inch) the V8 does? Wow! I need to get one of those man. Now why would any industry pass this up? I can see a whole new rotary re-powering black market starting up over night if this had any resemblance to reality.

The bottom line is, HP and torque curves should align for the most part, in a power plant that will be asked to provide 90% output 90% of it's operational time. A rotary can't do this as Rick Tyler's specs of the 13B clearly show. Running a WOT or near so would mean the engine is 3,300 RPM (there abouts) over it's max torque RPM. I wonder what the torque curve for a rotary looks like when it's over twice the RPM for max torque. Is it any where near 135 ft. lbs.? Probably not, or we'd all be going "Zoom . Zoom" right?

[ 02-10-2003, 02:31 AM: Message edited by: SailBoatDude ]

[Matt Middleton]

posted by SailBoatDude:
Reciprocating mass is what develops torque. It would be nice if it were that easy, because then you could increase the torque of any engine by adding a heavy flywheel. But it doesn't really work that way. The physics don't add up- heavy rods and pistons would tend to slow the engine down. Only the flywheel (OK, maybe the crank, too) maintains the rotational intertia, an that only serves to smooth out the pulses inherent in a piston engine. It doesn't add torque.

Wow! I need to get one of those man. Now why would any industry pass this up? Like Rick said, there are some engineering difficulties with the engine. Part of the reason that rotary engines got a bad rap is that a few carmakers tried to use them without sufficiently addressing these problems, and so their engines were terrible. Mazda did their homework, and had a great experience as a result. They've been putting them in cars for thirty-something years now, I think, and are about to introduce another to their line.

Later,
Matt Middleton

[John Gearing]

I had a Mazda RX-7 with the 12A engine for 15 years and put 100,000 miles on it, giving it a total of over 150K miles. The engine ran flawlessly. The trick is that you have to use the right oil (not synthetic), change it regularly, and keep the sump topped up. The Mazda motor is designed to pump sump oil into the air/fuel mixture as a way of getting lube into the combustion chamber, therefore, if you don't keep the sump topped you can literally run yourself out of oil. This is something, in my experience, that many RX-7 owners either never knew about (it used to be printed on the cover of the owner's manual in huge letters) or forgot. The rotary has a stock redline of around 7K rpm and with tweaking will easily top 10,000. IIRC the formula for HP takes RPM as a big factor, so increasing the RPM results in higher HP figures. The main drawback to the proliferation of the rotary powerplant in Mazda's cars (once upon a time they offered a rotary pick'em-up-truck, as well as a rotary sedan) is lousy gas mileage. I was doing well to get 19mpg with my RX-7, with fairly reasonable driving. Putting rotaries in their whole line would have made it tough for Mazda to meet CAFE standards. The 12A and 13B engines are two-rotor affairs, but Mazda has had a 3-rotor mill available in Japan for years, and their LeMans winning race car had 4 rotors. In theory,it is relatively easy to add additional rotors, though I would expect that cooling problems might develop. The twin-turbo in the last-generation RX-7 developed about 250 HP on the same 13B engine IIRC. I have no idea how a rotary would fare as a marine powerplant, but simply note that the use of reduction gear sounds like a good one.

[Rick Tyler]

Originally posted by SailBoatDude:
Reciprocating mass is what develops torque. The relative lack of the substantial mass of the crank, rods, and pistons in a rotary means it's easier to slow down a loaded rotary power plant compared to a reciprocating engine typically found in gas and diesel arrangements.

<snip>
Lets face facts, a jet needs near twice the engine displacement to develop the same power a conventional prop needs. If we take the 13B specs and translate them to conventional engines then everybody and their brother would be repowering with a rotary because on paper they are hands down winners.
<snip>
The bottom line is, HP and torque curves should align for the most part, in a power plant that will be asked to provide 90% output 90% of it's operational time. A rotary can't do this as Rick Tyler's specs of the 13B clearly show. Running a WOT or near so would mean the engine is 3,300 RPM (there abouts) over it's max torque RPM. I wonder what the torque curve for a rotary looks like when it's over twice the RPM for max torque. Is it any where near 135 ft. lbs.? Probably not, or we'd all be going "Zoom . Zoom" right?Fuel burning and being converted to rotary motion creates torque. Rotating mass does not. Rotating mass helps even out the power pulses to make the whole system smoother, but it does not make more torque. If mass is good, why are marine engines getting lighter year after year? According to Dave Gerr, older gasoline marine engines (more than 50 years ago) weighed 50 to 85 pounds per horsepower. The Caterpillar 3208 diesel has 11.6 pounds per horsepower. Although Gerr does not say this, I'd be willing to bet that every component in the Cat 3208 weighs less than every component in that old gasoline engine.

There are at least a couple of companies now selling rotary engines for marine use. You might want to take a look at Rotary Power International (http://www.rotarypowerinternational.com/Spec%20Sheets.htm) to become more familiar with the technology. RPI shows the torque curve of an 11.6 liter gasoline rotary engine with 500 HP at 3,600 RPM and torque of 750 lb-ft at 3,300 RPM. That sould be adequate.

I apologize for using the specs of an old auto engine (the 13B) instead of doing the work to find a marine rotary example in my last post. Any engine works best for the application for which it was designed, and marine rotaries are are no exception.

The specific output of piston engines have improved so much in the last 20 years that rotaries may not have much of an advantage any more, but it does not have anything to do with their ability to deliver torque or power. They may still have packaging and weight advantages, and they could produce less vibration, especially when compared to smaller piston engines.

- Rick Tyler

[ 02-10-2003, 02:58 PM: Message edited by: Rick Tyler ]

[Dan McCosh]

The rotar in a rotary spins at 1/3 the crankshaft speed, with three power pulses per revolution of the rotar itself. This is why the engine is more compact than a piston engine. The combustion chamber is an inefficient shape, which translates into poor specific fuel consumption.
There is no reason why a rotary marine engine couldn't be developed (considerable work was done on aircraft rotaries), but I would be suspicious of a conversion from a car engine. Cooling, gearing, etc. would be problematic unless engineered for the purpose. It's an interesting idea, though.

[ion barnes]

I am not up on the rotary engines but some of the previous posts are misleading.
I have had the impression that the rotors were part of the crank not geared to it.
They are water cooled therefore, a heat exchanger can be employed, you just have to figure out the BTUs being developed so as to equal the heat exchanger requirments.
The torque issue can be handled by adding to the flywheel mass, if required. Thats why you see very robust flywheels on single or twin piston engines, partly to smooth out the punch of the firing stroke but also to keep it spinning, and once it is spinning, just try to stop it!and they were direct drive.
A transmission is a consideration, but only after you have worked out the premise of the intended use or application. Something like a hydroplane may use a direct drive and thus, a very small prop, or reduce the shaft speed from the crank speed, which ups the torque and means you can increase or adjust the size of the prop.
I met a gentleman from Seattle some 25 years ago, who had a powerboat with twin Pratt& Whitney gas turbines. They turned up close to 75,000 rpm if my memorey is correct, and went thru a couple of reduction boxes and full feathering props. He actually used the pitch to absorb most of the torque. ie high rpm and fine pitch which is no different than a Sabb twin diesel with feathering prop. The guy's name is Chuck Lyford.

[Dale R. Hamilton]

You guys have succeeded in getting me interested in rotary marine power. I'm planning on building Ray Sargeants runabout that he had powered with a marinized Subaru engine- because transome height was quite limited. I don't want to fool with an automobile engine- and don't want props, struts, rudder if I can avoid them. This rotary just 23" high-perfect- can be coupled to a tranny and a jet drive system which should make a 14', 900lb boat fly. Anmybody know what one of these motors will cost?

[cs]

I've currently got a RX-7 with about 157,000 miles on it. Now I'll admit I don't know near enough about rotary engines, but this baby runs like it was brand new. I've never ran out of torque at any RPM range. The rotary engine is about the most impressive engine I've seen. Like John said I only get 20 mpg, but as long as I keep oil in her she keeps giving all that I ask of her.

I would like to see the rotary developed even further.

Chad

[ion barnes]

Dan McCosh; you have caused me to have a sleepless night trying to understand your comment about the rotor and 1/3 crank speed. The light came on! You are refering to the fact that the rotor is three sided and there is a power stroke/pulse every third of a rotation or every 120 degrees. Thats good because its like having 3 cylinders for every rotor without the vibration of the pistons and rods stopping and starting at the top and bottom of their stroke. Need more power? consider coupling serveral of these puppies together inline.
I have also considered the fact that you could possibilly isolate a rotor so that once you are up to speed you could consievably cruise on less that the full compliment of cylinders/rotors. Just a thought dont take it too seriously but its done with diesels so....

[John Gearing]

Actually, the rotors are geared to the crankshaft (more properly known as the output shaft). The chamber is not circular, it is more elipsoidal in shape. IIRC it is the gearing that is responsible for the non 1:1 relationship between rotor RPM and shaft RPM. And yes, in theory you can just add layers of rotor assemblies (and an appropriately-lengthened output shaft) to build a bigger, more powerful engine. This is essentially what Mazda has done with the Cosmo (their Japan-only car that has a 3 rotor engine) and their race cars (which had 4 rotor engines). Incidentally, for the race engines, Mazda used a separate oil sump with special oil for the oil injection system.

Here's a good site that explains the basics:
http://www.eng.fsu.edu/~shih/eml4421/students'%20web%20pages/rotary%20engine/parts.htm

For more on HP and Torque...
http://www.offroaders.com/info/tech-corner/reading/horsepower-torque.htm

[Jonathan Lauter]

Hello all: I'd like to present some clarifications regarding marine rotary engines. Although I represent Rotary Power Marine Corporation, I'll try to keep this information as objective and generic as possible, in keeping with the forum rules against self-promotion.

Apologies for the length of the post, and also if I'm covering ground that may be well understood by many!

1.Power and torque: All engines produce power by burning fuel at a particular rate. The rate at which energy is released from the fuel (say, BTUs per second) minus the rate at which heat is wasted going into the exhaust and cooling systems (which includes the friction losses due to sliding parts and pumping air into and out of the engine) equals the power produced by the engine. Power is defined as the ability to do a certain amount of work in a certain amount of time. Power is needed to move a boat at a particular speed. (The work is moving the boat against hull resistance over a given distance, power comes into play when one wants to get the boat through that distance at say 30kts instead of 1kt). Torque is defined as the ability to do a certain amount of work without regard for time. The mathematical equation that relates torque and power in any engine is HP=(Torque(ft-lb) x RPM)/5252. The maximum power an engine can produce is limited by its ability to convert fuel energy. So, for a given engine, the max power is a fixed quantity. The torque output, however, can be changed by applying a gear ratio. The power at the transmission output shaft is essentially unchanged from the input (reduced only by internal friction losses), whereas the torque at the output shaft is now equal to the engine torque times the transmission gear ratio. Theoretically, any desired torque is available by changing the gear ratio as required. Relating this back to practical issues, this means that the tiniest of engines can be geared to produce massive amounts of torque. Theoretically, the tiny motor in a wristwatch could move an aircraft carrier by using enormous amounts of gear reduction. The aircraft carrier would be moved at an infinitesimally slow rate, but it would be moved nonetheless. To move the aircraft carrier at a higher speed, more POWER is required. Moving to more practical cases, some boats are harder to accelerate onto plane, and these need more power at lower boat and engine speeds. It is usually easier to look at a torque curve than a power curve to see the lower speed engine characteristics. An engine that has a torque curve that reaches a maximum at lower RPM and falls off as speed increases will provide proportionally more power at lower speed than an engine with a flatter torque curve. Conversely, this engine will not be as responsive at higher speeds, as the power production is not increasing as fast as it is in the engine with the flatter torque curve. Selecting an appropriate gear ratio for a given application requires an understanding of the hull characteristics and how they relate to a suitable propeller selection. The engine power, RPM, gear reduction, and hull resistance will dictate the choice of propeller diameter and pitch, and there is often some iteration required to obtain the best choice of parameters. Most marine engines use transmissions with gear ratios other than 1:1. This is no different for a rotary engine, but since the rotary produces its power over a wider speed range than a piston engine, a deeper reduction is usually used. The deeper reduction multiplies the engine torque so that torque at the propeller (which is the ONLY place it counts) is adequate for all reasonable applications. Finally, on the issue of rotating mass and torque -- rotating mass stores energy. It takes energy to accelerate the mass, and that energy can be released to the driveline if the driveline load increases momentarily. That is why a car or truck with a heavier flywheel has an easier clutch engagement than one with a light flywheel. The heavy flywheel releases energy to the driveline helping to cover the sudden increase in load. Conversely, the heavy flywheel engine will have noticeably slower throttle response since a portion of the engines power has to accelerate the flywheel instead of moving the vehicle. Diesel engines have very high rotating mass (inertia). This is part of why their throttle response is sluggish. Rotary engines have very low rotating mass. Rotary throttle response is exceptionally rapid. Heavy flywheels are also used to dampen instantaneous torque fluctuations in engines with few cylinders or engines with very large cylinders. Rotary engines have inherently smooth torque production, and don't require high mass flywheels to achieve smooth idle quality.

2: Application of rotary engines to jets and props. Rotary engines have been very successfully applied with all common drive systems -- conventional inboard props, sterndrives, surface piercing drives, and jetdrives. Since rotary engines have no valve train and no reciprocating parts, they love to run at high RPM with no vibration or reliability issues. This does make them very well suited to use with jets, but it doesn't make them any less suited for props! Early in the history of marine rotary engines, a company based in Idaho was marketing rotary engines towards the jet boat segment. This was probably because of their location where river boats were commonly jet powered and because the rotary's above-stated suitability. Also, the light weight of the rotary helped keep draft to a minimum. We have found that despite the "conventional wisdom" that rotary engines don't have enough low end torque, the rotary can do very well in propeller driven craft as long as the gear ratio and propeller are properly matched. In lighter hulls, the significant weight savings of the rotary engine helps boats perform exceptionally well. We can provide interested parties with many examples of prop driven rotary boats with excellent performance.

3: Specific ratings for current rotary engines. Our model 175c is rated 175hp at 6250 RPM. Max torque is about 147 ft-lbs, and the torque curve is very flat from about 3500 RPM right up to full rated speed. Our supercharged 240Si produces 240hp at 6500 rpm, and about 205 ft-lbs. The torque curve is also very flat, and the supercharger really boosts the low speed torque as well. Late model RX-7 engines (same displacement as ours) are rated at up to 280hp (twin turbo), and have produced 760hp for drag racing.

4: Reliability and Durability: The basic rotary engine has only three major moving parts. There are no reciprocating parts and no valve train. This makes the basic engine very smooth and reliable. The engine is capable of running extended periods at or above our rated speeds (in fact, we rate the engines at speeds lower than their automotive counterparts only because of limitations with the available marine transmissions). We do not have different intermittent or continuous ratings. Issues with engine sealing have been resolved many years ago, and we have not experienced any reliability or durability concerns with these engines. Mazda (the makers of our engine blocks) sold over 2 million rotary cars, and are taking orders for the new rotary powered RX-8 to start deliveries in May. All of our engines are fresh water cooled for added durability, and have water jacketed exhaust systems. All common service items are top mounted -- starter, alternator, fuel pump, oil filter, remote oil drain. We keep all parts in stock for overnight delivery as required anywhere in the US, a couple of days for overseas destinations. Many external items are available from marine supply houses, and in the unlikely event of an internal engine failure, we can supply an exchange block, rebuild the existing block, or parts can be obtained from Mazda automotive dealers. (Fuel and electrical system parts all meet US Coast Guard regulatory requirements, and must be RPMC approved replacements only).

5: Cost. Our engines represent a good value in the market. Complete drivelines are significantly less expensive than outboard motors, with similar power to weight ratio, better fuel economy, cleaner emissions (Our engines meet California emissions standards through 2007), and the added reliability of fresh water cooling. Our engines are a little more expensive than piston engines, but we offer a far smaller installation envelope and a large weight savings, combined with very low vibration and very easy maintenance.

Please post any questions or comments, or contact me privately for more information!

[cs]

Jonathan, Very informative post. Since I got my RX-7 I have come to respect the power and durability of the rotary engine. I'm an old piston guy, but in terms of performance they seem to fall short of the mark. If we can only get them a little more fuel efficient.

Chad

[Jonathan Lauter]

Ah, yes -- fuel efficiency! In cars, the rotary's fuel economy is OK for a sports car, which is to say, not too great! In a boat, however, the fuel economy is actually quite good. This is mostly because of the weight savings of the engine. At only 315lbs compared to 760lbs for a V-6, rotary engines can reduce a boat's weight by as much as 20%. This translates into sizeable fuel economy improvements. Typical cruise fuel economy for our 175c ranges from 5 to 7 GPH depending on the boat. The Kenner 18 on our website cruises at 5.5 GPH, mid 30's mph. A twin engine Pacemaker Wahoo (26' x 10' beam, weight around 8000lbs) cruises in the upper 20's at 7 GPH per engine. Another reason marine fuel economy is surprisingly good is that the rotary doesn't have as much internal friction as a piston engine. Friction losses tend to go up with the square of engine RPM. Piston engines, tuned and developed for automotive use at typical road-load speed well less than 2500RPM, suffer pretty badly from friction losses as they start to operate at 4000 to 4800 rpm. Rotary's, while not inherently more efficient than piston engines, don't suffer nearly as badly at the higher RPMs typical of marine use. Most RX-7 drivers will tell you that MPG doesn't get very much worse driving at 75mph compared to 55mph. This is because the engine isn't suffering from higher friction losses. In the final analysis, we have never done a repower where the fuel economy didn't stay the same or improve when compared to the original power.

Jon

[cs]

Jon I went and looked at your site. This motor of yours looks good even though I couldn't help but notice all the photos were in go fast fiberglass boats. :(

How would these motors do as an aux. motor in a wood sailboat.

Chad

[Alan D. Hyde]

There have been several excellent posts here, with Jonathon's being particularly informative. Thanks to all.

This type of material does great credit to the contributors, and to the Forum.

Learning something every day is what keeps our minds in working order (in my own case, such as it is).

Alan

[ 02-12-2003, 04:53 PM: Message edited by: Alan D. Hyde ]

[ion barnes]

I agree with Alan, and thank you Jon, the rotary(Wankle) engine has been in and out of the news for many years as a novelty and very much unappreicated. Too bad, it does have alot of potential.

[Jonathan Lauter]

Thanks all for the kind words.

I think you'll be seeing more about rotary engines in general over the next few months. Mazda is taking orders at their dealerships for the new rotary RX-8, scheduled for delivery beginning in May. Also, watch Boating Magazine and Trailer Boats for coverage of some new Rotary Power Marine Corporation projects. We're also working with a couple of small builders of wooden replicas, so perhaps they'll show up in Wooden Boat at some time. If anyone is interested in a rotary repower of a wooden boat, I'll make sure we post pictures on our website. (I'd like to provide some balance against the plastic, also!)

Regarding the sailboat auxiliary question, I don's see any reason it wouldn't be suitable. 175hp is more than most sailboats require, but the engine can be geared/propped to supply less power, and it will still be a lot smoother, lighter, and less odorous than a diesel. At less than 400 lbs including transmission, I'd guess the engine weighs about the same or maybe a little less than an Atomic 4?

Jon

[cs]

Jon I'm glad you came back to this post. I got a few questions about your rotary. This will be in comparsion with my RX, so here goes.

Do you have issues with the engine flooding? With my RX-7 ( and this is typical with other RX-7) if it don't start on the first try it floods. Or if you let up the first time before it starts it floods. Or if the weather abruptly changes it floods. Granted this only happens about 2 or 3 times a year, but when it does it is a pain to start.

Second how expensive are parts? With the RX-7 I've never had to buy engine parts, but I've had to buy accessories (i.e. alternators, switches, clutch lines, etc.) and they are on the high end of the price range.

These are just a few things that lay awake at night thinking about. ;)

Chad

[Jonathan Lauter]

Hi:

We haven't had any flooding problems. We use totally different fuel systems than the automotive ones. The 175c uses a 2 bbl Holley marine carburetor, and the 240Si uses our own RXeTronic fuel injection / distributorless ignition system. I think the RX-7 flooding problems were due to an anomoly in the injection software, there are numerous posts in the various RX-7 forums about this, and I think there are even some aftermarket fuel pump cut-out devices sold to correct the problem.

Other than the engine block itself, all parts are non-Mazda. Our prices are comparable to other marine engine company prices for similar items (not real cheap, sorry, but not ridiculous either), and some items are available through aftermarket sources (belts, seawater pump impellers, spark plugs, carburetor parts, etc.).

Jon

[John Bell]

I saw a press release sometime last year about a rotary diesel marine engine. Can anyone comment about the pros and cons of such an engine?

[cs]

Jon can you give me a link to the RX-7 forum that you recomend the most?

Chad

[Jonathan Lauter]

Chad, I don't follow the RX-7 forums much, so I can't really direct you to a good one, sorry.

Jon

[rustnrot]

Be careful how you interpret a diesel engine. I think those "diesel" rotaries still utilize the Otto 4 cycle spark ignition and not the Diesel cycle. In other words, they are more or less a multi-fuel engine that uses spark ignition rather than compression ignition as in a true Diesel cycle engine. There are many piston engines setup this way also. Of course, being able to use diesel *fuel* in a boat means not having to worry about myriad of USCG requirements for gasoline containment, transfer and use. For example, using only diesel fuel, "ignition protected" components are not required and ventilation requirements are relaxed as well.