Wankel or not to Wankel?
 

I just recently purchased a Baja Force 370 ....in the mode of upgrading from my Force 320. I have plenty of time to build and big aspirations for the project wanting to make it an all around good boat.

Aside from going fast on the water and not being stranded at the dock on moderate chop days running at decent speeds, I like to do other things on my boat besides drink beer...like, dive and fish....or just comfortably cruise. Problem is, almost all of the go-fast boats have a cheesy bench seat with a sundeck.... wasted space in my opinion. Center consoles are just for fishing and have cheezy cuddies... However, most of the go fast boats are stuck with this configuration (bench seat and sundeck) since the engines gobble up all the space. So, for the past week, it has dawned on me, this boat needs several Mazda rotaries. Why not? I'm very familar with rotaries...especially in marine. But if I was to put say...four turbocharged 13Bs, would this be a bad idea?

Pros:
Added Space: lay down a floor from the existing floor clear back to the transom... Add optional seating (lounge or bolsters) as I wish in the back.
Reliability: Rotaries love continuous power....they hate stop and go which is why they have limited success in cars. Bottom line...hp/cid for hp/cid, the rotary is more reliable than piston motors.
Power Density: none better than a hopped up rotary. Top dragsters get 1000 hp out of the 13Bs.
Simple: no valve train to fail, no pistons to squeek, no crank to fracture. The eccentric shaft that come with them never fail. You can run 1800 deg EGTs...all day...
Availability: 2 million 13B motors were sold and continue to sell today
Heat Issues: Unlimited heat sink to cool the motors either the ocean (via closed loop cooling) or lake of your choice as the heat sink
Cost: Cheap...cheap...cheap....running 13Bs can be had for $1000 each.

Cons:
No V-8 sound
Effort to perform the install.

Maybe I'm missing something, but why has the rotary not been a bigger force in the boating community?

I hear things like lack of torque...hog wash!! The 4 rotor 787 LeMans rotary put out 450 ft-lbs out of 320 cid 4 stroke equivalent....that is higher than any pistonian will do naturally aspirated comparing ft-lbs/cid. Not happy with the RPM?...that is what gear boxes are for!

Simply put, the rotary has volumetric efficiency and tight package...also, not so fuel thirsty as some believe. They consume .47 lbs/hp/hr compared to a very efficient pistonian at .45 lbs/hp/hr (BBCs don't qualify as "efficient" pistonians!!). Is it just the V8 sound that stop these from being a more prevalent conversion?

I'm thinking four turbocharged 13Bs for my Baja and then a new floor in the back over the motors. I would get about 400 hp per motor on pump gas in around 6000+ RPM. Any laughs or heckles out there? I think 1600 hp would get the big Force 370 turd moving....

They make tq at high rpm.I don't think it will be able to get out of the water.Exhaust temp,what,1700*? Times 4.Huge mufflers to control that ear drum spliting noise.Huge air cleaners to control.....see previous line.They don't sound good.RoadRaced against RX-7s before they were forced to use mufflers.Oh,so thankful they were behind me.That's about it for now.Good luck with that project.See ya at the dock. BOB

They are noisy...couldn't agree more! I ran one without a muffler and almost lost my hearing. After putting on a somewhat small muffler and water injection...it was surprisingly quiet. Definitely space for all the mufflers...water injected on the rear transom. Well if torque is considered to be a sticking point...wouldn't (4) 300hp mercs get my boat moving? If so, why wouldn't (4) 400hp correctly propped rotaries get it moving? Dry exhaust till the water injected muffler/waterbox a must...done it before..not too hard.

Doing 4 might be a challenge. But, you're right. They are fairly cheap, readily available, and stout little engines. This video might help you make up your mind...

http://www.youtube.com/watch?v=bpxK2ub-qCs

You will probably replace the rotor tip seals every year. This is the primary weakness of the Wankel design. I bet that running 3/4 throttle under load will wear those seals much faster than if it was in a car.

First it will burn oil, then lose compression efficiency..

I think the biggest problem to overcome would be absolute lack of low end torque. Maybe a pair of smaller turbos could combat this a bit and still put you about 400hp if sized right but then you have to worry about cooling etc. And one fueling problem on a boosted rotary making that kind of power and its done...They just are NOT forgiving...ONE small fuel issue under power and the Apex seal is gone... Running at high boost/power almost ALL the time, Just wont be reliable enough for use in a boat. Look into the turbo boxer engines from the new subaru STi. They make good power, Will be a lot more forgiving than a rotary and the cylinders are horizontally opposed so they wont need much headroom but again still lacking low end torque. I work on modern high hp boosted engines every day and the main problem I run into when thinking about using one of them in a boat is 1) They need to run on high octane fuels to put out the kind of top end power a big block would and 2) Nearly all of them will have NO power until 3k at BEST when making upwards of 400hp. (Im talking about 4 and 6 cyl. cars only) Trust me I would LOVE to put one of the motors I work on into a boat but while its GREAT in a car I just simply don't think they would cut it in a boat. Also, I would not use drag racing as a good reference for how reliable an engine will be in a boat.. A drag race is too short to see the effects of the engine thermally overload over an extended period of time. Run almost ANY high HP drag motor under load for an extended period of time and watch how fast the engine will overload and fail you would be amazed.

There is a company or two that specialize in Mazda rotory conversions. A magaize article was written several years ago about it. If I recall it right it was the lack of low end torque that they complained about. I believe it was connected to a jet pump too.

good idea in thought.. I think this has been discussed before a few times. I think in a small light boat you would be ok for a novelty, but I think in a bigger boat you will have a lot of problems to overcome. Also if you run the turbos, how do you plan on keeping that engine compartment cool? Especially if you are going to make it smaller. Again It sounds like a good idea, but it seems that there would be way to much engineering involved to make it a daily driver type of thing.. Again just my opinion..

I personally like the idea of diesels, they are powerful & efficent. Evidentally VW is trying to also make an entrance into marine with one of thier diesels.

The diesels have the low end torque to get you up & moving. The only difficulty is getting some of these revving some bigger Rpm's .. Hoever Volvo & Yanmar and some others are doing a pretty good job..

Jamie / Lakeside

.

Jamie,

VW had a marine diesel display at the Miami boat show. Looks promising. They're going after replacements for 350's and 454's in heavy boats.

The twin turbo version of the 93-95 RX-7 has plenty of torque. The problem one would have is the extreme exhaust temp and noise. I have seen glowing manifolds and turbos. Given that the rotary engine in a boat it would see more cooling capicty that could cure that but these things are prone to air pockets and I dont know what would happen to them if a cool manifold was next to a hot exhaust port.
Contact Mazda Competition. Im shure its been tried. They were allways very helpfull when I was racing. If you find a way to make it work please let me know. I may be wrong but I believe that engine has the record for hp and torque vs weight and displacement to this day.
If you want to share ideas on this project please feel free to e-mail me at [email protected]
Keep in mind they are sort of a 2 stroke and suck gas.

Are you planning on 4 drives? Or can these rotaries be direct coupled? I have friends who get excited about auto engines in airplanes (including rotaries) after all the special machining for mounts, cooling, exhaust and drive coupling the low entry fee for the engine is lost in the specials. Guys like you do advance the state of the art and for that we are all grateful. If you do want to enjoy deck space and speed perhaps a different design is in order. If you want to make your new acquisition go fast with a weird aft deck space then perhaps a single or twin turbine would give you what you want.

I have wondered about doing something similar except with a 2jz-gte. The JDM engines are plentiful and cheap. The exhaust might be tough though. There are supras out there running 800 plus hp through a stock short block without any longevity issues. In the end, it's probably only a pipe dream for me.

Rene

Whether it is 4 two rotor motors or 2 four rotor motors, I think there is enough cubic displacement with turbos for low end torque. Bottom line...need 8 of the rotors turning with some turbo setup.

The water cooled exhaust is no big deal. I've done a conversion on jetskis five years ago. The prototype worked wonderfully. My interest was lost in the project after getting the prototype working good...starting initial production and then finding there is a limited audience in the low buck jetski industry.

In this scenario, I find that getting a boat that offers everything is pricey...at least for a lowly engineer like myself. So I'm interested in making my boat somewhat of a crossover...not purely go fast, not boring fishing boat, not a slow cruiser...I want it all!!! Although I have two big boats parked at my house, I'm interested in having one that serves all my South Florida needs.

I measured once, twice, again and again....can't do what I want without the rotary solution. Deck space will essentially double. Now how far do I take this? Do I start out mild with lets say 500hp per side or go for the 800 hp? My approach...maybe start 500 hp per side (four rotors), then crank up the boost and play with props down the road.

Robustness all depends on what HP I end up with. I have a few tricks up my sleeve to guarantee their life span FAR out exceeds a BBC. Most of the tricks are known, a few are not which I keep close guarded. Break down the failure modes and all are addressed with simple mods and metallurgy.

Tell you the truth, fishing off my boat is a pain, and diving off my boat is a bigger pain. Getting 12 people out on my boat is cluttered so what am I to do...run with 6 people each weekened with beers???? boring....gets old.

Seeing as though I'll no longer have the sounds of music with V8s in the back...it is simple...get the motors quiet...no one cares what a rotary sounds like!..as long as it performs.

Turbines won't work for what I want to do. First, they are obviously cost prohibitive. Second, they are tremendously inefficient at part throttle which is where many boat owners spend most of their time. Third, the heat is a bare to deal with. Working as a propulsion engineer for a helicopter company...I know first hand all the external temps of turbine engines...they need significant entrained airflow to keep the engine bay cool...let alone heat soak issues. I'm sure the offshore guys running turbines have specific procedures and necessary space to keep their hulls from melting. And lastly...why would I go through the pains of developing something just for myself? Part of me says, if it works for me...great...if it works for others, even better!!

What's the plan? Make some mockups, start initial conception...then start some drawings to get parts made. Looks like some lessons learned from a jetski conversion will transpose well into this boat project. It's exciting to say the least.

Diesels? If any of you have seen the Audi diesel run in Sebring...absolutely..they have a place in boats. But, when a suitable powerplant comes to surface, you'll need an equally impressive gearbox to go with it. And how does that meet my current need of being cost effective?...well, certainly not in the near term so I'll stick with the rotary and plunk out a few more dollars at the pump.

Sounds like there may be a few skeptics...but this just fires my motivation :D

As you are aware, all of the low end torque issues can be remedied with tuning and porting specs. Not a huge issue to tackle. Apex seals and heat soak of internals will be a bigger issue, but if you claim to have those under control, then more power to ya. For watching your installation costs, have you considered putting one 2 rotor in front of another 2 rotor and coupling their "crankshafts" to make a poor man's 4 rotor? It would improve engine bay access, keep plenty of airspace along the sides, and eliminate the need for a bizarre and expensive gearbox system. You can get Bravo III drives in up to a 2.20:1 ratio. You can get a Bravo I X drive up to a 1.65:1 ratio.

People run B1's at 5000 rpm with 1.26:1 ratio all the time. This gives you a propshaft rpm of about 4000rpm.
With 1.50 gears (XR) you get the same 4000 rpm at the prop with 6000 motor rpm. With 1.65 gears (B1 X) you get 4000 prop at 6600 motor revs. With 2.00 gears (B3 XR) you get 4000 at the prop(s) at 8000 motor revs, and with 2.20 gears (B3 X) you get 4000 at the prop with 8800 motor revs.

Running a bravo based drive, I'd keep my torque under 450 ft lbs. Assuming a fairly flat torque curve, that gives you a ceiling of 700hp at 8000 rpm. If you only rev your wankels to 6500, then you need to limit yourself to 550hp per drive. Tower bearings will be your biggest concern on a 7000+ rpm Bravo. Need the best tower bearings you can find, and a stiff billet cap.

I do think running motors inline into a easily available bravo setup will be your cheapest option. The weirder you get with special stuff, the more it costs when it pukes.

mc

I have been wondering about these motors for some time.

Can these engines be installed vertically instead of horizontally?

I think these would be great on an Outboard tower and lower unit.

I thought there was someone in Louisiana that was offering these back in the 80's-90's?

The current 4 stroke outboards are weak and these certainly have potential to make some turbo charged power and they seem to be light.

I think your on to something. I used to build/race RX7's and wondered why they we not used in boats.
I think two 2 rotor 13B's that have been built up and ported would run that boat well.
Do it! I think it would be fun and interesting project.

mc,
Thanks for the pointers. The drives are what I'm not familiar with, so, your info helps immensely on the initial sizing and approach of things.

I'll likely couple (2) two rotors together..have some thoughts on that. I do like the idea of the Bravo 3 since it allows more playing down the road. Any idea what these go for? Are these available on the used market yet?

You can run rotors vertical but the problem, you have to reconfigure the oil sump pick up. The other problem, if you spind the motor too fast, I think oil would build up in the lower rotor causing added mass. Not necessarily a problem at low RPM but might froth on you at high RPM. The rotors rather be horizontal so the oil drains off from inside the rotors easier.

Another challenge is getting the correct matched diesel turbo for the rotary. Diesels seem to be the only turbos out there with the turbine housing water cooled...maybe I'm wrong about this. Wrapping the hot turbine section with foil or exhaust wrap tape is not a viable option in my opinion.

I also raced in/against rotaries...it's like a chainsaw on steroids :D Pleeease make sure you can muffle that exhaust and somehow change the frequency.
I'm surprised no one has piped up with the "would you drive it uphill, fully loaded, in 1st gear" stipulation for marinizing an engine. But along those lines, consider a "proof of concept" by dropping your powerplant in a truck and driving it around fully loaded...or perhaps take it to a mud pit. Yes, cooling will be different. But if you can torture it in a hard-working truck, you're further along with the confidence it will truly survive.
I'm a huge fan of the underdog, of untried possibilities. But as a much more applicable powerplant I look at the newest LS-X variant of the small block chevy. It's been around for ten years, it's leaps and bounds better than previous SBCs, and with a small change in exhaust manifold dimensions it's practically a bolt-in replacement. But Mercruiser is still using the old stuff...
Be sure you're ok if it turns out to be a useable novelty at best.

Like I said in my earlier post, the apex seals are going to be a problem as a boat motor is 80%+ loaded most of the time. Many people have played around with different seal materials including a carbon matrix, ceramic, and many different steels. The problem is that when the seal goes, it usually destroys the rotor, the other two apex seals and the rotor housing. One other cause of seal failure is detonation, and we all know what that can do in a piston engine. However, even a slight ping under load can break 2mm and 3mm seals.

If you have the misfortune of overheating the engine, you might as well do a complete teardown and rebuild because your coolant seals will be cooked.

In a nutshell, if you have the time and intestinal fortitude to put it into a boat, then good luck. You might just get some fun and noisy boating in between rebuilds.:cool-smiley-011:

-Larry

Well you are getting alot of advice. Here is some more a surface drive should take your intended power. A roots blower with an intercooler might help the torque issue.

another solution might be marinizing a set of flat 8,10 or 12 cyl engines. give you the compact hieght with a slightly more converntional powerband.

Going to rotary power is more out of necessity than novelty. Outboards are too expensive (four of them) and clutter the back end of the boat. V8s simply gobble up too much head room preventing a nice continuous floor from the helm back to the transom. Pancake engines (VW, Porsche, Subaru) would get to be too expensive.

Horsepower levels have to start conservative. But my wishes of the rotary are not some pie in the sky dream. I have had excellent results in a jetski application with continous max power. But where I take my lead from with continuous power versus reliability claims is the aviation community. The aviation guys are quite wise when it comes to TBO, simplicity, and failure modes. Some Aviation TBO claims are 3000 hrs at 150 hp for a Mazda two rotor. At cruise, I would suck down 300 hp per side...so what, four rotors and I get 3000 hrs? I'll have to rebuild the boat before the motors!

The thought crossed my mind today that maybe this has to be a 6 rotor naturally aspirated rather than a turbo 4 rotor. I can easily get 600 hp in naturally aspirated form from a 6 rotor and not deal with the detonation issues and low end torque problem inherent with a single turbo rotary. Naturally aspirated rotaries love low octane. So if this is the path, then it sounds like figuring out a reliable coupling mechanism between motors is the key. One company has been working on a six rotor, but I'm not sure where they are with it.

I've heard from credible sources that ceramic apex seal rotaries can withstand deto without issue. But, they are $2000 a set (for two rotors). It's all about how far I want to take this but at the end of the day, I want my old 37 Baja to hit the 70s...reliably....and with all the space and not the expense of other methods.

As a side note to speak of rotary robustness...I've run my rotary jetski without oil for about 5 minutes (oil line broke and I didn't believe the oil pressure gage when it read zero). After filling it up with oil, the engine proceeded to run for another 4 hours before developing a vibration. Upon disassembly, the one rotor journal bearing was chunked up pretty good. So, I'd have to say that is an acceptable failure mode....try that with a Chevy at max power! But, I'm not here to diss the Chevy. If I could get Chevies to fit in the boat I want to have, I'd do it.

I think it would be more practical if you can make the power you want/need keeping the motors NA. Boost just kills rotory reliability and making high HP would be a real challenge to quiet those motors enough while not restricting flow and causing another potential detonation problem. High HP rotors are awesome!..When they are not broken!! haha If you want to stay boosted, Why don't you build one of the motors, Bring it to a dyno with load control and see how it holds up? Would be a shame to go through all the trouble of rigging the boat with them to find out the motors wont handle it well. If it doesn't hold up $$ spent wouldn't be too bad. I am also very underdog appreciative person!!! Try it out...You never know!

I was interested in putting two turbo RB30 engines in my boat. When built right these have same bore/stroke as the 2jz but they have variable valve timing on the intake cam to aid help turbo lag and GREATLY increases low end torque. Costs will not allow me to pursue. :mad:

They are available................
 

Peak torque is 184ft/lb @6700rpm
Peak Horsepower is 275hp at 8500rpm
164 torque @ 4500rpm!!!!!!

Boooooo! haha j/k But those number need alot of work... Put a 7k stall converter on it?? haha

rexx, i'm absolutely intrigued with your concept. i've loved rotaries since the mid '70s when my brother and i raced matching rx4s; the damn things were built-proof. i think your idea for 6 rotors a side (3x2) naturally aspirated is a winner.what an interesting concept, an offshore boat with a lot of room in the cockpit. 600 hp a side will get your boat in the 70+ speed range you like. i also like the surface drive approach unless of course the konrad guys want to send you over a couple of test units. keep us posted. - jeff

Hey man, I just pointed out marinized parts are available. I have no connection with Atkins or their partner:
http://www.camdensuperchargers.com/

I was just messing around..lol

It's settled then...time to get to the drawing board.

The correct prop and about 6 rotors per side should do. Wonder what 12 rotors will sound like....must have muffler!! Start out naturally aspirated...then maybe a supercharger or a few turbos will find their way on the setup...maybe just some higher RPMs. Can't put too much horsepower into the old Baja or it's likely to experience rapid disassembly...

I'll post pictures as the project progresses.

http://www.youtube.com/watch?v=bpxK2ub-qCs
Obviously not a good setup for your needs but this thing moves pretty damn good!

I liked the sound in the video. Seemed like it moved that flat-bottom boat right along.

I hear ya...gotta start with a good baseline though, then amp it up. The fact of making turbine hp down the road gets me pumped...but, gotta stay focused and start simple.

Ed, if that little boat was flat bottomed, he would have done quite a few endos after pulling the big boat he was next to. That boat had some Vee or it would have simply swapped ends!

That sound reminds me of the jetski I built back in 2002. Only two rotors...but without a muffler, it sounded like it was powered by nitromethane...down right nasty.

lol rotor = Pissed off bee hive!

you keep talking about this " 6 rotor" like it actually exists. when mazda tried to race the 4 rotor in gtp it needed a muffler roughly the size of the entire side of the car and the heat generated would routinely light the car on fire... and these were the factory guys that actually knew what they were doing. when it came by on the straight at daytona it sounded like an f 16 at about 185 db. and they don't make enough torque to do anything at all. yes you can turbo it or supercharge it and make 300 hp at 8500 rpm... but at 3500 trying to get up on plane you are going to need rocket assist. and you better plan to have an oil cooler roughly the size of your swim platform.

its an interesting notion... and fun to talk about... but the practical application falls into the " what the hell are you thinking about " catagory. do some hard research about the thermodynamics and fuel efficiency of that motor. they are about the worst on the planet... reliable ? yes... nearly bullet proof. applicable to boats or trucks or farm equipment that need grunt ? no.

but its your time and money...

I keep hearing about budget. What is your budget for the turn-key solution? What is your projected height of this package? Shaft height must be very low, which means you will be gearing up the shaft height with a custom box capable of lots of torque if you plan on bravos. You may go straight out if you use surface drives. Xr drives will cost you about 10K each and surface drives are more. Are you thinking that you are going to extend your cockpit floor back to the transom without a step? The dyno idea is a good suggestion; however you will be spending many thousands for enough time to test your theories about endurance. I suggest you buy a beater direct drive boat, direct couple and run her hard for 40 hours to test out your predictions. Your new boat ain't no jet ski I am guessing 15,000#s fully dressed. Someone has probably powered up a 37 to say 650HP a side and do they go 70?

My boat is stated to be at 10,000 lbs with two big blocks. I don't think it unreasonable for 1200 hp to get it at around 70 mph. From what I understand, over 800 hp total gets it over 60 mph.

There is a budget or should I say, prohibitive financial direction. I can figure out to put different powerplants into whatever setup, but if someone tells me it is $4k per motor times four (outboards)...that math is simple and cannot be done. I have nearly four rotaries in my garage...probably end up picking up another 4 rotaries to complete the project. They average about $500-$1000 ea...but each one will be rebuilt at a cost of $500 each.

The biggest cost will be the coupling. No...don't think it has been done before, but then again, I'm guessing a nutty propulsion engineer has never been signed up to the task.

Muffler will be about 3-4 cubic feet each and fed with water...should quiet them nasty rotaries nicely :)

No coupling system needed. Just need to adapt a 454 flywheel or ringgear to the rotary counterbalancer, then build a billet adapter from the mercruiser bravo housing to the rotary engine. Straight forward.... Coupling the motors will be another interesting task...but nothing difficult. Just need compliant couplers and there are many to chose from.

rexx,
this is really exciting. a few thoughts: 1.) there is always the turndown pipe option for idling/low speed noise reduction. 2.) as a strategic excercise, reverse your chronology on engineering challenges; since it seems that you've got the bascic powerplant issues solved or have the ability to solve them, spend most all of your initial energy on the ancillary systems- cooling water delivery/pumps, hydraulic systems/steering, adequate electrical systems/charging, marinized fueld management/delivery and filtration, engine mounting, placement/ x dimension considerations, quality air delivery and backfire prevention. etc. etc.if you were to run into engineering or financial challenges you'd know it before you made the whole leap - keep us posted - jeff

Hmmmm...first stumbling block. I measured wrong. I can't get 3 two rotor motors installed as initially planned....short by about an inch or so if accessories are included.

Now what! Well, I can either supercharge 2 two rotors or revert back to the 454s. If I revert back to the 454s, about one foot of deck space will be lost on the longitudinal axis. Plenty of space to be had with the 454s and seats moved further aft and a storage area would be included of the would-be very short sundeck. So now the quandry, do I attempt to pull this off with rotaries or stick with BBCs and lose about one foot of deck space? The lazy side of me says stick with 454s...the crazy engineer side of me says go with two 2 rotor motors fed by roots type blowers. This will take more pondering for sure...it was a slam dunk with three 2 rotor N/A rotary motors.

I still don't understand how you are going to get a deck back to the transom, over the top of the rotary’s using the bravo o/d input shaft w/o a drop box.