baronbob

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.

oldandtired

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

Rexx

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

mcollinstn

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

Rik

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.

BillR

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.

Rexx

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.

handfulz28

I also raced in/against rotaries...it's like a chainsaw on steroids 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.

ljsmith1

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.

-Larry

baronbob

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.