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

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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.