Wankel engines in boats?

[superbenk]

I know this is an engine question, but there isn't an engine forum that it fits in so I'm putting it in the non-engine forum

Anyhow, just reading about Wankel engines & wonder if they've been used in boats at all? If not, why not? I really don't know much about them, but they seem interesting.

Just curious.

 

[robert graham]

Re: Wankel engines in boats?

I believe it's a very legitimate question that I've thought about often. With their rotating rather than reciprocating mass, relative simplicity and high power to weight ratio looks like they could be a viable option. Maybe there's some key element in the workings of the Wankel engine that makes it unsuitable for marine applications, but Mazda's had great luck with them in cars. Hopefuly someone on here can shed some light on this subject.

 

[Alumarine]

Re: Wankel engines in boats?

One reason might be that they have no low end torque.
You have to rev them high.
They work ok in a car because of the transmission.

 

[mommicked]

Re: Wankel engines in boats?

What about it turning a jet of some kind,instead of a prop?maybe spin it up and then add water? i bet it would blow alot of bubbles until it got primed!!!they turn 10 or 12000 rpm don't they?

 

[Fed up]

Re: Wankel engines in boats?

One reason might be that they have no low end torque.
You have to rev them high.
They work ok in a car because of the transmission.

not to mention the rebuild on one, man they have like 80 seals..... but to reinforce what Marc said, those babies like the revs.

 

[nlain]

Re: Wankel engines in boats?

It has been many years but I think I read an article years ago where they did try to make boat motors out of them, they used 3 rotors instead of 2 like the auto engine, they could never get the balance right on them and eventually gave up on the idea. I do not state this as fact, as I said I think I remember.

I had an RX2, the tighter you wound it the stronger it got, they do like the revs.

 

[tswiczko]

Re: Wankel engines in boats?

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

 

[mommicked]

Re: Wankel engines in boats?

Years ago I had a hotrod smallblock Ford that I thought I was abuseing until I rode in a friends RX7.He was trying to sell it to me though!!he powershifted it all the time and it ran fine until he sold it after a few yrs

 

[superbenk]

Re: Wankel engines in boats?

One reason might be that they have no low end torque.
You have to rev them high.
They work ok in a car because of the transmission.

That's another question I have - why don't boats have transmissions at all? I know the prop acts somewhat like the torque converter in an automatic transmission, but why not different gearing for a broader range?

What about it turning a jet of some kind,instead of a prop?maybe spin it up and then add water? i bet it would blow alot of bubbles until it got primed!!!they turn 10 or 12000 rpm don't they?

I think the RX-8 redlined at 7000-8000 rpm.

 

[Stachi]

Re: Wankel engines in boats?

fixed pitch propellors can achieve a speed where they lose power...

 

[Summer Fun]

Re: Wankel engines in boats?

If I remember correctly the Wankel engine as no RPM limitations .

It just keeps going and going ... am I right ??.

 

[smokeonthewater]

Re: Wankel engines in boats?

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

um......................................... WOW

 

[RotaryRacer]

Re: Wankel engines in boats?

I have my share of time playing with rotarys...specifically Wankels.

There have a been a few applications in the marine environment.

OMC played with Wankels for a while. They made a few race motors.

Atkins Rotary has about the only current Wankel marine application. They use Mazda blocks and have marine specific parts.

http://www.atkinsrotarymarine.com/

 

[RotaryRacer]

Re: Wankel engines in boats?

Mazdas motors have redlines around 7-8k. They will rev higher.

Wankels definitely have a RPM limits. The apex seals start to chatter and will disenigrate when you get up to 10-12k for extended periods.

 

[JB]

Re: Wankel engines in boats?

Back in the early 70s I was doing a consulting job for Johnson in Milwaukee. My client took me for a ride in a tinny with a 35HP rotary outboard prototype. It was developed from their snomobile rotary.

Hole shot was more like hole poop and the prop kept cavitating about the time it got to around 8Krpm. He said they had zero luck getting the torque curve short enough for one ratio and one try at variable ratio like they used in their snomobiles was even worse . . .too heavy.

It was also unacceptably noisy.

 

[86 century]

Re: Wankel engines in boats?

I have had some of the same thoughts.

The rotaries power to weight ratio if phenomenal compared to a standard piston eng.

I have seen a few v-drive boats with power glide transmissions.

I don't see why you couldn't replace the trany in an inboard or a merc trs drive with a two or three speed of your choice. Other than needing to modify the mounts and drive shaft. keeping it cool may be an issue.

 

[PBJT]

Re: Wankel engines in boats?

Boats don't have transmissions because they are not like a vehicle. To achieve top speed on a boat you need 100% of the engine power which is produced at or near the max rpm. A 300 hp sb is only produces 300 hp at high rpm so if you gear it down you would loose power and slow down. When you cruise it is a different story and why you can use a different prop for pulling, cruising but will effect top speed. Remember if you want to go fast or produce more power in your car you need it to shift down and bring up the rpms.

 

[smokeonthewater]

Re: Wankel engines in boats?

Boats don't have transmissions because they are not like a vehicle. To achieve top speed on a boat you need 100% of the engine power which is produced at or near the max rpm. A 300 hp sb is only produces 300 hp at high rpm so if you gear it down you would loose power and slow down. When you cruise it is a different story and why you can use a different prop for pulling, cruising but will effect top speed. Remember if you want to go fast or produce more power in your car you need it to shift down and bring up the rpms.

FAIL

Boats USUALLY don't have multi speed transmissions because they don't need them enough to justify the added bulk, weight, cost, and complexity.

Some dragboats run th400's so they can accelerate faster with the same high pitch prop that gives them their top speed.

It is not about needing top rpms... we have gear reductions for a reason

cars have something that boats do not.... traction..... imagine driving a 5 speed car on ice.... You could easily put it in 3rd and go from a dead stop and drive all day in that one gear

 

[PBJT]

Re: Wankel engines in boats?

It is not about needing top rpms... we have gear reductions for a reason

I will try and keep it simple for you...

it takes 300 hp to make my boat go 40 mph. In order for my engine to make 300 hp I need to rev it to 5000 rpm cause my naturally asperated 5.7 produces hp on a torque curve that peaks there. So If I shift it gears and attempt to spin my prop faster and decrease my engine rpm to go even faster I loose hp and my wind resistance and friction on the water is still adding up fast. Thus I can not go any faster than what my max prop pitch can be in any given ratio with the same hull and hp. Drag boats are different they don't want to loose bottem end for top end and need both the win a race....we can save weight and drive train because 3 to 6 sec time to plane is exceptable.

there are more variable then prop pitch, prop rpm, fd ration and torque curves, hp curves ect, nothing is an absolue but an engine only push something so fast till you need more engine.

Sorry off topic from, op

 

[Mischief Managed]

Re: Wankel engines in boats?

I will try and keep it simple for you...

it takes 300 hp to make my boat go 40 mph. In order for my engine to make 300 hp I need to rev it to 5000 rpm cause my naturally asperated 5.7 produces hp on a torque curve that peaks there.

The torque peak is far lower, down around 3500 RPM on your engine. The HP peak is closer to 5000.