2 speed trans in boat

[Mastar]

my bigger fear is running out of Fuel before I get back home....

Yep, ive done it too many times in my old boat. Hopefully the x-star gauge reads a little more accurate than my old malibu.

I like the idea of variable pitch props. Probably a little too complex for now.

Oh and my current 2007 silverado has 4 speed. Have to drop it in 4wd low to get up the boat ramp without bogging down

[Z71_Silvy]

Think about it, 50 years ago 4 gears were plenty in a car. Now 6 isn't even enough.

50 years ago? I had a 4-speed in my 2006 Silverado.

But the 8-Speed in my Jeep is a gem. Power whenever I need it and great fuel economy.

[Stevext23]

There are several geared turbofans. https://en.wikipedia.org/wiki/Geared_turbofan

And, just like propeller driven planes, the pitch of those props actually rotates depending on the speed to manage the angle of attack requirements for efficient thrust.

[stevenbratt]

The physics of airplanes is much closer to boats than cars. Don't know of any multi speed gear boxes on airplanes either (but they certainly could exist). Some can change the pitch of the propeller. This allows for more torque for takeoff and landing. Good because the stall speed is lower and it actively brakes the aircraft on landing. Then adjust to less pitch for cruising speed and better fuel efficiency.

I don't see why this wouldn't work on boats too but I don't want that kind of complexity or moving parts on my boat prop. Interesting topic but single speed with the correct engine and prop is as complicated as I want it on my boat and it works reasonably well.

There are also other factors with controlling prop pitch to make sure the engine isn't destroyed.

Overall I think the system would be too complex and costly for anything other than a large cruiser.

[Keith2230]

The physics of airplanes is much closer to boats than cars. Don't know of any multi speed gear boxes on airplanes either (but they certainly could exist). Some can change the pitch of the propeller. This allows for more torque for takeoff and landing. Good because the stall speed is lower and it actively brakes the aircraft on landing. Then adjust to less pitch for cruising speed and better fuel efficiency.

I don't see why this wouldn't work on boats too but I don't want that kind of complexity or moving parts on my boat prop. Interesting topic but single speed with the correct engine and prop is as complicated as I want it on my boat and it works reasonably well.

[LDA6339]

What about a big twin engine yacht with 4 props and 4 screws but only 2 engines and once the thing got on plane it switched from the two props for torque to the two props pitched for cruising? I wonder if that could work or be worth the time and money


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[MattsCraft]

lots of discussion on big boat forums - to get it right a variable pitch prop would be needed..

This does work - I had one one my Cobalt - Speed friction clutch built into the prop - It was like having a 2 speed transmission - Better hole shot & lower RPM for cruising. The only issue I had was if you went into a really hard turn with the prop in the higher pitch position the boat would bog down a bit until it would switch into the lower pitch position. You actually had to pull of the throttle so the clutch would switch, then get back into it. Expensive, but a really cool option for an I/O. I think I paid like $1000 for a 3 blade stainless at the time, looks like they double that now.

Always thought someone should make one for an inboard

http://aerostarmarine.aerostaraircraft.com/ppp.html

[lashburn1]

I'm always concerned about running high rpm while cruising, so I will usually cruise around at 25 mph getting passed by pontoons ! Is it much harder on engines to run at higher RPMs?

we have Wake Boats.....everyone passes us

With our 7.4 522 HP X46.. I can keep up with most boats heading up and down the River... but its like 4000-5000rpm... and I will pay for it at the pump.
my bigger fear is running out of Fuel before I get back home....

[Mastar]

I'm always concerned about running high rpm while cruising, so I will usually cruise around at 25 mph getting passed by pontoons ! Is it much harder on engines to run at higher RPMs?

[toddvdh]

It's not about spinning the prop faster. It's about keeping prop rpm the same while lowering the engine rpms.

Set cruise at 30mph in your car, then downshift 1 gear while not touching the cruise control. The car will stay the same speed but the engine rpms will increase. Now up shift 1 gear and the rpms drop again.

It would the same thing in a boat. It's doable I think. Getting the ratios right and shifting smooth would be the hard part. Think about it, 50 years ago 4 gears were plenty in a car. Now 6 isn't even enough.

[Z71_Silvy]

I would imagine that at some point the hull can only go so fast and the prop can only be spun so fast (all things being the same other than a 2nd gear).

I would imagine the prop would eventually cavitate too from spinning too fast. I would think it can only move so much water.

[mikeg205]

lots of discussion on big boat forums - to get it right a variable pitch prop would be needed..

[EricB]

I get that there is way more friction to deal with than a car. But it seems like at a certain point cruising you have plenty of power you just need the prop to spin faster . At 4000 if you shifted to another gear and still had 3000 rpm you don't think there would be enough power?

Good question. If your throttle position does not change though, you would still be using the same, if not more fuel. Depends on reading engine load (vacuum). Now if you could back off on the throttle like a car, then you'd be on to something!

[Mastar]

It all has to do with load, hp and running surface. Think of it this way; if it takes 3400 rpm (and 1/2 throttle) to move your boat 34 mph, shifting to a higher gear will load your engine down and thus will drop your speed. Your engine does not have the hp to maintain the speed given the load. It does not work the way a car does because a car is in a light throttle-cruise mode almost 80% of the time.

I get that there is way more friction to deal with than a car. But it seems like at a certain point cruising you have plenty of power you just need the prop to spin faster . At 4000 if you shifted to another gear and still had 3000 rpm you don't think there would be enough power?

[Stevext23]

Well, the new geared turbofans for jet engines means it is way more fuel efficient. Complaints previously of Clunkyness is just bad engineering. The PDK transmission from Porsche proves complicated trannies can be silk - and better.