would boats be faster if outboards had gears+transmission?

[noob_boater]

I'm a noob with outboards, but from what i've seen, an outboard basically revs in just 1-forward gear. If it had a transmission with gears like a car 1-6, would it make the outboard faster?

a dude i know got a 300HP outboard on his 20 ft bass boat and at full throttle, he says it goes up to 80mph.. I know it takes more power to move objects through water, but i expected the boat to do at least 120mph max speed with 300 HP..

 

[jigngrub]

Re: would boats be faster if outboards had gears+transmission?

80 mph is pretty fast on the water.

There are boats with 400 hp motors that don't even do 70 mph and they brag and think they're hot stuff.

 

[MWG2600]

Re: would boats be faster if outboards had gears+transmission?

Generally on the water you have to quadruple your hp to double your speed.

 

[foodfisher]

Re: would boats be faster if outboards had gears+transmission?

Prop pushing water would stop or slow too much between gears to allow shifting with effeciency.

 

[Howard Sterndrive]

Re: would boats be faster if outboards had gears+transmission?

I'm a noob with outboards, but from what i've seen, an outboard basically revs in just 1-forward gear. If it had a transmission with gears like a car 1-6, would it make the outboard faster?

no, your outboard doesn't make much power at lower rpms
if you shifted to a higher gear, the rpm would drop, the engine would have no power, the boat would slow and drop off plane and you'd find yourself shifting back to low gear again.

 

[H20Rat]

Re: would boats be faster if outboards had gears+transmission?

You would go slower... The advantage is that you could get out of the hole quicker. Boats are already essentially in top gear. If the engine/prop/boat are matched, WOT will put you at your maximum speed without overrevving. Going up in gear would simply drop your rpm's, and lower your engine's HP output.

 

[dannyual767]

Re: would boats be faster if outboards had gears+transmission?

Howard and smokingcrater are correct.

 

[5150abf]

Re: would boats be faster if outboards had gears+transmission?

Most boats that can go 120 have multiple engines and probably at least 1000-1200 horsepower, Uncle had a 24' Fountain with 2 427s @450 each and it would run in the 80s, it takes very serious HP to run fast on water.

As far as a trans goes if it worked someone would have come out with one by now, I have seen variable pitch props which is essentially the same thing but again those are on huge HP boats.

 

[Chris1956]

Re: would boats be faster if outboards had gears+transmission?

Some years ago, Mercury had a prop that could shift gears automatically and RPM increased. It appeared to be a set of blades that could swivel to change pitch, plus some springs and weights to cause them to "shift up", when RPM increased. I never heard much about them. I think they were called "power2" or something.

 

[Chris1956]

Re: would boats be faster if outboards had gears+transmission?

Propeller airplanes routinely had variable pitch props. Since airplanes and boats are more closely related than boats and automobiles(IMHO), maybe there is a practical use for variable pitch props.

 

[spdracr39]

Re: would boats be faster if outboards had gears+transmission?

Propeller airplanes routinely had variable pitch props. Since airplanes and boats are more closely related than boats and automobiles(IMHO), maybe there is a practical use for variable pitch props.

This is a good comparison as resistance on the water increases with speed just as an airplane through air. Your enemy is weight, heat, and space. You also want the least amount of moving parts for reliability. This could be done but would require a totally redesigned hull and engine package and would not be practical because of cost.

 

[oldjeep]

Re: would boats be faster if outboards had gears+transmission?

Power 2 prop with an exploded view
http://www.crowleymarine.com/mercury-outboard/parts/2439_0.cfm

Only $780 to try one out
http://www.ebay.com/itm/MERCURY-48-..._Accessories_Gear&vxp=mtr&hash=item2c6618cf74

 

[steelespike]

Re: would boats be faster if outboards had gears+transmission?

I think there was a prop called "Torque Shift".There was a video showing hole shot the boat nearly leaped out of the water then as rpm increased would shift to the higher speed pitch.Very expensive and no longer in business. There is a member here with
some of these props and parts.

 

[Scott Danforth]

Re: would boats be faster if outboards had gears+transmission?

there are two speed gear boxes for Volvo Penta drives http://www.stepdrive.co.uk/

 

[Texasmark]

Re: would boats be faster if outboards had gears+transmission?

If you have a propeller with ports in it, you already have one of sorts. At low speeds the exhaust gasses flow over the blades and decrease the density of the water allowing the engine to develop it's rpms which gets it's hp developed and this helps a heavy stern boat, like a bass boat get on plane fast.

Once up, the water flowing by the holes and the suction caused at the rear of the thru-hub exhausted prop makes the path of least resistance for the gasses, the prop exhaust outlet to the rear. Thus the holes are effectively closed off and the propeller gets solid water and boat speed increases.

Mark

 

[sstone]

Re: would boats be faster if outboards had gears+transmission?

If you could make one of the right size and strength for boat, something like a cvt (continuously variable transmission may be able to get high revs and thus lots of power to the prop at low speeds and that high resistance speed right before planing. Once on plane, the resistance is lower than when you're pushing water, so the cvt could slide down to the high output speed end and give a boosted top end. It's essentially a transmission with infinite ratios that when done correctly provides the right amount of torque and power when needed and speed when desired.
Also, since the basic premise of the transmission is a belt turning a cone, it can "slide" between ratios without having to engage a clutch and stop power transmission to the prop while shifting. It also offers theoretically infinite ratios between the low (maybe 5:1) and high (possibly 1:1 or 1.5:1, depending on horsepower) ends of the range. The only problem I can see with this is longevity, belts aren't the strongest and cvt's are usually used on atv's and compact cars with little 4-bangers. On a big v8 with 500 hp, you'd either slip the belt or burn it up in a hurry. Another issue is fitting the machinery in a stern drive.
But if you could make it work, it'd be the equivalent of clutching during a drag race: keep the rpm's the same throughout the launch (usually where the best torque is) while gradually letting out the clutch to increase speed.

 

[Silvertip]

Re: would boats be faster if outboards had gears+transmission?

Can't imagine how much weight all of these suggestions would add to a drive system. With big four stroke outboards already weighing as much as the boat (tongue in cheek) another 50 pounds or more of gearing would eat up any performance advantage. Gearing would help with hole shot but does nothing for top end since engine rpm and the prop determines that.

 

[SolingSailor]

Re: would boats be faster if outboards had gears+transmission?

Just thinking about this idea, and having experience only on the ocean, on displacement boats:
In heavy seas, when you may want to proceed slowly upwind, but still need power to get over waves and to maintain control, I think it would be nice to be able to shift down, or reduce prop pitch, while maintaining engine rpm and power. On large boats, variable pitch props are not uncommon. Very expensive though. Outboards are probably already in high gear -- a low gear might be an economical solution.
Faster? I think not.

 

[H20Rat]

Re: would boats be faster if outboards had gears+transmission?

IThe only problem I can see with this is longevity, belts aren't the strongest and cvt's are usually used on atv's and compact cars with little 4-bangers. On a big v8 with 500 hp, you'd either slip the belt or burn it up in a hurry. Another issue is fitting the machinery in a stern drive.

There are already CVT's in vehicles that are at 300hp, and I've got word those same CVT's were massively overdesigned, and would handle a 500 hp v8 in a boat without too much problem. (a transmission in a boat is under lighter duty than a car, since the prop can slip)

Vehicle CVT's generally don't use belts, they use metal chains with all the pins sticking out of the links. The pulleys are hydraulically powered, and controlled by a computer. (no weights/springs) Clamping force between the pulleys is insane!

 

[Texasmark]

Re: would boats be faster if outboards had gears+transmission?

Well, obviously my answer was a waste of time. Maybe I need to get a beer, kick back in the recliner, and watch the Bearing Sea Crabbers. Apparently do as much good.

Mark