Interesting question / debate ????

[Valv]

I have an interesting question I'd like to ask.<br />Why manufacturers don't add a transmission of any kind to I/Os where instead of running motors at 4000/5000rpm and use a lot of gas, they could run at 1500/2000rpm like automotive models ?<br /><br />Think all the gas we will save, noise, parts from motors revving too high. It could be a 2 speed manual or automatic. Parts also should be same as automotive.

 

[snapperbait]

Re: Interesting question / debate ????

Well it a good question.. The only simple answer is that to add a transmission with gears to lower the engine RPM would be like trying to run your boat with a prop with a pitch thats double that of what you are using...You would have to a least double the horsepower and torque of the engine to make it all work.. And you must also take into account the power it takes to turn the transmission which in most automotive examples is at least 15% of the engines horsepower output...<br />There are some two speed transmissions, but they are used on inboards under special conditions like high HP Drag race boats (using a powerglide) and in some heavy diesel offshore sportfishing applications.. <br />I ,like you, wish it would work, but untill they invent some new kind of physics laws I don't think it's going to fly...So were stuck with going slow and burning alot of go-go juice...

 

[f_inscreenname]

Re: Interesting question / debate ????

I have often thought this myself. They do have props that "change gears". It goes from a set pitch (so you have a hole shot). Then it moves up in pitch (by using springs)as your motor can handle it. I think the tranny idea is a good one. Just think if you could make your outdrive go from 1.68 to 1 (for a good hole shot) to say 1 to 1 at when you build enough speed, as it goes through its gears. I am still not clear on why this would not work. It should work like a car you would think. 1st gear to get it going and so on to build power till you reach 1 to 1 at a lower RPM. Then you would have all that throttle left. You may not reduce RPS's but would go a lot faster. Then back down when you reduce power. Kind of a tranny in reverse. Instead of reducing RPM's, building gear ratios.

 

[snapperbait]

Re: Interesting question / debate ????

I've tried three times to post all the math pertaining to this question but every time I do the D*** power goes out... So just take my word for it.. It won't work.. Well it could work, but the gear ratios would be so close it would not be worth the effort and extra parts to make it so.. Trust Me!!.. And: Florida Power & Light stinks.. So there...

 

[Dhadley]

Re: Interesting question / debate ????

There is a two speed transmission that will work. And it works pretty well. Boatbuilders and the buying public dont wqant to give up the additional space inside the boat.

 

[beckerdg]

Re: Interesting question / debate ????

Thinking out loud here. <br /><br />When I am cruising my truck down the level highway I am probably using something like 10-20% of the horsepower of what the engine is capable of producing and it runs in overdrive. <br /><br />Towing a 5000 lb boat and trailer up a steep hill, using pretty much all power, it drops down to at best 2nd gear. I think I am getting about 2 to 4 mpg at that point in my truck.<br /><br />I am thinking pushing a boat through the water at planing speeds is pretty much like always climbing that hill. Your using mucho gas because you need all that power. Just throttle back and see how fast you drop off plane. I think water transport is only efficient with a displacement hull not a planing hull. <br /><br />I could be wrong though. Here is a 23ft aussie boat they claim burns 2.5gph doing 38 with a funky outdrive I have never seem before.<br /><br /> http://www.dbdmarine.com/gallery/

 

[snapperbait]

Re: Interesting question / debate ????

Thank you JollyRogerX... You said it exactly the way I wanted to... Thats a scarey lookin outdrive there.. Kinda like an arneson...

 

[zakaih7]

Re: Interesting question / debate ????

I have given some thought to this as well...and I think it would require a varible pitch prop and a transmission to really work well. I don't know what is involved in varible pitch props but the trans part should be fairly straight forward.<br />seems to me tho that fuel economy would not be one of the major benefits to this set-up as it will still take the same amount of force to plane the boat and hold the plane at any given speed. The only advantage I can see is that you could possibly go faster and have better hole shots......but that would also depend on the variablity of the prop. Unless hydro-planes are much more effiecent than a planing boat and then I suppose it would be possible to get more fuel economy. Drag is drag as far as I can see...correct me if I am wrong.<br />anyway that is my thought on the subject.<br /><br />Michael<br />zakiah7

 

[beckerdg]

Re: Interesting question / debate ????

Yes, it does look like an Arneson, except it is not a surface drive and uses a regular prop. I think you would have to put a red flag on it when towing it sticks out so far. If it lives up to the manufacturer's claims it could become popular.

 

[Bob_VT]

Re: Interesting question / debate ????

Just wanted to cloud the issue a bit The fuel running drag boats have a transmission that divides the power to two seperate drive shafts AND the the props are geared UP! The props on a drag boat turn at close to 12,000 rpm thus over 200mph runs!<br /><br />Bob

 

[snapperbait]

Re: Interesting question / debate ????

If the manufacturer of that boat's claim of 2.5 GPH at 38MPH is "accurate" then that thing gets 15.2MPG... BULLS#$% more like 2.5MPG.... 15.2..Thats better than my truck..

 

[Tacklewasher]

Re: Interesting question / debate ????

A tranny would do nothing for reducing the cruising RPM's unless it was an overdrive tranny. The reason a tranny is needed in a auto is because the tires can't slip when starting up. To go from zero without a tranny would mean you have to drop to near zero RPM. The tranny just lets you run in the normal RPM range at slower speeds. In the water, this is done by prop slippage. <br /><br />So, why not an O/D gear in a boat? Because you are using all the horsepower the motor puts out to get the speed you want. H/P is a function of torque and RPM. Drop the RPM and you drop H/P and you loose speed. That's why my truck downshifts on hills. To keep the speed I have to change RPM's to be in the power band.<br /><br />So, if you really want better mileage, slow down. Just like I don't drive my truck at WOT, don't drive the boat at WOT and you will use less gas

 

[beckerdg]

Re: Interesting question / debate ????

My feeling too snapperbait. It says on their site (I cut and pasted)<br /><br />Length 7.47 M<br />Beam 2.5 M<br />Deadrise 50º at the bow & 24º at the stern<br />Weight loaded 3 Tonnes<br /><br />Speed: 38MPH @4400RPM<br />Fuel Consumption: 2.5 Gal per Hour<br /><br />Has to be a misprint. I think they work with Nasa. Half the specs are metric the other in english. Somewhere there was a miscalculation.

 

[Capt Ken]

Re: Interesting question / debate ????

I guess I need to dig out some old trade mags. Wasn't too long ago, while sitting in my office (head) and catching up on my paperwork (reading) there was a clip about a two speed transmission hooked to an outdrive that they were testing. I would almost bet it was Mercruiser. Gave the speed and fuel comparisions between this unit and a straight outdrive. Time to plane was faster and cruise rpms were lower. **** that old timer's disease.

 

[orca]

Re: Interesting question / debate ????

G'Day. I think that Mercury were experimenting with a variable pitch prop. I have seen one but I have never tried one on a boat.

 

[DJ]

Re: Interesting question / debate ????

Valv,<br /><br />Boats do not coast. Thus they need near peak torque and horsepower all of the time.<br /><br />The "switchpitch" props. have been somewhat succesful.<br /><br />Also a trans. (multiple speed) would add considerable weight and cost.

 

[Bear]

Re: Interesting question / debate ????

2-speed gearbox:<br /> http://www.fbdesign.it/pagine/pleasure38.htm <br /><br /> http://zf-marine.com/Gears/SGSummary1.cfm?UF=1&SG=Pleasure_2_Speed&Duty=Pleasure&Page=1 <br /><br />Try a search "yanmar 300 2-speed" http://www.yahoo.com

 

[Valv]

Re: Interesting question / debate ????

Wow, this is a good debate.<br /><br />I think there is a way we could do with reducing gas consumption and wear and tear of units.<br /><br />So far ZF (which is one of the best transmission builder in Europe) has almost my answer (thank you Bear), I just don't want to see the "price tag"....<br /><br />Djohns19 also has a point, but when I'll win the lottery (next week... ) I'll use some of the money to invent something for you guys... <br /><br />In the meantime, thank you all for your replies, even if I think it's still a good debate to discuss.<br /><br />Val

 

[Link]

Re: Interesting question / debate ????

Valv <br />What a great question! And I don't think there is<br />anyone here who hasn't thought about that!<br />And I'd bet if money, time, and resources were<br />not a problem we would all (here) love to try<br />and prove snapperbait's math wrong! <br /><br />Won't be done but I'd love to try! / Play??<br /><br />snapperbait: Please don't ever try to print that<br />math! I had (one) copy of a book that explained<br />it! Would break my poor slow puter <br /><br />JollyRogerX:<br />I just ran across DBD Marine this evening looking<br />for all things about sail boats! I'm going to<br />make a new post on it to see what others think!

 

[conimicut1]

Re: Interesting question / debate ????

Is it possible, maybe, is it economically feasible, probably not. It would have to cost a few grand and unless you drive your boat for 8 hours a time everyday it wouldn't make up the difference. Switch props, maybe. Fuel injection vs a carb now you are getting close!