Siochair
Well-Known Member
Not quite gears... but has anyone heard anything about Yellowfin? It seems to have quietly faded away after the initial fanfare of news.
has car-like gears ever been tried on a boat ?
- Thread starter BOATKID
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Latestarter1
Well-Known Member
Funny,
I seem to have said this a few times before, however penny never seems to drop.
'Propellers drive boats not engines and they are only efficient at one speed' unless vp
Yes ZF still do two speed gearboxes however they have never been anything other than a solution looking for a problem.
I suggest a visit on to Amazon 'The Propeller Handbook' Author Dave Gerr.
I seem to have said this a few times before, however penny never seems to drop.
'Propellers drive boats not engines and they are only efficient at one speed' unless vp
Yes ZF still do two speed gearboxes however they have never been anything other than a solution looking for a problem.
I suggest a visit on to Amazon 'The Propeller Handbook' Author Dave Gerr.
oceanfroggie
Well-Known Member
Only with variable pitch probs which are impractical on small leisure boats.
MapisM
Well-Known Member
Huh? There's a wide choice of them available already.
Tried and tested, though obviously not all boats are worth the additional cost.
And you don't need to look at exothic builders, either: see ZF website.
Tried and tested, though obviously not all boats are worth the additional cost.
And you don't need to look at exothic builders, either: see ZF website.
PCUK
Well-Known Member
Finally, how about air ventilation as used on Bransons Blue Riband attempt boat? Air caused slip therefore engine revs increased to get boat onto plane, once up air off and prop' bites fully to give more speed.
A simple relatively two gear arrangement!
A simple relatively two gear arrangement!
Eventide26
Well-Known Member
Yes - Car like gears can be used.
The boat you see here, yes sorry its a raggie, but myself and my father did an engine and gearbox conversion from a Robin Relient engine.
We used the 4th gear and blanked off the other gears and re-used the reverse gear as is. We then matched a suitable pitched fixed prop.
First trials worked well, even though we both laugh as her stern sank with the increased grunt, and I joking added that we may have to add trim tabs/forums/images/graemlins/grin.gif
That aside I can't see any reason why any other gear box couldn't be used provided you can work with the ratios of the gears.
The boat you see here, yes sorry its a raggie, but myself and my father did an engine and gearbox conversion from a Robin Relient engine.
We used the 4th gear and blanked off the other gears and re-used the reverse gear as is. We then matched a suitable pitched fixed prop.
First trials worked well, even though we both laugh as her stern sank with the increased grunt, and I joking added that we may have to add trim tabs/forums/images/graemlins/grin.gif
That aside I can't see any reason why any other gear box couldn't be used provided you can work with the ratios of the gears.
jfm
Well-Known Member
"'Propellers drive boats not engines" is a kinda simplistic pseudo profound statement. It is nonsense to suggest the engine is irrelevant. Wheels drive cars but wheels are hardly the whole story of car propulsion.
Latestarter1
Well-Known Member
Remember, props drive boats, engines don’t, they turn PROPELLERS. Nothing simplistic or pseudo profound about that statement at all.
In vehicle engineering transmissions ratios are absolute, and with warm lubricants driveline losses are well understood and are accurately calculated so there is no point making any comparison between wheels and propellers.
1) All engines do is rotate PROPELLERS----As my Dad would say that’s ´ipso facto´, period, with no questions wanted or allowed!! He meant it, trust me.
2) Any prop under a given set of circumstances absorbs a certain amount of Hp, and therefore a specific amount of fuel per hour.
3) Let’s take a ´theoretical´ boat; it will require a certain amount of Hp to make it go say 22 knots. If that’s 250 HP per engine, then regardless of what the engines POTENTIAL power is available at a given rpm at 22 knots the governor will only give the amount of fuel required to generate the amount of power the propeller is asking for.
To sum up the propeller ‘asks’ and the engine ‘gives’ therefore who is in charge of this game, certainly not the engine.
Just a final plea; please please get a copy of the Propeller Handbook, it is now down to just over £7 on Amazon for a new copy for winter reading.
In vehicle engineering transmissions ratios are absolute, and with warm lubricants driveline losses are well understood and are accurately calculated so there is no point making any comparison between wheels and propellers.
1) All engines do is rotate PROPELLERS----As my Dad would say that’s ´ipso facto´, period, with no questions wanted or allowed!! He meant it, trust me.
2) Any prop under a given set of circumstances absorbs a certain amount of Hp, and therefore a specific amount of fuel per hour.
3) Let’s take a ´theoretical´ boat; it will require a certain amount of Hp to make it go say 22 knots. If that’s 250 HP per engine, then regardless of what the engines POTENTIAL power is available at a given rpm at 22 knots the governor will only give the amount of fuel required to generate the amount of power the propeller is asking for.
To sum up the propeller ‘asks’ and the engine ‘gives’ therefore who is in charge of this game, certainly not the engine.
Just a final plea; please please get a copy of the Propeller Handbook, it is now down to just over £7 on Amazon for a new copy for winter reading.
VicS
Well-Known Member
[ QUOTE ]
dont think I'll invite the dragons in on this one
[/ QUOTE ]
Too late pal. I'm here waiting. Half a dozen virgins first though please. I'll cook them myself.
dont think I'll invite the dragons in on this one
[/ QUOTE ]
Too late pal. I'm here waiting. Half a dozen virgins first though please. I'll cook them myself.
graham
Well-Known Member
An old friend of mine had a Reliant Robin engine complete with original gearbox in a 36 ft converted wooden ships lifeboat. He went ahead in 3d gear at abouit 6 or 7 knots.It would go astern but with limited power even on full revs.He used to joke about leaving it in gear when parked. /forums/images/graemlins/smile.gif
jfm
Well-Known Member
No dispute on points 2 and 3, I never said anything to the contrary! I dont think we're disagreeing on anything substantial here, so I wont make any argument. Perhaps it was just semantics: when you say "All engines do is drive props" I would take issue with the word "all", which suggests that turning a prop is a simple straightforward thing to do and so the engine can be ignored when engineering the propulsion system. No worries 
Thanks for the book reference. The first chapter is freely readable on Amazon. To be honest, there is nothing wrong with it but it is aimed a "mechanic level" practical prop selection. It doesn't seem to cover the real physics and fluid dynamics of how a prop blade really works, not is it intended to. Even in the first chapter there were some strange statements from a guy with that level of qualifications. Like "In order for horsepower to propel a boat it must be converted to a twisting force rotating the propeller". It's amazing that an engineer would write that. You cannot "convert" horsepower to force. They are dimensionally not equivalent. Rather, you have no horsepower if you do not have a force; there is no way at a true engineering level you can convert one to the other becuase they must co-exist side-by-side at the same time- they are not alternatives. Ok one can guess what Gerr meant, but as I say this is not a real analysis of the physics and engineering of props, and I don't think the author intended it to be. It's a lot more colloquial than that. I'll order the book though - thanks!
Thanks for the book reference. The first chapter is freely readable on Amazon. To be honest, there is nothing wrong with it but it is aimed a "mechanic level" practical prop selection. It doesn't seem to cover the real physics and fluid dynamics of how a prop blade really works, not is it intended to. Even in the first chapter there were some strange statements from a guy with that level of qualifications. Like "In order for horsepower to propel a boat it must be converted to a twisting force rotating the propeller". It's amazing that an engineer would write that. You cannot "convert" horsepower to force. They are dimensionally not equivalent. Rather, you have no horsepower if you do not have a force; there is no way at a true engineering level you can convert one to the other becuase they must co-exist side-by-side at the same time- they are not alternatives. Ok one can guess what Gerr meant, but as I say this is not a real analysis of the physics and engineering of props, and I don't think the author intended it to be. It's a lot more colloquial than that. I'll order the book though - thanks!
MapisM
Well-Known Member
Hmmm.... I don't dare evaluating how pseudo profound your view is, but simplistic it is for sure.
I'm even tempted to say that it's simplistic ipso facto, period... /forums/images/graemlins/grin.gif
Take your previous comment about ZF twin speed transmission as "a solution looking for a problem", for example.
According to your view, Fabio Buzzi had no practical reasons to use it on most of his boats.
How funny is it that many of those boats are record holders in various categories?
Just think about a high performance diesel boat, driven by surface props/transmissions.
You carefully design everything - engines, hull, transmissions, props in order to achieve consistent cruising speeds in excess of 60kts, and possibly with a very extended range (=fuel=weight).
Do you have an idea of the RPM range through which the engines should be able to deliver sufficient power, from minimum to maximum speed, with the capacity to get over the hump in between?
At least 3 thousands RPM - maybe more. And there's no way any kind of prop can get round such constraint, on this type of boat.
So what, I hear you say? It's sufficient to install engines capable of spinning efficiently from say 600 to 4.000 RPM.
True, if only such engine would exist. As long as it doesn't, the twin speed gearbox IS a solution to a problem.
Oh, and on a side note, it's a truly fantastic piece of engineering - you should see one disassembled to appreciate it.
I'm even tempted to say that it's simplistic ipso facto, period... /forums/images/graemlins/grin.gif
Take your previous comment about ZF twin speed transmission as "a solution looking for a problem", for example.
According to your view, Fabio Buzzi had no practical reasons to use it on most of his boats.
How funny is it that many of those boats are record holders in various categories?
Just think about a high performance diesel boat, driven by surface props/transmissions.
You carefully design everything - engines, hull, transmissions, props in order to achieve consistent cruising speeds in excess of 60kts, and possibly with a very extended range (=fuel=weight).
Do you have an idea of the RPM range through which the engines should be able to deliver sufficient power, from minimum to maximum speed, with the capacity to get over the hump in between?
At least 3 thousands RPM - maybe more. And there's no way any kind of prop can get round such constraint, on this type of boat.
So what, I hear you say? It's sufficient to install engines capable of spinning efficiently from say 600 to 4.000 RPM.
True, if only such engine would exist. As long as it doesn't, the twin speed gearbox IS a solution to a problem.
Oh, and on a side note, it's a truly fantastic piece of engineering - you should see one disassembled to appreciate it.
Siochair
Well-Known Member
That's very interesting information thank you but can I take it from your reply that you have not heard any further news of Yellowfin as in my question? /forums/images/graemlins/frown.gif
Its_Only_Money
Well-Known Member
As jfm says it fixes a problem most boats don't really have and certainly don't have the room/cost benefit to get.
Stepdrive was specifically aimed at older diesels that struggled to plane, giving them a lower gear allowed easier planing and then the upper ratio allowed for efficient on-the-plane performance.
Modern diesels fixed this by beefing up their torque curves so largely negating the benefit.
Not sure how many stepdrives were ever fitted???
Stepdrive was specifically aimed at older diesels that struggled to plane, giving them a lower gear allowed easier planing and then the upper ratio allowed for efficient on-the-plane performance.
Modern diesels fixed this by beefing up their torque curves so largely negating the benefit.
Not sure how many stepdrives were ever fitted???
SteveA
Well-Known Member
To be pedantic the majority of propellors are variable pitch - their pitch vares from the boss to the blade tips. The only ones that i know of that don't are the old seagull flat bladed props.
Controllable pitch propellors are usually fairly fancy, expensive affairs but I did come across a simple system using a rod contol - this was fitted on ships lifeboats driven from an air cooled SABB diesel so I guess it would only be suitable for lower power units. The engine was governed for constant speed and control was by what looked like a large gearbox lever.
Controllable pitch propellors are usually fairly fancy, expensive affairs but I did come across a simple system using a rod contol - this was fitted on ships lifeboats driven from an air cooled SABB diesel so I guess it would only be suitable for lower power units. The engine was governed for constant speed and control was by what looked like a large gearbox lever.
