(Newbie) why don't Boats use Multi-Gear Transmissions?

Some thoughts on Transmissions

To all on this thread: For years, may folks used vdrives with various automotive automatic transmissions, most also used custom version that removed the converter, but still utilized the shift points. I grew up near St Louis and spent many days in old V-drive flatbottoms running turbo400s, and powerglides. All of them had manual valve bodies. The goal was to have a big pitch prop for high end, and the low gear for getting onto plane and idle quality(carbs and blowers!). See http://www.rexmar.com/page133.html for a current version of the t400 for vdrives.

I think there are still some advantages to this approach, but the weight issue needs to be overcome.


Jeff D Rauscher

 

Thanks for all those answers!
I've had to change my login name due to a new email address, but I'm the originator of the post. The thought was bugging me again, so as I do every once in a while, I put 'why don't boats have gears ' into google and suddely realised i had found my own post from months before!

At the time I thought Id got no responses as Im used to forums that email you once someone has answered your thread. I'm glad it has generated so much interest and that it's not just me that keeps returning to this simple question.

The reason I'm thinking about it again is this week I'm optimising my prop on a small RIB.

I have to use one prop for pulling wakeboards/ quick acceleration and another for top speed. That strikes me as a bit like only being able to use one gear in a manual car each day! One day you might pick second if you were just going to the shops, the next you might pick third if you were going on a long motorway trip. Picking 4th or 5th would never really be an option as you wouldn't be able to pull away from standstill effectively enough. And imagine how bad on fuel it would be! I know this is an exaggeration due to the different mediums cars and boats operate in, but come on! This is stone age technology we're still using in our boat engines isn't it? The prop I use for skiing is my second gear, the one I use for top end is 3rd. But I want access to gears 1, 4, 5 and 6, and I don't want to buy four more props and I dont want to have to take the engine out of the water and get a spanner out to change those gears!

I can't help thinking that with gears in my RIB I could select a lower gear to tow things and a higher one to cruise distances under low load and get away with running a bigger pitch in a general purpose application.. and only one prop to limit buggeration factor. I could use a relatively high pitch prop but get away with it whilst retaining decent acceleration by gunning it through the gears

The engine would not need clutch as a sequential motorcycle gearbox can be shifted in and out of gear without one (though might very briefly need a bit of load taking off the throttle while accelerating up through the box).

The more I think about it the more I want to put a motorcycle engine and trans in a boat! I accept that I was optimistic on my guess at motorcycle economy at WOT, but if the cruising rpm can be reduced, economy will surely be better?

Another of the benefits is in the price of the technology. I know it needs adapting, but look at the price of an insurance write off 1000cc 4 stroke sports bike, compared with a 140hp for stroke outboard motor. And the sportsbike's got brakes and wheels and tyres and plastics and a fuel tank etc. you could sell to fund the marine drive parts.

I maintain that boat engines only typically have one forward gear because of the complexities that existed as they were being developed in the first decades of the 20th century. A 1910 boat engine with gears would have probably been weak and unreliable and therefore unacceptable in the marine context, though I bet there were a few in those days due to the low engine power available.... single gear boats have persisted because of the early reliability issues and the fact that the slight compressibility of water has let us get away with it... to a certain extent. This is just the direction in which they have evolved.

I maintain that if you were inventing a planing boat from scratch now with a clean sheet of paper and it needed to work effectively and controllably and economically as possible at all speed ranges from 0- 50 knots, it would probably have gears.

Complexities like gearboxes are cheap now compared with the price of fuel. The era of geared boats for all is long overdue in my book!

 

I am the creator of this post and I have never changed my email address or changed my login User name.

While this last post is well written and thought out, it was not posted by myself, User ID = Kalagan.

I just wanted to clarify that, but thanks for the great input on the topic.

Kalagan

 

What was so well thought out? this:
>>>The era of geared boats for all is long overdue in my book<<<

It remains a stupid and unnecessary idea!
A CPP is cheaper, more reliabe, proven and off the shelve available.

But this question pops up every other month.

 

2 gear automatic type transmissions have been tried and have been used on offshore power boats for 30 years.

 

I can't help thinking that with gears in my RIB I could select a lower gear to tow things and a higher one to cruise distances under low load and get away with running a bigger pitch in a general purpose application.. and only one prop to limit buggeration factor.


Any you think a custom multi speed tranny will be cheaper than just a spare prop?

With conventional shaft & mechanical gear the power losses are only 2 or 3% ,efficiency untouchable with any other setup.

FF

 

My apologies Kalgan, I mistook this one for a similar thread which I originated some time ago asking the same question. It is at http://www.boatdesign.net/forums/diy-marinizing/why-dont-boats-have-gears-24747.html

 

Yank ski boats have used auto tranny's for 30+ years.
Art Carr
Offshore race boats were using them just a few years back but have been banned.
Weisman was the leader of that but ZF still make them.
( id like to see a 30 year old one Frosty, who made them then?)
Drag boats use the same Lenco's as they use on the land