Why don't RIBs have gearsticks?

Mouldy · 13 March 2007, 10:28

or an overdrive button for economy?

fast fred · 13 March 2007, 10:42

the drag of water on a hull makes it not work well at all on most hulls.

Mouldy · 13 March 2007, 11:02

So maybe a big torquey diesel on a stepped hull?
Does anyone use gears or a cvt transmission like my mum's old DAF?

Pete7 · 13 March 2007, 11:48

Quote:

Originally Posted by Mouldy

or an overdrive button for economy?

Like this one ?

http://www.stepdrive.co.uk/stepdrive.htm

Pete

Hightower · 13 March 2007, 13:14

Getting a variable pitched prop would be the same as gears wouldn't it?

Cookee · 13 March 2007, 15:51

Surface drives sometimes have 2 speed gearboxes - they fir them to Sunseekers for instance. Class 1 boats also have them, I think they are limited to 2 or 3 gears now.

jwalker · 13 March 2007, 20:09

Quote:

Originally Posted by Hightower

Getting a variable pitched prop would be the same as gears wouldn't it?

Kinda similar but the variable pitched prop would be better because at lower speeds the low pitch would hold the water better. Not to take anything away from the gearbox cos I'd like one if it was available but I've seen me open the throttle wide on the back of a wave at about 15mph and been aware that the props are showing sign of breaking away. With the extra torque the gearbox would apply to the props, they may well let go.

I'd actually like the gearbox to change up at higher speed rather than change down at lower speed. If the boat was set up with a fine(ish) pitch prop so as to give good performance in the lower and mid range, then when up to cruising speed it would change up sorta like an overdrive. A small disadvantge would be the low pitch prop not being quite so efficient at higher speeds but overall it could be very satisfactory.

joakimhansson · 13 March 2007, 22:01

http://fbdesign.it/a38rib.php

Take a look at this!

Nos4r2 · 13 March 2007, 22:42

I'm sure I heard of an outboard from MANY years ago that used a CVT setup-but the CVT was effectively the throttle as the engine RPM stayed constant.

I think it was one of the marine engineers from Iboats.com that was talking about it-and it wasn't April 1st.

Bigmuz7 · 13 March 2007, 22:54

Apart from lawn mowers , surely outboards are one of the last class of engines that do not have gears, I've wondered about this for ages, bikes have them and like outboards have rediculous rpm ranges, but we dont?, and why not ? Seems strange to me ?? Ok it means a clutch mechanism and all that but tractors have had amazing shift mechanisms under power since the 70's? .. the tech isnt new, is it the cost ?

codprawn · 14 March 2007, 03:59

Props just aren't suited to gearboxes. That's why planes use variable pitch instead of change gears.

Pete7 · 14 March 2007, 09:57

Quote:

Originally Posted by codprawn

Props just aren't suited to gearboxes. That's why planes use variable pitch instead of change gears.

Being able to wind up a diesel until the turbo really kicks in then changing up would be an advantage in getting a boat on the plane. However I suspect the costs of developing such a system is the main draw back.

Pete

Cookee · 14 March 2007, 10:12

The Trimax in Buzzis RIB is the same system fitted to the Sunseekers, he has just made it fit the hull as one unit.

Jono · 14 March 2007, 10:19

Quote:

Originally Posted by Pete7

Being able to wind up a diesel until the turbo really kicks in then changing up would be an advantage in getting a boat on the plane. However I suspect the costs of developing such a system is the main draw back.

Pete

Rip out that ropey ol' Coal burner and put a proper engine in... there's another option.

Pete7 · 14 March 2007, 10:43

Quote:

Originally Posted by Jono

Rip out that ropey ol' Coal burner and put a proper engine in... there's another option.

Oi, thats my pride and joy

at least some of us on here have got a boat, even JK .......

Jono · 14 March 2007, 11:41

Quote:

Originally Posted by Pete7

.... at least some of us on here have got a boat, even JK .......

*ahem*.. you'd be amazed at what's in my shed....

Nos4r2 · 14 March 2007, 20:38

Quote:

Originally Posted by Jono

*ahem*.. you'd be amazed at what's in my shed....

Is that amazed or disgusted?

Mouldy · 16 March 2007, 09:58

Mouldy · 16 March 2007, 10:01

Quote:

Originally Posted by codprawn

Props just aren't suited to gearboxes. That's why planes use variable pitch instead of change gears.

Is this for acceleration? Essential for a plane even on water (anyone got a flying boat? I'd like a go - Free self contained accommodation for 2 in the Isle of Man for 100th anniversary TT celebrations in June to the lucky winner)

Once the boat speed is achieved at 4/5ths open throttle, wouldn't a higher gear drop the engine revs and maintain prop revs assuming the engine has the torque to manage the gearing?
You'd lose reponsiveness if the speed over water and engine revs drop - current, headwind etc - so perhaps an automatic/autopilot/cruisecontrol combo is required. Come on AquaTechs - sort it out not just for top end sunseekers - I bet a widebody 7mCoastline would be perfect - top cruising speed at 1/3rd throttle, extended range...

Cookee · 16 March 2007, 16:16

Quote:

Originally Posted by Mouldy

Is this for acceleration? Essential for a plane even on water (anyone got a flying boat? I'd like a go - Free self contained accommodation for 2 in the Isle of Man for 100th anniversary TT celebrations in June to the lucky winner)

Once the boat speed is achieved at 4/5ths open throttle, wouldn't a higher gear drop the engine revs and maintain prop revs assuming the engine has the torque to manage the gearing?
You'd lose reponsiveness if the speed over water and engine revs drop - current, headwind etc - so perhaps an automatic/autopilot/cruisecontrol combo is required. Come on AquaTechs - sort it out not just for top end sunseekers - I bet a widebody 7mCoastline would be perfect - top cruising speed at 1/3rd throttle, extended range...

Actually you really don't need a gearbox for most smaller boats under around 30 feet - the acceleration is acceptable and they rev out at top speed, so a gearbox is just an unnecessary expense! (and pointless)