marine gearboxes and clutches

[kashurst]

just wondering why boat gearboxes in either shaft drive or out drive have the clutch in the gearbox
in a shaft drive the clutch is often a multi-plate wet clutch operated by high oil pressure
in an outdrive, 2 cone clutches of small diameter

why don't boats have an automotive style clutch on the flywheel? It could be a lot bigger diameter, out of the water and if it was from a car/truck relatively cheap and simple. Then the gearboxes could be much simpler just a few gears, syncros and a dog clutch to lock the gear to the shaft.

 

[volvopaul]

just wondering why boat gearboxes in either shaft drive or out drive have the clutch in the gearbox
in a shaft drive the clutch is often a multi-plate wet clutch operated by high oil pressure
in an outdrive, 2 cone clutches of small diameter

why don't boats have an automotive style clutch on the flywheel? It could be a lot bigger diameter, out of the water and if it was from a car/truck relatively cheap and simple. Then the gearboxes could be much simpler just a few gears, syncros and a dog clutch to lock the gear to the shaft.

Kevin I see where you are coming from , there is always a BUT , the but is space , the shorter the drivetrain the better for accommodation , that’s why your old T50 was on V drives so the aft cabin could be fitted in , had it been on conventional shafts the design would have been a lot different.

Many years ago , more than I can remember I left school 1980 to be precise , I was thrown into work , the machinery had 16 speed gearboxes , some 24 speeds , crude with no synchromesh but it worked , it was heavy and very big , a huge twin plate clutch on a flywheel 2 ft in diameter . Moving into the marine industry some years after the simplicity a bit to see was a different story , because a boat is always going uphill there was no need for any gears other than forward or reverse .

Most engines above 200hp then used hydraulic multi plate oil feed clutches , very simple to produce hardly ever wore out .
Over the years they just got bigger , my early Volvo years saw many of Volvopenta MS2 and MS 3 boxes destroyed , I remember the turbo 36 hitting the market early 80s with twin 158 hp engines and a tiny MS3 box with a cone clutch , they didn’t last for ever and were a swine to get out the boat .

Things have moved on in reliably but the concept has stayed the same for shaft drive boats , even the stern drives are pretty much from the same pen .
The japs brought out the hydradrive Yamaha , very expensive but silky smooth and reliable , they very rarely let water in .

Volvo have at last brought out another drive that has a clutch pack and electric operation , I’m not sure how reliable it will be fending off water ingress to the electrical parts inside , let’s see.
IPS is the biggest space saver but as we all know it has its flaws, is reliable but when it does go wrong it’s expensive.

If you can think of another way Kevin get your pen and paper out , let’s make a fortune .

 

[Portofino]

why don't boats have an automotive style clutch on the flywheel? It could be a lot bigger diameter, out of the water and if it was from a car/truck relatively cheap and simple. Then the gearboxes could be much simpler just a few gears, syncros and a dog clutch to lock the gear to the shaft.

Could it be because there’s basically only one top gear and a huge weight load discrepancy between say a 16 or 24 speed HGV and a boat .
Boat could be 15 to [ insert your own number ] tons .
So let’s put a dry plate automotive clutch in , proportionately sized diameter wise within the engine room space constraints.
Engage F .
There’s gonna be a huge amount of slip , burn , friction , heat etc at the moment the 600 rpm flywheels clutch plates touch .
Sure when you get planing 2 mins later the prop slips but at 0.1 sec the weight and prop pitch will kill a dry plate .
Then think about a windy day fuel pontoon manoeuvre F R FR F R F etc etc now you have momentum, to overcome never mind a static set off from anchor up .
You are gonna need huge ish hydraulic pressure etc to press the automotive dry plates together anyhow due to as said overcoming the huge inertial by crucially starting in top gear eve time .
The truck will be in low box 1 st out of 12/24 or what ever .

A wet oil for filled twin disc set up appropriately sized will be smaller and arguably lighter and because it’s wet the friction manifest in just warmer oil and most have an oil cooler to boot .All that happens with a bout of FRFRFR in quick succession is warmer oil .
As VP says the plates last for ever .
Would you want your dry plate set up to expire unannounced in a FRFRFR etc etc exercise......... and bash your boat ?
Sure