What's going to happen ? (Shaft v Outdrives)

Re: What\'s going to happen ? (Shaft v Outdrives)

Hmm,to use a motorcar example both the Hillman imp and that dangerous american thing that Ralph Nadar moaned about both had all the weight right aft and both handled like pigs.
That engine needs to mounted midships to keep the centre of gravity where it belongs keeps the props in the water.As for that Botnia,fine fast little sheltered estuary craft,but down here only one type of boat is to been seen out in ALL weathers come what may,our big heavy Nelson pilot boat and if that is safely ashore then only the life boat will be seen, outdrive boat in bad weather.Yea right. /forums/images/graemlins/grin.gif
 
Re: What\'s going to happen ? (Shaft v Outdrives)

OK fair enough if we are talking life saving stuff costing £1.2m operating in storm force conditions but by heck you are going to pay big time in fuel burn in one of those jobbies. To get 14 metres to top out at just 25 knts you need twin 1000 hp MAN's on V drives sucking go go juice by the tanker load, hardly a fair comparison but on the other hand many Euro rescue services are using big ribs on drives with very little limit on sea conditions they can operate in.

The whole point here was effeciency, cost, performance, value for money etc, not what can we have if we have millions to spend.

The plain truth is outdrives (modern I hasten to add) will always be more efficient, quieter, more cost effective and better performance per hp than any shaft system can ever be and coupled to the right hull is as seaworthy as any shaft drive on the market today....unless you want to go out in storm conditions .....but this is the real world so drives will always win the day....so there....nah, nah, nah, nah......rssssssssssssp /forums/images/graemlins/blush.gif
 
Re: What\'s going to happen ? (Shaft v Outdrives)

You have'nt been out in a Botnia Targa in bad weather then?...shame....never mind you can wave to him as he passes you at twice your speed burning half the fuel .

Keep those trottles nailed on them there shafts, the earth thanks you.
 
Re: What\'s going to happen ? (Shaft v Outdrives)

Mike, if you look again at my post, it was concerned with sports cruisers up to 42'. Perhaps "pretty ineffecient" was a bit strong, shall we agree on "slightly less effecient" There is certainly some loss through the powertrain, V drive boats are usually a knot or two down on outdrive versions.
 
Princess V40 on Shafts - the facts

Interesting thread.

Having had both outdrives and shafts on sports boats, I can't imagine going back to outdrives. It cost an arm and a leg in maintenance, props etc, was difficult to handle at slow speed, was difficult to optimise for efficiency/speed etc (messing about with trim tabs and leg angle). Also noisier knot for knot (outdrive engine revving higher than shaft driven). That point also does not convince me about the fuel efficiency point - 33 knots at 2800 rpm (shafts), or 35 knots at 3800 rpm (outdrives).

Here are some typical fuel usage stats from this season in the V40 on shafts...

76 miles on 291 litres (Port Solent to Weymouth and various other short trips)

132 miles on 500 litres (Weymouth to Cherbourg and return)

100 miles on 366 litres (Yarmouth to Weymouth to Port Solent)

71 miles on 287 litres (Weymouth to Guernsey)

Typical cruising speeds on these trips between 22-24 knots depending on conditions.

22 knots achieved at approx 2000rpm

30 knots achieved at approx 2600rpm

33knots achieved at approx 2800rpm (Max RPM)
 
Re: What\'s going to happen ? (Shaft v Outdrives)

Looks like and outdrive boat in bad weather to me, storm 10 to be precise...................

ribbadweather.jpg
 
Re: Princess V40 on Shafts - the facts

Since the V40 on outdrives would probably be either KAD44's it would be interesting to know the fuel consumption on outdrives to give a comparison, but based on the fact that on shafts you need 370hp, but on outdrives need 260hp to achieve a slightly higher top speed, would suggest outdrives are significantly more efficient
 
Re: Princess V40 on Shafts - the facts

No. Of course not. I'm making a general point that engines driving outdrives will rev higher than one driving a shaft.

Examples - Sunseeker Portofino 34 (my old boat) on outdrives. Driven by AD41's max rpm 3800.

My current boat - V40 - on shafts driven by TAMD63p's max rpm 2800.

More comparable example. Sessa OY42 on outdrives. Max RPM 3900. (KAD300).

So, higher RPM equals greater noise and more fuel, but a smaller engine, so each rpm will use less fuel.

KAD300 = 3.6 litre. TAMD63P = 5.5 litre (I think).
 
Re: What\'s going to happen ? (Shaft v Outdrives)

Well not in my limited experience actually. My previous boat was an Azimut 46 with Cat3208TA 442hp engines driving straight shafts and that boat had a top speed of 27.5knots clean. My present boat is a Ferretti 46 with the same engines but driving thru V drives and that has almost exactly the same top speed. In actual fact, the Ferretti ia a bigger heavier boat than the Azimut so you would expect a slower top speed
I do agree that V drives will cause a small efficiency loss but I think other factors like hull design and weight distribution will have much more effect
 
Re: What\'s going to happen ? (Shaft v Outdrives)

[ QUOTE ]
You have'nt been out in a Botnia Targa in bad weather then?...shame....never mind you can wave to him as he passes you at twice your speed burning half the fuel .

[/ QUOTE ]


Amazing that pilots/RNLI don't use them then, perhaps you should have a word?

And twice the speed on half the fuel eh? Remarkable. /forums/images/graemlins/crazy.gif

[ QUOTE ]

Keep those trottles nailed on them there shafts, the earth thanks you.

[/ QUOTE ]

Oh dear, so you're saving the planet by using outdrives as you blast your big heavy twin six litre diesel boat along for fun now! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif

Ho hum...
 
Re: Princess V40 on Shafts - the facts

I agree. If it's top speed you want, then choose a boat with outdrives (or surface drives, or jets). If you want low noise, low stress reliable cruising, with easy berthing and lower engine wear, then choose shafts.

It all depends on what you want.
 
Re: What\'s going to happen ? (Shaft v Outdrives)

RNLI and Pilots have completely different needs so most are either in house designed or custom built for a very specific purpose, they would be naff all use for private use and vise versa.

RNLI have experimented with outdrives and jets quite recently and use outdrive ribs as test beds for equipment and training. As the technology and reliabilty has improved enormously on drives you may very well see drives on rescue boats in the near future /forums/images/graemlins/shocked.gif.

Yep /forums/images/graemlins/smirk.gif, about half the fuel on my 14 metre s/s with twin 350's against 14m Trent with twin Man 1000's, only I am going at 37 knts and they are flat out at only 25 knts, ok so I am not out there in storm 10 and can't maintain 25 knts in gale 8 but I'll get home safe and sound eventually.

Well at least I am making some effort to save the planet /forums/images/graemlins/cool.gif, Mr Pilot with his twin 500's on shafts does'nt care, someone else is paying the bill /forums/images/graemlins/blush.gif.
 
Re: Princess V40 on Shafts - the facts

I'm not sure about this. Surely it's to do with the individual engines as to their rev range. I would have thought that KAD44's driving either shaft or outdrives will operate in the same rpm. For example, my AD41's on outdrives rev to around 3800 max, and cruise at around 3400. A friends boat, with the same engines but on shafts, runs at the same rpm, though being a semi displacement boat, cruises at somewhat slower rate of knots. Can anyone confirm either way?
 
Re: Princess V40 on Shafts - the facts

My last S37, not as big as the V40 of course, but on Mercruiser D4's (220 hp), used (as an example from the log), 72 gals(or 327 litres) for the 117 miles Solent to St Peter Port, which compares pretty favourably, cruising those engines at 3200rpm. Not trying to get into an argument here, but I don't think your basic premise about rpm differences for the same engine on shafts v outdrives is rightt. I stand to be corrected by an independant arbitrater however!!
 
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