Outdrives - a commercial perspective,

Real World Boating.

It would appear that the main proofs regards fuel efficiancy between shafts and legs is always and without exception by quoting the most favorable figures in favour of outdrives either from journalists or boat builders..
We apparently all blast about at 35knots from the second we turn the key until we return from our non stopping adventure a few hours later.
No mention that much of your trip could involve bimbling about for quite a while before being able to open the throttles or just merely toddling along simply because its nice day or very uncomfortable at speed due to sea state.What about when you get to the othe end and have to slow down to moor or finding somewhere to anchor.
In the real world of actual boating betcha the fuel savings are nowhere near the claims when you take into account the fact that the differences are much closer at slower speeds possibly virtually disappearing at displacement and most boats will not spend as much time as WOT as required.
A mix of speeds is far more likely and far less favourable to the claims of outdrive fanatics who curiously all seem have outdrives.:)
Average boat usage 50 hours PA.Perhaps 50% at high speed.?
Alledged savings starting to vanish fast now :)
 
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cryan said:
Yes but tat is different boats, different engines, different hull shapes etc etc all of which affect fuel economy.To have any sort of reliable comparison test you would need identical boats with identical engines with identical ballast loads in the same sea state/tide/wind etc or better a test tank.
Again I'm not saying outdrives are less efficient I just doubt the scale of difference. The only stuff I can find online on the subject is as you describe above which are not really scientific and don't explain the reasons why and never seem to have identical engines/hulls etc.
I was in the Cruise industry when podded propulsion started to be introduced and attended a few technical meetings on them. Fuel efficiency was never given as a plus point. Manoeuvring, space in engine rooms were the main reasons. The reduction on tug requirements. Rolls Royce designed the forward facing prop pod (now seen on Volvo IPS) as they thought it was more efficient than conventional pods but not conventional props. Some offshore support boats I have been on had pod thrusters that were used for dynamic positioning but were retracted into the hull when steaming because their profile reduced hull efficiency.
There must be some literature on the subject so I'll keep looking. It is unfortunately the curse of an engineer to question common perception and to mistrust salesmen. :)
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That's because the Tug and "Carnival" 2000 cabin cruise ship are not planning boats.
Re rudder it's drag but right behind the vectored water that the single props have whipped up = kills thrust -unless you repower like the Pershing .
This is a fair comparison as a said weight, size ( read waterline length) hull shape ,almost identical
SS is 3.54 beam and Pershing 3.4 m .
If it had twin Kads with shaft with 285 HP + rudder , no way it would be able 8000kg + loaded to reach those speeds .in fact it just has not got the torque required ., to spin up the same pitch of prop.
Not a problem for the CAT 7.2 L .however with a DPG outdrive with Duoprop s it only needs a kad 300 -for like/ like performance .
It's about as like to like as one get .
Drag difference it's not so much as things sticking down like the leg or P bracket ,shaft , but where the obstruction is relation to the newly formed water jet generated by the prop .
Sticking a blade directly behind it ( rudder) kills shaves off thrust .Then slanting it ( shaft angle) 15-30 degrees is also a no brainier.So like for like you need shed loads of torque that the CATs provide to keep up with the Beamier SS .
 
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As oldgit said above, your only taking into account time spent on the plane which is a proportion of running time. If planing efficiency is a main concern then jets would be a better option. Far more simple engineering with very few loses in drive line efficiency and less maintenance costs. The reason I mentioned cruise ships was in respect to the hydrodynamic efficiency of the pod/leg shape. At manouvering and non planing speeds a conventional shaft is probably equal in efficiency?
I just think the average owner will not see the fuel savings advertised. And in respect of this thread, I don't see any advantage for commercial users outside perhaps angling charters and even then I think there are better options. Even if they were as efficient as claimed they are simply not tough enough.
 
julians said:
This is as close as I can find to a scientific test, but still done by a magazine, and they're comparing v drive to stern drive. I Guess v drives are similar to shaft drive, but maybe they're a bit more lossy due to the v drive aspects, but a bit less lossy due to having less shaft in the water?

http://www.searay.com/boat_graphics/electronic_brochure/company22491/TST_9.pdf
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I didnt even know what a v drive was until i googled it!
Certainly a fair whack difference in fuel consumption once on the plane, i did notice that the v-drives dont have that hole in the fuel usage at just under planing speed like the sterndrive model has.

I have noticed that with my boat, you either potter or fly anything in between uses more fuel and is pointless.

Lynall
 
julians said:
This is as close as I can find to a scientific test, but still done by a magazine, and they're comparing v drive to stern drive. I Guess v drives are similar to shaft drive, but maybe they're a bit more lossy due to the v drive aspects, but a bit less lossy due to having less shaft in the water?

http://www.searay.com/boat_graphics/electronic_brochure/company22491/TST_9.pdf
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Thanks for the link. V-drives are not common on UK built boats; in fact AFAIK, Sunseeker is the only British builder that has used them on some models. On the other hand, they are common in Italian built boats. The major advantage over straight shaft drive is, of course, that the engines can be located further aft which leaves more space for accommodation forward. In other respects, V-drive boats handle just like straight shaft drive boats. However, there is a penalty to be paid for the V drive installation and that is power loss compared to straight shaft drive because of the V drive gearbox. Nobody I've spoken to has been able to give me a definitive answer to how large that power loss is but I have heard figures in the region of 5-15% which is quite a substantial loss so in actual fact, comparing sterndrive against V drive, as this test report does, is not the same as comparing sterndrive against straight shaftdrive.
FWIW, I've owned 3 boats around the same size with the same Cat 3208TA 435hp engines, 2 with straight shaftdrive and 1 with V drive. The approx top speeds of all 3 were as follows

Princess 470 (straight shaftdrive) 30kts
Azimut 46 (straight shaftdrive) 29kts
Ferretti 46 (V drive) 27kts

Its not quite a fair comparison as I owned the 470 in UK waters whereas the other 2 were in the Med and I would expect the 470 to lose at least a knot in warmer Med waters. However, the difference between the straight shaftdrive Princess and Azimut against the Ferretti shows the power loss inherent with V drive systems. I see that some boatbuilders still persist with V drive installations, presumably because of the accommodation advantages and I'm told that modern V drive gearboxes are now more efficient so possibly the performance difference against straight shaftdrive is reduced now
 
Thanks for the link. V-drives are not common on UK built boats; in fact AFAIK, Sunseeker is the only British builder that has used them on some models. On the other hand, they are common in Italian built boats. The major advantage over straight shaft drive is, of course, that the engines can be located further aft which leaves more space for accommodation forward. In other respects, V-drive boats handle just like straight shaft drive boats. However, there is a penalty to be paid for the V drive installation and that is power loss compared to straight shaft drive because of the V drive gearbox.
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Given that all modern boats are self draining, and the deck is normally a straight run through from the transom to the saloon without a step, there is plenty of room under the saloon or the cockpit to put the engines? Nearly all boats have the windscreen located at about the midpoint of the hull, which would also allow the engines on a shaft drive to be located well forward. Cabins etc will always be in front of the windscreen location.

I can't see how outdrive or shaft drive would alter the layout of the boat?
 
rustybarge said:
Cabins etc will always be in front of the windscreen location.
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Well, thats not correct. On many boats, even older designs, at least one of the cabins is normally located under the saloon and/or lower helm station floor. Thats one of the reasons you find that the lower helm is often on a raised plinth in order to provide headroom for the cabin below. On modern boats above, say, 45ft, it is now de rigeur to place a full beam master cabin amidships and that has to go well aft under the saloon. Pushing the engines further aft as in a sterndrive, V drive, IPS installation allows the designer to put an amidships master cabin in relatively small boats these days. However, the downside of that is that in order to provide full standing headroom in the amidships cabin, the saloon floor has to be raised which is why boats have become taller these days.
 
just a small point on V drive gearboxes - there is only one more gear in a V drive than a straight through gearbox, so technically yes there is a further gearbox power loss but its small. The 5% - 15% power loss you quote is typical of the entire gearbox whether its V drive or straight through. The performance difference you identified is unlikely to be because of the V drive. My Sealine T50 with V drives when compared by MBY with Fairline, Princess and Sunseeker 50 footers was more fuel efficient and just as fast with less power.
 
kashurst said:
just a small point on V drive gearboxes - there is only one more gear in a V drive than a straight through gearbox, so technically yes there is a further gearbox power loss but its small. The 5% - 15% power loss you quote is typical of the entire gearbox whether its V drive or straight through. The performance difference you identified is unlikely to be because of the V drive. My Sealine T50 with V drives when compared by MBY with Fairline, Princess and Sunseeker 50 footers was more fuel efficient and just as fast with less power.
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Fair point kashurst but on my V drive Ferretti, there were 2 gearboxes, the standard Cat transmission bolted on to the back of the engine and an additional gearbox which reversed and offset the drive back under the engine so there was more than just one additional gear in the system. Did your T50 have a single gearbox or 2?
 
I think there is a bit of thread drift here? The post was about whether or not outdrives are suited to commercial boats therefore cabin space, aft or otherwise, is not a concern.
 
cryan said:
I think there is a bit of thread drift here? The post was about whether or not outdrives are suited to commercial boats therefore cabin space, aft or otherwise, is not a concern.
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Yup, guilty as charged. I hold my hands up and promise not to do it again, your honour
 
The Police in London run Targa 31's on outdrives and clock up loads of hours. Couple of years ago they a had T31 up for sale with Volvo AD41's on DP290 drives for £75K, it had only done 12000hrs! Would be interesting to know how many drives it consumed in that time, I think Volvo used to reccomend the drive was reconditioned every 1000hrs but I hope thats not true as mine are getting there fast!
 
Chris_d said:
The Police in London run Targa 31's on outdrives and clock up loads of hours. Couple of years ago they a had T31 up for sale with Volvo AD41's on DP290 drives for £75K, it had only done 12000hrs! Would be interesting to know how many drives it consumed in that time, I think Volvo used to reccomend the drive was reconditioned every 1000hrs but I hope thats not true as mine are getting there fast!
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12000 hours is a lot for the AD41'a and not to mention the drives! I give my DPE drives to the best VP authorized drive guy in my area (which btw is the hometown of volvo
penta) every 2 years and I am running behind the 1000h limit but he says one of my drives is still like new, not the other one though which has also had some water in it a few years back ( I skipped the every 2 years seal change thinking it was not needed) so I'd agree with others on the services needed to keep them happy. The basic mechanics of the drives are pretty simple and as long as you get the bellows on the right way, don't rip them with the power wash and keep the water out (seals changed every 2 years) and fresh oil every year they should be ok for many, many hours.
 
A_8 said:
12000 hours is a lot for the AD41'a and not to mention the drives! I give my DPE drives to the best VP authorized drive guy in my area (which btw is the hometown of volvo
penta) every 2 years and I am running behind the 1000h limit but he says one of my drives is still like new, not the other one though which has also had some water in it a few years back ( I skipped the every 2 years seal change thinking it was not needed) so I'd agree with others on the services needed to keep them happy. The basic mechanics of the drives are pretty simple and as long as you get the bellows on the right way, don't rip them with the power wash and keep the water out (seals changed every 2 years) and fresh oil every year they should be ok for many, many hours.
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Like mine and thousands others 160 ,000 Vp DPG outdrives ( 2001-2005) out there worldwide
Not to mention all the other versions past/ resent
 
I,ve got a very simple new design for outdrives,trouble is I,m too old to develop it.It would revolutionise outdrives.Must leave the idea in my will.Yes I,m very serious!!
 
Can anyone using IPS or pod drive tell me what they think about this drive system, how reliable, how expensive to maintain ? Sorry I am new to the Forum and may have missed past threads on the subject. I am thinking of buying a boat with IPS fitted but apart from the sale hype and Volvo brochure, very little information otherwise on pod drive. There is an article comparing it with shaft drive on MBY magazine couple of years back but I find it rather superficial with little data on its long term reliability issue, not much use actually. Also I think at present Volvo only offers 2 years warranty. Do they offer extended warranty on the IPS ? Thanks.
 
Portofino said:
Like mine and thousands others 160 ,000 Vp DPG outdrives ( 2001-2005) out there worldwide
Not to mention all the other versions past/ resent
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Chum of mine was really looking forward to an "experience" on a Sunseeker Portfino in the Solent over the weekend .
Unfortunately it had to be cancelled due to "mechanical" problems.
Of course it may have merely been that the speedometer had stopped working or one of the press studs on the canopy was loose.. :):):)
 
Post 2005 , most have D6 and DPH 'Mech " problems are well documented on here.
Sat on mine in the sunshine after a day out with friends to Cap Ferrat .
3100 rpm cruise 27 knots 65L / hour .
Fuel is now €1-55 here and € 1-65 in Antibes .
We have followed VP maintenance schedules ,by VP agents .
Boat has been turn key from a mech piont of view .I can only say it as it is Oldgit .
 
rustybarge said:
So which is least worse, the Merc alpha or the Volvo dpg?
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Pass on that cos the piont is this = if you do many hours ( like use your boat in the sea as opposed to floating caravan in the marina ) then the fuel savings -same for the " commercial " perspective are so much @ € 1,60 / L that any bills planned or otherwise pale into insignificance , over the same shaft set up ! .
 
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