Outdrives - a commercial perspective,

[Deleted User YDKXO]

Short answer, yes. On speed/fuel burn at WOT, at least.
Otoh, partial load and acceleration are among the "raisons d'être" I previously mentioned, together with the neutralization of prop walk in single installations.

People generally don't cruise at WOT. My understanding is that the duoprop is usually more fuel efficient at midrange cruising speeds

 

[MapisM]

People generally don't cruise at WOT.

True. As it's true that DPs can give a better holeshot, and also a lower minimum planing speed.
But the faster the boat speed, the less efficient it is to have a lot of blades spinning in the water.
In a 60kts boat, anywhere from 30 to 50kts qualifies as midrange speed, and you will struggle to find such boats equipped with DP outdrives.

 

[Deleted User YDKXO]

In a 60kts boat, anywhere from 30 to 50kts qualifies as midrange speed, and you will struggle to find such boats equipped with DP outdrives.

Well I'm sure that the next time Princess make a 60kt boat, they'll use a single prop sterndrive

 

[Portofino]

Actually, they have a few "raisons d'être", but efficiency is not one of them.
At VP they can say what they wish, but whenever top efficiency is critical, you will never see a duoprop sterndrive.

Look arround duo prop ! -speak to Lars @ delta yachts re 80 AGAIN -drop efficiency into the conversation
Compare fuel comp with JFM,s twin CAT C-32 on shafts ?( 6 Vs 2 props)
@ 350 hp -370 hp and associated torque of a D6 back in 2004 -theres only so much the existing " leg" could take .
No prob - simple ask the techies / spannermen to come up a beefier casing/ shafts/bearingings/trust washers -etc
They did - but starting to get heavey - No prob instead of hanging off the stearn ,mount a couple of M in .
Those props can be bigger ( both of them ) - turn the "leg" or outdrive round .Ask the Chinese to knock up a circuit board for $ 10 -get a 6 th former to knock up some software as an A level project and bingo ------ Jotstick docking - well you know-boys like there toys ?
iPS -now just sit back and wait for fuel prices to go N
While you waiting ask the techies( gotta keep them busy ) to IPS the D12 /13 - never know folks / market just might kinda wake up to fuel efficiency .

Duoprops work more effiently in " everyday" leisure craft where top speed is high 30's say delta80 s 37 knots and normal cruise is where you want it - 22-28 knot

For me my 11-12m SS ( VP -kad 300's -DPG ) uses less fuel than a Pershing 37 also 11-12m but for same performance needs twin CAT 350's or yanmar 370's on shifts

3.7L Vs 6 L - both 3000rpm - one uses less fuel - same speed - no prizes for figuring out which?

Looking at a 40% reduction in fuel like for like infact mines a heavier boat -but at real usable speeds not 60knots-or WOT

Next time Princess make a boat - IPS ?? ( that's Duoprop to you MapishM )

 

[Portofino]

Crikey even the Yanks are now at it -Duoproping up -says it all really
http://www.yachtingmagazine.com/yachts/sportfishing-boats/spencer-70-ips

 

[rbcoomer]

Well, comparing surface sterndrives with traditional shafts is a bit unfair, TBH.
If a hull is suitable for surface legs, the alternative (if any) are surface transmissions, whose drag is on par with outdrives, if not lower.

Sorry MM, I hadn't meant to draw direct comparison between surface drives and shafts, I was clumsily trying to illustrate that with a sterndrive, up to half of the prop often 'hides' behind the transom and that must impact on drag to some degree? Accept the fact that with surface drives it's more a case of out of the water altogether rather than out of the water path (whatever the terminology for that is?)...

 

[Oscar24]

Slight thread creep, but
Didnt Caudwell marine bring out a new drive system that was going to 'revolutionise' the outdrive market?

Saw one once on the back of a large RIB but that was on a trailer......

 

[lynall]

Thanks for the replies, Im still not 100 percent, but think I have a better understanding.
Mines a single prop vp drive and prop walk can be a pain.

 

[RogerRat]

People generally don't cruise at WOT. My understanding is that the duoprop is usually more fuel efficient at mid-range cruising speeds

Have to agree here. I suppose on high speed boats, 70 MPH plus then a sing prop is just as likely but I think this is more like due to durability. When boats are travelling at 40 knots plus on DPH duo props, there is very little in the water, just cavitation plate downwards and the drives get really hot, needing water spray cooling, special synthetic oils and regular changing @ 20 hour intervals.

Trimming btw, makes very little difference to hull speed on our type of boats but important on small light 'speed boats' often fited with single drive.
This thread drifts as quick as Coracal with no dagger board!

http://www.youtube.com/watch?v=fiVqjQqyTyM

 

[MapisM]

Look arround duo prop ! -speak to Lars @ delta yachts re 80 AGAIN

Nah, thanks for your suggestion, but that's not going to happen. And I'm sure some folks around here will understand why...

Re. all the rest of your defense for duoprop/IPS, feel free to trust VP claims, if you wish. But wake me up when you will have real world efficiency comparisons between dual vs. single propeller solutions, because I can't recall to have seen any, even from VP themselves.
And even leaving aside outdrives, where - believe it or not - I'm aware of DPX vs. Merc B1 comparisons on the same hull and power, where the latter achieved 8 (EIGHT, not a typo) knots more top speed, you don't think that VP invented azipods with their IPS, do you?
Just look at where efficiency REALLY matters, i.e. commercial applications. Whilst there's plenty of pods in such applications, dual propellers practically do not exist.

 

[MapisM]

Sorry MM, I hadn't meant to draw direct comparison between surface drives and shafts, I was clumsily trying to illustrate that with a sterndrive, up to half of the prop often 'hides' behind the transom and that must impact on drag to some degree? Accept the fact that with surface drives it's more a case of out of the water altogether rather than out of the water path (whatever the terminology for that is?)...

No worries, but I'm afraid we are at cross purposes, at least to some extent.
When you say that with a sterndrive (in general) the upper half of the prop is "sheltered" by the transom, that's actually true only for surface outdrives, which are installed in such way that the nose cone is aligned with the boat keel.
In "normal" outdrives, it's the cavitation plate which is aligned with the keel, and the whole prop is "exposed" to (and "grabs") the water flow, not just the lower half.

Then again, also in these installations, the lower half "pulls" more than the upper half anyway, for various reasons. But this is another matter altogether, and it's the reason behind the prop-walk effect - which is to some extent present in any propulsion, shafts included.

 

[lynall]

Have to agree here. I suppose on high speed boats, 70 MPH plus then a sing prop is just as likely but I think this is more like due to durability. When boats are travelling at 40 knots plus on DPH duo props, there is very little in the water, just cavitation plate downwards and the drives get really hot, needing water spray cooling, special synthetic oils and regular changing @ 20 hour intervals.

Trimming btw, makes very little difference to hull speed on our type of boats but important on small light 'speed boats' often fited with single drive.
This thread drifts as quick as Coracal with no dagger board!

http://www.youtube.com/watch?v=fiVqjQqyTyM

Syn trans oil in my drive as std.

 

[Latestarter1]

Quote: "The Skipper is a mate of mine. They are D3 200's driving DPS."

http://www.bumblebee.gg/

Although, 'Bumblebee' looks great and 200Hp should be plenty, the D3 set up has not proven too well, I hear. It appears to be too weak in some experts' opinions, it was really designed for use on light weight sub 30 footers for weekend use.

I would have thought that for commercial use a D4-260 or D6-350 would on DPH drives (even with the extra weight) would have been much more industrial and with the extra power and torque, comes the lower operating revs, fuel savings and greater duty cycle.



I hope this brings you back on thread.:encouragement:

RR

Bumblebee is exactly the type of vessel I was referring to when I mentioned vessels seen at Seawork which end in tears.

I would be interested in seeing business plan. No clue as to annual hours, however built 2012, D3 engines rated Volvo category 4 (Special Light Duty Commercial). Suggest that annual maintenance costs plus total replacement of engines/drive leg certainly by year five, very possibly before, will make financials real difficult to stack up.

I have done a lot of work for company operating small commercial vessels in Niger Delta. Shaft drive, water jet drive and outboards a plenty. Outdrives........Not a single one.

 

[RogerRat]

I have done a lot of work for company operating small commercial vessels in Niger Delta. Shaft drive, water jet drive and outboards a plenty. Outdrives........Not a single one.[/QUOTE


If only you had posted this on page one, says it all really and on point! :encouragement:

Thanks,
RR

 

[Garold]

No clue as to annual hours, however built 2012, D3 engines rated Volvo category 4 (Special Light Duty Commercial). Suggest that annual maintenance costs plus total replacement of engines/drive leg certainly by year five, very possibly before, will make financials real difficult to stack up.
.

How many hours use per annum is this special light duty limit?
And, is there a certain recognised number of hours where stern drives become more costly then?

Cheers
Garold