Outdrives - a commercial perspective,

Deleted User said:
Yeah they're good boats but that really illustrates the point. They're aimed primarily at the boater who likes to do a bit of fishing. Most boaters buy a boat in which they have to accommodate family and friends and thats where outdrive boats really score
Click to expand...

My Hardy 26, single shaft drive with 3 berths. If out drive it would have 2 double berths, perhaps a terrible mistake by Hardy? But I wouldn't have bought it if it had o/d
 
Deleted User said:
I don't think its a case of either outdrive or shaftdrive. For sub 35ft boats, shaftdrive isn't really viable because the engine is further forward and eats up too much accommodation space (yes I know there are some sub 35ft boats with shaftdrive but they are heavily compromised on accommodation). In fact thats one of the major reasons why outdrives have been so successful; it has allowed boat builders to offer far more accommodation in smaller boats than they could have dreamt of with a shaftdrive installation. The other reasons of course are ease of installation and superior performance/efficiency. Effectively what outdrives have done is to open up the whole small boat market to a new type of customer, the weekend boater who buys a boat for fun rather than work. In fact I'd be willing to bet that most boaters on this forum had an outdrive powered boat as a first boat. Yup its easy to criticise outdrives for higher maintenance costs and, arguably, more difficult slow speed handling but without outdrives, I bet many of us would never have got into boating
Click to expand...
+1. My first 3 boats had outdrives.
 
I'll take your bet - first four boats had those funny Raggie things, all but the first (a Laser dinghy) had shafts as well. First stinkpot was a shaft at 28' with aft cabin. Current twin shafts. All future will have shafts.
 
Would a v-drive shaft drive boat (if that's the correct description) not offer the best of both worlds? Engines mounted further aft for space and shafts for reliability?
 
Whopper said:
Would a v-drive shaft drive boat (if that's the correct description) not offer the best of both worlds? Engines mounted further aft for space and shafts for reliability?
Click to expand...

I think the new trusty 28 has that config. I would that thought a good solution, just not sure why it is not used more? Perhaps someone will come tell us?
 
Deleted User said:
I don't think its a case of either outdrive or shaftdrive. For sub 35ft boats, shaftdrive isn't really viable because the engine is further forward and eats up too much accommodation space (yes I know there are some sub 35ft boats with shaftdrive but they are heavily compromised on accommodation).
Click to expand...

Humph.
 
Between our family we have about 30 years experience of boats with outdrives of all flavours (merc/volvo, single/duoprop).

They've been reliable, so I wouldnt have any qualms about owning outdrives. But I did have a merc alpha 1 drive fail 4 years ago, a gear in the upper drive sheared some teeth off, probably a manufacturing fault as the oil didnt have any water in it. You win some you lose some.

But the key thing is that none of the boats we've owned have had any option to have anything other than outdrives, it just wasnt an option to have shafts. These were all boats on the smaller side (between 20 -40 foot). BUt all these boats have lived in the water 365 days of the year. As long as you maintain them as per manufacturers instructions (and you accept that fact when you buy the boat), I think they'll be fine.

If you buy an older boat with outdrives and you dont know the history of the maintenance regime , then I reckon they're at higher risk of failing (and everything fails eventually just through normal use anyway), but you need to go into that with your eyes open. They are infinately more complex than shafts, and with that comes a higher risk that a link in the chain will fail, and when it does fail, the complexity means that they will cost more to rectify.

If we had decided we will only have a shaft drive or outboard boat, then our choice of boats over the last 30 years would have been massively restricted, and at the end of the day this restriction in boat choice pretty much make the descision for you.
 
Am I the only person in the world who has had no problems with out-drives or something? Going on what you read here you'd think they're gonna blow up upon immersion to the water.

I've had an Alpha 1, DP 290, 2 x DP 290 and now 2 x DPH and zero problems (mind you, I maintain them!).

Or have I just jinxed myself?
 
 
julians said:
Between our family we have about 30 years experience of boats with outdrives of all flavours (merc/volvo, single/duoprop).

They've been reliable, so I wouldnt have any qualms about owning outdrives. But I did have a merc alpha 1 drive fail 4 years ago, a gear in the upper drive sheared some teeth off, probably a manufacturing fault as the oil didnt have any water in it. You win some you lose some.

But the key thing is that none of the boats we've owned have had any option to have anything other than outdrives, it just wasnt an option to have shafts. These were all boats on the smaller side (between 20 -40 foot). BUt all these boats have lived in the water 365 days of the year. As long as you maintain them as per manufacturers instructions (and you accept that fact when you buy the boat), I think they'll be fine.

If you buy an older boat with outdrives and you dont know the history of the maintenance regime , then I reckon they're at higher risk of failing (and everything fails eventually just through normal use anyway), but you need to go into that with your eyes open. They are infinately more complex than shafts, and with that comes a higher risk that a link in the chain will fail, and when it does fail, the complexity means that they will cost more to rectify.

If we had decided we will only have a shaft drive or outboard boat, then our choice of boats over the last 30 years would have been massively restricted, and at the end of the day this restriction in boat choice pretty much make the descision for you.
Click to expand...
That's very well put and reflects my own experiance having vertually zero probs/ downtime with Vp duo props DPG over the past 8-9 seasons -all servised per VP schedule by a VP dealer .
Fuel over the current ownership period has moved from 78 cent / L ---- to € 1-60 /L
So even if one or both are wrecked then replacing them I figure in 1000 hrs I will be £££ in .
Thing is I have not spent any more € than normal maintenance .
At the fuel pontoon laughing all the way to bank ,while going faster ( well in the boat ) .
I guess with Alt -that make a total of 3 ?? Of us .
 
kashurst said:
have you looked at some of the old MBY boat reports where they test similar boats, one with outdrives, one on shafts. I think there was one done on the sealine S43 possibly others
Click to expand...

I was meaning a more scientific test. Journalists write with emotion and a magazine test has far to many variables to give real answers. I, and I know several other engineers who think the same, have always been a bit sceptical about the claims on efficiency that outdrive manufacturers claim. Hydrodynamically I doubt there is a huge difference as most shaft drive hulls are designed to channel the flow of water into the leading edge of the prop where as the lead in on drives is less. The transoms on an outdrive set up will almost certainly cause more drag(obviously not on IPS pods) and mechanically I cant imagine that the losses are less on an outdrive leg as opposed to a shaft. That leaves the ability to trim as the only real efficiency advantage of outdrives and I am not convinced that for the majority of users that will make that much of a difference at the fuel pump.
Outdrives can save a lot of space but thats not really important for workboats.
If anyone knows of any test tank data or similar I would love to read it, just to solve the riddle I've created in my head questioning the sales bumpf. :)
 
cryan said:
I was meaning a more scientific test. Journalists write with emotion and a magazine test has far to many variables to give real answers. I, and I know several other engineers who think the same, have always been a bit sceptical about the claims on efficiency that outdrive manufacturers claim. Hydrodynamically I doubt there is a huge difference as most shaft drive hulls are designed to channel the flow of water into the leading edge of the prop where as the lead in on drives is less. The transoms on an outdrive set up will almost certainly cause more drag(obviously not on IPS pods) and mechanically I cant imagine that the losses are less on an outdrive leg as opposed to a shaft. That leaves the ability to trim as the only real efficiency advantage of outdrives and I am not convinced that for the majority of users that will make that much of a difference at the fuel pump.
Outdrives can save a lot of space but thats not really important for workboats.
If anyone knows of any test tank data or similar I would love to read it, just to solve the riddle I've created in my head questioning the sales bumpf. :)
Click to expand...

Cryan, there are a couple of good reasons for drives to be more efficient than shafts, firstly they can be trimmed to give max thrust in the right direction. Secondly, the are no rudders causing additional drag.
 
rafiki_ said:
Cryan, there are a couple of good reasons for drives to be more efficient than shafts, firstly they can be trimmed to give max thrust in the right direction. Secondly, the are no rudders causing additional drag.
Click to expand...

Yes but they are in effect rudders and will likely cause as much if not more drag. As I mentioned above trim adjustment will help.
I'm not really proposing that they are less efficient only that I doubt the efficiency gain, if any, is quite what the manufacturers claim.
 
A Shafty -Pershing 37 with CAT 350 7.2 L and a SS Portofino 35 ( 37 ft) Kad300 3.7 L with DPG legs / outdrives
Boths boats more/ less same size -Acually to be pedantic the Persing is 15cm narrower .
However similar performance both max ish loaded arround 34-36 knots both cruise 26-28 knots
The shafty cat3126's consume @ 2600rpm 18 gallons / hr each = 36 x4.5 =162L/Hr
Sunseeker with the outdrives @ 3000rpm same speed consumes 75 L/hr -Yup that's both engines combined .
Go away and google it all up .
Partly the shafty needs 2x7.2 L But the outdrive 2x3.7 L
Also the points rafik mentions ,above
That's almost double the fuel bill,same size,wieght, of boat for same performance .
So 1000hrs later???
Can I remind everyone that in 2005 fuel was 65cents/L. Now north of € 1-60 /L ish?..l
 
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. :)
 
You must log in or register to reply here.

Share this page

Top