herdman
Active Member
just wondering what are the main advantages/disadvantages to saildrive units compared to normal shaft driven props - is it just that they are cheaper to install?? any advice much appreciated...
saildrive vs shaft drive - pros and cons??
- Thread starter herdman
- Start date
Bodach na mara
Well-Known Member
Strewth, 35 minutes and no opinions! Well. for what it is worth, I would not touch Saildrive. All that stuff about gaskets, I would not like a bloody great hole in my boat filled with a sheet of rubber. And what about corrosion? Aluminium castings underwater?
Shaft drive has been about for over a centuary. The problems are well understood and can be solved. When I see 100-year-old boats floating happily with Sairdrives, I will reconsider.
Shaft drive has been about for over a centuary. The problems are well understood and can be solved. When I see 100-year-old boats floating happily with Sairdrives, I will reconsider.
savageseadog
Well-Known Member
Advantages of sail dive:
Close coupling of engine and drive no alignment or vibration problems and smaller installation.
Coupling of engine, drive and prop inherently stronger and less prone to failure.
Propellors are often deeper in the water, less prone to fouling and better drive.
Less regular routine maintenance of drive train
Sail Drives incorprate cooling water source deep in the water one less hole and more reliable cooling.
Disadvantsges:
More expensive
Giant hole to be cut in the hull
Maintenance liability with seal (inner and outer) to be replaced at intervals. Difficult and expensive job
Catastrophic failure of seal will fill the boat. How likely that is I'm not sure.
Close coupling of engine and drive no alignment or vibration problems and smaller installation.
Coupling of engine, drive and prop inherently stronger and less prone to failure.
Propellors are often deeper in the water, less prone to fouling and better drive.
Less regular routine maintenance of drive train
Sail Drives incorprate cooling water source deep in the water one less hole and more reliable cooling.
Disadvantsges:
More expensive
Giant hole to be cut in the hull
Maintenance liability with seal (inner and outer) to be replaced at intervals. Difficult and expensive job
Catastrophic failure of seal will fill the boat. How likely that is I'm not sure.
Tranona
Well-Known Member
For the builder, easier to engineer installation and cheaper to install, although clearly not a big issue in the mass production sector as the split of volume is about 50/50 with the two big French builders use mostly shafts, but most others use saildrives.
For the user pros are Smooth running, little prop walk as thrust is parallel to the waterline, no stuffing box to drip, no cutless bearing to wear. Cons are Potential breach of seal (but not really an issue), corrosion of aluminium housing of leg, potential internal damage if seawater gets inside leg.
Some will also argue that the "fine" engineering is unsuitable for rugged sea use. Essentially the same unit is used from about 20 to 75 hp, so either overengineered at the bottom end or marginal at the top!
In reality, they have been in service now for over 20 years, and although one can find cases to illustrate the cons, they are rare. Important to change the anodes regularly and make sure shaft seals are not damaged.
If you watch the posts you will see more issues with "conventional" installations. Questions on saildrives are usually about the seal (replace or not), anodes and props - folders rather than the standard fixed.
To me it would not be a deciding factor in boat choice.
For the user pros are Smooth running, little prop walk as thrust is parallel to the waterline, no stuffing box to drip, no cutless bearing to wear. Cons are Potential breach of seal (but not really an issue), corrosion of aluminium housing of leg, potential internal damage if seawater gets inside leg.
Some will also argue that the "fine" engineering is unsuitable for rugged sea use. Essentially the same unit is used from about 20 to 75 hp, so either overengineered at the bottom end or marginal at the top!
In reality, they have been in service now for over 20 years, and although one can find cases to illustrate the cons, they are rare. Important to change the anodes regularly and make sure shaft seals are not damaged.
If you watch the posts you will see more issues with "conventional" installations. Questions on saildrives are usually about the seal (replace or not), anodes and props - folders rather than the standard fixed.
To me it would not be a deciding factor in boat choice.
flaming
Well-Known Member
Other pros are better weight distribution, more streamlined protrusion so less drag under sail. These days all high end race boats and cruiser racers use saildrives.
smee
Well-Known Member
I've had both and the only one that gave me a 2 grand overhaul bill was the saildrive, plus 5-7 yearly bill in excess of 500 quid for new rubber seal. Enough said!
michael_w
Well-Known Member
I've had boats with both. Much prefer standard shaft arrangement. The compactness of a saildrive means that the boat builder shoehorns the thing in and makes jobs like getting to the dipstick, lift pump and the like nigh on impossible.
I find the lack of prop walk a real pain. Get the prop walk right and use The Force to berth your boat.
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I find the lack of prop walk a real pain. Get the prop walk right and use The Force to berth your boat.
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Stemar
Well-Known Member
Another factor against the saildrive, at least in some cases, is that the prop's a long way from the rudder. This complicates matters when you want to use a burst of power on full rudder to spin the boat without building up speed.
Tranona
Well-Known Member
In practice that is usually not a problem. Many boats fitted with saildrives are potentially overpowered and have big effective rudders - even if they are further away from the prop than in a long keel boat. A quick burst of throttle gets water flow over the rudder and response is quick, sometimes too quick.
I own both types of boat/propulsion and they are just different rather than one better than the other. With my long keeler I can perform party tricks - provided in reverse they include a turn to port. I can also spin in its own length - one way. So I always try to plan a course of action that recognises this. On the other hand my saildrive boat goes where I want it to, backwards, forwards, left or right. Takes some getting used to after a lifetime of long keels!
I own both types of boat/propulsion and they are just different rather than one better than the other. With my long keeler I can perform party tricks - provided in reverse they include a turn to port. I can also spin in its own length - one way. So I always try to plan a course of action that recognises this. On the other hand my saildrive boat goes where I want it to, backwards, forwards, left or right. Takes some getting used to after a lifetime of long keels!
Mrnotming
Well-Known Member
Yep. subject pretty well covered now.lovely quiet vibration free engine with the saildrive.Original Propellor became swiss cheese (aluminium alloy) Anode was only slightly corroded.Suspect electrical fault on nearby boat and/or steel pilings adjacent were the culprits.Own boat was also connected to AC. Buy a galvanic isolator unit for about £99 and have it installed in the earth wire after this enters the boat. Some types have a test facility. (various brands ).Or do as I do now and use solar energy to charge batts whilst away from the boat.the big donut keeps the water out for many years but now these are date stamped and should be replaced at year 7. Probably go for a CV joint on the prop shaft next time.More expensive initially, but unless as I was able to do, you can replace the donut yourself, the bill will be staggering as the parts are abouot €300 ,and the labour can be x but probably not less than €1500.In some boats the joinery has to be moved!I like the present vessel so I 'll hopefully end up doing the job again someday!
Maybe Volvo will come up with a 20 year type by then!
Maybe Volvo will come up with a 20 year type by then!
uforea
Well-Known Member
Don't understand your "less prop walk as the thrust is parellel to the water line", can you explain further please. Apologies if this is thread drift.
Ted
Ted
Tranona
Well-Known Member
Most conventional shafts are at an angle (usually 10 degrees) downwards. This means the water flow coming off each the blades is unequal and the "walk" is dependent on the handing of the prop. With a parallel drive the thrust is equal off each blade, therefore does not exert a sideways force.
It is most noticeable at low speeds and in reverse when maneouvering. Sometimes as in my long keeler once the boat moves to port in reverse due to prop walk there is no way it will come back as the rudder is ineffective. I use this to my advantage and almost always reverse out of my marina berth turning to port then a quick kick ahead to straighten up followed by a long reverse down the lane between berths hanging on for dear lfe to the tiller! Often get applause, but actually it is easier than trying to get her to reverse to starboard then going out ahead.
Once the boat has steerage way forward then the prop walk effectively disappears as the rudder takes over directional control.
Hope this helps
It is most noticeable at low speeds and in reverse when maneouvering. Sometimes as in my long keeler once the boat moves to port in reverse due to prop walk there is no way it will come back as the rudder is ineffective. I use this to my advantage and almost always reverse out of my marina berth turning to port then a quick kick ahead to straighten up followed by a long reverse down the lane between berths hanging on for dear lfe to the tiller! Often get applause, but actually it is easier than trying to get her to reverse to starboard then going out ahead.
Once the boat has steerage way forward then the prop walk effectively disappears as the rudder takes over directional control.
Hope this helps
Tranona
Well-Known Member
Should have added that if you run in reverse while moored up you can see the difference in water flow on each side of the boat. Mine has a strong stream on starboard side, little on port. Hence the stern goes to port in reverse.
