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Old 03-01-2008, 19:16   #1
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Saildrive vs Shaft Drive

Hello,

I have been comparing boats trying to decide which would be the best one for me. I would like to to long range cruising. Maybe a circumnavigation. I have done a lot of reading and asked some very experienced and knowledgable people for their opinions.

I am coming to the conclusion that for long range cruising, a shaft drive or prop shaft is much better than what seems to be the more typical saildrive.

How do you feel about this?

Which boats in the 35 to 42 foot range came with, or now come with a shaft drive?

Thanks,
Jeff Lessnau
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Old 03-01-2008, 19:21   #2
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This is too open a question.
Any fin keeled sailboat could be built either. A full keel dictates shaft drive in your size range.
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Old 03-01-2008, 19:25   #3
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I don't see it as a factor. In older boats you will find shaft drives common.

I find it hard to imagine you getting down to two boats and the only factor being the drive. In then end all boats are not perfect. You end up with a set of choices that include only the boats you can buy at the time.
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Old 03-01-2008, 19:31   #4
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I am looking for the boat which is as close to perfect
for my purpose I can find.

I quote some info I found online below:

Though it's time-consuming to correctly align the gearbox and propshaft, shaftdrives have the distinct advantage that the stainless steel propshaft and bronze prop allow the use of slow-leaching copper antifoulings. These paints last much longer than the non-copper paints needed for aluminium saildrive legs, and if your boat is steel, stainless steel and bronze are less susceptible to electrolysis than an aluminium leg.
Although to my knowledge very few (if any) saildrive diaphragms leak, if your boat is left afloat unused for long periods, there's more security in having a small stern gland than relying on rubber diaphragms.
When I interviewed bareboat charter operators in the Whitsundays about their drive system preferences, their main gripe was the fine coral particles from reefs in the area. They said that these particles blocked saildrive cooling-water intakes with monotonous regularity. Once the unscreened intakes of a saildrive leg had clogged, the hull had to be slipped and the drive leg removed to clear the blockage, unlike the separate cooling-water intakes of shaftdrive motors, which could be cleaned by simply diving over the side and removing the grit with a screwdriver.
Saildrives generally have only one gear ratio choice and the ratio is the same ahead and astern to facilitate counter-rotation. But even with small shaftdrive Yanmar diesels such as the 1GM10, three different ratios are offered and the two taller ratios have a higher ratio ahead than astern. This allows the engine to reach its torque band faster and reduces overloading when going astern to stop the yacht or when using the engine to back off a sandbar.
To reduce overall size and weight, most saildrive gearboxes have dog clutches whereas shaftdrive boxes have cone clutches that allow for a more progressive take-up of ahead or astern gear and have a longer lifespan. Shaftdrive maintenance is also lower than saildrives because only the shaft and prop are exposed to seawater and the gearbox may be serviced from within the hull.
CHOICE DEPENDS ON APPLICATION
As most new fibreglass yachts come standard with saildrives your drive system choice is severely limited.
If you're fitting-out from scratch a fibreglass yacht with a separate keel and rudder for harbour racing, the ability to concentrate engine and drive system weight amidships makes a saildrive very attractive.
But if you're fitting-out a cruising yacht, especially a heavy displacement hull designed for passagemaking that won't be frequently slipped, then I'd recommend staying with a shaftdrive.
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Old 03-01-2008, 19:35   #5
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knowing your local environment will help alot. as this is a global board, are you in the US or another country? which one?
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Old 03-01-2008, 19:38   #6
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I live in USA for now.

Michigan along the Saint Clair river.
My ultimate goal and purpose for my boat would be circumnavigation.
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Old 03-01-2008, 19:43   #7
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I can't remember if it's the tin or copper based paint that is banned here.

In the class of boat your looking at 35-40ft it realy is of minor consequence which drive config is in place. Both have advantages, both have disadvantages.

Accept that there is no perfect boat and accept the comprimise. To get something sea kindly, you loose pointing, to get something that point, you'll loose tracking ability.

A shaft "can" be hard to align. but it's easier than stopping the leak from a torn boot. A new shaft and prop might cost 800, a new SD unit can go above 2000 quickly.
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Old 03-01-2008, 19:55   #8
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35-42 foot.

Quoting a very wise (and friendly) man:

Saildrives make it easy to manufacture yachts, but it leaves the owners with real problems. You have big problems with dissimilar metals in the saildrives and when water gets in the lower unit, you have strife. If you hit something with the saildrive you are in trouble. Then you also have that thick membrane plugging the hole in the hull where the sail drive sits.

I personally wouldn't take a boat offshore with sail drives. I would do coastal cruising, Bahamas - that sort of thing. But for a round the world trip, it's a prop shaft for me. A prop shaft is easy to maintain; I still have the origional shafts after fourteen years of ownership. I have changed the cutlass bearings three times - a fairly easy job.

If I'm going to be in remote atolls and distant patches of paradise, I don't want to have to deal with the problems that accompany saildrives.
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Old 03-01-2008, 19:59   #9
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your confusing me greatly...in one post you talk positively about SD's now you don't?

the simplest easiest drive to live with is none. Next to that would be a shaft.
What do you want? Are you looking for justification to buy a saildrive?
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Old 03-01-2008, 20:06   #10
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Sorry about your confusion.

Yes. I am looking for justification of a saildrive over a shaftdrive for long distance cruising.

I believe shaftdrive is better.

What boats would you suggest I look at which have shaftdrive?

Thank you.
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Old 03-01-2008, 20:13   #11
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For what it's worth our 91 Privilege 39 is shaft driven. I like the advantages, but it was in no way a go/no-go factor... We looked at boats with shaft, sail, and sonic drives but it was just never the determining factor.
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Old 03-01-2008, 20:25   #12
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Yes. The Privilege 39 has been at the top of my list, but it is my understanding that most P39's came with saildrives?
I am also concerned about headroom on the P39's saloon. I am 6'1 and would like to be able to stand erect. How much room do you have?

I read that the Privilege 37 had more headroom?
Are they simular quality boats?

Are there any other simular boats with shaftdrive?

Shaftdrive is not my only concern, but it is important to me.

Jeff
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Old 04-01-2008, 03:51   #13
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I'm an idiot..I never noticed this was the multi forum...

Personally I would avoid saildrives on a multi. I think they are more used to save cabin space for people.
To do any real service you need to haul the boat out. This can be expensive as well as a logistical nightmare with a 20+ft beam.
With shafts you can dive the boat and pull a shaft at anchor if necessary. Shaft do increase the possibility of catching a pot or wrapping the dingy painter. But I think the ability to service them is more important.
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Old 04-01-2008, 05:02   #14
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As already stated, there are pros and cons to both designs. One characteristic of sail drives not yet mentioned (unless I missed it) is that a saildrive setup more easily permits isolated engine rooms. A shaft drive setup on cruising boat sizes we're talking about almost certainly means the engine will be in the living spaces. This is a deal breaker for some people, not others. (In fairness, some cats have engines with saildrives located under aft bunks and are obviously not isolated.)

Many cats with sail drives have them well aft specifically so that the engine rooms can be separated from the rest of the boat by water tight bulkheads. A sea water system or diaphram failure that results in an flood cannot result in flooding the hull and would only flood a little above the design waterline.

Add in the benefit of not having engine room smells and having lower noise in the living spaces, and having perhaps better engine access makes isolated engine rooms attractive to many folks.

Dave
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Old 04-01-2008, 07:28   #15
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Hi Everyone, this is my first post. I'm a surveyor and have looked at a lot of cats with sail dirves, and since the question was raised, I offer some things that I have found.
Sail drives have some advantages - they are less drag than a straight prop and strut, the prop thrust is horizontal and not on an angle as with a shaft drive, they take up less space, and they are less labor to install than a shaft drive.
The disadvantages are - they require more maintenance and are more prone to problems. Let me explain - 1. The gearcase (leg) is aluminum and is always submerged - you must be vigilant in keeping the zinc in good condition to protect the aluminum. The zincs can be replaced by a diver but ut is easier to do out of the water. 2. The shaft seals and gear oil should be replaced/changed at every haul-out. It is very common to find salt water in the gear oil due to leaking shaft seals - I think many people forget about the seals. Unfortuantely, to do both both jobs the boat needs to be out of the water. 3. The hole in the bottom of the boat is large compared to a shaft opening. Although you have 2 rubber seals if they both fail (very rare), you do have a large amount of water entering. 4. They are expensive to repair or replace.
There may be other advantages and disadvantages, but these stick out in my mind.
If I were buying a boat and had a choice, I would opt for a straight shaft drive, because they are easier to take care of, which means more time for enjoying the boating (what it's all about).
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