Shaft Vs Saildrive

aluijten

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As far as I know there are a few advantages to a saildrive:
Because the whole system is one rigid 'mass' you only need the three suspension point to take the load from the engine and the driving forces. This leads to less vibration, making the motorring more comfortable. There is not alignment issue between the drive shaft and the engine.

Drawbacks are:
Expensive rubber manchet to seal off the hole through the hull. If the rubber manchet fails you will have very wet feet, in other words the failing behaviour of a saildrive is poor compared to a drive shaft seal/bearing. Other problems are corrosion of the sail-drive leg and leaking sealings at the propshaft bearing enableing water in the transmission fluid/oil.

Arno
 

Gunfleet

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I think the main advantage in saildrives is to the builder. Properly maintained I don't see any probs with either. Don't maintain either type and you can expect trouble. Possibly if you were going on the type of blue water sailing where you have to repair things with a plastic bag, some bits of wood and some epoxy plus an old baked bean tin hammered out flat by a native, saildrives are not for you.
 

snowleopard

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the biggest reason for choosing a saildrive is that it is cheap to install. you simply cur a hole for the leg, fibreglass the mounting plinth into the hull, drop in the engine and it's done. no fiddling around fitting the shaft or aligning the engine.

once it's in, a saildrive doesn't leak and needs no adjustment of the stern gland, there are no cutless bearings to wear out and the installation is quieter because the engine can be mounted on soft rubber blocks.

the downsides include the fact that the prop is generally further from the rudder so making response to the helm slower. it is necessary to lift out to do some maintenance work e.g. gearbox oil change.

generally shaft drive props are right-handed and saildrive left handed.

the risk of getting water through the rubber diaphragm is a non-issue.

next question?
 

aluijten

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snowleopard,

If the the risk of getting water through the rubber diaphragm is a non-issue, then why is the damn thing so expensive to replace and do many insures require regular replacement?

Just a question on my mind...

A.
 

tom52

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The expense is labour and the usual exhorbitant cost of boat parts.
As for insurers, its the same reasoning that insists on renewing standing rigging after 10 years irrespective of condition/use.
Its your expense not theirs, it slightly reduces the risk of a claim and provides potential 'wriggle room' for the insurer if you do not comply
 

BlueChip

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I have had both shaft and saildrive on boats I have owned.
A sail drive is quieter, the Yanmar water seal has a double seal with water sensor between.
With sail drive there are no alignment problems. I never found lack of prop walk an issue - in fact I get significant prop walk with my sail drive with a 3 bladed folding prop
One benefit with sail drive and a fin keeler is that because the drive is much closed to the keel there is less chance of getting rope round the prop
Another benefit is that without a prop shaft you win a lot of locker space behind the engine
You pay your money and take your choice
 

Koeketiene

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Agree with all the points you make.

Prefer a saildrive any time. Seems to be a lot of snobbery about. Some people will just not accept a saildrive. The same way they claim that to go to sea in anything else than a 14ton longkeeled juggernaut is unsafe and asking for trouble.
 
G

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Aluijten,

I have a boat with a Nanni 14hp saildrive, installed by the previous owner.

Due to this being fitted with an incompatible single lever control (Ultraflex which opened the throttle before engaging the gear) which caused damage to the gear engagement dog and the gear change linkage, had to remove the engine and repair the saildrive.

The saildrive was ready to refit by the time I visited LBS.

A tour of all the manufacturers of saildrives revealed that the "routine change of sealing diphragm every seven years" is a hangover from a Volvo suggestion of 'five years', later increased to seven, when there was no long term experience.

They all now say "indefinate but long life" and 'never had one fail' or 'only one failure due to accidental damage when working on boat'

We should, therefore, strongly resist pressure from insurance companies for routine renewal.

The cost of renewal is high:-

Diaphragm c. £200
Days work to remove engine?
Another day to refit.

All to support Volvo's (understandable) initial caution.
 
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