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Old 12-03-2014, 15:36   #106
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Re: Saildrives?

Originally Posted by georgetheleo View Post
It may sound silly but Im afraid of and irrationally opposed to saildrives. Bascally all I really know of them is: the larger Yamaha ones develope slipping "cones" and need special tools and big bucks to repair.what if you are in timbucktooo? The smaller Yamahas dont have this problem but are limited to 30hp. The Volvo saildrives are much more reliable but the volvo engines are not and parts cost a fortune. Why cant saildrives be converted to straight shat drives if there is room? What about those Beta saildrives and engines? Comments please--- Thank You
I agree with you. I had a Belize cat with the Yanmar SD50 and had lots of trouble cost me shed loads of money to get them replaced. We are looking at an Isara 45 catamaran which has shaft drives and mid engine. A lot less hassle.
I would not buy a cat with sail drives again. .

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Old 12-03-2014, 16:39   #107
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Re: Saildrives?

Originally Posted by catsrule View Post
I would not buy a cat with sail drives again. .
Sort of like saying that you wouldn't buy another car because you had one with a bad engine. 99.9999% of all production boats have sail drives that work perfectly.

All those defective Yanmar SD 50 with bad cone clutches should have been recalled by Yanmar. It's clearly a scare on there reputation to sell defective sail drives and not recall and repair them. Shame on them.

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Old 12-03-2014, 16:41   #108
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Re: Saildrives?

Andrew, looks like you have given this a good study. I haven't looked through your numbers carefully, but assume they are correct.

I wondered about the CoE of oil, but never went to the trouble of finding it. My theory was just speculation, and whether it was fact or not would have no bearing on anything I might do about the saildrive. I was already developing the idea of the expansion tank to relieve pressure differentials from any cause.

But one thing I think your analysis of a simple shape might miss is that the housing is not a uniform shape. The key thing is that the area of the top surface of the oil is small, if the picture in my mind of the upper leg is correct, as compared to the rest of the oil "vessel". Sort of like (but not so extreme) the magnified rise and fall of the liquid in a glass thermometer.

Originally Posted by Andrew Troup View Post
This is my second attempt at this post.

When I pressed "Submit", the forum software evidently thought I was intending to surrender, and decided I wasn't logged on, and tossed my first submission out the air-lock into cyberspace.

(... even though I had just logged back in after the site came back after a maintenance period, and my name appeared at the top of the same page)


I did a quick calc to make sure my intuition here was not off-beam.

Conveniently, because the coeff for alu is double that for steel, and the latter similar to oil, I was able to do the calc for a steel sternleg containing a fluid with a zero coefficient. The answer should be about the same.

(Alu: 20 millionths linear expansion per deg C; Steel and Oil: 10 millionths)

The volume of a 100mm cubic (1 litre) steel container, for 1 deg C increase, would grow to about 1.00001^3 of the original size, or ~ 1.00003
Hence a volumetric increase of 1.00003 – 1 , or 0.00003 litres

so for a 30 degree C rise, the volumetric increase would be thirty times this, or 0.0009 litres, say 0.001 litres, or one-thousandth of a litre

Which would *roughly* be a level change of one tenth of a millimetre in the original container. (because 100mm level change corresponds to a whole litre)

in US customary units: a change in level of about four one-thousandths of an inch, for a temperature change of about 85 degrees F.
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Old 12-03-2014, 16:52   #109
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Re: Saildrives?

I wouldn't let saildrives stop me from buying a cat I really wanted, but I would much rather have straight shaft. Saildrives to me just don't make sense.

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Old 12-03-2014, 22:03   #110

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Re: Saildrives?

I'd rather a light cat that sails very well and use outboards.

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