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Old 21-10-2005, 05:52   #16

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I think I understand. Recalling my physics days from college and summing up previous comments, let me try and think this one through (forgive me it is Friday morning and I am just starting my coffee ) .

On beamy high displacement boats it takes more torque to effectively push them in the water. Because the torque required is more determined by type (2, 3, 4 blade) and size of prop (dia in inches) needs to be sized to the *boat* (weight and hull shape), not so much the engine. Then a determination of torque necessary to efficiently swing that propeller must be considered to size the engine. Then HP neccessary to efficiently drive it up to hull speed. (Shaft diameter determination is there in between too.)

This is why large displacement powerboats have deep pitched 4 blade (or more) props. Racing sailboats can get away with shallow pitched 2 blade props.

A WestSail 42, being more beamy and heavy then modern sailboats of the day, will probably require a larger more deeper pitched prop, therefore more torque, to effectively push it through the water.

Does that sound like a reasonable thought process?

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Old 21-10-2005, 10:44   #17
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Prop pitch and diameter is a function of the engine and transmission to attain maximum rpms at the high end of the throttle. For any particular setup there will one particular prop diameter and pitch given the number of blades you may desire.

Overly pitched causes damage, reduction of engine rpms, and at slow rpms it makes a terrible sounding setup as the engine can't really spin the prop well. (been there, done that, spent $600 for a new prop).

So the good news , bad news is. Change the engine you change the prop. There really isn't any choices in the prop dimensions.

I just replaced a prop that was close but not correct from the dreaded PO. I now motor faster and the engine sounds much smoother at all rpms. A good prop shop should be able to tell you easily what is the best one you need but you need to pick the transmission and engine first.

Spinning a propeller won't be efected by your beam and displacement. It's just water vs the propeller. It will spin the same no matter the boat. The speed you eventaully get is where all the rest of it comes to play. Your boat just needs a bit more than a boat of similar length.

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37 15.7 N 76 28.9 W
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Old 22-10-2005, 08:44   #18
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The other concern with a turbocharged engine is heat. The turbocharger works by using kinetic and thermal energy from the exhaust to compress air coming into the engine. Typically, you wrap the exhaust to maintain the heat. This is then routed to the turbocharger. The turbocharger gets VERY hot. The concern is you have to have sufficient space and airflow within the engine space to get rid of this heat. So, although the engine is smaller, some of the things you add to optimize the turbo may result in using more space in the engine compartment.

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Old 02-11-2005, 04:48   #19
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Time for my 2 cents worth. I agree with all the comments about turbo not being the best option for the normal sailboat applications. If we are all unable to convince you, then here are a few things (based on my experience) to watch for/do.
1. Back pressure caused by wet exhausts, especially ones that exit below the waterline can cause a lot more axial thrust than the turbo is designed to deal with. Make sure you have a back pressure test performed after installation and that it conforms with the manufacturer's specs.
2. Make sure that normal air flow in you engine compartment (with the engine not running) does not cause the turbo to turn. Not as likely with a wet exhaust and trap but still possible. This will lead to expensive failure.
3. Learn how to remove the compressor housing and clean the dirt from the turbine and housing, especially with a crankcase breather return into the air intake. Even what may just look like a stain can dramatically reduce the turbo performance. Do this at each oil change. A lot of people get scared of touching a turbo and this myth has been propagted by the servicing industry. As long as you don't go any further than the compressor housing and use a good solvent and soft brush you won't get into any problems.
If you fly me to wherever you are I can show you how

Wheels, where can I source one of those cartridge pressure pot thingies around Nelson/Marlborough. They sound just the ticket for a fleet of boats I used to be engineering manager for in Elaine Bay? Out of 17 engines in the fleet 14 were turbocharged and we were having to service them often.
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Old 02-11-2005, 10:39   #20
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Old 10-11-2005, 09:21   #21
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pressure oiling thingy

Alan, I would be interested in getting one of these things also. I recently aquired a boat with a virtually new (less than 100 hrs) Volvo 2003T. This is my first dealling with a turbo engine, but not my first experience with Volvo, so I hope to avoid any expensive parts replacments.

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