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Old 02-15-2011
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Backing up a Morgan 32.5...

I have a good friend that recently purchased a Morgan 32.5, a beautiful, very roomy craft with a 12-foot beam. It draws just 4-feet, and sails like a dream. It's powered with a Yanmar 3GM30 24.1 HP engine and has a 3-blade prop. Not sure what the prop specs are. The boat motors along at about 5 knots going forward, however, backing up is a real problem. Achieving steerage while in reverse is nearly impossible without constantly taking the engine in and out of gear. The boat fails to overcome the prop walk.

The keel is very thick, and so is the rudder. Just wondering if a wider 2-blade prop would provide better steerage than the current 3-blade.

Any answers to this dilemma would be greatly appreciated.

Gary
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Old 02-15-2011
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Is it a fixed three-blade prop? If so, changing to a feathering prop may help more than switching to a two blade fixed prop.
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Old 02-15-2011
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Don't know but ibnterested in an answer. We have a boat also with a wide keel and rudder, we are useing a large 2 blade prop and also experience prop walk in reverse. He may have to do what we do and just be used to the fact that it will only back in one direction, and compensate for it.
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Old 02-15-2011
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What type of keel ? full, fin etc.
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Old 02-15-2011
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You're going to get prop walk. I suspect from your comment about going in and out of gear that you aren't getting the boat moving fast enough to get steerage. You need a lot of water flow over the rudder in reverse to be able to steer the boat.
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Old 02-15-2011
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Quote:
Originally Posted by SVAuspicious View Post
You're going to get prop walk. I suspect from your comment about going in and out of gear that you aren't getting the boat moving fast enough to get steerage. You need a lot of water flow over the rudder in reverse to be able to steer the boat.
I was thinking the same thing--insufficient water flow over the rudder. The prop is a fixed, 3-blade and there's very little clearance between the prop and the rudder, and the prop and the fin keel. In fact, the fit is so tight that I don't believe you could remove the prop without first removing the rudder--it's that tight. I'll be at the marina tomorrow and I'll try to see if I can read the information on his prop.

Gary
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Old 02-15-2011
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I have a similar boat and it definetely helps to get some speed before trying to steer w the rudder. I use a 3 blade and was told by the original owner that he replaced a two blade for that reason
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Old 02-15-2011
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As I understand it prop walk is due to the shaft being inclined ie sloping downward. I would think this is a proportion of the total thrust developed. So a folding prop will give less overall thrust in reverse but while this lessens prop walk only in proportion. A two blade prop is also likely to be less effective. The kiwi prop claims to reduce the problem but I think you will find there is not enough room to fit it.
Accelerating rapidly will give more prop walk as the prop accelerates faster than the boat with slippage so that suggests accelerating slowly.
Once the boat is moving at a couple of knots you will get some steerage. Whether that is enough to overcome prop walk is a matter of trial and error. It could be but may not. However taking it out of gear should give you some steerage. Against that in a practical sense is the effect of windage. If the bow is blowing off adding to prop walk you have little chance of her not going where she wants. I also suspect a dirty prop also doesn't help particularly in getting drive astern.
The issue primarily arises with docking.Coming out in a marina you only have a short distance to build up speed to get steerage and then stop. As long as I arrange to get clear of the dock I have given up worrying about whether I can turn or not, because as soon as I hit ahead I can start to turn with the wash on the rudder and then with greater responsiveness in ahead. Then when I slow the prop walk helps the turn.
If one was reversing in against the wind you get enough speed over a greater distance ie lengthwise to be able to go into neutral and steer that way if the prop walk is unfavourable. Again the wind helps or hinders.
I don't think prop walk is entirely bad. It actually can help making difficult ie sharp turns at low speed eg entering the berth bow first.
I think it just takes practice working out the likely effect of wind prop walk tide and going astern. Once you get used to the idea that steering in reverse and in gear at low speeds may not go as you wish you can live with it. That is you deal with what is happening and adapt. Frankly some prop walk can be useful and you can utilise more of it at times when the wind is working against you.
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Old 02-16-2011
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I was at the marina today, looked at the prop and it appears to be a 16 X 10, but not completely sure about the size because the lettering is obscured a bit by several layers of paint. There are no barnacles on the prop, and in fact it's very clean. However, its close proximity to the keel and rudder may hinder propulsion in both forward and reverse. Additionally, the rudder only swings about 30 degrees to port and about 35 degrees to starboard, which may have some bearing on steerage as well.

The trailing edge of the keel and the leading edge of the rudder are both essentially flat surfaces. I'm thinking this may be blocking much of the prop thrust in both directions. Also, the boat sails much faster than it motors, which seems to support this theory. Attached is a photo I took this afternoon of the prop and how it's situated.

Gary
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Old 02-16-2011
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thank you very much for your responses to my back up problem
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