Difficulty;maneuverability underpower, 35' sailboat shoal keel - SailNet Community

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Old 06-27-2011
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Difficulty;maneuverability underpower, 35' sailboat shoal keel

I recently posted a thread on docking and that I was having a difficult time with our recently purchased Pearson 35' with a shoal draft. Since then, my wife and I are tyring to become certified in a few ASA sailing courses. The first course, we used our sailboat and even the instructor had a really hard time manuvering the sailboat underpower, especially in reverse as the boat had it's own agenda in reverse. The next course we used a Hunter 31 (newer model). Although I prefer a heavier sailboat, the boat moved on a dime underpower and we were able to back in a very tight space, manuver around, etc...

Question is: Why is the Pearson 35 so differcult underpower, especially in reverse? Is it the shoal draft that is not allowing the sailboat to perform turns in reverse?
Any other sailers with a 35' + sailboats with shoal draft that has similar issues?

Our instructor that weekend pointed out all the larger Cape Dorys that were docked bow in because that also had shoal draft and they would have the same problem going in reverse. That is what he said, not me.

Thanks in advance!
Patrick
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Old 06-27-2011
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Hello,

I have an O'day 35, shoal keel (4.5' draft) and fixed 3 blade prop. I would say that my boat is easy to maneuver under power. In reverse it has a good amount of prop walk, but once water is flowing past the rudder I can steer in either direction.

I use that to my advantage. I can spin the boat (clockwise only) in it's own length using 'back and fill' by alternating forward and reverse.

If I have to back up somewhere, the key is to have the boat aimed about 45 degrees from where I want to go, then the prop walk aims me in the right direction about the same time I have steerage.

What prop do you have? I race on a C&C 34 with deep keel and 2 blade folding prop. That boat is uncontrollable in reverse. The blades just don't seem to do anything. Motor too slowly and the blades don't open all the way. Rev too high and they cavitate.

Barry
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Old 06-27-2011
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I believe it is a 12-7 three blade prop. I just recently purchased this spring and did not make any notes on the size of the prop but looking at pictures, it seems to be a 3 blade prop.

I have a Yanmar 3GM30F engine. One problem that I need to fix is that the throttle cable is too short and only gets the engine upto 2,500 RPM - max. I believe the yanmar engines like to run close to 3,000 RPM. Perhaps getting it to the proper RPMs will help.
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Old 06-27-2011
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Quote:
Originally Posted by patrscoe View Post
I believe it is a 12-7 three blade prop. I just recently purchased this spring and did not make any notes on the size of the prop but looking at pictures, it seems to be a 3 blade prop.

I have a Yanmar 3GM30F engine. One problem that I need to fix is that the throttle cable is too short and only gets the engine upto 2,500 RPM - max. I believe the yanmar engines like to run close to 3,000 RPM. Perhaps getting it to the proper RPMs will help.
I have the same engine on my Catalina 320 with 3 blade fixed prop. I never reach 2,500 rpm in reverse. My guess is that if you apply more power (above 2,500 rpm) the boat is just going to walk to the side more. You got to get water moving past the rudder sufficient that it will overcome the walking forces. If you haven't done so, take the boat out in open water and play with it a bit. Find out how your boat wants to lie naturally. Mine likes beam to the wind. When you start to try to back, start here so that wind is not adding to propwalk to spin you around faster. You have to give it some power, but my guess is that 2,000 is more than enough. Let the boat do its walking. Keep the rudder centerlined and when you start to use it, use just a little rudder angle...too much acts as a brake towards reverse movement. You may be able to help it going in reverse, by periodically shifting to neutral so propwalk is interrupted, thus allowing you to covert some of the motion to reverse movement. Alternate in and out of gear to see if you can't build more motion in reverse. As you gradually build speed in reverse and increase water flow past the rudder, you should be able to gradually keep the engine in reverse gear longer. If you were to get the boat moving in reverse in open water, you could then just drive it in reverse down the fairway into your slip (looks funny and you might get some smart remarks, but which is more important, trying to handle the boat like others and having difficulty, or getting the boat into the slip efficiently). Some of the Pearsons have prop and shaft offset from center line. This might be a reason that you are having so much problem backing.

Last edited by NCC320; 06-27-2011 at 10:40 AM.
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Old 06-27-2011
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The shaft is centered with the rudder and shoal keel. It's frustrating because going in bow first makes it very difficult leaving the dock and also getting my children from the finger docks on to the sailboat. Also if I can figure out the reverse problem, I will be able to enter into the dock much slower and will be able to stop quicker as I put it in forward gear which has more power to stop while going in revervse.

I will try a couple of your ideas of shifting into reverse and then putting it back into neutral, and repeat until I get going. I always turn the opposite way of the prop walk, perhaps you are right and it is just reducing the flow of water over the rudder and really just preventing me from gaining the speed to overcome the prop walk. Will try to just keep the wheel somewhat centered and see if it will eventually overcome the walk.
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Old 06-27-2011
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I have the same Yanmar...on a 35 C&C MKIII with a 2 blade prop.

First thing I would say...it doesnt necessarliy like 3000 rpm thats a bit high and will use a great bit more deisel per anount of speed than necessary.
Our Yanmars sweet spot is 2500 to 2700, but of course everyone is different.

Secondly every boat has its own characteristics in reverse,, some have full keels, skeg rudders speade rudder etc. It takes a while to learn yours. You Pearson should not be too bad...the meain thing is to start with a burst to get the water moving across the rudder so you get steerage. From there your will have to figure our how your boat handles. Take it near a mooring ball and practice.

dave
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Old 06-27-2011
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Thanks Dave.
In reference to the 3000 RPMs, our sailing instructor for the certified course stated that the Yanmars like to run at 3000 and also the marina where the sailboat was originally purchased, so I was assuming they knew more then I did. It can run upto 2500 RPM and the throttle handle will not go any farther. 2500 to 2700 RPM does make sense, it seems to sound good at 2500. And it has a few hours on it.... so perhaps not running it too hard would be best.
My Pearson is a heavy 35 footer with a displacement of 13,000 + lbs. I am realizing very fast that it takes a little bit to stop.
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Old 06-27-2011
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Quote:
Originally Posted by patrscoe View Post
I believe it is a 12-7 three blade prop. I just recently purchased this spring and did not make any notes on the size of the prop but looking at pictures, it seems to be a 3 blade prop.

I have a Yanmar 3GM30F engine. One problem that I need to fix is that the throttle cable is too short and only gets the engine upto 2,500 RPM - max. I believe the yanmar engines like to run close to 3,000 RPM. Perhaps getting it to the proper RPMs will help.
How did you determine your cable was too short? Diesels will not obtain their rated RPM when an incorrectly sized propeller is installed.
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Old 06-27-2011
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I don't think your problem has anything to do with the shoal draft. Make sure your prop is clean first. If you still can't rev-up, you may be over propped. You may need to get the pitch of your prop reduced a little. That may also be the reason for too much prop walk.
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Old 06-27-2011
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I was told by the marina (location where I purchased the sailboat this spring) that the cable needed to be adjusted or replaced, and that it should run at a higher RPM.
Not sure what prop is on the boat, from pictures I taken this spring, it looks like a 12-7, not sure though. Would have to dive down and take a quick measurement but will unable to obtain the pitch.
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