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Go Back   SailNet Community > On Board > Gear & Maintenance > 3 blade prop question.
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Thread: 3 blade prop question. Reply to Thread
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Topic Review (Newest First)
11-30-2008 10:37 PM
BarryL
Prop Location and Prop Walk

Hello,

My O'day 35 had a 3 blade fixed prop, and the prop is located most of the way aft. My boat has a lot of prop walk, so I don't think the prop location will have any bearing on the amount of prop walk there is.

When I first put my boat in reverse, it will turn about 45 degrees before I gain enough speed to have steerage. Since I know this and anticipate it, it's not really a problem.

I try to take advantage of the prop walk when I approach the dock. I like to come to the dock with the dock on my port side. I aim at the dock at a 45 degree angle. When the bow is close to the dock (and I am moving at 1 kt or less) I put it in reverse and rev up the engine for a few seconds. That stops the forward motion and pulls the stern right up to the dock.

Good luck,
Barry
11-30-2008 10:01 PM
SteveInMD Some boats are better than others in reverse. If I can't get it to go where I want in reverse, I fall back on the method of using short bursts of forward thrust to (which put good flow across the rudder) get the point pointed in the right direction, then back up and hope for the best. Use as many short bursts of forward as needed to realign and then hit reverse again. The boat doesn't have to actually move forward, but just get forward flow past the rudder from the prop wash.
11-30-2008 04:12 PM
JiffyLube Our boat is not easy to steer in reverse either, especially if the wind has picked up. I only really need reverse when getting out of our slip, and I've learned with practice how to get out pretty good.

I put the transmission in reverse, give the engine a lot of power just long enough to get the boat to back up. Then I immediately take the power off, and put the transmission in neutral. Once the prop stops turning in reverse the rudder begins to take over, because it has enough water flowing over it without the effects of prop walk from the prop.

I start out of the slip with the rudder turned in the direction I want to go in, and as soon as the water flows over the rudder I begin turning.

If I back out and keep the transmission in reverse after I stop the power, the prop is still turning interfering with the water flow over the rudder, and inhibiting the boat from pivoting on its axis...at least that's my experience.

I envy those that can back into their slips back wards, but I'd be afraid to try that maneuver with out boat.
11-30-2008 02:22 PM
baboon Thanks for the input. Looks like I will probably stick with the prop I have for now. I understand that no sailboat will back with any control until you have some movement in reverse. Mine might be a bit worse than average given the midship location of my prop. My pet theory is that a boat with a prop near the stern will be "pulled' along in reverse, making it a little more likely to back strait. With a midship prop against the keel my boat seems prone to pivit on its prop/keel in whatever direction it is pushed by the wind or current. The current set up is fine for quick acceleration and stopping.
11-30-2008 01:42 PM
SEMIJim Um, correct me if I'm wrong, but ISTM no sailboat maneuvers worth a damn in reverse until she gets some way on--other than perhaps smaller boats, with outboard engines, where the prop itself can be turned.

Jim
11-30-2008 08:10 AM
sailingdog I don't think a folding prop would help much, as folding props generally aren't much better than fixed props in reverse, and many are worse. What you probably want is a feathering prop, which usually increases efficiency of the boat in reverse, as the blades feather to re-orient themselves in reverse. A good one that is fairly reasonably priced is the Kiwi Prop.

Also, please do remember that until the boat is actually making way in reverse, you're not going to have any steering.
Quote:
Originally Posted by baboon View Post
The facts (let's keep SD happy)
Early 70's Tartan 30 with 3 cyl 18 hp diesel. Fin keel, skeg hung rudder, properly sized and pitched 2 blade prop in place. The engine on this boat sits on the keel, the shaft exits aft the keel and the prop is RIGHT there. No strut, no exposed shaft, just prop with the zinc aft of the prop. Forward is fine, sailing is good as the shaft is marked in the bilge and the prop can therefore be aligned with the keel verticaly.

The problem. Reverse is a mess. The boat will go where it wants, period. In an adverse wind or current the boat is almost uncontrollable. You can push the tiller any way you want, until you get a good speed up it does not matter.

The question. Would a good folding 3 blade prop help. The issue is NOT speed or efficeincy, it is control in reverse at low speed.

Thanks.
11-29-2008 09:16 PM
brak My boat does not steer in reverse at all. She does have a full keel, which explains a lot - but the prop is a properly sized 3 blade. I can certainly gain a lot of speed in reverse fairly quickly, but steering just does not happen. So, there is no guarantee that a 3 blade prop will help you steer - this may simply be an issue with your boat's underwater configuration.
11-29-2008 08:43 PM
Rockter My own ship takes a while to gain steerage going astern. If there is an meaningful wind, it really is difficult, particularly when reversing into a pontoon finger arrangement. I am happy to have moved to a longer dock for that reason.

In reverse, you can normally tell when you are gaining directional control as the rudder begins feeling "heavy", in my case through the wheel.

If the rudder is feeling "easy", it ain't steering.

If the ship you have is moving forward ok with the prop you have, I would be inclined to leave it as is.

Changing props doesn't always improve things.
11-29-2008 07:03 PM
btrayfors A 3-blade Maxprop will almost certainly help you in reverse. Mine does. I've had it for 18 years and tens of thousands of miles of sailing. Made a very BIG difference when I replaced the fixed prop. The blades set themselves to pull as well in reverse as in forward. It did NOT significantly increase drag in forward (no change in boat speed vs. a 2-blade fixed prop; maybe even a bit of a gain).

It did not help in forward; same thrust as fixed prop. But in reverse, it made all the difference. You have to learn to work with the prop walk, but the ability to put on some speed (or brakes) in reverse quickly makes a big difference in boat handling.

Bill
11-29-2008 06:12 PM
sailingfool A three blade prop should have no effect on your backing, only on your pocketbook. If you bought a prop like a two blade MaxProp, you might get some improvement just from the better drive in reverse, allowing you to steer sooner.
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