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Old 18-09-2013, 16:48   #1
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Maneuverability at slow speeds

Does a boat with a wide shoal draft keel have better maneuverability at slow in-harbour speeds than a deep, narrow keel?
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Old 18-09-2013, 16:53   #2
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Re: Maneuverability at slow speeds

A narrow keel is more maneuverable. In most instances, it's irrelevant because full-keel boats are maneuverable.
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Old 18-09-2013, 16:56   #3
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Re: Maneuverability at slow speeds

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Originally Posted by Srah 1953 View Post
Does a boat with a wide shoal draft keel have better maneuverability at slow in-harbour speeds than a deep, narrow keel?
Thanks

The narrow keel is more maneuverable and more resistant to prop wash as well. I have "parallel-parked" my boat with only one foot of water to work in. She turns on her central axis. I could do turns with this boat tight enough to throw people off (don't think I haven't been tempted, either! )
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Old 18-09-2013, 17:09   #4
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Re: Maneuverability at slow speeds

Boats turn near their centers. It's a question of how quickly/responsively they do it.
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Old 19-09-2013, 04:08   #5
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Re: Maneuverability at slow speeds

Hi all.
Thanks for these. I was thinking that a narrow chord needs water flowing over it and that in crosswinds that a boat with a narrow keel would be more likely to be blown off course.
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Old 19-09-2013, 04:50   #6
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Re: Maneuverability at slow speeds

Some might interpret the terms "narrow & wide" as the athwartship thickness of the keel, so the trait could be identified as a long keel or fin keel as well to avoid confusion. Certainly, the fin keel boat will pivot at a point near the position of the keel when turning far quicker and easier than the full keel boat and the fin keel boat can be operated in reverse with much easier control. The full keel boat can also be maneuvered well, but with different techniques. Turns are better made with the full keeled boat by using short duration bursts from the engine to turn at low speeds, using prop wash and prop walk. These terms, "prop wash & walk" also seem to be often confused. The prop wash is the flow of water from the propeller that moves across the surface of the rudder when in foward or propelled across the keel when the engine is in reverse. The prop walk is the tendency for the spinning "right hand" propeller to move the stern to starboard in forward and to port in reverse. The prop walk in forward is easily overcome by the prop wash over the angle-adjusted rudder, but the keel, at a fixed position, can not compensate for prop walk when in reverse. A common strategy for long keel boats, with less manneuverability in reverse, is to use the prop walk as a tool to allow turn in a narrow space. This is often accomplished by choosing to turn the long keel boat to starboard, even if this is the long way around to reach your goal, by keeping the helm hard to starboard with short basts of engine power alternating in forward and reverse (This would be all opposite with a boat having the less common "left-handed" prop). In addition, all this needs to be moderated by how your individual vessel responds to what wind and current may be present.
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Old 19-09-2013, 05:26   #7
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Re: Maneuverability at slow speeds

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Originally Posted by Srah 1953 View Post
Does a boat with a wide shoal draft keel have better maneuverability at slow in-harbour speeds than a deep, narrow keel?
Thanks
Since you have a Jeanneau Sun Odyssey 409, I'm guessing that you mean a true "shoal" keel, as european boat designers make them. Which means your keel is probably something like 1.60 meters and not the normal 1.95 or 2.10 meters.

So you are not talking about a long keel boat. Yours also probably has a 400 kg "torpedo bulb" on the bottom.

A couple of years ago I had a Bavaria 33 with a "normal" keel and a friend had one with a "shoal" keel. Just for fun we tested them against each other. My normal keel sailed a couple degrees closer to the wind and we think (couldn't prove it) that it maneuvered better in the harbor. Certainly we both felt there was a bit less side-slipping in strong winds with the normal keel.

I would suggest that if the skipper knows what he (she) is doing when docking, it is a moot point.
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Old 19-09-2013, 07:26   #8
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Re: Maneuverability at slow speeds

i sail a barge with a deep fulll wide keel and when i need to be maneuverable i goose throttle appropriately to move her as i wish. is surprising how tight these can turn..surprised even me.
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Old 19-09-2013, 07:32   #9
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Re: Maneuverability at slow speeds

Consider the affect of current and wind. It takes a tremendous amount of wind to push a full keel boat laterally through the water, so cross winds are fairly irrelevant. Current, however, has a huge impact.
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Old 19-09-2013, 10:03   #10
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Re: Maneuverability at slow speeds

A keel that is deep but short (fore and aft) will be more manuverable since there is less resistance to turning...until it hits bottom, then the shallow but long keel will be more manuverable.

The ultimate option is a retractable keel but that comes with maintenance complications.

The choice is about where you boat. Last fall the water levels were down in the fall on the Great Lakes. When the deep draft boats when in and out, they had to reverse and go forward several times to get out of thier slips and into deep water. We simply pulled up the boards and went about our buisness.
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Old 19-09-2013, 10:41   #11
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Re: Maneuverability at slow speeds

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Originally Posted by Srah 1953 View Post
Hi all.
Thanks for these. I was thinking that a narrow chord needs water flowing over it and that in crosswinds that a boat with a narrow keel would be more likely to be blown off course.

Depends on the boat and how strong the crosswinds are, but my boat, with its relatively high freeboard combined with a very "finny" keel is more likely to be blown off course at slow speeds. Lots of fun in a crowded marina unless you know how to make it work for you.

What I do is capitalize on the boat's tendencies at that time. Sometimes that means turning 180ļ, but if I work with the boat instead of fighting it, I can maneuver this boat very well in tight spaces. Where this boat gets into trouble is when you ignore where it wants to go and try to fight it. At low speed in little room to maneuver, that just won't work well with this boat.

By using this boat's innate tendencies I once sailed her into a slip -- with no sails up. I had no steering, but I did have power, so I goosed her in forward, the wind on the freeboard turned the bow, and of course the rest of the boat followed. Once I was solidly in the slip I used reverse to slow her down and avoided a real "bumper cars" situation in the marina. The fellow whose slip it was was out on an extended cruise and had no problem letting me use his slip for couple of days.

Turned out that when my boat guy had put my new rudder in, he forgot to cross the steering cables. The result was that she steered like a tiller boat. All I knew was that the boat wasn't steering right, so I stopped steering and let the wind do it. The wind was from the north and the slip went east and west, so it was a perfect time to use the wind.

While boats with full keels have some definite advantages, I bet mine is easier to back up.
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Old 19-09-2013, 11:35   #12
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Re: Maneuverability at slow speeds

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Consider the affect of current and wind. It takes a tremendous amount of wind to push a full keel boat laterally through the water, so cross winds are fairly irrelevant. Current, however, has a huge impact.
Thank you all.
I don't agree with the above comment insofar as my shoal draft (1.6m as suggested) (not full keel) boat is concerned. I know that if I let the boat stop just for a second while manoeuvring (which sometimes can happen between forward and reverse), the wind will take it and it can be hard to get it back before you hit something. I'm told that this is common for big beamy boats with wide top sides.
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Old 19-09-2013, 11:55   #13
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Re: Maneuverability at slow speeds

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Originally Posted by Srah 1953 View Post
Thank you all.
I don't agree with the above comment insofar as my shoal draft (1.6m as suggested) (not full keel) boat is concerned. I know that if I let the boat stop just for a second while manoeuvring (which sometimes can happen between forward and reverse), the wind will take it and it can be hard to get it back before you hit something. I'm told that this is common for big beamy boats with wide top sides.

Yes, it is, so make working with the wind (and current) part of your plan.
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Old 19-09-2013, 18:30   #14
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Re: Maneuverability at slow speeds

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Originally Posted by Srah 1953 View Post
Thank you all.
I don't agree with the above comment insofar as my shoal draft (1.6m as suggested) (not full keel) boat is concerned. I know that if I let the boat stop just for a second while manoeuvring (which sometimes can happen between forward and reverse), the wind will take it and it can be hard to get it back before you hit something. I'm told that this is common for big beamy boats with wide top sides.
Very well could be. I'm at 2m, with a cut-away foot but otherwise a full keel. I've skippered catamarans where we would literally line up parallel to an end tie in a cross wind and just maintain attitude while getting blown laterally onto the dock. With my boat the current will have a much more pronounced impact.

Another note regarding boats turning at their centers, if I remember my schooling right they turn (on average) 2/3 of the way forward when going forward and 1/3 forward when going in reverse. So the pivot point shifts forward when going forward, and shifts aft when going aft.

Again, that was just in school, but it seems to play out with how the monohulls I've experienced behave.
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