Giddy Boat, hard to steer a straight line We bought Moon River late last year, did some work to her over the months and brought her from Lowtown to Shannon Harbour over the last few days. My problem is that in low revs she has a mind of her own and will go anywhere other than where she is intended to go. At decent revs she is fine and steady. Her rudder is approx 3 feet from her stern. Has anyone else had similar problems and if so how did you get over them? Evanhttp://www.iwai.ie/forum/read.php?1,42689,42689#msg-42689Sun, 19 May 2013 13:56:02 +0100 Phorum 5.2.6a http://www.iwai.ie/forum/read.php?1,42689,42864#msg-42864 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42864#msg-42864Yes, and it also has an RSJ welded to the keel from about 4 ft from the bow to the rudder but no further.The boat is really comfortable and we are very pleased with her otherwise but the steering is a definite problem that I will have to sort out. She is also quite giddy when you step onto her, but I think I can resolve that with some strategic ballast,
Thanks for your interest.
Evan]]> Evan O'Keeffe IWAI Waterways Discussion ForumThu, 19 Apr 2012 21:34:53 +0100 http://www.iwai.ie/forum/read.php?1,42689,42792#msg-42792 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42792#msg-42792
T]]> Capt Cautious IWAI Waterways Discussion ForumTue, 17 Apr 2012 13:18:18 +0100 http://www.iwai.ie/forum/read.php?1,42689,42788#msg-42788 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42788#msg-42788
Dave]]> Dave McCabe IWAI Waterways Discussion ForumTue, 17 Apr 2012 13:06:56 +0100 http://www.iwai.ie/forum/read.php?1,42689,42784#msg-42784 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42784#msg-42784 OceanFroggie IWAI Waterways Discussion ForumTue, 17 Apr 2012 09:38:57 +0100 http://www.iwai.ie/forum/read.php?1,42689,42782#msg-42782 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42782#msg-42782
not quite sure what you are getting at here. The static pivot point will not move forward. It will be approximately midships when the vessel is stopped (somewhere near the geometric centre of the waterplane area), moving forward as the vessel gains headway. It will move astern of its static position with sternway. Hope that clarifies it. This is why a vessel becomes more directionally stable as it gains headway, the pivot point moves forward , and less rudder is required to maintain course as the turning moment is greater. With slow speeds the force created by the rudder to overcome the turning moments created by the water pressure ahead of the vessel is generally not enough (particularly on vessels with a large block coefficient (brick shaped)), and requires either more rudder, or more flow past it. The rudder, if of inadequate design, will stall and become ineffective as angle increases, and the vessel will wander off course. A kick ahead, or sometimes a reduction of rudder angle can alleviate this.

CC

Quote:
OceanFroggie
Quote:
Evan O'Keeffe
Noel,
Thanks for getting back to me.The rudder is about 9 inches from the prop. But one of the main problems I feel is that the prop is about 3.5 ft from the stern.It would be very difficult to extend the shaft and the rudder.The rudder is approx 18 inches square.
Evan

Hi Evan. Prop/Rudder relationship sounds fine. If the hull was lengthened as suggested by John then the pivoting moment has moved forward alright (ie rudder thrust offset moved closed to center of vessels pivot point). At low speed you might need short bursts of higher throttle to swing the stern to the left or right. Trevor's idea of a nozzle tube surrounding the prop sounds interesting. It would certainly eliminate prop walk, instead transferring the wasted energy into forward thrust. I assume there is no keel after/behind the rudder as that would destroy low speed steering.
]]> Capt Cautious IWAI Waterways Discussion ForumTue, 17 Apr 2012 09:31:08 +0100 http://www.iwai.ie/forum/read.php?1,42689,42779#msg-42779 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42779#msg-42779
A more directional flow into and out of the propellor - possibly combined with a high lift rudder (schilling type design - easily home buit) instead of a flat plate rudder if things are REALLY bad will alleviate things.

These rudders are ideal for the likes of barges, and they are to be found all over the inland waterways of europe. I have used them extensively on larger vessels. Almost as good as a side thruster.

CC]]> Capt Cautious IWAI Waterways Discussion ForumTue, 17 Apr 2012 08:50:11 +0100 http://www.iwai.ie/forum/read.php?1,42689,42777#msg-42777 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42777#msg-42777Quote:
Evan O'Keeffe
Noel,
Thanks for getting back to me.The rudder is about 9 inches from the prop. But one of the main problems I feel is that the prop is about 3.5 ft from the stern.It would be very difficult to extend the shaft and the rudder.The rudder is approx 18 inches square.
Evan

Hi Evan. Prop/Rudder relationship sounds fine. If the hull was lengthened as suggested by John then the pivoting moment has moved forward alright (ie rudder thrust offset moved closed to center of vessels pivot point). At low speed you might need short bursts of higher throttle to swing the stern to the left or right. Trevor's idea of a nozzle tube surrounding the prop sounds interesting. It would certainly eliminate prop walk, instead transferring the wasted energy into forward thrust. I assume there is no keel after/behind the rudder as that would destroy low speed steering.]]> OceanFroggie IWAI Waterways Discussion ForumTue, 17 Apr 2012 07:09:28 +0100 http://www.iwai.ie/forum/read.php?1,42689,42769#msg-42769 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42769#msg-42769
simply google "Kort Nozzle". You'll soon get the picture.

good luck - happy meanderings

CC]]> Capt Cautious IWAI Waterways Discussion ForumMon, 16 Apr 2012 23:01:54 +0100 http://www.iwai.ie/forum/read.php?1,42689,42768#msg-42768 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42768#msg-42768
If memory serves me right Moon Rivers aft sun deck was extended and converted to an aft cabin and a length of steel added to the keel .

John]]> j doyle IWAI Waterways Discussion ForumMon, 16 Apr 2012 23:01:11 +0100 http://www.iwai.ie/forum/read.php?1,42689,42767#msg-42767 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42767#msg-42767Evan
[attachment 3330 MoonRiverNearInistiogue-CliffJeffers.jpg]]]> Evan O'Keeffe IWAI Waterways Discussion ForumMon, 16 Apr 2012 22:03:45 +0100 http://www.iwai.ie/forum/read.php?1,42689,42763#msg-42763 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42763#msg-42763Would you have a sketch of the nozzle configuration, I would be interested in trying anything that seemed reasonable.
Thanks,
Evan]]> Evan O'Keeffe IWAI Waterways Discussion ForumMon, 16 Apr 2012 21:47:09 +0100 http://www.iwai.ie/forum/read.php?1,42689,42762#msg-42762 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42762#msg-42762Thanks for getting back to me.The rudder is about 9 inches from the prop. But one of the main problems I feel is that the prop is about 3.5 ft from the stern.It would be very difficult to extend the shaft and the rudder.The rudder is approx 18 inches square.
Evan]]> Evan O'Keeffe IWAI Waterways Discussion ForumMon, 16 Apr 2012 21:43:30 +0100 http://www.iwai.ie/forum/read.php?1,42689,42708#msg-42708 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42708#msg-42708I use a nozzle on my survey boat - you'll lose transverse thrust, but the prop is protected from impact with shopping trolleys etc. It is a little more prone to weed entanglement.

CC]]> Capt Cautious IWAI Waterways Discussion ForumSun, 15 Apr 2012 22:56:41 +0100 http://www.iwai.ie/forum/read.php?1,42689,42697#msg-42697 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42697#msg-42697 ROBERT McCLEAN IWAI Waterways Discussion ForumSat, 14 Apr 2012 22:15:15 +0100 http://www.iwai.ie/forum/read.php?1,42689,42695#msg-42695 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42695#msg-42695 John Geary IWAI Waterways Discussion ForumSat, 14 Apr 2012 21:52:08 +0100 http://www.iwai.ie/forum/read.php?1,42689,42693#msg-42693 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42693#msg-42693 ROBERT McCLEAN IWAI Waterways Discussion ForumSat, 14 Apr 2012 21:11:10 +0100 http://www.iwai.ie/forum/read.php?1,42689,42690#msg-42690 Re: Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42690#msg-42690Quote:
Evan O'Keeffe
We bought Moon River late last year, did some work to her over the months and brought her from Lowtown to Shannon Harbour over the last few days.
My problem is that in low revs she has a mind of her own and will go anywhere other than where she is intended to go.
At decent revs she is fine and steady.
Her rudder is approx 3 feet from her stern.
Has anyone else had similar problems and if so how did you get over them?
Evan

Hi Evan. Few questions to help diagnose. Assume the boat is single engine shaft drive with a keel?
How far is the rudder located behind the prop? It should be almost immediately behind the prop.
What size is your rudder?
Is your steering by cable or hydraulic line?
Noel]]> OceanFroggie IWAI Waterways Discussion ForumSat, 14 Apr 2012 15:27:14 +0100 http://www.iwai.ie/forum/read.php?1,42689,42689#msg-42689 Giddy Boat, hard to steer a straight linehttp://www.iwai.ie/forum/read.php?1,42689,42689#msg-42689My problem is that in low revs she has a mind of her own and will go anywhere other than where she is intended to go.
At decent revs she is fine and steady.
Her rudder is approx 3 feet from her stern.
Has anyone else had similar problems and if so how did you get over them?
Evan]]> Evan O'Keeffe IWAI Waterways Discussion ForumSat, 14 Apr 2012 14:30:52 +0100