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

Quote:

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

with the information provided, I guess it is impossible to diagnose the problem, as there are so many variables to be considered. It is also probably worth bearing in mind that some vessels are permanently endowed with "shopping trollley" handling characteristics, especially at low speeds. Anyone who has driven a "regal" craft with the so called "fastrac" hull will understand what I mean. The handling is inherently dreadful and is the result of the hull shape and not something that can be corrected. A bit like the one in the "Dellboy" series where Dell pretends to the lady dog-walker in the park that he is a "dog training expert" and has won Crufts awards, and when the lady then tells Dellboy that her little dog keeps "eating little holes in her carpet" and what should she do ?, Dell replies; "Oh thats easy to cure, Get a new carpet !!".

I have a Regal 2150 single engine, fastrac hull, alpha drive and know exactly what Robert means!. I suspect though that its got more to do with the single propellor on the Alpha drive. A counter-rotating propellor seems to help a lot on larger Regal craft. Its ok from 7 knots though.

John Geary
(Rose - E - Belle)



Edited 1 time(s). Last edit at 14/04/2012 21:55 by John Geary.

In reply to John Geary's comments, yes absolutely, the regal fastrac hull is fab at medium and high speeds, but at an idle it is terribly difficult to keep straight.

We've a program on our larger vessels putting nozzles around the prop. This dramatically improves directional stability, and also results in fuel savings. The improved flow from the propellor to the rudder surfaces is responsible for the improved directional stability, and the more directional flow of water, coupled with reduced rudder movement is responsible for fuel savings. This would doubtless scale very effectively - its used on a lot of small vessels, particularly towing vessels where high efficiency is required.
I 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

www.anglingcharts.com

Mucking about in boats.

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

CC,
Would you have a sketch of the nozzle configuration, I would be interested in trying anything that seemed reasonable.
Thanks,
Evan

Attached is a picture of Moon River a number of years ago. The prop is approx where the "R" for river is on the side and the rudder is approx under the "n" in Moon.
Evan

Evan .

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

Hi Evan,

simply google "Kort Nozzle". You'll soon get the picture.

good luck - happy meanderings

CC

www.anglingcharts.com

Mucking about in boats.

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.

OceanFroggie

Lengthening a vessel has the effect of improving directional stability, not reducing it. This is due to the increase in beam / length ratio.

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

www.anglingcharts.com

Mucking about in boats.



Edited 1 time(s). Last edit at 17/04/2012 08:51 by Capt Cautious.

Dear OF,

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.

www.anglingcharts.com

Mucking about in boats.

I think we are on the same hymn sheet, my lexdisic words perhaps not clear.

OceanFroggie

does the boat have a kneel?

Dave

Squat actually.

T

www.anglingcharts.com

Mucking about in boats.

Dave,
Yes, 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