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Old 30-10-2014, 10:59   #46
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Re: New boat pulls to starboard under power, prop?

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Originally Posted by Lodesman View Post
It might be the perspective of the photo, but it looks like the prop is on backwards.
I was a bitch getting that stupid taper to go on. Using a bigger hammer worked.
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Old 30-10-2014, 11:07   #47
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Re: New boat pulls to starboard under power, prop?

I don't think it's prop walk either, but the prop wash over the rudder, causing the rudder to deflect, which is what I believe the owner thinks too. It's the rudder that is being pulled, not the boats stern moving to the side. This is easy to compensate for with a trim tab, problem is without it being an adjustable tab you would have to split the difference, it would pull half as hard, but under sail it would pull the same amount the other way.
Thrust alignment is another way to compensate for it, and it what is used in a lot of single engine airplanes, but as the boat is built, changing thrust alignment would be tough
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Old 30-10-2014, 11:11   #48
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Re: New boat pulls to starboard under power, prop?

My Island Packet has an almost overbalanced spade rudder, it pulls to port a little under power, manual says it's normal and recommends when extended motoring like on the ICW to friction down the rudder to prevent this pull. It's nothing that objectionable, just if you turn loose of the wheel under power, she will turn to port, every time.
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Old 30-10-2014, 12:52   #49
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Re: New boat pulls to starboard under power, prop?

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Originally Posted by SVTatia View Post
I hope you are being facetious.... I defy anyone to install a prop backwards.
Not at all. It's a truism that if it can be installed incorrectly, someone has done it to some boat somewhere, and it was usually a previous owner that did it.

Most props I've seen sweep backwards. Look at the photo - as I said it might just be a tricky perspective, but it looks like the forward and trailing edges both sweep forward.
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Old 30-10-2014, 13:52   #50
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Re: New boat pulls to starboard under power, prop?

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Originally Posted by Lodesman View Post
Not at all. It's a truism that if it can be installed incorrectly, someone has done it to some boat somewhere, and it was usually a previous owner that did it.

Most props I've seen sweep backwards. Look at the photo - as I said it might just be a tricky perspective, but it looks like the forward and trailing edges both sweep forward.
I'm looking for a magician. Were can I find that guy that put a prop on backwards?
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Old 30-10-2014, 14:10   #51
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Re: New boat pulls to starboard under power, prop?

Either that is a left hand turning prop, or somehow the picture is reversed, like when you put a slide in the projector backwards.
even if you found a way to put a prop on backwards, it would still pull, just the leading and trailing edges swap places and it loses efficiency.
Putting the prop on backwards was an old model airplane trick to slow down an airplane to give you a chance to learn it.
Didn't any of you guys fly a Cox PT-19 as a kid ?
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Old 30-10-2014, 19:49   #52
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Re: New boat pulls to starboard under power, prop?

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Originally Posted by Lodesman View Post
Not at all. It's a truism that if it can be installed incorrectly, someone has done it to some boat somewhere, and it was usually a previous owner that did it....
What I meant to say was that unless the "installer" changes the taper, it would be physically impossible to fit the shaft into the prop.
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Old 31-10-2014, 03:02   #53
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Re: New boat pulls to starboard under power, prop?

I finally used some common sense yesterday and powered the boat up tied to the pontoon.

At around 1/4 power I could feel a slight kick on the wheel to port, then as I added power wheel became more twitchy and then 1/2 to 3/4 then to full gradually pulled wheel over to starboard.

So its the prop wash on the rudder for sure and not the stern of the boat being dragged to port.....

I wish it was the the prop as thats easy and relatively cheap to fix. I talked to a David at Axiom Propellers and he came back with a different shape prop with 24" and 20 degree angle (???) but I really think I have to look at angle of prop and somehow model the wash on a fluid dynamics software of some sort to see how its hitting the rudder.

I kind of think that a skeg hung would not have this problem in that the wash hits an immoveable object, splits in half then washes over prop......

Also thinking that building a skeg rudder on this, a steel, boat would not be out of the question or even that expensive (relative to how I value the boat going straight....under power.)

Yesterday spent the day wading through other issues and made huge gains in understanding the water ballast and pumping systems, yes it has these too, its a very complex boat for a cruiser.....of course, had bought a new Jabsco Par 2.9 in advance thinking it was the same as the Par 3 was replacing, wasn't .....then managed to replace microswitch on broken pump and have now a new spare that I am installing in a bilge area thats presently served only with a manual pump....... the joys of boat ownership that I have missed so much for 10 years...
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Old 31-10-2014, 06:57   #54
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Re: New boat pulls to starboard under power, prop?

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Originally Posted by SVTatia View Post
What I meant to say was that unless the "installer" changes the taper, it would be physically impossible to fit the shaft into the prop.
I got that, and agree it's unlikely, but the possibility exists that some fool has bored out the prop to make it fit. It's moot anyway.
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Old 31-10-2014, 08:25   #55
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Re: New boat pulls to starboard under power, prop?

Not that its relevant but prop on wrong way round was something I thought may be the problem, very easy to solve. (Wishful thinking)

But never mind the taper, its possible with a hydraulic box and electrical controllers (joysticks, there are no morse on the boat) to have a wrong handed prop going the wrong way around, you would still go forward and backwards but with quite a different characteristics on wash....and performance.

Just a comment from the OP...to let you all know I am still looking at this problem and your posts.
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Old 31-10-2014, 08:27   #56
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Re: New boat pulls to starboard under power, prop?

Before I went tearing the rudder off, try some other things first, like a tab between the prop and rudder that will deflect the wash from the prop, but being that it is not attached to the rudder it won't have an effect when sailing, it will of course add some drag, but with that big wheel you have now, you already have considerable drag.

Surely tearing the rudder off and changing design is the last resort, if nothing else losing the balance portion of the will drive the rudder steering forces way up, necessitating a larger wheel or at least different steering gear.

It still sounds like more of a thrust misalignment issue than a rudder issue though to me.
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Old 31-10-2014, 11:00   #57
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Re: New boat pulls to starboard under power, prop?

It's a steel boat, maybe the rudder has been built with some non-symmetry causing the pull. I do know that a lot of wash on a rudder does cause some weird feel in the helm... maybe it's just that and the "balance" portion of the rudder (being closer to the prop wash) causing the feel... Various boats "drag" the rudder a lot when sailing due to weather helm... maybe "why worry" when motoring?
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Old 31-10-2014, 11:38   #58
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Re: New boat pulls to starboard under power, prop?

Quote:
Originally Posted by brightontrader View Post
I finally used some common sense yesterday and powered the boat up tied to the pontoon.

At around 1/4 power I could feel a slight kick on the wheel to port, then as I added power wheel became more twitchy and then 1/2 to 3/4 then to full gradually pulled wheel over to starboard.

So its the prop wash on the rudder for sure and not the stern of the boat being dragged to port.....

I wish it was the the prop as thats easy and relatively cheap to fix. I talked to a David at Axiom Propellers and he came back with a different shape prop with 24" and 20 degree angle (???) but I really think I have to look at angle of prop and somehow model the wash on a fluid dynamics software of some sort to see how its hitting the rudder.

I kind of think that a skeg hung would not have this problem in that the wash hits an immoveable object, splits in half then washes over prop......

Also thinking that building a skeg rudder on this, a steel, boat would not be out of the question or even that expensive (relative to how I value the boat going straight....under power.)

Yesterday spent the day wading through other issues and made huge gains in understanding the water ballast and pumping systems, yes it has these too, its a very complex boat for a cruiser.....of course, had bought a new Jabsco Par 2.9 in advance thinking it was the same as the Par 3 was replacing, wasn't .....then managed to replace microswitch on broken pump and have now a new spare that I am installing in a bilge area thats presently served only with a manual pump....... the joys of boat ownership that I have missed so much for 10 years...
Is it possible to have a pintle on the bottom of the current rudder when adding a skeg? I prefer a skeg just for rudder protection.

I believe you have some horrific tides and currents. Is it possible the port pull was caused by that at a minimum prop. wash?

You never did tell me your speed made good at 2500RPM to quench my curiosity about your slippage.

Keep us updated you have cause a bunch of interest.
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Old 09-11-2014, 23:57   #59
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Re: New boat pulls to starboard under power, prop?

Well am still investigating problem but now have a new one in that the joystick only slips the engine in and out of gear and the engine is starting with about 1/2 thrust only and no rev control.....joysticks are a new thing to me and trying to work out how they work so can fix this issue...

But answering one poster, under power got 7knts, should get 8knts, previous owner reckoned he got 8, I am not convinced after my 30 hour trial run getting the boat to Brighton..

I have had an offer of a prop from Axiom, the designer reckoned it was the wash from the 1-3 o'clock portion of prop hitting rudder and that the Axiom has a more even wash, he was offering a money back if it doesn't fix problem guarantee but has gone quiet after I asked for that in writing...

Will follow up today.....with him,,
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Old 10-11-2014, 11:10   #60
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Re: New boat pulls to starboard under power, prop?

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Originally Posted by brightontrader View Post
Well am still investigating problem but now have a new one in that the joystick only slips the engine in and out of gear and the engine is starting with about 1/2 thrust only and no rev control.....joysticks are a new thing to me and trying to work out how they work so can fix this issue...

But answering one poster, under power got 7knts, should get 8knts, previous owner reckoned he got 8, I am not convinced after my 30 hour trial run getting the boat to Brighton..

I have had an offer of a prop from Axiom, the designer reckoned it was the wash from the 1-3 o'clock portion of prop hitting rudder and that the Axiom has a more even wash, he was offering a money back if it doesn't fix problem guarantee but has gone quiet after I asked for that in writing...

Will follow up today.....with him,,
Thanks for the speed. If my assumptions are right about your power an reaching rated RPMs you slippage is 38% @ 7kn. I'd buy that with a displacement hull any day.
I think reckoned is very optimistic with 8kn . Good luck with the joy stick and a prop. with a difference cup.
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