Are IPS hulls shallower V than shaftdrive?

  • Thread starter Thread starter Deleted User YDKXO
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I saw an IPS flybridge berth a couple of years ago.
Calm conditions.

AS it went sideways the whole boat tipped to the extent the helmsman looked like he was going to head butt the boat at the side he was trying to miss.

The boat swung like a pendulum.

The tipping motion could also be linked to the lower IPS prop.
as the prop is on a stalk it has a lever effect on the boat.

A shaft prop is only a few inches away from the hull does not have the lever effect.
It is a pivot action against the stern with a slight sideways paddle effect.

When 'dodging' waves I would hate a breaking wave to hit the underside of the hull at the same time as the IPS pendulum swings into effect /forums/images/graemlins/shocked.gif
 
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I still get a quiet satisfaction from reversing my boat into a tricky crosswind Med mooring without denting anything just using the engines and no thruster so, IMHO, joystick control would make it too easy but then I'm probably a luddite in this respect /forums/images/graemlins/smile.gif

[/ QUOTE ]Was thinking the same thing. Or as Clarkson might say, what would be the point of or enjoyment in driving a sports car with automatic steering. It takes all the fun out of boat handling.
 
You have a point there M, however that kind of simplifies things a little too much.

Joystick is indeed a real 'get out of jail card ' for many boaters starting out on their boating career but it is also adding to the safety factor of berthing and close quarter manoeuvring. It is not intended to replace good seamanship in any way. Any client of ours that expresses concern or is not used to a boat of this size we automatically put them on a day skipper course, in the cost of the sale its peanuts to us but saves a fortune to the client in dinked gel coat, bent stainless not to mention dented pride.

One could take the same scenario with people moving from shafts to out drives, "oh yes I have been boating for years no problem to me", stick them on a twin out drive 45 SC and they are all over the place tying to get to grips with O/D's. Conversely shafts could be seen as mamby pamby boating compared to the skill of helming an OD boat with no thruster in a 3 knt tide and a cross wind.

What Joystick offers is an 'aid' to helming, berthing, close too maneuvering etc, why make life difficult and why put off new boaters with the stress and anxiety of trying the berth etc. I know several chaps at our marina are terrified of coming back after a day out, they don't use their boats that often so skill levels and confidence drops between outings, sort of takes the shine off the whole experience for them.

One could even level that at very experienced boaters too when the weather turns and entering a new port in a howling cross wind or tide, you can see the stress level build the closer they get. Me ! I don't give a fiddlers, me and my joystick will plonk her in there, piece of cake.

I would also say that if you want to get into the finery of Joy stick use you, after considerable practice (skill) can do some incredible things with it, OK all a bit show offy but get really into it and you and do things like perfect 360 circles around say a mooring buoy in 2 knts of tide keeping the bow exactly 1m off the buoy and the boat always 90 degrees to the buoy. Pointless maybe but if one talks about skill Joystick takes things to another level.

I suppose the same argument could be levied at Pilots who adopted joy stick in commercial aircraft, I guess traditionalist are still flying by yoke and cable operated throttles but I doubt I feel any less safer with the chappie flying joystick than Mr old school.

I would also mention that it is not necessarily the established boaters that will bring the industry out of recession it will be as much to do with new blood coming to the market looking for ways to spend their money, they are as critical to recovery as any die hard boater trading up, in fact more so as they are less likely to have part exchanges which have to be offloaded, as they say Cash is king at the moment not half your stock tied up in second hand vessels. In that vein new boaters are less likely to be swayed with old values and shiny badges. They are looking for the best value for money, the most efficient, good design and engineering and if it is easier to get to grips with the whole sweaty hands 'can I berth this thing' mores the better.

..........brought to you by the marketing department of VP, Cummins and ZF /forums/images/graemlins/wink.gif
 
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..........brought to you by the marketing department of VP, Cummins and ZF

[/ QUOTE ]Chapeau to their mktg consultant!
Well, I did apologise in advance, didn't I? /forums/images/graemlins/wink.gif
 
Daka you dont measure the lever by measuring the distance from the prop to the hull surface, you measure it from the prop to the axial roll centre of the hull, which is quite a long distnace on boat a shaft and an IPS boat. In fact it's about the same distance on IPS as shaft.

(Of course on a shaft boat you measure from the rudder not the prop, but I know you meant that)
 
Very fair points, Trev, but we oldies don't want these newbies making fools of us by mooring their new IPS Absolutes perfectly whilst we feck it up in our shaftdrive dinosaurs. The point is that we want them to suffer the crunched grp and dented pride whilst accumulating experience, just like us. It's just not fair that a silly little joystick can turn a newbie into a boat berthing god in a few hours /forums/images/graemlins/smile.gif
 
Yup, I was also thinking about Daka's point.
Only surface transmissions and waterjets can make a difference in this respect, I suppose.
 
I accept I could be wrong and I havent the time for a long argument today (I dont do them any more).

If you are considering the propulsion stream of water then I possibly agree.

However we are looking at slow speed manoeuvring and also need to consider where the pull (reverse) comes from.

IPS pulls from a low point at the side of the hull.

Props pull from the bow.
 
Mapis, another point. As set out in my post above, there is an extra 4-6% twisting torque cause purely by the cosine effect. That's easily understnadable. But there is also a sine effect, and it's bigger. The sine of the IPS's turning force force operates downwards on the port drive and upwads on the starboard drive when the boat is steering to port, and that force multiplied by the horizontal distance from the IPS drive to the roll axis producs a turning moment that simply doesn't exist on a shaft boat

Worse still, the sine of 20degress is .34. Blimey! So in a tight turn, you'll have a couple of hundred kgf horizonatal force in a shaft+rudder boat to turn the hull on the sea, and in an IPS boat you have in addtion 68% of that force multiplied by the distance from drive to roll centre (say 1-1.3m) acting as a twisting torque banking the boat harder into the turn. Blimey!

The sine of 10deg is .17 (sine waves are near-linear, close to zero) so no wonder volvo like IPS boats to have flat deadrise aft!

That's what your engineer friend had in mind I think. It makes my cosine effect relatively insignificant. I think you covered this in your post earlier on by the way, just without the maths :-)
 
Yup, I think that's what I was trying to say earlier
 
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Props pull from the bow.

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I was up till 4am last night so might struggle today but you've lost me there! :-)
 
I've just read your post Deleted User. Sorry, I'm saying the same as you and mapis, you guys were there first, and I was just trying to put some half-arsed mathematics on it cos I find it useful to see whether an expected effect is a 4% item or a 68%er, or whatever.

But yes, agreeing with you. And I agree with your ludditery too, and applaud you. I'm right there with you. I want to know what each prop is doing, and not leave it to a joystick

A completely separate aspect to this (and let's not go there now) is unreliabilty of Volvo's control engineering and software. This joystickery does break down, and when it does you can't fix it with a socket set. That's another reason to be a luddite :-) Boat manufs often fail to grasp the gravity of a breakdown, and seem to live in car-land when you phone the AA or go to Avis and rent another. If you're in an anchorage in Sardinia and you dont speak italian and have guests aboard who've gone to a lot of trouble to make the holiday, or charterers who paid £20k for the week, it's a friggin big deal if the holding tank pump breaks, let alone the boat's drive system. So old fashioned engineering really does have its attractions /forums/images/graemlins/grin.gif
 
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Props pull from the bow.

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I was up till 4am last night so might struggle today but you've lost me there! :-)

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If your boat was tied up and you stuck your helm to port and reverse , there would be a stream of water, current from the bow, as the boat is long there will not be much change in boat level .

If you do the same with ips there would be a pull from starboard midships.
boats tip easily from side to side due to narrow beam and the ips boat rocks, this is what I saw happen, it was noticeable and would frighten skipper and crew alike.
 
Well, ok, but I wouldn't call that a prop pulling from the bow!

But you're not comparing like with like. The IPS is producing a much bigger turning effect, so of course it will tip the boat more. If you merely matched the shaft boat turning effect, which would mean only a small amount of helm over in the IPS boat, you wouldn't get the rocking

I have no experience driving ips joystick but from watching them the impression I get is that the electronics blip the throttle far too much and also the boat is in gear far too much of the time, sort of overdoing things then correcting itself. In a shaft boat in normal berthing you never use anything more than idle rpm and you are in neutral, just gliding, 75% of the time. That, imho, is why ips boats rock n roll - too much throttle and not enough gliding!
 
In the example I saw, the IPS boat was all but berthed in a finger berth, but too close to the boat at the side and too far away from the finger pontoon for his crew to jump.
The skipper wanted to move 2 ft toward his finger pontoon.

The boat hull moved about 1 ft closer to the finger.

The Flybridge moved 2 1/2 foot towards the boat on the other side.*

As the skipper only wanted to move slightly there was not any throttle increase used.


* Happy to accept this 2 1/2 foot as an exaggeration , but that is how I remember it.
 
The last time I had an engine control system problem, I mended it with a screwdriver. But it's the same with cars and, indeed, other types of machinery. So much electronics and computer power is used these days to monitor and control systems. That's fine for the first owner but I feel sorry for the 2nd, 3rd and so on owners who doubtless will have to wrestle with simple problems that they can't or don't know how to fix. It is another whole subject but boats are generally way behind the times when it comes to fault diagnostics and remote monitoring of those diagnostics
 
Most experienced skippers love berthing, it's the cherry on top of the cake at the end of a passage. /forums/images/graemlins/wink.gif Joysticks would enable newbies to cheat and never have to learn how to berth - ever! /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif /forums/images/graemlins/wink.gif Agree with Deleted User, the jury is still out on long term TCO, maintenance and reliability of ips.

PS: On a serious note, I'd hate to see joysticks eliminate the challenge and fun from boat handling.

PS2: Comparision of joystick v's control yoke in aircraft has no validity, they perform identical functions and required identical handling skills. IPS joystick eliminates two throttle levers and the helm wheel, and ensures skipper may never understand what's going on under his bum! /forums/images/graemlins/smile.gif
 
I'm torn on that one. I sort of agree with you and Deleted User, and also enjoy getting it right with engines in and out of gear, but on the other hand it's a bit elitist to want something to be harder, just so less people can do it. On the same principle shouldn't we all rip the chart plotters out of our boats, and navigate on dead reckoning, or even better go out and buy a sextant? Does it matter if the IPS helmsman knows what is happening at each prop to make the boat turn, any more than a motorist needs to understand how a steering rack works?
 
I think it does matter because, one day sooner or later, the joystick will fail and the helsman will be left with just his throttles and steering wheel to play with so he needs to understand their effect. I don't think the car steering wheel example is valid because, fundamentally, the controls of a car haven't changed in nearly 100years, it's just the way they execute their function that has changed. To turn a car, you still have to turn a steering wheel. OK, now the steering is power assisted and/or electric but the effect on the car of turning the wheel is the same as ever. I don't think anyone's marketed a car with all wheel steer and joystick control yet /forums/images/graemlins/smile.gif
 
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