More about IPS

[JLL]

Hi everyone,
I´m dealing with the installation of IPS system in a new 37' powerboat. The hull bottom, structure and weights were modified to match the Volvo requirements for the system.
When sailing beam reach (wind perpendicular to heading), the skipper must correct the heading continuously, and when doing so, the boat suffer a heel of about 5º (too much for a powerboat!).
Other bigger boats (about 43') with IPS sails very fine and don´t make the above.

Any idea to help?
Jaime

[SailDesign]

What is IPS?

Steve

[cyclops]

It is a ( new to Volvo ) sterndrive unit that is shoved up the bottom of the hull to take the place of the propellor shaft and propellor. It can rotate for steering. It is locked in the vertical position. It is the simplest piece of drive you could make.---------------------------------- It should therefore be much cheaper than a stern drive unit.

[cyclops]

If the hull design of the 43' and the new 37' are the same. Then I think the weight and height of the IPS drive package is higher than a shaft and propellor drive and becomes noticable at about 40' in your hull designs. Assuming the cabins and above deck structures are not greater in volume or construction weight. You are top heavy.

[dougfrolich]

I do not see the IPS system possition higher than other installations, actually they seem compact. They seem like a great idea to me.

[cyclops]

What is the lean angle of your old inboard and shaft drive boats with the same wind and water conditions. My Geometry in boating is useless. BUUT. IPS drives combine the thrust WITH the rudder. So that the old inboard diverted only some SMALL AMOUNT of prop thrust to steering and the force was at the rear most end of the boat. The IPS turns the ENTIRE FORCE of the prop to the new course correction. It is very possible the IPS drives are pushing the boat UPWARDS in the direction of steering.-----A course change of the same DRIVE ANGLE in 0 mph wind and current is needed with a Inclinemeter to make a comparison. My guess is the IPS drives propellors are FARTHER FOWARD than the old inboards. This would require the drives to turn MORE and start to push one side of the hull up in all turns. ----------------------- The other possibility is at speeds the drive is very touchy to the fixed trim angle. You may need trim tabs.

[JLL]

Hi,
Thanks Cyclops, IPS (Inboard Performance System) works in a similar way as Saildrive for sailboats. The main difference with above is that includes a steering system electronically managed by software, so the whole unit woks as a propulsion and steering unit. You could find more in www.volvo.com/VolvoPenta/Global/en-gb.
The image of Dougfrolich is clear. Enclosed is a drawing of the 37' shaft drive unit and the 37' IPS . Although the longitudinal position of engines changes, as well the hull bottom, in the new IPS boat we move items related previous shaft drive boat (tanks, gen set, batteries,..) to obtein the same CoG as we have in the shaft drive.

Our lean angle at 0 Kn is 0º, at 20 Kn -6,3º and at 32kn-3,5º in shaft drive as well in IPS boat.The problem I have is not the trim angle but the heel angle that occurs when we want to correct the heading running beam reach that doesn´t occurs with shaft drive.

[JLL]

OOps, sorry a new image is enclosed
Hope you could see it!

[cyclops]

Thanks for the scale drawing. It elimanates all possibilites of causing you problems except 1. The old hull has a partial tunnel to reduce draft. the new hull does NOT. Reasons?------- IPS IS A FLAT BOTTOM drive by design. It can NOT function in tunnels without looking terrible in efficiency. -------In a simple statement. The IPS drive turns ALL 100 % OF THE THRUST to the new rudder angle at what ever the power setting is. A prop and rudder WILL NEVER be able to divert more than probably 35%. ----------IPS at the same MAXIMUM RUDDER ANGLE as a prop and rudder will therefore develope 3 X the side thrust. Which, depending on wind speed, direction AND BOAT SPEED can all add to a very powerfull, deep, side thrusting force. A simple thrust vector / rudder area chart should bare this out. The IPS probably has a RESTRICTED amount of rudder angle allowed to try and hide this basic design problem. ---------------------------A computer should never need to control a rudder and engine unless there is a unusual set of operating conditions that a human would not be able to do fast enough. -----------------------------------These are my opinions. Could be right or wrong. Should be simple enough to find out with a few field tests.

[JLL]

Hmmm... you´re right Cyclops. It reminds to me that the first IPS units must be reprogrammed in order to lower the high list angles obteined when manoeuvring and turning at high speeds.
Maybe, one solution may come by cutting gas (throttle) when turning (even for smaller turning) to lower that side thrust and related list.This could be done in an automatic way to avoid dangerous handling of the boat.
If above is possible, I will inform about the results of sea trials. Thanks

A computer should never need to control a rudder and engine unless there is a unusual set of operating conditions that a human would not be able to do fast enough.

This is ONE of the major disagreements I have with autohelm / autopilot systems, mostly for what i term very fast boats (< 30 knots) which operate in moderate seas.

I know professional lobster boat skippers, with vessels capable of 40 knots + who won't hear of auto pilots for this very reason...unpredictable responses to sudden changes in vessel attitude, (eg. falling off a slop into a hole at speed for example, just WHAT errroneous corrections might a computer controlled auto pilot make in that circumstance?).

I also see that some newer auto pilot systems have a form of "artificial intelligence" - where the system continually "learns" from corrections it makes, and subsequent positions / direction the vessel heads - how the vessel reacts and modifys it's own responses. Perhaps over time - such a system if intuitive (and fast enough) MIGHT approach a humans ability to react to unusual conditions - but I still have doubts.

I think it's an area of navigation that SHOULD perhaps be talked about more - before electronics geniuses take us somewhere (with naivgation tools) we don't necessarily want to go.

Cheers!

[cyclops]

I, and my son in law, are the ONLY 2 people who run the boat by HAND ONLY. I would not care how long the trip. I DO NOT TRUST A LUMP OF QUARTZ AND SILICON. Now or ever. It does not see or rationalize a speeding Off Shore Racer coming at us at all. Or no one on the bridge of a yacht. Humans eyes and knowledge. It has no hair on the back of it's neck. So it never senses danger. ------That is all. Have a nice cruise.

[67-LS1]

Kind of unrelated, but could the IPS system be used in a single engine application?

[cyclops]

OF course. Can a Duo-prop be used alone? Of course. However there are people who would just replace 1 shaft of a 2 shaft setup to save money. That could definately cause handling problems.

[67-LS1]

Do you think Volvo might use the "puller" propeller concept on an outdrive in the future? Would there be any value to it?