IPS - where does the rope cutter fit?

[AHoy2]

N.B. casual query - no technology wars required.

Having dipped in to some of the other recent threads where IPS featured this subject cropped up in my mind.

Having had a tilting drive leg available on my previous boat the move to a single shaft drive boat had me more than a little concerned about clearing a fouled prop. A rope cutter has given me (some) peace of mind but I have not noticed any designs being promoted for IPS - I assume a fouled prop is just as likely if not more so. With boats in the IPS price range is it a matter of keeping a submersible in the "tender garage"?

A.

 

[TigaWave]

It would be possible withe the QuicKutter but...... we need the cooperation of the leg builders as we need to bolt to the housing. Being oil filled this presents a few questions and may need some adapting. But we know it could face forwards and would not effect performance. If more customers ask, their attitude may change.

We have a cutter for an oil filled outboard leg (Suzukis) and we know this works with no risk of damage. But again the manufacturers don't like bolting things to their housings.

Other oil filled drive designers (www.seatorque.com) are adapting their system to take the cutter as they see it as a benefit, but Volvo don't seem interested. They have been approached on the issue more than once.

 

[Deleted User YDKXO]

Ahoy2, that's an excellent point and I suspect the answer will not be easy wuth a dup prop system. I would also think that forward facing props of the IPS system are even more vulnerable than aft facing ones. Tigawave's system might give some protection to the rear prop but not to the front one. I hope that somebody at Volvo has thought about this

 

[holderone]

Thats interesting, I have an IPS system and when I casually asked the same question about rope cutters to an engineer and I was told that due to the forward facing aspect of the props they are less likely to get fouled up?

 

[Deleted User YDKXO]

Did you believe him? IMHO, a standard shaft system with rear facing props, often protected by a keel or a tunnel has a better chance of avoiding a rope foul than IPS. The IPS props are forward facing and sitting well clear of the hull and are IMHO more vulnerable to a rope foul. Then IPS has 2 props just to make sure that any rope or netting is well and truly wound on and a substantial leg to catch any debris that misses the props!
V interesting to hear about your future experience with IPS on this matter and general performance

 

[TigaWave]

Actually (I hate to disagree but) in all probability it will work with forward facing props, it works very well when you run astern into rope with the outboard or shaft version.

The reasoning is.
You are protecting against debris getting wrapped tight between rotating (prop blade) and fixed structures (leg). This happens which ever way the unit is heading.

The shaver cutter works by allowing a few turns of this wrapping to take place and thus force the debris into the fixed blade.

Rope caught by a forward facing prop will wrap the debris tightly between the prop and the leg, causing shaft damage, seal damage or both. The worst thing for oil filled legs is the simplest to deal with...fishing line. At least with IPS you will limit the damage to the leg and gears in the leg. With shaft systems damage can range from bent P brackets to gearboxes pulled off.

 

[Nickcf]

Don't imagine it will any less effective on a forward facing prop. The cutter sits on the prop shaft immediately next to the prop itself. A rope cutter will only attempt to prevent rope, already caught in the prop blades, being wrapped around the shaft which is what will cause an engine stall.
If the rope/net is big enough then a rope cutter will not be effective as nothing (other than a sharp knife) will get it off the prop once it is twisted round the blades, even though the shaft may be clear to rotate. You still can't go anywhere as the vibration will limit engine revs to tickover at best.

 

[oceanfroggie]

I was told that it was NOT possible by a local volvo agent.

Time will tell - for IPS it's early days yet, lets see what the TCO is like over time.