mad_boater
Well-Known Member
Would rope cutters reduce top speed?
Rope cutters
- Thread starter mad_boater
- Start date
DAKA
Well-Known Member
when I researched I came to the conclusion they would steel 1-2 knots off my cruise speed and maybe 10% in fuel , however there is one that doesnt http://www.h4marine.com/QuicKutter01.htm
unfortunately it hasnt featured in this months MB&Y rope cutter report but worth a read if you havent seen it yet.
SAMYL
Well-Known Member
Probably not make any significant difference to speed but a rope around your prop will 
Latestarter1
Well-Known Member
Rope cutters create 'dirty' water just ahead of the propeller, therefore simple answer is YES
mad_boater
Well-Known Member
That makes sence.I know if the props are fouled with barnicles it can make a big difference to speed and more important the dreaded fuel consumption.
sarabande
Well-Known Member
That amazes me ! There can be very little laminar flow around the shaft and boss, and I am at a loss to see how a rope cutter could affect flow on the (much greater) blade area, which is where the propulsive effect is generated.
Always willing to learn, though
.Latestarter1
Well-Known Member
That amazes me ! There can be very little laminar flow around the shaft and boss, and I am at a loss to see how a rope cutter could affect flow on the (much greater) blade area, which is where the propulsive effect is generated.
Always willing to learn, though
Laminar flow around 'P' bracket is sensitive to several factors for example distance of propeller from supportng strut, propeller shaft size etc etc. My own vessel has tapered nylon fairing tube before the 'P' bracket in order to reduce shaft disturbance on the waterflow even before the bracket.
Excellent book on the subject of everything under water is the 'Propeller Handbook' by Dave Gerr ISBN 0-07-138176-7 for paperback version.
Wife took one look at the book when it arrived from Amazon and went away shaking her head muttering about sad peoples reading matter...........
mad_boater
Well-Known Member
That amazes me ! There can be very little laminar flow around the shaft and boss, and I am at a loss to see how a rope cutter could affect flow on the (much greater) blade area, which is where the propulsive effect is generated.
Always willing to learn, though
I had my boat preasure washed and barnicles removed not long ago. The hull was a little fouled with sludge but the props and shafts were quite badly crusted,it gave me another 4 knts.I would have thought anything that reduces the smooth flow over the props be it blades boss or shafts would have an effect.Then again I also could be wrong.
DAKA
Well-Known Member
In that case even the quickcutter may have more of an effect than I thought.
That was the only cutter left in my 'things to consider again box'.
DougH
Well-Known Member
When I took delivery of my Sunseeker Manhattan 60 in 2009 I asked for rope cutters to be fitted.
Sunseeker advised against fitting such devices as in their experience the rpoe cutters were the cause of subsequent cavitation problems and slight prop damage.
Cannot comment as to what the damage would be but I have found the Sunseeker Technical Dept. very competent as you would expect.
Sunseeker advised against fitting such devices as in their experience the rpoe cutters were the cause of subsequent cavitation problems and slight prop damage.
Cannot comment as to what the damage would be but I have found the Sunseeker Technical Dept. very competent as you would expect.
oceanfroggie
Well-Known Member
We fitted them about 5 years ago and haven't noticed a difference in speed or fuel. Wouldn't be without them. Got us "out of jail" on more than a few occasions!
Andrew_Fanner
Well-Known Member
Being on the Thames I would not be without them. The Tideway can have a lot of nasty stuff as well. I see the issue on speed, just don't get affected by it, I'd lose far more with snarlups.
Bandit
Well-Known Member
From what i have heard over the years rope cutters can cause erosion of the prop and will cause a drop in speed for the same rpm/power say a knot or so.
However I use rope cutters and used them in anger.
I have also caught a tarpaulin and spent 5 hours more at sea and a diversion to get it removed with rope cutters fitted.
I have also seen several boats where subtantial damage has been caused to shaft, props or p brackets costing mucho spondulicks.
Its a choice, personally I would not be without them.
Look after them , replace bearings if necessary.
The Aussie H4 looks interesting?
However I use rope cutters and used them in anger.
I have also caught a tarpaulin and spent 5 hours more at sea and a diversion to get it removed with rope cutters fitted.
I have also seen several boats where subtantial damage has been caused to shaft, props or p brackets costing mucho spondulicks.
Its a choice, personally I would not be without them.
Look after them , replace bearings if necessary.
The Aussie H4 looks interesting?
Powersalt
Well-Known Member
Hi,
After much deliberation I took the advice of our volvo agent and had the aussie rope cutters fitted as I was informed they would not give a drop in performance.
I was shocked at the fitting price as some engineering work had to be done to get them right but since then I cant notice any difference in performance and speed.
Would not be without them now
After much deliberation I took the advice of our volvo agent and had the aussie rope cutters fitted as I was informed they would not give a drop in performance.
I was shocked at the fitting price as some engineering work had to be done to get them right but since then I cant notice any difference in performance and speed.
Would not be without them now
Neil_Y
Well-Known Member
water flow just to add my 2p
I response to latestarter that "rope cutters create dirty water", as others have said not all cutters present a flat surface to the general water flow. Disc and scissor types present a relatively small area but the surface is at right angles to the normal flow, like an air brake on a glider wing that is designed to disrupt laminar flow.
The spool used with the quicKutter can actually help improve the water flow to the prop as it can be tapered between the diameter of the prop hub and the stern tubes, you can see this on an RNLI Tamar installation where the prop hub is smaller than the stern tube OD.
I response to latestarter that "rope cutters create dirty water", as others have said not all cutters present a flat surface to the general water flow. Disc and scissor types present a relatively small area but the surface is at right angles to the normal flow, like an air brake on a glider wing that is designed to disrupt laminar flow.
The spool used with the quicKutter can actually help improve the water flow to the prop as it can be tapered between the diameter of the prop hub and the stern tubes, you can see this on an RNLI Tamar installation where the prop hub is smaller than the stern tube OD.
Jim@sea
Well-Known Member
Probably not make any significant difference to speed but a rope around your prop will
When I was selling my boat I took the potential buyer out for a sea trial. Little did I know that on my way out a rope attached to part of a fishing net wrapped itself around my propeller. So out at sea the boat was 20% down on speed and the engine was labouring and would not reach maximum revs.
Anyway the buyer was prepared to buy the boat at a reduced price. It was only when I took the boat out of the water that the rope was seen.
So for my next boat I will have a rope cutter.
PS. I had a lobster pot rope around my propellor 30 years ago.
So its becoming a common occurance.