Prop diameter/pitch

[Proper Job]

Ocelot has (alegedly) got a 26 x 12 prop on her. Engine tickover is around 250rpm and maxing out at 1000. 2:1 reduction gearbox. She draws around 3' at the stern and about 2' at the bow. I roughly calculated her displacement to be around 19 tonnes.

 

I can run past moored boats at around 300-350 rpm with causing them to move (to much) and think that she may be a little under prop'ed. As she's coming out for blacking in the near future I was thinking about getting the pitch increased a bit. I think it would make the JP work a little harder without compromising low speed manouverablity.

 

The question really is. If you have a deep draft boat, what prop diameter/pitch combination are you running at what shaft speeds (mine being 125 to 500 rpm)?

[denboy]

20 hp kelvin p4 prm 160 2 to 1 box onto a 22 x 18 prop and go past boats on tick over with no problems

[MoominPapa]

18HP Lister FR2

 

21” x 18" prop 2:1 reduction, so shaft speed is 200rpm tickover to 900rpm flat out (in theory, I've not yet done a "flat out" test since I fitted a tacho)

 

At tickover things are very slow and controlled, but I doubt I could add more prop without running out of horses.

 

MP.

 

Edited to add: the current tickover engine speed (400rpm) is below Lister's spec, so I might have to up that to 600rpm, which would be fine with current prop.

Edited again: We draw 34" to bottom of skeg.

Edited March 3, 2009 by MoominPapa

[NB Alnwick]

Kelvin K3 with direct drive to a 24" x 24" prop - which could be bigger - ideally 29" x 24". Engine/shaft speed varies between 140 and 600 rpm - the higher figure is not suitable for canals. We draw 33" under the stern (more when under way) and up to 30" where the curve of the bows meets the bottom plate. The latter dimension can reduce by six inches or so when we are very low on water but this also has the effect of dropping the stern down another two or three inches. We had calculated our displacement at between 20 to 25 tons.

[DHutch]

26" Dia, 32" pitch, and a DAR of around 1.

- Stright through to engine, cruising speed aroun 150rpm, flatout at 330/350 depending depth of water.

 

 

Daniel

[dove]

Achilles- Gardner 4LW, PRM500 1:1.5 Tick over 425rpm max 1300rpm Prop-24 x 16 with broad blades ( should be 27 x 16 )

draft 28" at tick over - fenders floating at speed.

 

Dove- Gardner 4L2, gardner No.2 reversing box 1:1 tick over 250rpm I think, max 1000rpm prop 23 x 18

draft 36"

 

Andrew

[tony collins]

Engine 4108 perkins: 17" x 11" prop on a 3:1 reduction box proved to underpropped. Same prop on 2:1 with an Isuzu 4B33 proved to be slightly over propped. Both on a 45ft n/b.

 

Tony

Edited to include draft 2'-3" at a standstill.

Edited March 3, 2009 by tony collins

[robkg]

Hi,

My set up is similar to Alnwick. 70', approx 2' 6'' draught, Kelvin K2 through 1:1 gearbox turning a 24'' x 24'' prop.

Feels just about right for slow revs cruising and sociable boat passing.

 

Rob

[Nickhlx]

Hi,

My set up is similar to Alnwick. 70', approx 2' 6'' draught, Kelvin K2 through 1:1 gearbox turning a 24'' x 24'' prop.

Feels just about right for slow revs cruising and sociable boat passing.

 

Rob

 

 

Does a 3 or 4 blade prop make much difference to speed if pitch / diameter the same ? ( or what differences does it make - smoother/ less vibes ?)

 

Nick

[Yoda]

More blades the better.

 

In fact, you can reduce the prop diameter considerably buy having a five bladed design.

[Nickhlx]

More blades the better.

 

In fact, you can reduce the prop diameter considerably buy having a five bladed design.

 

 

So if it was an option to have a "four" fitted as opposed to a "three", would it help with mpg / more speed for given revs ?

 

Builder said he fitted either and changed to the other if the first "sung" whatever that is !

 

Nick

[hughc]

3' static draught over full length (55'). Ford BSD3 42 bhp @ 2200 on a 2:1 box. Prop. 23 x 13 Crowther High Effiiciency. Usual range of propeller 300 - 600 rpm. On deep water 1000- 1200 engine rpm. gives max. hull speed. On a confined channel a fast tickover creates no discernable wash just a slight rise and fall of the water level. Regards, HughC.

[Timleech]

Ocelot has (alegedly) got a 26 x 12 prop on her. Engine tickover is around 250rpm and maxing out at 1000. 2:1 reduction gearbox. She draws around 3' at the stern and about 2' at the bow. I roughly calculated her displacement to be around 19 tonnes.

 

That pitch sounds very small, a quick back of envelope sum suggests it would give a max theoretical speed of 5.6 mph @ 1000 rpm with zero slip. Normal max for a JP is 1200 rpm though which would give a theoretical 6.7 max mph if the engine will drive it up to that speed.

Good for towing if it loads the engine fully, not so good for speed trials.

 

Tim

[blackrose]

Some of you have mighty big props!

 

I think mine's 19" x 13" (3 bladed) Izusu 55/ PRM 150

[Neil TNC]

Ah!...a few teeny weeny non plonkyprops have come out of the woodwork!

 

Earnest (58ft 6in R&D Slipper stern) Beta BV1903 (43) / PRM 150 2:1 / 26" + dropped skeg draught, was initially fitted with a 17" x 12", which was grossly under propped.

After 6 months it was replaced with a second hand (only test run) Crowther 18" x 13".

If anything Earnest is now very slightly overpropped, but the engine will swing it up to 2700rpm and it does pull up on a sixpence.

This much mangled and self-fettled prop is still going strong, after 9 years.

I have had for many years a spare brand new Crowther of the same size (who confirmed that this was the ideal sized prop, for the kinda stuff we do)

[Proper Job]

That pitch sounds very small, a quick back of envelope sum suggests it would give a max theoretical speed of 5.6 mph @ 1000 rpm with zero slip. Normal max for a JP is 1200 rpm though which would give a theoretical 6.7 max mph if the engine will drive it up to that speed.

Good for towing if it loads the engine fully, not so good for speed trials.

 

Tim

I did a similar back of a fag packet calculation and came to the same conclusion. It barely moves at tick-over and can easily be manoeuvred in to locks at 300+ rpm (in-fact, is more responsive due to the propwash over the rudder plate).

 

The engine is only ever lightly loaded and I need to give it a bit more work to do.

 

I can still pull Bones off the mud even when she forgets to take it out of gear and is still full ahead

 

I'd like to achieve tick-over for lock work and passing moored boats etc, about 400 - 500 rpm for canal work, 600 - 700 rpm for deep water river and a few revs spare (just in case)

[Timleech]

I did a similar back of a fag packet calculation and came to the same conclusion. It barely moves at tick-over and can easily be manoeuvred in to locks at 300+ rpm (in-fact, is more responsive due to the propwash over the rudder plate).

 

The engine is only ever lightly loaded and I need to give it a bit more work to do.

 

I can still pull Bones off the mud even when she forgets to take it out of gear and is still full ahead

 

I'd like to achieve tick-over for lock work and passing moored boats etc, about 400 - 500 rpm for canal work, 600 - 700 rpm for deep water river and a few revs spare (just in case)

 

Are you limited to the 1000 rpm you quoted? I think the original (CS) engine was rated for 1000 rpm only.about 18bhp, but 21 @ 1200 was the standard for a long time. It does make a big difference to the prop size.

 

Tim

[Lewis 53]

We had problems with the performance of our boat and got advice from every one we could think of. Eventually we were directed to Crowthers Marine Manchester (really in Oldham)and they sorted it out after asking a lot of pertinant questions. Very helpful. (No personal connection with this company).

 

 

OOPS just noticed Crothers mentioned before. Sorry

[Proper Job]

Are you limited to the 1000 rpm you quoted? I think the original (CS) engine was rated for 1000 rpm only.about 18bhp, but 21 @ 1200 was the standard for a long time. It does make a big difference to the prop size.

 

Tim

Tim

 

The plate on the engine advises: JP3M - 27hp @ 1000rpm. I think some of the later engines and constant speed generating sets where up-rated to 30hp @ 1200.

 

IIRC the CS series of engines was only available up to 2 cyliners. I used to have a startomatic gen set once. It was a single and was rated as 6hp @ 650rpm

[Timleech]

Tim

 

The plate on the engine advises: JP3M - 27hp @ 1000rpm. I think some of the later engines and constant speed generating sets where up-rated to 30hp @ 1200.

 

IIRC the CS series of engines was only available up to 2 cyliners. I used to have a startomatic gen set once. It was a single and was rated as 6hp @ 650rpm

 

 

Weelll, the JP wasn't a JP until WWII, it was known by its rating and had a CS engine number.

 

I hadn't twigged that you were talking about a JP3, I'd assumed a twin. I'm now sure your prop is far smaller than it could be.

 

Tim

[casper ghost]

Casper (43 foot, 21inch draft) has a Sabb 10 single cylinder, 2:1 box with an 18x14 prop.

It can just about do over the speed limit and I woudn't want to go on a big river with it.

 

I think boats are far too over-powered these days.

[Naughty Cal]

Casper (43 foot, 21inch draft) has a Sabb 10 single cylinder, 2:1 box with an 18x14 prop.

It can just about do over the speed limit and I woudn't want to go on a big river with it.

 

I think boats are far too over-powered these days.

 

You can never have too much power

[n.b.Goldie]

You can never have too much power

You most certainly can when the boat spends its life on the canal doing just over tickover, the cylinders glaze, the exhaust smokes and the oil gets sludgy very quickly.

 

A forum member involved in rebuilding canalstars (I cannot remember his name but its not baldock) has said in the past that a thick tar-like sludge is found in the sumps of canal boat engines that is not found in the sumps of used and abused industrial versions. I believe he put this down to the light use that canal engines experience.

 

Apart from rivers, does anyone know of any good stretches of canal where you can 'open her up' without coming across moored-boat after moored-boat after moored-boat after moored-boat after moored-boat....................?

[Naughty Cal]

You most certainly can when the boat spends its life on the canal doing just over tickover, the cylinders glaze, the exhaust smokes and the oil gets sludgy very quickly.

 

A forum member involved in rebuilding canalstars (I cannot remember his name but its not baldock) has said in the past that a thick tar-like sludge is found in the sumps of canal boat engines that is not found in the sumps of used and abused industrial versions. I believe he put this down to the light use that canal engines experience.

 

Apart from rivers, does anyone know of any good stretches of canal where you can 'open her up' without coming across moored-boat after moored-boat after moored-boat after moored-boat after moored-boat....................?

 

Fossdyke is the one that springs to mind, however we are spoilt for choice and have all the big rivers to play on and open her up.

 

There must surely be other places.

[alan_fincher]

Apart from rivers, does anyone know of any good stretches of canal where you can 'open her up' without coming across moored-boat after moored-boat after moored-boat after moored-boat after moored-boat....................?

I always reckon there's no better way to give an engine a good work-out than to really open up in one of the major tunnels. A nice narrow channel, offering lots of drag, but no banks to wash away. (Take a look at Mike Askin's Jam 'Ole video where boats are exiting Blisworth!)

 

Providing nobody is coming the other way, of course.

 

Much of the Paddington Arm will allow a lot of power, with no wash, and long stretches of it are free of moored boats, (not that anybody ever seems to slow down much on the Paddington or Regents anyway, it's generally deep enough for it not to be an issue, it seems......)