Overpropped?

[Snowgoose-1]

Its a Wauquiez Victorian 27 - pretty rare in Britain VICTORIAN 27 - sailboatdata
can't remember gearbox ratio off hand but it's an early Hurth - I'l check tomorrow

Nice looking boat. A further consideration is the prop located in an aperture . The thrust reduces when the blades pass north and south of the deadwood. Some years ago , with a similar boat as yours, compromised and chose a two bladed turbine prop which reduced drag when sailing. Might be worth considering when talking to prop specialists.

 

[Daydream believer]

If that were my boat, I would be wanting a feathering prop for it though. Alas, they are pricey.

Why would you want a feathering prop & what one?

 

[Tranona]

A feathering prop would indeed be a good idea. However it is not clear from the drawing of the boat whether there is enough room in the aperture for the blades to pivot. Then cost - close to £2k for a 13 or 14" Featherstream.

The boat is relatively light and a simple 3 blade prop is more than adequate for propulsion purposes with the amount of power available. 2 blade props do not work well in small apertures like this because the blades are masked by the keel at the same time and the reduction in drag is small unless you can devise a means of locking the shaft with the blades behind the keel. Boat seems to have been running with a 3 blade all its life.

 

[B27]

Why would you want a feathering prop & what one?

Because it's a pretty nice sailing boat, and hanging a paddle wheel for a big engine on the back of it is just obscene.
It will sail much better with a sailing boat prop, but there won't be room for a folding one I assume.

 

[B27]

The other possibility might be a smaller diameter of similar pitch.

Used fixed props are often quite cheap, if you want to experiment.
Cutting the tips off the blades is a DIY proposition.

It depends on your goals. I want my boat to sail well and how optimally it motors is much less important, so long as I can make progress into a bit of wave and weather, and have some thrust in case I run aground. It's a big plus that it's not too rough or noisy motoring in calm conditions. An extra half a knot under motor would not be something I'd want to pay for.

I would suggest finding out the gearbox ratio and looking at what you have, against the books and models/online calculators, to make sure you understand where you are starting from and you don't have a limited engine or anything weird going on.

I found Dave Gerr's Propellor Handbook useful.

 

[jonathanhsm]

Many thanks all - my goal in all this is to get the motor working in the proper rev range ...with an extra bit of power if I need it at the moment it only achieves max revs - 3600 - in neutral. Bollard pull is about 2500. WOT... and there's no difference in the last third of throttle travel.
And I don't think I'm achieving top hull speed ... judging by all the boats that overtake me in the channel home ¬!!

As I have the boat out of the water chipping away several layers of antifoul I thought I might as well sort the prop.

FYI the gearbox is HBW100-3R A=2.72 B=1.83.

I'm afraid this is all gobbledegook to me but on your advice I'll contact supplier to either get new prop or my one re-engineered.

 

[Tranona]

2.72 is the reduction ratio in forward and 1.83 in reverse. this changes things and you 15*11 is not so far out. The bigger the reduction ratio the lower the shaft speed so the larger the propeller. The programme I use suggests a 15*10, So your initial idea is sound. 1" change of pitch at this shaft speed is between 250-300 change in rpm, so coming down 2" would get the engine up to over 3000 which will give you the power to achieve hull speed easily. It will also improve reverse which I would guess is a bit fierce with the current prop.

The prop if it is good condition may well stand a repitch of 2". Discuss it with the propeller suppliers. If you are around the Solent then Hamble Propellers in Swanwick would be my first choice for refurbishing.

 

[jonathanhsm]

I am around the Solent - (Lymington) so that's very helpful. You say prop might stand a 2 inch repitch but on your calculations I only need one inch ...yes ?

 

[Tranona]

1" will only get revs up 250 or so. Discuss it with Hamble Propellers if you use them.

I have just changed pitch on my boat because it was set for a different gearbox then I ended up with. Easy for me because it is a Featherstream so just fitting aa new set of stops. revs went up from around 2900 to just under 3200.

The 11hp you need is at roughly 3000 but as you have the power to get nearly another knot makes sense to tap some of it.

 

[B27]

There is a 15x9 2 blade on the bay of E. £40 plus p'n'p.
Obviously the taper needs to be right and the RH or LH sense.
ISTM you won't get much machining work done for that, and there's no going back.
Are we sure that the reduction ratio is higher in ahead? That sounds odd to me!
Kind of begs the question 'what RPM i can you get in reverse?' Not that I recommend trying it unless the boat is very firmly aground or tied up!

If the smaller number was the ahead reduction, it would be more inline with the observations?

Is the gearbox happy to run either hand of prop, or is 'astern' gear only suitable for intermittent use?

 

[jonathanhsm]

thanks for that - I'm not sure about a two bladed prop for aforementioned reasons - ie it might not work very well in a 'well' between skeg and rudder.

I'll try Hamble propellors first. Meanwhile I've found this manufacturer in Spain ...

https://marinero24.com/propulsion/propeller-b-15-09?_route_=propulsion/propeller-b-15-09

200 quid so not too eyewatering ... but presumably I'd have to pay duty etc. Anyone ever heard of them ?

 

[oldharry]

Try one fo the online prop calculators like Vicprop - Prop calculator for Displacement and semi-displacement hulls . Easy to use and usually pretty accurate.

 

[Colvic Watson]

We were overpropped. Changing the prop for the correct size and pitch made little difference gently motorsailing but a huge difference to high raved motoring and slow speed manoeuvring, particularly in astern, much more predictable. In addition she's faster under sail. But then we were very over propped!

 

[scottie]

It might be worth checking if the gearbox rotation is correct
it has been suggested that ratio should be other way again possibly to save expense of new prop or not lifting boat to change and just running that way?

 

[Tranona]

There is a 15x9 2 blade on the bay of E. £40 plus p'n'p.
Obviously the taper needs to be right and the RH or LH sense.
ISTM you won't get much machining work done for that, and there's no going back.
Are we sure that the reduction ratio is higher in ahead? That sounds odd to me!
Kind of begs the question 'what RPM i can you get in reverse?' Not that I recommend trying it unless the boat is very firmly aground or tied up!

If the smaller number was the ahead reduction, it would be more inline with the observations?

Is the gearbox happy to run either hand of prop, or is 'astern' gear only suitable for intermittent use?

You only have to google the Hurth specs to find that the reduction ratio is correct, although the current reverse is a much more sensible 2,15. correct. The 1.86 is standard on the lower reduction ratios only now. The gearbox only runs one way. As you can see a definite A and B ratio.
simplicity-marine.com/ZF10M/Technical.htm

It is not uncommon to have this difference, The TMC equivalent with a 2.65 forward has a 2:1 reverse.

The high shaft speed in reverse will result in low revs but good stopping power.

 

[Tranona]

thanks for that - I'm not sure about a two bladed prop for aforementioned reasons - ie it might not work very well in a 'well' between skeg and rudder.

I'll try Hamble propellors first. Meanwhile I've found this manufacturer in Spain ...

https://marinero24.com/propulsion/propeller-b-15-09?_route_=propulsion/propeller-b-15-09

200 quid so not too eyewatering ... but presumably I'd have to pay duty etc. Anyone ever heard of them ?

A 3 blade 15" Radice from Lake Engineering is roughly £400+VAT so worth looking at refurbishing and repitching your current one.

 

[jonathanhsm]

I've spoken to Hamble propellors and of course the efficacy of repitching depends on the state of the prop ...hard to see because it's buried under layers of antifoul.
So I need to get it shot blasted .... any recommendations for shot blasters lymington area?

Meanwhile if it's not feasible as per my previous post anyone heard of this lot ? ... https://marinero24.com/propulsion/propeller-b-15-09?_route_=propulsion/propeller-b-15-09
About half the price of a prop in the UK.
Thanks as ever

 

[B27]

It might be worth checking if the gearbox rotation is correct
it has been suggested that ratio should be other way again possibly to save expense of new prop or not lifting boat to change and just running that way?

Indeed.
The R in the gearbox number indicates a RH rotating input.
A gear is opposite input/output
the prop in the picture is RH.

Which way does the engine go? Clockwise looking at the flywheel generally. But exceptions are possible....

Check the basics to understand where you are, before attempting to move forwards.

 

[Tranona]

Indeed.
The R in the gearbox number indicates a RH rotating input.
A gear is opposite input/output
the prop in the picture is RH.

Which way does the engine go? Clockwise looking at the flywheel generally. But exceptions are possible....

Check the basics to understand where you are, before attempting to move forwards.

See post #35. The ratios are correct. If it were the other way round you would not even be able to get 1200rpm with that size prop.

The issue is a lot simpler than you are trying to make out. The prop is nearly right now that the actual ratio of 2.72 is known. A reduction of pitch of between 1 and 2" would get the revs up to allow the boat to achieve hull speed.

That large reduction ratio is commonly used to reduce shaft speed so that you can run a larger diameter propeller which is beneficial on a long keel boat like this where the centre part of the prop is masked by the keel. On my Eventide with a long keel we originally fitted a Yanmar 1 GM with a 3.1:1 reduction to run a 15" flat pitch feathering prop (or a 14" fixed blade) and later a Nanni 14 with a 2.65:1 using the same propellers (not at the same time!). The Yanmar gave 5 knots and the Nanni 5.6 knots. My current Golden Hind has a Beta 30 and a PRM 2.5:1 runs a 17" 3 blade Featherstream.

When these higher revving engines are fitted in modern boats where there is cleaner waterflow they usually use a 2:1 and a smaller propeller. 12" with the 10-15hp 13" with the 20, 14" with the 25 and 15" with the 30. Taken from Beta recommendations.

 

[jonathanhsm]

A 3 blade 15" Radice from Lake Engineering is roughly £400+VAT so worth looking at refurbishing and repitching your current one.

Now that I have cleaned up the prop I see to my embarrassment that the size is actually 13 X 11 not 15 X 11 !? So that seems to be about the right size ... But on the principle that I still need a rev gain of 600 rpm plus, does that mean I should be looking for a 13 X 9 inch propellor ?

Re pitching my old one will cost around 140 quid. I have seen a new (old stock) 13 X 9 for 200 quid, which would mean I would still have my old prop if I'd made some gross miscalculation - or if the problem lay elsewhere. What do you think ?