New Prop

[Stemar]

Having re-engined, I now need a new prop. I've calculated that a 15 by 10 should be about right, but I could go up to 16" without getting too close to the hull.

Are there any advantages/disadvantages to having a smaller diameter, larger pitch or larger diameter, smaller pitch?

Also, any suggestions for sources? SIBS exhibitors come out around £200 + drat

See my Want Ad in the wanted section if you happen to have one lying around.

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[snowleopard]

a 16x9 will give slightly better thrust than the 15x10 for the same revs (that's in choppy conditions. the smaller coarser prop would give slightly higher speed in flat calm).

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[steve28]

I have a new 15x10 rh standard 1 inch taper

Its brand new, just got the calculation wrong the first time.


steve



<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by steve28 on 16/09/2004 17:04 (server time).</FONT></P>

 

[ShipsWoofy]

I presume that is down to the cone of thrust, but could you explain why the difference. Why would the smaller prop be less useful in chop. Are you saying that the smaller prop with bigger pitch will loose grip quicker or is it something more fundamental?

It is probably quite obvious, but I am genuinely interested as I am currently trying to decide what size props to fit. Have been putting it off long enough.

<hr width=100% size=1><A target="_blank" HREF=http://www.topcatsail.co.uk>Woof</A>

 

[Capt_Scarlet]

I bought a prop from T Norris Ltd - 0208 560 3453 - www.tnorrismarine.co.uk

Can't remember the size, but think it was about £130 + VAT

Seemed to work ok....

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[snowleopard]

that's the story i was given by a prop manufacturer when i had the same choice.

for tugs etc with variable pitch props they get the most thrust with the props set fine.

an extra inch diameter will give around 20% more working area so it should be more efficient.

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[ShipsWoofy]

So which way did you decide, speed or thrust?

As I expect to be using engines when I am not sailing I think speed is the best target, but then if I need to move the boat in poor weather....

wow, what a choice...

<hr width=100% size=1><A target="_blank" HREF=http://www.topcatsail.co.uk>Woof</A>

 

[TheBoatman]

If you talk to Norris's in London They will tell you the best prop size. They will want to know the engine Hp, gear box ratio and hull length.

I buy all my props from them and have never had a problem.

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[dickh]

From your profile you have a Snapdragon 24 - a 15" x 10" prop sounds too large - what is your HP?
I have a Jaguar 27, 18HP engine, 2:1 reduction, revving to 3600. Initially when I had the boat wouldn't go above 2800 under load with a 15" x 9" x2 bladed prop. I had it repitched to 15x8 and it's now at 3200/3300rpm under load. I'm happy with this.
As others say, try speaking to a several prop manufactures with all your details and then take your pick.

<hr width=100% size=1>dickh
I'd rather be sailing... /forums/images/icons/smile.gif

 

[Stemar]

That's right, I have a Snapdragon 24. I fried my MD1 a week after a mate was given a 28 HP Volvo 2003. Way over the top I know, but pauvreté oblige, so now I've got the most overpowered Snappy in the South.

Current thinking is a water ski on the bottom of each keel...

Not so minor detail, It's a 25mm shaft rather than a 1" one, having checked the old receipts that came with the boat

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[snowleopard]

i think of mine as a motor-sailer so expect to want to power upwind in heavy stuff. the diffence between 10.5 and 11 knots top speed in flat water is purely academic so it's thrust before speed every time.

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[nordic_ranger]

Re: 16x9

I have a new 16x9 two bladed prop RH. standard taper, for sale if you are interested.
£50 includes postage. PM me if you are interested.

Jim.

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