Prop size- Cinder 22

[sailorman]

Hi chaps
Cinder Class 22 ft o/all
disp (cant remember) say 2 1/2 tons
engine Yanmar 1gm 9 hp @ 3600
the existing prop is a 13 x 12 which doesnt allow engine to gain anywhere near full revs.
my guess is around 13 x 8
any info would be greatly appreciated.
all partisipiants will go into a free draw 1st prise a 2 1/2 ltr tin "Teaknatin" teak colour



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[oldharry]

Cinder class sloop displacement aprox 1.3 tons

What is the reduction ratio of your gearbox? You will have no success trying to spin a prop at 3600rpm speed on a displacement hull.

Assuming reduction is 2:1. Max shaft speed would be 1800rpm Shaft speed should not exceed around 2200 rpm
so the minimum reduction required is around 1.8 : 1. This should be marked on the gearbox.

AT 2:1 reduction you need a size 20 prop, around 12x8. At 2200rpm shaft speed you need around size 18 which would be 10 x 8

Ring Lancing Marine. They will know the correct size of prop for your engine/hull size. 01273 410025.

Props are too expensive to play guessing games with. But size your size 25 prop wil be considerably too coarse for your 9hp engine unless the shaft speed is reduced to around 1000 - 1100 rpm - getting on for 3:1!

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[sailorman]

thanks for the responce ( your first in the hat)
the reduction is 2.21 giving a shaft spd of 1500 @ 3600 rpm so the book states
thanks
roger

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[oldharry]

9hp at 1500rpm requires a 12 x 8 prop for 5kts water speed.

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[sailorman]

thanks for that
i have e-mailed Lansing as u suggested

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[sailorman]

reply from Lancing Marine.
not really very helpfull as i would rather change the prop to keep the full Dia & change to the correct pitch.

vAs you have ample power for the vessel, I wouldn't worry too much if you don't make your max revs.

If your present prop is a 2-blade of around 33% B.A.R., then
I would just take a bit off of the diameter, say 1/2" off of each blade at a time, if necessary going as small as 11" diameter till you are comfortable with the revs and the boat speed.

One problem that does exist with Yanmar is that if you push
the speed lever too hard with a heavily loaded prop, you get black smoke from the exhaust, so DON'T PUSH TOO HARD!
cheers
roger



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[calloo]

Hello
I think you need a 13 by 7 three bladed prop. with I ins tapered shaft. By a strange coincidence I have an old one going for a modest price. If I can help contact me.
Martin

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[oldharry]

12 x 8 and 13 x 7 will give pretty much the same result. If it fits, go for it!

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[ShipsWoofy]

we may have something in common here and the ability for a mutual swap.

My port prop is too small, I do not Know it's size but it struggles to push Top Cat along, but does allow my 1GM to reach full revs. I am looking for a 13" x 10" and your 13 x 12 will most certainly do the job. 1" shaft, I think 1:10 taper.

The prop I have, I think is in the region of 12 x 8, I need to run her up the beach to take it off and have it measured or polish it to look for markings. It was matched to a vetus 12hp motor.

If you are interested PM me, though I am away to cornwall in the darkness tomorrow morning I will be back Saturday and will contact you.

This might really suit us both.

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

 

[sailorman]

the shaft is 3/4 inch
thanks anyway
roger

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[brianrunyard]

According to Propcalc, with a 2.21:1 reduction you require a 12" x 9" to give 5.7 knots hull speed.
Regards,
Brian

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[sailorman]

thanks
great ere init
roger

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