Granada Atlantica 375 prop size??

[stuart2476]

hi all, hope someone can help
lost my prop at the weekend, all back safely
im unsure of prop size for the above boat, i fully understand there are calculations to find the prop size, however after talking to suppliers its never exact and is a gray area. The boat was made in 1986 and the manufacturers no longer exist.
Does anyone own this boat , im looking for dimensions of a standard prop, non folding (wish i had the money x) 2 blade, maybe 3 if recommended.
i know it between 14 and 16" in diameter because i have a refurb receipt, but no pitch.
any help would be great
regards all
Stuart

[more]

Originally Posted by stuart2476

hi all, hope someone can help
lost my prop at the weekend, all back safely
im unsure of prop size for the above boat, i fully understand there are calculations to find the prop size, however after talking to suppliers its never exact and is a gray area. The boat was made in 1986 and the manufacturers no longer exist.
Does anyone own this boat , im looking for dimensions of a standard prop, non folding (wish i had the money x) 2 blade, maybe 3 if recommended.
i know it between 14 and 16" in diameter because i have a refurb receipt, but no pitch.
any help would be great
regards all
Stuart

https://vicprop.com/free-propeller-sizing-calculators?
but consider your engine lose some power by aging

[TrentePieds]

More gave you the answer :-)! Use that prop calculator. You will need the parameters for your boat, which you haven't given us, so you might as well just go ahead and feed them into the calculator when you find them.

But you might tell us what boat you have and what prop the calculator tells you :-)

TrentePieds

[TrentePieds]

Ah, forgive me you boat type is in the heading :-)

So running the data from SailboatData through the VicProp calculator I get 17"D x 11"P.

Your boats ACTUAL parameters may be different from those given in SailboatData which may be the reason that you had a prop of different diameter.

So we are sorta back where we were: You gotta determine the parameters asked for by the calculator. They engine specification is most important in this regard, so what engine and transmission do you have?

TrentePieds

[stuart2476]

ok just to clarify

ive used these calculators, many thanks
these can differ.
they come out with various answers, last one said 16 x 11

what im after is a same boat owner who can advise on either original prop or one they are using and recommend suitable replacement

this is because the original company making the boat would have recommended a size through testing etc, Granada Yachts no longer exist

the boat make model is in the title !!!! xxxxx

happy sailing thanks

[stuart2476]

ok i will supply info so you can see, its interesting anyway
im learning a lot about props

[stuart2476]

lwl 30ft 5"

beam at WL 11ft

12000 kg this is approx 6500kg before additions at manufacturer

26bhp, it is a 28 bhp volvo 2003 but age loss adjusted

revs 2800 again age related should be 3200

120s 2.2 : 1 ratio

not sure about bearings but is 1.5% per bearing on shafts

[RobertBarnes]

YBW.COM has a Grenada owners group. Not sure how active, but may lead you in the right direction. Good luck!

[donradcliffe]

Don't forget the shaft size.

[Geoff 3016]

Hi Prop diameter governed by tip speed generally between 6500 & 10,000 feet/min . Stay closer to 6500 and this will allow for intermitent loadings and not cavitate. Also take into account that you require a minimum of 10% of your blade diameter as clearance from your hull . I would recommend that you go for 3 blade sailer shape blades not equipoise. 2 blades very awkward to balance properly (amazing how many places cannot balance 2 blade properly).For your prop diameter is bollard pull, pitch is for your speed .Any calculation you do will always be approximate and will need adjusting after sea trials.

[stuart2476]

this boat was made from Granada Yachts Denmark (not Grenada)

its on a volvo penta 120s , whatever shaft that is, no inputs for shaft size anyway

not sure what you mean by tip speed 6500, 10000 feet min etc? ie staying closer to 6500?

[more]

Originally Posted by stuart2476

its on a volvo penta 120s ,

not sure what you mean by tip speed 6500, 10000 feet min etc? ie staying closer to 6500?

also i don't know this strange funny imperial mesure.
you must keep engine under 2300 rpm and propeller rpm under 1200 beter 900-1000 rpm
we change in charter volvo saildrive propeller 1-2 times in a year. pick this 16 x 11 next year if you lose speed take this 17x11 3 blade of corse

[Geoff 3016]

Funny imperial measurements . Prop diameter 16 inches ,pitch 11 inches.All of these numbers are in imperial.
max engine rpm divide by gearbox reduction gives shaft rpm
circumference of swept circle by prop, (diameter times 22/7) x shaft rpm equals tip speed in inches divide by 12 gives you feet / minute.

[TrentePieds]

Hm.. We can all do the math, even in metric if we absolutely must. Damn awkward system, tho! Just fine if you are a microbiologist or an astrophysicist. If your concern is with things that will be occupied or used by Homo sapiens, then gimme the imperial system every time :-)!

And Stuart, since you asked: The reason for having regard to the "tip speed" of the prop is that beyond a certain tip speed (that speed depending on the viscosity of the medium the prop is working in), the transmission of energy from prop to medium breaks down. i.e. the prop "cavitates" by tearing the medium, in our case water, apart, so that cavities - i.e. voids - are generated in it.

Cavitation denotes a waste of energy and can be damaging to the prop as the voids collapse again.

By analogy: In wind turbines the tip speed of the rotor blades is kept below the speed of sound. "Breaking the sound barrier" is merely a way of saying that the air around the blade tip (or an aircraft) is cavitating.

TP

[Geoff 3016]

Hi again, by my calculation you require a prop 16.4 " diameter x 11 "pitch. so either 16 or 17 inch diameter would be fine . But as with anything there is usually a compromise and here it comes, the calculated max speed with this prop is 7.4 knots which is above your hull speed which would allow you to throttle backand maintain hull speed . But to achieve this you need a prop that is 50% disc area ratio (that is that the surface area of the blades amount to 50% of the swept circle area ) . Most manufacturers do not make a prop with this blade area , a sailer prop is usually about 35% and an equipoise prop approx 65%. personally I would go with the sailer prop and add an extra inch of pitch and allow a little extra slippage .Hope this is of some help to you . Good Luck.