prop size (yamaha 80 on phantom 16)

[L&N]

does anybody know what is the best size prop for a 16ft phantom with a 80hp on the back the outboard is jacked up but not to the max as the water pickups are standard. i have a 18p stainless on at the moment but dont know the rpm's or speed as no gauges :0( so can anybody advise on experiance with this setup or similar rig?????

thanks in advance.....

[Jon Fuller]

Are you sure it's a Phantom?

[L&N]

Originally posted by jon fuller
Are you sure it's a Phantom?

defiantly a phantom. its one of the original ones. they changed the top mould after this one. do you know the best prop size??

[Jon Fuller]

Before the current 16, the original had a droop snoop (fwd deck curved down toward sharp end), but I wasn't aware Steve had ever done that type of hull/deck joint (horizontal, with rub rail pushed on, like a Marshan)

Dunno about props, but I would guess at 50mph ish, and from there you could have a pretty good educated guesstimate, assuming you know max rpm of the 90, and the gear ratio, work it on 12-14% slip, you should get pretty close.

[L&N]

thanks for the way to work it out but im not 100 % at maths, has anyone had experiance with this size rig????

[Jon Fuller]

Do you know the ratio of the 90? and do you know the WOT RPM? if you know these we can work it out, like I said, I would guess at 50 ish, mebbe a bit more depending on weight, a class III 1.3 16 phantom would do somewhere just over 55.

[hightower]

Can't help you with the hull, but I run a 1990 80AETO on the back of my 5.5m RIB and with a 17" x 13.25 Raptor I would get about 43mph at 4400rpm MAX, I've bought a 15" X 13.5 Alloy genuine Yam, but haven't had a chance to use it. Hopefully this weekend.

Andy

[L&N]

Originally posted by jon fuller
Do you know the ratio of the 90? and do you know the WOT RPM? if you know these we can work it out, like I said, I would guess at 50 ish, mebbe a bit more depending on weight, a class III 1.3 16 phantom would do somewhere just over 55.

jon,
cheers for the help but i dont know the ratio.

[termite]

13:26 if my memory is correct but it was a long time ago.

T

[Jon Fuller]

Nearly harf parst one! ...so! :frog:

[hightower]

Yamaha service manual says 26/13 or 2.00

Doesn't mention WOT but 87.5hp@5000rpm and 90@5500, Oh yes it does!! There's a range from 4500-5500, I suppose depends what prop your running, but 5500rpm Max.

Book also mentions prop sizes from 3X14X11 to 3X13X25 but that covers the 60 to 90hp range of engines and I assume that they are all Alloy props.

Hope that helps

[Jon Fuller]

Hope it's comes up with more sense than the Lancing marine program:lol:lol:

That told us (after we'd done 80 at Windermere with a 1.36:1 drive, and a 25" prop @ 5150rpm) that we needed a 19" pitch prop :dizzy:

[Jon Fuller]

about 1800kgs

[Captain Chaos]

Originally posted by Matt
What's the total weight of the rig and I can plug some numbers in to the 'puter and see what it comes up with.

what do you need to know then??

you can tell me if my Phantom will do over 25mph? and whether i need to fit a poop collecter and ducting from my pants!

Whats your gizmo say about the fletcher:

Length - 5.1 M
weight - 700kg
200 hp @ 5600rpm x 21 pitch

[Jon Fuller]

700kgs!



Sorry, i'm doin it agin:bang:

[Captain Chaos]

Just remember fuller....I know where you live:duell:

700kgs, for fletcher, interior, tanks + merc.....thats quite reasonable 'n it??

you got the funky prop slip/ efficiency/ speed equation then?

[hightower]

I rekon those prop calculators r shat. I'm running a 17 raptor on a 80 Yam and getting 43mph, cals telling me more like 30

[hightower]

But here's the funny thing Mat. Tacho is reading 4400rpm and I don't quite understand it. Either Tacho is wrong, both GPS (31knots) and speed impellor on depthsounder (43mph) is wrong, there is a newish (3year old gearbox fitted) to ratio could be different or prop markings are wrong. I've got a 15X13.5 alloy prop to try so I'll let you know how I get on.

[Captain Chaos]

..

you could also try what 1000kgs and a 22 rinning 5500 for ex on the phantom?

or send m,e the formula!!

[Jono]

Originally posted by Matt
Everyone knows ribs are faster than hard boats .........


Feckin' right Nobba! Give me toobs over horsepower anyday......me gran's ol' piles cushion wiv a seagull fitted is faster than that heap o'shite "Instant Fumble".... and it'll cope wiv an hurricane... and it'll carry 18 lardy blokes...and it'll cross the Norf Sea on a thimblefull of fuel..and it'll............ NURSE!NURSE!

[Jon Fuller]

Working out the predicted speed of a boat is a tricky thing.
My experience says that most of us can make a pretty accurate guess on what the top end will be for a given setup, then use the oul equasion for working out what prop is required, based on the estimated top end, known ratio, and known max RPM.

If the boat is a known factor, ie, one is rigging a 26 extreme, or a 28 phantom, or a 21 phantom, then we have a very good history to work from, and as long as there are no major changes in the likely efficiency of the setup, ie, you are only really changing weight (CK) or power, then the 'Levi' formula seems to work pretty well.
This requires you to know the 'constant' No, which represents the basic efficiency/performance of the hull/drive.

Therefore, if your gonna take your Formula29, and add 200hp to the existing 600, you could calc quite accurately what your speed increase will be. Or work backwards, if you've increased your power, this will tell you how much more power, based on the speed increase.

I'm sure there are plenty of equasions for this, Matt could inform us there, but the crux is, to double the speed, you need to quadruple the power.

[Jon Fuller]

Originally posted by Jono
Feckin' right Nobba! Give me toobs over horsepower anyday......me gran's ol' piles cushion wiv a seagull fitted is faster than that heap o'shite "Instant Fumble".... and it'll cope wiv an hurricane... and it'll carry 18 lardy blokes...and it'll cross the Norf Sea on a thimblefull of fuel..and it'll............ NURSE!NURSE!

Excellent!

whenever I hear Nurse,...Nurse, can't help thinking of Peter Cook/Dudly Moore...god bless em.

"We're not going to change your sheets again Mr Hastings!"...:well:

[L&N]

Cheers all for the help but im even more confused now:bang:

can anyone tell me the best size prop i should buy then??

[Jon Fuller]

OK, if we assume the 5500rpm WOT to be correct, and that it is indeed a 2:1 gear box, and make a guess at about 50mph top end, or mebbe a tad more, then it calculates that you would need a 23" prop @ 5500rpm, assuming a 12% slip.

So, 22 or 23" pitch is my .02 pence worth.

It must be revving it's bollocks off with an 18p, as I reckon 41mph at the redline with this prop.

All this goes out the window if it weighs a load, or is an obscure inefficient hull (although I hear what your saying about it being a P16)

You really need to borrow some props to get a better idea, and BUY A TACHO!

[L&N]

Originally posted by Johnson
OK, if we assume the 5500rpm WOT to be correct, and that it is indeed a 2:1 gear box, and make a guess at about 50mph top end, or mebbe a tad more, then it calculates that you would need a 23" prop @ 5500rpm, assuming a 12% slip.

So, 22 or 23" pitch is my .02 pence worth.

It must be revving it's bollocks off with an 18p, as I reckon 41mph at the redline with this prop.

All this goes out the window if it weighs a load, or is an obscure inefficient hull (although I hear what your saying about it being a P16)

You really need to borrow some props to get a better idea, and BUY A TACHO!


EXCELLENT!!!!!!!!

that is good to know what the maths work out at. i'll start trying at that size....

thanks very much...........
:cheers:

[Phantom 19]

I used to run a 20" LaserII,

You can get that 80 up to a 90 by changing the exhaust and main jets, blank the oilpump and premix 50:1, or get even more Hp by fitting aftermarket exhaust.

My Yams always cooled fine jacked up to top hole on 16.

[Cat]

I used to run a 22x14 ss yam prop on a lightweight 16 sat in tandem with engine at 26Inches,I dont know what it weighed but it was very light,at the time it was the fastest in the northern series 1999
Cat

[Ciao]

Originally posted by L&N
Cheers all for the help but im even more confused now:bang:

can anyone tell me the best size prop i should buy then??

The best prop ever used on a Phantom 16' with a Yam 90hp was made by Phil Rolla www.rolla-propellers.ch/ for Brian Eastham KIN Ell Fire (2 x 3b World Champion) 86 87

It was a four bladed cleaver.

It pushed the boat at 57 mph (timed on Windermere)

Not only was it quick, but kept the boat balanced, with no hooks, stuffs etc.

[Wacky Racer]

22 yam prop is the way to go, used to run one on my 16 Ring and Reiver years ago.

[captain]

Yamaha 20 prop, standard trim (unbutchered) is the one you want, I hold the O.C.R World 1.3lt speed record 60.43mph and two nat championships using a yam 90 on an Argo 17sorta like a Phantom, must prove something. Got a Phantom 16 with yam 90 and 20 yam prop now for fun and she really flies, no good if you want to pull a skier though.