prop size (yamaha 80 on phantom 16)

L&N · 05-07-2004, 09:30 AM

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 · 05-07-2004, 09:45 AM

Are you sure it's a Phantom?

L&N · 05-07-2004, 10:12 AM

Quote:

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 · 05-07-2004, 10:23 AM

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 · 05-07-2004, 05:09 PM

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

Jon Fuller · 05-07-2004, 05:13 PM

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 · 06-07-2004, 12:33 AM

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 · 06-07-2004, 08:17 AM

Quote:

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 · 06-07-2004, 11:20 AM

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

T

Jon Fuller · 06-07-2004, 12:26 PM

Nearly harf parst one! ...so!

hightower · 06-07-2004, 09:01 PM

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 · 06-07-2004, 09:43 PM

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

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

Jon Fuller · 06-07-2004, 10:00 PM

about 1800kgs

Captain Chaos · 06-07-2004, 10:22 PM

Quote:

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 · 06-07-2004, 10:23 PM

700kgs!

Sorry, i'm doin it agin

Captain Chaos · 06-07-2004, 10:37 PM

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

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

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

hightower · 06-07-2004, 10:50 PM

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 · 06-07-2004, 11:29 PM

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 · 06-07-2004, 11:43 PM

..

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

or send m,e the formula!!

Jono · 07-07-2004, 08:14 AM

Quote:

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!