how do I know what size my prop is?

Portholme · 13 January 2011, 10:43

dumb newb question if ever there was one.....

I want to try a different prop on my RIB. It's on a Mariner 60 ELPT EFI 2002.

How do I know what 'size'/pitch etc the existing one is? I imagine it's like tyre sizes - easy when you know how!!

Also, what does WOT stand for?

Cheers

Richard

Erin · 13 January 2011, 11:02

WOT is 'wide open throttle'. i.e. full revs

Prop size is normally stamped on the side of the prop e.g. 14 x 12 which would mean 14" diameter and 12" pitch. If it doesn't say it somewhere then there is probably a part number instead which would give you the size off the manufacturer's tables.

Portholme · 13 January 2011, 11:25

excellent, thanks very much

martini · 13 January 2011, 11:41

Some Merc props might just have a part number stamped on, in which case just google the number.

Downhilldai · 13 January 2011, 13:39

If it's a genuine Merc/Quicksilver prop, the part number will be stamped on the mating surface of the prop, where it meets the thrust washer.

I've got a couple of props here to suit your motor. Let me know what pitch you're looking for and I may be able to help you out.

Portholme · 16 January 2011, 13:03

Thanks downhill dai.

That's the problem, I'm all a bit new to this and don't know what I don't know!

The only number I can see on the prop is 23, by the thrust washer.

I'm now trying to work out whether to go smaller diameter or shallower pitch. What difference does each make to the overall performance?

To reiterate, I want to get on the plane easier when fully loaded. If I get 25 knots top whack I'd be pretty happy.

Sorry to sund like a dumba*s - it's just that on this topic I am!

martini · 16 January 2011, 14:50

What's your current top speed? And maximum rpm currently achieved?

Erin · 16 January 2011, 15:58

He'll still need to find out the pitch on his current prop, to decide how much to increase or decrease it depending on rpm etc.

There must be some other numbers stamped on it somewhere. Have you checked both ends of the hub Portholme. Make sure the thrust washer is corroded onto the hub covering the numbers.

Downhilldai · 16 January 2011, 17:54

matt h has a similar size Zodiac with the same motor and he uses a 15" pitch prop - his 14" was too fine. I've got a 15" pitch genuine Merc prop here, if you're interested.

Portholme · 16 January 2011, 19:46

Downhilldai

I'm interested but I guess it depends what you are after for the prop.

you want a PM me?

Cheers

Richard

Portholme · 16 January 2011, 19:49

Martini

fully loaded about 3500rpm and only about 17-18 knots. I remember thinking I've sailed skiffs faster than this!!!!

with just me 5500 rpm plus, 30knots plus

but it nearly always has the whole family on

Downhilldai · 16 January 2011, 20:03

5500 is good for that motor - the rev limiter comes in at 5950rpm.

BUT, if you normally run it heavily loaded, then you need a finer pitch. Need to know what pitch is on there now. It won't be a 23"

Portholme · 16 January 2011, 20:48

thanks, our forum and PM messages are passing like ships in the night.

I'm going to have to either take a punt or try and find out what pitch the existing prop is. I can't find any markings at all! I wonder if it was some generic after market job the previous owner put on. it is very corroded!

martini · 16 January 2011, 21:57

I was hoping you'd say max rpm 2000 or something ridiculous then we'd know what the number 23 was referring to

What is your definition of fully loaded? With just you it sounds like about the right prop whatever size it is. I'm surprised you're losing that much top end when adding weight, being a 60hp it should cope with a fair bit extra.

Downhilldai · 16 January 2011, 22:22

Some photos of the 15" pitch prop and its box.

Portholme · 16 January 2011, 22:29

As i've researched this during the day I now have no idea what the 23 is either!

The prop on it is horribly corroded and certainly doesn't have any part number or pitch stamped on it. I think it must be an aftermarket one.

Downhilldai and I have had a discussion and I'm having a prop off him to try. I'll give that a go and see what's what.

Thanks for all your help folks, this is a really friendly forum.

BTW loaded means the wife and I, two teenage kids and two youngsters plus kit for the day. The problem might be that the other boat is a Boston Whaler Dauntless 180 with a Yamaha 150. It might just be my expectation but when we had a 13 foot Dory and a 25hp o/b as a kid I remember having to move around the boat to get it to plane. Very frustrating and if I can get the Zodiac to pop up more easily I'll be pleased - or I'll be after a bigger RIB!!!!

When I say newb, I've spent my whole life on boats, but this is the first RIB and I've never had to change a prop!

Downhilldai · 16 January 2011, 22:48

I'm not familiar with your boat, so did a search for some images. Is it the same hull as in this post?

http://rib.net/forum/showpost.php?p=...&postcount=476

Portholme · 17 January 2011, 15:19

yep, that's it. Very much a leisure boat - nothing 'offshore' about it at all. Still good fun though.

9D280 · 17 January 2011, 17:32

Quote:

Originally Posted by Portholme

BTW loaded means the wife and I, two teenage kids and two youngsters plus kit for the day.

As a rough ballpark each adult is approx 80Kg. On a 4m rib, 4 of you will almost double the weight of the hull, and that's before you add fuel!

Sounds like you may want to hang onto your current prop for days you might be asked to help out as a recscue boat (I guess if you sailed skiffs you have contacts in the dinghy world who will inevitably need rescue cover for a big event!

)

Downhilldai · 17 January 2011, 21:03

Given the hull profile, I reckon you'll need a 13" or 14" pitch prop on the F60 to get the boat planing comfortably with the typical load you carry. The 15" may be ok if you're single handed.

If, on reflection, you don't want the 15", just let me know.