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Old 18 May 2020, 14:06   #1
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Country: UK - England
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Prop for Mercury 40HP efi

Hi,
I have an Arimar 430 Rib (later became a valiant 430 I believe), that I bought mainly for the engine 2003 mercury 40Hp EFI 3cyl - buy an engine get a rib free - type of deal - yes it was a late night ebay purchase

The engine is good (now the fuel system is cleaned out and the cracked battery terminal is replaced) and I figured fairly often hulls come up minus an engine but while it holds air I am getting some use out of it. (It doesn't look to bad from a distance!

In the past someone has added a (nasty) central console and moved the steering forward so its console butts up against the front seat. This seems to work quite well for single handed use. the original 'manufacturer' steering console position and seat put all the weight at the back. Given that at some trim angles / speeds it can throw water over the transom I am glad to be sat further forward.

The 40 was the biggest engine option recommended when the rib was new.

The Rib is ok and I am slowly improving it and my mind has turned to the prop. It currently has a fairly abused Michigan vortex 992406 which apparently by looking up the part number is 10 3/8" dia 13" Pitch (3 blade).

My thinking was to replace that with a new one and then evaluate it. However doing a bit of research, this diameter / pitch seems a little small for a 40HP on a 4.3m rib.

The solas prop selector for 40Hp 4 stroke mercury are all larger dia with a range of pitches either side.

Messing with the mercury prop selector, it has higher pitch for props of that diameter.

Playing with the michigan wheel prop selector I couldn't make it select my prop for my engine

The previous owner of my boat used it for fishing and freely admitted he didn't know much about boats and was a bit scared of it - he replaced it with a little SIB.
I don't know if he fitted the current prop or the owner before him, I suspect it was him that bounced it off the bottom though.I gave it a clean up with a file and straightened out a small ding but it is not an ideal candidate for testing.
Last summer flat out I had about 23knots on the GPS and if anything it seems to want to over rev, I have to be fairly careful to avoid the rev limiter.
That was 1/2 tank fuel me 90Kgs and my daughter about 40kgs on board.

I don't really know if that is good or bad!

Is anyone running a similar sized rib with a mercury/mariner 40hp 3 cylinder four stroke? If so care to share prop size.

If not shall I just go with my original plan and start by putting a new one as fitted previously.

(use is to be general blatting about in reasonable weather - maybe pull a ringo with the kids in Christchurch bay and the odd trip round to Poole or the Solent.

Thanks for reading and for any advice!

Tony
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Old 19 May 2020, 02:56   #2
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You should be able to get a slightly higher pitch prop on there, but I wouldn't go much bigger if you'll be carrying loads every now and then. The EFI engines tend to have better torque than carb versions
Easiest way to get a bit more out of it is to swap to a stainless prop, less flex and more speed. I've got brand new Yamaha 14 stainless semi cleavers which would work well, they're often referred to as YBS - yamaha black stainless for 139.99 brand new. Bought about 10 of them because they were so cheap, the 13/15/16 pitch versions are 459.99 odd new from yamaha
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Old 19 May 2020, 05:03   #3
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Quote:
Originally Posted by Roflhat View Post
You should be able to get a slightly higher pitch prop on there, but I wouldn't go much bigger if you'll be carrying loads every now and then. The EFI engines tend to have better torque than carb versions
Easiest way to get a bit more out of it is to swap to a stainless prop, less flex and more speed. I've got brand new Yamaha 14 stainless semi cleavers which would work well, they're often referred to as YBS - yamaha black stainless for 139.99 brand new. Bought about 10 of them because they were so cheap, the 13/15/16 pitch versions are 459.99 odd new from yamaha
Thanks sent you a private mail.
Tony
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Old 19 May 2020, 06:27   #4
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Look up the recommended Wide Open Throttle rpm range given by your engine's manufacturer.
Test what you've currently got by running at WOT with what you usually have on board kit & people wise & trim adjusted to give best speed.
Note the rpm achieved & see if this falls within the specified range.
Once you know that you can - if necessary - change props to suit.
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Old 19 May 2020, 06:43   #5
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Originally Posted by paintman View Post
Look up the recommended Wide Open Throttle rpm range given by your engine's manufacturer.
Test what you've currently got by running at WOT with what you usually have on board kit & people wise & trim adjusted to give best speed.
Note the rpm achieved & see if this falls within the specified range.
Once you know that you can - if necessary - change props to suit.
Thanks, but as the current prop is past its best - will this actually tell me much?

Tony
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Old 19 May 2020, 06:47   #6
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Probably not a huge amount, but it's a pretty tried and tested setup. You can run 11-16 ish pitch, depending on what you want from the boat. For towing skiers etc lower pitch, better acceleration, higher pitch higher speed and generally lower fuel burn as long as it's not overpropped. For that setup I'd go for 13 or 14 as an all rounder
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Old 19 May 2020, 08:14   #7
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The other thing is - it was fitted with Doel Fins - I am not sure it needs them - it has the biggest recommended engine option and when running flat out it sometimes tends to fall onto a chine and get a bit skittish. I have read this can be a feature of the fins - they can lift the boat too far and it can drop back / catch a wave.
Also looking at the plate on the gearbox the engine might be a little low so I might try lifting it. but want to do one change at a time. Will get out this week with the fins removed and hope for some flat water.

Oh and that reminds me gearbox is 2;1 if that makes any difference for prop.

Tony
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Old 19 May 2020, 15:41   #8
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Well managed to sneak out for a while this evening and it was relatively calm in Christchurch bay - As I remembered from last year it does go over 6000 rpm easily with the current prop and one person on board. I think it was slightly faster without the fins and while not quite balanced (on my own weight felt too far forward) it felt easier to understand what was going on. Was too choppy to get a good look at the GPS.
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Old 19 May 2020, 16:18   #9
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Hi, I've a Ocean Runner 4.2M with mariner 40HP EFI. It's running a BlackMax 10-1/4" 14 pitch 3 blade and at WOT it's at 6000rpm (recommended max). Solo normal load (35L fuel, anchor, ect approx 60kg)
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Old 20 May 2020, 04:42   #10
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Originally Posted by Wozizname View Post
Hi, I've a Ocean Runner 4.2M with mariner 40HP EFI. It's running a BlackMax 10-1/4" 14 pitch 3 blade and at WOT it's at 6000rpm (recommended max). Solo normal load (35L fuel, anchor, ect approx 60kg)
That's great thanks, I did order a 10 1/4 dia 14" pitch yesterday - looking forward to trying it out!

Tony
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